Title: Study of spin structure of nucleon in COMPASS - measurements for transversity with a transversely polarized target
1Study of spin structure of nucleon in COMPASS -
measurements for transversity with a
transversely polarized target
T. Matsuda Uni. of Miyazaki, Japan on behalf
of the COMPASS collaboration
- 1. The COMPASS experiment at CERN
- 2. Transversity measurements
- 1-hadron asymmetries
- (Collins Sivers asymmetries)
- (2) 2-hadron correlation asymmetry
- (3) L polarimetry
- 3. Summary and outlook
Joint Meeting of Pacific Region Particle Physics
Communities (DPF2006JPS2006) Oct.29-Nov.03,2006
Honolulu, Hawaii, USA
21. The COMPASS experiment at CERN
The aim of COMPASS (muon beam program)
?gluon polarization ?longitudinal quark
polarizations (g1d, ?q flavour
decompositon) ?Transversity
Using Longitudinal PT
Transverse PT
Also Hadron beam program is scheduled.
Data taking History 2002 muon run (Longitudinal
Transverse Pol. Target) 2003 muon run
(Longitudinal Transverse Pol. target) 2004
muon run (LT Pol. Target and Hadron Pilot run)
2006 muon run (only Longitudinal Pol. Target)
(muon beam share longitudinal PT 80,
transeverse PT 20)
3--COMPASS spectrometer--
Beam 160 GeV m 2 . 108
m/spill (4.8s duration/16.2s repetition)
Polarization m Beam 80 LiD Targetlt50gt
m beam
Common Muon and Proton Apparatus for Structure
and Spectroscopy
4?Compass 6LiD Polarized target?
Dynamic Nuclear Polarization Dilution factor
40 Maximum Polarization57
Longitudinal orientation
beam
Transverse orientation
5Data taking by the transversely polarized target
through 2002-2004
2002 11 days of data taking (19), 2 periods
2003 9 days of data taking (14), 1 period
2004 14 days of data taking (24), 2 periods
trigger (large x, Q2)
DAQ, on line filter
Reconstructed DIS events
62. Transversity measurement
- (0) Transversity introduction
- (1) Transversity 1-hadron asymmetries
- ( Collins Sivers asymmetries)
- (2) Transversity 2-hadron correlation asymmetry
- (3) Transversity L polarimetry
7What is Transversity?
- Nucleon structure functions
- are described with 3 functions
- completely at leading twist
- in the parton model.
- Only DTq(x) is unknown !
- Dq(x) is different from DTq(x)
- because rotation does not
- commute with Lorentz boost
- in relativity.
- (Dq(x)DTq(x) in non-relativity)
- Dq(x) is a chirally even function,
- DTq(x) is a chirally odd function (quark
helicity flip).
longitudinal
transverse
DTq(x) does not couple with gluon structure
function, then its evolution with Q2 will be
unlike Dq(x).
(Soffers inequality)
Inqualities
8 How do we measure transversity?
- Quark helicity is conserved in totally
- Inclusive Deep Inelastic Scattering(IDIS)
- and transversity is not measured by IDIS,
- because transversity needs quark helicty flip
- in a helicity base.
- (The quark coupling to gluon and photon preserve
chirality.) - In case of Semi-Inclusive Deep Inelastic
Scattering(SIDIS) - it is possible to measure transversity, because
SIDIS allows both flip and non-flip cases. - Then we measure SIDIS events to study
transversity. - To measure chirally odd quark distribution
functions like transversity, - we need phenomena with chirally odd
fragmentation functions. - At COMPASS we measure transversity by following 3
methods. - (1) Collins asymmetry (Sivers asymmetry is
measured simultaneously.) - (2) 2-hadron correlation asymmetry
- (3) L polarimetry
9Collins and Sivers asymmetries Collins angle
Sivers angle.
- fS azim. angle of inital quark spin
- fS azim. angle of struck quark spin
- fS p- fS (due to helicity conservation)
- fh azim. Angle of leading hadron
Leading hadron
- Collins angle
- (Azimuthal angle of a leading hadron around a
struck quark spin ) - FC fh - fS ( fh fS- p)
- Sivers angle
- (Azimuthal angle of a leading hadron around an
initial quark spin (nucleon spin)) - FS fh - fS
Initial quark spin (Target spin)
Struck quark spin
Scattering plane
quark direction
Leading hadron
(Breit frame)
10Collins asymmerty and Sivers asymmetry
spin independent part
FF
PRL96(2006)232002
Collins FF measured by BELLE
spin dependent part
- If the spin information of the struck quark
propagates to the fragment function, we observe
Collins asymmetry.
Transversity
Collins asymmetry?
