# Presentation: 118610

## First Result from the pp2pp Experiment Włodek Gurynfor pp2pp collaboration Brookhaven National Laboratory, Upton, NY, USA

- Introduction – pp2pp physics program;
- Description of the experiment;
- Engineering run in 2002;
- Data analysis and results;
- Summary and outlook.

## Total and Differential Cross Sections, and Polarization Effects in pp Elastic Scattering at RHIC

**S. Bueltmann, B. Chrien, A. Drees, R. Gill, W. Guryn*, I. H. Chiang, D. Lynn, C. Pearson, P. Pile, A. Rusek, M. Sakitt, S. Tepikian**
*Brookhaven National Laboratory, USA*
**J. Chwastowski, B. Pawlik**
*Institute of Nuclear Physics, Cracow, Poland*
**M. Haguenauer**
*Ecole Polytechnique/IN2P3-CNRS, Palaiseau, France*
**A. A. Bogdanov, S.B. Nurushev, M.F Runtzo, M. N. Strikhanov**
*Moscow Engineering Physics Institute (MEPHI), Moscow, Russia*
**I. G. Alekseev, V. P. Kanavets, L. I. Koroleva, B. V.  Morozov, D. N. Svirida**
*ITEP, Moscow, Russia*
**M. Rijssenbeek,  C. Tang, S. Yeung**
*SUNY Stony Brook, USA*
**K. De, N. Guler, J. Li, N. Ozturk**
*University of Texas at Arlington, USA*
**A. Sandacz**
*Institute for Nuclear Studies, Warsaw, Poland*
- * spokesman

## Polarized Proton Collisions in RHIC

## PP2PP Physics program

-  Beam energy between 25 and 250 GeV;
-  Transverse polarization up to 70%;
-  Polarization can be chosen on a bunch-by-bunch basis (good for eliminating detection systematics!);
- Allows to measure spin dependence of proton-proton elastic scattering
- CNI region:
**0.0004 < -t < 0.02 (GeV/c)****2**** √s = 200 GeV **
**0.0004 < -t < 0.13 (GeV/c)****2**** √s = 500 GeV **
******tot****, ********, B, d********/dt, ****A****N****(t), A****NN****(t)  **
**********ot**** = 600 ********barn (~1%), ******** = 0.005 (4%),******** A****N****(t), ********A****NN****(t) = 0.001**
- Medium |t| region:
**0.02 < -t < 1.3 (GeV/c)2 ****√s = 500 GeV**
**diffractive minimum (peaks and bumps) and their spin dependence****   **

- Design parameters

## pp2pp experiment studies the dynamics and spin dependence of hadronic interaction through proton-proton elastic scattering

**Perturbative QCD Picture**

- s = (p1 + p**2** )**2** =   (C.M energy)2      t  = (p1 – p**3** )**2** = - (four momentum transfer)2
- s ****** ******** **t****** **1 (GeV/c)2 – Non-perturbative regime
- Elastic scattering  d/dt + optical theorem  total cross section **tot**

## Summary of Existing Data 

**50**

**500**

**PP2PP**

- Summary of Existing Data

## Principle of 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 beam without breaking accelerator vacuum

- Beam transport equations    relate measured position at detector to scattering angle
-       x  =  a11 x0  +  Leff  θx         Optimize so that  a11  small and  Leff  large
-       θx =  a12 x0  +  a22 θx         x0 can be eliminated by measuring θx

- *

- Similar equations for y-coordinate
- We found that because of the roll, misalignment, of the quadrupoles there is a mixing between x and y.

## pp2pp Experimental Setup in Engineering run 2002Elastic and Inelastic Detectors

## Running Conditions in 2002

- Running conditions during a pp2pp, 14 hour dedicated run:
- Beam momentum                       *p* = 100 GeV/*c*
- Number of bunches per beam   *N*B = 55        used 35 bunches
- Beam scraped to emittance          *ε*  12 π •10-6 m
-                       and intensity        * I*   5•1011 protons  in each beam
- Beam optics used                        *β** = 10 m
- Beam polarization (working #)   *P*b = 0.24  0.02
- Closest approach of first detector strip to beam about
-             15 mm  15 beam    *t*min = -4•10-3 GeV2
- Collected ~1 million triggers of which >30 % are elastic events

## Data Analysis: Colinearity

- Correlation plots of *x*- and *y*-coordinates using elastic triggers with reconstructed tracks of scattered protons

## Beam Angular Divergence

- Good agreement between width of *θ**x* and *θ**y * distributions for measured and simulated events with emittance of:
*      ****ε *****= 12 π •10****-6**** m**
- And vertex size:
-       ******z**** = 70 cm**
*   **Δθ**x  * 150 μrad
*   **Δθ**y  *   70 μrad

