Physics Le e s B 772 (2017) 567–577
Con en s lis s a ailable a ScienceDi ec
Physics Le e s B
www.else ie .com/loca e/physle b
Cen ali y dependence o he pseudo apidi y densi y dis ibu ion o
cha ged pa icles in Pb–Pb collisions a √sNN =5.02 TeV
.ALICE Collabo a ion
a i c l e i n o a b s a c
A icle his o y:
Recei ed 9 Janua y 2017
Recei ed in e ised o m 19 June 2017
Accep ed 9 July 2017
A ailable online 14 July 2017
Edi o : L. Rolandi
We p esen he cha ged-pa icle pseudo apidi y densi y in Pb–Pb collisions a √sNN =5.02 TeV in
cen ali y classes measu ed by ALICE. The measu emen co e s a wide pseudo apidi y ange om −3.5
o 5, which is sufficien o eliable es ima es o he o al numbe o cha ged pa icles p oduced in he
collisions. Fo he mos cen al (0–5%) collisions we find 21 400 ±1 300, while o he mos pe iphe al
(80–90%) we find 230 ±38. This co esponds o an inc ease o (27 ±4)%o e he esul s a √sNN =
2.76 TeV p e iously epo ed by ALICE. The ene gy dependence o he o al numbe o cha ged pa icles
p oduced in hea y-ion collisions is ound o obey a modified powe -law like beha iou . The cha ged-
pa icle pseudo apidi y densi y o he mos cen al collisions is compa ed o model calcula ions — none
o which ully desc ibes he measu ed dis ibu ion. We also p esen an es ima e o he apidi y densi y
o cha ged pa icles. The wid h o ha dis ibu ion is ound o exhibi a ema kable p opo ionali y o
he beam apidi y, independen o he collision ene gy om he op SPS o LHC ene gies.
©2017 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY license
(h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by SCOAP3.
1. In oduc ion
In ul a- ela i is ic hea y-ion collisions a dense and ho phase
o nuclea ma e is c ea ed [1–4]. This phase o QCD ma e is
conside ed o be a plasma o s ongly in e ac ing qua ks and glu-
ons and is he e o e labelled he sQGP [5]. The mul iplici y o
p ima y, cha ged pa icles p oduced in hea y-ion collisions is a
key obse able o cha ac e ise he p ope ies o he ma e c ea ed
in hese collisions [6]. The s udy o he p ima y cha ged-pa icle
pseudo apidi y densi y (dNch/dη) o e a wide pseudo apidi y (η)
ange and i s dependence on colliding sys em, cen e-o -mass en-
e gy, and collision geome y is impo an o unde s and he ela-
i e con ibu ions o pa icle p oduc ion om ha d sca e ings and
so p ocesses, and may p o ide insigh in o he pa onic s uc u e
o he in e ac ing nuclei.
We ha ep e iously epo ed measu emen sonp ima y cha ged-
pa icle pseudo apidi y densi ies o e a wide pseudo apidi y ange
in Pb–Pb collisions a he cen e-o -mass ene gy pe nucleon pai
√sNN =2.76 TeV [7]. In his Le e , we s udy hese dis ibu ions in
he pseudo apidi y in e al om −3.5 o 5a a collision ene gy o
√sNN =5.02 TeV as a unc ion o he cen ali y. Pseudo apidi y is
defined as η≡− log( an(ϑ/2)), whe e ϑis he angle be ween he
cha ged-pa icle ajec o y and he beam axis (z-axis). Nuclei a e
ex ended objec s, and hei collisions can be cha ac e ised by cen-
ali y — he expe imen al p oxy o he un-measu able dis ance
E-mail add ess: [email p o ec ed].
be ween he cen es o he colliding nuclei (impac pa ame e ).
Ap ima y pa icle is a pa icle wi h a mean p ope li e ime τ
la ge han 1cm/c, which is ei he a) p oduced di ec ly in he
in e ac ion, o b) om decays o pa icles wi h τsmalle han
1cm/c, es ic ed o decay chains leading o he in e ac ion [8]. In
his Le e , all quan i ies epo ed a e o p ima y cha ged pa i-
cles, hough we will omi “p ima y” o b e i y.
Wi h he la ge pseudo apidi y co e age a ailable in ALICE, we
can eliably es ima e, o all cen ali y classes, he o al numbe
o cha ged pa icles p oduced in he collisions. We he e o e also
p esen he fi s measu emen o he o al cha ged-pa icle mul i-
plici y in Pb–Pb collisions a √sNN =5.02 TeV as a unc ion o he
numbe o nucleons pa icipa ing in he collisions (Npa ).
Finally, we ans o m he measu ed dNch/dηdis ibu ion o
he 5% mos cen al collisions in o cha ged-pa icle apidi y densi y
(dNch/dy), and we examine he cen e-o -mass ene gy dependence
o he wid h o ha dis ibu ion. The apidi y (y) o a pa icle
wi h ene gy Eand momen um componen pzalong he beam axis
is defined as y ≡1
2log([E+pz]/[E−pz]). The compa ison o he
wid h o he dNch/dya di e en collision ene gies p o ides an
insigh in o he cons ain s on he o e all p oduc ion mechanism
o cha ged pa icles.
2. Expe imen al se up
A de ailed desc ip ion o ALICE and i s pe o mance can be
ound elsewhe e [9,10]. In he ollowing, we b iefly desc ibe he
de ec o s ele an o his analysis.
h p://dx.doi.o g/10.1016/j.physle b.2017.07.017
0370-2693/©2017 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by
SCOAP3.
568 ALICE Collabo a ion / Physics Le e s B 772 (2017) 567–577
The Silicon Pixel De ec o (SPD), he inne mos pa o he Inne
T acking Sys em (ITS), consis s o wo cylind ical laye s o hyb id
silicon pixel assemblies co e ing |η| <2 and |η| <1.4 o he inne
and ou e laye s, espec i ely. Combina ions o hi s on each o he
wo laye s consis en wi h acks o igina ing om he in e ac ion
poin o m ackle s.
