Harut Avakian (JLab)

PAC34, JLab, January 271

Harut Avakian (JLab)Harut Avakian (JLab)

PAC34 JLab, January 27, 2009

Proposal PR12-09-09:

Measure helicity distributions and the Collins fragmentation of kaons in SIDIS

Studies of spin-orbit correlations in kaon electroproduction in DIS with longitudinally polarized hydrogen and deuterium targets

Spokespersons: H. Avakian, E. Cisbani, K. Griffioen, K. Hafidi, P. Rossi


The CLAS Collaboration


Outline

IntroductionkT-effects with longitudinally polarized target

Double spin asymmetries and kT-widthsSingle Spin Asymmetries and the Collins effect

Projections for 12 GeVSummary

Transverse structure of the nucleon and correlations between longitudinal and transverse degrees of freedom.


z

sin2moment of the cross section for unpolarized beam and longitudinal target

U unpolarizedL long.polarizedT trans.polarized

SIDIS kinematical plane and observables

Transverse spin effects are observable as correlations of transverse spin and transverse momentum of quarks.


Single hadron production in hard scattering

h

Target fragmentation Current fragmentation

Fracture Functions

xF

M

0-1 1

h

h

PDF GPD

kT-dependent PDFs Generalized PDFs

Wide kinematic coverage of large acceptance detectors allows studies of hadronization both in the target and current fragmentation regions

xF - momentum

in the CM frame

xF>0 (current fragmentation)

xF<0 (target fragmentation)

h


Transverse Momentum Dependent (TMD) Distributions

Quark polarization

Nucleon polarization

Real and imaginary parts of the L≠0 interference contributions

•kT – leads to 3D description with 8PDFs

Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al)

Twist-3


A1 PT-dependence in SIDIS

M.Anselmino et al hep-ph/0608048

+ ALL can be explained in terms of broader kT distributions for f1 compared to g1

02=0.25GeV2

D2=0.2GeV2

In perturbative limit predicted to be constant

Como-2005

constituent quark model (Pasquini et al).


u/u

(dipole formfactor), J.Ellis, D-S.Hwang, A.Kotzinian

Helicity distributions: Diquark model

Difference in q+=f1+g1 (quark aligned with proton spin) and q-=f1-g1 - (anti-aligned) kT-dependences may lead to observable effects

JMR model

Jakob, Mulders, Rodrigues, Nucl. Phys. A 1997

q

DqMR , R=s,a

For given x the sign of the polarization is changing at large kT


A1 PT-dependence in SIDIS

M.Anselmino et al hep-ph/0608048

+ A1 suggests broader kT distributions for f1 compared to g1

- A1 may require non-Gaussian kT-dependence for different helicities and/or flavors

02=0.25GeV2

D2=0.2GeV2

0.4<z<0.7


Collins asymmetry with longitudinally pol. proton

Collins effect measurement with longitudinally pol. target provide access to the chiral-odd Ralston-Soper-Mulders-Tangerman (RSMT)

distribution functions and probes the polarized fragmentation function

Correlation between the transverse momentum and transverse spin of quarks in longitudinally polarized proton

First discussed by Kotzinian & Mulders (1996)

-

Clean observable: no Sivers type contributions, no twist-3 contributions


Transversely polarized quarks in the long. polarized nucleon

Light cone constituent quark model Pasquini,Cazzaniga & Boffi, Phys.Rev.D78:034025,2008

Brodsky & Yuan (2006)


Collins SSA measurements

+(u,d) K+ (u,s)

• K+ and + asymmetries consistent within error bars •K- and - asymmetries may have opposite sign

e+e-→hhX

Observed SSA show strong dependence on the final state hadron

BRAHMS

p↑p→hX


Collins effect

Simple string fragmentation (Artru model)

Sub-leading pion opposite to leading

(into page)

L=1

production may produce an opposite sign AUT

Leading opposite to leading (into page)

hep-ph/9606390 Fraction of in eX

% left from eX asm

20%

40%

~75%

~50%Fraction of direct kaons may be significantly higher than the fraction of direct pions. LUND-MC


The Collins function

First calculation of the Collins functionBacchetta et al, Phys.Lett.B659:234-243,2008

The Kaon Collins effect may be significant!

