First High pT Physics Prospects

with the

Photon Spectrometer at ALICE

Kenta Shigaki(Hiroshima University )

for the ALICE Collaboration

3rd Joint Meeting of DNP’s of APS and JPSOctober 14, 2009

Waikoloa, Big Island, Hawaii

+ all PHOS and PWG4 (jet/photon) collaborators

Most Relevant Members

2/12Oct.14, 2009

Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

Kenta Shigaki Aya Hiei Hisa Torii

LHC/ALICE/PHOS status and schedule high pT neutral mesons in first year of

ALICE– statistics and pT reach

– technical challenges and resolutions first high pT physics prospects

– 0 in Pb+Pb run in 2010– more work in progress

summary and concluding remarks

Presentation Outline

Oct.14, 2009

3/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

collisions in 2009/12; physics awaited in 2010 ALICE under commissioning

– cosmic data taking ongoing– LHC beam (p and Pb) also seen

3(/5) PHOS modules installed; being cooled down

LHC/ALICE/PHOS Status & Schedule

4/12Oct.14, 2009

Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

September, 2009Pb beam injection oriented

Jet Quenching at LHC

Oct.14, 2009

5/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

higher pT reach + stronger suppression than RHIC– clearer measurement of quark energy loss

e.g. quark flavor/spin dependent suppression?

“day-1” ALICE physics program– enough acceptance with initial 3 PHOS modules

assumptions:– 10 TeV p+p;

5×1028 cm2s1;180 days×10%

– 0 in NLO/CTEQ6M/KKP;particle ratios from PYTHIA

– 3/5 PHOS geom. coverage (~ high pT limit) only

Statistics + pT Reach in 1st p+p Run

Oct.14, 2009

6/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

assumptions:– 3.9 TeV Pb+Pb;

5×1025 cm2s1;30 days×10%;~ 10% central (b < 5 fm)

– NLO pQCD×PYTHIA×N-N binary scaling (1,150 for central Pb+Pb)×suppression (0.1)

– 3/5 PHOS geom. coverage (~ high pT limit) only

Statistics + pT Reach in 1st Pb+Pb Run

Oct.14, 2009

7/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

statistics not really an issue

LHC First Year versus Years at RHIC

8/12Oct.14, 2009

Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

Technical Experiencesand More

multi-photon decay channels challenging kinematic cut optimization to improve S/B careful combinatorial background

subtraction PHOS: highest resolution ever in RHI

experiments

PHENIX 0Au+Au peripheral (cent

60~92 %)3.5 < pT < 4.5 [GeV/c]

pT() [GeV/c]

S/√

B

(sig

nifi

cance

)

before cut optimization

after cut optimization

PHENIX example 0

Oct.14, 2009

9/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

WA9813 GeV Pb+Pb

nucl-ex/0108006

PHENIX200 GeV Au+Aurun 2

ALICE14 TeV p+p

GEANT simulation

single particle simulation– NLO pQCD×PYTHIA×N-N binary

scaling×suppression– mass reconstruction in ALICE analysis framework

acceptance for multi-photon decays two-cluster resolution (merging effect) photon identification

1 M central Pb+Pb HIJING at 3.9 TeV– locally generated at Hiroshima

“hybrid” approach– multiplicity effects in next steps

embedding study by combining the two

Feasibility Evaluation Ingredients

0

Oct.14, 2009

10/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

better S/B, not necessarily S/(S+B), at higher pT

0 in ~ 10% central Pb+Pb at 3.9 TeV; RAA = 0.1 5×1025 cm-2 s-1, 30 days, 10% uptime

feasible up to >> 10 GeV/c more species (, , K0

s) under study

S/B and S/(S+B)

Oct.14, 2009

11/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

0 peak visible in central Pb+Pb HIJING

consistent S/B in NLO/HIJING hybrid evaluation– multiplicity effects to be tested by embedding

Proof of Hybrid Approach Applicability

pT = 3 GeV/c pT = 4 GeV/c pT = 5 GeV/c

pT = 6 GeV/c pT = 7 GeV/c pT = 8 GeV/c

pT = 9 GeV/c pT = 10 GeV/c

Oct.14, 2009

12/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

with ID

new physics prospects at very high pT at LHC ALICE at LHC starting in months (finally!) neutral meson yields in first year very promising

– both for p+p and Pb+Pb runs real issue: S/B ratio, significance S/(S+B)

– especially for multi-body decays (e.g. , K0s) in Pb+Pb

0 feasible even in central Pb+Pb work in progress: , , K0

s

– solid basis on RHIC experiences physics from very beginning of LHC operation!

Summary and Concluding Remarks

Oct.14, 2009

13/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki

discard highly asymmetric pairs to reduce BG– background concentrated at high (

asymmetry)

– acceptance only at low at low pT

– optimized for 0: < 0.7 at pT 3 GeV/c

– two photon separation only at high at very high pT

minimum cut option

more complicated cuts for > 2 body cases– e.g. 0–0 energy asymmetry in K0

s case

Famous Kinematic Cut: Asymmetry

Oct.14, 2009

14/12Hawaii ’09 – First High pT Physics Prospects with PHOS at ALICE – K.Shigaki