# Presentation: 281814

## Preliminary Result of AN Measurement in pp Elastic Scattering at RHIC, at  s = 200 GeV Włodek Gurynfor pp2pp collaboration Brookhaven National Laboratory, Upton, NY, USA

**OUTLINE of the TALK**
- Description of the experiment
- Description of analysis
- Results and interpretation
- Where do we go from here?

## Spin Dependence in Elastic Scattering

- Five helicity amplitudes describe proton-proton elastic scattering

- Some of the measured quantities are

## Principle of the Measurement

- Elastically scattered protons have very small scattering angle θ*****, hence beam transport magnets determine trajectory scattered protons
- The optimal position for the detectors is  where scattered protons are well separated from beam protons
- Need Roman Pot to measure scattered protons close to the beam without breaking accelerator vacuum

- Beam transport equations **relate measured position at the detector to scattering angle**.

**x****0****,y****0****:  Position at Interaction Point**
**Θ*****x**** Θ*****y ****:  Scattering Angle at IP**
**x****D****, y****D****   :  Position at Detector**
**Θ****x****D****, Θ****y****D**** :  Angle at Detector**

## Angle (hit) Correlations Before the CutsEvents with only eight hits

- Note: the background appears enhanced because of the “saturation” of the main band

## Hit selection

- Pedestal value, pedestal width ( and dead channels (only six) were determined;
- Valid hit, single strip, has dE/dx > 5 above the pedestal;
- Cluster size is  5 consecutive strips above pedestal cut;
- Valid hit  in the  Si plane for event reconstruction:
- is a cluster whose dE/dx > 20 ADC counts above pedestal and
- is within fiducial area of the detector (slide);
- has for a y-plane y >  0.2mm from the edge of the detector.
- Coordinate for x and y formed from adjacent hits in Sin for each Roman Pot
- After finding matching hits in x and y:
- Choose events with one track in x and one track in y and   6hits.
- Veto on the Sc signal in the opposite arm, TDC cut.
- Choose collinear tracks within 3 in angles.
- Plot dN/dt and calculate asymmetries.

## Calculation of Scattering Angle

- Using matched hits scattering angels can be calculated.
- Use transport and and average (x0, y0) and beam angles obtained from vectors reconstructed using all eight RPs.
- Make z-vertex correction using ToF.

## Collinearity:x before and after z-correction, and y

## Determination of AN

- Use *Square-Root-Formula** *to calculate raw and false asymmetries, since it cancel luminosity dependence. It uses ,  and  ,  bunch combinations.

## Preliminary Results: Full bin 0.011 < -t < 0.029 (GeV/c)2

**Fit A****N**** cos(********) dependence to obtain A****N**

**A****N****(******

- Preliminary

- Preliminary

## Results: PYellow+ PBlue = 0.67 (central value) and CNI curve (tot ,  from world data, B from pp2pp result)

- Note: PYellow+ PBlue = 0.67 can vary by ± 15% ( a working number)

- One point for the full
- t-interval [0.011,0.029]

- Two points for two half   intervals

- Preliminary

- Preliminary

## Future Possibility – Big Improvement

| s (GeV) | * | |t|-range (Gev/c)2 | Typical errors |
| --- | --- | --- | --- |
| 200 | 20 m | 0.003 < |t| < 0.02 | B = 0.3, tot= 2 – 3 mb
 = 0.007 and AN=0.002 |
| Cost: $ 25k |  |  |  |

## Summary

- We have measured the single spin analyzing power AN in polarized pp elastic scattering at s = 200 GeV in t-range [0.011,0.29] (GeV/c)**2**.
- The A**N** is  4-5 from zero.
- The A**N** is  1-2 away from a CNI curve, which does not have hadronic spin flip amplitude.
- We discussed interpretation of the result by Larry Trueman and Boris Kopeliovich.
- RHIC is a great and unique place to do this physics!