DIS 2006 TSUKUBA April 21, 2006 Alessandro Bravar Spin Dependence in Polarized Elastic Scattering in the CNI Region A. Bravar, I. Alekseev, G. Bunce, S

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 !


||||,

||,

||,

||,

||,

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


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


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


polarimeters


pppp p pp p


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


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-


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


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


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


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


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


ppC C p p CC


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


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


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

Documents

DIS 2006 TSUKUBA April 21, 2006 Alessandro Bravar Spin Dependence in Polarized Elastic Scattering in the CNI Region A. Bravar, I. Alekseev, G. Bunce, S