Sixth International Conference on Perspectives in Hadronic Physics

Hard Photodisintegration of a proton Pair

n(slow) )p(high p )p(high p He tt3 ++→γ

12 - 16 May 2008(Miramare - Trieste, Italy)

Tel Aviv University ,

Tel Aviv, Israel

E. Piasetzky

Kinematics:

)sin( )(sin 2

1 cm

2 θθ γγ EMEp cmdt ≈=

1) (4 M 2 M ) ( d2

d2 +≈+=+= γγγ EEpps d

]1)[cos(2E ]1)[cos( 2

M - s ) - (

2d2 −≈−≈= cmcmNppt θθ γγ

0cm 90 FOR =θ

GeV/c 1.5 p , 4 t,GeV 12 s GeV 2 t22 ≈−=≈= GeVEγ

GeV/c 2.5 p , 10 t,GeV 24 s GeV 5 t22 ≈−=≈= GeVEγ

photodisintegration is an efficient way to reach the hard regime.

To obtain the same s in NN scattering Pp ~ 2 Pγ.

γ

p

d/pp

n/pLAB

γ d/ppn/p

pGeV 5 - 2 =γE

CM

High – energy photodisintegration of the deuteron

npd ),(γ

The bremsstrahlumg endpoint technique:

It is enough to measure the proton momentum vector

The incident photon energy

The recoil neutron kinematics

Assuming two-body reaction

To ensure two-body reaction the reconstructed photon energyIs limited to the endpoint – the π mass

d

p

n

p

n

γ

Radiator

PhotonElectron

3Hep

p

µµ

HRS

n

θRadiator

PhotonElectron

d

npd ),(γ

Backgrounds are subtracted by “radiator out” and empty target runs

Build in quality-control – empty region beyond the endpoint

Exclusive large-momentum-transfer scattering

)f( S st)2-n(N- A DCB nnn

CDABdt

d +++=

→∝

σ

N = 1 + 6 + 3 + 3 – 2 = 11

) ( ) ( tt phighnphighpd +→γFor

Notice:

410 GeV/c) 4( / GeV/c) 1( ≈== γγσσ

Edtd

Edtd

scaling

•Dimensional (Constituents) counting rule:

(GeV) γE

)(GeV 222dmW −

Δ(1232)

N*(1520)D13 ?

Leading order pQCD underestimates cross sections for intermediate energy photo - reactions

Deuteron elastic form factor

FF (Q2 = 4 GeV2) calculation/data < 10-3

Meson photoproduction

Real Compton scattering

)pQCD scaling scaling --\ pQCD(

Farrar, Huleihel, Zhang PRL 74, 650 (1955)

Farrar, Huleihel, Zhang NP B 349, 655 (1991)

Brooks, Dixon PRD 62 114021 (2000)

p

n

d

Millions of diagrams like this

The observation of the scaling indicates the onset of the quark – gluon degrees of freedom, the appropriate underlying physics is not Leading order perturbative QCD.

γ

How to use experimental data to replace sum over many diagrams

Theoretical models:

How the photon is coupled

What diagrams can be neglected

p

n

dF (p)

F (n)

F (p)

F (n)

RNA (Reduced Nuclear Amplitude)

Experimental nucleon FF gluon exchanges within the nucleons

Neglect diagrams with gluon exchanges between the nucleons

Photon can interacts with any quarks

)(p

1 (n)F (p)F

)m-(s

1 2

2t

2222

dcmf

dt

d θσ∝

Brodsky , Hiller PRC 28, 475 (1983)

p

n

dF (p)

F (n)

F (p)

F (n)

TQC (Two - Quark Coupling)

gluon exchanges within the nucleons Experimental nucleon FF

Photon interacts with the exchange pair of quarks

)()(

1 (n)F (p)F

)m-(s

1 2

222

22d

cmfsdt

d θσΛ−

∝

Radyushkin

gluon exchanges between the nucleons neglected

p

n

d

HRM (Hard rescattering Model)

p) (2 lowdψ

qTγ

NNNNT →

Convolution of large angle pn scattering amplitude , hard photon – quark interaction vertex, and low momentum nuclear wave function

The pn scattering amplitude is obtained from large angle pn data

Frankfurt, Miller, Sargsian, Strikman PRL 84, 3045 (2000).

Quark – Gluon String model (QGS)

3 q exchange with an arbitrary number of gluon exchanges

Regge theory - nonlinear trajectory

Grishina et al. EUR. J. Phys. A 10, 355 (2000)

pn

d F(

F

F

F

)(p

1 (n)F (p)F

)m-(s

1 2

2t

2222

dcmf

dt

d θσ∝

pn

dp) (2 lowdψ

qTγ

NNNNT →

)()(

1 (n)F (p)F

)m-(s

1 2

222

22d

cmfsdt

d θσΛ−

∝

dN N

g

See M. Sargsian talk

RNA

HRM

CQM

QGS

See Sargsian talk

How are such large transverse - momentum nucleons produced?

