09/30/'06SPIN2006, T. Horaguchi1 Measurement of the direct photon production in polarized proton-proton collisions at s= 200GeV with PHENIX CNS, University

09/30/'06 SPIN2006, T. Horaguchi 1

Measurement of the direct photon production in polarized proton-

proton collisions at s= 200GeV with PHENIX

CNS, University of Tokyo

Takuma Horaguchi

09/30/’06 for the RSC Meeting


Contents

• Physics Motivation• Experimental Setup

– RHIC– PHENIX

• Direct Photon Production• Cross Section• Isolation Cut Method• Double Spin Asymmetry• Summary


Physics Motivation

• Spin Puzzle from polarized DIS experiment

• Origin of proton spin– Gluon spin– Orbital angular momentum of quark and gluon

• RHIC-Spin– The first polarized proton-proton collider– Interaction of quark-quark, quark-gluon, gluon-gluon– Direct photon production (qg→γg)

gqLG 2

1

2

1ΔΣ～ 20-30%


Relativistic Heavy Ion Collider• The first polarized proton-pr

oton collider• Beam energy:50-250GeV in

proton-proton collision • √s=200GeV (2005)• Beam polarization is 47%(2

005).• Luminosity is 3.8pb-1 (2005)• The beam polarization and l

uminosity will be improved in 2006 Run.– Beam polarization : 60%.– Luminosity : 7.5pb-1

PHENIX

STAR

Brahmspp2pp


PHENIX Detector• ElectroMagnetic Calorimeter

(EMCal)– Measurement of photon & electro

n energy and position– Acceptance

• |η|< 0.35, Δφ=180 degree

– Distance from collision point : 5m– High pT photon trigger

• Beam-Beam Counter (BBC) & Zero Degree Calorimeter (ZDC)– Used for relative luminosity meas

urement


Direct Photon Production

• A test of pQCD• Measurement of t

he polarized gluon distribution function

• Determination of the sign of the gluon distribution function

proton beam

proton beam

or

or

gluon

photon

Quark-Gluon Compton Scattering


Direct photon cross section

To be submitted soon

• Obtained the final plot of the Run2003 data

• Direct Photon signal– Subtraction of backgro

und

• Evaluation of the photons from hadron decay


Direct photon cross section

To be submitted soon

• pQCD calculation describes the our data

• The 4 orders of magnitude on

the cross section is obtained.• Systematic error is as follows


Isolation-cut method

• Suppression of the photon from Jet

• Isolation Cut

– ΣEi : The sum of the energy within R<0.5

– ΣPi : The sum of the energy within R<0.5

EPER R

ii

1.05.0 5.0

Isolation cut

Rphoton

Direct photon

RPhoton in Jet

Photon in Jet

Photons and charged particles

Single photon

22 R


Ratio of the direct photon• Theory curves

– Two fragmentation fuction – Three scale factors

• At high pT region (pT>7GeV/c)– The result shows many of dir

ect photons are isolated.– Theory predictions agree wel

l to the result• For low pT region

– The theory curve is higher. But the effect of underlying event is in the data

• Pi0 photons (from jet) are suppressed as we expected qualitatively.


From Run5 dataX10 luminosity of Run3Cross Section in Run2005

• Pi0 tagging method and isolation cut method

• It is consistent to Run3 result

• Wider pT range


Double longitudinal spin asymmetry

Rdd

Rdd

PPALL

21

1

ALL

qgqLLLL a

xq

xq

xg

xgA

)(

)(

)(

)(

2

2

1

1

• Double longitudinal spin asymmetry (ALL)– Measurement of the polarized gluo

n distribution

– dσ++ : Beam helicity is parallel.

– dσ+- : Beam helicity is unti-parallel

– P1,2 : Beam polarization

– R : Relative-Luminosity(L++/L+-)

• Direct Photon ALL

– Depend on the polarized gluon distribution function of the first degree.

– Determination of the sign of the gluon distribution function

TAKUMA


Effect of the Background• The effect of the backgro

und A_LL

• The assumption is– ALL

bg ～ ALL pi0 photon

• If GRSV-max is assumed– rALL

bg ～ 3% (pT=10GeV/c)

• Working on the measurement of the pi0 photon ALL from data

bgLL

isoLL

sigLL rAArA )1(

Pi0 A_LL (GRSV-max)

sig

bg

N

Nr

bgLL

isoLL

sigLL rAArA )1(

Isolation cutR=0.5, f=0.1minE=0.15GeVPmin=0.2GeVPmax=15GeV


Outlook for the Future

• Run 2005– Luminosity:3.8pb-1– Polarization:47%


• Working on the analysis of direct photon A_LL for the Run2005 data


Summary

• We obtained the final result of direct photon cross section in Run2003. It was submitted to the PRL.

• We obtained the preliminary result of the direct photon cross section with pi0 tagging method and isolation cut method in Run2005.

• We are working on the analysis of the direct photon A_LL for the Run2005 data.



Outlook for the Future



• Working on the analysis of direct photon A_LL for the Run2005 data


Signal fraction in the samplesubtraction method (pi0 partner Emin=0.5GeV)

all hadron

all pi0(tagged + missing partner)

green band shows systematic error size.Common parts are cancelled.(normalization, acceptance)

signal fraction in the sample.(Merged pi0 are already rejectedby the photon shape cut)


(iso)Signal fraction in the sample

pi0 isolated photon (with partner)

isolated pi0 photon　　　 (missing partner)

Isolation cutR=0.5, f=0.1minE=0.15GeVPmin=0.2GeVPmax=15GeV

isolation cut method (pi0 partner Emin=0.5GeV)

The message: By applying a photon cut and an isolation cut, the purity is increased.

Isolated signal fraction in the sample.(Merged pi0 are already rejectedby the photon shape cut)


Analysis methodDirect photon signal= All photon sample – photons from hadron’s decay (mainly pi0)

All photon sample

From EMCal clusters charge track veto Photon shape cut

Estimation of photons from hadron’s decay

Measurement of pi0 production cross sectionEstimate yield of photons based on pi0

Add other hadron’s (eta etc.) contribution

Cocktail method Pi0 tagging method

Tag pi0 photons with its partnerEstimate them bin by bin

Multiplied by the missing ratio to estimate the total

Add other hadron’s (eta etc.) contribution

Conventional method,It isn’t a direct count of the background

Newly appliedIt is a simple method.

Documents

09/30/'06SPIN2006, T. Horaguchi1 Measurement of the direct photon production in polarized proton-proton collisions at s= 200GeV with PHENIX CNS, University