Title: SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM COMPASS
1SINGLE HADRON TRANSVERSE SPIN ASYMMETRIES FROM
COMPASS
Franco BradamanteUniversity of Trieste and INFN
Trieste
on behalf of the COMPASS Collaboration
Kyoto, October 3, 2006
2THE 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
3THE 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
4DATA 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
5SINGLE HADRON ASYMMETRIES
unpol B and T
transvely polarised target
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
6EVENT 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
7ASYMMETRIES 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!
8COLLINS ASYMMETRIES 2002-2004
- small errors (1)
- small asymmetries
- cancellation between p and n
- (lh and ah)
9COLLINS 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)
10SIVERS ASYMMETRIES 2002-2004
- small errors (1)
- small asymmetries
- cancellation between p and n
- (lh and ah)
11What 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
12p, 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
13p, K SIVERS ASYMMETRIES 2003-2004
GPD2006
14p, K Collins Asymmetries 2003-2004
GPD2006
again, difficult to see an effect
15SUMMARY
- 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
16One 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 18COLLINS 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
19SIVERS ASYMMETRY
important theoretical work on the interpretation
of the data use of the HERMES 2002-2004
data to exctract/check the Sivers DF