DIS 2006 TSUKUBA April 21, 2006 Alessandro Bravar Spin Dependence in Polarized Elastic Scattering in...
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Transcript of DIS 2006 TSUKUBA April 21, 2006 Alessandro Bravar Spin Dependence in Polarized Elastic Scattering in...
DIS 2006TSUKUBA
April 21, 2006Alessandro Bravar
Spin Dependence in PolarizedSpin Dependence in Polarized
Elastic Scattering in the CNI RegionElastic Scattering in the CNI Region
A. Bravar, I. Alekseev, G. Bunce, S. Dhawan, R. Gill,
H. Huang, W. Haeberli, O. Jinnouchi, K. Kurita, Y. Makdisi,
A. Nass, H. Okada, N. Saito, H. Spinka, E. Stephenson,
D. Svirida, T. Wise, J. Wood, A. Zelenski
D I S 2 0 0 6 Alessandro Bravar
RHIC beams +internal targets fixed target modes ~ 14 GeV
The Elastic Process: KinematicsThe Elastic Process: Kinematics
recoil protonor Carbon
(polarized)proton beam
scatteredproton
02 inout pptpolarized
proton targetor Carbon target
essentially 1 free parameter:
momentum transfer t = (p3 – p1)2 = (p4 – p2)
2 <0
+ center of mass energy s = (p1 + p2)2 = (p3 – p4)
2
+ azimuthal angle if polarized !
elastic pp kinematics fully constrained by recoil proton only !
D I S 2 0 0 6 Alessandro Bravar
||||,
||,
||,
||,
||,
5
4
3
2
1
MMts
Mts
Mts
Mts
Mts
Helicity Amplitudes for spin ½ ½ Helicity Amplitudes for spin ½ ½ ½ ½ ½½Scattering process described in terms of Helicity Amplitudes i
All dynamics contained in the Scattering Matrix M(Spin) Cross Sections expressed in terms of
spin non–flip
double spin flip
spin non–flip
double spin flip
single spin flip
? M
identical spin ½ particles
formalism well developed, however not much data !
only AN studied / measured to some extent
observables:
3 -sections
5 spin asymmetries
4321*52 Im
4),(
sdtd
tsAN
NA
4*32
*1
252 Re2
4),(
sdtd
tsANN
NNA
D I S 2 0 0 6 Alessandro Bravar
The Very Low The Very Low tt Region Regionaround t ~ 103 (GeV/c)2 Ahadronic ACoulomb
INTERFERENCE
CNI = Coulomb – Nuclear Interferencescattering amplitudes modified to include also electromagnetic contribution
hadronic interaction described in terms of Pomeron (Reggeon) exchange
electromagnetic single photon exchange
= |Ahadronic + ACoulomb|2
unpolarized clearly visible in the cross section d/dt charge
polarized “left – right” asymmetry AN magnetic moment
+P
iemi
hadi
hadi e
D I S 2 0 0 6 Alessandro Bravar
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 (Lapidus & Kopeliovich):
hadronic spin- flip modifies the QED“predictions”
interpreted in terms of Pomeron spin – flip and parametrized as
AANN & Coulomb Nuclear Interference & Coulomb Nuclear Interference
hadflipnon
hadflip
hadflipnon
emflipN CCA *
2*
1
1)p pphad
Zt
yy
y
m
ZA
pAtot
pAtotp
N 81
1
82
2/3
2
25 2
1
2
1
2
1II ppp
AN (t)
had
p
had
m
ts
)(5
D I S 2 0 0 6 Alessandro Bravar
polarimeters
D I S 2 0 0 6 Alessandro Bravar
pppp p pp p
D I S 2 0 0 6 Alessandro Bravar
pppp pppp and and pppp pppp with a Polarized Gas Jet Targetwith a Polarized Gas Jet Target
LRRL
LRRL
TN
NNNN
NNNNP
A1
NN
NNPP
ABT
NN1
RHIC polarizedProton beams
polarizedgas JETtarget
ANbeam (t ) AN
target (t )
for elastic scattering only!
Pbeam = Ptarget . B / T
D I S 2 0 0 6 Alessandro Bravar
The Atomic H Beam The Atomic H Beam SourceSource
separationmagnets(sextupoles)
H2 dissociator
Breit-Rabipolarimeter
focusingmagnets(sextupoles)
RF transitions
holding field magnet
recoil detectorsToF, EREC; REC
record beam intensity100% eff. RF transitionsfocusing high intensityB-R polarimeter
Ptarget ~ 0.924 ± 0.018
OR
Pz+ OR Pz
-
H = p+ + e-
D I S 2 0 0 6 Alessandro Bravar
pppp elastic data collected elastic data collected
Hor. pos. of Jet 10000 cts. = 2.5 mm
Num
ber
of e
last
ic p
p ev
ents
FWHM ~ 6 mmas designed
• recoil protons unambiguously identified !
