1\leq i\leq k\\}$ $\displaystyle\cup$ $\displaystyle\\{z_{i},\neg
z_{i},c^{z}_{i}\mid 1\leq i\leq p\\}$ $\displaystyle\cup$
$\displaystyle\\{x_{i}^{\prime},\neg x_{i}^{\prime}\mid 1\leq i\leq
n\\}\cup\\{win_{S},win_{U},s\\}$ $\displaystyle\mathrm{AP}=$ $\displaystyle S$

$\displaystyle\Delta_{must}=$ $\displaystyle\\{(x_{i},c^{x}_{i+1}),(\neg
x_{i},c^{x}_{i+1})\mid 1\leq i\leq n-1\\}$ $\displaystyle\cup$
$\displaystyle\\{(y_{i},c^{y}_{i+1}),(\neg y_{i},c^{y}_{i+1})\mid 1\leq i\leq
k-1\\}$ $\displaystyle\cup$ $\displaystyle\\{(z_{i},c^{z}_{i+1}),(\neg
z_{i},c^{z}_{i+1})\mid 1\leq i\leq p-1\\}$ $\displaystyle\cup$
$\displaystyle\\{(x_{n},c^{y}_{1}),(\neg
x_{n},c^{y}_{1}),(y_{k},c^{z}_{1}),(\neg y_{k},c^{z}_{1})\\}$
$\displaystyle\cup$
$\displaystyle\\{(x_{i}^{\prime},x_{i+1}^{\prime}),(x_{i}^{\prime},\neg
x_{i+1}^{\prime})\mid 1\leq i\leq n-1\\}$ $\displaystyle\cup$
$\displaystyle\\{(\neg x_{i}^{\prime},x_{i+1}^{\prime}),(\neg
x_{i}^{\prime},\neg x_{i+1}^{\prime})\mid 1\leq i\leq n-1\\}$
$\displaystyle\cup$ $\displaystyle\\{(x_{i},\neg x_{i}^{\prime}),(\neg
x_{i},x_{i}^{\prime})\mid 1\leq i\leq n\\}$ $\displaystyle\cup$
$\displaystyle\\{(x_{n}^{\prime},win_{S}),(\neg x_{n}^{\prime},win_{S})\\}$
$\displaystyle\cup$
$\displaystyle\\{(win_{S},win_{S}),(win_{U},win_{U}),(z_{p},s),(\neg
z_{p},s)\\}$ $\displaystyle\cup$ $\displaystyle\\{(c^{y}_{i},win_{U})\mid
1\leq i\leq k\\}$ $\displaystyle\cup$ $\displaystyle\\{(c^{z}_{i},win_{S})\mid
1\leq i\leq p\\}$

$\displaystyle\Delta_{may}=$
$\displaystyle\\{(c^{x}_{i},x_{i}),(c^{x}_{i},\neg x_{i})\mid 1\leq i\leq
n\\}$ $\displaystyle\cup$ $\displaystyle\\{(c^{y}_{i},y_{i}),(c^{y}_{i},\neg
y_{i})\mid 1\leq i\leq k\\}$ $\displaystyle\cup$
$\displaystyle\\{(c^{z}_{i},z_{i}),(c^{z}_{i},\neg z_{i})\mid 1\leq i\leq
p\\}$ $\displaystyle\cup$ $\displaystyle\\{(x_{i},win_{U}),(\neg
x_{i},win_{U})\mid 1\leq i\leq n\\}$ $\displaystyle\cup$
$\displaystyle\\{(x_{i}^{\prime},win_{U}),(\neg x_{i}^{\prime},win_{U})\mid
1\leq i\leq n\\}$ $\displaystyle\cup$
$\displaystyle\\{(s,x_{1}^{\prime}),(s,\neg x_{1}^{\prime})\\}$

$\lambda(t)=\\{t\\}$ for every state $t$, and the initial state is
$init=c^{x}_{1}$.

We consider the formula

$\displaystyle\varphi=$
$\displaystyle(\neg\varphi_{SAT}\land\varphi_{checkSat}\land AG\neg win_{U})$
$\displaystyle\lor$ $\displaystyle(EFwin_{S}\land AG\neg win_{U})$
$\displaystyle\lor$ $\displaystyle\varphi_{checkUnsat}$

with

$\displaystyle\varphi_{checkSat}=$ $\displaystyle
AG(\bigwedge_{i=1}^{k}AX(y_{i})\lor AX(\neg
y_{i}))\land(\bigwedge_{i=1}^{k}(EX^{2n+2i-2})EX\top)$

$\displaystyle\varphi_{checkUnsat}=$ $\displaystyle
EF(\bigvee_{i=1}^{p}EX(z_{i})\land EX(\neg
z_{i}))\lor\bigvee_{i=1}^{p}(EX^{2n+2k+2i-2})AX\bot$

and $\varphi_{SAT}$ is $\psi$ where every $x_{i},y_{i},z_{i}$ has been
replaced by respectively $EFx_{i},EFy_{i}$ and $EFz_{i}$, and every $\neg
x_{i},\neg y_{i},\neg z_{i}$ by respectively $AG\neg x_{i},AG\neg y_{i},AG\neg
z_{i}$. This construction can be done in logarithmic space. The formulas
$\varphi_{checkUnsat}$ and $\varphi_{checkUnsat}$ ensure that the players
never allow transitions to both or neither variables from a
$c_{i}^{x},c_{i}^{y}$ or $c_{i}^{z}$ state.

Suppose there exists $T$ such that $\mathtt{Sat}$ wins with $T\cup\\{s\\}$ but
loses with $T$. As all $x_{i},\neg x_{i},x_{i}^{\prime},\neg x_{i}^{\prime}$
have a may transition to $win_{U}$, there has to be either a path from
$c^{x}_{1}$ to $c^{y}_{1}$ in $T$, or a path in $T$ from $c^{x}_{1}$ to some
$x_{i}$ or $\neg x_{i}$, from there a transition to some $x_{i}^{\prime}$ or
$\neg x_{i}^{\prime}$, and a path in $T$ from there to $win_{S}$, otherwise
$\mathtt{Unsat}$ wins both games. In the second case, $\mathtt{Sat}$ wins
without $s$, thus we have to be in the first case. In particular for every
$x_{i}\in T$, $x_{i}^{\prime}\notin T$ and for every $\neg x_{i}\in T$, $\neg
x_{i}^{\prime}\notin T$.

As a result, there has to be a path in $\mathcal{M}$ (using may and must
transitions) to all $c^{x}_{i},c^{y}_{i},c^{z}_{i}$ from $c^{x}_{1}$. In order
for the games with $T$ and $T\cup\\{s\\}$ to have different winners, every
$c^{y}_{i}$ has to be in $T$ (as they have a may transition to $win_{U}$) and
similarly every $c^{z}_{i}$ has to not be in $T$. The formulas
$\varphi_{checkSat}$ and $\varphi_{checkUnsat}$ force both players to pick
exactly one outgoing transition from each $c^{x}_{i},c^{y}_{i},c^{z}_{i}$.

Now observe that the choice of transitions from $s$ has no impact on the
satisfaction of $\neg\varphi_{SAT},\varphi_{checkSat},AG\neg win_{U}$ or
$\varphi_{checkUnsat}$. As $\mathtt{Unsat}$ has a winning strategy when
$\mathtt{Sat}$ only has $T$, this same strategy will ensure that
$\mathtt{Sat}$ can only win by satisfying $EFwin_{S}\land AG\neg win_{U}$ in
the game with $T\cup\\{s\\}$. In order to satisfy $EFwin_{S}\land AG\neg
win_{U}$, there has to be a path in $T$ from $s$ to $win_{S}$. As a result, at
least one of $x_{i}^{\prime},\neg x_{i}^{\prime}$ has to be in $T$. As we have
seen before, for every $x_{i}\in T$, $x_{i}^{\prime}\notin T$ and for every
$\neg x_{i}\in T$, $\neg x_{i}^{\prime}\notin T$, thus at most one of
$x_{i},\neg x_{i}$ can be in $T$ for all $1\leq i\leq n$. Further, we have
seen that at least one of $x_{i},\neg x_{i}$ has to be in $T$.