The Fo wa d Mul iplici y De ec o (FMD) is a silicon s ip de ec-
o which, eco ds he ene gy deposi ed by pa icles a e sing he
i . The de ec o co e s he pseudo apidi y egions −3.5 <η<−1.8
and 1.8 <η<5, and has almos ull co e age in azimu h (ϕ), and
high g anula i y in he adial (η) di ec ion.
The hi d de ec o sys em used in his analysis is he V0. I
consis s o wo sub-de ec o s: V0-A and V0-C co e ing he pseudo-
apidi y egions 2.8 <η<5.1 and −3.7 <η<−1.7, espec i ely,
each made up o scin illa o iles wi h a iming esolu ion <1ns.
The as signals om ei he o V0-A o V0-C a e combined in a
p og ammable logic o o m a igge signal and o ejec back-
g ound e en s. Fu he mo e, he combined pulse heigh signal o
bo h sub-de ec o s o ms he basis o he classifica ion o e en s
in o di e en cen ali y classes [11].
The Ze o-Deg ee Calo ime e (ZDC) measu es he ene gy o
spec a o (non-in e ac ing) nucleons wi h wo componen s: one
measu es p o ons and he o he measu es neu ons. The ZDC is
loca ed a abou 112.5 m om he in e ac ion poin on bo h sides
o he expe imen [9]. The ZDC also p o ides iming in o ma ion
used o selec collisions in he o -line da a p ocessing.
3. Da a sample and analysis me hod
The esul s p esen ed he e a e based on da a collec ed by AL-
ICE in 2015 du ing he Pb–Pb collision un o he LHC a √sNN =
5.02 TeV. Abou 100 000 e en s wi h a minimum bias igge e-
qui emen [12] we e analysed in he cen ali y ange om 0% o
90%. The minimum bias igge o Pb–Pb collisions in ALICE, which
defines he so-called isible c oss-sec ion, is defined as a coinci-
dence be ween he A (z>0) and C (z<0) sides o he V0 de ec o .
The s anda d ALICE e en selec ion [13] and cen ali y es ima-
o based on he V0–ampli ude [11] a e used in his analysis. The
e en selec ion consis s o : exclusion o backg ound e en s using
he iming in o ma ion om he ZDC and V0 de ec o s; e ifica-
ion o he igge condi ions; and a econs uc ed posi ion o he
collision. As discussed elsewhe e [11], he 90–100% cen ali y class
has subs an ial con ibu ions om QED p ocesses and is he e o e
no included in he esul s p esen ed he e.
The measu emen o he cha ged-pa icle pseudo apidi y den-
si y a mid- apidi y (|η| <2) is ob ained om a ackle analysis
using he wo laye s o he SPD. The analysis me hod used is iden-
ical o wha has p e iously been p esen ed [12,14,15]. No e ha
no a emp is made o co ec o known deficiencies, such as de i-
a ions in he numbe o s ange pa icles o ans e se momen um
(pT) dis ibu ions compa ed o expe imen al measu emen s [11,16,
17], in he e en gene a o s used o ob ain he co ec ions om
simula ions (e.g., HIJING). I is ound, h ough simula ion s udies,
ha ackle econs uc ion fi s and o emos depends on he local
hi densi y and only weakly on pa icle mix and ans e se mo-
men um. Fo example, he defici o s ange pa icles in he e en
gene a o e ec s he esul by less han 2%. Since he e en gene a-
o s gene ally, a e de ec o simula ion, p oduce a local hi densi y
ha is consis en wi h wha is obse ed in da a, we obse e a co -
espondence be ween he ackle samples o bo h simula ions and
da a. On he o he hand, changing he numbe o ackle s co e-
sponding o s ange pa icles a pos io i o ma ch he measu ed el-
a i e yields d ama ically biases he simula ed ackle sample away
om he measu ed, hus en ailing sys ema ic unce ain ies ha a e
beyond he e ec o he known e en gene a o deficiencies, and
Fig. 1. [Colou online.] Cha ged-pa icle pseudo apidi y densi y o en cen ali y
classes o e a b oad η ange in Pb–Pb collisions a
√sNN =5.02 TeV. Boxes a ound
he poin s eflec he o al unco ela ed sys ema ic unce ain ies, while he filled
squa es on he igh eflec he co ela ed sys ema ic unce ain y (e alua ed a
η=0). S a is ical e o s a e gene ally insignifican and smalle han he ma ke s.
Also shown is he eflec ion o he 3.5 <η<5 alues a ound η=0(open ci cles).
The line co esponds o fi s o he di e ence be ween wo Gaussians cen ed a
η=0( GG) [7] o he da a.
as such do no imp o e he accu acy o he measu emen s. Ins ead,
a ia ions on he e en gene a o s a e used o es ima e he sys em-
a ic unce ain ies as de ailed elsewhe e [12,14,15].
In he o wa d egions (−3.5 <η<−1.8 and 1.8 <η<5), he
measu emen is p o ided by he analysis o he deposi ed ene gy
signal in he FMD. The analysis me hod used is iden ical o wha
has p e iously been p esen ed [7,14]: as a is ical app oach o cal-
cula e he inclusi e numbe o cha ged pa icles; and a da a-d i en
co ec ion — de i ed om p e ious sa elli e-main collisions — o
emo e he la ge backg ound om seconda y pa icles.
4. Sys ema ic unce ain ies
Fo he measu emen s a mid- apidi y he sou ces and de-
pendencies o he sys ema ic unce ain ies a e de ailed elsewhe e
[7,12,15]. The magni ude o he sys ema ic unce ain ies is un-
changed wi h espec o p e ious esul s, and amoun s o 2.6% a
η=0 and 2.9% a η=2, mos o which is co ela ed o e |η| <2,
and la gely independen o cen ali y.
The sys ema ic unce ain y on he o wa d analysis is e alua ed
using he same echnique as o p e ious esul s [7]. We find ha
he unce ain y is unco ela ed ac oss ηan ha i amoun s o 6.9%
o η>3.5and 6.4% elsewhe e wi hin he o wa d egions.
