1. CLAS12 European Workshop
Physics requiring RICH
Contalbrigo Marco
INFN Ferrara
CLAS12 European Workshop
February 26, 2009
Contalbrigo Marco CLAS12 European Workshop February 2009

2. Kaon in SIDIS Approved by PAC34: PR12-09-07:
Studies of partonic distributions using semi-inclusive production of Kaons
PR :
Studies of Boer-Mulders Asymmetry in Kaon
Electroproduction with Hydrogen and Deuterium Targets
PR :
Studies of Spin-Orbit Correlations in Kaon Electroproduction in DIS with polarized hydrogen and deuterium targets
Contalbrigo Marco CLAS12 European Workshop February 2009

3. The Spin Structure of the Nucleon
Describe the complex nucleon structure in terms
of partonic degrees of freedom of QCD
Important testing ground for QCD
Phys Lett B647 (2007) 8-17
Latest news from Deep
Inelastic Scattering (DIS)
DS=0.33±0.03
Phys. Rev. D 75 (2007)
DG small at 0.02<x<0.3
From DIS and pp scattering
e-print
Proton’s spin Jq Jg
Understanding of the orbital motion of quarks crucial!!!
Contalbrigo Marco CLAS12 European Workshop February 2009

4. Distribution Functions (DF) Fragmentation Functions (FF)
Correlation Functions
Distribution Functions (DF)
Fragmentation Functions (FF)
N/q U L T
q(x)
Dqh(z)
Hadron ID provides flavor tagging !!
constrain the unpolarized strange sea
disentangle distribution and fragmentation functions
Contalbrigo Marco CLAS12 European Workshop February 2009

5. Strange parton distribution
Isoscalar target
Charge conjugation in FF K
Constrain strange sea
Reduce uncertainty on NS
(and S) fragmentation functions
PR : H2 & D2 (54 days) X
Contalbrigo Marco CLAS12 European Workshop February 2009

6. Distribution Functions (DF) Fragmentation Functions (FF)
Correlation Functions
Distribution Functions (DF)
Fragmentation Functions (FF)
N/q U L T
Dqh D
Hadron ID provides flavor tagging !!
flavor decomposition of quark helicity
Contalbrigo Marco CLAS12 European Workshop February 2009

7. Helicity distribution
Flavour decomposition of quark helicity
Is the light sea symmetrically polarized ?
Contalbrigo Marco CLAS12 European Workshop February 2009

8. Helicity distribution
Flavor decomposition
• Constrain very well the valence
• Explore the valence-sea transient
• Check sea polarization symmetry
• Improve phenomenological fits
indirect information on DG
Hep-ex
Isoscalar method
Flavor decomposition of quark helicity
PR : NH3 (30 days) & ND3 (50 days)
Contalbrigo Marco CLAS12 European Workshop February 2009

9. ALL PT-dependence in SIDIS
M.Anselmino et al hep-ph/
m02=0.25GeV mD2=0.2GeV2 LL
ALL
Constituent quark model (Pasquini et al).
0.4<z<0.7
p+ ALL suggests broader kT distributions for f1 compared to g1
p- ALL may require non-Gaussian kT-dependence for different helicities and/or flavors
Contalbrigo Marco CLAS12 European Workshop February 2009

10. ALL PT-dependence in SIDIS
M.Anselmino et al hep-ph/
m02=0.25GeV mD2=0.2GeV2
proton
deuteron
GRSV-2000+Kretzer
PR : NH3 (30 days) & ND3 (50 days)
Azimuthal asymmetry sensitive to the difference of kT -widths in PDFs
Complete set required for the flavor decomposition (H,D target + K,p ID)
Contalbrigo Marco CLAS12 European Workshop February 2009

