Measurements of Transverse Spin Effects in SIDIS

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Measurements of Transverse Spin Effects in SIDIS
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Outlook

• Introduction
• Asymmetries
• Transversity DF
• from Single Hadron
• from Two Hadrons
• from Hyperons
• Sivers DF
• Other TMD
• Near/Far Future
• Conclusions

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What you will w/not find

• Review of all Deuteron Results
• w/not 2007 proton results
• They are on their way
• ½ PB of data processed
• Data quality checks ongoing
• Late Spring

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Spectrometer

• longitudinally polarised muon beam
• longitudinally or transversely polarised
  target
• momentum and calorimetry measurements
• particle identification

MuonWall
SM2
E/HCAL
E/HCAL
Straws SDC MWPC W45
SciFi Silicon Micromegas GEMs
SM1
Polarised Target
Muon Wall
RICH
m beam

• Beam
• Luminosity 5 . 1032 cm-2 s-1
• intensity 2 108 µ/spill
  (4.8s/16.8s)
• momentum 160 GeV/c

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Target
solid state target operated in frozen spin mode

• 2002-2004 6LiD
• dilution factor f 0.38 polarization PT
  5020 of the time transversely
  polarised
• during data taking with
• transverse polarization
• dipole field always ?
• polarization reversal in the 2 cells after 5
  days

two 60 cm long cells with opposite polarisation
(systematics)
dN/dz
4000
2000
zvtx (mm)
0
0
-1000
1000
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Event Selection

• DIS cuts
• Q2 gt 1 (GeV/c)2
• 0.1 lt y lt 0.9
• W gt 5 GeV/c2
• All hadron selection
• z gt 0.20
• pt gt 0.1 GeV/c
• Plus for leading hadron
• zl gt 0.25
• No signals in the CALOs from neutral particles
  with z gt zl

Statistics 2002 - 2004 8.5 106 positive
hadrons 7.0 106 negative hadrons
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Hadron Identification

• Hadron identification is based on RICH response
  several studies performed on the stability in
  time of the detector.
• Cherenkov thresholds p 2 GeV/c
• K 9
  GeV/c
• p 17
  GeV/c
• 2 s p/K separation at 43 GeV/c
• In the leading hadron sample
• 76 pions
• 12 kaons

positive negative
leading ? 3.4M 2.8M
leading K 0.7M 0.4M
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Kinematics inclusive
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Kinematics - SI
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K0 Reconstruction
Z(V0) Z(prim. vtx.) gt 10 cm ? angle of target
pointing lt 0.01 rad ? Mpp MK0 lt 20 MeV/c² ?
pt, arm gt 0.025 GeV/c ? pt, K0 gt 0.1 GeV/c
K0 target pointing
Armenteros
S/B 15
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TRANSVERSITY
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Transversity DF
quv, dv, qsea quark with spin parallel to the
nucleon spin in a transversely polarised nucleon
DTq(x) q??(x) - q??(x) h1q(x), dq(x), dTq(x)

• Properties
• probes the relativistic nature of quark dynamics
• no contribution from the gluons ? simple Q2
  evolution
• Positivity Soffer bound..
• first moments tensor charge.
• sum rule for transverse spinin Parton Model
  framework
• it is related to GPDs
• is chiral-odd decouples from inclusive DIS

Soffer, PRL 74 (1995)
Bakker, Leader, Trueman, PRD 70 (04)
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How To
the Transversity DF is chiral-odd ?survives
only by the product with another chiral-odd
function can be measured in SIDIS on a
transversely polarised target via quark
polarimetry
L N??l h X Collins Asymmetry (Collins FF)
L N??l L X L polarization (FF of q?? L)
L N??l hh X Two hadrons asymmetry (Interference FF)
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Single hadron asymms.
Collins and Sivers terms in SIDIS cross sections
depend on different combination of angles

• ?C ?h - ?s
• Collins angle
• ?S ?h - ?s Sivers angle

• ?h azimuthal angle of the hadron
• ?s azimuthal angle of the transverse spin of the
  initial quark
• ?s azimuthal angle of the transverse spin of the
  fragmenting quark

?s p - ?s (spin flip)
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Collins Effect
Collins effect a quark with an upward
(downward) polarization, perpendicular to the
motion, prefers to emit the leading meson to the
left (right) side with respect to the quark
direction i.e. the fragmentation function of a
transversely polarized quark has a spin dependent
part And the resulting measured asymmetry
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Unidentified Hadrons

• only statistical errors shown (1), systematic
  errors considerably smaller
• small asymmetries compatible with 0 for both
  and hadrons
• NP B765 (2007) 31-70

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Identified Hadrons
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Naïve Interpretation
(parton model, valence region)

• proton data

? unfavored Collins FF favored Collins FF
at
variance with unpol case u quark dominance (d
quark DF unconstrained)

