Summary Jet results in QM2017
Shingo Sakai (Univ. of Tsukuba, CiRfSE)

1

Introduction (1)n Strong suppression of high pTparticle production in heavy-ion
collisionsn Due to energy loss of partonsin hot & dense QCD mattern Energy loss mechanizmn Collisional energy lossn Collisions with medium
n Radiative energy lossn Induced gluon emissionn Jet measurementn Address parton & medium
interaction which allows tostudy energy loss
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Introduction (2)n A strong suppression of jets has observed at LHC
n Detailed mechanism of the energy loss can be studied
n Energy dependence, di-jets & Flavour dependence (jet level)n Fragmentation function & Jet structure (inside of jet, constituent level)3Jet RAA in PbPb at 5.02 TeV (0-10%)
ATLAS-CONF-2017-009, M. Spoutan Jet RAA in 0-10% in 5 TeV PbPb collisions
n Observed suppression up to 1 TeV
n 2.76 TeV up to 400 GeV/cn Similar suppression between 2.76 TeV and 5.02 TeV (no collision energy dependence)4

y-dependence of RAA in PbPb at 5.02 TeVATLAS-CONF-2017-009, M. Spoutan Rapidity dependence of jet productionn Low pT:n No y dependencen High pT:n More suppression atforward rapidityn increasing steepnessof the spectran increasing quark-jet fraction
with y(EPJ C76, 2016, no. 2, 50)

Reference: RAA(|y|<0.3)
5Jet RpPbn Jet production in pPb
n control experiment : expect to be absence of hot & dense QCD mattern No modification of jet production (RpPb = 1)
n No significant rapidity dependence6B-jet production in pPb and PbPb

n Similar b-jets suppression as inclusive jetsn Model prediction: heavy quarks loss less energy than light quarks
n Heavy-flavour jets (b-jets & c-jets) are consistent with unity in pPb collisionsn Heavy quarks also lose significant energy in the matter
K. Jung7

Momentum balance of b-jet
n Similar suppression (RAA) between
Inclusive and beauty jets
n Double ratio of dijet and b-dijetn Large double ratio if b-jets
are less quenchn Similar momentum imbalance
between dijet and b-dijetn Similar b-jet quenching andInclusive jet

K. Jung8

Momentum balance of Z-Jet & γ-Jet
arXiv: 1702.01060, R. Bi

ATLAS-CONF-2016-110, P. Steinberg

n Photons and W/Z bosons don’t interact with the medium
n No energy loss of trigger particle (photons and W/Z)n No bias from suppression in trigger particle on recoil jets => absolute energy loss
n pT balance of the jets is modified, shift to lower x due to energy loss in jets9

Jet Fragmentation in PbPb (1)
ATLAS-CONF-2017-005, R. Slovak
n Fragmentation function in PbPbn Enhancement at low z
n Suppression at intermediate z
n Enhancement at high z
n No √s effectn Enhancement at low z
n Due to energy loss by partons istransferred predominantly tosoft particles
n Enhancement at high z
n Consistent with different quenchingof quark and gluon jets
(EPJ C76, 2016, no. 2, 50)
z: longitudial momentum fraction10Jet Fragmentation in PbPb (2)n Centrality dependence of fragmentation functionn Strong modification in most central collisionsn Similar fragmentation function as pp in peripheral collisions
11

R. Slovak

Jet Fragmentation in pPb
ATLAS-CONF-2017-004

R. Slovakn No modification of the fragmentation functions is observed fromlow pT to high pT jets in pPb collisions at 5.02 TeV
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Jet-track correlation

ppn Particle distribution w.r.t. axis of leading jets (>120 GeV/c)n A excess of low pT particles (pT < 3 GeV/c) extending to largeΔr from jet axis is found13

H. Trauger

Jet – medium interactionn Enhancement at large R due
to jet – medium interaction ?
n A model with energy loss
+ hydrodenamical model
well represents the enhancen Full jets shower interact
with medium by radiative& collisional processn Deposit the energy tothe medium and then evolvewith the mediumhydrodynamically.
arXiv:1701.07951
14Jet shape in PbPb : pT dispersion

n pTD：pT dispersion
n Jets with fewer constituents have higher pTD
n pp: consistent with PYTHIA predictions (QCD)n PbPb: shift to higher pTD => less constituents than pp
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D. CaffarriJet shape in PbPb : radial momentn g：radial moment (jet width)n Large g: broadened jets , small g: collimated jetsn pp: consistent with PYTHIA predictions (QCD)n PbPb: shift to lower g => jets are more collimated
16D. CaffarriJet shape in PbPb : Jet Massn Jet Mass; M = √ E2 – pT2 – pZ2n Increase if a significant amount of the radiated gluons are captured with in jet conen On the other hand, depletion due to energy loss
n Jet mass in PbPb, especially pT<100 GeV/c, shifted to lower mass w.r.t. the mass inpPb
D. Caffarri17

Momentum balance of hard splitting partons
CMS-PAS-HIN-16-006

n Momentum balance of two partons that from high pT partonn Modification of subjet balance observed in central PbPb collisionsn Medium modified splitting
18Y. ChenSummary} Reached TeV order in jet measurement}

Still observed strong suppression of jet production} Medium still ‘opaque’ such high pT jets}

Heavy flavour (beauty) jet is suppressed same as inclusive(light flavour) jets} In side of jet}

Enhancement at low Z} Enhancement soft particles (pT<3 GeV/c) at large R¨ Well represented jet – medium interaction model}

Modified jet shape} Narrowing of the core of jets}
19Modified splitting of high pT partons