11. Distribution Functions (DF)
TMDs Correlation Functions
pp pX
Distribution Functions (DF)
Off-diagonal elements: interference of partial-wave function for different
orbital momentum states ┴ ┴
SIVERS
Quark orbital
angular momentum ┴ ┴ ┴
GPD E
GPD ET
pT<2 GeV/c
√s = 20 GeV xF AN
pp pX
anti-green remnant
green quark
Contalbrigo Marco CLAS12 European Workshop February 2009

12. Distribution Functions (DF) Fragmentation Functions (FF)
Sivers Function
Distribution Functions (DF)
Fragmentation Functions (FF)
N/q U L T
Contalbrigo Marco CLAS12 European Workshop February 2009

13. Sivers function p+ (u,d) K+(u,s)
M.Anselmino et al hep-ph/
D. de Florian et al., Phys. Rev. D75 (2007)
p+ (u,d) K+(u,s)
Clear example of flavor sensitivity thanks to hadron ID
From kaon vs pion comparison
Unpolarized SIDIS provides detailed description of FFs
Polarized SIDIS provides information on sea contribution to Sivers:
• saturation of sbar
• clear negative tendency for dbar
Contalbrigo Marco CLAS12 European Workshop February 2009

14. Sivers function Still preliminary data Role of evolution ?
CLAS12 with transverse target
Contalbrigo Marco CLAS12 European Workshop February 2009

15. Distribution Functions (DF) Fragmentation Functions (FF)
TMDs Correlation Functions
NA10
E866
E615
hp mmX
BOER-MULDERS
Spin Orbit effect
Distribution Functions (DF) ┴
g1L ┴ h1 ┴ ┴ ┴
ee ppX
COLLINS
Quark spin probe
Fragmentation Functions (FF)
N/q U L T
Contalbrigo Marco CLAS12 European Workshop February 2009

16. Non-collinear SIDIS off unpolarized targets
ep e’hX
longitudinal to
transverse photon flux
Intrinsic kT
“Cahn effect” (1978)
g1L h1
Contalbrigo Marco CLAS12 European Workshop February 2009

17. Cosnf moments (Up to 2008) cosf cos2f No hadron identification
EMC (1987)
EMC (1987)
E665 (1993)
ZEUS (2000)
No hadron identification
No charge separation
Poor statistics for cos2f
Qualitative agreement with
expectations based on Cahn model, but investigation far to be conclusive
Contalbrigo Marco CLAS12 European Workshop February 2009

18. SIDIS off unpolarized targets
ep e’hX
longitudinal to
transverse photon flux
Leading
twist
g1L h1
Contalbrigo Marco CLAS12 European Workshop February 2009

19. FUU structure func. Expansion up to twist 3
pQCD CORRECTIONs
Convolution integral over transverse momenta with implicit sum over quark flavours
BOER-MULDERS x COLLINS
Access to partonic transverse
spin and momentum correlations
in distribution and fragmentation
CAHN EFFECT
Sensitive to partonic intrinsic
transverse momentum
extracted only from Drell-Yan
same sign for u and d
in agreement with most of the models
sign change between DY and SIDIS
• universality of TMDs
Boer-Mulders function: x
Fit to Drell-Yan DATA
PhysRevD77 (2008)
Fundamental prediction of QCD !
Contalbrigo Marco CLAS12 European Workshop February 2009

20. FUU structure func. Expansion up to twist 3
BOER-MULDERS x COLLINS
Convolution integral over transverse momenta with implicit sum over quark flavours
Access to partonic transverse
spin and momentum correlations
in distribution and fragmentation
CAHN EFFECT
Sensitive to partonic intrinsic
transverse momentum
Dfav
-Dunf
FIT TO BELLE DATA
Transversity 2008, Ferrara
Collins function:
extracted from e+e- collider data (BELLE)
at much higher scale than SIDIS
to be investigate at SIDIS scale too
• evolution of TMDs
only for pions
still unknown for kaons
• strange vacuum
• strangeness in the nucleon
Contalbrigo Marco CLAS12 European Workshop February 2009