Kaon Pion

HERMES/COMPASS/Belle

spectator model


CLAS12LTCC

FTOF

PCAL

ECHTCC

Lumi = 1035cm-2s-1

High beam polarization 80%High target polarization 85%NH3 (30 days) ND3 (50 days)

Wide detector and physics acceptance (current/target fragmentation)

Replace 2 sectors of LTCC with a proximity RICH detector

2/3 cm

60/80 cm

pad cathode coated with CsI film

Proximity Gap

~4 K- separation at ~5 GeV/c


Q2>1GeV2

W2>4 GeV2(10)y<0.85MX>2GeV

SIDIS kinematics

Kaon distributions in ep e’KX

High energy kaons are at small angles (<30o)

LUND-MC

More kaons at small x

forward


ALL PT-dependence

•Azimuthal asymmetry sensitive to the difference of widths in PDFs•Proton and deutron data provide a complete set required for the flavor decomposition

Anselmino et al, Phys.Rev.D74:074015,2006.

proton deuteron

GRSV-2000+Kretzer


Collins fragmentation: Longitudinally polarized target

•Study the Collins function of kaons•Provides independent information on the RSMT TMD

Kotzinian-Mulders Asymmetry

proton deuteron

Pasquini et al.


Collins Effect: from asymmetries to distributions

Combined analysis of Collins fragmentation asymmetries from proton and deuteron may provide independent to e+e- (BELLE)Information on the underlying Collins function.

need


Summary

Probe the Collins polarized fragmentation function of kaons

Provide complementary to pions info on the flavor and helicity dependence of quark transverse momentum distributions

Study the transverse polarization of quarks in the longitudinally polarized nucleon through measurements of the leading twist chiral-odd Ralston-Soper-Mulders-Tangerman distribution function.

Study higher twist effects and probe T-odd distributions in a wide range of Q2

Beam request: 80 days of CLAS12@ 11 GeV with L=1035cm-2sec-1 (shared with E12-07-107) with longitudinally polarized NH3(30days) and ND3(50 days) with RICH upgrade

Latest experimental data indicate that spin-orbit correlations may be significant, leading to hadron flavor dependent

observable spin and azimuthal asymmetries

Precision measurement of spin and azimuthal asymmetries (sin2, cos and sin in kaon production in DIS will allow us to:


Support slides….


A Rich detector for CLAS12

A Rich detector would strongly enhance the CLAS12

capabilities in particle identification and would open

possibilities for new physics

Contalbrigo Marco PAC34 27 January 2009

2/3 cm

60/80 cm

pad cathode coated with CsI film

Proximity Gap

Replacement of LTCC with proximity focusing CsI Rich detector

good separation of /K/p in the 2-5 GeV/c momentum range

no impact on the baseline design of CLAS 12 minimum impact on spectrometer performaces

RICH


Low energy electromagnetic processes, especially Møller scattering of beam electrons off atomic electrons are the main contributor to the background load in an open large acceptance spectrometer such as CLAS12.

The full event and background load has been measured with CLAS, e.g. for DVCS process at 5.7 GeV. The GEANT simulation reproduces hit occupancy on tracking chambers.

We used the calibrated simulation code to extrapolate to 11 GeV and simulate the same process at higher luminosity for CLAS12 situation.

This background was also studied in a full Geant4 simulation.

CLAS12 - Electromagnetic Background


5 T Magnetic Field and Shielding

Photons

One Event

Electrons

Photons

One Event

Shielding

Background at L=1035cm-2s-1, T = 150ns

CLAS12


CLAS12 – Electromagnetic & Hadronic Rates

Deposited Energy detector > 20 KeV

32.3 0.85

RICH (5o-30o) (in 2 sectors)

Photons Hadrons

(in MHz)

L1 31.3 2.5 L2 31.1 2.2 L3 24.6 2.2

SVT (5o-35o)

Photons Hadrons

DC1 (5o-35o)

1.7 3.1

Photons Hadrons

Comment: For deposited energy of 20 KeV RICH would see about 35 hits in 1μsec window, randomly distributed over ~20 m2 and uncorrelated with track in DC. This is a very conservative estimate as for electrons to be knocked out from the RICH radiator > 500 KeV energy deposition is needed.


