1. Transverse Spin Physics
With CLAS12
Contalbrigo Marco
INFN Ferrara
Workshop on Partonic Transverse Momentum in Hadrons:
Quark Spin-Orbit Correlations and Quark-Gluon Interactions
March 12-13, 2010 Duke University

2. Partonic Transverse
MoMentum

3. Quantum Phase-Space Distributions of Quarks
Wpu(x,kT,r) “Mother” Wigner distributions
Probability to find a quark u in a nucleon P with a certain polarization in a position r & momentum k
d3r
d2kT
(FT)
GPD
TMD PDFs: fpu(x,kT),…
GPDs: Hpu(x,x,t), …
d2kT dx
x=0,t=0
Form Factors F1pu(t),F2pu(t )..
Measure momentum transfer to target
Direct info about spatial distributions
Measure momentum transfer to quark
Direct info about momentum distributions
pT< 2 GeV/c
√s = 20 GeV xF AN
PDFs fpu(x),…
SSA
Proton
spin puzzle
M. Contalbrigo
Duke Workshop 2010 3

4. TMD correlators Distribution Functions (DF)
Off-diagonal elements are important objects:
Distribution Functions (DF)
Interference between wave functions with
different angular momenta: contains infos
about parton orbital angular momenta ┴ ┴
Testing QCD at the amplitude level
g1L ┴ ┴ ┴ h1
3D description in momentum space
Fragmentation Functions (FF)
Bacchetta, PRD78 mostra un gafico diverso, con shift positivo per gli u. Da dove viene davvero il grafico ?
PRD 78 (2008)
M. Contalbrigo
Duke Workshop 2010 4

5. The 3D description of the nucleon
Distribution Functions (DF)
SIVERS
Quark orbital
angular momentum
BOER-MULDERS
Spin orbit effect
Impact parameter space ┴ ┴
anti-green remnant
green quark
GPD E
GPD ET+2HT ~
Deformations by ┴ ┴ ┴
3-momentum space
i.e. Sivers: spin-orbit correlations with same matrix element of anomalus magnetic moment, and GPD E
M. Contalbrigo
Duke Workshop 2010 5

6. Correlation Functions and SIDIS
Distribution Functions (DF) ~
Fragmentation Functions (FF)
q(x)
Dqh(z)
Rich phenomenology but rather involved observables
Target type and hadron ID provide flavor tagging !!
constrain valence and sea
disentangle distribution and fragmentation functions (test factorization, HT)
Multidimensional analysis resolves kinematic correlations !!
M. Contalbrigo
Duke Workshop 2010 6

7. Several observables already measured… with matches and mismatches
Collins
Sivers
Boer-
Mulders
M. Contalbrigo
Duke Workshop 2010 7

8. 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
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
Crucial: completeness
flavor tagging and five-fold differential
extraction in all variables
(x,z,Q2,PT) to have
all dependencies resolved
Still incomplete phenomenology is asking for new inputs
Contalbrigo Marco CLAS12 European Workshop February 2009
M. Contalbrigo
Duke Workshop 2010 8

9. JLAB 12

10. Reccomendation 1
We recommend the completion of the 12 GeV Upgrade at Jefferson Lab.
 It will enable three-dimensional imaging of the nucleon, revealing hidden aspects of its internal dynamics.
 It will complete our understanding of the transition between the hadronic and the quark/gluon descriptions of nuclei.
 …
M. Contalbrigo
Duke Workshop 2010 10

11. Upgrade magnets and power supplies
add Hall D
(and beam line)
6 GeV CEBAF
CHL-2
Upgrade magnets and power supplies
12 GeV CEBAF
Beam current mA
Beam polarization 85 %
: Construction (funded at 99%)
May 2012
6 GeV Accelerator Shutdown starts
May Accelerator Commissioning starts
October 2013
Hall Commissioning starts
Pre-Ops (beam commissioning)
Enhance equipment in existing halls
M. Contalbrigo
Duke Workshop 2010 11

12. Your Text Here The SIDIS landscape EIC Complementary experiments
Limit defined by luminosity
Different Q2 for same x range
Your Text Here
EIC
1034
Resonance region
1032
1031
1035
Complementary experiments
Matches valence
M. Contalbrigo
Duke Workshop 2010 12

13. broad kinematical range
CLAS12
L~ 1035 cm-2s-1
PCAL
FTOF
LTCC
HTCC EC
SVT
CTOF
5T solenoid
toroid
large luminosity
H and D targets
10 nA electron beam
85% beam polariz
broad kinematical range
NH3 ND3 target
85 % polarization
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)
multi-purpose detector
for fixed target electron scattering experiments
Q2>1GeV2
W2>4 GeV2
y<0.85
MX>2GeV
Wide detector acceptance
allows current & target
fragmentation measur.
Contalbrigo Marco CLAS12 European Workshop February 2009
M. Contalbrigo
Duke Workshop 2010 13