As a result, the set of $x_{i}$ in $T$ with $1\leq i\leq n$ matches a
valuation $\nu_{1}$ of $x_{1},\cdots,x_{n}$. Let $\nu_{2}$ be a valuation of
$y_{1},\cdots,y_{k}$, suppose $\mathtt{Sat}$ picks transitions matching
$\nu_{2}$ from the $c^{y}_{i}$. As $\mathtt{Unsat}$ wins the game in which
$\mathtt{Sat}$ owns only $T$, and as the satisfaction of both
$\varphi_{checkSat}$ and $AG\neg win_{U}$ is guaranteed by the strategy of
$\mathtt{Sat}$, the only possibility is that $\neg\varphi_{SAT}$ is
dissatisfied, which $\mathtt{Unsat}$ can only achieve by picking transitions
matching a valuation $\nu_{3}$ of $z_{1},\cdots,z_{p}$ such that the
combination of $\nu_{1},\nu_{2}$ and $\nu_{3}$ satisfies $\varphi$. As a
result, the $\exists\forall\exists$SAT instance is true.

Now for the converse, suppose there exists a valuation $\nu_{1}$ such that for
all $\nu_{2}$, there exists $\nu_{3}$ such that their combination satisfies
$\psi$. Let $T$ be such that
$T\cap\\{x_{1},\ldots,x_{n},\neg{x_{1}},\ldots,\neg{x_{n}}\\}$ and
$T\cap\\{x_{1}^{\prime},\ldots,x_{n}^{\prime},\neg{x_{1}}^{\prime},\ldots,\neg{x_{n}}\\}$
both match $\nu_{1}$, $T$ contains every $c^{x}_{i}$ and $c^{y}_{i}$ but does
not contain $c^{z}_{i}$ for any $1\leq i\leq p$.

Let us first look at the game in which $\mathtt{Sat}$ has states
$T\cup\\{s\\}$. As one of $\\{x_{i},\neg x_{i}\\}$ belongs to $T$ for all
$1\leq i\leq n$, $\mathtt{Sat}$ can choose transitions so that there is a path
from $c_{1}$ to $c_{n+k+1}$, and a transition from $s$ to $win_{S}$.

If $\mathtt{Unsat}$ gives no outgoing transition to one of the $c_{i}$ with
$n+k+1\leq i\leq n+k+p$, then $\varphi_{checkUnsat}$ is satisfied, thus so is
$\varphi$. As a result, there is a path from $c_{n+k+1}$ to either $win_{S}$
or $s$, and thus also $win_{S}$. Hence $\varphi$ is satisfied in every case,
$\mathtt{Sat}$ wins that game.

Now let us study the game in which $\mathtt{Sat}$ only owns $T$. No matter
which strategy $\mathtt{Sat}$ chooses, $\mathtt{Unsat}$ can guarantee that
$EFwin_{S}\land AG\neg win_{U}$ is not satisfied by allowing the transition to
$win_{U}$ from every $x_{i},\neg x_{i}x_{i}^{\prime},\neg x_{i}^{\prime}$ it
owns, and not allowing any transition from $s$. This way, all paths to
$win_{S}$ go through states with a transition towards $win_{U}$.
$\mathtt{Unsat}$ can also ensure that $\varphi_{checkUnsat}$ is not satisfied
by picking transitions matching some valuation from the $c_{i}$ he owns.

Assume $\mathtt{Sat}$ has a winning strategy to ensure that
$\varphi_{checkSat}\land\varphi_{checkSat}\land AG\neg win_{U}$ is satisfied.
As $\varphi_{checkSat}$ and $AG\neg win_{U}$ are satisfied, the choices of
transitions of $\mathtt{Sat}$ from the $c_{i}$ have to match $\nu_{1}$ and a
valuation $\nu_{2}$ of $\\{x_{n+1},\cdots,x_{n+k}\\}$. There exists a
valuation $\nu_{3}$ of $\\{x_{n+k+1},\ldots,x_{n+k+p}\\}$ such that the
combination of $\nu_{1},\nu_{2}$ and $\nu_{3}$ satisfies $\psi$. Then if
$\mathtt{Unsat}$ chooses transitions from the $c_{i}$ he owns matching
$\nu_{3}$, $\neg\varphi_{SAT}$ is not satisfied by the resulting structure,
contradicting the existence of a winning strategy for $\mathtt{Sat}$.

We have proven the proposition. ∎

Proof of Theorem V.4.  The importance computation problem associated to
definition V.1 is $\textsc{\\#P}^{\Sigma_{2}^{\textsc{P}}}$-complete.

###### Proof.

The upper bound is easily obtained by considering the machine which guesses an
ordering $\pi$ of the elements of the partition $S_{1},\ldots,S_{n}$, computes
the set $J$ of indices appearing after $s$ in $\pi$, and then calls a
$\Sigma_{2}^{\textsc{P}}$-oracle twice to determine the winner when
$\mathtt{Sat}$ owns $\bigcup_{j\in J}S_{j}$ and when $\mathtt{Sat}$ owns
$\bigcup_{j\in J\cup\\{i\\}}S_{j}$. The number of accepting runs of the
machine is then precisely the number of permutations $\pi$ matching the above
condition.

Now for the lower bound, we proceed in two steps. First we show that the
following problem is $\textsc{\\#P}^{\Sigma_{2}^{\textsc{P}}}$-complete.

$Count\exists\forall\exists$SAT:

$\begin{cases}\text{Input:}&\text{A SAT formula }\psi\text{ over variables
}\\\ &\\{x_{1},\ldots,x_{n},y_{1},\ldots,y_{m},z_{1},\ldots,z_{r}\\}.\\\
\text{Output: }&\text{The number of valuations of the }x_{i}\text{ such
that}\\\ &\text{for all valuations of the }y_{i}\\\ &\text{there exists a
valuation of the }z_{i}\text{ such that}\\\ &\text{the combination of those
valuations satisfies }\psi.\end{cases}$

Then we show that the importance computation problem reduces to
$Count\exists\forall\exists$SAT.

For the first part, let $M$ be a nondeterministic Turing machine with an
oracle solving a $\Sigma_{2}^{\textsc{P}}$-complete problem (say
$\exists\forall$SAT). We can assume without loss of generality that $M$ only
makes one query to the oracle, and accepts if and only if the answer is
negative.

Indeed, say $M$ has to make queries $\psi_{1},\ldots,\psi_{k}$ to the oracle,
all over existential variables $y_{1},\ldots,y_{m}$ and universal variables
$z_{1},\ldots,z_{r}$. It can nondeterministically guess the answers of the
oracle and delay the verification to the end of the run.

Now let us define the order $\leq$ on valuations of the existential variables
as the lexicographic order, a valuation $\nu$ being seen as the tuple
$(\nu(y_{1}),\ldots,\nu(y_{m}))$ and with the convention $\bot\leq\top$. Then
for the positive answers $M$ can guess a _minimal_ witness valuation for the
$y_{i}$ with respect to $\leq$, negate the formula. The problem, given a
$\exists\forall$SAT instance and a valuation of the existential variables, of
checking whether this is the minimal valuation witnessing the satisfiability
of the formula, is clearly in coNP, thus also in $\Pi_{2}^{\textsc{P}}$. As a
result $M$ can guess the minimal valuation of the $y_{i}$ witnessing the
satisfiability of the formula, and then turn it into a $\exists\forall$SAT
formula unsatisfiable if and only if the guess is correct.

Finally, in the end $M$ has to make the oracle check a disjunction of
$\exists\forall$ formulas, it can rename variables in order to merge them all
into one equivalent $\exists\forall$ formula, and accept if and only if the
oracle rejects that formula.