The sys ema ic unce ain y on dNch/dηdue o he cen ali y
class defini ion is es ima ed as 0.6% o he mos cen al and 9.5%
o he mos pe iphe al class [15]. The unce ain y is es ima ed
by using al e na i e cen ali y defini ions based on SPD hi mul-
iplici ies and by a ying he ac ion o he isible had onic c oss-
sec ion. The 80–90% cen ali y class has some esidual con am-
ina ion om elec omagne ic p ocesses de ailed elsewhe e [11],
which gi es ise o a 4% addi ional sys ema ic unce ain y on he
measu emen s.
In summa y, he o al sys ema ic unce ain y a ies om 2.6%
a mid- apidi y in he mos cen al collisions o 12.4% a he e y
o wa d apidi ies o he mos pe iphe al collisions.
5. Resul s
Fig. 1 p esen s he cha ged-pa icle pseudo apidi y densi y as
a unc ion o pseudo apidi y o en cen ali y classes. The mea-
su emen s om he SPD and FMD a e combined in egions o
o e lap (1.8 <|η| <2) be ween he wo de ec o s by aking he
weigh ed a e age using he non-sha ed unce ain ies as weigh s.
Finally, based on he symme y o he collision sys em, he esul
is symme ised a ound η=0, and ex ended in o he non-measu ed
ALICE Collabo a ion / Physics Le e s B 772 (2017) 567–577 569
Fig. 2. [Colou online.] To al numbe o cha ged pa icles as a unc ion o he mean
numbe o pa icipa ing nucleons [11]. The o al cha ged-pa icle mul iplici y is
gi en as he in eg al o e dNch/dηo e he measu ed egion (−3.5 <η<5) and
ex apola ions om fi ed unc ions in he unmeasu ed egions. The con ibu ion
om unmeasu ed η egions amoun s o ≈30% o he o al numbe o cha ged
pa icles. The unce ain y on he ex apola ion o he unmeasu ed pseudo apidi y
egion is smalle han he size o he ma ke s. The con ibu ion o he sys ema ic
unce ain ies om he cen ali y de e mina ion and elec omagne ic p ocesses a e
anishing compa ed o he con ibu ion om he la ges di e ences be ween he
fi ed unc ions. A unc ion inspi ed by ac o isa ion [18] is fi ed o he da a, and
he bes fi yields a =51.5 ±7.3, b =0.16 ±0.05.
egion −5 <η<−3.5by eflec ing he 3.5 <η<5 alues a ound
η=0. Complemen ing esul p e iously epo ed a mid- apidi y
[15], we find dNch/dη||η|<0.5=17.52 ±0.05(s a ) ±1.84(sys)and
Npa =7.3 ±0.1in he 80–90% cen ali y class.
The measu ed dis ibu ions a e fi ed wi h ou unc ions GG,
P, T, and B[7], which a e he di e ence o wo Gaussian dis-
ibu ions cen ed a η=0; a pa ame isa ion p oposed by PHO-
BOS [18]; a apezoidal o m; and a pla eau connec ed o Gaussian
ails, espec i ely. To ex ac he o al numbe o cha ged pa i-
cles, we calcula e he in eg al and unce ain y om he da a in he
measu ed egion and use he in eg als o he fi ed unc ions in
he unmeasu ed egions up o he beam apidi y ±ybeam =±8.6.
As o he p e ious measu emen s a √sNN =5.02 TeV, he cen al
alue in he unmeasu ed egions (−8.6 <η<−3.5 and 5 <η<
8.6) is aken om he fi o he unc ion T, while he unce ain y
is e alua ed as he la ges di e ence be ween he fi ed unc ions
scaled by 1/√3[7,14]. The o al cha ged-pa icle mul iplici y is
shown in Fig. 2 e sus he mean numbe o pa icipa ing nucle-
ons (Npa ) es ima ed om a Glaube calcula ion [11,15]. A e
emo ing co ela ed sys ema ic unce ain ies, we obse e an in-
c ease in he o al numbe o cha ged pa icles o (27 ±4)%wi h
espec o he measu emen s a √sNN =2.76 TeV [7] o all cen-
ali y classes. The line shown in Fig. 2 co esponds o a fi o
a unc ion inspi ed by ac o isa ion [18]. The unc ion illus a es
scaling by numbe o pa icipan pai s, wi h a small pe u ba ion
p opo ional o he cubic oo o he numbe o pa icipan s. As
he numbe o nucleon–nucleon collisions (Ncoll) scales oughly
like he squa e o he numbe o pa icipan s Ncoll ≈N2
pa [19], we
see no indica ion o scaling by numbe o nucleon–nucleon colli-
sions. The obse ed o al Nch dependence on Npa p o ides no
e idence o any significan inc ease in he numbe o ha d sca e -
ings be ween he pa icipa ing nucleons and pa ons.
In Fig. 3, we compa e he cha ged-pa icle pseudo apidi y den-
si y o he 0–5% mos cen al collisions o h ee models: HI-
JING [20]; EPOS–LHC [21]; and KLN [22,23], also o he 0–5%
mos cen al, excep o KLN which is shown o he 0–6% cen al-
i y class. Two e sions o HIJING a e used: e sion 1.383, wi h je
quenching disabled, shadowing enabled, and a ha d pTcu -o o
2.3 GeV; and he newe e sion 2.1 [24]. Bo h a e wo-componen
models wi h a so and ha d sec o defined by a pTcu -o sep-
a a ing he wo. In he 2.1 implemen a ion, HIJING uses an up-
g aded pa ame isa ion o he nuclea pa on dis ibu ion unc-
Fig. 3. [Colou online.] Compa ison o dNch/dηin he 0–5% (0–6% o KLN) mos
cen al collisions o wo e sions o HIJING, KLN, and EPOS–LHC model calcula ions
o he measu ed dis ibu ion.
