Table Of ContentNuclearand
ParticlePhysics
Proceedings
NuclearandParticlePhysicsProceedings00(2017)1–5
Medium modification of averaged jet charge in heavy-ion collisions
Shi-YongChena,Ben-WeiZhanga,EnkeWanga
aKeyLaboratoryofQuark&LeptonPhysics(MOE)andInstituteofParticlePhysics,CentralChinaNormalUniversity,Wuhan430079,China
7
1
0 Abstract
2
Jetchargecharacterizestheelectricchargedistributioninsideajet. Inthistalkwemakethefirsttheoreticalstudy
n
a ofjetchargeinhigh-energynuclearcollisionsandcalculatenumericallythemediumalternationsofjetchargedueto
J partonenergylossinthequark-gluonplasma. Thepartonmultiplescatteringinhot/denseQCDmediumissimulated
2 by a modified version of PYQUEN Monte Carlo model with 3+1D ideal hydrodynamical evolution of the fireball.
1 Our preliminary results show that the averaged jet charge is significant modified in A+A collisions relative to that
inp+p. Thedifferentfeaturesofquarkjetchargeandgluonjetchargeinheavy-ioncollisions,andthesensitivityof
]
h jetchargemodificationstoflavourdependenceofenergylossareobserved,whichcouldthenbeusedtodiscriminate
t quarkandgluonjetaswellastheirenergylosspatternsinheavy-ioncollisions.
-
l
c Keywords: averagedjetcharge,jetquenching,quark-gluonplasma
u
n
[
1. Introduction yearsago[8]. Thisobservablehasbeeninvestigatedex-
2 perimentally in deep inelastic scattering studies to un-
v
derstand the correlation between the quark model and
8 One very important purpose of high energy heavy-
hadrons. Since then, jet charge observables have been
0 ion collisions performed at RHIC and LHC is to study
3 thecreationandthepropertiesofQuark-GluonPlasma utilized in tagging the charge of b-quark jets, hadroni-
1 callydecayingW bosons,anddistinguishingquarkjets
(QGP), a new form of matter with deconfined quarks
0 from gluon jets [9, 10]. Recently, ATLAS Collabora-
and gluons created during these collisions. It has been
.
1 shownthatthejetquenching,ortheenergylossofafast tion publis√hed their measurement of jet charge in dijet
0 eventsin s = 8TeVp+pcollisions[11]. Inthistalk
partontraversingthenucleicouldbeusedaverysensi-
7
wemakeafirsttheoreticalinvestigatationofjetcharge
tiveprobetocalibratethedensityandtemperatureofthe
1
in relativistic heavy-ion collisions and see its medium
: QCDmatter[1]. Theattenuationofpartonenergyloss
v modificationinrelativetohadroniccollisions[12]. We
willengenderthesuppressionofleadinghadrons[1,2]
i
X aswellasalternationsoffulljetobservablesinthehigh- show that parton energy loss of the energetic partons
intheQGPwillchangetheelectricchargedistributions
r energy nuclear collisions such as jet shapes and frag-
a inafulljetanddemonstratetheobviousdistinctionbe-
mentation functions [3, 4], single jet cross section [5],
tweenquarkandgluonjetcharges,whichcanbeusedas
di-jettransversemomentumasymmetry[6]andtagged
jet p imbalance[7],etc. aexcellenttooltostudythedifferentpatternsofenergy
T
lossforquarksandgluons[13,14].
With the advance of expereimental measurements
and theoretical calculations of jet quenching, it is of The paper is organized as follows. In Section 2 we
importance to explore the jet quenching effect on new discuss jet charge at p+p collisions and then show the
full jet observable with distinct features. A very in- theoreticalframeworkofcomputingjetchargeinA+A
teresting jet observable is jet charge, which gives the reactions including jet quenching effect. In Section 3
electric charge distribution in a recosntructed jet and the preliminary results of medium modification of jet
wasfirstlyproposedbyFieldandFeynmanalmostforty chargeareprovidedwithdiscussions. Atlast,wegivea
S.Y.Chen,B.W.ZhangandE.Wang/NuclearandParticlePhysicsProceedings00(2017)1–5 2
briefsummaryinSection4. provideareasonablebaselineforcalculatingjetcharge
inheavy-ioncollisions.
