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Physics requiring RICH
Contalbrigo Marco
INFN Ferrara
CLAS12 European Workshop February 26, 2009
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Kaon in SIDIS
Approved by PAC34
PR12-09-07 Studies of partonic distributions
using semi-inclusive production of Kaons
PR12-09-08 Studies of Boer-Mulders Asymmetry in
Kaon Electroproduction with Hydrogen and
Deuterium Targets
PR12-09-09 Studies of Spin-Orbit Correlations
in Kaon Electroproduction in DIS with polarized
hydrogen and deuterium targets
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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
Protons spin
Jg
Jq
Understanding of the orbital motion of quarks
crucial!!!
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Correlation Functions
Distribution Functions (DF)
Fragmentation Functions (FF)
Dqh(z)
q(x)
Hadron ID provides flavor tagging !!
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Strange parton distribution
Isoscalar target Charge conjugation in FF
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Correlation Functions
Distribution Functions (DF)
Fragmentation Functions (FF)
D
Hadron ID provides flavor tagging !!
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Helicity distribution

• Flavour decomposition of quark helicity
• Is the light sea symmetrically polarized ?

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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
Isoscalar method
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ALL PT-dependence in SIDIS
LL
ALL
0.4ltzlt0.7
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
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ALL PT-dependence in SIDIS
proton
deuteron
GRSV-2000Kretzer
PR12-09-09 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)

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TMDs Correlation Functions
Distribution Functions (DF)
Off-diagonal elements interference of
partial-wave function for different orbital
momentum states
-
-
-
-
-
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Sivers Function
Distribution Functions (DF)
Fragmentation Functions (FF)
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Sivers function
M.Anselmino et al hep-ph/0805.2677 D. de Florian
et al., Phys. Rev. D75 (2007) 114010
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
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Sivers function
Still preliminary data
Role of evolution ?
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TMDs Correlation Functions
Distribution Functions (DF)
-
-
-
-
-
Fragmentation Functions (FF)
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Non-collinear SIDIS off unpolarized targets
g1L
h1
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Cosnf moments
(Up to 2008)
cosf
cos2f
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
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SIDIS off unpolarized targets
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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
Fundamental prediction of QCD !
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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
Collins function
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Cos2f moments
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 ?
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SIDIS off unpolarized targets
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FUU structure func. Expansion up to twist 3
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Cosf moments
Large negative effect confirmed !
How large is the uncertainty in predictions
from intrinsic transverse momentum
distribution ? Is Cahn effect diluted by other
terms ?
Is the difference between p and p- the sign
of a non-zero boer-mulders ?
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Boer-Mulders kaon asymmetry _at_ CLAS12
Line Phys Rev D78 045022 Boer-Mulders from
Sivers Collins from ee- data
Band Phys Rev D78 034035 Boer-Mulders from
DY data Collins from chiral limit
Excellent precision vs model uncertainties
PR12-09-08 54 days at L1x1035 cm-2s-1
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Collins function transversity
Distribution Functions (DF)
Fragmentation Functions (FF)
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Collins function transversity
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Executive summary
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
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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)

Q2gt1GeV2 W2gt4 GeV2 ylt0.85 MXgt2GeV
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Kinematic dependence of K/? ratios
Critical for separation moment range 2ltPKlt5 and
qlt25 degree
PEPSI LEPTO predictions
Only reliable is p identification
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CLAS12 Acceptance MC studies
CLAS12 SIDIS MC (LUND-PEPSI) used to study
azimuthal moments from acceptance and radiative
corrections for different pions.
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CLAS12 Acceptance MC studies
CLAS12 SIDIS MC (LUND-PEPSI) used to study
azimuthal moments from acceptance and radiative
corrections for different pions.
After acceptance correction the generated
azimuthal moments are recovered with an error lt
10 (dominant contribution to systematics)
Even better results expected with a
fully-differential analysis
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A Rich detector for CLAS12
Only reliable is p identification
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A Rich detector for CLAS12
A Rich detector would strongly enhance the
CLAS12 capabilities in particle identification
and would open possibilities for new physics
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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
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2-D Collins moments for p
-
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1-Hadron Production (ep epX)
le
ST
le
SL
le
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Other leading twist DF
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Target SSA measurements at CLAS

• Complete azimuthal coverage crucial for
  separation of sinf, sin2f moments

ep?epX
CLAS PRELIMINARY
p1sinfp2sin2f
W2gt4 GeV2
Q2gt1.1 GeV2
ylt0.85
0.4ltzlt0.7
MXgt1.4 GeV
p1 0.0590.010 p2-0.0410.010
p1-0.0420.015 p2-0.0520.016
p10.0820.018 p20.0120.019
PTlt1 GeV
0.12ltxlt0.48
No indication of Collins effect for p0 (x20 more
data in 2009)
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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

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p multiplicities in SIDIS
ep?epX
M.Aghasyan
Hall-C
DSS (Q22.5GeV2)
DSS (Q225GeV2)
p/- multiplicities at large z diverge from SIDIS
predictions p0 multiplicities less affected by
higher twists 0.4ltzlt0.7 kinematical range, where
higher twists are expected to be small
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Structure of the Nucleon
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!