Deeply Virtual ω Production

47
Deeply Virtual ω Production Michel Garçon & Ludyvine Morand (SPhN-Saclay) for the CLAS collaboration MENU 2004, Beijing e - e -’ p p’ ω *

description

e -’. ω. e -.  *. p. p’. Deeply Virtual ω Production. Michel Gar çon & Ludyvine Morand (SPhN-Saclay) for the CLAS collaboration. MENU 2004, Beijing. Which picture prevails at high Q 2 ?. Meson and Pomeron (or two-gluon) exchange …. (Photoproduction). ω. π , f 2 , P. - PowerPoint PPT Presentation

Transcript of Deeply Virtual ω Production

Page 1: Deeply Virtual  ω Production

Deeply Virtual ω Production

Michel Garçon & Ludyvine Morand (SPhN-Saclay)

for the CLAS collaboration

MENU 2004, Beijing

e-

e-’

p p’

ω

*

Page 2: Deeply Virtual  ω Production

Which picture prevails at high Q2 ?Which picture prevails at high Q2 ?

Meson and Pomeron (or two-gluon) exchange …

… or scattering at the quark level ?

π, f2, Pρ0 σ, f2, P

ω π, f2, P

Φ P

Flavor sensitivity of DVMP on the proton:

ω

ρ0 2u+d, 9g/4

ω 2u-d, 3g/4

Φ s, g

ρ+ u-d

γ*LωL

6

2

4

),(),,)((

1)(1

Q

tfdxdztxbEaH

ixz

z

QQdt

d MSL

(Photoproduction)

(SCHC)

Page 3: Deeply Virtual  ω Production

CLAS: high luminosity run at 5.75 GeVCLAS: high luminosity run at 5.75 GeV

First JLab experiment with GPDs in mind

(october 2001 – january 2002)

- polarized electrons, E = 5.75 GeV

- Q2 up to 5.5 GeV2,

-Integrated luminosity: 30 fb-1

- W up to 2.8 GeV

W = 2.8

2

.4

2

1.8 G

eV

e- p e- p ωπ+ π- π0

Page 4: Deeply Virtual  ω Production

Identification of channelIdentification of channel e- p e- p ωπ+ π- π0

m2

(2m)2

- 0

n +…

0

Separation of :

+ - 0 (M = 783 MeV, = 8 MeV)

0 + - (M = 770 MeV, = 151 MeV)

through missing mass

Page 5: Deeply Virtual  ω Production

Determination of CLAS efficiency in 4DDetermination of CLAS efficiency in 4D

Analysis Code

CLAS GEANT simulation Event Generator

Ngen Nacc

For each 4D bin : eff = Nacc/Ngen

4 kinematical variables=> 4D efficiency table

Q2, xB, t,

eff ~ 5%

Q2 (

GeV

2 )

xB

28 millions events 20 days

through simulation

Page 6: Deeply Virtual  ω Production

xB from 0.16 to 0.70

Q2 f

rom

1.6

to 5

.6 G

eV2

+ binning in or t

Background subtractionBackground subtraction

Page 7: Deeply Virtual  ω Production

Extraction of σγ*p->pωExtraction of σγ*p->pω

*

0

( , )1 1 1( , )

2

2 2( , ) int

2 QnFp p radBR eff eff effCC EC wQ x L Q xV B B

BQxBx

*p

p

(b

)

Q2 (GeV2)

0.16 < xB < 0.22 0.22 < xB < 0.28 0.28 < xB < 0.34

0.58 < xB < 0.640.52 < xB < 0.580.46 < xB < 0.520.40 < xB < 0.46

0.34 < xB < 0.40

Q2 (GeV2)Q2 (GeV2)Q2 (GeV2)

Bin to bin syst. errors included = 15-18%

Main sources :• background subtraction = 8 or 12%• efficiency calculation = 8%

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Comparison with previous dataComparison with previous data

Compatibility with DESY data (1977)

Disagreementwith Cornell data (1981)

Q2 range much extended with our data

Page 9: Deeply Virtual  ω Production

(deg)

d/d

(b

/rd)

Differential cross sections in Differential cross sections in

* 1cos 2 2 1 cos

2p pd

T L T TT Ld

=> First indication of helicity non conservation in s-channel

TT e

t T

L (b

)

0.40 < xB < 0.46

0.22 < xB < 0.28 0.28 < xB < 0.34

0.46 < xB < 0.52 0.52 < xB < 0.58 0.58 < xB < 0.64

0.16 < xB < 0.22 0.34 < xB < 0.40

Q2 (GeV2) Q2 (GeV2) Q2 (GeV2) Q2 (GeV2)0, 0TT LT

Page 10: Deeply Virtual  ω Production

Differential cross sections in tDifferential cross sections in t

Large t range, up to 2.7 GeV2.

