# Presentation: 547535

## Phenix Local Polarimeter

- Abhay Deshpande
- For
**Manabu Togawa & Yoshinori Fukao**** **
- IP12 Local Polarimeter Collaboration

- Slides based on recent talk by Naohito Saito at BNL

- UPDATE

- RHIC Spin Meeting: AD

- 7/29/02

## Summary

- Reminder of the experimental setup
- East Side Story: Lead Tungstate Electromagnetic Calorimeter
-      * Particle ID (g vs. n) purities and efficiencies
-         -- Pythia & GEANT dependence
-      * Detector Asymmetries
-         -- Independent of Physics asymmetries
-      * Analyzing power extraction
-      * Remaining mysteries...??
- West Side Story: Zero Degree Calorimeter
-      * Calibrated using cosmics
-      * Asymmetry observed for neutrons
- Comparison of EMCal & ZDC ... in progress.

- RHIC Spin Meeting: AD

- 7/29/02

## Where abouts.... and lay out...

- polarimeter

- Iron
- (magnet)

- Charged veto
- (plastic scinti.)

- Neutron PID
- (plastic scinti.)

- hodoscopes

- EAST

- WEST

- IP12

- RHIC Spin Meeting: AD

- 7/29/02

## Calorimeter Performance

- Energy & Position resolution measured at test beam measurement
- at SLAC FFTB August 2001: (n X 10 GeV electron beam); n=1,2...

- Position resolution: ~1.1 mm
- Energy resolution:

- RHIC Spin Meeting: AD

- 7/29/02

## Invariant Mass Distribution:  M

- (MeV/c**2)

- Two Photon Inv. Mass

-  signal clearly
-    visible
-  Used to refine tower
-    by tower calibration

- Combinatorial
- background

- RHIC Spin Meeting: AD

- 7/29/02

## Particle Identification

- Neutron 1 & 2

- Preshower

- ChargeVeto

- DX Magnet
- Steel Plate

- PbWO4
- Calorimeter

- Blue beam

- EAST

- RHIC Spin Meeting: AD

- 7/29/02

## Efficiency & Purity: MC Study

**Efficiency******

**Efficiency********n******

**Purity******

**Purity********n******

- EAST

- RHIC Spin Meeting: AD

- 7/29/02

## Particle ID in Data vs. Simulation

- Ratio < 100%
- Remaining
- Contamination

-  Data: Need pure photon sample
-    Photon enriched sample with pi0
-        mass cut.

-  Contamination at low energies
-     Pythia-6 employed
-         n/  1:1
-         10% n contamination in 
-         25% g contamination in n
-     Depends also on hadron shower
-         development
-          Geisha and Fluka available
-              Fluka gives a better
-              agremennt with data.

- EAST

- RHIC Spin Meeting: AD

- 7/29/02

## Contamination in  and 0 samples...

- Significant Difference in Combinatorial Background
- Slightly higher number of clusters in exp. Data
- Lower Energy shows worse 2 distribution in exp. Data
-  Contamination should be studies as a function of Energy

**Exp.**

**Sim.**

**15-20 GeV**

**30-40 GeV**

**50-60 GeV**

- EAST

- RHIC Spin Meeting: AD

- 7/29/02

## Compare Data vs. MC

- PYTHIA: Photon Source
- PYTHIA says 95% of photons originate in 0
- Compared Following Ratio:9.6%(exp) vs 11.7%(sim)
- GEANT: Hadron Shower Algorithm
- GHEISHA vs FLUKA
- Compared identified /*n*
- 64:36 (exp)
- 78:22 (GHEISHA) vs 67:33 (FLUKA)
- PYTHIA dependence is not eliminated yet i.e. no other
-     generator has been tried...

- RHIC Spin Meeting: AD

- 7/29/02

## Detector & Physics Asymmetries

- Detector Asymmetry is very sensitive to Beam Position
- Extract Slope and Intercept
-     from Detector Asymmetry as
-     a function of Energy
- Minimize Both Slope and
-      Intercept  Around +5mm

**-10mm**

**10mm**

**Slope******

**Intercept******

**Slope**********

**Intercept**********

- RHIC Spin Meeting: AD

- 7/29/02

## Detector & Physics Asymmetries for Neutrons

- All Asymmetries calculated using the SQRT formula

- 10mm change in center imparts a 20% variation in DA;
- No effect on Physics Asymmetries

- Detector Asymmetry

- Physics Asymmetry

- EAST

- RHIC Spin Meeting: AD

- 7/29/02

## Neutron Asymmetry: Correlation with polarization

-  Clear correlation observed
-   Neutron deposited energy > 20 GeV
-  Analyzing power is ~5%
-   Slope = -4.6% \pm 0.8%
-  Simple average: -5.9%
-  Beam polarization uncertainties
-    simple average vs. lumi weighted
-    RHIC pol. Systematics, unknown
-        analyzing power at 200 GeV
-  Photon Contamination in neutron
-   samples

- Stat errors only
- Beam pol. Uncertainties
- Not included yet

- RHIC Spin Meeting: AD

- 7/29/02

## Spatial Distribution Data vs. MC

-  X distribution for data/MC matching is fine
-  Y distribution: seems peaked at the center
-  Obstacle in the beam pipe?

***x*****-distribution**

***x*****-distribution**

**Exp. data**

**Exp. data**

***y*****-distribution**

***y*****-distribution**

**Sim. data**

**Sim. data**

- Wire mesh???

- RHIC Spin Meeting: AD

- 7/29/02

## The WEST Side story.... ZDC/3

**Setup: Lead block +  g veto + ZDC/3 + Post shower**
-    Pb block + g-veto provide excellent  rejection (<0.1%)
-    ZDC/3 provides good energy resolution
-    Post shower provides satisfactory x resolution

- Post Shower

- ZDC/3

- - veto

- Lead block

- Yellow
- beam

- RHIC Spin Meeting: AD

- 7/29/02

## ZDC response to neutrons

- Modest non-linearity in neutron energy response

- RHIC Spin Meeting: AD

- 7/29/02

## ZDC/3 Asymmetry for neutrons !

- Updated results
- Run523-541; 19 runs
- Left: < -5 mm
- Right: > + 5mm
- Gamma Veto < 0.6 MeV
- Collision trigger ONLY
- 2.7M “neutron” samples
- Analyzing Power is consistent with EMCal side?
- EMCal +/-/4
- ZDC +/-/2

- RHIC Spin Meeting: AD

- 7/29/02

## Detector & Luminosity Asymmetries

- Find:
- Detector Asymmetry < 10%
- Luminosity Asymmetry < 2%

**Detector asymmetry**

**Luminosity Asymmetry**

- RHIC Spin Meeting: AD

- 7/29/02

## Comparison: PbWO4 vs. ZDC/3

-  Neutron asymmetry diluted by:
-    Photon contamination (25% in PbWO4) and <1% in ZDC
-  Integration over azymuthal angle
-    PbW04: 0.90 and ZDC: 0.64
-    Detailed GEANT underway
-  Presently:
-   Analyzing power: A differs by > 4 
-   PbWO4 : A = -8.7% +/- 0.5
-   ZDC/3 : A = -5.0 +/- 0.5

- RHIC Spin Meeting: AD

- 7/29/02

## To Do....

- Refine current studies:
-      finalize PID, PYTHIA, GEANT
-      Understand the correct dilution factors
-      User better RHIC polarization values (Account for the
-          yellow, blue beam analyzing powers, lumi weighted vs.
-          intensity weighted)
- 1st Draft for publication....Within a month or so...

- RHIC Spin Meeting: AD

- 7/29/02