Fig. 4. [Colou online.] To al numbe o cha ged pa icles as a unc ion o
√sNN o
he mos cen al collisions a AGS (0–5% Au–Au) [25,26], SPS (0–5% Pb–Pb) [27,28],
RHIC (0–5% and 0–6% Au–Au) [18,29,30], and LHC (0–5% Pb–Pb) [14]. The do ed,
dashed, and ull lines a e ex apola ions om fi s o lowe ene gy esul s [14], while
he dash-do ed line is a fi o e all ene gies, including
√sNN =5.02 TeV.
ions. This esul s in a la ge c oss sec ion o so p ocesses and a
smalle c oss sec ion o je p oduc ion. The KLN model is based on
Colou -Glass-Condensa e ini ial condi ions, while EPOS-LHC uses
so-called pa on-ladde s which had onise in a medium. While
none o he h ee models desc ibe he measu ed cha ged-pa icle
pseudo apidi y densi y o e he ull pseudo apidi y ange, we ob-
se e some di e ences: HIJING 1.383 o e -p edic s he cha ged-
pa icle p oduc ion especially away om η≈0; EPOS–LHC and
HIJING 2.1 consis en ly unde -p edic he cha ge-pa icle p oduc-
ion; whe eas KLN, EPOS–LHC, and HIJING 2.1 gi e a shape ea-
sonably close o he obse ed dis ibu ion. No shown in Fig. 3,
o bo h HIJING 1.383 and EPOS–LHC, hese obse a ions hold o e
all cen ali y classes i.e., HIJING 1.383 consis en ly p oduces a oo
many pa icles away om mid- apidi y and EPOS–LHC consis en ly
unde -p edic s he cha ged-pa icle yield o e he ull η ange.
These ends become inc easingly mo e p onounced o mo e pe-
iphe al collisions.
Fig. 4 shows he o al numbe o cha ged pa icles p oduced
in he mos cen al hea y-ion collisions as a unc ion o he col-
lision ene gy, anging om √sNN =2.6GeV o 5.02 TeV [14]. The
do ed, dashed, and ull-d awn lines in he figu e ep esen ex ap-
ola ions om lowe ene gy esul s o he cu en op LHC ene gy o
√sNN =5.02 TeV. None o hese p edic ions ully desc ibe he da a.
A efi o he simple model o a loga i hmic-dampened powe -law
in he squa e collision ene gy (s) including om he lowes o he
highes ene gy esul s, shown as he dash-do ed line, does accu-
a ely desc ibe he o al numbe o cha ged pa icles a all a ailable
ene gies.
570 ALICE Collabo a ion / Physics Le e s B 772 (2017) 567–577
Fig. 5. [Colou online.] Es ima e o dNch/dyin he mos cen al (0–5%) Pb–Pb
collisions a √sNN =5.02 TeV. Also shown a e he Landau–Wong [31], Landau–
Ca u he s [32], Gaussian, and double-Gaussian dis ibu ions.
Fig. 6. [Colou online.] Scaling beha iou as a unc ion √sNN o he wid h o he
cha ged-pa icle o -pion apidi y-densi y dis ibu ion wi h espec o he Landau–
Ca u he s wid h ( op) and apidi y ange (bo om). Cha ged-pion poin s om AGS
and SPS a e adap ed om he li e a u e [33], while he PHOBOS (filled c osses) [34]
and BRAHMS (open c osses) [30] cha ged-had on poin s a e ansla ed om he co -
esponding dNch/dη esul s.
We can calcula e he Jacobian ans o m om η o apidi y
yby assuming he same ans e se momen um dis ibu ion o
(an i-)p o ons, and cha ged kaons and pions, and he same pa -
icle a ios in Pb–Pb collisions a √sNN =5.02 TeV as in √sNN =
2.76 TeV. The esul is p esen ed in Fig. 5 o he 0–5% mos cen-
al collisions. The e ec on he Jacobian om he change o pT
spec a and pa icle a ios when inc easing he collision ene gy by
almos a ac o wo is e alua ed using he EPOS–LHC model [21].
I is ound, ha he e ec is a mos 3‰ on bo h dNch/dyand y—
much smalle han he sys ema ic unce ain y and η esolu ion o
he analysis. Fig. 5 also shows he expec ed cha ged-pa icle apid-
i y densi ies om he Landau–Ca u he s [32] and Landau–Wong
[31] models, bo h assuming Landau hyd odynamics i.e., based on
a eac ion scena io wi h ull s opping o he eac ion pa ne s and
a subsequen he modynamic e olu ion. The measu emen s, how-
e e , a e seen o be consis en wi h a Gaussian dis ibu ion wi h a
wid h o 4.12 ±0.10, much wide han he wid h expec ed om
he wo models. A bes pa ame e fi o he sum o wo Gaussian
dis ibu ions wi h means symme ic a ound y =0, is indis inguish-
able om he single Gaussian case.
In he op pa o Fig. 6 we compa e he wid hs o he
cha ged-pa icle o -pion apidi y densi y dis ibu ion ex ac ed
om measu emen s o he expec ed wid h σ2
L-C =log(√sNN/2mp)
om Landau–Ca u he s, whe e mpis he p o on mass, a colli-
sion ene gies anging om 2.6GeVup o 5.02 TeV. An inc ease
o ≈7% o σdNX/dy/σL-C is seen om he √sNN =2.76 TeV AL-
ICE measu emen s [14]. The ull e olu ion is consis en wi h an
almos linea ise as a unc ion o log√sNN om he op SPS en-
e gy a √sNN =17.3GeV. I can be shown [35] ha he wid h o
he apidi y-densi y dis ibu ion in Landau hyd odynamics scales
as σdNX/dy∝1/(1 −c2
s), whe e csis he speed o sound in he ma -
e . The li e ime o he sys em scales in e sely wi h cs, and gi en
ha he measu ed wid h is la ge han he p edic ed by Landau
hyd odynamics, i is an indica ion ha , gi en he conside a ions
abo e, he li e ime is sho e han sugges ed.
