1. on behalf of the COMPASS collaboration
“Spin physics at COMPASS-II and perspectives of the spin physics at JINR”
D.Peshekhonov
JINR, Dubna
on behalf of the COMPASS collaboration
20 Jule 2010
D.Peshekhonov

2. Plan Introduction - nucleon spin - status of the problem
Spin physics at COMPASS-II
- GPD (DVCS)
- TMD (SIDIS, Drell-Yan)
Spin physics at JINR
- NICA facility
- spin physics program at NICA
20 Jule 2010
D.Peshekhonov

3. Nucleon spin SQM: up and down quarks carry the nucleon spin!
EMC: Quarks spins contribute little (1987/88) ΔΣ = 0.12
20 Jule 2010
D.Peshekhonov

4. Nucleon spin SQM: up and down quarks carry the nucleon spin!
EMC: Quarks spins contribute little (1987/88) ΔΣ = 0.12 s
quarks gluons orbital
small ~0.15
Still poorly
known
unknown
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5. Laboratories & SLAC CERN 49 GeV e– 160/280 GeV µ+ DESY RHIC JLab
GeV pp
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6. & Experiments E80 E130 E142/3 E154/5 EMC SMC COMPASS HERMES
1970
1980
1990
2000
SLAC
CERN
DESY
JLab
RHIC
E80
E130
E142/3 E154/5
EMC
SMC
COMPASS
HERMES
CLAS/HALL-A
Phenix/Star
A worldwide effort since decades
20 Jule 2010
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7. Tools to study the spin structure
DIS
SIDIS pp
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8. Parton Distribution Functions
unpolarised PDF
quark with momentum xP in a nucleon
well known – unpolarized DIS
q(x)
f1q (x)
helicity PDF
quark with spin parallel to the nucleon spin in a longitudinally polarised nucleon
known – polarized DIS
Dq(x)
g1q(x)
Against (в зависимости от) of the beam and target polarizations we have an access to the different PDF
transversity PDF
quark with spin parallel to the nucleon spin in a transversely polarised nucleon
DTq(x)
h1q(x)
chiral odd, poorly known
20 Jule 2010
D.Peshekhonov

9. Structure function g1(x,Q2)
Examples of some results
Structure function g1(x,Q2) p d
very precise data
only COMPASS for x < 0.01 (Q2 > 1)
deuteron data:
ΔΣ= 0.33±0.03±0.05
Δs+Δs = =−0.08±0.01±0.02
(ΔΣ = a0, evol. to Q2=∞)
20 Jule 2010
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10. The quark flavours LO semi-inclusive data analysis
Examples of some results
The quark flavours
LO semi-inclusive data analysis
20 Jule 2010
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11. Bjorken sum rule Examples of some results from neutron β decay
20 Jule 2010
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12. Data not yet in global fits
Examples of some results
Gluon polarization from PGF
Data not yet in global fits
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13. What’s next? Focus on transverse structure of the nucleon COmmon1
COmmon
Muon and
Proton
Apparatus for
Structure and
Spectroscopy
Focus on transverse structure of the nucleon
Transverse size and orbital angular momentum (GPDs) →
→ DVCS & DVMP with μ beams
Transv.Momentum Dependent PDFs:
Sivers, Boer-Mulders, sign change from SIDIS to DY,
additional TMDs (pretzelozity, worm-gear) →
→ Drell-Yan with  beams
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14. Exploring the 3-dimensional phase-space structure of the nucleon24
Exploring the 3-dimensional phase-space
structure of the nucleon
From Wigner phase-space-distributions (Ji, PRL 2003, Belitsky, Ji, Yuan PRD 2004)
We can build « mother-distributions » (Meissner, Metz, Schlegel, JHEP 0908: )
and derive
GPD: Generalised Parton Distribution (position in the transverse plane)
TMD:Transverse Momentum Distribution (momentum in the transv. plane) k
PDF GPD TMD
20 Jule 2010
D.Peshekhonov

15. SPS proton beam: 2.6 1013/spill of 9.6s each 48s, 400 GeV/c
Secondary hadron beams (, K, …): /spill, GeV/c
Tertiary muon beam (80% pol): /spill, GeV/c
-> Luminosity ~ 1032 cm-2 s-1 GPD with + and a 2.5m long LH target
~ cm-2 s-1 DY with - and a 1.1m long NH3 target
LHC
COMPASS
CNGS
Gran Sasso
732 kms
SPS
high energy beams, broad kinematic range, large angular acceptance