**N. Öztürk**

*Δθ**y*

*Δθ**x*

**N. Öztürk**

## Event Reconstruction

**Elastic event: good track in two “opposite” set of detectors**
- SSD coordinate was calculated using energy weighted average of the position of the strips belonging to the isolated cluster of no more than three hits;
- Correlation between tracks in two Roman Pots:                                                      require that (x2 + y2) be within “radius” : (x2 + y2) < 16 (x2 + y2 );
- At least six out of eight hits belong to the track;
- No more than two planes with hits in “non” elastic arm;
- Select events within uniform t-acceptance tcut

## |t |--Acceptance

- Find region in |*t** *|- and -space with full acceptance coverage and high statistics

- Event Sample  196,000 events:
- 159,250 events  (   0  <  < 180o )
- 122,437 events  ( 45o <  < 135o )
-   58,511 events  ( 45o <  < 135o )
-  & 0.010 GeV2   |*t** *|   0.019 GeV2 )

## Extracting B  from dN/dt-Distribution

- Fit |*t** *|-distribution with

- fixing tot51.6 mb and  0.13 and keeping *B * as a free parameter in range 0.010 GeV2   |*t** *|   0.019 GeV2results in
*            ****B***** = (**** ****16.3 ******** 1.6 ) GeV****-2**

***B***** = (**** ****16.3 ******** 1.6 ) GeV****-2**

## Systematic and Correlation Errors

- Systematic Errors were evaluated using Monte Carlo  simulations:
- Beam emmitence;
- Vertex position spread in x, y, z;
- Incoming beam angels – major source;
- Beam transport uncertainty;
-                   Total Systematic Error 0.9 (GeV/c)**-2**
- Correlation between fitted parameter B and values of ********and ****:
************±**4 mb ****=> ******–/+ **0.07 (GeV/c)****-2**** **
****±******0.02 ****=> ******±******0.32 (GeV/c)****-2**

## RESULT

- b = 16.3 ± 1.6 (stat.) ± 0.9 (syst.) (GeV/c)-2

- Analysis done by two independent groups is in agreement.

## Donnachie&Landshoff

**Donnachie&Landshoff**
**OPE Model**

**Bourrely, Soffer, Wu **

## Running Conditions 2002-03

**Systematic error improvement in 2003 due to:**
- Excellent silicon detector efficiency;
- Measurement of local angles with new Roman Pot stations;
- Improved beam optics measurement;
- Van der Meer beam scans for luminosity measurement.

## Conclusions and Plans

**Conclusions**
- A promising physics result for *b* and *A**N* from engineering run 2002
- Excellent silicon detector performance in physics run 2003
- Good statistics obtained - waiting for physics results.
**New proposal for 2004 and beyond (****to be considered by PAC Sept 29, 2003****)**
- Run with current setup **(***********tot******, d************/dt, b, ************, A******N******, A******NN*****)**
- *=20 m, pbeam=100 GeV/c  0.003*<|t|<*0.02(GeV/c)2;
- *=10 m, pbeam=250 GeV/c  0.025*<|t|<*0.12(GeV/c)2.
- Put Roman Pots between DX and D0 magnets **(*****d************/dt, b, A******N******, A******NN*****)**
- *=3m, pbeam= 250 [100] GeV/c  0.2*<|t|<*1.3(GeV/c)2 [0.02*<|t|<*0.12(GeV/c)2 .]
- Upgrade RHIC quadrupoles power supply at our IP to run with *=100m and move Roman Pots to 70m  position **(***********tot******, d************/dt, b, ************, A******N******, A******NN*****)**
- *=100m, pbeam=100 and 250 GeV/c  *|t| *CNI region

## Spin Physics with pp2pp

- Five helicity amplitudes describe proton-proton elastic scattering

- Φ1(*s*,*t *)  <++|M|++>
- Φ2(*s*,*t *)  <++|M|-->
- Φ3(*s*,*t *)  <+-|M|+->
- Φ4(*s*,*t *)  <+-|M|-+>
- Φ5(*s*,*t *)  <++|M|+->

- Measure:

- Φn(*s*,*t *)  <h3 h4 |M|h1 h2>
-                   with  hx = *s*-channel helicity
-                                   p1 = -p2  incoming protons
-                                   p3 = -p4  scattered protons
- Φ+(*s*,*t *) = 1⁄2 ( Φ1(*s*,*t *) + Φ3(*s*,*t *) )

## Actual transport: (x0, y0) not known also coupled  because of the quad roll

- Actual transport: (x0, y0) not known also coupled  because of the quad roll

- Yellow

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