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New Results from PP2PP Experiment at RHIC
Andrzej Sandacz
Soltan Institute for Nuclear Studies, Warsaw

• Spin in elastic scattering at asymptotic
  energies

• Experiment PP2PP

• Results on spin observables from PP2PP

• Future program with STAR

Seminar of Nuclear Physics Division
WUT, Warsaw, May 24, 2005
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Proton - Proton Elastic Scattering at Asymptotic
Energies
p
p
Diffractive process, exchanged vacuum quantum
numbers
p
p
QCD Picture

• Coupling of Pomeron to the nucleon spin poorly
  known

• Still no compelling experimental evidence for
  Odderon

If Odderon coupling to proton weaker than that of
Pomeron, best to look

• at high energies - non-diffractive
  background vanishes

• using interference between amplitudes - e.g.
  through spin observables

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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 ASL, ALL
formalism well developed, however not much data !
at high energy only AN measured to some extent
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Polarized cross-sections and spin parameters
- cross section for one beam fully polarized
along vector normal to the scattering plane
- cross section for both beams fully polarized
along vector normal to the scattering plane
ASS - similar definition as for ANN
but cross section for beams polarized
along vector in the scattering plane
where - beam momentum
Cross section azimuthal dependence for
transversely polarized beams
- blue beam polarization vector
- yellow beam polarization vector
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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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AN for pp ? pp _at_ 100 GeV
from RHIC jet polarimeter

with hadronic spin-flip
Im r5 0.002 0.029 Re r5 -0.006 0.007
?2/ndf 10 / 12
preliminary

• uncertainty on the
• (Dr 0.03) parameter
• can change at the same level

stat sys errors used in fits
hadronic spin flip contribution consistent with
zero (1 s level)
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AN for pC p C _at_ 100 GeV
from RHIC carbon polarimeter
r5pC µ Fshad / Im F0had
statistical errors only
1 s contour
preliminary
no hadronic spin-flip
spread of r5 values from syst. uncertainties
with hadronic spin-flip
best fit with hadronic spin-flip Kopeliovich
Truemann model PRD64 (01) 034004 hep-ph/0305085
systematic uncertainty
forbidden asymmetries
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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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Roman Pot Stations at RHIC
station RP2
station RP1
Roman Pot above the beam
to IP
Roman Pot below the beam
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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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Si detector package
Al strips 512 (Y), 768 (X), 50µm wide100 µm
pitch

• 4 planes of 400 µm Silicon microstrip detectors
• 4.5 x 7.5 cm2 sensitive area
• 8 mm trigger scintillator with two PMT readout
  behind Silicon planes.
• Run 2003 new Silicon manufactured by Hamamatsu
  Photonics.
• Only 6 dead strips per 14112 active strips.

implanted resistors
SVX chips
Trigger Scintillator
bias ring
guard ring
Detector board
Si
1st strip?edge 490 µm
LV regulation
Michael Rijssenbeek
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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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Calculation of asymmetry AN
Polarized cross section for both beams polarized
vertically
Square root formula
In this formulae luminosities, apparatus
asymmetries and efficiencies cancel
where
Beam polarization (PBPY)/-- 0.880.12,
(PB - PY)-/- -0.050.05 Crosscheck ?N
(predicted)? (PB - PY)-/-AN ?-0.0011 ? ?N
(measured)-0.00160.0023
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Single spin asymmetry AN
Raw asymmetry ?N for 0.01lttlt0.03 (GeV/c)2

Statistical errors only
Arm A Arm B
S. Bueltmann et al. Phys. Lett. B632(2006)167
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AN(t) and fit of r5

N. H. Buttimore et. al. Phys. Rev. D59, 114010
(1999)
where tc -8pa / stot

? is
anomalous magnetic moment of the proton
Re r5 -0.033 0.035 Im r5 -0.43 0.56
our fit
no hadronic spin flip
Only statistical errors shown
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Calculation of double spin asymmetries
f2/f0.05(1i)
E.Leader, T.L.Trueman The Odderon and spin
dependence of high-energy proton-proton
scattering, PR D61, 077504 (2000)
f2/f0.05
f2/f0.05i
External normalization using the machine bunch
intensities Lij?IiBIjY on bunches with
given i,j combination Raw asymmetry
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ANN and ASS from pp2pp
PBPY0.198 0.064

• Distributions in the arms A and B are averaged
• Distributions ?(?) were fitted with (P1sin2?
  P2cos2?)
• P1PBPYASS
• P2PBPYANN

Statistical errors only
PRELIMINARY
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Physics from double spin asymmetries
, where

• Im r2 0.0019 0.0052

• 
  -0.19 0.53 mb

Assuming Pomeron Odderon exchange
phase of F2 shifted by 90o wrt F
and about the same as Fem

• Re r2 -0.025 0.065

r2 well consistent with zero,
still small (5) contribution
of Odderon not excluded
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New results - summary

• First measurements of spin asymmetries AN , ANN
  and ASS at a collider energy

vs 200 GeV and small t

• AN more than 4s different from 0

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

• Double spin asymmetries consistent with zero,
  small contribution of Odderon

not excluded

• 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
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Physics with Tagged Forward Protons with the STAR
Detector at RHIC Proposal to the STAR
Collaboration H. Spinka Argonne National
Laboratory, USA R.E. Chrien, R. Gill, W. Guryn,
B. Hackenburg, J. Landgraf, T.A. Ljubicic, D.
Lynn, C. Pearson, P. Pile, S. Tepikian, K.
Yip Brookhaven National Laboratory, USA A. A.
Bogdanov, S.B. Nurushev, M.F Runtzo 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 SUNY
Stony Brook, USA A.Sandacz Soltan Institue for
Nuclear Studies, Warsaw, Poland Contact
person E-mail guryn_at_bnl.gov Phone [phone]
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Implementation at RHIC
Detectors to
tag forward protons
and detector with good acceptance and particle
ID to measure central system
Roman Pots of PP2PP and STAR
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Extension of STAR program to include diffractive
physics (with spin)

• Phase I for elastic scattering
• Rotate RP1,3 (full acceptance over ? !) and move
  to STAR IP (spin rotators !!) ?
  (?tot, d?/dt, b, ?, AN , ANN , ASS , ALL , ALS)
• ?20m, pbeam100 GeV/c ? 0.003 lt tlt 0.02
  (GeV/c)2
• ?10m, pbeam250 GeV/c ? 0.025 lt tlt
  0.12(GeV/c)2.

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Rotating RP1 and RP3
Full acceptance at ?s 200 GeV Without IPM and
kicker
With IPM and kicker