single-spin asymmetry in interference fragmentation on a transversely polarized hydrogen target at...
DESCRIPTION
Access to transversity 1 hadron semi-inclusive DIS : Collins FF (chiral odd) 2 hadron semi-inclusive DISTRANSCRIPT
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