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SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM COMPASS

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Franco Bradamante. good fits to the proton HERMES DATA with ... Franco Bradamante. comparison of the same calculations with the COMPASS 2002-04 data ... – PowerPoint PPT presentation

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Title: SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM COMPASS


1
SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM
COMPASS
Franco BradamanteUniversity of Trieste and INFN
Trieste
on behalf of the COMPASS Collaboration
Kyoto, October 3, 2006
2
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

3
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
4
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
5
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
6
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
7
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!

8
COLLINS ASYMMETRIES 2002-2004
  • small errors (1)
  • small asymmetries
  • cancellation between p and n
  • (lh and ah)

9
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)

10
SIVERS ASYMMETRIES 2002-2004
  • small errors (1)
  • small asymmetries
  • cancellation between p and n
  • (lh and ah)

11
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
12
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
13
p, K SIVERS ASYMMETRIES 2003-2004
GPD2006
14
p, K Collins Asymmetries 2003-2004
GPD2006
again, difficult to see an effect
15
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
16
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

17
  • riserva

18
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
19
SIVERS ASYMMETRY
important theoretical work on the interpretation
of the data use of the HERMES 2002-2004
data to exctract/check the Sivers DF
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