Photon physics in ALICE Y.Kharlov D.Peressounko IHEP RRC “Kurchatov Institute” for the ALICE collaboration and

Photon physics Direct photon – jet correlations   Neutral meson spectra, R AA, v 2 … Chemical composition:  0, ,  Direct photon spectra, R AA, v 2 … Inclusive, Isolated, Thermal  inclusive  isolated  thermal 2 2-Apr-2009Photon physics with ALICE

ALICE setup in 2009: section at  =0 PHOS: |  |<0.125  : 100 o 3/5 installed EMCAL: |  |<0.7  : 110 o 2/5 installed PHOS: high-granularity photon spectrometer (20 X 0 ) acceptance:  =100 , |  |< k PbWO 4 crystals 2.2  2.2  18. cm 3 5 modules 64  56 crystals each energy range: GeV EMCAL large aperture Pb-Sc electromagnetic calorimeter (20 X 0 ) acceptance:  =107 , |  |<0.7 13k towers 6  6 cm supermodules 24  48 towers each energy range: GeV CERN-ALICE-TDR Apr-2009Photon physics with ALICE

Photon detectors resolutions PHOS EMCAL  E /E (%)  x (mm) R ip (cm) 460   (MeV) p t =1-2 GeV 5.5 MeV 428 ITS+TPC+TRD < MeV ~ Apr-2009Photon physics with ALICE 3.3 Me V 0.8<p t <2 GeV

 0 measurement well separated clusters  invariant mass analysis < 10 GeV/c in EMCal < GeV/c in PHOS merged clusters not spherical  shower shape analysis GeV/c in EMCal GeV/c in PHOS 5/36 p   GeV/c   identified as   identified as   p+p   as     as  5 2-Apr-2009 Photon physics with ALICE PHOS EMCAL

 0 and  measurement PHOS 6 2-Apr-2009Photon physics with ALICE See poster K. Aamodt et al., for  0 /  via converted photons Conversion PHOS,  0 PHOS,  Conversion,  0 m  (GeV)

 0 in central Pb-Pb collisions at 5.5 ATeV 2-Apr-2009Photon physics with ALICE Only event mixing technique reveals  0 peak at low p T 7

Acceptance for  , ,  measurement Acceptance is normalized per |y|<0.5,  =2  8 2-Apr-2009Photon physics with ALICE

ALICE trigger for photon physics ALICE minimum bias trigger:  Accepts almost any pp collisions based on signals in inner and forward ALICE detectors  Trigger busy time is determined by the slowest detector in a trigger partition.  Although collision rate in pp is high (3.5 kHz), event rate can be as slow as 200 Hz which corresponds to effective luminosity L=5  cm -2 s -1. PHOS trigger:  Can select events with high energy deposited in 2  2 or 4  4 crystals  If the trigger partition with PHOS includes fast detectors, event rate is defined only by the luminosity  The higher the trigger threshold, the lower event rate is, and the slower detectors can be included into the trigger partition  EMCAL  Same as PHOS, but with different thresholds  TRD  Trigger on e + e - pair with high p t and small opening angle.  Under investigation 9 2-Apr-2009Photon physics with ALICE

PHOS L0 trigger rate in 10 TeV L0 definition: 2x2 (4x4) cells energy sum > threshold somewhere in PHOS 10 2-Apr-2009Photon physics with ALICE Setting PHOS L0 threshold to a moderate value (~500 MeV) results in low enough data taking rate with minimal effect of a trigger busy time. Rate is calculated under assumption of 3.5 kHz collision rate

 0, ,  and  cross sections in pp 2-Apr-2009 Photon physics with ALICE NLO pQCD + CTEQ5M + KPP. Bands indicate possible uncertainties in QCD scale [P. Aurenche, et al., Eur. Phys. J. C 13,347 (2000)] pp  0 Xpp  X LO pQCD: Pythia 6 pp  X pp  X 11

Expected yields in first ALICE run 12 2-Apr-2009Photon physics with ALICE Integrated luminosity, nb -1 Run time T L, cm -2 s -1 5    days month months

Accesible range in Pb+Pb colisions Binary scaled p+p cross 5.5 TeV (INCNLO) N binary calculated using [F.Arleo et al., hep-ph/ ] centrality class 0-10% L PbPb =5·10 26 [cm -2 s -1 ] T = 1·10 6 [s] ∫L = 0.5 [nb -1 ] R AA =0.2 R AA =1 Pb+Pb  dir +X Pb+Pb  0 +X 2-Apr-2009Photon physics with ALICE 13