14. broad kinematical range
CLAS12
L~ 1035 cm-2s-1
PCAL
FTOF
LTCC
HTCC EC
SVT
CTOF
5T solenoid
toroid
large luminosity
H and D targets
10 nA electron beam
85 % polarization
broad kinematical range
NH3 ND3 target
85 % polarization
Pion and kaon, …. SSA
Replace 2 sectors of LTCC with a
proximity RICH detector to identify
Kaons approved by JLab PAC34
charged particle
radiator
drift electrode
Proximity gap
Photocathode
Contalbrigo Marco CLAS12 European Workshop February 2009
M. Contalbrigo
Duke Workshop 2010 14

15. TMDs with
UNPOLArized targets

16. Distribution Functions (DF)
TMD correlators ┴
g1L h1
Distribution Functions (DF)
M. Contalbrigo
Duke Workshop 2010 16

17. Unpolarized target @ CLAS12
Boer-Mulders spin-orbit effect
s-1cm-2
LH2 LD2 targets
kaon
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
Measurements of kinematic (x,Q2,z,PT) will probe HT distribution functions PR
ATT: corrente tipica 10 nA, e per HD-ice 1-2 nA, polarizzazione fascio 85 %
L’andamento con 1/Pt descritto da Bacchetta in PT matches
Pbeam = 85 %
In the perturbative limit
1/PT behavior expected
ALU~ 1/Q (Twist-3)
M. Contalbrigo
Duke Workshop 2010 17

18. Unpolarized target @ CLAS12
PT-dependence of azimuthal moments allows studies of transition from
non-perturbative to perturbative description
(Unified theory by Ji et al, PT matches and mismatches by Bacchetta et al).
In the perturbative limit
1/PT2 behavior expected
Perturbative region
4<Q2<5 GeV2
Talk di Harut al PAC 30
Da dove prende Boer-Mulders ???
Non-perturbative TMD
s-1cm-2
LH2 target
M. Contalbrigo
Duke Workshop 2010 18

19. Longitudinal Polarized
TMDs with
Longitudinal Polarized
targets

20. Distribution Functions (DF)
TMD correlators ┴
g1L h1
Distribution Functions (DF)
M. Contalbrigo
Duke Workshop 2010 20

21. Longitudinal Target Spin @ CLAS12
s-1cm-2
NH3 and ND3 target
Constituent quark model (Pasquini et al).
proton
M.Anselmino et al hep-ph/
Phys.Rev.D74:074015,2006
m02=0.25GeV mD2=0.2GeV2
Helicity dependence of kT-distribution of quarks
M. Contalbrigo
Duke Workshop 2010 21

22. Longitudinal Target Spin @ CLAS12
Transversely polarized quarks in long polarized nucleon
Leading twist, sensitive to spin-orbit correlations
Curves, χQSM, Efremov et al,
Czech J Phys 55 (2005) A189
proton
deuteron
s-1cm-2
NH3 and ND3 target
OK con referenze
Plot in alto dal PR , curve da Efremov et al., Czech J Phys 55 (2005) A189 hep-ph/
Plot in basso dal PR , curve colorate da CQM con diverse wave functions Pasquini et al, PRD78 (2008) ,
in questo papero anche relazione h1T=g1L-h1
curve in nero sono limiti da relazione con h1 Avakian et al., PRD77 (2007) ,
Curves
colored: CQM, Pasquini et al,
PRD78 (2008)
black: Avakian et al,
PRD77 (2008)
M. Contalbrigo
Duke Workshop 2010 23

23. Collins effect Simple string fragmentation (Artru model) L=1
Sub-leading pion opposite to leading (into page)
Simple string fragmentation (Artru model)
L=1
r production may produce an opposite sign AUT
Leading r opposite to leading p(into page) r
hep-ph/
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
unknown for kaons
• strange vacuum
• strangeness in the nucleon
unknown for vector mesons
Fraction of direct kaons may be higher than the fraction of direct pions.
LUND-MC
M. Contalbrigo
Duke Workshop 2010 24

24. Transversely Polarized
TMDs with
Transversely Polarized
targets

25. CLAS transversely polarized HD-Ice target
HD-Ice target vs std nuclear targets
Heat extraction is accomplished with thin aluminum wires running through the target (can operate at T~ mK)
Pros
Small field (∫Bdl~ Tm)
Small dilution (fraction of events from polarized material)
Less radiation length
Less nuclear background (no nuclear attenuation)
Wider acceptance much better FOM, especially for deuteron
H and D may be independently polarized
Cons
HD target is highly complex and there is a need for redundancy due to the very
long polarizing times (months).
Need to demonstrate that the target can remain polarized for long periods with an electron beam with currents of order of 1-2 nA
Additional shielding of Moller electrons necessary (use minitorus)
P= 95 % H , 70 % D
HD-Ice target at ~ 1-2nA NH3 at ~ 5-10 nA
Recuperare valori di polarizzazione, aggiungere che H e D possono essere polarizzati indipendentemente
Details of the HD were already presented by Volker. In addition SIDIS will benefit significantly
From absence of nuclear material, which complicates the final analysis due to nuclear attentation effects.
And here also crucial for this experiment will be the demonstration that target can remain polarized for long periods
With electron beam currents ~1-2 nA.
Untested for electrons (suggestive but unverified evidence of slow depolarization from beam-generated free radicals)
M. Contalbrigo
Duke Workshop 2010 26

