Slajd 1

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Results from PP2PP Experiment at RHIC
Andrzej Sandacz
Soltan Institute for Nuclear Studies, Warsaw
on behalf of PP2PP Collaboration
XVII th Rencontres de Blois
Château de Blois, France, May 15-20, 2005
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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. Ljubicic,
  D. Lynn, C. Pearson, P. Pile, A. Rusek, M.
  Sakitt, S. Tepikian, K. Yip
• 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
• S. Khodinov, M. Rijssenbeek, L. Whitehead, S.
  Yeung
• SUNY Stony Brook, USA
• K. De, N. Guler, J. Li, N. Öztürk

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Spin Effects in Elastic Scattering at Collider
Energies

• Scientific interest

Some constraints from general principles of Field
Theory
e.g. allowed growth of single spin-flip /
nonflip amplitude ln s as s ? 8 (at fixed t)
Non-perturbative region of QCD ( t lt 0.05
GeV2 )
but spin-flip probes smaller distances ( 0.2
fm ) in nucleon
than non-flip interaction ( 1 fm )
Details of static constituent quark structure of
nucleon
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?
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Helicity Amplitudes for Spin ½ ½ ? ½ ½
Scattering process described in terms of Helicity
Amplitudes fi All dynamics contained in
the Scattering Matrix M
Observables cross sections and
spin asymmetries
spin nonflip double spin flip spin
nonflip double spin flip single spin flip
also ASS, ASL, ALL
formalism well developed, however not much data
! at high energy only AN measured to some extent
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Properties of Helicity Amplitudes at Small t and
Large s

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

• at large s, mostly unmeasured, but using
  reasonable assumptions

based on
a) extrapolation of experimental data at low
energies
b) theoretical arguments factorisation
and/or asymptotic dominance of
exchanges with definite CP1 or CP-1
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AN Coulomb Nuclear Interference
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
µ(m-1)p µspphad
AN (t)
needed phenomenological input
stot, ?, d (diff. of Coulomb-hadronic
phases), also for nuclear targets em. and
had. formfactors
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Published AN Measurements in the CNI Region
pC Analyzing Power
E950_at_BNL p 21.7 GeV/c PRL89(02)052302
pp Analyzing Power

E704_at_FNAL p 200 GeV/c PRD48(93)3026
no hadronic spin-flip
with hadonic spin-flip
AN()
no hadronic spin-flip
r5pC µ Fshad / Im F0had Re r5 0.088
0.058 Im r5 -0.161 0.226 highly
anti-correlated
-t
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RHIC-Spin Accelerator Complex
RHIC pC CNI polarimeters

absolute pH polarimeter
BRAHMS PP2PP
PHOBOS
RHIC
PHENIX
Siberian Snakes
STAR
Siberian Snakes
Spin Rotators
5 Snake
LINAC
BOOSTER
AGS
Pol. Proton Source
AGS quasi-elastic polarimeter
AGS pC CNI polarimeter
Rf Dipoles
200 MeV polarimeter
20 Snake
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The Setup of PP2PP
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Principle of the Measurement

• Elastically scattered protons have very small
  scattering angle ?, 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 Tx Ty
Scattering Angle at IP xD, yD Position at
Detector TxD, TyD Angle at Detector
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Elastic Event Identification

• Inner RPs used for elastic event
  reconstruction higher acceptance
  

• Events with hits in all four RPs of an arm ?
  full reconstruction

of scattered protons momenta
? better knowledge of of mean vertex coordinates
and beam angles at IP
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Hit Correlations Before the Cuts
example
Width mainly due to

• beam emittance

e 15 p mm mrad

• spread of vertex position

sz 60 cm
Background inelastic interactions, beam halo and
beam-gas interactions
After the cuts the background in the final sample
is 0.5 2
depending on y (vertical) coordinate
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Elastic Event Selection

• match of coordinates on opposite sides of IP

within 3s for x and y coordinates

• hit coordinates in the acceptance area of the
  detector

• events with multiple matches excluded

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 lt
0.035
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Experimental Determination of AN
Use Square-Root-Formulae to calculate spin (
??, ?? ) and (??, ?? ) asymmetries In this
formulae luminosities, apparatus asymmetries and
efficiencies cancel
Where
can be neglected wrt 1 ( lt 0.03 )
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e1(F) whole t range 0.010
lt t lt 0.030 (GeV/c)2
Fit AN cos(j) dependence to obtain AN
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AN from PP2PP
Compared to CNI Prediction without Hadronic
Spin-Flip
Preliminary
Only statistical errors shown
Beam polarization during the data taking in 2003
PY PB 0.88 0.12
Preliminary
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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 RPs)

• uncertainties on Lxeff and Lyeff
  6.4

• neglected term with double-spin asymmetries
  3.0

All above
8.4
Beam polarization error (preliminary)
13.6
Total systematic
16.0
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AN for pp?pp in the CNI Region
where tc -8pa / stot

, ? is
anomalous magnetic moment of the proton
fit to measured AN(t) Re r5 , Im r5

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r5 from PP2PP
Preliminary
Preliminary
Re r5 -0.042 0.037 , Im r5
-0.51 0.59
Statistical and systematic errors added in
quadratures
13.6 normalisation error due to beam
polarisation uncertainty, not included
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Effect of an Error on the Beam Polarization
( p0 Re r5 , p1 Im r5 )
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Summary and Outlook

• First (preliminary) measurement of AN at a
  collider energy

vs 200 GeV, small t

• AN more than 4s different from 0

• AN systematically 1s above CNI curve with no
  hadronic spin-flip

• Possible improvement of accuracy of AN and
  measurements of

(ANN, ASS, ALL, ASL)
double-spin asymmetries at RHIC
offer a unique chance to directly probe spin
coupling of Pomeron
and search for Odderon