Target Fragmentation studies at JLab M.Osipenko in collaboration with L. Trentadue and F. Ceccopieri, May 20,SIR2005, JLab, Newport News, VA CLAS Collaboration.

Target Fragmentation studies at JLab

M.Osipenko in collaboration withL. Trentadue and F. Ceccopieri,

May 20,SIR2005,JLab, Newport News, VA

CLAS Collaboration

May 20, 2005 M. Osipenko 2

Plan of StudySemi-inclusive

reactions

Light mesons () Baryons (p, n, )

targetfragmentation

currentfragmentatio

n

currentfragmentation

targetfragmentation

fracturefunctions

fragmentationfunctions

Diffraction

double momentsin pQCD

Pomeronstructure function

separation separation

Low Q2?

momentumsum rule


SI Structure functions

5 22

1 22 4

2

3 422

41

2

1 12 22 cos cos 2

1 1

T

h

L

T T

Ed ME Mxyxy H y H

dxdydzdp d Q p E

Mxy Mxyy yp pE Ey H H

Mx MxQQyE yE

2( , , , )i i TH H x Q z pUnpolarized cross section is described by four functions:

5 2

2 4

41 sin

T

LUe LT

d sxy y H

dxdydzdp d Q

Beam longitudinal polarization asymmetry produces one more structure function:

longitudinal polarization of CEBAF beam achieves 85%

separation requires a measurement of 5-dimensional cross section


SIDIS2 , ,Q x fixed

22 ( ) ( )h

q q qq

H e f x D z 22 ( , )h

q qq

H e M x z

In the Bjorken limit:

Currentfragmentation

Targetfragmentatio

n

( )qf x

( )hqD z

( , )hqM x z

factorizationproved

factorizationis not necessary

1 22H xH

3H 4H

This mixture is presentlystudied at JLab


Longitudinal Momentum

+ p

CEBAF beam energy in combination with CLAS acceptance allow to explore current fragmentation for light mesons and target fragmentation for baryons. ( )2 h CM

F

px

W In DIS Feynman permits to disentangle two regions,

however, at small invariant masses W separation is ambiguous.

target

target

target

currentcurrent

current

6 GeV beam energy


Rapidity gap at CLAS

2

2

1ln ln

1CM

Mulders hm xz

z Q x

Separation of the current and target fragments:Berger criterion 2CM

+

p1

log2

h h

h h

E p

E p

Usefulkinematics

ExclusiveBoundaryMX~Mn

DIS only!

Q2=2 GeV2

W>

2 G

eV

current

current

No kinematical cuts!We have to study entireset of mechanisms.


New CLAS dataUnpolarized Semi-inclusive electroproduction of + has been recently measured with CLAS.For the first time complete 5-dimensional cross sections were extracted.Direct separation of different SI structure functions.

x=0.28-0.32z=0.16-0.19

pT=0.41-0.53 GeV

Q2=2.23-2.66 GeV2

Prelim

inary

Prelim

inary

CLAS


+ production results

Prelim

inary

Prelim

inary

CLAS preliminary results suggest dominance of the current fragmentation mechanism in H2 down to rather low Q2 and z values,No significant target fragmentation contribution is found.

Q2=3 GeV2

CLAS

Prelim

inary

Prelim

inary

Q2=2.4 GeV2, x=0.26, z=0.23

CLASThe same pT behavior for all structure functions => trivial kinematical factors for azimuthal asymmetries <cos> and <cos2>H3 contribution is negativeH4 is mostly positiveSuggest only internal transverse motion of quarks (Cahn)?

LO QCD prediction given by a product of GRV PDFs and Kretzer FFs saturates experimental data leaving no room for large positive target fragmentation contribution.

current


Nucleon Semi-Inclusive

2 2 2min9 8.4W M P

Possible reactions on the proton: epe′p′X and epe′nX

currentfragmentation

targetfragmentation

GeV2

JLabHERA

Below pp-threshold there is no need for kinematical cuts! Direct access to the fracture functions M(x,z,Q2) and their properties.

22 ( , )h

q qq

H e M x z

LTapproximation

only!


Diffraction

1 22 2( , , , ) ( )(1 ) ( , )Rhq R

R

M x z t Q F t z F x Q s 1z In the Regge limit and

2( , )RF x Q structure function of the Regge trajectory

HERA

( ) b tF t e

R Regge trajectory intercept, 1.1 for Pomeron

epe′p′Xepe′nX

0.07 0.45t CLAS

0.3 5t

CLAS sees diffraction!

Need p-n difference to select of pure gluonic content of exchanged object.


Fracture Functions

2

3

0

1cos ( )

2H d

2

4

0

1cos 2 ( )

2H d

2 2( , , , ) ( , ) ( , )h Pq PM x z t Q f x t F Q

Separation of different fracture functions: MT,ML, MLT etc. related to different structure functions H1, H2, H3 etc.

Extraction of various moments and comparison to pQCD

Test of diffractive factorization of the fracture functions

H1 and H2 Rosenbluth separation

1 12 1 1 2

0 0

( ) ( , , )n mnmM Q dxx dzz M x z Q

max max1 12 2 2

2

0 0 0 0

( , , , ) (1 ) ( , ) ( , , , )t t

Ndt dzzM x z t Q x F x Q dt dzzM x z t Q

Contribution of the target fragmentation in the pion electroproduction

( )P

P P qx

Pq

P

x

x where


SummaryMeasured + semi-inclusive electro-production in the JLab region does not show a large target fragmentation contribution suggesting therefore naïve pQCD picture,We are extracting polarized and unpolarized proton and neutron semi-inclusive electroproduction cross sections at highest JLab beam energy 6 GeV: epe′p′X and epe′nX

TO DO:Comparison of pT dependences to theory (Cahn, Berger, pQCD),

Separation different fracture functions MT, ML, MLT etc.,Test of diffractive factorization hypothesis,Extraction of the fracture function moments and a comparison to pQCD predictions,Contribution of the target fragmentation in pion SIDIS at JLab.