Rpd-

Both ratios agree with PDF models for z<0.7 (Mx>1.4 GeV)


Unfavored to favored ratio consistent with HERMES and EMC for z=0.55

D-/D+ from Deuteron + to - ratio


multiplicities in SIDIS ep→e’X

+/- multiplicities at large z diverge from SIDIS predictions0 multiplicities less affected by higher twists0.4<z<0.7 kinematical range, where higher twists are expected to be small

DSS (Q2=2.5GeV2)

DSS (Q2=25GeV2)

M.AghasyanHall-C


Uncertainties



Combined analysis of Collins fragmentation asymmetries from proton and deuteron may provide independent to e+e- (BELLE)Information on the underlying Collins function.

need


Higher Twist SSAs and Quark-Gluon Correlations

Target sin SSA (Bacchetta et al. 0405154)

Discussed as main sources of SSA due to the Collins fragmentation

In jet SIDIS only contributions ~ D1 (Sivers type)

With H1┴ (0)≈0 (or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions

Transversely polarized quarks


SSA with unpolarized target

quark polarization


SSA with unpolarized target

quark polarization


SSA with long. polarized target

quark polarization


SSA with long. polarized target

quark polarization


CLAS: Fraction from baryonic decays in SIDIS

Significant fraction from target fragmentation at pion momenta below 2 GeV


Dilution factor in SIDIS

Multiple scattering and attenuation in nuclear environment introduces

additional PT-dependence for hadrons

Fraction of events from polarized hydrogen in NH3

Nu,Np -total counts from NH3 and carbon normalized by lumi

u, p -total areal thickness of hydrogen (in NH3), and carbon target

Cn=Nitr/Carbon ratio (~0.98)Diff. symbols for diff x-bins

-


CLAS12: Acceptance deformation due to incomplete azimuthal coverage

No significant effect seen from limited coverage by RICH

Lab


Inbendin/outbending configurations

Different polarities increase the acceptance of positive and negative hadrons.


Critical for separation moment range 2<PK<5 and <25 degree

Kinematic dependence of K/ ratios


Q2>1GeV2

W2>4 GeV2(10)y<0.85MX>2GeV

SIDIS kinematics

Kaon distributions in ep e’KX

High energy kaons are at small angles


A Rich detector for CLAS12MC simulation: 3 cm thick C5F12 radiator 80 cm CH4 proximity gap 1 cm pixel pad size 5 o-30 o radiator polar angle

4 K- separation at 5 GeV/c 80 % kaon eff. with 1:1000 rejection 95 % kaon eff. with 1:100 rejection

Contalbrigo Marco PAC34 27 January 2009

Already with 2 sectors gain of factor~3 in the relevant z region of interest


Transverse Momentum Dependent (TMD) Distributions

Quark polarization

Nucleon polarization

Real and imaginary parts of the L=0 and L=1 interference contribution

Related to transversity by Lorentz Invariant relations.

In constituent quark model (Pasquini et al).

•kT – leads to 3D description with 8PDFs


Compare SIDIS experiments

COMPASS/HERMES/CLAS

cover different Q2 for the

same x-range

x=0.3 → Q2=~2 GeV2 (CLAS),

~7 GeV2 (HERMES)

~30 GeV2 (COMPASS)


HERMES: Diffractive corrections to DIS



Combined analysis of Collins fragmentation asymmetries from SIDIS and e+e- (BELLE) would allow separation of transverse spin distributions (Anselmino et al., arXiv:0707.1197 )

need

Brodsky & Yuan (2006)

CLAS12


JLab@12GeV: Inclusive DIS

BBS/LSS no OAM

PDF measurements at large x provide additional information on OAM

BBS/LSS with OAM


The Large-Nc Behavior of the PDFs

Use the large Nc limit of QCD to study TMD PDFs

qg interaction constant

In color singlet Feynman diagrams every vertex

loop

Introduced by ‘t Hooft in1974

isospin

Nc-

power

P.Pobylitsa hep-ph/0301236


The Large-Nc limit of QCD to study TMD PDFs

3 – isospin Pauli matrice

t1,t2 – isospin projection of

quark fields

(3)uu =1, (3)dd=-1

Change sign from + (SIDIS) to – (DY)

Nucleon mass M=O(Nc)

Large-Nc approach predicts signs and relative Nc power of TMDs, used in phenomenology.

