1. Measurements of Transverse Spin Effects in SIDIS

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

3. 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

4. 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 cm-2 s-1
intensity µ+/spill (4.8s/16.8s)
momentum GeV/c

5. Target solid state target operated in frozen spin mode 2002-2004: 6LiD
superconductive
Solenoid (2.5 T)
3He – 4He Dilution
refrigerator (T~50mK)
Dipole (0.5 T)
solid state target operated in frozen spin mode
: 6LiD
dilution factor f = 0.38 polarization PT = 50% ~20% 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)
-1000
1000

6. Event Selection DIS cuts: Q2 > 1 (GeV/c)2 Statistics 2002 - 2004:
0.1 < y < 0.9
W > 5 GeV/c2
All hadron selection:
z > 0.20
pt > 0.1 GeV/c
Plus for leading hadron:
zl > 0.25
No signals in the CALOs from neutral particles with z > zl
Statistics :
8.5 * 106 positive hadrons
7.0 * 106 negative hadrons

7. Hadron Identification
Hadron identification is based on RICH response: several studies performed on the stability in time of the detector.
Cherenkov thresholds: π ~ 2 GeV/c
K ~ 9 GeV/c
p ~ 17 GeV/c
2 σ π/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

8. Kinematics – inclusive

9. Kinematics - SI

10. K0 Reconstruction Z(V0) – Z(prim. vtx.) > 10 cm
● angle of target pointing < 0.01 rad
● |Mpp– MK0| < 20 MeV/c²
● pt, arm > GeV/c
● pt, K0 > 0.1 GeV/c
K0 target pointing
Armenteros
S/B ~ 15

11. TRANSVERSITY

12. Bakker, Leader, Trueman, PRD 70 (04)
Transversity DF
q=uv, 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 spin in Parton Model framework…………
it is related to GPD’s
is chiral-odd: decouples from inclusive DIS
Soffer, PRL 74 (1995)
Bakker, Leader, Trueman, PRD 70 (04)

13. How To L Nl’ h X Collins Asymmetry (Collins FF) L Nl’ L X
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)

14. 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)

15. 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

16. 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]

17. Identified Hadrons

18. Naïve Interpretation proton data
(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
refs!
some (small) effect expected even if
 cancellation between Tu (x) and Td (x) access to Td (x)
F. Bradamante
Genova, 27 febbraio 2008

19. Two Hadrons R= angle between lepton S= azimuthal angle of initial
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´= π - S (fragmenting quark) R
RS= R - S´
= R + S - π
(A. Bacchetta, M. Radici, hep-ph/ )
(X. Artru, hep-ph/ )

20. Azimuthal Asymmetries
z=z1+z2
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-y+y2/2)
PT: Target polarisation ≈ 0.5
Under measurement
in e+e- (BELLE)
expected to depend on the hadron
pair invariant mass
(X. Artru, hep-ph/ )

21. Selection DIS cuts: Q2 > 1 GeV2/c2 0.1 < y < 0.9
W > 5 GeV/c2
Hadron selection:
z1, > 0.1 (current fragmentation)
xF1,2 > 0.1
z1+z2 < 0.9 (exclusive rho)
RICH identification of π, K

22. Two hadron asymm.s Expected Small
(Radici/Bacchetta, PRD74(2006)114007)

23. Identified 2 Hadrons

24. 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 rich

25. z-order two identified hadrons

26. L Polarimetry

27. Results

28. SIVERS DF

29. 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:

30. 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]

31. Identified Hadrons

32. Naïve Interpretation proton data deuteron data
asymmetry for p+ > 0, asymmetry for p- ≈ 0
 Sivers DF for d-quark ≈ - 2 Sivers DF for u-quark 2
deuteron data
preliminary
the measured asymmetries compatible with zero suggest
F. Bradamante

33. 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

34. Other TMD’s

35. Sidis Xsection From A. Bacchetta et al.,
JHEP 0702:093, e-Print: hep-ph/

36. 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

37. Results - LO

40. Transverse Target SSA for exclusive r (Q2>1)
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

41. Selection Besides standard DIS cuts: Q2 > 1 GeV2/c2
0.1 < y < 0.9
W > 5 GeV/c2
Exclusive r selection:
only 3 outgoing particles m, p+, p-
0.01 < pT2 < 0.5 [(GeV/c)2]
missing energy -2.5 GeV< Emiss<2.5 GeV
Inv. Mass -0.3 MeV/c2 < Mpp – Mr < 0.3 MeV/c2

42. Results

43. 2007 RUN

44. Target in 2007 solid state target operated in frozen spin mode
2007: NH3
dilution factor f = 0.14 polarization PT = 90%
2  3 cells
Beam line
Cavity 1
Cavity 2
Cavity 3
Thermal screen
Microwave power
Coupling hole

45. Projected errors for full statistics (45x1012 m)

46. 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

47. Coming Soon Future programs 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…

48. THAT’S ALL… (FOR NOW!)