• deuteron data

some (small) effect expected even if ?
cancellation between ?Tu (x) and ?Td (x)
access to ?Td (x)
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Two Hadrons
z-axis virtual photon direction x-z plane
lepton scattering plane
?R angle between lepton scattering plane
and two-hadron plane
?S azimuthal angle of initial quark
versus lepton scattering plane
?S p - ?S (fragmenting quark)
R
?RS ?R - ?S ?R ?S - p
(A. Bacchetta, M. Radici, hep-ph/0407345)
(X. Artru, hep-ph/0207309)
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Azimuthal Asymmetries
zz1z2
Target single spin asymmetry ARS(x,z,Mh2)
and
N(?RS) Number of events for target
spin up () and down (-)
f Dilution factor 0.38 D Depolarisation
factor D(1-y)/(1-yy2/2) PT Target
polarisation 0.5
Under measurement in ee- (BELLE)
expected to depend on the hadron pair invariant
mass
(X. Artru, hep-ph/0207309)
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Selection

• Hadron selection
• z1,2 gt 0.1 (current fragmentation)
• xF1,2 gt 0.1
• z1z2 lt 0.9 (exclusive rho)
• RICH identification of p, K

• DIS cuts
• Q2 gt 1 GeV2/c2
• 0.1 lt y lt 0.9
• W gt 5 GeV/c2

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Two hadron asymm.s
Expected Small
(Radici/Bacchetta, PRD74(2006)114007)
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Identified 2 Hadrons
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z-order two identified hadrons

• Motivations
• Hadrons with higher relative energy carry more
  information about the fragmenting quark
  polarization
• For leading hadron pairs signal enhancement is
  predicted

PID with 2003-04 rich
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z-order two identified hadrons
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L Polarimetry
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Results
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SIVERS DF
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SIVERS Mechanism

• The Sivers DF is probably the most
  famous between TMDs
• gives a measure of the correlation between the
  transverse momentum and the transverse spin
• Requires final/initial state interactions of the
  struck quark with the spectator system and the
  interference between different helicity Fock
  states to survive time-reversal invariance
• Time-reversal invariance implies
• to be checked
• In SIDIS

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Unidentified hadrons

• only statistical errors shown (1), systematic
  errors considerably smaller
• small asymmetries compatible with 0 for both
  and hadrons
• NP B765 (2007) 31-70

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Identified Hadrons
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Naïve Interpretation

• proton data

asymmetry for p gt 0, asymmetry for p- 0 ?
Sivers DF for d-quark - 2 Sivers DF for
u-quark
the measured asymmetriescompatible with zero
suggest
F. Bradamante
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Small SIVERS on D hint for small Lg
the measured asymmetry on deuteron compatible
with zero has been interpreted as Evidence for
the Absence of Gluon Orbital Angular Momentum in
the Nucleon S.J. Brodsky and S. Gardner, PLB643
(2006) 22
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Other TMDs
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Sidis Xsection
From A. Bacchetta et al., JHEP 0702093,2007.
e-Print hep-ph/0611265
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Results - LO
g1T is the only parton DF which is chiral-even,
T-even, leading twist function in addition
to the unpolarised DF and to the helicity DF
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Results - LO
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Transverse Target SSA for exclusive r (Q2gt1)

• Motivations
• Hard exclusive meson production (HEMP) is a way,
  complementary to DVCS, to access GPDs
• Vector mesons Transverse Target Single Spin
  Asymmetry AUT(fh,fS) connected to GPD E
• E allows flip of proton helicity, while quark
  helicity is not flipped ? overall helicity is not
  conserved
• angular momentum conservation implies transfer of
  orbital angular momentum

Ji Sum Rule
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Selection

• Exclusive r
  selection
• only 3 outgoing particles m, p, p-
• 0.01 lt pT2 lt 0.5 (GeV/c)2
• missing energy -2.5 GeVlt Emisslt2.5 GeV
• Inv. Mass -0.3 MeV/c2 lt Mpp Mr lt 0.3 MeV/c2

• Besides standard DIS cuts
• Q2 gt 1 GeV2/c2
• 0.1 lt y lt 0.9
• W gt 5 GeV/c2

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Results
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2007 RUN
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Target in 2007
solid state target operated in frozen spin mode
2007 NH3 dilution factor f 0.14
polarization PT 90
2 ? 3 cells
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Projected errors for full statistics (45x1012 m)
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Summary
precise deuteron data from COMPASS are now
available Collins and Sivers asymmetries h, p,
K other 6 TMDs sin(3fh-fS), sin(fS),
sin(2fh-fS), cos(fh-fS), cos(2fh-fS),
cos(fh) Two hadron asymmetries pp, pK,
KK Transverse Lamba polarization all the
measured deuteron asymmetries are very small, and
compatible with zero COMPASS data on deuteron
allows to determine the d-quark
contribution present phenomenological studies
can describe at the same time the BELLE (FF), the
HERMES (proton) and COMPASS (deuteron)and have
allowed a first extraction of the transversity
distribution DTq At the same way COMPASS and
HERMES data have allowed a first extraction of
the Sivers DF
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Coming Soon

• Deuteron
• Cahn and Boer-Mulders asymmetries ? unpol
• g2
• Proton
• Collins Sivers
• Little further in time all the rest
• Future programs
• Drell-Yan see M. Chiosso talk
• Precision measurement for better flavour
  separation and measurements of first moments

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THATS ALL(FOR NOW!)