M. Djordjevic 1

Theoretical predictions of jet suppression: a systematic comparison

with RHIC and LHC data

Magdalena DjordjevicInstitute of Physics Belgrade, University of Belgrade

M. Djordjevic 2

Jet suppression

Light and heavy flavour suppressions are excellent probes of QCD matter.

Suppression for a number of observables at RHIC and LHC has been measured.

Comparison of theory with the experiments allow testing our understanding of QCD matter.

M. Djordjevic 3

1) Initial momentum distributions for partons2) Parton energy loss3) Fragmentation functions of partons into hadrons

4) Decay of heavy mesons to single e- and J/psi.

Jet suppression

hadrons

1)

production

2)

medium energy loss

3)

fragmentation

partons e-, J/psi

4)

decay

Dynamical energy loss

Computed radiative and collisional energy loss in finite size dynamical QCD medium of thermally

distributed massless quarks and gluons.

Abolishes approximation of static scatterers.M. D. PRC 80:064909 (2009), M. D. and U. Heinz, PRL 101:022302 (2008).

Finite magnetic mass effects. M. D. and M. Djordjevic, PLB 709:229 (2012)

Includes running couplingM. D. and M. Djordjevic, arXiv:1307.4098 (PLB, in press)

M. Djordjevic 5

Numerical procedure• Light flavor production Z.B. Kang, I. Vitev, H. Xing, PLB 718:482 (2012)

• Heavy flavor production M. Cacciari et al., JHEP 1210, 137 (2012)

• Path-length fluctuations A. Dainese, EPJ C33:495,2004.

• Multi-gluon fluctuations M. Gyulassy, P. Levai, I. Vitev, PLB 538:282 (2002).

• DSS fragmenation for light flavor D. de Florian, R. Sassot, M. Stratmann, PRD 75:114010 (2007)

• BCFY and KLP fragmenation for heavy flavor M. Cacciari, P. Nason, JHEP 0309: 006 (2003)

• Decays of heavy mesons to single electron and J/psi according to

M. Cacciari et al., JHEP 1210, 137 (2012)

• Temperature T=304 MeV for LHC and T=221 MeV for RHIC. M. Wilde, Nucl. Phys. A 904-905, 573c (2013) (ALICE Collab.)

A. Adare et al., Phys. Rev. Lett. 104, 132301 (2010) (PHENIX Collab.)

M. Djordjevic 6

Generating predictions

• Provide joint predictions across diverse probes

charged hadrons, pions, kaons, D mesons,

non-photonic single electorns, non-prompt J/psi M. D. and M. Djordjevic, arXiv:1307.4098 (PLB, in press)

• Puzzles (apparently surprising data)

Measured charged hadron vs. D meson supression

M.D., PRL 112, 042302 (2014)

• Concentrate on all centrality regions

M. D., M. Djordjevic and B. Blagojevic, arXiv:1405.4250 All predictions generated

By the same formalismWith the same numerical procedureNo free parameters in model testing

M. Djordjevic 7

Comparison with LHC data (central collision)

Very good agreement with diverse probes!

M. D. and M. Djordjevic, arXiv:1307.4098 (PLB, in press)

M. Djordjevic 8

Heavy flavor puzzle at LHC

Significant gluon contribution in charged hadrons

Much larger gluon suppression

RAA (h±) < RAA (D)

M. Djordjevic 9

Charged hadrons vs D meson RAA

RAA (h±) = RAA (D)Excellent agreement

with the data!

Disagreement with the qualitative expectations! M.D., PRL 112, 042302 (2014)

ALICE data

M. Djordjevic 10

Hadron RAA vs. parton RAA

D meson is a genuineprobe of bare charm quark suppression

Distortion by fragmentation

Charged hadron RAA = (bare) light quark RAA

M.D., PRL 112, 042302 (2014)

M. Djordjevic 11

Puzzle explanation

RAA (D) = RAA (charm)RAA (light quarks) = RAA (charm)

RAA (h±) = RAA (D)

Puzzle explained!