In all the above transformations, the number of accepting runs of the machine
stays the same as the non-deterministic transitions we added (in order to
guess minimal valuations witnessing satisfiability of $\exists\forall$SAT
formulas) yield at most one accepting run (as the existence of such a
valuation is equivalent to the existence of a single minimal one).

An adaptation of the classical construction proving that $\exists\forall$SAT
is $\Sigma_{2}^{\textsc{P}}$-complete allows us to construct in polynomial
time, given an input $w$ for $M$, a formula
$\varphi_{1}((x_{i}),(q_{i}),(s_{i}))$ such that the following conditions are
equivalent for all valuations $\nu$ of the $x_{i}$, $q_{i}$ and $s_{i}$:

  * •

$\nu$ satisfies $\varphi_{1}((x_{i}),(q_{i}),(s_{i}))$

  * •

the $\nu(x_{i})$ encode a sequence of non-deterministic choices of $M$, the
$\nu(s_{i})$ encode a correct run of $M$ following those choices, and the
$\nu(q_{i})$ encode the query made to the oracle at the end of this run

We can also construct in polynomial time a formula $\varphi_{2}((y_{i})_{1\leq
i\leq m},(z_{i})_{1\leq i\leq r},(q_{i})_{1\leq i\leq p},(u_{i})_{1\leq i\leq
k})$ simulating the oracle such that a valuation of the $q_{i}$ satisfies
$\exists(y_{i}),\forall(z_{i}),\varphi_{2}((y_{i}),(z_{i}),(q_{i}),(u_{i}))$
if and only if the $q_{i}$ encode a valid instance of $\exists\forall$SAT. As
a result the formula

$\displaystyle\forall(y_{i}),\exists(z_{i}),(x_{i}),(q_{i}),$
$\displaystyle\varphi_{1}((x_{i}),(q_{i}),(s_{i})\land\varphi_{2}((y_{i}),(z_{i}),(q_{i}),(u_{i}))$

is satisfied by a valuation of the $x_{i}$ if and only if $M$ has a run
accepting $w$ following the choices encoded by this valuation. Thus the number
of accepting runs of $M$ is precisely the number of valuations of the $s_{i}$
witnessing the validity of

$\displaystyle\exists(x_{i}),\forall(y_{i}),\exists(z_{i}),(s_{i}),(q_{i}),$
$\displaystyle\varphi_{1}((x_{i}),(q_{i}),(s_{i})\land\varphi_{2}((y_{i}),(z_{i}),(q_{i}),(u_{i})$

The problem $Count\exists\forall\exists$SAT is therefore
$\textsc{\\#P}^{\Sigma_{2}^{\textsc{P}}}$-hard.

Finally, $Count\exists\forall\exists$SAT can be reduced to the importance
computation problem for 2-turn CTL using the same construction as in the proof
of Proposition V.3. Note that the $x_{i},\neg x_{i}$ for all $n+1\leq i\leq
n+k+p$, as well as $win_{S},win_{U}$, all have no outgoing may transitions,
thus have importance $0$ and thus, by a similar argument as in Lemma III.6,
can be ignored in the computation of the importance. We will now only consider
sets of states containing none of those. Then one can observe that the teams
$T$ allowing player $\mathtt{Sat}$ to win with $T\cup\\{s\\}$ but not with $T$
are exactly the teams $T$ such that

  * •

$T$ contains all the $c_{i}$ for $\leq n+k$ and no other $c_{i}$.

  * •

$T\cap\\{x_{i},\neg x_{i}\mid 1\leq i\leq n\\}$ and
$T\cap\\{x^{\prime}_{i},\neg x^{\prime}_{i}\mid 1\leq i\leq n\\}$ match a same
valuation $\nu$ witnessing the validity of the $\exists\forall\exists$SAT
formula.

Then we have that all the teams $T$ such that $(s,T)$ is critical (and
containing none of the aforementioned states with importance $0$) have the
same size $M$.

We obtain that the number of valuations witnessing the validity of the
$\exists\forall\exists$SAT formula is $\frac{P!}{N!M!(P-M-1)!}N!I(s)$, with
$N$ the number of states in the constructed MTS and $P$ the number of states
minus the $x_{i},\neg x_{i}$ for $n+1\leq i\leq n+k+p$, $s$, $win_{U}$ and
$win_{S}$. Hence we have a reduction from $Count\exists\forall\exists$SAT to
the importance problem for 2-turn CTL. As $\frac{P!}{N!M!(P-M-1)!}$ can be
computed in polynomial time, the latter problem is
$\textsc{\\#P}^{\Sigma_{2}^{\textsc{P}}}$-complete. ∎


ANA-LARG-2019-01-PAPER.bib bib/ATLAS.bib bib/CMS.bib bib/ConfNotes.bib
bib/PubNotes.bib The Phase-I Trigger Readout Electronics Upgrade of the ATLAS
Liquid Argon Calorimeters The Phase-I trigger readout electronics upgrade of
the ATLAS Liquid Argon calorimeters enhances the physics reach of the
experiment during the upcoming operation at increasing Large Hadron Collider
luminosities. The new system, installed during the second Large Hadron
Collider Long Shutdown, increases the trigger readout granularity by up to a
factor of ten as well as its precision and range. Consequently, the background
rejection at trigger level is improved through enhanced filtering algorithms
utilizing the additional information for topological discrimination of
electromagnetic and hadronic shower shapes. This paper presents the final
designs of the new electronic elements, their custom electronic devices, the
procedures used to validate their proper functioning, and the performance
achieved during the commissioning of this system.  JINST pdftitle=LAr
document,pdfauthor=The ATLAS LAr Collaboration

###### Contents

  1. 1 Introduction
  2. 2 Overview of the LAr readout electronics
  3. 3 New Front-End electronics
    1. 3.1 Baseplanes
    2. 3.2 Layer Sum Boards
    3. 3.3 LAr Trigger Digitizer Boards
      1. 3.3.1 Analog-to-Digital Converter

##  1 Introduction

During the second Large Hadron Collider (LHC) Long Shutdown (LS2), the Liquid
Argon (LAr) calorimeters of the ATLAS experiment have been equipped with new
trigger readout electronics [phase1tdr], which provides digital information to
the ATLAS trigger system [TRIG-2011-02]. The purpose of this so-called Phase-
Iupgrade is to enhance the physics reach of the experiment during the upcoming
operation at increasing LHC luminosities. ATLAS ran in the Run 2data taking
period (years 2015–2018) at a typical maximum instantaneous luminosity of
$1.9\times$and with an average mean number of proton-proton interactions of
$\avgmu=33$ [ATLAS-CONF-2019-021]. During Run 3(years 2022–2025) the
instantaneous luminosity was originally expected to increase to a peak value
of $3\times$, with $\avgmu\approx 80$ [phase1tdr]. The updated LHC plan for
Run 3targets a beam intensity increase of 50% compared to Run 2with a
luminosity leveled to $2\times$over periods up to 12 hours. The center-of-mass
energy will also be raised from =13 to 13.6. These changes will result in an
overall detector occupancy increase, while the first level trigger (L1)
bandwidth will remain at 100kHz during Run 3. If the currently used LAr
trigger readout system, referred to as _legacy_ trigger readout in the
following, were to remain unchanged, the transverse energy () trigger
thresholds would need to be raised, degrading the physics performance. To
avoid this efficiency loss and enhance the physics reach of the experiment in
Run 3and beyond, the new system installed during LS2 increases the readout
granularity by up to a factor of ten: instead of summing the of calorimeter
cells in areas as small as $\Delta\eta\times\Delta\phi=0.1\times 0.1$ to form
the so-called _Trigger Towers_ of the legacy readout, additional lateral and
longitudinal segmentation is introduced to form smaller clusters called _Super
Cells_. Trigger Towers are typically split longitudinally into four layers,
and some layers are split laterally along $\eta$ into four strips each. One
Super Cell can thus cover an area as small as
$\Delta\eta\times\Delta\phi=0.025\times 0.1$, depending on which longitudinal
layer it is located in. In addition, the precision and range of the
measurement is also increased. Consequently, the background rejection at
trigger level is improved due to better filtering algorithms being possible
already at L1, based on topological discrimination between electromagnetic
shower shapes and hadronic activity. In particular, the resulting electron,
photon and tau lepton identification is more efficient. Furthermore, thanks to
more advanced reconstruction algorithms and better pile-up subtraction
techniques, the energy resolution for electromagnetic, jet and missing objects
is improved, leading to a sharper rise of the per-event trigger efficiency
toward its plateau value.

