0 ALL analysis in PHENIX

Outline• Relative luminosity

- estimation of systematic error- ALL in ZDC/BBC

• LocalPol• Counting number of 0’s• Result

K. Tanida (RIKEN/RBRC) RSC meeting 11/18/03

ALL

(P) Polarization (L) Relative Luminosity(N) Number of pi0s

LNLN

LNLN

PPA

YBLL ||

1

++ same helicity+ opposite helicity

How to get relative luminosity?• Principle: R=N++/N+- -- from any counter (trigger)

• BBCLL1 trigger - coincidence of two Beam-Beam Counters- small background (~ 10-4)- high statistics (detects ~ 1/2 of all collisions)- ALL

BBC: expected to be small, need confirmation

BBC-NorthBBC-South

144.35 cm

⊿η = 3.0 ~ 3.9

⊿φ = 2π

Method of accuracy estimation• Cross-check by ZDCLL1 trigger

(Zero Degree Calorimeter) - low background (~ 10-4) - statistics: moderate (~ 3% of BBCLL1)

• N(ZDCLL1)/N(BBCLL1) must be constant • Crossing-by-crossing, fill-by-fill ratio calculation

Blue: Yellow: We have all spin combinations in each fill

• GL1p scaler counts both BBCLL1 and ZDCLL1for each crossing

• Required accuracy: constant to 10-3 level for each fill.

Significant deviation from constant. Why?

crossing-by-crossing ratio

2/dof = 346/45

BBC Z vertex (cm)

coun

ts

run 87693

crossing 74

crossing 90

Possible explanation – detector acceptance

• Extreme cases - Flat acceptance N: area - Narrow acceptance N: height

• ZDCLL1: Z-vertex resolution ~ 20 cm (wider acceptance)• BBCLL1: ~ 5 cm (narrower) (both have Z-vertex cut at ±30 cm)

Correlation with Z-vertex width

We understand the reason now correction

[cm]

2/dof = 55.1/45

Z-vertex width [cm]

After correction

Relative luminosity accuracy < 0.09% (stat. limited)

2/dof = 54.8/45

Alternative correction• Actual vertex width is not yet available in most runs

(will come soon)• Alternative width estimation

use ZDCout/ZDCin ratio - ZDCin: ZDCLL1 counts with Z-vertex cut of 30 cm - ZDCout: ZDCLL1 outside of ZDCin. (both are counted crossing-by-crossing) wider vertex distribution larger ratio

Actual accuracy estimation-- Bunch fitting

• Crossing-by-crossing analysis, taking care of possibleeffect of ALL in BBC and ZDC

• For i-th crossing, calculate r(i) = NZDCLL1(i)/NBBCLL1(i)corrected for vertex width

• Fit r(i) by r(i) = C[1+ALL

BBC/ZDCPB(i)PY(i)]fit parameter: C, ALL

BBC/ZDC

• You will get C, ALLBBC/ZDC, their errors, and 2

- accuracy is obtained as ALLBBC/ZDC

(x PBPY)- 2 gives a good check for systematic errors.

2 vs stat. error – before correction

statistical error (LL, stat)

2 /do

f

w/o vertex width correction

2/dof = 1+(syst/stat)2

syst = 0.002

correlating syst ~ 0.002

1 point/fill

statistical error (LL, stat)

2 /do

f 2/dof = 1+(syst/stat)2

syst = 0.001

correlationis weak, butstill some systematic effect remains

bad fill

2 vs stat. error – after correction

fill 3735

Result & BBC/ZDC ALL

• Systematic error seen 2 correction required• If 2/dof is larger than 1, then enlarge statistical error

by sqrt(2/dof) – conservative correction

• Averaged result: ALLBBC/ZDC = (1.8±1.8) x 10-3

(without vertex width correction, ALL is ~2 larger)

• This corresponds to relative luminosity accuracy of R = 2.5 x 10-4

Achieved the goal

• ZDC-BBC ALL is 0 consistent we can use both for reference of ALL = 0

• We reached ALLBBC/ZDC=1.8 x 10-3

- this is dominated by statistics of ZDC, so it’s rather conservative estimation- actual relative luminosity is given by BBC

• In 0 analysis, vertex position dependence of acceptance is the same as BBCLL1 because- BBC hits are required in the analysis- PHENIX central arm acceptance is almost flat for 0 within the region we are using (±30 cm)

Some notes

Remaining tasks for rel. luminosity• Apply offline Z-vertex cut

- better resolution: ~ 5 cm ~ 2 cm (effect is found to be small)

• Full accuracy estimation using real vertex distribution. - correction for other than vertex width?

• Study effect of multiple collisions - negligible in Run3, significant for higher luminosity.

• Z-vertex dependence of acceptance (efficiency)for BBCLL1, 0 and other reaction channels. - reaction channel specific relative luminosity. - BBCLL1 itself is almost perfect for 0 case, but may be not for other channels.

