results from pp2pp experiment at rhic andrzej sandacz xvii th rencontres de blois sołtan institute...
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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