In he bo om pa o Fig. 6 we compa e he wid h o he
dNch/dydis ibu ion o he a ailable apidi y ange (2ybeam). We
obse e no dependence o his a io om √sNN =17.3 GeV and
upwa d, indica ing ha he a ailable phase–space cons ains he
wid h o ha dis ibu ion. The cha ged-had on measu emen s a
RHIC (c osses) om he BRAHMS [30] and PHOBOS [34] mea-
su emen s o dNch/dηa e con e ed o dNch/dyusing he same
me hod as applied o he ALICE da a. P e iously, cha ged-pion
measu emen s om BRAHMS ha e been epo ed [33]. These da a
a e no included because a e-e alua ion using RHIC Run-4 Au–Au
da a has no been finalised [36].
F om he obse ed spscaling o he cha ged-pa icle pseudo a-
pidi y densi y a mid- apidi y [15] we expec a 20% inc ease o e
√sNN =2.76 TeV in he le el o dNch/dη||η|<0.5and om he ex-
ac ed wid h o dNch/dywe obse e an addi ional 7%, consis en
wi h he inc ease o 27% o e √sNN =2.76 TeV in he o al numbe
o cha ged pa icles p oduced in √sNN =5.02 TeV collisions.
6. Conclusions
The cha ged-pa icle pseudo apidi y densi y is measu ed in Pb–
Pb collisions a √sNN =5.02 TeV o e he psuedo apidi y ange
−3.5 <η<5. The o al numbe o cha ged pa icles p oduced is
de e mined owing o he la ge pseudo apidi y accep ance o AL-
ICE. The la e inc eases by wo o de s o magni ude om he mos
pe iphe al o he mos cen al collisions and scales app oxima ely
wi h he numbe o pa icipa ing nucleons. The inc ease in he
o al numbe o cha ged pa icles ela i e o
√sNN =2.76 TeV is es-
ima ed o be (27 ±4)%. The cha ged-pa icle apidi y densi y o
he mos cen al collisions is ex ac ed, and he wid h o ha dis-
ibu ion is compa ed o p edic ions om he Landau–Ca u he s
and Landau–Wong hyd odynamic models. I is ound ha he mea-
su ed cha ged-pa icle apidi y densi y becomes inc easingly wide
as a unc ion o collision ene gy han p edic ed by Landau hy-
d odynamics. The wid h o he cha ged-pa icle apidi y densi y
is seen o scale wi h he beam apidi y, which implies ha he
a ailable phase space de e mines he longi udinal ex end o he
cha ged-pa icle p oduc ion. The phase space dominance s a s a
he op SPS ene gy and pe sis o wo o de s o magni ude up o
he op LHC ene gy.
Acknowledgemen s
The ALICE Collabo a ion would like o hank all i s enginee s
and echnicians o hei in aluable con ibu ions o he cons uc-
ion o he expe imen and he CERN accele a o eams o he
ou s anding pe o mance o he LHC complex. The ALICE Collab-
o a ion g a e ully acknowledges he esou ces and suppo p o-
ided by all G id cen es and he Wo ldwide LHC Compu ing G id
(WLCG) collabo a ion. The ALICE Collabo a ion acknowledges he
ollowing unding agencies o hei suppo in building and un-
ning he ALICE de ec o : A.I. Alikhanyan Na ional Science Labo a-
o y (Ye e an Physics Ins i u e) Founda ion (ANSL), S a e Commi -
ee o Science and Wo ld Fede a ion o Scien is s (WFS), A menia;
Aus ian Academy o Sciences and Na ionals i ung ü Fo schung,
Technologie und En wicklung, Aus ia; Conselho Nacional de De-
sen ol imen o Cien ífico e Tecnológico (CNPq), Uni e sidade Fed-
e al do Rio G ande do Sul (UFRGS), Financiado a de Es udos e
P oje os (Finep) and Fundação de Ampa o à Pesquisa do Es ado
ALICE Collabo a ion / Physics Le e s B 772 (2017) 567–577 571
de São Paulo (FAPESP), B azil; Minis y o Science & Technology o
China (MSTC), Na ional Na u al Science Founda ion o China (NSFC)
and Minis y o Educa ion o China (MOEC), China; Minis y o Sci-
ence, Educa ion and Spo and C oa ian Science Founda ion, C oa-
ia; Minis y o Educa ion, You h and Spo s o he Czech Republic,
Czech Republic; The Danish Council o Independen Resea ch–
Na u al Sciences, he Ca lsbe g Founda ion and Danish Na ional Re-
sea ch Founda ion (DNRF), Denma k; Helsinki Ins i u e o Physics
(HIP), Finland; Commissa ia à l’Ene gie A omique (CEA) and Ins i-
u Na ional de Physique Nucléai e e de Physique des Pa icules
(IN2P3) and Cen e Na ional de la Reche che Scien ifique (CNRS),
F ance; Bundesminis e ium ü Bildung, Wissenscha , Fo schung
und Technologie (BMBF) and GSI Helmhol zzen um ü Schwe i-
onen o schung GmbH, Ge many; Minis y o Educa ion, Resea ch
and Religious A ai s, G eece; Na ional Resea ch, De elopmen and
Inno a ion Office, Hunga y; Depa men o A omic Ene gy, Go -
e nmen o India (DAE) and Council o Scien ific and Indus ial
Resea ch (CSIR), New Delhi, India; Indonesian Ins i u e o Sci-
ence, Indonesia; Cen o Fe mi -Museo S o ico della Fisica e Cen-
o S udi e Rice che En ico Fe mi and Is i u o Nazionale di Fisica
