STARSTAR

Igor Alekseev (ITEP) for the STAR Collaboration 1

XV Workshop on High Energy Spin PhysicsDubna, Russia, October 8-12, 2013

XV Workshop on High Energy Spin PhysicsDubna, Russia, October 8-12, 2013

Results on the Transverse Double Spin

Asymmetries in the elastic pp-scattering at √s=200 GeV

STAR Helicity amplitudes for spin ½ ½ → ½ ½

Igor Alekseev (ITEP) for the STAR Collaboration 22

spin non–flip

double spin-flip

spin non–flip

double spin-flip

single spin-flip

1

2

3

4

5

, | |

, | |

, | |

, | |

, | |

, , ,

EM HADi i i

s t M

s t M

s t M

s t M

s t M

s t s t s t

0031 Im

4Im

4 tttot ss

02Im8

tT s

031Imπ8

σσσΔ

tL s

Observables: cross sections and spin asymmetries

25

24

23

22

212

||4||||||||2

sdt

d 4321

*52 Im

4),(

sdtd

tsAN

4*32

*1

2

52Re2

4),(

sdt

dtsANN

*43

*212

Re4

),(

sdt

dtsASS

Matrix elements

STAR

Cross-section azimutual angular dependence for transversely polarized beams:

Polarized cross-sections and spin parameters

Igor Alekseev (ITEP) for the STAR Collaboration 33

;

NN SSA A

|| pn

pns

0 1 ( ) ( )( ) ( )( )N B Y NN B Y SS B YA P P n A P n P n A P s P s

BP

YP

- is the normal vector to the scattering planen

- is the vector in the scattering plane, normal to the initial momentum

; - polarizations of two colliding beams

2

2 22 1 ( ) cos ( cos sin )B Y N B Y NN SS

d dP P A P P A A

dtd dt

Double-spin asymmetry

ANN – polarization normal to the scattering plane

ASS – polarization vector in the scattering plane

No angle dependence - luminosity normalization required !

STAR Probing Odderon

Igor Alekseev (ITEP) for the STAR Collaboration 4

E.Leader, T.L.Trueman“The Odderon and spin dependence of high-energy proton-proton scattering”,

PR D61, 077504 (2000)

•Pomeron and Odderon are 90deg out of phase

•5% Odderon contribution → 5% ANN

T.L.Trueman

“Double-spin asymmetry in elastic proton-proton scattering as a probe

for the Odderon”, arXiv:hep-ph/0604153v1 (2006)

Regge poles only

Regge poles and cuts

No odderon

Odderon spin-flip coupling ≈ Pomeron spin-flip coupling

Odderon spin-flip coupling ≈ ρ spin-flip coupling

S=200 GeV2

S=2002 GeV2

S=5002 GeV2

100x ANN(No Odderon)

ANN(Odderon flip=ρ flip)

S=200 GeV2

STAR

Igor Alekseev (ITEP) for the STAR Collaboration 55

HJet@RHICPRD79(09)094014

pp2pp@RHICs = 200 GeVPLB647(07)98

ANN : existing data

HJet@RHICPRD79(09)094014

STAR

Both beams were transversely polarized with 60% polarization.

Excellent detector performance – nearly 100% efficiency and only 5 dead/noisy strips per ~14000 active strips.

2π acceptance in φ. Ideal optics β*= 21m and terms

other than LEFF in the transport matrix were very small.

0.003 < -t < 0.03 A good statistics of about 2·107

elastic events with background less than 1%.

Experimental conditions

Igor Alekseev (ITEP) for the STAR Collaboration 6

STAR detector

Horz. RPs

Vert. RPs Vert. RPs

Horz. RPs

Detector Package

PBPY= 0.372±0.052 *Averaged for our fills from the official Run’09 CNI polarimeter results

https://wiki.bnl.gov/rhicspin/Results

Normalization using beam beam counters – critical issue: see presentation by D. Svirida for details

STAR

Double spin asymmetries analysis uses the same set of elastic events with the same cuts. Single spin asymmetries from current analysis repeated those of published result which was

based on square root formula

Single spin asymmetry result

Igor Alekseev (ITEP) for the STAR Collaboration 7

Phys. Lett. B719 (2013) 62-69

STAR

Raw asymmetry

Igor Alekseev (ITEP) for the STAR Collaboration 8

2 2( ) ( cos sin )

( ( ) ( )) ( ( ) ( ))

( ( ) ( )) ( ( ) ( ))

NN B Y NN SSP P A A

K K K K

K K K K

STAR PRELIMINARYOnly statistical errors shown

STAR r2 and r4

Igor Alekseev (ITEP) for the STAR Collaboration 99

Error bars represent statistical only errors (boxes) and total uncorrelated errors including those due to background subtraction.Accurate formulas from:

N.H. Buttimore et al.

[hep-ph/9901339] r5 taken from AN result from the same data sample at STAR:

Phys. Lett. B719 (2013) 62-69Grey bar – common systematic uncertainty on (ANN+ASS)/2 due to luminosity normalization(ANN+ASS)/2 is consistent with Hjet data, but higher precision.Formally, r4 can be obtained from the fit, yet r4=0 is not a bad hypothesis

(ANN-ASS)/2 points average to a good zero

Fit r2

Fit r4

STAR PRELIMINARY

STAROne-σ ellipses

Igor Alekseev (ITEP) for the STAR Collaboration 1010

STAR PRELIMINARY

Im r2 is well constrained – small negative value. Re r2 is compatible with 0

r4 components are only 1.2σ and 1.7σ from 0 Re r4 is large because of kinematic factor m2/t. Assumption r4=0 is reasonable

As a conclusion

The most precise measurement of the transverse double spin asymmetries in the CNI region at collider energies performed. Over the whole interval ANN and ASS are small and (ANN+ASS)/2= –0.0051±0.0006(stat)±0.0012(sys)

(ANN-ASS)/2= 0.0005±0.0009(stat)±0.0006(sys)

Our result differs from the current theory predictions and could indicate non-zero Odderon spin-flip coupling.