Jet quenching and holography:
experimental aspects

Oliver Busch
University of Tsukuba
Heidelberg University
Oliver Busch – XIIth Quark Confinement and the Hadron Spectrum, Thessaloniki1Jet quenching and holography:
experimental aspects(focus on light flavour energy loss)

Oliver Busch
University of Tsukuba
Heidelberg University
Oliver Busch – XIIth Quark Confinement and the Hadron Spectrum, Thessaloniki2

Jet quenching and holography:
experimental aspects(focus on light flavour energy loss)(not a comprehensive experimental summary)
Oliver Busch
University of Tsukuba
Heidelberg University
Oliver Busch – XIIth Quark Confinement and the Hadron Spectrum, Thessaloniki

3

Hadron nuclear modification factor• high-pT hadron as a proxy for jet:small experimental uncertainties, but often
difficult to calculate for theory (fragmentation needed)• experimental biases: high-z fragment, ‘hard’ fragmentation pattern• connection to parton kinematics
not straight forward

CMS PAS HIN 15-015

Jets in heavy-ion collisions• jet reconstruction in heavy-ion collisions :high underlying event background from soft particles not related tohard scattering• relevant scale for quenching effects likely Tmed : several 100 MeV• compromise between experimental uncertainties and physics significance• parameters:• constituent pT (150 MeV/c - 2 GeV/c)• jet radius (0.2 - 0.5)
• fragmentation biases(minumum leading constituent pT,match to tracking jet, … )• jet pT (40 - several 100 GeV/c)• (semi-)/inclusive(ALICE JHEP 09 (2015) 170)

Jet nuclear modification factor• strong suppression,

similar to hadron RAA→ parton energy notrecovered inside jet cone
• increase of suppression
with centrality,
weak pT dependence• JEWEL:- microscopic pQCD
parton shower + gluon
induced emissions• YaJEM:- detailed fireball model- parameterisation of radiative and collisionalenergy loss

Phys.Lett. B746 (2015) 1
JEWEL: PLB 735 (2014)
YaJEM:PRC 88 (2013) 014905• different models reproduce observed jet suppression→ further constraints needed, more differential measurements !

6

Democratic branching ?
• democratic branching expected in strongly coupled energy loss (?)• jet fragmentation measured by ATLAS, CMS:

modest modification of jet fragmentation compared to pp• high-z region seems unmodified / only weakly modified• enhancement at low pT• also note CMS results for splitting
functions(CMS-HIN-16-006)

7

Jet and high-pT hadron v2• path-length dependence of energy loss:CMS, PRL 109 (2012) 022
ATLAS, PRL 111 (2013) 152• elastic ~L
ALICE, Phys. Lett. B753 (2016) 511• pQCD ~L2
ALICE, Phys. Lett. B719 (2013) 18• strong coupling ~L3
JEWEL: K.C. Zapp, F. Kraus, U.A. Wiedemann,JHEP 1303 (2013) 080

0.3ALICEch jet

Pb-Pb sNN = 2.76 TeV
R = 0.2 anti-k T, |η |<0.7
jetv230-50%, Stat unc.

Syst unc. (shape)

ch jetv20.2

Syst unc. (correlated)calo jet

ATLAS v 20.2v 2ch jetv 2part, v 2jet• v2 described by JEWEL (pQCD based)

30-50%

ALICE

30-50%, JEWEL

ch jetv230-50%, Stat unc.

Pb-Pb sNN = 2.76 TeV

Syst unc. (shape)

R = 0.2 anti-k T, |η |<0.7
jet

Syst unc. (correlated)part

CMS v 2 {|∆η|>3} 30-50%
part

ALICE v 2 {|∆η|>2} 30-50%

0.10.100(b)0p50

T, track> 0.15 GeV/c , p

T, lead> 3 GeV/ c100150partjetp , p (GeV/c )
T(b)

20p

30

4050

T

Oliver Busch – XIIth Quark Confinement and the Hadron Spectrum, Thessaloniki

T, track60> 0.15 GeV/c , p lead > 3 GeV/ cT

70

80 90 100ch jetp(GeV/c )T8• many other measurements …

jets

1/N

• transverse structure by CMS(pTjet ~100 GeV/c)• girth (average transverse width)by ALICE (pTjet > 40 GeV/c)

dN/dg

Transverse jet profile3025

ALICE Preliminary
Pb-Pb sNN = 2.76 TeV
Anti-k T charged jets, R = 0.2
40 < p jet,ch < 60 GeV/c20

T

ALICE Data
Shape uncertainty
Correlated uncertainty
PYTHIA Perugia 11

15
10
500

ALI−PREL−101580

0.02

0.04

0.06

0.08

0.1

0.12gCMS,
Phys. Lett. B 730 (2014) 2439