Results from PP2PP Experiment at RHIC

Andrzej Sandacz

XVII th Rencontres de Blois

Sołtan Institute for Nuclear Studies, Warsaw

on behalf of PP2PP Collaboration

Château de Blois, France, May 15-20, 2005

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

S. Bültmann, I. H. Chiang, R.E. Chrien, A. Drees, R. Gill, W. Guryn*, J. Landgraf, T.A. Ljubičič, D. Lynn, C. Pearson, P. Pile, A. Rusek, M. Sakitt, S. Tepikian, K. Yip

Brookhaven National Laboratory, USA

J. Chwastowski, B. PawlikInstitute of Nuclear Physics, Cracow, Poland

M. HaguenauerEcole Polytechnique/IN2P3-CNRS, Palaiseau, France

A. A. Bogdanov, S.B. Nurushev, M.F Runtzo, M. N. StrikhanovMoscow Engineering Physics Institute (MEPHI), Moscow, Russia

I. G. Alekseev, V. P. Kanavets, L. I. Koroleva, B. V. Morozov, D. N. SviridaITEP, Moscow, Russia

S. Khodinov, M. Rijssenbeek, L. Whitehead, S. YeungSUNY Stony Brook, USA

K. De, N. Guler, J. Li, N. ÖztürkUniversity of Texas at Arlington, USA

A. SandaczInstitute for Nuclear Studies, Warsaw, Poland

* spokesman

Spin Effects in Elastic Scattering at Collider Energies

Scientific interest

Non-perturbative region of QCD ( | t | < 0.05 GeV2 )

Details of static constituent quark structure of nucleon

Some constraints from general principles of Field Theory

e.g. allowed growth of single spin-flip / nonflip amplitude ~ ln s as s → ∞ (at fixed t)

but spin-flip probes smaller distances ( ~ 0.2 fm ) in nucleon

than non-flip interaction ( ~ 1 fm )

If spin-flip present, e.g.

compact diquark in the nucleon or

anomalous color-magnetic moment of quarks or

isoscalar magnetic moment of the nucleon

At high energy exchange of Pomeron dominant

Pomeron coupling to nucleon spin?

||,

||,

||,

||,

||,

5

4

3

2

1

Mts

Mts

Mts

Mts

Mts

Helicity Amplitudes for Helicity Amplitudes for SSpin ½ ½ pin ½ ½ →→ ½ ½ ½ ½

031Im4

ttot s 02Im

8

tT s 031Im

π8σσσΔ

tL s

Scattering process described in terms of Helicity Amplitudes i

All dynamics contained in the Scattering Matrix M

spin non–flip

double spin flip

spin non–flip

double spin flip

single spin flip

formalism well developed, however not much data ! at high energy only AN measured to some extent

4321*52

Im4

),(

sdt

dtsAN

4*32

*1

252

Re24

),(

sdt

dtsANN

NA

NNA

Observables cross sections and spin asymmetries

25

24

23

22

212

||4||||||||2

sdt

d

also ASS, ASL, ALL

Properties of Helicity Amplitudes at Small t and Large s

at small t, due to the conservation of the angular momentum

||,5 tts ||,4 tts

||,,, 2420

ttststst

at large s, mostly unmeasured, but using reasonable assumptions

a) extrapolation of experimental data at low energies

b) theoretical arguments: factorisation and/or

asymptotic dominance of exchanges with definite CP=1 or CP=-1

tsts ,, 31

based on

the left – right scattering asymmetry AN arises from the interference of

the spin non-flip amplitude with the spin flip amplitude (Schwinger)

in absence of hadronic spin – flip contributions

AN is exactly calculable (Kopeliovich & Lapidus)

hadronic spin- flip modifies the QED ‘predictions’

hadronic spin-flip usually parametrized as

AANN & Coulomb Nuclear Interference & Coulomb Nuclear Interference

emflipnon

hadflip

hadflipnon

emflipN CCA **

21

1)p pphad

AN (t)

hadhad

p

had

m

tr 3155 2

1

Im

needed phenomenological input: σtot, ρ, δ (diff. of Coulomb-hadronic phases), also for nuclear targets em. and had. formfactors

PublishedPublished AANN MMeasurements in the CNI easurements in the CNI RRegionegion

pp Analyzing Power

no hadronicspin-flip

-t

AN

(%)