Breaking a transverse compact object formed before the absorption?

) GeV/c 2 p ( ≈dψDouble hard scattering?

) MeV/c 300 P ( ≤dψ

But comparing calculations with the data do not reveal the underlying

physics .

RNA

HRM

Hard Photodisintegration of a proton pair

n(slow) )p(high p )p(high p He tt3 ++→γ

What new can we learn from that?

How are such large transverse momentum nucleons produced ?

Transitions from meson exchange to quark exchange

Scaling

Oscillations

3He

p

p

n

p

pµµ

HRS

HRS

Radiator

PhotonElectron

nppH e ),(3 γThe bremsstrahlumg endpoint technique

High – energy photodisintegration of a proton pair in 3He

Experiment E03-101

JLab. June 2007

a spectator neutron kinematics.

0. 90=mcθ

Hard photodisintegration of a proton pair

18

Experimental setup

e¡

Jefferson Lab

0.8-6 GeV

A

CB

Experiment E03-101

Hard photodisintegration of a proton pair

19

Experimental setup

Beam line

HRSHRS

Experimental Hall A

Experiment E03-101

Hard photodisintegration of a proton pair

20

Experimental setup

Electrons 3He cryotarget

Radiator

Photons

Target Chamber

Copper foils 1-6% r.l

Experiment E03-101

µ

Backgrounds are subtracted by “radiator out” and empty target runs

Build in quality-control – empty region beyond the endpoint

Beam energy

[GeV] γE

Radiator in

Radiator out

counts

With radiator

No radiator

Neutron momentum distribution based on 3He Wave function of R. Schiavilla, et al., PRL. 98, 132501 (2007), and references therein.

Correcting for the finite acceptance of the second spectrometer

Simulation assumes photon energy distribution based on Matthews and Owens NIM 111, 157-168 (73).

3He

p

pn

p

p

simulation

data

GeV 7.1=γE

Momentum of the proton [MeV/c]

Momentum of the proton [MeV/c]

HRS_right HRS_left

HRS_right HRS_left

angle of the proton [Deg.]

angle of the proton [Deg.]

Momentum of the neutron [MeV/c]

[Mev] γE

nα

Target position

[mm]

MC 2.1%

DATA 2.9%

Δ/D=-37%

MC 5.4%DATA 6.4%Δ/D=-19%

MC 16.3%DATA 16.6%Δ/D=-1.5%

MC 19.7%DATA 18.8%Δ/D=5%

MC 13.6%DATA 11.9%Δ/D=13%

MC 8.6%DATA 10.9%Δ/D=-28%

MC 5.9%DATA 5.1%Δ/D=12.5%

MC 13.5%DATA 15.3%Δ/D=-13%

MC 13.6%DATA 11.9%Δ/D=12.5%

MC 100%

DATA 100%

Box number

GeVE 7.1=γ

We (temporarily) assigned an extrapolation error of 15% to the data

At low photon energy

% 1 pn) ( / pp) ( 33 ≈→→ HeHe γσγσpn γγ σσ <<ppGeV/c 0.5 E ≤γFor

Laget NP A497 (89) 391, (Saclay data).

Magnitude of pp vs. pn hard photodisintegration

γ

ρπ ,0p

p

p

p

MEC is the dominant process

pp pair : only a neutral pion can be exchanged, its coupling to the photon is weak.

0 ≈ppγσ

Expected Results

Normalized to deuteron Absolute for 3He

Expected Results

See M. Sargsian talk

Expected Results

In contrast to low energy observations, nonperturbative models predict a large cross

section for the pp break up.

What are the relevant degrees of freedom?

This is an indication for quark – gluon dynamicsThe exchange particles in the diproton photodisintegration reaction are: Neutral at low energies where meson exchange dominates. Charged at high energy where quark exchanges dominate.

γE

?1

10

pn / σσ pp

The energy dependence of the pp/pn break up can map the transition

from hadronic to quark – gluon domain

preli

mina

ry

The new data were normalized to the preliminary CLAS data !

Preliminary Results

Δ(1

620)

S31

, N

*(16

50)S

11N

*(16

75)D

15,

N*(

1680

)F15

Δ(1

230)

preli

minary

preli

mina

ry

The new data were normalized to the preliminary CLAS data !