Small t : diffractive regime (d/dt ebt)

Large t : cross sections larger than anticipated

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Comparison with JML modelComparison with JML model

Model includes exchange of π0, f2, P

12( )2

12

F QQ

p p’

ω*

π0

Small |t|

* ω

p p’

Large |t|THIS WORK

12( , )2

12 ( )

F Q tQ

t

2

22

)(1

)0(1)(

t

t

(J.-M. Laget, to be published in Phys. Rev. D)

Page 12: Deeply Virtual  ω Production

Second part of data analysis: study of ω decaySecond part of data analysis: study of ω decay

• ω channel identification

• Determination of CLAS efficiency in 6D

• Study of ω decay

Angular distribution of ω decay products

(study of e-pπ+π-X final state)

Determination of ω polarization Test of s-channel helicity conservation (SCHC)

6D efficiency table

Q2, xB, t, , θN, φN

eff ~ 0,5%

0

Page 13: Deeply Virtual  ω Production

Study of ω decay (2)Study of ω decay (2)

041 1

1( ) 1 2 cos 2

2rNW N

3 1 1 2(cos ) 1 3 1 cos

4 2 204 0400 00N NrW r

3 1 1 2(cos , , ) 1 3 1 cos4 2 2

22 Re sin 2 cos sin cos 2

2 2 2cos 2

04 0400 00

04 0410 1 1

1 1 1 111 00 10 1 1

2 210

sin cos 2 Re sin 2 cos sin sin 2

2sin 2 2 Im sin 2 sin Im sin sin 2

2 (1

1 1

N N N

N N N N

N

r r

r r

r r r rN N N N N

N N N Nr

W

r

2 2 2) cos sin cos 2 Re sin 2 cos sin cos 2

22 (1 )

5 5 5 511 00 10 1 1

6 6sin 2 Im sin 2 sin Im sin sin 210 1 1

N N N N N N

N N N

r r

N

r r

r r

N

cosN

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ω decay study : φN dependenceω decay study : φN dependence

41 00

1r => other indication of non conservation of helicity in the s-channel

Determination of 041 1r

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Contribution of L from VGG (GPDs) and JML (Regge) models

Contribution of L from VGG (GPDs) and JML (Regge) models

VGG model:M. Vanderhaeghen, P. Guichon, M. Guidal

<W> = 2.1 GeV

<W> = 2.8 GeV

L

T + L

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Conclusions and perspectivesConclusions and perspectives

• Precise measurements of the e-p e-p reaction at high Q2

and over a wide range in t• Exclusive reactions are measurable at high Q2 (even with the current « modest » CEBAF energy) • First significant analysis of decay in electroproduction

• Cross sections larger than anticipated at high t• SCHC does not hold for this channel• Evidence for unnatural parity exchange

0 exchange very probable even at high Q2

What do we learn ?What do we learn ?

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• JML model (Regge) : Good agreement when introducing a t dependence in the form factor suggests coupling to a « point » object at high t (hep-ph/0406153)

• VGG model (GPDs) :Direct comparison not possible since L not measuredNevertheless handbag diagram contributes only about 1/5 of measured cross sections no incompatibility→ ω most challenging/difficult channel to access GPD

• Explore physical significance of high t behaviour • Systematic study of other processes (e-p e-p 0, , ) in view of an interpretation in terms of GPDs• Measurements feasible up to Q2=8-9 GeV2 with CEBAF@12 GeV

PerspectivesPerspectives

Comparison to modelsComparison to models

Page 18: Deeply Virtual  ω Production

linea

r

saturation

Regge theory applied to vector meson productionRegge theory applied to vector meson production

α(t)

t

(Jean-Marc Laget et al., see also talk of Marco Battaglieri)

Regge trajectories exchange in t channel

0

parameters

=

coupling constants g ij

12( )2 21 /

F QQ

Extension to electroproduction case

*

add a parameter = electromagnetic form factor

2( )F Q0 exchange dominance

at W ~ few GeVin ω photoproduction

Page 19: Deeply Virtual  ω Production

FACTORIZATION

GPD formalism for vector mesonsGPD formalism for vector mesons

In the Bjorken regime :

Collins et al.