16. GPD Functions Allow for a unified description of form factors
and parton distributions
Allow for transverse imaging (nucleon tomography)
and give access to the quark angular momentum
(through E)
Total orbital momentum:
X.-D. Ji, Phys. Rev. Lett. 78 (1997) 610
x is not x-Bjorken
  xB / (2-xB)
20 Jule 2010
D.Peshekhonov

17. Tomographic image of the nucleon
t = −ΔT2
For fixed x GPD H describes the distribution of the
transverse distance b of the constituent carried
fraction x of the longitudinal momentum p from the
center of the nucleon
20 Jule 2010
D.Peshekhonov

18. Experimental requirements for DVCS
μ p  μ’ p  μ’ 
~ 2.5 m Liquid Hydrogen Target
~ 4 m Recoil Proton Detector (RPD)
SM2
ECAL2
SM1
ECAL1
ECALs upgraded
+ ECAL0 before SM1:
increase hermeticity
decrease background
enlarge acceptance μ p’
20 Jule 2010
D.Peshekhonov

19. Contributions of DVCS and BH at E=160 GeV
Deep VCS
Bethe-Heitler μ’ * θ μ p 
d  |TDVCS|2 + |TBH|2 + Interference Term
Monte-Carlo
Simulation
for COMPASS
set-up with
only ECAL1+2
Missing
DVCS acceptance
without ECAL0
BH dominates study of Interference DVCS dominates
excellent  Re TDVCS study of dDVCS/dt
reference yield or Im TDVCS  Transverse Imaging
20 Jule 2010
D.Peshekhonov

20. DVCS GPDs need a world-wide effort
Global analysis over large kinematic range mandatory
COMPASS-II: from HERA to JLAB 11 GeV kinematics
The GPD H can be constrained by beam charge and spin (μ+μ−) combinations using an unpolarized proton target
E GPDs require transversely pol. target (later)
20 Jule 2010
D.Peshekhonov

21. Re H (,t)= P dx H(x,,t) /(x-)
Deeply Virtual Compton Scattering
Study the transverse imaging with +, - beam and unpolarized 2.5m long LH2 (proton) target
SCS,U
 d( +) + d( -) 
Im(F1 H)
Using SCS,U and integration over  
and BH subtraction
dDVCS /dt ~ exp(-B|t|)
 d( +) - d( -)
DCS,U
 Re(F1 H)
Re H (,t)= P dx H(x,,t) /(x-)
Im H (,t)= H(x= ,,t)
20 Jule 2010
D.Peshekhonov

22. Deeply Virtual Compton Scattering
B(xB) = b0 + 2 α’ ln(x0/xB)
α’ slope of Regge traject
without any model we
can extract B(xB)
B(xB) = ½ < r2 (xB) >
r is the transverse
size of the nucleon
20 Jule 2010
D.Peshekhonov

23. Parton Distribution Functions
8 PDFs at LO
Azimuthal asymmetries with different angular modulations in the hadron and spin azimuthal angles, Φh and Φs
aka
Sivers
Transversity
Boer–
Mulders
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24. Experimental check of the change of sign of
TMDs confronting Drell-Yan and SIDIS results
The T-odd character of the Boer-Mulders and Sivers function
implies that these functions are process dependent
`gauge link changes sign for T-odd TMD’, restricted universality of T-odd TMDs
FSI
ISI
Need experimental verification
Test of consistency
of the approach
Boer-Mulders
Sivers
20 Jule 2010
D.Peshekhonov

25. Polarised Drell-Yan
COMPASS-II: 190 GeV/c − beam on transversely pol. proton target
− valence u-antiquark picks nucleon’s u quark in valence region (u-quark dominance)
Access to transversity , the T-odd Sivers and Boer-Mulders TMDs and `pretzelozity’
20 Jule 2010
D.Peshekhonov

26. The Drell-Yan process in π- p15
The Drell-Yan process in π- p
Access to TMDs for incoming pion  target nucleon
TMD as Transversity, Sivers, Boer-Mulders, pretzelosity
Hadron plane
Collins-Soper frame (of virtual photon)
,  lepton plane wrt hadron plane
target rest frame
S target transverse spin vector /virtual photon
Lepton plane

27. DY and COMPASS set-up π- 190 GeV
Key elements for a small cross section investigation at high luminosity
Absorber (lesson from tests) to reduce secondary particle flux
COMPASS Polarised Target
Tracking system and beam telescope
Muon trigger (LAS of particular importance - 60% of the DY acceptance)
RICH1, Calorimetry – also important to reduce the background

28. COMPASS polarized DY
dominated by the annihilation of a valence anti-quark from the pion and a
valence quark from the polarised proton xp
large acceptance of COMPASS in the
valence quark region for p and π
where SSA are expected to be larger x
xF=x−xp xF
20 Jule 2010
D.Peshekhonov

