photon physics in alice y.kharlov d.peressounko ihep rrc “kurchatov institute” for the alice...

Photon physics in ALICE

Y.Kharlov D.Peressounko IHEP RRC “Kurchatov Institute”

for the ALICE collaboration

and

Photon physics

Direct photon – jet correlations

g

, , ,..p h w

Neutral meson spectra, RAA, v2…Chemical composition: p0,h, w

Direct photon spectra, RAA, v2… Inclusive, Isolated, Thermal g inclusive

g isolated g thermal

22-Apr-2009 Photon physics with ALICE

ALICE setup in 2009: section at h=0

PHOS: |h|<0.125 Df: 100o

3/5 installed

EMCAL: |h|<0.7 Df: 110o

2/5 installed

PHOS:high-granularity photon spectrometer (20 X0)• acceptance: =100, ||<0.12• 18k PbWO4 crystals 2.22.218. cm3

• 5 modules 6456 crystals each• energy range: 0.1-100 GeV

EMCALlarge aperture Pb-Sc electromagnetic calorimeter (20 X0)• acceptance: =107, ||<0.7• 13k towers 66 cm2.• 11 supermodules 2448 towers each• energy range: 0.1-250 GeVCERN-ALICE-TDR-014


Photon detectors resolutions

PHOS EMCAL

sE/E (%)

sx (mm)

Rip (cm)

222

12.13.13.1

EE

22

44.026.3

E

460

222

8.47.13.11

EE

sp (MeV)pt=1-2 GeV

5.5 MeV

428

E

3.55.1

ITS+TPC+TRD

< 160

16 MeV

~1

2


3.3 MeV0.8<pt<2 GeV

p0 measurementwell separated clusters invariant mass analysis

< 10 GeV/c in EMCal< 30-50 GeV/c in PHOS

merged clusters not spherical shower shape analysis

10 - 30 GeV/c in EMCal 50 - 100 GeV/c in PHOS

5/36p T (GeV/c)

g identified as g

g identified as p0

p+p

p0 as p0

p0 as g


PHOS

EMCAL

p0 and h measurementPHOS


See poster K. Aamodt et al., for p0/h via converted photons

Conversion

Conversion

PHOS,p0

PHOS, h

Conversion,p0

mgg (GeV)

0 in central Pb-Pb collisions at 5.5 ATeV


Only event mixing technique reveals 0 peak at low pT

7

Acceptance for p0, h, w measurement

Acceptance is normalized per |y|<0.5, =2

)2 0.5,yin edN(gen'

)PHOSin sprod'decay all(

N

A


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=51027 cm-2s-1. PHOS trigger:

Can select events with high energy deposited in 22 or 44 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 pt and small opening angle. Under investigation


PHOS L0 trigger rate in pp @ 10 TeVL0 definition: 2x2 (4x4) cells energy sum > threshold somewhere in PHOS


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

Photon physics with ALICE

0, , h and w cross sections in pp

2-Apr-2009

NLO pQCD + CTEQ5M + KPP.Bands indicate possible uncertainties in QCD scale[P. Aurenche, et al., Eur. Phys. J. C 13,347 (2000)]

pp0X ppX

LO pQCD: Pythia 6

ppX ppX

11

Expected yields in first ALICE run


Integrated luminosity, nb-1

Run timeT

L, cm-2s-1

51027 51028 31030

3 days 1.3 13 780

1 month 13 130 7800

3 months 39 390 22000

Accesible range in Pb+Pb colisions

Binary scaled p+p cross section @ 5.5 TeV (INCNLO)

Nbinary calculated using [F.Arleo et al., hep-ph/0311131]

centrality class 0-10%

LPbPb=5·1026 [cm-2s-1]

T = 1·106 [s]

∫L = 0.5 [nb-1]

