# Presentation: 614626

## First 0 ALL results from PHENIX

- Division of Nuclear Physics, APS
- Tucson, AZ, November 1, 2003
- A.Bazilevsky,
- Brookhaven National Laboratory
- For PHENIX Collaboration

## ALL

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

- ++ same helicity
- + opposite helicity

- “Yellow” beam   “Blue” beam

## RHIC as polarized proton collider

- Run-2 configuration

- partially installed for Run-3

- “Blue” and “yellow” rings

## PHENIX Detector

_**Philosophy:**_
-  **High rate capability & granularity**
** ****Good mass resolution and particle ID**
** ****Sacrifice acceptance**

- 0 reconstruction and
- high pT photon trigger:
- EMCal: ||<0.38, =
- Granularity  = 0.010.01
- Minimum Bias trigger and Relative Luminosity:
- Beam-Beam Counter (BBC):
- 3.0<||<3.9, =2

## Beam Polarization

- Spin direction confirmation
- With RHIC Spin Rotators and PHENIX Local Polarimeter (forward neutron transverse asymmetry AN, see talk by A.Dashpande)
- _Confirmed_
- Longitudinal component of the spin direction
- PHENIX Local Polarimeter
- _Long. Spin Component was_ SL/S=0.99 and 0.97 _(for blue and yellow beams)_
- Absolute polarization scale
- With RHIC CNI polarimeter
- _Estimated to be  ~30%_
- This error does not change the significance of non-zero ALL, because it scales both value and error in the same way (but it does change the comparison to theory)

## Relative Luminosity: Results

- Achieved relative luminosity precision R=2.510-4
- Pessimistic estimation limited by ZDC statistics (30 times less than BBC statistics used in Rel. Lum. measurements)
- ALL of BBC relative to ZDC consistent with 0 (<0.2%)
- Strong indication that both ALLs are zero (very different kinematical regions, different physics signals)

- Beam Beam Counter (BBC) used
- Zero Degree Calorimeter (ZDC) as a cross check

- BBC

- ZDC

## 0 Data Set

******0 Data Set**

- s=200 GeV 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(<P****b****P****y****>)~26%**
- Minimum Bias data
- To obtain “unbiased” 0 cross section at low pT
- For high pT photon trigger efficiency study

- Pi0 efficiency plateaus for pT>4 GeV/c
- Limited efficiency at pT<4 GeV/c:
- 	1-2 GeV/c: 6%
- 	2-3 GeV/c: 60%
- 	3-4 GeV/c: 90%
- 	4-5 GeV/c: 95%
- Monte Carlo reproduces Data well

- Trigger efficiency for pi0s

## 0 Cross section

******0 Cross section**

- Results consistent with pQCD calculation
- Favors a larger gluon-to-pion FF (KKP)
- _Important confirmation of __theoretical foundations for spin program_
- Run3 results reproduce Run2 results
- _Confirm the Run-3 data reliability and consistency_
- Run3 data reaches even higher pTs; results will be finalized soon

- Run-2 results

- 9.6% normalization error not shown

**accepted to PRL,**
**hep-ex/0304038**

## Pi0 reconstruction for ALL

- 2-3 GeV/c
- Bckgr=17%

- 3-4 GeV/c
- Bckgr=7%

- 4-5 GeV/c
- Bckgr=5%

- 1-2 GeV/c
- Bckgr=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

## Pi0 counting for ALL

**N********0****: **
- 25 MeV/c2 around ***0* peak (and also 15 and 35 MeV/c2 for cross checks)
**N****bck1****: **
- Two 50 MeV/c2 wide areas adjacent to ***0* peak
**N****bck2****: **
- 250 MeV/c2 wide area between  ***0* and ** peaks

| pt
GeV/c | N0
15 MeV/c2 | N0
25 MeV/c2 | N0
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 |

- N0 and Nbck accumulated statistics

## ALL measurements

- Procedure
- Collect *N* and *L *for ++ and + configurations (sum over all crossings) and calculate ALL for each fill (a few hours of running, constant beam polarization)
**(*A**LL*) is based only on *N****0* stat. error
- Average ALL over fills; use 2/NDF to control fit quality; use “bunch shuffling” to check syst. errors

- ++ same helicity
- + opposite helicity

## ALL Calculations

- ALL averaged over fills

- 3-4 GeV/c

- 1-2 GeV/c

- 4-5 GeV/c

- 2-3 GeV/c

- 1-2 GeV/c
- ALL= -2.8%±1.2%
- 2/ndf = 64/48
- 2-3 GeV/c
- ALL= -2.2%±1.5%
- 2/ndf = 34/48
- 3-4 GeV/c
- ALL= -0.2%±3.3%
- 2/ndf = 49/48
- 4-5 GeV/c
- ALL= -2.3%±7.4%
- 2/ndf = 39/48

- for N0 in 25 MeV/c2 window

## Bunch shufflingto check for syst. errors

**Bunch shuffling**to check for syst. errors

- ALL

- 2-3 GeV/c

- All <2/NDF> are ~1

- Bunch shuffling = Randomly assigns helicity for each crossing

- 2/NDF

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

- Widths are consistent with obtained errors (ALL)

- 2-3 GeV/c

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

## Cross Checks

- Different mass window cut for N0
- 15, 25 and 35 MeV/c2 cuts
- All results are consitent
- Different photon PID
- All results are consitent
- Parity violating ALL’s
- ++ vs  and + vs +
- All are consistent with 0 within 1.5 (as expected)
- Parity violating single spin asymmetries AL
- All are consistent with 0 within 1.5 (as expected)

## 0 ALL from pp at 200 GeV

| pT
GeV/c | 
(rbck) |  | 
(Background subtracted) |
| --- | --- | --- | --- |
| 1-2 | -0.0280.012 (45%) | -0.0060.014 | -0.0460.025 |
| 2-3 | -0.0220.015 (17%) | -0.0350.027 | -0.0190.019 |
| 3-4 | -0.0020.033 (7%) | 0.0940.092 | -0.0090.036 |
| 4-5 | -0.0230.074 (5%) | 0.380.24 | -0.0450.079 |

- 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)
- Relative luminosity contribution to 0 ALL error is <0.2%
- pT smearing correction is not included

## 0 ALL: PHENIX vs theory

- B.Jger e al., PRD67, 054005 (2003)

- 0 ALL sensitive to gluon polarization in the proton

- gg

- qq

- gq

- Fraction of pi0s produced

## Summary

- First 0 ALL results from long. polarized pp collisions at s=200 GeV with average beam polarizations of 26% presented
- Results presented in four pT bins in the range 1-5 GeV/c
- ALL sensitivity in the lowest pT bin (1-2 GeV/c) is 2.5% (1.2% without background subtracted)