The Phase-Iupgrade project is part of a broad upgrade program of the LAr
calorimeters through the lifetime of the LHC and is fully compatible with the
future Phase-IIupgrade program of the ATLAS experiment planned for the third
Long Shutdown (LS3) in 2026–2028.

This paper presents the new system, initially proposed in Reference
[phase1tdr] and installed during LS2, together with its performance. The final
designs of the new electronic boards and their Application-Specific Integrated
Circuits (ASICs) are described as well as the procedures used to validate
their proper functioning. The basic performance achieved during the
commissioning of this system is also presented. In 2, the legacy readout
electronics is briefly recapitulated and the new trigger readout electronics
is introduced, as are the new data paths. The new electronics installed on the
ATLAS detector (Front-End) and off the detector (Back-End) is described in
3LABEL:sec:be, respectively. Finally, the integration tests performed to
validate the full chain of this new readout electronics are reported in
LABEL:sec:integration before the conclusions are presented in
LABEL:sec:conclusion.

##  2 Overview of the LAr readout electronics

The readout electronics of the LAr calorimeters is designed to record energies
approximately ranging from 50 to 3, measured in 182418 calorimeter cells. The
energy resolution of the calorimeter for electromagnetic showers can be
written as $\sigma_{E}/E=a/\sqrt{E}\oplus b\oplus c/E$, with an intrinsic
sampling term $a$ that is typically 10–11% $\sqrt{\GeV}$ [TestBeam2006,
TestBeam2007], a constant term $b$ that is 1–2% [PERF-2017-03], and a noise
term $c$ that is 10–600 without pile-up contribution [LArElecPerf2010] and is
expected to be 30–3 in Run 3pile-up conditions [phase1tdr], depending on the
pseudorapidity region considered (up to $|\eta|<3.2$). The triangular pulse
coming from the ionization in a LAr cell is shaped into a bipolar pulse that
is sampled at 40MHz. The digitized samples are read at the L1 trigger rate,
that can go up to 100kHz. The LAr calorimeter system is composed of four
different components: the electromagnetic barrel (EMB) and end-caps (EMEC),
both referred to as EM calorimeters; the hadronic end-cap (HEC); and the
forward calorimeter (FCal). These components are divided in two sides, A and
C, oriented respectively along the positive and negative $z$-axis of the
experiment. The LAr readout electronics is divided into a Front-End and a
Back-End system, both interconnected by cables and optical fibers as shown in
Figure 1.

Figure 1: The ATLAS LAr calorimeter electronic architecture as of LHC Run 3.
The new LAr boards are highlighted in orange. This diagram depicts the EM
calorimeters; HEC and FCal electronics are slightly different.

The Front-End system is composed of 58 Front-End Crates (FECs), each hosting
at most two baseplanes which interconnect the following legacy system boards:

Front-End Boards (FEBs):

process typically 128 channels, each in a specific longitudinal layer of the
calorimeter. They amplify, shape, sample and digitize the ionization signals
and transmit them to the Back-End readout. The analog sums needed for the
trigger system are also prepared by the Linear Mixers and the Layer Sum Boards
(LSBs), both hosted on the FEBs. The Linear Mixer electronics is part of the
shaper chip located on the FEB motherboard, while the LSB is a plug-in card
connected to the Linear Mixer.

Tower Builder Boards (TBBs):

form the legacy Trigger Towers from the analog sums provided by the LSBs over
the FEC baseplanes. The Trigger Tower analog signals are sent to the L1
trigger system via copper cables. In the HEC and FCal no further sums need to
be produced after the LSB. Therefore, Tower Driver Boards (TDBs) are used in
place of TBBs.

Calibration Boards:

inject current calibration pulses whose shape is close to the pulse generated
from the LAr ionization signal.

Controller Boards:

receive the configuration and monitoring commands from the Serial Protocol for
Atlas Calorimeter [SPAC] (SPAC) masters installed in the Back-End Readout
Crates. Controller boards receive also the Timing Trigger and Control [TTC]
(TTC) signals coming from the Back-End TTC crates. They distribute the SPAC
and TTC commands to the other legacy boards in the FEC.

Some FECs also host monitor boards transmitting the information from the
sensors measuring possible mechanical stresses of the detector and the LAr
temperature and purity. Another function of some of the monitor boards is to
measure the status of the FECs’ low-voltage power supplies. Each electronic
board in a FEC is conductively cooled using two aluminium plates placed on
each side of the board. These aluminium plates are part of a leak-less water
cooling system.

On the Back-End side, two legacy systems are present:

Readout Crates (ROCs):

Versa Module Eurocard (VME) crates hosting Readout Driver boards (RODs) that
read the Analog-to-Digital Converter (ADC) data sent by the FEBs and compute
energy ($E_{\textrm{C}}$) and time ($t_{\textrm{C}}$) for each cell signal at
the L1 trigger rate. The ROCs also house the SPAC master boards and the
Trigger Busy Modules (TBMs). The latter collect the busy signals from the RODs
and distribute the TTC signals.

TTC crates:

VME crates containing the modules that receive the TTC commands from the ATLAS
Central Trigger Processor (CTP) system or generate locally these commands and
transmit them to the other LAr boards.

The LAr electronics upgrade extends the legacy system with new Front-End
components, sending the Super Cells’ digital data to new Back-End components,
which compute and transmit the Super Cells’ to the new trigger system. The
architecture as of Run 3is illustrated in Figure 1. This new LAr trigger
readout system is composed of new Layer Sum Boards providing the analog sums
for the higher trigger readout granularity; new baseplanes to route the
increased number of analog signals and host the new LAr Trigger Digitizer
Boards (LTDBs) that digitize the Super Cell analog signals at 40MHz and
provide the legacy sums for the TBBs; and new Back-End boards, the LAr Digital
Processing Blades (LDPBs), that read the Super Cell ADC signals from the
LTDBs, compute the Super Cells’ and send them to the new L1 trigger system.
This new trigger system comprises a set of Feature EXtractors (FEX) with three
subsystems targeting electromagnetic (eFEX), jet (jFEX) and global (gFEX)
features [ATLAS-TDR-23]. The choice to convert the Super Cells’ energy to at
the LDPB level was made to simplify the LTDB design. The LDPB is built in
Advanced Telecommunications Computing Architecture (ATCA) format and comprises
one ATCA carrier blade named LAr Carrier (LArC) and up to four Advanced
Mezzanine Cards (AMCs) called LAr Trigger prOcessing MEzzanines (LATOMEs). The
hardware control and monitoring of each blade proceeds via an Intelligent
Platform Management Controller (IPMC) plugged into the LArC. In total, 124
LTDBs are installed on the 114 new baseplanes. Furthermore, 30 LDPBs
corresponding to 30 LArCs and 116 LATOMEs, are installed in three ATCA shelves
placed in one 19-inch rack. This new LAr system uses also three separate
Front-End LInk eXchange (FELIX) [felix] systems, comprising a total of 30
FELIX boards.

Figure 2: The ATLAS LAr calorimeter digital trigger readout system installed
during the second LHC long shutdown.