RAA=0.2RAA=1

Pb+Pbgdir+X Pb+Pbp0+X

2-Apr-2009 Photon physics with ALICE13

Isolated direct photons

Y. Mao et al., Eur.Phys.J.C57:613-619,2008

IC: R =0.3, S(pT)=2 GeV/c IC: R =0.2, pT>2 GeV/c

G. Conesa et al., ALICE-INT-2005-014, NIM A 580 (2007) 1446


See posters Y.Mao and R. Ichou

g fragmented

gisolated

2 PHOS modules5 PHOS modules

Isolated Spectra in EMCALpp @ √14 TeV PbPb @ √5.5 TeV PbPb @ √5.5 TeV, qhat = 50

pp = PYTHIAPbPb =PYTHIA (signal) +HIJING (UE) Full reconstruction in ALICE

g-jet (signal); jet-jet (p0 –hadron background)

15

g-hadron correlations

G. Conesa, Proceedings of Science, PoS (HIGH-pTLHC) 003

All associated charged hadrons with pT > 2 GeV/c

PYTHIA pp collisions √s=14 TeV


g-h correlation in pp and AA

xEzpout kT

pTa

XE= -pTh · pT / |

pT|2

EPJC (2008) 57: Y. Mao

background photonsbackground soft hadrons

XE

DAA = CFAA/CFpp

pTt


See poster Y.Mao

PYQUEN

Conclusions ALICE is well equipped by photon detectors

PHOS in 2008-2011 EMCAL in 2009-2011 ITS, TPC installed; TRD in 2008-2010

ALICE will measure direct photon, neutral meson spectra, -hadron and -jet correlations, jet fragmentation functions

The first 1-month LHC run with pp@10 TeV results in 0 spectrum up to pT<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 pt>10 -15 GeV/c

Gamma-hadron correlations can be constructed for isolated photons


Thanks

Special thanks to Gustavo Conesa and Ana Marin

ALICE collaboration


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% X0 vertex -> end of TPC (r = 2.6 m)

– very little dependence on dNch/dy up to 8000 (important for systematics !)

21

Momentum resolution ~ 5% @ 100 GeV

Impact parameter < 50 mm for pt > 1.5 GeV

Oct 2008 Split J. Schukraft22

• stable hadrons (p, K, p):

– dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (HMPID)

• leptons (e, m) – transition radiation (TRD), muon spectrometer

• photons, ,h p0 – e.m calorimeters (PHOS, EMCAL)

• decay topology (K0, K+, K-, , L 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 h=0

23

ITS: |h|<0.9 Df: 2p

TPC: |h|<0.9 Df: 2p

PHOS: |h|<0.125 Df: 100o

3/5 installed

EMCAL: |h|<0.7 Df: 110o

2/5 installed

HMPID: |h|<0.6 Df=57.6o

7/7 installed

TRD: |h|<0.9 f: 2p*

6-7/18 installed

TOF: |h|<0.9 f: 2p*

18/18 installed*Holes are made in front of 3 PHOS modules

PHOS status1 module was installed and commissioned in ALICE in 2008

2 more modules will be installed in 2009

Completed (all 5 modules) in 2010-2011


EMCAL statusTDR passed.

2 supermodules were installed in March 2009.

3 (4) supermodules to be installed in 2009.

Completed (11 supermodules) in 2011.


LHC run scenarios


Nominal LHC scenario for ALICE:• pp collision energy: 14 TeV• luminosity: 31030 cm-2s-1

First LHC run scenario: • pp collisions at 10 TeV (?)• luminosity: 51028 cm-2s-1 (?)• Data taking time: from days to monthsIf PHOS is triggered by the ALICE minimum bias trigger, then event rate

is limited by 200 Hz: Leff = 51027 cm-2s-1 If PHOS is triggered by its standalone L0 trigger on high pT, event rate is

defined by pT spectrum onlyIntegrated luminosity, nb-1

Run timeT

L, cm-2s-1

51027 51028 31030

3 days 1.3 13 780

1 month 13 130 7800

3 months 39 390 22000

Raw 0 spectrum in pp@10 TeV: N(pT) and S/B ratio


Photon detectors of ALICE

EMCAL

PHOS

EMCAL

PHOS

PM

D


photon physics in alice y.kharlov d.peressounko ihep rrc “kurchatov institute” for the alice...

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