2. Theoreticalframework
0.18
The momentum-weighted electric charge sum of averaged full jet charge
0.16
hadronsinthejet,calledtheaveragedjetcharge,isde- averaged quark jet charge
finedas: ge 0.14 1/2 averaged gluon jet charge
(cid:88) ar 0.12 s = 2.76 TeV
Qiκ =h∈jetzκhQh (1) d jet ch 00..0180
e
wfrahcetrieoniionfditchaetejestthcearjreitefldabvyouthr,eafnrdagzmhiesntthaetemdohmadernotunmh verag 0.06
a 0.04
with electric charge Q . κ is a power parameter which
h
0.02
variesfrom0.1and1toadjustthebiasofhadronswith
differenttransversemomentum. 0.00
60 80 100 120 140 160 180
pT,jet(GeV)
0 .2 4 A T LA S data k = 0.3 aFnigdufruell2j:eTtshienppT+pdeapte2n.7d6enTceeVo.fjetchargesforquarkjets,gluonjets
e [e] 000 ...122 802 AApyTTtLLhAAiaSS6 +ddfaaattsaat jekk t== 00..57 p p s1/2 = 8 T e V Moreover, we calculate the jet charge for quark and
rg 0 .1 6 gluon jets respectively in Fig. 2. It is shown that the
a
e Jet Ch 000 ...111 024 fdcehiaffaterugrreeensot.offBajeegctlacuuhosanerggjeeltufooisnrqacupaaprrrrikoeasacnnhdoingeglluezocentrroijceitcnshaaarregweqh,uoijlteeet
g
ra 0 .0 8 range of p . The averaged full jet charge is the com-
ve 0 .0 6 T
A 0 .0 4 binationofchargesofquarkandgluonjetsaftertaking
0 .0 2 intoaccounttheirrelativecontributions.
0 .0 0 Theoretical studies and experimental measurements
0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0
have shown that fast partons traversing the QGP
p Tjet(G e V ) mediumshouldsuffermultiplescatteringwithotherpar-
tonsandloseenergyduetocollisionalandradiativepro-
Figure1:Thecomputedaveragejetchargesfortheleadingjetindijet cesses. Inourcalculationw1ewillusePYQUEN(PYthia
eventsasafunctionofthejettransversemomentum.Theexperiment
QUENched)model[17]tosimulatepartonenergyloss
databyATLAShavealsobeenshownforacomparison.
in the QGP medium. PYQUEN is one of the Monte
Firstly we study jet charge in p+p collisions. It has Carlo models of jet quenching and built as a modifica-
tion of jet events obtained for hadronic collisions with
beenshownthattheenergyandandjet-sizedependence
pythia 6.4. The details of the used physics model and
ofmomentsofjet-chargedistributionscanbecalculated
simulationprocedurecanbefoundin[17]. Themodel
in perturbative QCD in [9]. here, we employ the MC
hasincludebothradiativeandcollisionalenergylossof
eventgeneraterpythia6withthePerugia2012tune[16]
to simulate particle production in p+p collisions, and hard partons, as well as the realistic nuclear geometry.
Thecollisionalenergylossisconsideredbytheformula:
the FastJet package [15] is used to construct final state
jets. Shown in in F√ig. 1 are the results for jet charge dEcol 1 (cid:90) tmax dσ
in p+p collisons at s = 8 TeV from pythia6+fastjet = dt t. (2)
dl 4Tλσ dt
compared with ATLAS recent data [11]. One can ob- µ2
D
serve that jet charge goes up with increasing jet trans-
Theradiativeenergylossissimulatedintheframeworks
versemomentum,andthedistributionswithlargerκare
ofBDMPSmodel[18,19],whichgives[17]:
higher [12]. Decent agreement can be seen between
etchxheparefgroeilmloaewtnit√nalgsdw=aeta2u.a7sne6dtThteehVesaptmh+eepoarcepotpilcrlioaslaiocchnaslt,couwlpahrtieicodhnic.mt jaIeynt dEdrlad = 2απs(Lµ2D)(cid:90)ωEmindω[1−y+y22]ln|cos(ω1t1)| .(3)
S.Y.Chen,B.W.ZhangandE.Wang/NuclearandParticlePhysicsProceedings00(2017)1–5 3
and psubleadarethetransverseenergyofthejetswiththe
T
0.11 highestandsecond-highest p ,respectively.
0.10 jet charge pp =1.0 T
e 0.09 jet charge PbPb =1.0 Shown in Fig. 3 are our theoretical predictions for
g
ar 0.08 jet charge pp =0.3 jet charges with κ = 0.3, 1 in Pb+Pb collisions with
h jet charge PbPb =0.3 √
et c 00..0067 s1/2 = 2.76 TeV sNN = 2.76 TeV at the LHC, the corresponding p+p
j 0.05 baselines, as well as their ratios [12]. It could be seen
0.04 that the jet quenching effect will increase the averaged
0.03
jetchargeinheavy-ioncollisionsandthisenhancement
0.02
p) 01.0.51 ismorepronouncedwithsmallerκ.
