SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM COMPASS

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SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM
COMPASS
Franco BradamanteUniversity of Trieste and INFN
Trieste
on behalf of the COMPASS Collaboration
Kyoto, October 3, 2006
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THE SPECTROMETER

• two stages spectrometer
• Large Angle Spectrometer (SM1)
• Small Angle Spectrometer (SM2)
• tracking, calorimetry, PID

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

• high energy beam
• broad kinematical range
• large angular acceptance

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THE RICH DETECTOR
THE TARGET SYSTEM
solid target operated in frozen spin mode

• threshold momenta
• pp 2 GeV/c
• pK 9 GeV/c
• pP 17 GeV/c

fully efficient for transverse data in 2003 and
2004
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DATA TAKING 2002-2004

• transversely polarised deuteron target
  20 of the running time

Collins and Sivers asymmetries published results
2002 prel results 2002-2004 with RICH
PID Two hadron asymmetries prel results
2002-2004 ? polarimetry prel results 2002-2003
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SINGLE HADRON ASYMMETRIES
unpol B and T
transvely polarised target

• SIDIS cross-section

long pol B and/or T

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

?s p - ?s
FS
at leading order
Collins
Sivers
beam polarization
independent angles ? independent extraction of
the asymmetries
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EVENT SELECTION
DIS events Q2 gt 1 GeV2 W2 gt 25 GeV2 0.1 lt y lt
0.9 hadrons pht gt 0.1 GeV/c z gt 0.2
(all h) z gt 0.25 (leading h)
?Q2? 2.4 (GeV/c)2
?W? 9.4 GeV/c2
?xBj? ? 0.035
2002 data
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ASYMMETRIES 2003-2004 vs 2002
results from 2003-2004 data released in April
(DIS2006) comparison with the published 2002 data
PRL 94 (2005) 202002

• increase in statistics by a factor of 7!

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COLLINS ASYMMETRIES 2002-2004

• small errors (1)
• small asymmetries

• cancellation between p and n
• (lh and ah)

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COLLINS ASYMMETRY
results from model calculations

• good fits to the proton HERMES DATA with
  Collins FF favoured unfavored, at variance
  with unpolarised case
• comparison with BELLE DATA ok universality
  of the Collins effect, hints on ?Tu
• comparison with the deuteron COMPASS 2002 DATA
  ok ?Td unconstrained

comparison with the new COMPASS 2002-2004 data

• agreement not so good as with COMPASS 2002 data
• from a global fit of all the present data
  probably stronger constrains on the transversity
  PDFs and in particular on ?Td (x)

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SIVERS ASYMMETRIES 2002-2004

• small errors (1)
• small asymmetries

• cancellation between p and n
• (lh and ah)

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What have we learnt over the past 2 years ?
Sivers Asymmetry

comparison of the same calculations with the
COMPASS 2002-04 data
preliminary COMPASS 2002-2004
preliminary COMPASS 2002-2004
Collins et al
Vogelsang and Yuan
preliminary COMPASS 2002-2004

• as in the Collins case, agreement not always so
  good as for 2002 data
• from a global fit of the present HERMES and
  COMPASS data probably stronger constrains on the
  Sivers DFs

Anselmino et al
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p, K ASYMMETRIES 2003-2004
same DIS event selection and hadron definition as
before plus PID based on RICH response
final sample
additional systematic tests RICH stability ?
systematic errors smaller than statistical ones
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p, K SIVERS ASYMMETRIES 2003-2004
GPD2006
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p, K Collins Asymmetries 2003-2004
GPD2006
again, difficult to see an effect
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SUMMARY

• New precise DIS deuteron data from COMPASS are
  now available
• In all the channels investigated in so far
• the measured deuteron asymmetries are very small,
  compatible with zero

Collins and Sivers asymmetries for positive
and negative hadrons, p, K
PRESENT PICTURE Collins u quark dominance
DT0D(fav.) - DT0D(unfav) for u
quark DTd from global analysis
(NEW COMPASS DATA) Sivers D0Tu - D0Td
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One of the most recent citations

• COMPASS 2002 data
• Evidence for the Absence of Gluon Orbital
  Angular Momentum in the Nucleon
• S.J. Brodsky, S. Gardner
• SLAC-PUB-12062, Aug 2006. Subm. Phys.Lett.B,
  hep-ph/0608219

• Due to the smallness of the anomalous magnetic
  moment of the
• deuteron the orbital motion of the quarks should
  not contribute to
• the Sivers SSA of the deuteron. Thus

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• riserva

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COLLINS ASYMMETRY
important theoretical work on the interpretation
of the data assumptions on ?Tq and fit of
HERMES 2002-2004 data to exctract the
Collins FF
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SIVERS ASYMMETRY
important theoretical work on the interpretation
of the data use of the HERMES 2002-2004
data to exctract/check the Sivers DF