Gluon Polarization Errors at PHENIX

Spin DiscussionMar. 24 & Apr. 14, 1998

Yuji Goto, RIKEN

gluon polarization measurement at PHENIX

• prompt photon measurement

• inclusive 0 measurement• heavy quark measurement

– J/• e+e-, +-

– open charm• single lepton• e coincidence

prompt photon ALL (from N.Saito)

)(ˆ1

1 qqgaFg

GGA LLp

p

LL

uncertainties

• x-independent uncertainties– beam polarization– luminosity

• x-dependent uncertainties– background subtraction– higher order correction– quark polarization– event selection

• uncertainties in x estimation– momentum scale– pT vs x

x-independent uncertainties

• beam polarization– absolute value 10%

• pion polarimeter - 10% by comparing E704• pC CNI

– absolute value 5%• pp with pol. hydrogen jet

– relative value Goal:<1%– polarimeter at PHENIX ? - longitudinal

x-independent uncertainties (contd.)

• luminosity– absolute value 10%

• machine luminosity from accelerator parameters• BBC + calculation

– absolute value 5%• Roman pot measurement at PP2PP

– relative value 10-4

• BBC - 100K counts/sec (crossing by crossing) - saturated• ZDC - 1K counts/sec (crossing by crossing)

x-dependent uncertainties• statistics for prompt photon

– 320pb-1 for sqrt(s)=200GeV– 800pb-1 for sqrt(s)=500GeV

G/G 5% - 30%statistical errorfor sqrt(s)=200GeV,pT=10 - 30 GeV/c,5GeV/c pT bin

x-dependent uncertainties (contd.)• background subtraction (for prompt photon)

– reconstruction of 0 and - 2-photon decay• background - escape photon, 2-photon merge, other decays• correction - asymmetry measurements of 0 and

– hadron & bremsstrahlung• full detector simulation necessary

– How much asymmetry remains after subtracting backgrounds considering their asymmetries ?

• event selection <1%?– trigger efficiency– acceptance– efficiency correction

• isolation cut

x-dependent uncertainties (contd.)

• background for prompt photon

b.g. <20%for sqrt(s)=200GeV,pT=10 - 30 GeV/c,5GeV/c pT bin

normalized by(2 detected)

20

20

normalized byafter isolation cut

x-dependent uncertainties (contd.)• background for prompt photon

charged hadron- E/p matching by EMCal and tracking

neutral hadron- shower shape anslysis by EMCal

Estimation must be donewith current algorithm

Algorithm must bedeveloped

x-dependent uncertainties (contd.)• theoretical uncertainties

– annihilation process (for prompt photon)

– higher order correction– fragmentation function– color singlet - octet model (for J/)– Q2

(from N.Saito)

fraction of <20%& experimental determination of is necessary

gqq

q,q

x-dependent uncertainties (contd.)

• higher order correction• L.E.Gordon and W.Vogelsang, PRD49 (1994) 170

LONLO

x-dependent uncertainties (contd.)

• quark polarization (for prompt photon)– DIS experimental error & theoretical calculation– E143 - g1

p/F1p error 20%-8% for x=0.04-0.25 in 15bins

– asymmetry measurement of W/Z(/DY)

hep-ph/9802357SMC - squaresE143 - solid circles [Q2>1(GeV/c)2] diamonds [Q2<1(GeV/c)2]

uncertainty in x estimation (for prompt photon)• momentum scale

– momentum resolution, binning effect– systematic uncertainty - non-linearity of EMCal

• PMT, FEE, shower leakage

– 1% non-linearity - 6% cross section error at sqrt(s)=500GeV, pT=20GeV/c

• pT vs x– correlation

– uncertainty due to kT

• binning effect

uncertainty >50%(* slope of asymmetry)

s

p2x T

uncertainty in x estimation (for prompt photon)• pT vs x - uncertainty by kT

– In PYTHIA initial radiation,

kT2=(1-z)Q2

z: splitting fraction of initial radiation

kT2=0

global analysis

ee 2 0 0 G eVee 5 00 G eV 2 0 0 G eV

5 0 0 G eV

J/ p rod uc tio n(from N .H ay ash i)

p ro m p t p h o to n p ro d u c tio n

and0 production,open charm,DIS,semi-inclusivemeasurements,...

(from N.Saito)

summaryx-independent uncertainties

beam polarization absolute 10% -> 5%relative Goal: <1%

luminosity absolute 10% -> 5%relative 10**-4 ?

x-dependent uncertaintiesstatistics (for prompt photon) 5% - 30% (for sqrt(s)=200GeV,

pT 10 - 30GeV/c, 5GeV/c bin)background subtraction (for prompt photon) <20% background (for sqrt(s)=200GeV,

(* uncertainty of pi0 asym.) pT 10 - 30GeV/c, 5GeV/c bin)hadron & bremsstrahlung ?event selection <1%theoretical annihilation process <20% background

(* uncertainty of quark pol.)higher order correction, etc. ?quark polarization 20% - 8% (for x=0.04 - 0.25 in 15 bins)

uncertainties in x estimationmomentum scale Goal: 1%pT vs x >50% * slope of asymmetrykT ?

global analysis ?