Single-spin asymmetry in interference fragmentation on a transversely polarized

hydrogen target at HERMES

Tomohiro KobayashiTokyo Institute of Technology

Semi-Inclusive Reactions (SIR) Workshop 2005 (May 19th)

Contents• Transversity & Semi-inclusive DIS with transversely polarized target• SSA in HERMES (data taking period : 2002~2004)• Conclusion

Motivation

Understand spin structure of the nucleon

Quark transversity is one of the important aspects of relativistic nature of quarks inside the nucleon.

Access to transversity

1 hadron semi-inclusive DIS

]P̂k[~ 11hT)sin( Hh

MIA S

UT

1H : Collins FF (chiral odd)

1h

[...]kz

Ppkp[...] Th

T)2(

T2

T2

ddI

2 hadron semi-inclusive DIS

Access to transversity

2 hadron semi-inclusive DIS

1h

hpA. Bacchetta and M. Radici, Proceedings of DIS’2004 (2004), hep-ph/0407345

： Interference FF (chiral odd)1H

GAgHhA LULR

~~ 11sin

11sin)sin( ~ HhA SR

UT

are not convoluted with .11Hh TT k ,p

Longitudinally polarized deuterium target

UTULUL AAA θsinθcos v.r.t. virtual photon directionw.r.t. beam direction

1111

sin

~ HBhGAgHhA

L

ULR

First measurement of Small asymmetry is observed

XPPkedke )()()()( 21

RULA sin

, s-p wave interference in ππ scattering theory

R. L. Jaffe, Xuemin Jin, and Jian Tan, Phys. Rev. Lett. 80, 1166 (1998)

P. Estabrooks and A. D. Martin, Nucl. Phys. B79, 301 (1974)

)()sin(sinsin),( ',11010

2,1 zHMzH spsp

scatteringnp using analysisshift phase

FF ceInterferen of dependenceM),(cos),(),cos,( 2,

12,

12

1 MzHMzHMzH ppsp

1H

dependenceM

Partial wave expansion

The sign changes at 0 MM

Spectator model for fragmentationRadici et al., hep/ph-0110252

No strong dependence.M

SSA in sin)sin( SRUTA

Event selection

Kinematic cuts : ≥ 1 GeV2

≥ 4 GeV2

≥ 0.023 0.1 < < 0.85 > 2.5 GeV (for DIS lepton) > 1 GeV (for Hadron)

> 2 GeV, whereE

ppyxW

Q

track

track

2

2

p

px

MMM

E2

22

Xeep SIDIS events with at least pion pair( ) appeared were analyzed.

,

To cut exclusive channel.

Data set : 2002~2004

Evaluate

DISDIS

DISDIS

/),,(/),,(/),,(/),,(1),,(NNNNNNNN

SA

SRSR

SRSR

TSRUT

UTA

0.54.75 TSwhere is the average target polarization. ( )TS

,...sin)sin(~ 11 HhSR

What is measured

)sin(10 SRaa

Fit

with

sin( )

1sin

0.040 0.009

R SUTA a

)(vs.sin SRUTA

009.0040.0006.0000.0

1

0

aa

11sin )sin(~ HhSRAUT

0.51 < < 0.97 GeVM011 Hh

sin)sin(ofdependence SRUTAM

Sign of the asymmetry does not change around

0 MM

sin)sin(10 SRaa

Fit

with 11sin)sin(~ HhA SRUT

1sin)sin( aA SR

UT

binning :0.25, 0.40, 0.55, 0.77, 2.0 [GeV]

M

Conclusion

• Transversity and interference fragmentation function are related to SSA :

• HERMES has been taking data with transversely polarized hydrogen target since 2002.

• SIDIS events with at least two hadrons ( ) were analyzed.

• Asymmetry of order 4% is observed.

• Around , asymmetry becomes large.

• No sign change is observed.

,

11sin)sin( HhA SR

UT

009.0040.0sin

)sin(

SRUTA

0 MM

Outlook

•3.5 M DIS evens in 2002~2004.

•3~3.5 M events is expected in 2005.

backup

spectrumM

With or without cut]GeV[2.0E

p

px

MMM

E2

22

spectrumz

With or without cut]GeV[2.0E

p

px

MMM

E2

22

double spin asymmetry

Beam polarization don’t affect to the asymmetry

sin)sin(sin)sin( SRSR cba

Fit

for both beam polarization.

11sin)sin(~ HhA SRUT

Beam polarization (%)

0Pfor 012.0040.0 0Pfor 011.0041.0

beam

beam

sin)sin(

bA SRUT

No double spin asymmetry

Angle distribution

Correlation in the distribution due to the HERMES acceptance and spectrometer magnet field.

) ,( SR

Monte Carlo studies show : no face asymmetriesDue to those correlations

]rad[R

]rad[s

) ,( SR

Single spin asymmetryXPPkedke )()()()( 21

SS

Target spin vector

Lepton scatteringplane

Hadron scattering plane

...cossin)( 10 RRR baaf fit with 1sin aA RUL ⇒

RULA sin