Nuclea e (INFN), I aly; Ins i u e o Inno a i e Science and Tech-
nology, Nagasaki Ins i u e o Applied Science (IIST), Japan Soci-
e y o he P omo ion o Science (JSPS) KAKENHI and Japanese
Minis y o Educa ion, Cul u e, Spo s, Science and Technology
(MEXT), Japan; Consejo Nacional de Ciencia y Tecnología (CONA-
CYT), h ough Fondo de Coope ación In e nacional en Ciencia y
Tecnología (FONCICYT) and Di ección Gene al de Asun os del Pe -
sonal Academico (DGAPA), Mexico; Na ionaal ins i uu oo sub-
a omai e ysica (Nikhe ), Ne he lands; The Resea ch Council o
No way, No way; Commission on Science and Technology o Sus-
ainable De elopmen in he Sou h (COMSATS), Pakis an; Pon ificia
Uni e sidad Ca ólica del Pe ú, Pe u; Minis y o Science and Highe
Educa ion and Na ional Science Cen e, Poland; Ko ea Ins i u e o
Science and Technology In o ma ion and Na ional Resea ch Foun-
da ion o Ko ea (NRF), Republic o Ko ea; Minis y o Educa ion
and Scien ific Resea ch, Ins i u e o A omic Physics and Romanian
Na ional Agency o Science, Technology and Inno a ion, Roma-
nia; Join Ins i u e o Nuclea Resea ch (JINR), Minis y o Educa-
ion and Science o he Russian Fede a ion and Na ional Resea ch
Cen e Ku cha o Ins i u e, Russia; Minis y o Educa ion, Science,
Resea ch and Spo o he Slo ak Republic, Slo akia; Na ional Re-
sea ch Founda ion o Sou h A ica, Sou h A ica; Cen o de Apli-
caciones Tecnológicas y Desa ollo Nuclea (CEADEN), Cubaene gía,
Cuba, Minis e io de Ciencia e Inno acion and Cen o de In es i-
gaciones Ene gé icas, Medioambien ales y Tecnológicas (CIEMAT),
Spain; Swedish Resea ch Council (VR) and Knu & Alice Wallenbe g
Founda ion (KAW), Sweden; Eu opean O ganiza ion o Nuclea Re-
sea ch, Swi ze land; Na ional Science and Technology De elopmen
Agency (NSDTA), Su ana ee Uni e si y o Technology (SUT) and O -
fice o he Highe Educa ion Commission unde NRU p ojec o
Thailand, Thailand; Tu kish A omic Ene gy Agency (TAEK), Tu key;
Na ional Academy o Sciences o Uk aine, Uk aine; Science and
Technology Facili ies Council (STFC), Uni ed Kingdom; Na ional Sci-
ence Founda ion o he Uni ed S a es o Ame ica (NSF) and Uni ed
S a es Depa men o Ene gy, Office o Nuclea Physics (DOE NP),
Uni ed S a es o Ame ica.
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A. He ghelegiu80, G. He e a Co al11, F. He mann 61, B.A. Hess94, K.F. He land36, H. Hillemanns34,
B. Hippoly e134, J. Hladky56, D. Ho ak38, R. Hosokawa131, P. H is o 34, C. Hughes128, T.J. Humanic 18,
N. Hussain43, T. Hussain17, D. Hu e 41, D.S. Hwang19, R. Ilkae 101, M. Inaba131, M. Ippoli o 82,76,
M. I an17, V. Isako 52, M.S. Islam48, M. I ano 34,99, V. I ano 88, V. Izuchee 113, B. Jacak75,
N. Jacazio26, P.M. Jacobs75, M.B. Jadha 47, S. Jadlo ska117, J. Jadlo sky117, C. Jahnke35,
M.J. Jakubowska138, M.A. Janik138, P.H.S.Y. Jaya a hna125, C. Jena81, S. Jena125, M. Je cic132,
R.T. Jimenez Bus aman e99, P.G. Jones103, A. Jusko103, P. Kalinak 55, A. Kalwei 34, J.H. Kang 142,
V. Kaplin76, S. Ka 137, A. Ka asu Uysal70, O. Ka a iche 52, T. Ka a iche a52, L. Ka ayan99,95,
E. Ka peche 52, U. Kebschull 59, R. Keidel 143, D.L.D. Keijdene 53, M. Keil34, M. Mohisin Khan17,iii,
P. Khan 102, S.A. Khan137, A. Khanzadee 88, Y. Kha lo 113, A. Kha un17, A. Khun ia48,
M.M. Kielbowicz119, B. Kileng 36, D.W. Kim42, D.J. Kim126, D. Kim 142, H. Kim142, J.S. Kim42, J. Kim 95,
M. Kim50, M. Kim 142, S. Kim19, T. Kim 142, S. Ki sch41, I. Kisel41, S. Kisele 54, A. Kisiel138, G. Kiss 140,
J.L. Klay6, C. Klein 60, J. Klein34, C. Klein-Bösing 61, S. Klewin95, A. Kluge34, M.L. Knichel95,
A.G. Knospe125, C. Kobdaj116, M. Ko a ago34, T. Kollegge 99, A. Koloj a i136, V. Kond a ie 136,
N. Kond a ye a76, E. Kond a yuk113, A. Kone skikh52, M. Kopcik117, M. Kou 92, C. Kouzinopoulos 34,
O. Ko alenko79, V. Ko alenko136, M. Kowalski 119, G. Koyi ha a Mee hale eedu47, I. K álik55,
A. K a ˇ
cáko á 39, M. K i da55,103, F. K izek 86, E. K yshen88, M. K zewicki41, A.M. Kube a18, V. Kuˇ
ce a86,
C. Kuhn 134, P.G. Kuije 84, A. Kuma 92, J. Kuma 47, L. Kuma 90, S. Kuma 47, S. Kundu 81, P. Ku ash ili79,
A. Ku epin52, A.B. Ku epin52, A. Ku yakin101, S. Kushpil86, M.J. Kweon50, Y. Kwon 142, S.L. La Poin e41,
P. La Rocca 27, C. Lagana Fe nandes122, I. Lakomo 34, R. Langoy40, K. Lapidus 141, C. La a59,
A. La deux65,20, A. La uca25, E. Laudi34, R. La icka 38, L. Laza idis34, R. Lea24, L. Lea dini95, S. Lee142,
