Transcript Document

RESULTS FOR
TRANSVERSE SPIN PHYSICS
AT COMPASS
Takahiro Iwata
Yamagata University
on behalf of the COMPASS Collaboration
The 6th Circum-Pan-Pacific Symposium on High Energy Spin Physics,
July 30 - August ２ 2007 @ Vancouver BC Canada
OUTLINE
The COMPASS Experiment
Transverse Spin Physics at COMPASS
Results on:
SIDIS single hadron asymmetries
Collins/Sivers asymmetries
positive and negative hadrons
p±, K±
Two identified hadron asymmetries
pp, pK, KK
Other target transverse spin dependent asymmetries
 Summary
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
THE EXPERIMENTAL SETUP
two stages spectrometer
• Large Angle Spectrometer (SM1)
• Small Angle Spectrometer (SM2)
tracking, calorimetry, PID
SciFi
Silicon
Micromegas
GEMs
Straws
SDC
MWPC
W45
E/HCAL
MuonWall
SM2
E/HCAL
SM1
MuonWall
Polarised Target
RICH
m beam
160GeV,
polarised (PT>50%)
Takahiro Iwata
• high energy beam
• broad kinematical range
• large acceptance
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
THE POLARIZED TARGET SYSTEM
solid target operated in frozen spin mode
– 4He Dilution
refrigerator (T~50mK)
3He
superconductive
Solenoid (2.5 T) Dipole (0.5 T)
dN/dz
4000
2000
0
two 60 cm long cells
with opposite polarization (systematics)
-1000
0
1000
zvtx (mm)
THE RICH DETECTOR
threshold momenta
● p = 2 GeV/c
p
● p = 9 GeV/c
K
● p =17 GeV/c
P
5m
photon
detectors
C4F10
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
DATA TAKING HISTORY 2002 – 2007
2002 160 GeV m beam & 6LiD Long./Trans. Pol. PT (~ 80/20)
2003 ditto
&
(~ 80/20)
2004 ditto
&
(~ 80/20)
Today’s Talk
2004 pilot run with hadron beam ( for hadron program)
2005 NO SPS beam (several upgrades)
2006 160 GeV m beam & 6LiD Long. Pol.
2007 ditto
Takahiro Iwata
& NH3 Trans. / Long. Pol. PT
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TRANSVERSE SPIN PHYSICS AT COMPASS
Transversity
quark with spin parallel to the
nucleon spin in a transversely
polarized nucleon
DTq(x) = q↑↑(x) - q↑↓(x)
h1q(x),
dq(x),
dTq(x)
from Collins asym. In single hadron production of SIDIS,
and two hadron asym. , L transverse polarization
TMD asymmetries
an intrinsic asymmetry in the parton transverse
momentum distribution induced by the nucleon spin
related to orbital angular momentum of quarks
from Sivers asym. in SIDIS single hadron production
and other transverse spin dependent asymmetries
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
SIDIS SINGLE HADRON ASYMMETRIES
angular distribution of a hadron wrt nucleon spin
Collins
Sivers
dσSIDIS  1 a1  sinFC  a2  sinFS  ...
fS = azim. angle of initial quark spin
fS’ = azim. angle of struck quark spin
fS= p- fS’ （due to helicity conservation)
fh = azim. angle of produced hadron
• Collins angle: Azim. angle of a
initial quark spin (nucleon spin)
struck quark spin
hadron wrt the struck quark spin
FC = fh - fS’ (= fh +fS- p)
Scattering plane
• Sivers angle: Azim. angle of a
hadron wrt the initial quark spin
(=nucleon spin)
FS= fh - fS
hadron
quark direction
（Breit frame）
modulation of angular distribution
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
COLLINS & SIVERS ASYMMETRIES
Collins Asymmetry
N h  FC   N h0   1  PT  DNN  y   AColl  sinFC 
± refer to the opposite orientation of the transverse spin of the nucleon
PT is the target polarisation;
DNN is the transverse spin transfer coefficient initial  struck quark, given by QED
Transvesity
A Coll 
2
0 h
e

Δ
q

Δ
q q T TDq
2
h
e

q

D
q q
q
Collins
fragmentation
function
non-zero Collins function gives transversity
Sivers Asymmetry
Nh  FS   Nh0   1  PT  ASiv  sinFS 
Sivers PDF (TMD)
A Siv 
Takahiro Iwata
2
T
h
e