Isolated direct photons Y. Mao et al., Eur.Phys.J.C57: ,2008 IC: R =0.3,  (p T )=2 GeV/c IC: R =0.2, p T >2 GeV/c G. Conesa et al., ALICE-INT , NIM A 580 (2007) Apr-2009Photon physics with ALICE See posters Y.Mao and R. Ichou  fragmented  isolated 2 PHOS modules 5 PHOS modules

Isolated Spectra in EMCAL √14 TeV √5.5 TeV √5.5 TeV, qhat = 50 pp = PYTHIA PbPb =PYTHIA (signal) +HIJING (UE) Full reconstruction in ALICE  -jet (signal); jet-jet (  0 –hadron background) 15

 -hadron correlations G. Conesa, Proceedings of Science, PoS (HIGH-pTLHC) 003 All associated charged hadrons with p T > 2 GeV/c PYTHIA pp collisions √s=14 TeV 16 2-Apr-2009Photon physics with ALICE

 -h correlation in pp and AA xEzxEz p out kTkT p Ta X E = -p T h · p T  / |p T  | 2 EPJC (2008) 57: Y. Mao background photons background soft hadrons XEXE D AA = CF AA /CF pp p Tt 17 2-Apr-2009Photon physics with ALICE See poster Y.Mao PYQUEN

Conclusions ALICE is well equipped by photon detectors  PHOS in  EMCAL in  ITS, TPC installed; TRD in ALICE will measure direct photon, neutral meson spectra,  -hadron and  -jet correlations, jet fragmentation functions The first 1-month LHC run with TeV results in  0 spectrum up to p T <25 GeV/c in PHOS (40 with PHOS L0 trigger) and similar pt range in EMCAL and conversion in central tracking system. Isolated direct photons can be measured in the range p t > GeV/c Gamma-hadron correlations can be constructed for isolated photons 18 2-Apr-2009Photon physics with ALICE

Thanks Special thanks to Gustavo Conesa and Ana Marin ALICE collaboration 19 2-Apr-2009Photon physics with ALICE

Backup slides

Tracking robust, redundant tracking from 100 MeV to 100 GeV –modest soleniodal field (0.5 T) => easy pattern recognition – long lever arm => good momentum resolution – small material budget: ~ 10% X 0 vertex -> end of TPC (r = 2.6 m) – very little dependence on dN ch /dy up to 8000 (important for systematics !) 21 Momentum resolution ~ 100 GeV Impact parameter 1.5 GeV

Oct 2008 Split J. Schukraft 22 stable hadrons ( , K, p): – dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (HMPID) leptons (e,  ) – transition radiation (TRD), muon spectrometer photons,  0 – e.m calorimeters (PHOS, EMCAL) decay topology (K 0, K +, K -,  D +,..), secondary vertices (c,b) Particle Identification Alice uses ~ all known techniques! PID from ~ 100 MeV to above 50 GeV

ALICE setup in 2009: section at  =0 23 ITS: |  |<0.9  : 2  TPC: |  |<0.9  : 2  PHOS: |  |<0.125  : 100 o 3/5 installed EMCAL: |  |<0.7  : 110 o 2/5 installed HMPID: |  |<0.6  =57.6 o 7/7 installed TRD: |  |<0.9  : 2   6-7/18 installed TOF: |  |<0.9  : 2   18/18 installed *Holes are made in front of 3 PHOS modules

PHOS status 1 module was installed and commissioned in ALICE in more modules will be installed in 2009 Completed (all 5 modules) in Apr-2009Photon physics with ALICE

EMCAL status TDR passed. 2 supermodules were installed in March (4) supermodules to be installed in Completed (11 supermodules) in Apr-2009Photon physics with ALICE

LHC run scenarios 2-Apr-2009Photon physics with ALICE 26 Nominal LHC scenario for ALICE: pp collision energy: 14 TeV luminosity: 3  cm -2 s -1 First LHC run scenario: pp collisions at 10 TeV (?) luminosity: 5  cm -2 s -1 (?) Data taking time: from days to months If PHOS is triggered by the ALICE minimum bias trigger, then event rate is limited by 200 Hz: L eff = 5  cm -2 s -1 If PHOS is triggered by its standalone L0 trigger on high p T, event rate is defined by p T spectrum only Integrated luminosity, nb -1 Run time T L, cm -2 s -1 5    days month months

Raw  0 spectrum in TeV: N(p T ) and S/B ratio 2-Apr-2009Photon physics with ALICE 27

Photon detectors of ALICE EMCAL PHOS EMCAL PHOS PMD 28 2-Apr-2009Photon physics with ALICE