The new trigger readout path is illustrated in Figure 2 with solid red arrows.
In order to ease the new system commissioning and have a fallback solution in
case of unforeseen issues, the legacy trigger readout is kept functional since
the LTDB sends the re-summed analog signals to the TBB, which will remain in
operation during at least the initial phase of the LHC Run 3. The legacy
trigger readout path is illustrated in Figure 2 with dashed red arrows.

Several other data paths are present in the system. A global monitoring path
utilizes a Full Mode [felix] data link between each LATOME and the FELIX
system that connects to the ATLAS main data readout (path in orange arrows in
Figure 2). Its purpose is to verify that the sent to the trigger system is
correct, by reading the Super Cell ADC data and the values for all events
selected by the first level trigger accept signal (L1A). Thus, this readout
allows a recomputation of the calculation performed in the LATOME boards.

A similar monitoring path utilizes the 10 Gigabit Ethernet (GbE) interface of
the ATCA shelf that hosts the LDPBs (blue arrow in Figure 2). This readout is
not connected to the ATLAS main readout but is used by a processing server
specific to the LAr system. It enables a more flexible and localized
monitoring to readout Super Cell ADC data and at the L1A signal rate or
optionally at any other rate, independently of the constraints present in the
ATLAS main data readout in terms of bandwidth and event rate.

The whole system is synchronized with the TTC signals (green arrows in Figure
2). These signals provide the 40MHz LHC reference clock, the L1A, the Bunch
Counter Reset (BCR), the Event Counter Reset (ECR) and the Trigger Type
commands. The BCR corresponds to the LHC orbit frequency and enables the
determination of the collision time of an event via its Bunch Crossing
IDentifier (BCID). The ECR is used to compute an event identifier and the
Trigger Type records which subsystem issued the L1A. The TTC signals are
transmitted to LTDB and LDPB through FELIX systems with Gigabit Transceiver
(GBT) [GBT1, GBT2] links.

The configuration of the LTDB and LDPB hardware proceeds via a ”Partition
Master” PC. This computer is connected to LTDBs in three stages: two Open
Platform Communications Unified Architecture (OPC UA) servers and a FELIX
system, connected to LTDBs via GBT links. The first OPC UA server takes care
of the LTDB configuration command generation, according to the run control
commands received from the Partition Master. The second OPC UA server packs
these specific commands to follow the GBT protocol. The Partition Master
connection to the LDPB is made directly via a 1GbE interface.

A Detector Control System [DCS] (DCS) handles the hardware monitoring: it
ensures that the hardware is operated under safe conditions and provides basic
safety mechanisms in case of failure. The connection to the LTDB is made with
a part of the same OPC UA and FELIX chain used for the configuration. The LDPB
is connected to the DCS via an OPC UA server and the ATCA shelf manager,
interfaced to the IPMC on the LDPB via an Intelligent Platform Management Bus
(IPMB).

Some differences exist in the signal processing between the main and trigger
readout systems: the analog signal processing in the main readout comprises
pre-amplification followed by shaping performed in three different gain
scales, such that three overlapping gains are obtained with a ratio of about
10. The bipolar shape is created with a time constant of 13ns. The samples
stored by the Switched Capacitor Array (SCA) analog pipeline chip are
digitized by a 12-bit ADC and sent to the Back-End system via a 1.6 Gigabit
per second (Gbps) optical link. In the trigger readout, the analog processing
has a similar shaping with only one gain scale, but with a special
conditioning described in LABEL:sssec:ltdb-motherboard. The Super Cells’
digital samples generated in the LTDBs are sent to the Back-End system with a
5.12Gbps optical link. While in the main readout the RODs compute the cell
energies and signal times at the L1A rate (up to 100kHz), the LDPBs of the
trigger readout compute the Super Cell transverse energies
($E^{\textrm{T}}_{\textrm{SC}}$) and signal times ($t_{\textrm{SC}}$) at the
LHC collision rate (40MHz).

The new trigger readout aims to have an Integral Non-Linearity (INL) for each
Super Cell channel below 1% with a Super Cell energy computation precision
below 250. Even under high pile-up data taking conditions, this computation
must remain unbiased.

In the following, the new hardware, as well as the procedures carried out to
validate its functionalities, are described in detail.

##  3 New Front-End electronics

###  3.1 Baseplanes

At each end of the barrel cryostat 32 calorimeter signal feedthroughs
[Axen:2005vb] are installed, distributed around the cylindrical periphery at
nearly uniform angles. Each of the two end-cap cryostats has 25 signal
feedthroughs distributed around the far end (from the collision point) of its
periphery. Each feedthrough with cold and warm flanges connected via vacuum
cables is made up of four pin carriers. Each pin carrier has either seven or
eight connectors and each connector has 64 signal pins. A pedestal spans two
adjacent feedthroughs and a FEC is mounted on each pedestal. Each FEC is
divided into two halves with a baseplane installed in each half for almost all
of the crates, see Figure 3. For each connector in a pin carrier a flex ribbon
cable carries 64 signals from the feedthrough to a connector on the back side
of the baseplane. The pins in this connector extend through to the front side
of the baseplane. A FEB has two 64-pin signal connectors and this board,
mounted in a FEC, plugs into the baseplane. Between the two signal connectors
on each FEB is a third 64-pin connector, which returns analog trigger signals
to the baseplane where they are routed to trigger-handling boards, also
plugged into the baseplane.

Figure 3: Perspective drawing of a FEC mounted on its pedestal. Simplified
sketches of the two baseplanes can be seen mounted on the pedestal inside the
crate.

For the Phase-I upgrade, new baseplanes are required (1) to accommodate the
finer trigger segmentation, (2) to make room for the LTDBs (Section 3.3), and
(3) to maintain the legacy Level-1 trigger system. The new mezzanine LSBs
(Section 3.2), mounted on the existing FEBs, provide more analog signals than
before onto the baseplanes, which are now routed to both the LTDBs and to the
existing TBBs or TDBs requiring additional signal layers on the baseplane
Printed Circuit Boards (PCBs). Because the LTDB baseplane connectors are wider
than those for the other boards plugged into the baseplane, there is no space
next to an LTDB for the Radio Frequency (RF) shields which protect the small-
signal inputs to the FEBs from extraneous noise. This requires, in some cases,
additional slots and/or significant re-arrangement of the baseplane slot
assignments, as well as thicker baseplane PCBs, whose thickness is highly
constrained by the existing size of the FEC and FEBs. Table 1 gives an
overview of the physical dimensions of the various baseplane types.

Table 1: Overview of the number of PCB layers, physical dimensions and numbers installed on the detector for the various baseplane types. Side A and side C are oriented along the positive and negative $z$-axis of the experiment. | EMB |  | EMEC
---
Standard
| EMEC
---
Special
HEC |  | FCAL
---
side A
| FCAL
---
side C
PCB layers | 12 | 12 | 14 | 12 | 16 | 16
Length [mm] | 388.00 | 388.00 | 522.73 | 260.00 | 450.60 | 490.00
Width [mm] | 415.00 | 415.00 | 415.04 | 415.00 | 406.40 | 406.40
Thickness [mm] | 2.40 | 2.40 | 2.36 | 2.36 | 2.36 | 2.36
# on detector | 64 | 32 | 8 | 8 | 1 | 1
|  |  |  |  |  |

The new EMB baseplane has the same number of slots (19) as the original
baseplane. Space for the single new LTDB comes from a previously unallocated
slot at one end of the FEC. Some FEBs have been shifted by one slot to allow
the LTDB to sit in the middle slot of the baseplane next to the TBB (see
Figure 4). The flex ribbon cable connections underneath the baseplane are then
also shifted by the same amount.