E704@FNALp = 200 GeV/cPRD48(93)3026

E950@BNLp = 21.7 GeV/cPRL89(02)052302

with hadonicspin-flip

no hadronicspin-flip

pC Analyzing Power

r5pC Fs

had / Im F0had

Re r5 = 0.088 0.058

Im r5 = 0.161 0.226

highly anti-correlated

RHIC-SpinRHIC-Spin Accelerator ComplexAccelerator Complex

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter

AGS quasi-elastic polarimeter

Rf Dipoles

RHIC pC “CNI” polarimeters

PHOBOS

RHIC

absolute pHpolarimeter

SiberianSnakes

AGS pC “CNI” polarimeter

5% Snake

The SetupThe Setup of PP2PP of PP2PP

221121 yxyxpp

,,

Principle of the Principle of the MeasurementMeasurement

• 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.

x0,y0: Position at Interaction Point

Θ*x Θ*y : Scattering Angle at IP

xD, yD : Position at Detector

ΘxD, Θy

D : Angle at Detector

=yD

D

xD

D

y

x

*0

*0

y

x

y

x

44434241

333231

24232221

141311

aaaa

Laaa

aaaa

aaLa

y

eff

x

eff

Elastic Event IdentificationElastic Event Identification

An elastic event has two collinear protons, one on

each side of IP

221121 ,, yxyxpp

Inner RP’s used for elastic event reconstruction; higher acceptance Events with hits in all four RP’s of an arm → full reconstruction

of scattered protons momenta

→ better knowledge of of mean vertex coordinates and beam angles at IP

Hit Correlations Before the CutsHit Correlations Before the Cuts

After the cuts the background in the final sample is ≈ 0.5% ÷ 2%depending on y (vertical) coordinate

Background: inelastic interactions, beam halo and beam-gas interactions

example

Width mainly due to

ε = 15 π mm · mrad

beam emittance

spread of vertex position

σz = 60 cm

Elastic Event SelectionElastic Event Selection

match of coordinates on opposite sides of IP;

within 3σ for x and y coordinates

hit coordinates in the acceptance area of the detector

After the cuts 1.14 million elastic events in t-interval

0.010 ≤ | t | ≤ 0.030 (GeV/c)2

Loss of elastic events due to the selections < 0.035

events with multiple matches excluded

Experimental Determination Experimental Determination of Aof ANN

Use Square-Root-Formulae to calculate spin ( , ) and (, ) asymmetries

In this formulae luminosities, apparatus asymmetries and efficiencies cancel

Where 22 sincos SSNNyb AAPP can be neglected wrt 1 ( < 0.03 )

εε11((ΦΦ) ) whole whole tt range: range: 0.01 0.0100 < < ||tt|| < 0.0 < 0.03030 (GeV/c) (GeV/c)22

Fit AN cos() dependence to obtain AN

Arm A Arm B

Statistical errors

Preliminary

Compared to CNI Prediction without Hadronic Spin-Flip

Only statistical errors shown

Beam polarization during the data taking in 2003: PY + PB = 0.88 ± 0.12

Preliminary

AN from PP2PP

Systematic Errors on AN

luminosities ans detector efficiencies cancel --

background 4.5%

beam positions at the detectors 1.8%

corrections to the standard transport matrices 1.4%

(using events detected in all four RP’s)

uncertainties on Lxeff and Ly

eff 6.4%

neglected term with double-spin asymmetries 3.0%

All above 8.4%

Beam polarization error (preliminary) 13.6%

Total systematic 16.0%

AN for pp→pp in the CNI Region

Denom

Nom

m

ttAN

5555 ImRe2]ImRe21[ rrt

trrNom c

22

12

t

t

t

tDenom cc

where tc = -8πα / σtot ,

κ is anomalous magnetic moment of the proton

fit to measured AN(t) Re r5 , Im r5

r5 from PP2PP

Statistical and systematic errors added in quadratures13.6% normalisation error due to beam polarisation uncertainty, not included

Preliminary Preliminary

Re r5 = -0.042 ± 0.037 , Im r5 = -0.51 ± 0.59

Effect of an Error on the Beam Polarization

( p0 ≡ Re r5 , p1 ≡ Im r5 )

Summary and Outlook

First (preliminary) measurement of AN at a collider energy

√s = 200 GeV, small t

AN more than 4σ different from 0

AN systematically ≈ 1σ above CNI curve with no hadronic spin-flip

Possible improvement of accuracy of AN and measurements of

double-spin asymmetries at RHIC (ANN, ASS, ALL, ASL)

offer a unique chance to directly probe spin coupling of Pomeron

and search for Odderon