Study of spin structure of nucleon in COMPASS - measurements for transversity with a transversely polarized target

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Study 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
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1. 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)
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--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
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?Compass 6LiD Polarized target?
Dynamic Nuclear Polarization Dilution factor
40 Maximum Polarization57
Longitudinal orientation
beam
Transverse orientation
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Data 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
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2. Transversity measurement

• (0) Transversity introduction
• (1) Transversity 1-hadron asymmetries
• ( Collins Sivers asymmetries)
• (2) Transversity 2-hadron correlation asymmetry
• (3) Transversity L polarimetry

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What 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
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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

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Collins 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)
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Collins 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
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Event selection for muons
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Event selction cont. for hadrons
zgt0.2 for all hadrons
for leading hadrons
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Collins 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
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Collins 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
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Collins, Sivers asymmetries
PID by RICH
All hadron zgt0.2
Leading hadron zgt0.25
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(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
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Two 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
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Event 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.
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2-hadron asymmetry (2002-2004 data)
very small or compatible to zero
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Leading Sub-Leading hadron pairs selections
Other pairs and other combinations analysis
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(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.
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L polarimetry event selection
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L polarizarion
L polarizarion
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3 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

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(No Transcript)
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x vs Q2 distribution
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Comparison 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.
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Comparison of COMPASS 2003-2004 results with
HERMES ones.
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Collins 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
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Collins 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
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COMPASS 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