Figure 4: Left: Photograph of an EMB Baseplane. The slot with three wider
baseplane connectors is for the LTDB. Just to the left of the LTDB is the slot
for the TBB and to the right is the Controller board slot. The calibration
board slot is on the far left and next to it is the monitor board slot. The
gold-colored RF shields surrounding connectors in the top and bottom rows
identify the FEB slots. Right: Close-up of an EMEC special baseplane showing
the RF shields and the wider LTDB connectors.

The EMEC crates house two different types of baseplanes. The EMEC standard
crate has baseplanes similar to the EMB but with one fewer FEB, leaving a slot
for an additional monitor board. The EMEC special crate has one baseplane for
the EMEC and another for the HEC. The EMEC special baseplane has two LTDBs and
it extends well beyond the center of the crate. The HEC baseplane in the other
side of the crate consequently has room for only 13 slots rather than the
normal 19 slots of the EMB baseplanes and the EMEC standard baseplanes. An
overview of the different boards which plug into the various baseplane types
can be found in Table 2.

Table 2: Overview of the different board types which plug into each of the baseplane types. | EMB |  | EMEC
---
Standard
| EMEC
---
Special
HEC | FCAL
FEBs | 14 | 13 | 17 | 6 | 14
LTDBs | 1 | 1 | 2 | 1 | 2
TBBs | 1 | 1 | 3 | 0 | 0
TDBs | 0 | 0 | 0 | 2 | 2
Calibration | 1 | 1 | 2 | 1 | 1
Controller | 1 | 1 | 1 | 1 | 1
Monitor | 1 | 2 | 0 | 0 | 1
Low Voltage Power | 0 | 0 | 0 | 2 | 0
Total | 19 | 19 | 25 | 13 | 21
|  |  |  |  |

The original FCal baseplanes had 19 slots, each fitting within one-half of a
FEC. The other half was used for devices which monitor the status of the
cryostats. The new FCal baseplanes each have two LTDBs and the baseplanes
extend two (three) slots into the now unused other half crate for the A-end
(C-end). Integrated into each new FCal baseplane are traces carrying pulses
from the calibration board through attenuating injection resistors (surface
mounted on the backside of the baseplane) to those pins on the baseplane
connectors which carry FEB signals.

Prototype and production baseplanes were subjected to a series of tests. For
those connector pins which are specified to be grounded, the impedance to
ground was confirmed to be consistent with zero. Likewise, connector pins
which are not specified to be grounded were also checked. The impedance of
traces on the baseplanes was measured with a time-domain reflectometer.
Continuity between trace ends was compared with the net lists. These mapping
tests were then compared with independent LTDB mapping requirements. Signal
integrity on the traces and cross-talk between near-by traces were measured
with a pulser and oscilloscope to verify that they met specifications. In the
case of the FCal baseplanes, the calibration injection resistors were all
measured for correct values. All baseplanes were shown to meet the
specifications.

###  3.2 Layer Sum Boards

In the LAr trigger readout, the first level of summing is provided by the
Linear Mixer, which sums over four channels in azimuth with different gains in
different regions of $\eta$. The upgrade to the trigger branch begins with the
ouput of this signal. The LSB is a plug-in card for the FEB that performs a
second level of summing of the analog signals [Buchanan:2008zza]. There are
two LSBs mounted on each FEB. For the Phase-Iupgrade, the new LSB output
provides signals for the finer granularity Super Cells in the front and middle
layers, while retaining the signals needed for the legacy trigger path
elsewhere. Six main types of new LSBs have been produced:

S2x8

The basic circuit on the board performs an analog sum of two input channels
from the Linear Mixer. There are eight copies of this circuit on each LSB.
There are 896 boards of this type required for the EMB and 192 for the EMEC,
with 288 reused from the original construction.

S2x8D

S2x8 LSBs were already used in the back layer of the EM calorimeters. For
Phase-I, this output signal must be sent to both the new LTDB and the legacy
TBB. A simple splitter is added to the S2x8 in order to produce this dual
output. There are 128 boards of this type required for the EMB and 160 for the
EMEC.

S1x16LN

This LSB has no summing function and only serves as a line driver for the
Linear Mixer signal. There are sixteen copies of this circuit on each LSB.
There are 448 boards of this type required for the EMB and 544 for the EMEC.

S1x12+S6x2

For the front section of the EMEC in the range $1.8<|\eta|<2.0$, the output
from the shapers covers the area $\Delta\eta\times\Delta\phi=0.0167\times
0.1$. These are sent individually to the LTDB, while sums of six inputs are
sent to the TBB. There are 128 boards of this type required for the EMEC.

S2x6D+S1x4

At the end of the EM Barrel ($|\eta|>1.4$), each LSB must handle four signals
originating from the middle layer and 12 signals from the back layer. The
signals from the back layer are summed and handled with the same circuitry as
the S2x8D and sent to the LTDB and TBB, while the four signals from the middle
are just passed directly to the LTDB as in the S1x16LN circuit. There are 128
boards of this type required for the EMB.

FCal

All the LSBs above form an unweighted sum of cells in a narrow region of
$\eta$, while in the FCal, one must perform a sum over a relatively wide range
in pseudorapidity, over which the conversion factor from energy to transverse
energy varies significantly. For this reason, the inputs to be summed on the
FCal LSBs are weighted to perform the conversion to transverse energy before
summing. This leads to a large variety of LSBs, which, within a given FCal
module, differ only by the weighting resistor values. All 56 FCal LSBs were
replaced by the new design.

The technical specifications for all the boards are that the gain should not
vary by more than 2% from nominal, the summing amplifier INL should be ¡ 1%,
and the Direct Current (DC) offset should be ¡ 2% of the maximum output
voltage. All boards were tested before and after a week-long burn-in. About
99% passed the specification and were delivered to CERN. As the replacement of
the baseplanes required that all electronics in the FECs be disconnected and
removed, all FEBs were brought to a surface laboratory. Here, the FEBs were
“opened” (i.e. the cooling plates dismounted) and the LSBs replaced by the new
boards. Figure 5 shows a photo of an example LSB.

Figure 5: Photo of an S1x16LN LSB. Only one side is shown. Half of the
components are on the other side. A one-euro coin is shown for scale.

###  3.3 LAr Trigger Digitizer Boards

An LTDB processes and digitizes up to 320 Super Cell signals (“channels”) and
transmits them via optical links to the Back-End, while also providing summed
analog legacy signals for the TBB via the new baseplanes. The following
sections describe the key ASICs for digitization and optical transmission, the
motherboard that houses them, the mezzanine card providing the power, quality
assurance and control for the assembled system as well as considerations on
compatibility with the Phase-IIupgrade.

####  3.3.1 Analog-to-Digital Converter

A custom, quad-channel, pipeline ADC was designed to process the shaped analog
signals from the LAr calorimeter Super Cells. These signals are continuously
sampled and digitized at 40 Megasamples per second. To digitize the energy of
the trigger signals, the ADC has a dynamic range of approximately 12 bits
(after calibration) with a required precision of at least 10 bits [phase1tdr].
Each ADC consumes 45mW per channel and has a latency of less than 125ns,
meeting the power and latency budgets at the system level of less than 145mW
per channel and 200ns, respectively.

Radiation tolerance is a key requirement for the ADC, as it is for all devices
located on-detector and within the substantial radiation field. The device
must operate reliably through the remaining LHC run, as well as the High
Luminosity LHC (HL-LHC) runs, with a total expected integrated luminosity of
3000


# WikiConv: A Corpus of the Complete Conversational History of a Large Online
Collaborative Community

Yiqing Hua
Cornell Tech
<EMAIL_ADDRESS>
Cristian Danescu-Niculescu-Mizil
Cornell University
<EMAIL_ADDRESS>
&Dario Taraborelli
Wikimedia Foundation
<EMAIL_ADDRESS>
Nithum Thain  Jeffery Sorensen  Lucas Dixon
Jigsaw, Google
nthain, sorenj<EMAIL_ADDRESS>
###### Abstract

We present a corpus that encompasses the complete history of conversations
between contributors to Wikipedia, one of the largest online collaborative
communities. By recording the intermediate states of conversations—including
not only comments and replies, but also their modifications, deletions and
restorations—this data offers an unprecedented view of online conversation.
This level of detail supports new research questions pertaining to the process
(and challenges) of large-scale online collaboration. We illustrate the
corpus’ potential with two case studies that highlight new perspectives on
earlier work. First, we explore how a person’s conversational behavior depends
on how they relate to the discussion’s venue. Second, we show that community
moderation of toxic behavior happens at a higher rate than previously
estimated. Finally the reconstruction framework is designed to be language
agnostic, and we show that it can extract high quality conversational data in
both Chinese and English.

