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IntroductionEPOS : general presentation
CharmPhotons
Hard probes and the event generator EPOS
B. GUIOT1 K. WERNER1
1Subatech, guiot@subatech.in2p3.fr
QGP-France-2013
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Outline
1 Introduction
2 EPOS : general presentation
3 Charm
4 Photons
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Outline
1 Introduction
2 EPOS : general presentation
3 Charm
4 Photons
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Outline
1 Introduction
2 EPOS : general presentation
3 Charm
4 Photons
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Results for multiplicity
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Ridge and v2 in pPb collisions
arXiv:1307.4379v1; K.Werner, M.Bleicher, B.Guiot, Iu.Karpenko,T.Pierog; Jul 2013
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Outline
1 Introduction
2 EPOS : general presentation
3 Charm
4 Photons
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Work on charm production
dissection of a pomeron : charm production
Initial State
Radiation
born
Done by Monte-Carlo techniques
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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 .
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
D+ meson
www.lpthe.jussieu.fr/~cacciari/fonll/fonllform.htmlarXiv : 1111.1553v2, 2012
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
D0 meson
www.lpthe.jussieu.fr/~cacciari/fonll/fonllform.htmlarXiv : 1111.1553v2, 2012
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Outline
1 Introduction
2 EPOS : general presentation
3 Charm
4 Photons
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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 )
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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)
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Results
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
CharmPhotons
Results
CMS data : arXiv : 1012.0799v2
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
IntroductionEPOS : general presentation
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
B. GUIOT, K. WERNER Hard probes and the event generator EPOS
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