CNI peak AN
1 < E REC < 2 MeV prompt eventsand beam-gas
sourcecalibration
recoil protons elastic pp ppscattering
background118 cts. subtracted
JET Profile: measured selecting ppelastic events
ToF vs EREC correlation
Tkin= ½ MR(dist/ToF)2
ToF < 8 ns
D I S 2 0 0 6 Alessandro Bravar
TDC vs ADC individual channels
Energy - Position correlationsEnergy - Position correlationsTkin 2 (i.e. position2)
pp elastic events clearly identified !
full
y ab
sorb
ed p
roto
nspu
nch
thro
ugh
prot
ons
reco
il e
nerg
y
punch throughrecoil protons
position
D I S 2 0 0 6 Alessandro Bravar
not corrected for themagnetic field
MX2 [GeV2]
Mp2
inelasticthreshold
num
ber
of e
vent
s (a
. u.)
FWHM ~ 0.1 GeV2
MM22XX (GeV(GeV22))proton
MM22X X distributiondistribution
80 cm from targetconvoluted withspectrometerResolution
MM22XX~ 0.1 GeV22
Missing Mass MMissing Mass MXX2 2 @ 100 GeV@ 100 GeV
MM22XX
simulations
D I S 2 0 0 6 Alessandro Bravar
AANN for for ppp p pp pp @ 100 GeV @ 100 GeV
no need of a hadronic spin – flip contribution to describe these data
no hadronicspin-flip
Re r5 = -0.001 0.009
Im r5 = -0.015 0.029
hadhad
p
had
m
tsr 3155 2)(
in the simplest assumption:spin-flip prop. to non-flip ampli.
source of systematic errors:1 PTARGET = 2 %
2 from backgrounds & event selection < 0.00163 false asymmetries: smallsimilar to statistical errors
2 ~ 13 / 14 d.o.f. (11 / 12)
hep-ex/0601001
D I S 2 0 0 6 Alessandro Bravar
AANNNN for for pppp pp pp @ 100 GeV @ 100 GeV
prel
imin
ary
source of sys. errors:
1 PT2 = 3 %
2 from backgrounds and event selections
~ 0.0013 rel. luminosity ~ 0.001
similar to stat. errors
NNB
T
TBTNN PPP
A
2
11
ANN basically 0 double spin – flip amplitudes (2 and 4)
are very small / do not contribute in this region
statistical errors only
D I S 2 0 0 6 Alessandro Bravar
ppC C p p CC
D I S 2 0 0 6 Alessandro Bravar
AANN for for ppCC p pC @ 100 GeVC @ 100 GeV
no hadronicspin-flip
with hadronicspin-flip
“forbidden” asymmetries
systematicuncertainty
best fit withhadronic spin-flip
Kopeliovich –Truemann modelPRD64 (01) 034004hep-ph/0305085
r5pC Fs
had / Im F0had
prel
imin
arystatistical errors only
spread of r5 values
from syst. uncertainties
1 contour
D I S 2 0 0 6 Alessandro Bravar
AANN ppCC p pC: Energy DependenceC: Energy DependenceA
N (
%)
Beam Energy (GeV)
prel
imin
ary
2003
- 20
05 d
ata
t = - 0.01 GeV2
t = - 0.02 GeV2
t = - 0.03 GeV2
t = - 0.04 GeV2
statistical errors only
E ?Asymptotic regime
No energy dependence ?
only statistical errors shown
normalization errors: ~ 10 % (at 3.9) ~ 15 % (at 6.5) ~ 20 % (at 21.7)
systematic errors: < 20 % - backgrounds - pileup - RF noise
D I S 2 0 0 6 Alessandro Bravar
SummarySummary measured AN
pp and ANNpp for elastic pp pp scattering at 100 GeV
with very high accuracy (statistical and systematic)
– |t| range: 0.0015 < |t| < 0.035 (GeV/c)2
AN data well described by CNI – QED predictions (Schwinger – Lapidus)these data do not require a hadronic spin-flip term
ANN ~ 0 over whole range with no “structure” (i.e. t – dependence)
measured ANpC for elastic pC pC scattering at 100 GeV (RHIC)
– zero crossing around |t| ~ 0.03 (GeV/c)2
pC data require substantial hadronic spin-flip !
measured ANpC for pC pC scattering over 3.5 < Eb < 24 GeV (AGS)
– Eb < 10 GeV/c: almost no t dependence & departure from “CNI” shape