Backgroundu-channel nucleon production:

~F2(x,Q2)2 2 2 2( ) (1 2 / )N Nu q p M Q qp Q

Higher Twist contribution


Fracture functions12

2 2 22

/(1 )

( )( , , , ) ( ) ( , , , )

2h i hSq q i

i x z

Q du xQ M x z t Q P u M z t Q

Q u u

max 12 2

2

0 0

( , , , ) (1 ) ( , )t

h qq

h

dt dzzM x z t Q x F x Q

•DGLAP evolution equation with standard splitting functions

•Momentum sum rule

•Process independent definition

1 2 2 1

1 1( ) ( ) ( ) ( )2 2 2 2

2 2

0 0

( , , , ) ( , ) ( , , , ) ( , ) ( )z z

j h N j N h N j N ijitr i i j i i j hard

ij i j

dxdxM x z t Q F x Q M x z t Q F x Q i j h

x x

Hadron-hadroncollisions

N1+N2hX+

In assumption of the factorization


Previous data

•Below pp-production threshold only target fragmentation can contribute

•Large t-range from 0.1 up to 4-5 GeV2

•Good particle identification: possibility to make p-n difference

•Polarization observables: new information on the fracture functions

Semi-inclusive nucleon electroproduction was measured at SLAC, Cornell, DESY, HERA and CERN. Only unpolarized data and most of variables are integrated over.

2 2 2min9 8.4W M P GeV2

HERA

Cornell

CERN


OutlineSemi-inclusive reactionsStructure functionsSIDISSeparation of different fragmentation regionsNucleon semi-inclusive electroproductionDiffractionPrevious measurementsExpected resultsSummary


Semi-inclusive Reactions

2 2Q q2

2

Qx

Pq

h hPp Ez

Pq

T T h hp p p p q 77777777777777777777777777777777777777777777777777777777

'h e 2( )ht p p

•Need to detect the scattered electron in a coincidence with the hadron h,•Require a good particle identification,•To extract the cross section in all five variables the complete 4 acceptance is necessary.

=> CLAS is the best place to do this!

5 independent variablesepe′hX


Kinematical Separation (for )

Separation is possible by means of a cut on the energy flow from the virtual photon to the measured hadron.

Currentfragmentation

Targetfragmentatio

n

log( )1

2 log( )

h h

h h

E p

E p

Hadron rapidity

Current

Target

x=0.3, Q2=3 GeV2

Pionelectroproduction


Kinematical coverageComplete measurement

of fracture functions:

•Almost whole z-range

•Possibility to access 5-dimensional cross section

•Allows to extract pT dependence

•Entire -range covered

GeV

2G

eV2

GeV2

E1-6

DA

TA

E1-6

DA

TA

E1-6

DA

TA

E1-6

DA

TA


Mulders Rapidity Gap

(1 )h h

t

p Ez

x P

2

2h h h

h h h

p p p

p p M

2 2k hM M p

( ) 2ln ln

CM

c Muldersc

h

qz

M

2 21ln ln ln

2h h h

CMh h h

p p p

p M M

h h hp E p

h hc

p Ez

q

( ) 2(1 )ln ln

CM

t Mulderst

h

x Pz

M

(1 ) (1 )W x ys x Mq qy

k E

ln lnCM

Mulders

h

Wz

M


Regge Approach

1 22 2( , , , ) ( )(1 ) ( , )Rhq R

R

M x z t Q F t z F x Q 2

1( ) , 5 8b tF t e bGeV

Structure functions of Regge trajectories CLAS-Note-01-006

1.08P

Need p-n difference to select of pure gluonic content of exchanged object.

neutron efficiency in

SC

neutronefficiency in EC

Two component duality: equivalence of Pomeron and the background

Test of Veneziano duality

( )( , ) ,ts t s s ( )( , ) ,ss t t t


Λ Polarization

0 1 cos CMpCM

p

dP

d

p

e e’

Λπ

1 2

6

(ud)-diquark is a spin and isospin singlet => s-quark carries entire spin of ,

uds

polarization in TFR provides information on contribution of strange sea to proton spin.

W.Melnitchouk and A.W.Thomas ‘96J.Ellis, D.Kharzeev, A. Kotzinian ‘96

Polarized beam gives unique possibility to perform an “acceptance independent” measurement of polarization in electroproduction.

– unique tool for polarization study due to it’s self-analyzing parity violating weak decay.

0.642 0.013

q

=1

q=1/2`q=1/2

K+ q=-s

(H. Avakian)


pT dependence

H2+H1

H3

H4

Distribution of Gaussian width of measured pT slopes for different structure functions.

Target Fragmentation studies at JLab M.Osipenko in collaboration with L. Trentadue and F. Ceccopieri, May 20,SIR2005, JLab, Newport News, VA CLAS Collaboration.

Documents

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current slide

clas q

target fragmentation

clas separation

jlab slide

clas acceptance

va clas collaboration