brahim morenostudents' seminar at bosen workshop Δvcs and generalized parton distributions...

Brahim Moreno Students' seminar at Bosen Workshop

ΔVCS and Generalized Parton Distributions

'epe

CLAS@Jlab


Outline

I. Generalized Parton Distributions

II. Beam Spin asymmetry

III. The experiment at Jlab

IV. First look at the Data


Generalized Parton Distributions

(GPDs)


In the Bjorken limit:

Large

Low

Fixed

General GPDs physics case

t

γ or mesonl’

l

γ*

N N’

standard notation

GPDs appear in the amplitudes of exclusive reactions

GPDs are a new way of describing the nucleon

l

)( 2Q

GPDs

γ

N

l’

N’

22 'llQ

2'NNt

'

2

2 llNb EEm

Qx


z

)( b

0

x

b

y

Nucleon form factor

)(xf

x1

x

xp

z

zy

Parton distribution

1

),( bxf

0

GPDs

GPDs : combine information from form factors and parton distribution

xfractionmomentumallongitudinawithcenternucleonfrombatbeto

nucleontheinquarkaforamplitudeyprobabilittherepresent

x

xp

z

zy

epep eXep MNlNl ''

Beam Spin Asymmetry


Beam Spin Asymmetry (BSA)

general case

kk

kk

dd

ddA

NN

NN

PA

1

k = number of independent variables P = polarization of incoming lepton

MNlNl ''

l = lepton, N= nucleon

l’= scattered lepton, N’= recoil hadron, M= photon or meson


Beam Spin Asymmetry (BSA)

DVCS example '' pepe

epep

Interference between DVCS and Bethe-Heitler processes

2

+ +

DVCS BHBH

cos1

sin

Aβ,α are combinations of

GPDs

BSA grants access to nucleon GPDs


Beam spin asymmetry: ΔVCS case

'epe

e

e’

γ* γ

Np

л

-N-Δ transitions at a partonic level

- large Nc approximation: ΔVCS can be

described in terms of standard GPDs

77

77

dd

ddA

GPDs N-Δ

L.L. Frankfurt, M. V. Polyakov,M. Strikman, M.VanderhaeghenPhys. Rev. Lett. 84: 2589-2592 (2000)

P.A.M Guichon, L.Mossé, M.Vanderhaeghen

Phys. Rev. D68 034018 (2003)


+ eep

+

2ΔVCS BHBH

FIRST measurement

P.A.M Guichon, L.Mossé,

M.Vanderhaeghen

Phys. Rev. D68 034018 (2003)


The experiment at Jefferson lab


Thomas Jefferson Laboratory (USA, Virginia)

Hall BHall B


Cherenkov Countersfor e/л separation

CLAS detector

Time-of-flight

counters (TOF)

Drift chambers (DC)to determine trajectories

to detect showering particles

Electromagnetic Calorimeter (EC, LAC)

Torus magnet

of charged particles

eep0 eep

for separation (DVCS)0

high energy resolution photon detector

Inner calorimeter (IC)

2005 data taking 35 days (from march to may 2005)

December 2006 : first thesis published (DVCS BSA)

2008 : second data taking period

Chronology

my arrival

2005 calibrations

2007 : ongoing analysis (DVCS , , , cross sections, , BSA ) 0 0

beam energy 5.776 GeV


First look at the data


Analysis plan

pepeeep '0''

Basic event selection: 1 electron, 1 proton, 3 photons

- reconstruct Δ particles via neutral pion reconstruction

- develop exclusivity cuts

- background and contamination studies

- Beam Spin Asymmetry results

e

e’

γ* γ

Np

л

Which one to choose ?

Before going further it would

be wise to have a preview of

the decay particles of Δ phase

space

Development of a kinematic

filter

Delta reconstruction

different photon combinations

GeVM p GeVM p

GeVM GeVM GeVM

GeVM p


Phase space generatorFirst look at the data


t random number uniformly distributed

Kinematic generator

max2

min22 ,QQQ

ν: random number uniformly distributed max2

min2 QQ eE,0

Q2: random number uniformly distributed

maxmin , ttt

t

0t mint max

LE LDVCS

E

ee’

γ* γ

Np

лt

Prediction for ΔVCS

8% events under 0 GeV

0'' peeep

)(0

GeVEE DVCS

DVCS photon = most

energetic one

First look at the dataSelection cuts

Selection cuts epepeep 0

Before cutsAfter cuts

Selection cuts: cut on epepeep 0

M

0m

m A B


A = second resonance region (~1.5 GeV)

B = third resonance region (~1.65 GeV)


Complementary slides


Kinematic generator

1** cos pEE p

Lp 1

** cos00 pEEL

2** cos00

2

pEEL

2** cos00

1

pEEL

Δ

γ

p

γ

0

*p

2

*p*

p

1


Kinematic generator

1cos uniformly distributed 1,1 1** cos pEE p

Lp

Lp

LL EEE 0

2cos uniformly distributed 1,1 2cos12

0

0

0

1

m

EL

LLL EEE1

02

Kinematic generator: validation '' pepe

generator resultdata


epep

epMM

epE

epp

epp

X

X

Xy

Xx

2

0epep

0

2

m

epMM X

02 epMM X

02 eMM X


Data analysisbackground and contamination

Overview

0 eep

R

RR

epep

epepep

epepep

0

0

000

0

epepep

epepep RR


Data

e1-dvcs experiment first part of 01-113 experiment

35 days (from march to may 2005) approved for 60 days

beam energy 5.776 GeV

123410.2 scmluminosity

to be completed next year

accumulated charge mC5.59

hydrogen target

More about GPDs

Standard GPDs

txE ,, txE ,,~

txH ,,~ txH ,,

γ

p’

e

e’

γ*

p

x-ξx+ξ

t

4 GPDs for each quark flavour

txC ,,1

txC ,,3

txHM ,, txH E ,,

txC ,,2

txC ,,4

txHC ,,

Transition N-Δ GPDs

3 transition vector GPDs

4 transition pseudo-vector GPDs

In the large Nc limit

txEtxEHtxH duMM ,,,,

3

2,,

txHtxHtxCtxC du ,,~

,,~

3,,,, 11

txEtxEtxCtxC du ,,~

,,~

4

3,,,, 22

Particle ID


cut on reconstructed vertex position

Particle ID: electron

Scattered electron identification

Fiducial cuts (EC,DC)

Cut on lost energy in inner part of EC: E_in>60 MeV

Cut on E/p vs p

Momentum threshold : p > 800 MeV

Cut on number of p.e’s produced in CC: 10*N > 25

id = 11



Fiducial cuts (EC)

Cut on lost energy in inner part of EC



pp

ppp

pppEtot

22

22

10.155,210.819,1)(

10.55,4115.03216.0)(

)(5.2)(

Cut on E/p vs p


Particle ID: proton

recoil proton identification

cut on reconstructed vertex position

Fiducial cuts (θ,φ)

Cut on calmes


photon identification:E > 150 MeV

Particle ID: photon

detected in ICfiducial cuts to avoid photons with hit near IC edgeassume all particles detected in IC are photons

detected in EC Fiducial cuts (EC) cut on β = l/t


Fiducial cuts

195.00

0

))(sin(27)(

52.0

93.08.16)(

),()()(

)(

pp

pp

ppp

p

cut

cut

cut

66.0

sin5.104.1)(

27),(

8.16

0

0sec

pp

p otor

o

electron

proton

photon

brahim morenostudents' seminar at bosen workshop Δvcs and generalized parton distributions...

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