Δ
q

D
q q 0 q
2
h
e

q

D
q q
q
orbital angular
momentum of quarks
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
DISTRIBUTIONS & EVENT SELECTION
2004 leading hadron
DIS events
Q2 > (1 GeV/c)2
W2 > 25 GeV2
0.1 < y < 0.9
hadrons
pht > 0.1 GeV/c
z > 0.2
(all h)
z > 0.25
(leading h)
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
COLLINS ASYMMETRIES
2002-2004
deuteron target
Published: NP B765 (2007) 31-70
• small errors (~1%)
• small asymmetries
2002 data [ PRL94 (2005) 202002] confirmed
• cancellation between p and n
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
HADRON IDENTIFICATION
same DIS event selection and hadron definition as
before
Threshold
Plus PID based on RICH
pions
~ 3 GeV/c
kaons ~ 9 GeV/c
protons ~ 17 GeV/c
hadrons
100%
no RICH information
after all cuts
pions
77%
kaons
12%
protons
final sample positive
Takahiro Iwata
all leading
5%
negative
3%
all
leading
pions
5.3 M
3.4 M
pions
4.2 M
2.8 M
kaons
0.9 M
0.7 M
kaons
0.6 M
0.4 M
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
p±, K± Collins Asymmetries
2003-2004
deuteron target
again, difficult to see an effect …
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
INTERPRETATION (COLLINS ASYMMETRY)
In valence region, neglecting sea quark contribution
HERMES proton data
p ,p
AColl
4DT uv DT0 D fav  DT dv DT0 Dunfav

4uv D fav  dv Dunfav
DT0 Dunfav  DTo Dfav
Non zero Collins asymmetry observed
p ,p
AColl
0

4DT uv DT0 Dunfav  DT dv DT0 D fav
4uv Dunfav  dv D fav
0
u-quark dominance
(d-quark not constrained)
COMPASS deuteron data
sensitive to both u- and d-quark
deut ,p 
Coll
A
with
0
3 DT uv  DT dv DT D fav
0
7 uv  dv
D fav
Dunfav  0.5Dfav
deut ,p 
Coll
A
0
3 DT uv  DT dv DT D fav

0
4.5
uv
D fav
DT0 Dunfav  DTo Dfav dv
DT dv  DT uv
0.5uv
opposite sign
Transversities for u- & d-quark
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
SIVERS ASYMMETRIES
2002-2004
deuteron target
Published in NP B765 (2007) 31-70
• small errors (~1%)
• small asymmetries
2002 data [ PRL94 (2005) 202002] confirmed
• cancellation between p and n
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
p±, K± SIVERS ASYMMETRIES 2003-2004
deuteron target
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
INTERPRETATION (SIVERS ASYMMETRY)
In valence region, neglecting sea quark contribution
HERMES proton data
p ,p
ASiv
4DT0 uv D fav  DT0 dv Dunfav

4uv D fav  dv Dunfav
with
p ,p
ASiv
0
Dunfav  0.5Dfav
dv

4DT0 uv Dunfav  DT0 dv D fav
4uv Dunfav  dv D fav
0
DT0 dv  2DT0 uv
0.5uv
COMPASS deuteron data
deut ,p
ASiv

deut ,p
ASiv

DT0 uv  DT0 dv
uv  dv
0
DT0 dv  DT0 uv
Consistent with models based on the HERMES data
J.C.Collins et al., Phys.Rev.D73(2006)01402,
M.Anselmino et al.,Phys.Rev.D72(2005)054028,
W.Vogelsang and Yuan,Phys.Rev.D72(2005)054028
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TWO HADRON ASYMMETRIES
modulation of the number of events in fRS
AUT (fRS ) 
N (fRS ) / N  N (fRS ) / N
N  (fRS ) / N  N  (fRS ) / N


tot

tot

sinfRS
 AUT
sin( fRS )

tot

tot
fS = angle of initial quark spin (=target spin)
fS’ = angle of final (struck) quark spin
fS= p - fS’
（due to helicity conservation)
fR = angle of two-hadron plane
fRS =fR –fS’ = fR +fS- p
transversity
sinfRS
AUT
Hi
h
f
i
e D q  x  H  z, M 


 e q  x  D  z, M 
2
i i
h
T
2
i i i
i
h
i
h
l-l’
2
h
i
fRS
2
h
 z, M  : interference
2
h
fragmentation
function( presently
unknown)
initial quark spin
Trento conventions
see hep-ph/0407345
Takahiro Iwata
quark direction
Breit frame
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TWO IDENTIFIED HADRON ASYMMETRIES
Event selection
DIS:
Hadrons:
• Q2>1GeV2
• positive(h1) & negative(h2) hadrons
• 0.1<y<0.9
• z= zh1+zh2 < 0.9 ( remove diffractiv r)
• W>5GeV
• PID by RICH
• Pth(p)+0.5 GeV/c < Pp < 50 GeV/c
• Pth(K)+1.0 GeV/c < PK < 50 GeV/c
Statistics from 2003 & 2004 data
p+ p- pairs 3.7 M events
p+ K- pairs 0.24 M events
K+ p- pairs 0.30 M events
K+ K- pairs 0.086 M events
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
p+ p- ASYMMETRIES
r
3.7 M (70%)
r
z=z1+z2
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
K+ p- ASYMMETRIES
K*
0.3 M (5.8%)
K*
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
p+ K- ASYMMETRIES
K*
0.25 M (4.5%)
K*
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
K+ K- ASYMMETRIES
f
0.09 M (1.6%)
f
small asymmetries compatible with 0
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TRANSVERSE SPIN DEPENDENT ASYMMETRIES.
SIDIS (1-hadron) crosssection based on
one photon exchange
18 structure functions
Azimuthal modulation
genrated by 14 functions
2 pol. independent
1 beam pol. dependent
2 target longitudinal pol. dependent
1 beam + target longitudinal
pol. dependent
5 target transverse pol. dependent
Sivers
3 double beam + target transverse
pol. dependent
‘Collins’
Asymmetries
wi fh ,fS 
BT
A
Beam
FBTi  h S 