p
b/ 1.4 ratio(PbPb/pp) = 1.0 This medium enhancement of jet charge in heavy-
P
Pb 1.3 ratio(PbPb/pp) = 0.3 ioncollisionsresultsmainlyfromthesuppressedgluon
ratio( 11..12 fgrlaucotniojnetdcuoenttorijbeuttqiounentochthinegc.hFarrogmedFisigtr.ib2uwtieonknoofwanthina-t
1.0 discriminative full jet is negligible. In heavy-ion colli-
40 60 80 100 120 140 160 180 200
jet sions,thegluonjetwilllosemoreenergyascomparedto
pT (GeV)
quarkjetanditsrelativefractioninafulljetwillbere-
Figure 3: The average jet charge distribution for the leading jet in ducedinnuclearcollisions.Therefore,inheavy-ioncol-
dijeteventsasafunctionofthejettransversemomentuminPb+Pb
andp+pcollisionsat2.76TeV. lisionsthepossibilityofobtainingaquark-originatedjet
is enhanced with respect to p+p, which leads to larger
jet charge because jet charge of quark is always much
To investigate jet observables, another important largerthangluonjet. Fig.2illustratesthenuclearmod-
ingredient of the model is the angular spectrum of ificationsofjetchargesforbothquarkjetandanindis-
medium-inducedradiation. Ithasbeenfoundthattore- criminativejet,andoneobservesthatthemediummod-
produceexperimentaldataonjetobservablessuchasin- ificationofquarkjetchargeisrathersmall.
clusivejetcrosssections,jetshapeandjetfragmentation
functioninheavy-ioncollisions,the”wide-angle”radi-
ationscenarioshouldbeusedinPYQUENmodel[21], 1.6
whichisalsoadoptedinthecalculationsofthiswork. 1.5 nuclear modification ratio for <Qfull jet>
It is noted that in the original version of PYQUEN nuclear modification ratio for <Qquark jet>
model,theevolutionoftheQGPisdescribedbyalon- 1.4
1/2
gitudinal expansion 1+1D1 Bjorken model with initial 1.3 s = =0. 32.76 TeV
conditionτ0 =0.6fmandT0 =1GeVatcentralPb+Pb atio 1.2
collisions. Inordertohaveamorerealisticevolutionof R
the fireball produced in relativstic heavy-ion reactions, 1.1
inamodifiedversionofPYQUENwehaveinsteadused
1.0
an event-by-event 3+1D ideal hydrodynamical model
withaninitialconditionτ =0.4fmandT =0.39GeV, 0.9
0 0
whichhasgivenanicedescrptiononthebulkproperties 0.8
inPb+PbcollsionsattheLHC[22]. 60 80 100 120 140 160
pT,jet(GeV)
Figure4: Thenuclearmodificationratiosofjetchargesforaquark-
3. Numericalresultsanddiscussions initiatedjetandanindiscriminativejet.
With the framework discussed in the last section, In conventional theoretical models of jet quenching,
we calculate the average jet charge distribution for the gluon is excepted to lose more energy than quark be-
leading jet in dijet events as function of the jet trans- cause of its large color factor with f = ∆E /∆E =
g q
verse momentum at the LHC energy. The candidate 9/4. However, the puzzle of proton over pion ratios in
particles used to reconstruct jets are required to have Au+Au collisions at RHIC seems challenge this rela-
p >500MeV.Jetsareclusteredbytheanti-k jetalgo- tion [13, 14] and our understanding of flavour depen-
T t
rithm[15]withradiusR = 0.4implementedinFastJet. dence of parton energy loss( gluons, light quarks and
Wealsomakeconstraintsofjetrapiditywith|η| < 2.1, massive quarks) is far from satisfactory. To investi-
thetwoleadingjetswith plead/psublead <1.5. Here plead gatethesensitivityofjetchargetothedifferentenergy
T T T
1
S.Y.Chen,B.W.ZhangandE.Wang/NuclearandParticlePhysicsProceedings00(2017)1–5 4
losspatternsofquarksandgluonsweconsidertwosim- 4. Summary
ple scenarios of energy loss patterns (Scenario I with
f = 9/4andScenarioIIwith f = 1)andthencalculate We calculate numerically the momentum-weighted
thecorrespondingjetcharges. sumofjetchargesinrelativisticheavy-ioncollisionsfor
the first time. It is shown that the jet charge is signifi-
cant modified by the jet quenching effect in the QGP
0.060 medium. Quark jet charge has shown a quite distinct
e
g 0.055 averaged jet charge in pp
har 0.050 averaged jet charge in PbPb, f = 9/4 feature with gluon jet charge, and the sensitivity of jet
ed jet c 000...000344505 s 1=/2 =0 .a23v.7e6ra TgeeVd jet charge in PbPb, f = 1 cahlsaorgienvteostfligaavtoeudr.dIetpecnodueldncbeeosfepenarttohnatejneetrgcyhalnogses iiss
g anexcellentobservabletodiscriminatequarkandgluon
a 0.030
er 0.025 jets and their energy loss patterns in heavy-ion colli-
v
a 0.020
sions.
0.015
p)0.010 WethankProf. X.N.Wang,WeiChenandG.Y.Ma
b/p 11..45 f = 1 for helpful discussions. This research is supported by
P 1.3 f = 9/4
Pb 1.2 theMOSTinChinaunderProjectNo. 2014CB845404,
atio( 011...901 and by NSFC of China with Project Nos. 11322546,
R 0.8 11435004,and11521064.
0.7
40 50 60 70 80 90 100 110 120
jet
pT (GeV)
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