26. Distribution Functions (DF)
TMD correlators ┴
g1L h1
Distribution Functions (DF)
M. Contalbrigo
Duke Workshop 2010 27

27. Collins asymmetry @ CLAS12
s-1cm-2
HD-ice (P=85%)
Curves fom A.V. Efremov et al
PRD76:094025,2006 x
Study AUT at large x (valence) where models are mostly unconstrined
Tensor charge
Curve da Efremov, probabilmente da PRD76 (2006) uscita postuma
ATT: dilution factor dell’HD-ice !!!
Solo proton quindi ? Aggiungere qui plots su tensor charge! Vedere prokudin at DIS 2008!!
M. Anselmino et al
hep-ph:
M. Wakamatsu hep-ph:
M. Contalbrigo
Duke Workshop 2010 28

28. non spherical shape of the nucleon
CLAS12
unpolarized beam, transv. target
non spherical shape of the nucleon
u quark
k=0
k=2.0 GeV S
B. Pasquini et al. arXiv: n
s-1cm-2
HD-ice (P=85%)
Avakian et al.,
PRD78,114024
OK con referenze
L’articolo di Avakian lavora col bag model e anche con spectator model Jackob hep-ph/ trovano
Asimmetria negativa entro I positivity bounds
HD-ice for transverse because the transverse magnet can not clean the Mollers->if I have low-lumi allora meglio HD-ice con high f
Relation in no-gluon models:
(in bag & spectator model)
M. Contalbrigo
Duke Workshop 2010 30

29. Sivers effect @ CLAS12 unpolarized beam, transverse target
s-1cm-2
HD-ice (P=85%)
S. Arnold et al
arXiv:
Manca referenza plot pioni
Plot dei K da LOI12 al pac34
Mettere 10^34 in lumi, con NH3 si escludono 2 settori e ho Pt broadening (f dipende da tutto e loro ne tengono conto, il dilution lo calcolano con target di Carbonio)
M. Anselmino et al
arXiv:
Eur.Phys.J.A39:89-100,2009
M. Contalbrigo
Duke Workshop 2010 31

30. GPDs @ CLAS12 ? Structure functions,
D. Mueller, X. Ji, A. Radyushkin, A. Belitsky, …
M. Burkardt, … Interpretation in impact parameter space
Structure functions,
quark longitudinal
momentum & helicity
distributions
Correlated quark momentum
and helicity distributions in
transverse space - GPDs
Proton form factors, transverse charge & current densities ?
M. Contalbrigo
Duke Workshop 2010 32

31. DVCS @ CLAS12 e p e p g Sample kinematics
Q2=2.2 GeV2, xB = 0.25, -t = 0.5GeV2
Ds ~ sinfIm{k1(F2H – F1E) +…}df
AUTx Target polarization in the
scattering plane
s-1cm-2
HD-ice (P=85%)
AUTy Target polarization perpendicular
to the scattering plane
OK con referenze
PUT lumi to 10^34
Asymmetries highly sensitive
to the u-quark contributions to
the proton spin.
M. Contalbrigo
Duke Workshop 2010 33

32. Exclusive r0 production @ CLAS12
Eu, Ed allow to map the
orbital motion of quarks.
2D (Im(AB*)) T
AUT ~
Q2=5 GeV2
A ~ 2Hu - Hd
B ~ 2Eu - Ed r0
A ~ Hd - Hu
B ~ Ed - Eu r+
s-1cm-2
HD-ice (P=85%)
OK con referenze
Confinment: distribution in PT and xT -> buono da usare. r0
A ~ 2Hu + Hd
B ~ 2Eu + Ed w0
Possible flavor decomposition
K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 B
M. Contalbrigo
Duke Workshop 2010 34

33. Summary
CLAS12 is a wide-acceptance high-luminosity high-polarization experiment
for a
comprehensive study of the partonic transverse degree of freedoms in the nucleon
Perform precise TMDs and GPDs measurements
Constrain models with multi-D approach
Test factorization
Important test of QCD: universality SIDIS vs Drell-Yan
Provide information on the Fragmentation (Collins, & polarized friends)
Study higher twist effects
Investigate non-perturbative to perturbative transition (along PT)
Contalbrigo Marco PAC January 2009
M. Contalbrigo
Duke Workshop 2010 35

34. 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