# Presentation: 861859

## 0 ALL results from PHENIX

- RHIC Spin Collaboration Meeting
- Torino, Italy, October 8-9, 2004
- A.Bazilevsky,
- Brookhaven National Laboratory
- For PHENIX Collaboration
- To be reported at SPIN2004 by Yoshi Fukao

## ALL

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

- ++ same helicity
- + opposite helicity

## PHENIX Detector

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

- 0 reconstruction and
- high pT photon trigger:
- EMCal: ||<0.35, =
- Granularity  = 0.010.01
- Minimum Bias trigger and Relative Luminosity:
- Beam-Beam Counter (BBC):
- 3.0<||<3.9, =2
- Local Polarimeter
- Zero-Degree Calorimeter (ZDC):
-  ||>6

## Beam Polarization (in PHENIX)

- Absolute polarization scale (_see O.Jinnouchi talk_)
- With RHIC CNI Polarimeter
- Relative uncertainty ~32% (will be decreased soon)
- 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)
- Long. component of the spin direction
- PHENIX Local Polarimeter vs RHIC CNI Polarimeter

## PHENIX Local Polarimeter

- SMD

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

- ZDC

- Vertical   ~ ±/2
- Radial    ~ 0
- Longitudinal  no asymmetry

- distribution

## Spin Long. Component

**Spin Long. Component**

*S**T* is measured with PHENIX Local Polarimeter

- Up-Down asymmetry

- Left-Right asymmetry

- Beam Polarization is pure longitudinal

- 0.06

- -0.06

- -0.06

- 0.06

## Relative Luminosity

- Beam-Beam-Counter (BBC) used as Relative Luminosity Monitor
*** *= 3.0-3.9
- Low background
- High statistics:
- Zero Degree Calorimeter (ZDC) used as a cross check
- Different kinematics & acceptances (|***|>6*)
- Bunch-by-bunch comparison of the number of hits in BBC and ZDC

- The same vertex cut |z|<30cm as in offline analysis is used
- BBC and ZDC have different position resolution  systematics due to variation of the z-vertex distribution
- After correction for the vertex width some residual systematics left (2/NDF1.8)

- LL(BBC) relative ZDC

- 0.004

- -0.06

- -0.002

## Relative Luminosity: Results

- Achieved relative luminosity precision R=5.810-4
- Rel. Lum. contribution for pi0 ALL less than 0.2%
- For average beam polarizations of 40%
- 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)

-   R vs Fill
- <R>=1.035

## Data set from Run4

- Data collected with high pT photon trigger
- Based on EMCal; Threshold ~1.6 GeV/c
- Rejection factor ~80
- Analyzed data sample: 	**21.4M events (~75 nb****-1****)**
**	****	****	****	****sqrt(<P****b****P****y****>)~40%**
- Minimum Bias data
- To obtain “unbiased” 0 cross section at low pT
- For high pT photon trigger efficiency study

## Photon trigger efficiency for 0

**Photon trigger efficiency for ********0**

- Data
- MC

- Pi0 efficiency plateaus for pT>4 GeV/c
- Limited efficiency at      pT<4 GeV/c:
- 	1-2 GeV/c: 10%
- 	2-3 GeV/c: 57%
- 	3-4 GeV/c: 86%
- 	4-5 GeV/c: 90%
- Monte Carlo reproduces Data well

- 0 pT (GeV/c)

## 0 ALL measurements

******0**** A****LL**** measurements**

- Signal + BG
- BG

- Photons in PHENIX EMCal:
- 	||<0.35, =1800
- Done in four pT bins from 1 to 5 GeV/c; collected statistics 1.8M
- Blue area used to estimate ALL of background under 0 peak
- Background contribution (*r*) under 0 peak varies from 31% in 1-2 GeV/c bin to 5% in 4-5 GeV/c bin

## ALL measurements

- Procedure
- Collect *N* and *L *for ++ and + configurations (sum over all crossings) and calculate ALL for each fill
- Average ALL over fills; use 2/NDF to control fit quality; use “bunch shuffling” to check syst. errors

- ++ same helicity
- + opposite helicity

## ALL Calculations

**A****LL**** Calculations**

- ALL averaged over fills for pi0+BG

- 3-4 GeV/c

- 1-2 GeV/c

- 4-5 GeV/c

- 2-3 GeV/c

- 1-2 GeV/c
- ALL= -0.6%±0.6%
- 2/ndf = 11/10
- 2-3 GeV/c
- ALL= 0.5%±0.9%
- 2/ndf = 6/10
- 3-4 GeV/c
- ALL= -1.8%±2.0%
- 2/ndf = 21/10
- 4-5 GeV/c
- ALL= 8.2%±4.6%
- 2/ndf = 12/10