##  1 Introduction

Compared to large-scale collections of conversations from social media Felbo
et al. (2017); Luo et al. (2012); Zhang et al. (2017); Tan et al. (2016) or
news comments Napoles et al. (2017), Wikipedia talk pages offer a unique
perspective into goal-oriented discussions between thousands of volunteer
contributors coordinating to write the largest online encyclopedia. Talk page
data already underpins research on social phenomena such as conversational
behavior Danescu-Niculescu-Mizil et al. (2012, 2013), disputes Wang and Cardie
(2014b), antisocial behavior Wulczyn et al. (2017); Zhang et al. (2018) and
collaboration Kittur et al. (2007); Halfaker et al. (2009). However, the scope
of such studies has so far been limited by a view of the conversation that is
incomplete in two crucial ways: first, it only captures a subset of all
discussions; and second, it only accounts for the final form of each
conversation, which frequently differs from the interlocutors experience as
the conversation develops.

In this paper, we undertake the challenge of reconstructing a complete and
structured history of the conversational process in Wikipedia talk pages,
containing detailed information about all the interlocutors’ actions, such as
adding and replying to comments, modifying or deleting them. To this end, we
devise a methodology for identifying and structuring these actions, while also
addressing the challenges spurring from the inconsistent formatting and the
raw scale of existing records. This results in the largest public dataset of
goal-oriented conversations, WikiConv, spanning five languages. The largest
component of this dataset is based on the English Wikipedia, and contains
roughly 91 million conversations consisting of 212 million conversational
actions taking place in 24 million talk pages.

By including details about how each conversation evolved, this corpus provides
an unprecedented view into the conversational process, as experienced by the
interlocutors. In fact, we find that about $40\%$ of discussion activity would
be missed by approaches that do not consider comment modifications and
deletions, and even more is missed when only considering the (final) static
snapshots of conversations. Furthermore, a manual review of the English
Wikipedia portion of the dataset reveals that $98\%$ of the reply structure is
recovered correctly and $98\%$ of the interlocutor’s actions are categorized
correctly.

Since the reconstruction pipeline does not rely on any language specific
heuristics, we also apply it to Chinese, German, Greek and Russian Wikipedia
Talk page archives, in addition to those from English Wikipadia. A manual
review of the conversations obtained from the Chinese Wikipedia Talk pages
shows a similarly high reconstruction accuracy with that obtained from the
English Wikipedia, suggesting that it is reasonable to apply the
reconstruction pipeline to different languages. To encourage further
validation, refinements and updates, we have open sourced the code and
published the
datasets.111https://github.com/conversationai/wikidetox/tree/master/wikiconv

Finally, we present two case studies illustrating how the corpus can bring new
insights into previously observed phenomena. We first analyze the
conversational behavior of a subset of English Wikipedia contributors across
the entire range of talk pages, and show that their levels of linguistic
coordination vary according to where the conversation takes place. Second, we
investigate the toxicity of deleted comments, and show that community
moderation of undesired behavior takes place at a much higher rate than
previously estimated.

##  2 Further Related Work

Past efforts aimed at characterizing conversations on Wikipedia talk pages
have either focused on snapshots of discussion threads Danescu-Niculescu-Mizil
et al. (2012); Prabhakaran and Rambow (2016); Wang and Cardie (2014b, a), or
have considered text segments in talk page history as incremental comments,
ignoring conversational turns and reply structures within these conversations
Wulczyn et al. (2017). The limitations of these approaches can be seen in
Figure 2, where, if we limit our analysis to only a snapshot of the final
state of the conversation, we miss the abusive comment introduced in revision
3 and removed in revision 4, and thus miss an important part of the experience
of the participants. In fact, this “hidden” activity accounts for one third of
all actions taken on talk pages in English Wikipedia.

The closest dataset to our work is Bender et al. (2011) which introduces the
Authority and Alignment in Wikipedia discussions corpus (AAWD), containing 365
talk page discussions. While acknowledging the complexity of conversational
behaviors on Wikipedia talk pages, the AAWD work falls short of providing data
on the deletions and follow-up changes to existing comments. Beyond addressing
this shortcoming, the dataset we introduce in this paper is many orders of
magnitude larger, containing 91 million conversations in English Wikipedia
alone.

Figure 1:  An example of Wiki markup and its rendered form from Wikipedia Talk Page Help.333mediawiki.org/wiki/Help:Talk_pages Figure 2:  Example conversation reconstruction. The action id in the ReplyTo column defines the conversation’s structure; The Parent column indicates history, showing how actions change earlier actions. Note that each revision (color-coded) can introduce multiple actions. English Wikipedia | Reconstruction Accuracy by Action Type
---|---
Number of | Action Type Breakdown | Boundary | Type | ReplyTo | Parent
Distinct users |  $4.4$M | Creation | $21\%$ | $100\%$ | $100\%$ | $100\%$ | $100\%$
Talk Pages |  $24$M | Addition | $39\%$ | $96\%$ | $100\%$ | $95\%$ | $100\%$
Revisions |  $120$M | Modification | $13\%$ | $97\%$ | $95\%$ | $97\%$ | $95\%$
Conversations |  $91$M | Deletion | $24\%$ | $94\%$ | $96\%$ | $100\%$ | $100\%$
Actions |  $212$M | Restoration | $3\%$ | $84\%$ | $98\%$ | $100\%$ | $99\%$
|  | All actions: | $96\%$ | $98\%$ | $98\%$ | $99\%$
Chinese Wikipedia | Reconstruction Accuracy by Action Type
Number of | Action Type Breakdown | Boundary | Type | ReplyTo | Parent
Distinct users |  $87$K | Creation | $22\%$ | $100\%$ | $100\%$ | $100\%$ | $100\%$
Talk Pages |  $2.2$M | Addition | $50\%$ | $96\%$ | $100\%$ | $100\%$ | $100\%$
Revisions |  $4.6$M | Modification | $9\%$ | $84\%$ | $94\%$ | $99\%$ | $97\%$
Conversations |  $4.4$M | Deletion | $16\%$ | $99\%$ | $90\%$ | $100\%$ | $98\%$
Actions |  $6.4$M | Restoration | $3\%$ | $97\%$ | $98\%$ | $100\%$ | $98\%$
|  | All actions: | $96\%$ | $98\%$ | $99\%$ | $99\%$
Table 1:  Summary statistics and reconstruction accuracy for the English and
Chinese Wikipedia talk page corpora. These statistics exclude actions that
result in empty content after markup cleaning (e.g., purely formatting edits).