3 – nucleon isospin

P.Pobylitsa hep-ph/0301236

Do not change sign (isoscalar)

All others change sign u→d (isovector)

Introduced by ‘t Hooft in1974

qg interaction constantIn color singlet Feynman diagrams every vertex

loop


GSIM12

Events for exclusive + production on proton (ep→e’+n)

Typical event


SIDIS (*p→X) cross section at leading twist (Ji et al.)

structure functions = pdf × fragm × hard × soft (all universal)

eUnpolarized target

Longitudinally pol. target

Transversely pol. target e

e

p

pBoer-Mulders

1998

Kotzinian-Mulders1996

Collins-1993

To observe the transverse polarization of quarks in SIDIS spin dependent fragmentation is required!

Do we understand well the helicity distributions?


Azimuthal Asymmetries in SIDIS

Due to color coherence the configuration with gluon inside the quark cone is more probable

Why <cos> < 0 ? Chay,Ellis,Stirling-1991

x

=180

=0


HT and Semi-Exclusive Pion Production E. Berger, S. Brodsky 1979 (DY), E.Berger 1980,A.Brandenburg, V. Khoze, D. Muller 1995

A.Afanasev, C.Carlson, C. Wahlquist Phys.Lett.B398:393-399,1997

+

Fragmentation +

0

• Azimuthal asymmetries with opposite sign from HT effects

• Effect may be suppressed for semi-exclusive 0 compared to +/-


Flavor Decomposition

Use double spin asymmetries for different targets and final state particles to extract the helicity distributions for different flavors

Sum over quark flavors

Extraction of kT-dependent distributions q+ (f1+g1) and q- (f1-g1) will require

unfolding of spin independent and spin dependent contributions

BBS/LSS no OAM

BBS/LSS with OAM

H.A.,S.Brodsky,A.Deur,F.Yuan (2007)


HT and Semi-Exclusive Pion Production E. Berger, S. Brodsky 1979 (DY), E.Berger 1980,A.Brandenburg, V. Khoze, D. Muller 1995

A.Afanasev, C.Carlson, C. Wahlquist Phys.Lett.B398:393-399,1997

+

Fragmentation +

0

• Azimuthal asymmetries with opposite sign from HT effects

• Effect may be suppressed for semi-exclusive 0 compared to +/-


3D structure of the nucleon

Wide kinematic coverage of large acceptance detectors allows studies of exclusive (GPDs) and semi-inclusive (TMDs) processes providing complementary information on transverse structure of nucleon

h

TMDs

Semi-Inclusive processes and transverse momentum distributions

,h

Hard exclusive processes and spatial distributions of partons

GPDs


Flavor DecompositionSum over quark flavors

Extraction of kT-dependent distributions q+ (f1+g1) and q- (f1-g1) will require

unfolding of spin independent and spin dependent contributions

BBS/LSS

BBS/LSS +OAM H.A.,S.Brodsky,A.Deur,F.Yuan (2007)

Large contribution from orbital motion


Non-perturbative TMD Perturbative region

Boer-Mulders Asymmetry: PT-dependence

In the perturbative limit 1/PT

2 behavior

expected (F.Yuan)

Missing: predictions for K-, dedicated predictions for K+

CLAS12

2<Q2<5 (2000h @ 11 GeV with 1035sec-1cm-2)


SSA in ep→e’X

contribution to SSA (~20%) may be responsible for the difference in andbeam SSA at large z

Larger fraction of from at low x and large z

PYTHIA at 5.7 GeV


Target SSA in exclusive production

Large positive 0 target SSA in the exclusive limit confirmed by CLAS at 5.7 GeV

HERMES 27.5 GeV

CLAS @5.7GeV

ep->e’p


Space and size of RICH sector (LTCC option)

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Harut Avakian (JLab)