RAA (h±) = RAA (light quarks)

M.D., PRL 112, 042302 (2014)

M. Djordjevic 12

Comparison with RHIC data (central collisions)

Very good agreement!

RHIC

M. Djordjevic 13

Non central collisions @ LHC (fixed centrality and charged hadrons)

An excellent agreement for different centrality regions!M. D., M. Djordjevic and B. Blagojevic, arXiv:1405.4250

M. Djordjevic 14

Non central collisions @ LHC (fixed centrality and D mesons)

Excellent agreement!

Predictions for upcoming measurements.

M. D., M. Djordjevic and B. Blagojevic, arXiv:1405.4250

M. Djordjevic 15

Also a good agreement for RHIC!

Non central collisions @ RHIC (fixed centrality and neutral pions)

M. D., M. Djordjevic and B. Blagojevic, arXiv:1405.4250

M. Djordjevic 16

RAA vs. Npart for RHIC and LHC

Very good agreement for both RHIC and LHC and for whole set of probes!

M. D., M. Djordjevic and B. Blagojevic, arXiv:1405.4250

M. Djordjevic 17

Assessing medium model

A robust agreement with suppression data, for different probes, experiments and centrality regions.

Predictions are generated with the same model, parameter set and with no free parameters.

NOTE: We use a sophisticated energy loss model, but do not explicitly include the medium evolution

(i.e. we take average/effective medium parameters).

M. Djordjevic 18

PROPOSAL: Medium evolution may not be a major effect in hard probe (>10 GeV) suppression.

HYPOTHESIS: High energy jets sense only the average (effective) medium conditions.

CONSEQUENCE: May significantly simplify both generating predictions and analyzing

phenomena behind experimental data.

Acknowledgement

Ministry of Science and Education in Serbia

FP7 Marie Curie International

Reintegration grant

L’Oreal UNESCOFor Women in Science

Serbia

Many thanks to:• M. Djordjevic and B. Blagojevic for collaboration on this project.• I. Vitev and Z. Kang for providing the initial light flavor distributions and

useful discussions. • M. Cacciari for useful discussions on heavy flavor production and decay

processes. • ALICE Collaboration for providing the preliminary data• M. Stratmann and Z. Kang for help with DSS fragmentation functions.

M. Djordjevic 20

Main results

The dynamical energy loss can simultaneously explain central-collision measurements for a

diverse set of probes at LHC and RHIC.

The formalism can explain puzzling data (“the heavy flavor puzzle at LHC”).

We obtain a very good agreement with the non-central collision data as well.

Results suggest that the medium evolution is not a major effect for suppression of hard probes.

M. Djordjevic 21

The end

M. Djordjevic 22

The dynamical energy loss formalism is based on HTL perturbative QCD, which requires zero magnetic mass.

Finite magnetic mass

However, different non-perturbative approaches show a non-zero magnetic mass

at RHIC and LHC.

Can magnetic mass be consistently included in the dynamical energy

loss calculations?

M. Djordjevic 23

Generalization of radiative jet energy loss to finite magnetic mass

M.D. and M. Djordjevic, Phys.Lett.B709:229,2012

zero magnetic mass

From our analysis, only this part gets modified.

2 2

2 2 2 2( )( )E M

E Mq q

Finite magnetic mass: , where .0.4 0.6M

E

24

A simple constraint on the magnetic massIf magnetic mass is larger than electric mass, the quark jet would, overall, start

to gain (instead of lose) energy in this type of plasma.

An apparent violation of the second law of thermodynamics.

It is impossible to observe a plasma with magnetic mass larger than electric

Various non-perturbative approaches suggest that, at RHIC and LHC,

0.4 < μM/μE < 0.6.

M.D. and M. Djordjevic, Phys.Lett.B709:229,2012

M. Djordjevic 25

Running couplingCollisional energy loss Radiative energy loss

k,c

q,a p

p

q

2( )vQ

2( )kQ

2( )E

2( )vQ

2( )E

2 2~ ( ) ( )coll v EE Q

2 2 2~ ( ) ( ) ( )rad k v EE Q Q

M. D. and M. Djordjevic, arXiv:1307.4098