F. Lehas84, S. Lehne 114, J. Leh bach41, R.C. Lemmon85, V. Len i105, E. Leog ande53, I. León Monzón121,
P. Lé ai 140, S. Li7, X. Li14, J. Lien40, R. Lie a a 103, S. Lindal20, V. Lindens u h41, C. Lippmann 99,
M.A. Lisa18, V. Li iche skyi45, H.M. Ljungg en33, W.J. Llope 139, D.F. Loda o53, P.I. Loenne21,
V. Logino 76, C. Loizides75, P. Lonca 118, X. Lopez71, E. López To es9, A. Lowe140, P. Lue ig60,
M. Luna don28, G. Lupa ello24, M. Lupi 34, T.H. Lu z 141, A. Mae skaya52, M. Mage 34, S. Mahajan 92,
S.M. Mahmood20, A. Mai e134, R.D. Majka141, M. Malae 88, I. Maldonado Ce an es62, L. Malinina67,i ,
D. Mal’Ke ich54, P. Malzache 99, A. Mamono 101, V. Manko82, F. Manso71, V. Manza i105, Y. Mao7,
M. Ma chisone66,129, J. Ma eš56, G.V. Ma gaglio i24, A. Ma go i106, J. Ma gu i53, A. Ma ín99,
C. Ma ke 120, M. Ma qua d60, N.A. Ma in99, P. Ma inengo34, J.A.L. Ma inez59, M.I. Ma ínez2,
G. Ma ínez Ga cía115, M. Ma inez Ped ei a34, A. Mas122, S. Masciocchi99, M. Mase a25, A. Masoni107,
A. Mas ose io32, A.M. Ma his96,35, A. Ma yja128,119, C. Maye 119, J. Maze 128, M. Mazzilli32,
M.A. Mazzoni110, F. Meddi22, Y. Melikyan 76, A. Menchaca-Rocha64, E. Meninno 29, J. Me cado Pé ez95,
M. Me es37, S. Mhlanga91, Y. Miake131, M.M. Mieskolainen45, D. Mihaylo 96, K. Mikhaylo 54,67,
L. Milano75, J. Milose ic20, A. Mischke53, A.N. Mish a48, T. Mish a57, D. Mi´
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C.M. Mi u58, N. Mohammadi 53, B. Mohan y 81, E. Mon es10, D.A. Mo ei a De Godoy61, L.A.P. Mo eno2,
S. Mo e o28, A. Mo eale115, A. Mo sch34, V. Mucci o a73, E. Mudnic 118, D. Mühlheim 61, S. Muhu i137,
M. Mukhe jee137, J.D. Mulligan141, M.G. Munhoz122, K. Münning44, R.H. Munze 35,60,96,
H. Mu akami130, S. Mu ay66, L. Musa34, J. Musinsky55, C.J. Mye s125, B. Naik47, R. Nai 79,
B.K. Nandi47, R. Nania106, E. Nappi105, M.U. Na u15, H. Na al da Luz122, C. Na ass128, S.R. Na a o2,
K. Nayak 81, R. Nayak47, T.K. Nayak 137, S. Naza enko101, A. Nedosekin54, R.A. Neg ao De Oli ei a34,
574 ALICE Collabo a ion / Physics Le e s B 772 (2017) 567–577
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J. No man127, A. Nyanin82, J. Nys and21, H. Oeschle 95, S. Oh141, A. Ohlson95,34, T. Okubo 46,
L. Olah140, J. Oleniacz 138, A.C. Oli ei a Da Sil a 122, M.H. Oli e 141, J. Onde waa e 99, C. Oppedisano 112,
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J. Pan139, A.K. Pandey47, S. Panebianco65, V. Papikyan 1, G.S. Pappala do108, P. Pa eek48, J. Pa k50,
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V. Pesko 60, Y. Pes o 5, V. Pe áˇ
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M. Płosko´
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S. Po eboeu -Houssais71, J. Po e 75, J. Pospisil86, V. Pozdniako 67, S.K. P asad4, R. P eghenella34,106,
F. P ino112, C.A. P uneau139, I. Pshenichno 52, M. Puccio25, G. Puddu 23, P. Pujaha i 139, V. Punin101,
J. Pu schke139, H. Q igs ad20, A. Rache ski111, S. Raha4, S. Rajpu 92, J. Rak126, A. Rako ozafind abe65,
L. Ramello 31, F. Rami 134, D.B. Rana125, R. Raniwala 93, S. Raniwala93, S.S. Räsänen45, B.T. Rascanu 60,
D. Ra hee90, V. Ra za44, I. Ra asenga30, K.F. Read87,128, K. Redlich79, A. Rehman21, P. Reichel 60,
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E. Scompa in112, R. Sco 128, M. Še ˇ
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S. Sumowidagdo49, K. Suzuki114, S. Swain57, A. Szabo37, I. Sza ka37, A. Szczepankiewicz138,
M. Szymanski138, U. Tabassam 15, J. Takahashi123, G.J. Tamba e21, N. Tanaka 131, M. Ta hini51,
M. Ta iq17, M.G. Ta zila80, A. Tau o34, G. Tejeda Muñoz2, A. Telesca34, K. Te asaki130, C. Te e oli28,
B. Teyssie 133, D. Thaku 48, S. Thaku 137, D. Thomas 120, R. Tieulen 133, A. Tikhono 52, A.R. Timmins125,
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1A.I. Alikhanyan Na ional Science Labo a o y (Ye e an Physics Ins i u e) Founda ion, Ye e an, A menia
2Benemé i a Uni e sidad Au ónoma de Puebla, Puebla, Mexico
3Bogolyubo Ins i u e o Theo e ical Physics, Kie , Uk aine
4Bose Ins i u e, Depa men o Physics and Cen e o As opa icle Physics and Space Science (CAPSS), Kolka a, India
5Budke Ins i u e o Nuclea Physics, No osibi sk, Russia
6Cali o nia Poly echnic S a e Uni e si y, San Luis Obispo, CA, Uni ed S a es
7Cen al China No mal Uni e si y, Wuhan, China
8Cen e de Calcul de l’IN2P3, Villeu banne, Lyon, F ance
9Cen o de Aplicaciones Tecnológicas y Desa ollo Nuclea (CEADEN), Ha ana, Cuba