FUU ,T
w f ,f
Target
Virtual photon
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
ASYMMETRIES I
sin(3fh fs )
AUT
 h1Tq  H1qh
Interpretation in QCD parton model
TMD
leading twist
sin(fs )
AUT
  M Q   h1q  H1qh  f1T q  D1hq 
Takahiro Iwata
Sivers + Collins
subleading
twist
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
ASYMMETRIES II
Sivers
sin(2fh fs )
AUT
  M Q   h1Tq  H1qh  f1T q  D1hq 
TMD
cos(fh fs )
ALT
 g1qT  D1hq
Takahiro Iwata
long.beam & trans. target
subleading
twist
leading twist
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
ASYMMETRIES III
cos(2fh fs )
LT
A
  M Q g  D
q
1T
h
1q
long. beam & trans. target
subleading
twist
cos(fs )
ALT
  M Q g1qT  D1hq
long. beam & trans. target
subleading
twist
again cancellation between the p and n for the deuteron ?
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
SUMMARY
New precise deuteron data from COMPASS are available
Collins and Sivers asymmetries for h±, p±, K±
(published : h±2002: PRL94(2005)202002,
h±2002-2004: NPB765(2007)31)
Two identified hadron asymmetries
All other target transverse spin dependent asymmetries
All the measured asymmetries are very small,
compatible with zero
PRESENT PICTURE
Takahiro Iwata
Collins:
DT dv  DT uv
from COMPASS
Sivers:
DT0 dv  DT0 uv
from COMPASS
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
OUTLOOK
near future: COMPASS will complete the analysis of the recorded
deuteron data
 K0 asymmetries
 exclusive r asymmetries on transversely polarised target  GPD E
 transverse effects from longitudinal data
 Cahn and Boer-Mulders effect
2007: COMPASS data available with a transversely polarised proton
target (NH3)
with 50 days expected , same precision at small x as for deuteron,
better at “large” x for the new PT magnet
on a longer time scale:
good perspective for
a measurement of polarized Drell-Yan process in COMPASS to
study transversity & Sivers & Boer-Mulders PDFs
and further measurements of transverse spin effects in SIDIS
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TRANSVERSE MOMENTUM DEPENDENT PDFs
Nucleon
long. pol.
unpol.
unpol.
f1 ( q)
number
density
Nucleon
Parton
long. pol.
Quark
trans. pol.
h1
BoerMulders
kT
trans. pol.

1T
Sivers
f
g1L ( Dq)
kT
T-odd
helicity
g1T
kT
h1 ( DT q)transversity
survive after
integration over kT
h1L
kT
h1T
kT
T-odd
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
L TRANSVERSE POLARIZATION
Transversity
 e Δ q x  Δ D  z
= fP D  y 
 e q xD  z
2
q
Λ
PT,ex
p
T
T
2
q
Λ /q
q
T
q
m
L
Λ /q
PT : target polarization;
f : target dilution factor
D(y): transverse spin transfer
coefficient initial  struck quark,
given by QED
p
p
PL  PL
 
PL  PL
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
L TRANSVERSE POLARIZATION
systematic errors not larger than statistical errors
RICH ID not used yet
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
RUN WITH TRANSVERSE POL. TARGET
transversely polarised deuteron target
~ 20% of the running time
2002
11 days of data taking,
2003
9 days of data taking,
2004
14 days of data taking,
DIS
events
(106)
2 periods
1 period
2 periods
2)
trigger
(large
x,
Q
Collins and Sivers
asymmetries
DAQ, on line filter
published results 2002
prel results 2002-2004
with RICH PID
Two hadron asymmetries
prel results 2002-2004
Λ polarimetry
prel results 2002-2003
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
COLLINS ASYMMETRY & GLOBAL FIT
• SIDIS (deuteron COMPASS/ proton HERMES) & Belle data
GLOBAL FIT
Ｂy Anselmino et al.,
PRD 75,054032(2007)
PRESENT PICTURE
DT0D(fav.) ~ - DT0D(unfav)
DTd not well constrained
from the global fit
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
SIVERS ASYMMETRIES & MODELS
model calculations to be compared with the COMPASS 2002-04 data
preliminary COMPASS 2002-2004
Vogelsang and Yuan
preliminary COMPASS 2002-2004
preliminary COMPASS 2002-2004
Collins et al
PRESENT PICTURE
Δ 0Tu  - Δ 0T d
Anselmino et al
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TWO HADRON ASYMMETRIES (all hadrons)
sinfRS
AUT
ARS =
DNN  f  PT
DNN : transverse spin transfer
coefficient initial  struck quark
f : target dilution factor
PT : target polarization;
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007
TWO HADRON ASYMMETRIES
z ordered pairs
Takahiro Iwata
Pan-Pacific 2007 @Vancouver, July 30 - Aug. 2 2007