*L LM

t small

1 11 1 1( , , )

0 1M

L H Ez

A dz dx a b x tz Q ix xi

Amplitude:

e-

p

p p+

q q-

x+x-

e-

p

M

*

L

LM

H, E

z

t=2

2 1*6L L L Lp pM

QA

Cross section:

Scaling law

= 0, , (see talk by Michel Guidal)

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Kinematical domain explored

Reson

ance

sW

=1,

8

W=M Inelastic

x B = 0,1

x B = 0,8

valen

ce quarks

ν (GeV)0,1 1 10 100

Q2 (

GeV

2 )

0,1

1

10M 1,8

2

2

QxB M

,q

xB

Elastic pQCD

Regge

gluons sea quarks

Elastic

Resonances

Deepinelastic

W (GeV)

2 2 2 2( ) 2W P q M M Q

M 1,8

Page 21: Deeply Virtual  ω Production

Electron identification

e-

10 RL

6 RLOUT

IN

Information from DC + CC + EC

e--

Pion rejection

Electron selection

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Hadron identification

Information from DC + SC

DC 22

)(Mp

pM

SC DCSC

SC

l

c t

0)( MSC M

+

p

Page 23: Deeply Virtual  ω Production

Identification of channel e- p e- p ωπ+ π- π0through missing mass

0

m2

0

Page 24: Deeply Virtual  ω Production

Background subtractionBackground subtraction

Event weighting : w=1/eff(Q2,xB,t,)

y(m) = Skewed Gaussian + Pol2

(peak + radiative tail) (background)

Fit of MX[e-pX] with :

Subtraction of y(m).

Integration of event number between 720 and 850 MeV.

Page 25: Deeply Virtual  ω Production

Determination of CLAS efficiency in 6D

6 kinematical variables=> 6D efficiency table Q2, xB, t, , θN, φN

118 millions events 63 days

through simulation

For each 6D bin : eff = Nacc/Ngen eff ~ 0,5%

Analysis Code

GPPGSIM Event Generator

Ngen Nacc

Page 26: Deeply Virtual  ω Production

Phase space (1)

Page 27: Deeply Virtual  ω Production

Phase (2)

Page 28: Deeply Virtual  ω Production

Experimental Q2, xB, t, , … distributions

e-p+-X

e-p+X

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CLAS system efficiency

4D

6D

Page 30: Deeply Virtual  ω Production

Formalism for ω decayFormalism for ω decay

Decay angular distribution :

elements of ω spin density matrix ε parameter of virtual photon polarization R = σL/σT (Rp : = T + L)

αρij

Deduce :

• ω polarization via

• SCHC test : (necessary condition)

• If SCHC, then separation σL, σT

• Test of hypothesis of natural parity exchange in the t-channel (NPE) :(necessary condition)04 04 1 1

00 1 11 2 2 1 12 011r r r r

βrijαρij

04 0400 001R r r

41 00

1r

0-, 1+UNPE0+,1- NPE

p p’

ω*

cos , , ; rijN NW

, ,f Ririj j

i, j meson helicity

virtual photon polarization

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Study of ω decay (2)Study of ω decay (2)

Determination of 0400r

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Bx

ω decay study (4)ω decay study (4)

2cos

sin 2

5 1

2 25

Re

0400

0 co2

410 s

4

r

r

N

N

04 04 1 100 1 11 2 2 1 12 011r r r r

exchange of unnatural parity

particle in the t-channel

Method of moments :2

Determination of 15 rij

parameters which should vanish if SCHC holds

combinaison which should vanish if NPE holds

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decay study (cont.)