10 Cen o de In es igaciones Ene gé icas Medioambien ales y Tecnológicas (CIEMAT), Mad id, Spain
11 Cen o de In es igación y de Es udios A anzados (CINVESTAV), Mexico Ci y and Mé ida, Mexico
12 Cen o Fe mi -Museo S o ico della Fisica e Cen o S udi e Rice che “En ico Fe mi”, Rome, I aly
13 Chicago S a e Uni e si y, Chicago, IL, Uni ed S a es
14 China Ins i u e o A omic Ene gy, Beijing, China
15 COMSATS Ins i u e o In o ma ion Technology (CIIT), Islamabad, Pakis an
16 Depa amen o de Física de Pa ículas and IGFAE, Uni e sidad de San iago de Compos ela, San iago de Compos ela, Spain
17 Depa men o Physics, Aliga h Muslim Uni e si y, Aliga h, India
18 Depa men o Physics, Ohio S a e Uni e si y, Columbus, OH, Uni ed S a es
19 Depa men o Physics, Sejong Uni e si y, Seoul, Sou h Ko ea
20 Depa men o Physics, Uni e si y o Oslo, Oslo, No way
21 Depa men o Physics and Technology, Uni e si y o Be gen, Be gen, No way
22 Dipa imen o di Fisica dell’Uni e si à ‘La Sapienza’ and Sezione INFN, Rome, I aly
23 Dipa imen o di Fisica dell’Uni e si à and Sezione INFN, Caglia i, I aly
24 Dipa imen o di Fisica dell’Uni e si à and Sezione INFN, T ies e, I aly
25 Dipa imen o di Fisica dell’Uni e si à and Sezione INFN, Tu in, I aly
26 Dipa imen o di Fisica e As onomia dell’Uni e si à and Sezione INFN, Bologna, I aly
27 Dipa imen o di Fisica e As onomia dell’Uni e si à and Sezione INFN, Ca ania, I aly
28 Dipa imen o di Fisica e As onomia dell’Uni e si à and Sezione INFN, Pado a, I aly
29 Dipa imen o di Fisica ‘E.R. Caianiello’ dell’Uni e si à and G uppo Collega o INFN, Sale no, I aly
30 Dipa imen o DISAT del Poli ecnico and Sezione INFN, Tu in, I aly
31 Dipa imen o di Scienze e Inno azione Tecnologica dell’Uni e si à del Piemon e O ien ale and INFN Sezione di To ino, Alessand ia, I aly
32 Dipa imen o In e a eneo di Fisica ‘M. Me lin’ and Sezione INFN, Ba i, I aly
33 Di ision o Expe imen al High Ene gy Physics, Uni e si y o Lund, Lund, Sweden
34 Eu opean O ganiza ion o Nuclea Resea ch (CERN), Gene a, Swi ze land
35 Excellence Clus e Uni e se, Technische Uni e si ä München, Munich, Ge many
36 Facul y o Enginee ing, Be gen Uni e si y College, Be gen, No way
37 Facul y o Ma hema ics, Physics and In o ma ics, Comenius Uni e si y, B a isla a, Slo akia
38 Facul y o Nuclea Sciences and Physical Enginee ing, Czech Technical Uni e si y in P ague, P ague, Czech Republic
39 Facul y o Science, P.J. Ša á ik Uni e si y, Košice, Slo akia
40 Facul y o Technology, Buske ud and Ves old Uni e si y College, Tonsbe g, No way
41 F ank u Ins i u e o Ad anced S udies, Johann Wol gang Goe he-Uni e si ä F ank u , F ank u , Ge many
42 Gangneung-Wonju Na ional Uni e si y, Gangneung, Sou h Ko ea
43 Gauha i Uni e si y, Depa men o Physics, Guwaha i, India
44 Helmhol z-Ins i u ü S ahlen- und Ke nphysik, Rheinische F ied ich-Wilhelms-Uni e si ä Bonn, Bonn, Ge many
45 Helsinki Ins i u e o Physics (HIP), Helsinki, Finland
46 Hi oshima Uni e si y, Hi oshima, Japan
47 Indian Ins i u e o Technology Bombay (IIT), Mumbai, India
48 Indian Ins i u e o Technology Indo e, Indo e, India
49 Indonesian Ins i u e o Sciences, Jaka a, Indonesia
50 Inha Uni e si y, Incheon, Sou h Ko ea
51 Ins i u de Physique Nucléai e d’O say (IPNO), Uni e si é Pa is-Sud, CNRS-IN2P3, O say, F ance
52 Ins i u e o Nuclea Resea ch, Academy o Sciences, Moscow, Russia
53 Ins i u e o Suba omic Physics o U ech Uni e si y, U ech , Ne he lands
54 Ins i u e o Theo e ical and Expe imen al Physics, Moscow, Russia
55 Ins i u e o Expe imen al Physics, Slo ak Academy o Sciences, Košice, Slo akia
56 Ins i u e o Physics, Academy o Sciences o he Czech Republic, P ague, Czech Republic
57 Ins i u e o Physics, Bhubaneswa , India
58 Ins i u e o Space Science (ISS), Bucha es , Romania
59 Ins i u ü In o ma ik, Johann Wol gang Goe he-Uni e si ä F ank u , F ank u , Ge many
60 Ins i u ü Ke nphysik, Johann Wol gang Goe he-Uni e si ä F ank u , F ank u , Ge many
61 Ins i u ü Ke nphysik, Wes älische Wilhelms-Uni e si ä Müns e , Müns e , Ge many
62 Ins i u o de Ciencias Nuclea es, Uni e sidad Nacional Au ónoma de México, Mexico Ci y, Mexico
63 Ins i u o de Física, Uni e sidade Fede al do Rio G ande do Sul (UFRGS), Po o Aleg e, B azil
64 Ins i u o de Física, Uni e sidad Nacional Au ónoma de México, Mexico Ci y, Mexico
65 IRFU, CEA, Uni e si é Pa is-Saclay, F-91191 Gi -su -Y e e, F ance, Saclay, F ance
66 iThemba LABS, Na ional Resea ch Founda ion, Some se Wes , Sou h A ica