29. TMDs at Drell-Yan: road map
2010 – COMPASS polarised SIDIS data (Sivers, transversity via global data fit)
COMPASS polarised Drell-Yan pi-p data – TMDs universality and T-odd TMDs sign change SIDISDY
2015  …… RHIC, NICA pp (un)polarised DY data
2020  GSI antiproton data
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30. Future DY experiments
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31. NICA Layout & Main Elements
Collider 2T
C = 336 m
KRION-6T & HILac
MPD
Synchrophasotron yoke
“Old” linac
Existing beam lines
(Fixed target exp-s)
Spin Physics Detector (SPD)
Beam transfer line
Nuclotron
2.3 m
4.0 m
Booster
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D.Peshekhonov 31

32. Spin Physics at NICA
The spin program at NICA is under preparation. The main topics are:
Studies of Drell-Yan processes with longitudinally and transversely polarized
p and D beams. Extraction of unknown and poor known PDFs
PDF from J/Ψ production processes
Spin effects in baryon, meson and photon production
Study of spin effects in various exclusive processes
Diffractive processes studies
Cross sections, helicity amplitudes and double spin asymmetries
(Krisch effect) in elastic reactions
Spectroscopy of quarkonium
20 Jule 2010
D.Peshekhonov

33. Spin Physics at NICA - polarized DY
From report by A. Nagaytsev, IWSS2010
The set of original software packages (MC simulation, generator etc.) were developed for the feasibility studies of DY polarized processes
The SSA asymmetries.
Top:access to transversity and Boer-Mulders PDFs (Sissakian, Shevchenko, Nagaytsev,PRD 72 (2005), EPJ C46 (2006))
Bottom: access to Sivers PDFs (Efremov,… PLB 612(2005), PRD 73(2006));
Asymmetries are estimated for 100 K DY events
20 Jule 2010
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NICA RoundTable Workshop IV A.P.Nagaytsev 33 33

34. Spare

35. From inclusive to exclusive reactions
COMPASS-II 2.3 23
From inclusive to exclusive reactions
Deep Inelastic Scattering
Deeply Virtual Compton Scattering
p  ’X
p ’p’ ’ 
Q²xB
GPDs * Q²
x+
x- p  t γ* x z p P’ z
x P
x P b y y
x boost
x boost
Distrib. de Partons q ( x )
Generalized Partons Distrib. H( x,,t ) Px
( Px, b )
Observation of the Nucleon Structure
in 1 dimension in 1+2 dimensions

36. DVCS: Transverse imaging at COMPASS
dDVCS/dt ~ exp(-B|t|)
ansatz at small xB
inspired by
Regge Phenomenology:
B(xB) = b0 + 2 α’ ln(x0/xB)
α’ slope of Regge traject
B with an accuracy of 0.1 GeV-2
α’ with an accuracy  2.5 
if α’  0.26 with ECAL1+2
if α’  with ECAL0+1+2
with the projected uncertainties
we can determine :

37. T-odd TMD in SIDIS and DY
`gauge link changes sign for T-odd TMD’, restricted universality of T-odd TMDs
SIDIS: FSI
DY:ISI
J.C. Collins, Phys. Lett. B536 (2002) 43

38. Single-polarised DY cross-section: Leading order QCD parton model, TMD PDFs universality
At LO the general expression of the DY cross-section simplifies to (Aram Kotzinian):
Thus the measurement of 4 asymmetries (modulations in DY cross-section):

39. DVCS GPDs need a world-wide effort
Global analysis over large kinematic range mandatory
COMPASS-II: from HERA to JLAB 11 GeV kinematics
H GPDs can be separated from BH and constrained by beam charge & spin (μ+μ−) combinations
E GPDs require transversely pol. target (later) 

40. Transversity PDF Couple to chiral odd Collins FF
Azimuthal cross-section asymmetry:
20 Jule 2010
D.Peshekhonov

41. Sivers function Sivers Asymmetry: proposed (1990, Sivers)
thought to vanish (1993, Collins)
resurrected (2002, Brodsky, Hwang, Schmitt)
different sign in DY and SIDIS
20 Jule 2010
D.Peshekhonov

42. SIDIS & Drell-Yan to study TMDs
Drell –Yan π- p  +-X
with intense pion beam (up to 109 /spill)
with the transversely polarised NH3target
with the COMPASS spectrometer equipped with an absorber -
Cross sections:
In SIDIS: convolution of a TMD with a fragmentation function
In DY: convolution of 2 TMDs ‘’’’
 complementary information and universality test ‘
20 Jule 2010
D.Peshekhonov