21. Sign change with hadron charge !p- p+
Cos2f moments
Boer-Mulders
All contributions
Cahn (twist 4)
V. Barone et al. Phys.Rev.D78:045022,2008
Non-zero !
Sign change with hadron charge ! ?
Experiments still working hard to control systematics
How large is the contribution at higher twist ?
How to compare different Q2 ?
Contalbrigo Marco CLAS12 European Workshop February 2009

22. SIDIS off unpolarized targets
ep e’hX
longitudinal to
transverse photon flux
Twist-3
Leading
twist
g1L h1
Contalbrigo Marco CLAS12 European Workshop February 2009

23. FUU structure func. Expansion up to twist 3
BOER-MULDERS + COLLINS
Access to Partonic transverse
spin and momentum correlations
In distribution and fragmentation
CAHN EFFECT
Access to Partonic intrinsic
transverse momentum
Contalbrigo Marco CLAS12 European Workshop February 2009

24. Cosf moments Large negative effect confirmed ! preliminary
How large is the uncertainty in predictions
from intrinsic transverse momentum
distribution ?
Is Cahn effect diluted by other terms ?
preliminary
Is the difference between p+ and p-
the sign of a non-zero boer-mulders ?
Contalbrigo Marco CLAS12 European Workshop February 2009

25. Boer-Mulders kaon asymmetry @ CLAS12
Line: Phys Rev D
Boer-Mulders from Sivers
Collins from e+e- data
Band: Phys Rev D
Boer-Mulders from DY data
Collins from chiral limit
Excellent precision vs model uncertainties
PR :
54 days at
L=1x1035 cm-2s-1
Contalbrigo Marco CLAS12 European Workshop February 2009

26. Distribution Functions (DF) Fragmentation Functions (FF)
Collins function & transversity
Distribution Functions (DF)
Fragmentation Functions (FF)
N/q U L T
Contalbrigo Marco CLAS12 European Workshop February 2009

27. Collins function & transversity
No kaon analysis
Valence poorly constrained
M.Anselmino et al hep-ph/
CLAS12 with transverse target
Contalbrigo Marco CLAS12 European Workshop February 2009

28. Executive summary Crucial: completeness
TMDs are a new class of phenomena
providing novel insights into the rich nuclear structure
Non-zero results from DIS experiments
provide promises but also open questions
Limited knowledge on transverse momentum dependences
Flavor decomposition often missing
Evolution properties to be defined
Role of the higher twist to be quantified
Universality Fundamental test of QCD
Still incomplete phenomenology is asking for new inputs
Crucial: completeness
flavor tagging and five-fold differential
extraction in all variables
(x,z,Q2,PT) to have
all dependencies resolved
Contalbrigo Marco CLAS12 European Workshop February 2009

29. CLAS12: experimental set-up
multi-purpose detector
for fixed target electron
scattering experiments
broad kinematical range
large luminosity
Polarized
beam
H and D targets
Pion and kaon, …. SSA
Large kinematic ranges accessible with CLAS12 are important for separation of
Valence region
Higher Twist contributions (Q2)
Perturbative regime (PT ≥ 1)
Q2>1GeV2
W2>4 GeV2
y<0.85
MX>2GeV
Contalbrigo Marco CLAS12 European Workshop February 2009

30. Kinematic dependence of K/ ratios
Critical for separation moment range 2<PK<5 and q<25 degree
central detector
forward detector K
PEPSI LEPTO predictions
Only reliable is p identification
Contalbrigo Marco CLAS12 European Workshop February 2009

31. CLAS12 Acceptance MC studies
CLAS12 SIDIS MC (LUND-PEPSI) used to study azimuthal moments
from acceptance and radiative corrections for different pions.
generated
reconstructed
ep+X PT
0.4
0.0
- 0.6
Contalbrigo Marco CLAS12 European Workshop February 2009

