hard probes and the event generator eposllr.in2p3.fr/sites/qgp2013/talks/etretat2013_guiot.pdf ·...

IntroductionEPOS : general presentation

CharmPhotons

Hard probes and the event generator EPOS

B. GUIOT1 K. WERNER1

1Subatech, [email protected]

QGP-France-2013

B. GUIOT, K. WERNER Hard probes and the event generator EPOS


CharmPhotons

Outline

1 Introduction

2 EPOS : general presentation

3 Charm

4 Photons



CharmPhotons

Motivations

pp collisions :

1 Benchmark for Pb-Pb collisions2 Test of pQCD , parton-based Gribov-Regge theory (in EPOS)

Heavy quarks :

1 Interaction with the dense medium : energy loss, heavyquarkonia

2 shadowing/saturation

Prompt and fragmentation photons :

1 comparison with experiments on isolated photon2 γ jet3 shadowing/saturation4 multiparton scattering : γ + 3 jets5 fragmentation photons could be a�ect by the medium



CharmPhotons

Simulation and multiparton interaction

High energy → multiparton interactions

non-inclusive observables are sensible to multiple interaction... But

hard to take this physics into account



CharmPhotons

Outline

1 Introduction


3 Charm

4 Photons



CharmPhotons

EPOS philosophy

EPOS = event generator 6= spectrum generator

1 experimental event = 1 EPOS event (we hope so)

slower than other generators like pythia (statistics)Can reproduce complicated e�ects (like the ridge)

Unify formalism :

The same treatment for pp, pA and AA



CharmPhotons

Regge and pQCD

Energy conserving multiple

scattering

Partons, parton ladders, and

strings

O�-shell remnants

Saturation

Multiple interaction treatment with the parton-based

Gribov-Regge theory



CharmPhotons

Results for multiplicity



CharmPhotons

Hard events

1 Partonic evolution done with

DGLAP, ISR

2 Hard partonic scattering at

LO (K ∼ 2 take into account

higher orders)

3 FSR



CharmPhotons

Collective behavior

Hydro event-by-event

Flux tubes form jet and bulk matter

Interaction between jet and bulk matter

arXiv:1203.5704v2; K.Werner, Iu.Karpenko, M.Bleicher, T.Pierog, S.Porteboeuf-Houssais; Jun 2012



CharmPhotons

Ridge and v2 in pPb collisions

arXiv:1307.4379v1; K.Werner, M.Bleicher, B.Guiot, Iu.Karpenko,T.Pierog; Jul 2013



CharmPhotons

Outline

1 Introduction


3 Charm

4 Photons



CharmPhotons

Work on charm production

dissection of a pomeron : charm production

Initial State

Radiation

born

Done by Monte-Carlo techniques



CharmPhotons

... and timelike cascade ⊗ fragmentation

For ISR and out born particles

Processes implying a charm :

g → cc̄

c → cg

Timelike cascade ∼ inverse of hard evolution

Q2 decreases from m2t = p2t +m2 to Q2

min ∼MeV +m2

String fragmentation



CharmPhotons

Hard evolution and ISR

Hard evolution done with DGLAP : increasing virtuality, Q2, of

spacelike parton

ISR = initial state radiation : production of small pt particles

emission probability :

dp(x ,Q2) ∝αs

2π

dQ2

Q2 pi→jk(x)

Threshold for Heavy quarks : xmax = Q2

Q2+m2 .



CharmPhotons

Born scattering

L.O QCD cross sections ⇒ High pt particles (K ∼ 2 for higher

orders)

Strong and electromagnetic processes

Threshold for Heavy quarks :

s > 4m2

|t|> s

2(1−β )−m2 with β =

√1−4m2/s



CharmPhotons

D+ meson

www.lpthe.jussieu.fr/~cacciari/fonll/fonllform.htmlarXiv : 1111.1553v2, 2012



CharmPhotons

D0 meson

www.lpthe.jussieu.fr/~cacciari/fonll/fonllform.htmlarXiv : 1111.1553v2, 2012



CharmPhotons

Outline

1 Introduction


3 Charm

4 Photons



CharmPhotons

Our project

In subatech, some people are working on Jetphox and isolated

photons (for ALICE experiment)

1 study of the experiment and of their criteria for isolated photon2 fragmentation photons : EPOS(DGLAP) -

Jetphox(fragmentation function)3 γ/jet

In order to compare our results → need of fragmentation

photons and isolation subroutine



CharmPhotons

Implementation

Fragmentation photons add in spacelike and timelike cascade

∼ αel/αs∼ α2

el/αs : neglected

pq→qγ (x) ∝ pq→qg (x)

Main modi�cation...

...Add the probability

dpel ∝αel

2π

dQ2

Q2 pq→qγ (vs dpstrong ∝αs(p

2t )

2π

dQ2

Q2 pq→qg )



CharmPhotons

Isolation subroutine

Cone de�ned by R =√

∆φ2 + ∆η2

∑pt < seuil ; pt =transverse impulsion of particles inside the

cone

Neutron not seen by detectors : we ignore its energy

Several choices :

R = 0.4 and seuil = 5 GeVR = 0.3 and seuil = 1.5 GeV

E�ective radius given for simulations (in experimental papers)



CharmPhotons

Results



CharmPhotons

Results

CMS data : arXiv : 1012.0799v2



CharmPhotons

Summary

EPOS give satisfying results for low and high energy physics

Simulation are long for rare events

We can reproduce the Et spectrum of photons from CMS.

Enough fragmentation photons??

Outlook :

Waiting for Alice publication on isolated photonsComparison with jetphox for fragmentation photonsD mesons vs multiplicity


hard probes and the event generator eposllr.in2p3.fr/sites/qgp2013/talks/etretat2013_guiot.pdf ·...

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