3 1 1 2(cos , , ) 1 3 1 cos4 2 2

22 Re sin 2 cos sin cos 2

2 2 2cos 2

04 0400 00

04 0410 1 1

1 1 1 111 00 10 1 1

2 210

sin cos 2 Re sin 2 cos sin sin 2

2sin 2 2 Im sin 2 sin Im sin sin 2

2 (1

1 1

N N N

N N N N

N

r r

r r

r r r rN N N N N

N N N Nr

W

r

2 2 2) cos sin cos 2 Re sin 2 cos sin cos 2

22 (1 )

5 5 5 511 00 10 1 1

6 6sin 2 Im sin 2 sin Im sin sin 210 1 1

N N N N N N

N N N

r r

N

r r

r r

cosN N

TT TL

1 1 5 511 00

3( ) cos 2 c 114 0os 0r r r rW

But :

' '

' '

1 * *1 1 11 11 1 111

, ,

1 * *0 1 01 01 0 100

, ,

111

100

N N N N

N N N N

r

r

T T T T

T T T T

' '

' '

5 * * * *10 11 11 10 10 1 1 1 1 1011

, ,

5 * * * *00 01 01 00

51

00 0 1 0 1 00

1

500 00

, ,

N N N N

N N N N

r

r

T T T T T T T T

T T T T T T T T

and

If SCHC then : 1 1 5 511 00 00 011r r r r and 0TTT L

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R extraction

'

2 2001 0 100

,N N

T T

0 if SCHC

'

240000

,N N

T

1 if SCHC

0040

400 00

10rR

R

10400 R

rR

SCHC

Theory :

Observation :

'

1 *01 0 100

,

10 00

N N

T Tr

' '

5 * *01 00 0 1 0000

, ,

50 00

N N N N

T T Tr T

So one can’t extract R.

Same helicity amplitudesthan the ones that come into play in 0

00

04

1

1

000400

Rr

r

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R extraction (cont.)

041

1

000400

Rr

r

Suppose SCHC holds, then :

One has found : 0400 0,44r

Then :1 0,44

1,460,54 1 0,44

L

TR

But : T L

So : 0,561

0,821

T

L

RR

R

Page 36: Deeply Virtual  ω Production
Page 37: Deeply Virtual  ω Production

0 meson production and JML model

Page 38: Deeply Virtual  ω Production

Comparison with JML model (cont.)<W> = 2.1 GeV

<W> = 2.8 GeV

Within this model, Data still favor a t-dependent πγω form factor. π0 exchange dominant for the whole Q2 range. σT dominant for the whole Q2 range.

Page 39: Deeply Virtual  ω Production

Form Factors => transverse position

Q2 = -t

Exclusive elastic reactionse-

e-

p

2Q

p

MotivationsMotivationsHigh Q2 reactions give access to internal dynamics of the nucleon

Deep inclusive reactions

Parton Distributions

longitudinal momentum fraction quarks contribution to nucleon spin

x = xB

e-

e-

px

2Q

X

Deep exclusive reactions

Generalized Parton Distributions

correlations ! quarkangular momentum

e-

e-

p p

ou M

x

2Q

x

t

x, t, ξ

e-

e-

*,q

Page 40: Deeply Virtual  ω Production

Link with FF and PD

0 access to correlations ,

x, dependence quark longitudinal impulsion

t dependence quark transverse impulsion

Ji sum rule :

GPD formalism (cont.)

g

gq

J

LG

J

L

q

21

21

qqqq

Page 41: Deeply Virtual  ω Production

VGG (GPDs) model

2 211

2 11 1

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

(1 )

b

bqDD x d d x C q D x

2, / 2, , a Q tH E DD x e

x,t, dependence parametrization:

2 parameters : bvalence et bsea

Corrections to leading order:

In fact Q2 non infinite

1 12

2

x i k perpx i

Q

In pratice :non perturbative effects at small Q2 averagedby « frozing » the strong coupling constantS to 0.56

Page 42: Deeply Virtual  ω Production

Contribution of L from VGG (GPDs) model (cont.)

Page 43: Deeply Virtual  ω Production
Page 44: Deeply Virtual  ω Production

* p

p

b

)

Q2 (GeV2) Q2 (GeV2)

Q2 (GeV2) Q2 (GeV2)

xxBB=0.31=0.31 xxBB=0.38=0.38

xxBB=0.45=0.45 xxBB=0.52=0.52

0 meson results at 4.2 GeV (Regge)

C. Hadjidakis et al.

Page 45: Deeply Virtual  ω Production

0 meson results at 4.2 GeV (GPDs)xxBB=0.31=0.31 xxBB=0.38=0.38

xxBB=0.45=0.45 xxBB=0.52=0.52Q2 (GeV2) Q2 (GeV2)

Q2 (GeV2) Q2 (GeV2)

* Lp

p L

b)

C. Hadjidakis et al.

Page 46: Deeply Virtual  ω Production
Page 47: Deeply Virtual  ω Production

G parity definition

yi IG Ce