32. CLAS12 Acceptance MC studies
CLAS12 SIDIS MC (LUND-PEPSI) used to study azimuthal moments
from acceptance and radiative corrections for different pions.
generated
reconstructed
ep+X PT
After acceptance correction
the generated azimuthal moments are recovered with an error < 10%
(dominant contribution to systematics)
Even better results expected with a fully-differential analysis
Contalbrigo Marco CLAS12 European Workshop February 2009

33. A Rich detector for CLAS12
LTCC
Only reliable is p identification
Contalbrigo Marco CLAS12 European Workshop February 2009

34. A Rich detector for CLAS12
2/3 cm
60/80 cm
pad cathode coated
with CsI film
Proximity
Gap
A Rich detector would strongly enhance the CLAS12
capabilities in particle identification and would open
possibilities for new physics
Replacement of LTCC with proximity focusing CsI Rich detector
 good separation of p/K/p in the 2-5 GeV/c momentum range
 no impact on the baseline design of CLAS 12
 minimum impact on spectrometer performace
Contalbrigo Marco CLAS12 European Workshop February 2009

35. A Rich detector for CLAS12
MC simulation:
 3 cm thick C5F12 radiator
 80 cm CH4 proximity gap
 1 cm pixel pad size
 5 o-30 o radiator polar angle
4s K-p separation at 5 GeV/c
80 % kaon eff. with 1:1000 p rejection
95 % kaon eff. with 1:100 p rejection
Already with 2 sectors gain of factor
~3 in the relevant z region of interest
without RICH
with RICH
Contalbrigo Marco CLAS12 European Workshop February 2009

36. 2-D Collins moments for p±
x vs z
z vs Ph ┴
Contalbrigo Marco CLAS12 European Workshop February 2009

37. 1-Hadron Production (ep epX)le ST
I[h1H1┴]
Transversity
& Collins d le
N/q U L T f1 h1 g1
h1L
f1T
g1T
h1 h1T SL le
Contalbrigo Marco CLAS12 European Workshop February 2009

38. Other leading twist DF
Contalbrigo Marco CLAS12 European Workshop February 2009

39. Target SSA measurements at CLAS
Complete azimuthal coverage crucial for separation of sinf, sin2f moments
ep→e’pX
p1sinf+p2sin2f
CLAS PRELIMINARY
W2>4 GeV2
Q2>1.1 GeV2
y<0.85
0.4<z<0.7
MX>1.4 GeV
p1= 0.059±0.010
p2=-0.041±0.010
p1=-0.042±0.015
p2=-0.052±0.016
p1=0.082±0.018
p2=0.012±0.019
PT<1 GeV
0.12<x<0.48
No indication of Collins effect for p0 (x20 more data in 2009)

40. Collins frag.: Longitudinally polarized target
Kotzinian-Mulders Asymmetry
proton
deuteron
Pasquini et al.
Study the Collins function of kaons
Provides independent information on the RSMT TMD
Contalbrigo Marco CLAS12 European Workshop February 2009

41. p multiplicities in SIDIS
ep→e’pX
Hall-C
M.Aghasyan
DSS (Q2=2.5GeV2)
DSS (Q2=25GeV2)
p+/- multiplicities at large z diverge from SIDIS predictions
p0 multiplicities less affected by higher twists
0.4<z<0.7 kinematical range, where higher twists are expected to be small

42. Structure of the Nucleon
GPDs/IPDs
d2kT
Wpu(k,rT) “Mother” Wigner distributions
d2rT
d2kT
TMD PDFs f1u(x,kT), .. h1u(x,kT)
quark polarization
PDFs f1u(x), .. h1u(x)
Gauge invariant definition (Belitsky,Ji,Yuan 2003)
Universality of kT-dependent PDFs (Collins,Metz 2003)
Factorization for small kT. (Ji,Ma,Yuan 2005)
Analysis of SIDIS and DVMP are complementary!
Contalbrigo Marco CLAS12 European Workshop February 2009