Spin-dependent FF
measure
transverse spin transfer coefficient
If quarks move asymmetrically around nucleon spin
orientation, we also observe Sivers asymmetry.
Sivers asymmetry
the effect of quark orbital motion in nucleon
measure
11Event selection for muons
12Event selction cont. for hadrons
zgt0.2 for all hadrons
for leading hadrons
13Collins and Sivers asymmetries for all hadrons
(2002-2004 data)
To be published in NPB hep-ex/0610068
All hadrons (zgt0.2)
Collins asymmetry
very small or compatible to zero
Sivers asymmetry
BlackPositive hadrons
White Negative hadrons
14Collins and Sivers asymmetries for leading
hadrons (2002-2004 data)
To be published in NPB hep-ex/0610068
Leading hadrons (zgt0.25)
Collins asymmetry
very small or compatible to zero
Sivers asymmetry
White Negative hadrons
BlackPositive hadrons
15Collins, Sivers asymmetries
PID by RICH
All hadron zgt0.2
Leading hadron zgt0.25
16(2) SSA in two hadron correlation Which angle we
measure? ? Trento conventions
see hep-ph/0407345
- fS azim. angle of inital quark spin
- fS azim. angle of struck quark spin
- fS p- fS (due to helicity conservation)
- FRS fR - fS ( fR fS- p)
Initial quark spin (Target spin)
Struck quark spin
RT
R(z2P1T-z1P2T)/(z1 z2) PhP1P2 RT is the
component of R Ph . fR azimuthal angle of
RT
quark direction
17Two hadrons correlation --the interference
frgmentaion function--
spin dependent part
spin independent part
FF
zz1z2
also should be measured
- If the spin information of the struck quark
propagates to the interference fragmentation
function, we observe the following asymmetry.
Transversity
measure
interference FF
transverse spin transfer coefficient
unknown at the moment
18Event Selection-two hadron correlation-
For hadron in order to select the current
fragmentation region zh gt 0.1 (then zh1
zh2gt0.2) xfh gt 0.1
For m same as others.
exclusive r band
K0
exclusive r cut
r0
We choose one positve hadron and one negative
hadron.
192-hadron asymmetry (2002-2004 data)
very small or compatible to zero
20Leading Sub-Leading hadron pairs selections
Other pairs and other combinations analysis
21(3) L polarimetry
Struck quark spin
Initial quark spin (Target spin)
Polarized fragmentation function describing the
spin transfer from the quark to the final state
L.
22L polarimetry event selection
23L polarizarion
L polarizarion
243 Summary Outlook
- transversity
- Collins and Sivers SSA shown
- 2002-2004 data (to be published in NPB,
hep-ex/0610068 ) - SSA in two hadron correlation shown
- 2002-2004 data (preliminary)
- L polarization shown 2002-2004 data
(preliminary) - asymmetries are small and compatible with zero.
- Why? Cancellation between proton and neutron
? - Many theoretical works have been done and are
ongoing.
- Next experiment
- Muon program with transverse proton target will
be going on in 2007.--gt complementary and
comparable accuracy to deuteron data expected
25(No Transcript)
26 x vs Q2 distribution
27Comparison of COMPASS 2002 results with HERMES
ones.
(COMPASSdeuteron, HERMESproton)
0.2
0.2
0.1
0.1
0.0
0.0
-0.1
-0.1
-0.2
-0.2
0.2
0.2
0.1
0.1
0.0
0.0
-0.1
-0.1
-0.2
-0.2
x
z
x
z
NoteThe sign of the original definition of
HERMES is opposite.
28Comparison of COMPASS 2003-2004 results with
HERMES ones.
29Collins and Sivers asymmetries forall hadrons
(2002 final results)
PRL 94(2005)202002
All hadrons(zgt0.2)
Collins asymmetry
Sivers asymmetry
White Negative hadrons
BlackPositive hadrons
30Collins and Sivers asymmetries for leading hadron
(2002 final results)
PRL 94(2005)202002
Leading hadrons (zgt0.25)
Collins asymmetry
Sivers asymmetry
White Negative hadrons
BlackPositive hadrons
31COMPASS Collaboration
More than 220 physicists from 30 Institutes
Bielefeld, Bochum, Bonn (ISKP PI), Erlangen,
Freiburg, Heidelberg, Mainz, München (LMU TU)
????? (LPP and LNP), ?????? (INR, LPI, State
University), . ????????
CERN
Helsinki
Warsawa (SINS), Warsawa (TU)
Nagoya/Chubu/Yamagata Miyazaki/KEK
Saclay
Praha
Lisboa
Torino (University,INFN), Trieste (University,INFN
)
Burdwan, Calcutta
Tel Aviv