Vertex distribution (BBCLL1)

offline Zvertex [cm]

coun

ts

reject

accept

reject

changes rel. lumi. by < 0.04% per fill (negligible)

PHENIX Local Polarimeter

SMD

Forward neutron transverse asymmetry (AN) measurements SMD (position) + ZDC (energy)

ZDC

Vertical ~ ±/2Radial ~ 0Longitudinal no asymmetry

distribution

Spin Longitudinal Component

ST is measured with PHENIX Local Polarimeter

1.03.19.02.34.97)(

yellowSL

Up-Down asymmetryLeft-Right asymmetry

222 ,1 radialTverticalTTTL SSSSS

0.05.09.04.13.99)(

blueSL

0 counting

Data collected with high pT photon trigger

Based on EMCal; Threshold ~1.4 GeV/c

Rejection factor ~110

Analyzed data sample: 42.7M events (~0.215 pb-1)

sqrt(<PbPy>)~26%

Minimum Bias data To obtain “unbiased” 0 cross section at low pT

For high pT photon trigger efficiency study

0 reconstruction for ALL

2-3 GeV/c Bckgr=17%

3-4 GeV/c Bckgr=7%

4-5 GeV/c Bckgr=5%

1-2 GeV/cBckgr=45%

Results obtained for four pt bins from 1 to 5 GeV/c

Pi0 peak width varies from 12 to 9.5 MeV/c2 from lowest to highest pt bins

Background contribution under pi0 peak for 25 MeV/c2 mass cut varies from 45% to 5% from lowest to highest pt bins

0 counting for ALL

N0: 25 MeV/c2 around 0 peak (and also 15 and 35 MeV/c2 for cross checks)

Nbck1: Two 50 MeV/c2 wide areas adjacent to 0 peak

Nbck2: 250 MeV/c2 wide area between 0 and peaks

ptGeV/c

N0

15 MeV/c2

N0

25 MeV/c2

N0

35 MeV/c2

Nbck1 Nbck2

1-2 1278k 1777k 2129k 1470k 3478k

2-3 874k 1059k 1146k 335k 989k

3-4 176k 201k 208k 27k 83k

4-5 34k 38k 39k 3.9k 12k

N0 and Nbck accumulated statistics

N0 statistical error estimation

Nbck2N0

ptGeV/c

N0

15 MeV/c2

N0

25 MeV/c2

N0

35 MeV/c2

Nbck1 Nbck2

1-2 1.134 1.220 1.302 1.360 1.708

2-3 1.047 1.081 1.114 1.178 1.406

3-4 1.015 1.026 1.037 1.101 1.222

4-5 1.008 1.015 1.021 1.059 1.162

In multi-0 events:

Comparison to naïve approach:

k

k

N

Nkk evenhance

2

0

22)(

dk/dNevdk/dNev

Fluctuation enhancement (squared) due to multi-particle events

evNevkN NkkNev

22222

0

02

0 NN

ALL measurements

Procedure1. Collect N and L for ++ and + configurations (sum over all

crossings) and calculate ALL for each fill2. Average ALL over fills; use 2/NDF to control fit quality; use

“bunch shuffling” to check syst. errors

NNPP

ALNLN

LNLN

PPA

YBLL

YBLL

1

||

1,

||

1

++ same helicity+ opposite helicity

ALL CalculationsALL averaged over fills

3-4 GeV/c

1-2 GeV/c

4-5 GeV/c

2-3 GeV/c 1-2 GeV/cALL= -2.8%±1.2%2/ndf = 64/48

2-3 GeV/cALL= -2.2%±1.5%2/ndf = 34/48

3-4 GeV/cALL= -0.2%±3.3%2/ndf = 49/48

4-5 GeV/cALL= -2.3%±7.4%2/ndf = 39/48

AL check for “yellow” beam

ptGeV/c

15 MeV/c2 25 MeV/c2 35 MeV/c2

1-2 0.0010.004 0.0000.003 0.0000.003 0.0020.004 0.0000.003

2-3 0.0010.004 0.0000.004 0.0000.004 0.0020.007 0.0020.005

3-4 0.0070.009 0.0110.009 0.0080.009 -0.0330.025

-0.0100.015

4-5 -0.0010.021

0.0040.020 0.0080.020 0.0200.064 0.0500.039

All are zeros within 1.5

LNLN

LNLN

PAL ||

1

bckLA 0 bck

LA 0 1bckLA 2bck

LAbckLA 0

AL check for “blue” beam

ptGeV/c

15 MeV/c2 25 MeV/c2 35 MeV/c2

1-2 -0.0010.004

0.0010.003 0.0000.003 -0.0020.004

-0.0000.003

2-3 0.0010.004 0.0000.004 0.0020.004 0.0090.007 0.0000.005

3-4 0.0040.009 0.0060.009 0.0060.008 -0.0040.024

-0.0360.015

4-5 -0.0240.021

-0.0160.020

-0.0160.019

-0.0110.062

0.0130.038

All are zeros within 1.5, except

LNLN

LNLN

PAL ||

1

bckLA 0 bck

LA 0 1bckLA 2bck

LAbckLA 0

0 ALL result

pT

GeV/c(rbck)

(Background subtracted)

1-2 -0.0280.012 (45%)

-0.0060.014 -0.0460.025

2-3 -0.0220.015 (17%)

-0.0350.027 -0.0190.019

3-4 -0.0020.033 (7%)

0.0940.092 -0.0090.036

4-5 -0.0230.074 (5%)

0.380.24 -0.0450.079

Polarization scaling error P ~30%: is not included Enters the ALL quadratically

Analyzing power AN(100 GeV) ~ AN(22GeV) is assumed

P~30%: combined stat. and syst. error for AN(22GeV) (AGS E950)

pT smearing correction is not included

bckLLA 0 bck

LLA 0LLA

Summary• Relative luminosity – systematics is mostly due to crossing by crossing variation of Z-vertex width and acceptance difference correction applied• Relative luminosity accuracy ALL = 1.8 x 10-3 achieved• Relative luminosity is reaction channel dependent - For 0 analysis, BBCLL1 is good enough.• Preliminary result for 0 ALL obtained• Various null tests – all OK statistical and systematic errors are well studied.