##  3 Conversation Reconstruction

Technically, comments are added to Wikipedia talk pages the same way content
is added to article pages: contributors simply edit the markdown of any part
of the talk page without relying on any functionality specialized for
structuring the conversations. Figure 1 gives an example of the discussion
interface and the resulting rendered conversation. Each edit results in a
revision of the whole page that is permanently stored in a public historical
record.444In some rare cases revisions are deleted, for example, if personal
information is accidentally written into a page. Because conversations on
Wikipedia have no ‘official’ underlying structure, and instead are organized
using indentation markup and other ad hoc visual cues, computational
heuristics are necessary to interpret conversational structure.
Actions. We model the conversational structure of interactions as a graph of
actions, as illustrated in Figure 2. Actions are categorized into five types:
$\bullet$ Creation: A conversation thread is started by adding a markup
section heading (e.g., Action 1 in Figure 2).
$\bullet$ Addition: A new comment is added to a thread (e.g., Actions 2 and
3).
$\bullet$ Modification: An existing comment is modified (e.g., Action 5); the
Parent-id indicates the original comment.
$\bullet$ Deletion: A comment or thread-heading is being removed (e.g., Action
4); Parent-id specifies the comment or thread-heading’s most recent action.
$\bullet$ Restoration: A deletion is being reverted, returning to the state
indicated by the Parent-id.
All action types except thread creations, thread deletions and thread
restorations also include a ReplyTo-id indicating the target of the reply.
From Page Revisions to Actions. Our reconstruction pipeline is a Python
program written for Google Cloud Dataflow (also known as Apache
Beam)555https://cloud.google.com/dataflow/ that operates on pages in parallel
and on the revisions of each page sequentially in temporal order.

Due to the large scale of Wikipedia data, we use external sorting for pages
that contains too many revisions to fit in a Dataflow worker’s memory. When
the number of revisions is too large for a Dataflow worker’s local disk, the
computation is performed in stages, a few years at a time.

Given the sorted set of a page-revisions, token-level diffs between sequential
revisions are computed using a longest common sequence (LCS)
algorithm.666github.com/google/diff-match-patch Each sequential diff is then
decomposed into the set of atomic conversation actions attributed to the user
who submitted the page revision. During the sequential processing of a page’s
revisions, two data structures are maintained: each comment’s current
character offset, and a list of deleted comments. The comment offsets are used
to interpret the difference between modification actions (edits within the
bounds of an existing action) and additions; the deleted comments are used to
identify restoration of comments.

We store the most recent 100 deleted comments between 10 to 1000 characters
long, for each page. This is used to compute when a comment is restored by
looking up deleted comments in a trie. The token length lower bound parameter
avoids short commonly added comments—like “Thanks!”—from being interpreted as
restorations. The upper bound ensures that occasional very long deleted
comments are skipped, to bound Dataflow workers’ memory usage.

Finally, reconstructed actions are processed using
mwparserfromhell777github.com/earwig/mwparserfromhell to clean the MediaWiki
formating. Note that, since arbitrary page changes are allowed, some actions
cannot be processed by the parser (about 1 in 200,000); in such cases, an
action’s raw MediaWiki markup is stored.

Table 1 shows summary statistics of the final dataset on English and Chinese
Wikipedia. The version of the raw data dumps processed were retrieved on July
1st 2018.

##  4 Evaluation of Reconstruction Quality

We evaluate the quality of the automatic reconstruction by manually verifying
a randomly drawn subset of (at least) 100 examples from each action category.
For each action we verify the accuracy of (1) the assigned action type, (2)
the token-level boundary of the comment, (3) the ReplyTo relation and (4) the
action’s Parent relation.

We conduct the evaluation for both English and Chinese data (Table 1). With
over $98\%$ of actions classified correctly in both languages, the dataset
exhibits a high annotation quality given its scale and detail. From the error
cases in the English data, 10% result from limitations in the current
technologies for HTML parsing and LCS matching. User behavior that we could
interpret but is not yet captured by our algorithm, such as moving ongoing
conversations to another talk pages accounts for another 24%. The remaining
errors were from edits that we were unable to interpret. By open sourcing the
reconstruction code, we encourage further refinements.

Figure 3:  (Left) Linguistic coordination depends on the discussion’s venue.
Error bars are estimated by bootstrap resampling. (Right) Deletion rate of
content over varying time periods.

##  5 Case Studies

We now briefly present two studies on English Wikipedia that highlight the
importance of (1) collecting the full history of Wikipedia across all pages
and (2) capturing the various types of interactions.

Linguistic Coordination. Danescu-Niculescu-Mizil et al. (2012) studied
language coordinations (i.e., in a conversation between $a$ and $b$, to what
degree is $b$ systematically adopting $a$’s language patterns when replying to
$a$) on a conversational corpus derived from $5,657$ User Talk pages: those
associated with, and managed by, a specific user. The study showed that social
status mediates the amount of linguistic coordination, with contributors
imitating more the linguistic style of those with higher status in the
community.

We now show that the coordination pattern of the page owners in the previous
dataset differs significantly based on where the conversation takes place. We
compare each contributor’s coordination patterns on their own user talk page
to patterns exhibited on talk pages of other contributors, as well as to those
on article talk pages—talk pages associated with a Wikipedia article. To avoid
confounding different populations (and fall into the trap of Simpson’s
paradox), we only include in the comparison users that had a sufficient amount
of contributions across all three venues. Figure 3 shows the three aggregated
coordination values computed by applying the methodology of the original paper
on 4 million addition actions that occurred before 2012.

Our results show with significant difference ($p<0.001$ calculated by one-way
ANOVA) that contributors coordinate the least when replying on other users’
talk pages, and most on their own talk page. This leads us to speculate a new
hypothesis: contributors have a different perception of status or respect on
their own page than on others. Such questions, which require more thorough
investigation that depends on observing how contributors interact across
different discussion venues, can be studied using the WikiConv corpus.

Moderation of toxic behavior. Wulczyn et al. (2017) measured prevalence of
personal attacks in a Wikipedia talk page corpus, and evaluated the fraction
of attacks that moderators follow up on with a block or warning ($17.9\%$).
However, because there was no structured history of comment deletion, the
authors were unable to measure the rate at which toxic comments are moderated
through deletion. Using the more complete datasets provided by WikiConv we
show that the fraction of problematic comments moderated by Wikipedians is
significantly higher than their initial estimate suggests.

We used the Perspective API888https://www.perspectiveapi.com to score the
toxicity of all addition and creation actions (which we refer to as “comments”
here).999We release the scores with the dataset. Each comment is further
classified as toxic or non-toxic according to the equal error rate threshold,
following the methodology of Wulczyn et al. (2017), where false positives are
offset by false negatives. The threshold is calculated by on the human labels
in the Kaggle Toxicity dataset of Wikipedia comments.101010The Jigsaw Toxicity
Kaggle Competition: goo.gl/N6UGPK Classification at this threshold yields
$86\%$ precision and $84\%$ recall.

We used the same method to labeled comments with the _severe toxic_ model.
Figure 3 shows the fraction of comments deleted by Wikipedians who are not the
author of the comment for different lengths of time; distinguishing between
comments labeled as toxic, severely toxic, and the background distribution.
The key observations here are that nearly $33\%$ of toxic comments are removed
within a day; and over 82% of severely toxic comments are deleted within a
day. This complements results previously reported by Wulczyn et al. (2017),
accounting for an additional type of community moderation that is revealed
using the detailed information about the history of the conversation provided
by our corpus.

##  6 Conclusion and Future Work

We introduced a pipeline that extracts the complete conversational history of
Wikipedia talk pages at a level of detail that was not previously available.
We applied this pipeline to Wikipedia in multiple languages and evaluated its
quality on the English and Chinese Talk page corpora, obtaining a high
reconstruction accuracy for both the Chinese and English datasets (98%). This
level of detail and completeness opens avenues for new research, as well as
for revisiting and extending existing work on online conversational and
collaboration behavior. For example, while in our use cases we have focused on
contributors deleting toxic comments, one could seek to understand why and
when an editor is deleting or rewording their own comments. Beyond refining
the heuristics and parsing methods used in our reconstruction pipeline, and
reducing the time to update the corpus, a remaining challenge is to capture
conversations that happen across page boundaries.

##  7 Acknowledgement

We thank Thomas Ristenpart, Andreas Veit for proof reading; Ben Vitale for
many helpful discussions on building the pipeline; and Jonathan P. Chang for
reporting data issues and discussing the challenges throughout. This project
is supported in part by NSF grant CNS-1558500.

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