## Bunch shufflingto check for syst. errors

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

- ALL

- 2-3 GeV/c

- All <2/NDF> are ~1
- Consistent with stat. distribution of 2/NDF (red)

- 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

## Other checks

- Different photon PID and 0 reconstruction cut
- Various mass range for 0 and BG
- Results are consistent
- Single asymmetry AL
- Parity violating double asymmetries: (++) vs (--) and (+) vs (+)
- Consistent with 0 as expected

## 0 ALL from pp at 200 GeV

******0**** A****LL**** from pp at 200 GeV**

| pT
GeV/c |  |  | (Run-4) | (Run-3) | (Comb) |
| --- | --- | --- | --- | --- | --- |
| 1-2 | -0.60.6 | -1.90.9 | 0.00.9 | -2.71.3 | -0.9 0.7 |
| 2-3 | 0.50.9 | -0.71.9 | 0.91.0 | -1.31.3 | 0.0 0.8 |
| 3-4 | -1.82.0 | -2.36.5 | -1.82.2 | -1.72.8 | -1.8 1.7 |
| 4-5 | 8.24.6 | -1817 | 9.74.9 | 0.76.2 | 6.2 3.8 |

- Run3 and Run4 results are consistent: 2=5.7, CL=22%

- hep-ex/0404027

## Comparison to theory

**Comparison to theory**

- Note considerable contribution of soft physics in the lowest pT point (50%)
- Comparison of Run3+4 with theory:
- GRSV-std
- 	21-24% (pT>1 GeV/c)
- 	27-29% (pT>2 GeV/c)
- GRSV-max
- 	0.00-6% (pT>1 GeV/c)
- 	0.01-13% (pT>2 GeV/c)

- Run3+4

- Consistent with GRSV-std
- Less consistent with GRSV-max

- B.Jager et al., PRD67, 054005 (2003)

## Summary

- PHENIX obtained results on ALL in 0 production from Run4 with average beam polarization 40%
- Run3 and Run4 results are consistent
- Stat. errors in Run3+4 combined results are 1.6 smaller than Run3
- The same conclusion as from Run3 (paper accepted by PRL): data consistent with GRSV-std and less consistent with GRSV-max
- Soon, expect to have considerably smaller scale uncertainty due to beam polarization

## Backup slides

## RHIC as polarized proton collider

- Run-2 configuration

- partially installed for Run-3

- “Blue” and “yellow” rings

## Loc. Pol. Asymmetry (Transverse RUN)

- This picture is raw asymmetry of blue (left) and yellow beam (right) in transverse run period (just 1 run period).
- In this period, we have 30.8 +- 2.5% and 25.9 +- 1.9% polarization for blue and yellow beam respectively. For estimate effective analyzing power at RUN4, I use
- Effective AN = (raw asymmetry) / polarization @ transverse run
- Though All transverse period, we got Effective AN as,
- 	**Blue : 6.21 +- 0.50%       Yellow : 6.39 +- 0.55%**

## 0 Cross Section in pp

- 9.6% normalization error not shown

- Phys. Rev. Lett. 91,
- 241803 (2003)

- NLO pQCD consistent with data within theoretical uncertainties
- PDF: CTEQ5M
- Fragmentation functions:
- Kniehl-Kramer-Potter (KKP)
- Kretzer
- Spectrum constrains D(gluon) fragmentation function
- Important confirmation of theoretical foundation for spin program
- Data from Run4 reproduce Run2 results

- Run2

## Pi0 reconstruction for ALL

**Pi0 reconstruction for A****LL**

- 2-3 GeV/c
- Bckgr=13%

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

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

- 1-2 GeV/c
- Bckgr=31%

- Results obtained for four pt bins from 1 to 5 GeV/c
- Pi0 peak width varies from 12 to 9 MeV/c2 from lowest to highest pt bins
- Background contribution under pi0 peak for 25 MeV/c2 mass cut varies from 31% to 5% from lowest to highest pt bins

## Alpha

- MC vs Data

- Data

## G: other experiments

- GRSV-max

- GRSV-std

- HERMES

- SMC

- PHENIX x-range

- Theory curves from W.Vogelsang
- HERMES: high pt hadron pairs (PRL84, 2584, 2000)
- Consistent with both GRSV-max and GRSV-std
- SMC: high pt hadron pairs (PRD70, 012002, 2004)
- Consistent with GRSV-std
- PHENIX: 0 ALL
- Consistent with GRSV-std

- So far all results are consistent with GRSV-std