Preliminary Results

Δ(1

620)

S31

, N

*(16

50)S

11N

*(16

75)D

15,

N*(

1680

)F15

Δ(1

230)

200 )5.4( /)5.2( ≈dtd

dtd σσ

Δ(1230)

preli

mina

ry

Preliminary Results

Δ(1

62

0)S

31

, N

*(1

65

0)S

11

N*(

16

75

)D1

5,

N*(

16

80

)F1

5

Δ(1

23

0)

Δ(1

23

0)

N*(

15

20)

Preliminary Results

Outlook

?

?Improved statistic

Breaking a transverse compact object formed before the absorption?

) GeV/c 2 p ( ≈dψDouble hard scattering?

) MeV/c 300 P ( ≤dψ

RNA

HRM

We can utilize the recoil neutron to study how such large transverse- momentum nucleons are produced .

α=( E - PZ) / m

nppHeαααααγ ++=+=+

213 30

213 n pp ααα −−=⇒

Outlook

Physics Letters B 578 (2004) 69–77

n

p

p

p

p

n

γ

γ

αn 1

αn 1

scalingVerify the scaling for another hard exclusive reaction

Extend the verification of photodisintegrartion scaling

5

11

4

11

10 )1(

)5( 10

)1(

)4( ≈

⎥⎥⎦

⎤

⎢⎢⎣

⎡

==

≈⎥⎥⎦

⎤

⎢⎢⎣

⎡

==

γ

γ

γ

γ

EsEs

EsEs

Utilize the recoil neutron to study scaling

nppHeαααααγ ++=+=+

213 30

213 n pp ααα −−=⇒

2dd M

2

3M E 2 +

−≈ n

ppsα

γ

α=( E - PZ) / m

±3%

±1 S n-

)(

∝→ ppppdt

dγ

σ

HRM, α(1-1.2) / α(0.8-1)

Outlook

energy oscillation

If HRM is valid (see Sargsian talk) and photodisintegration amplitude can be factorized

Hard photodisintegration data can

be related to NN scattering data

We also have data pp),( 12 γCOutlook

Acknowledgment

Physics Letters B 578 (2004) 69–77

“Hard Photodisintegration of a Proton Pair in 3He”

Brodsky, Frankfurt, Gilman, Hiller, Miller, Radyushkin, Piasetzky, Sargsian, Strikman

Hall A / JLab.

Spokespersons: R. Gilman, E. Piasetzky

Experiment E03-101 collaboration

Graduate student: Ishay Pomerantz (Tel Aviv University)

Theoretical support : M. Sargsian

3He

γ p

p

µµ

HRS

n

θ

3He

γ

p

pn

p

pµµ

HRS

HRS

High – energy photodisintegration of a proton pair in 3He

Step 1. MCEEP Randomly pick scattering angle for the first proton

Step 2. MCEEP Randomly pick photon energy [1] and neutron momentum [2]

Step 3. MCEEP Calculates momentum magnitude of the first proton and the momentum of the second proton

[1] MATTHEWS AND OWENS NIM 111, 157-168 (73) [2] R. Schiavilla, et al., Phys. Rev. Lett. 98, 132501 (2007), and references therein.

MC 2.1%

DATA 2.9%

Δ/D=-37%

MC 5.4%DATA 6.4%Δ/D=-19%

MC 16.3%DATA 16.6%Δ/D=-1.5%

MC 19.7%DATA 18.8%Δ/D=5%

MC 13.6%DATA 11.9%Δ/D=13%

MC 8.6%DATA 10.9%Δ/D=-28%

MC 5.9%DATA 5.1%Δ/D=12.5%

MC 5.4%DATA 6.4%Δ/D=-19%

MC 13.5%DATA 15.3%Δ/D=-13%

MC 13.6%DATA 11.9%Δ/D=12.5%

MC 100%

DATA 100%

Δ/D [%]

Box number

Box number

GeVE 7.1=γ

Hard photodisintegration of the deuteron has been extensively studied

What did we learn?

What are the current problems?

) ( ) ( tt phighnphighpd +→γ

=1/3

16 / ≈pnpp γγ σσ

])dt

d( /)

dt

d[( )F / (F / 2

nppnpnreduced

ppreducedpp

σσσσ γγ =

FF

FF

FF

FF

N1

N2

N1

N2reduced2

2N21

2N1 )(-tF )(-tF

dt

d

dt

d σσ∝

4 (-2) )F / (F dataG andG 22np M E =≈⇒

4 ratio) (charge )dt

d( /)

dt

d( 2 =≈pn

reducedppreduced

σσ

5 3

16

][

MeV/c 100p ][

pn)d (

pp) He (2

n2He

pp3

3

≈≈•≤

=→→

∫∫

pn

pp

dγ

γ

σσ

ψ

ψ

γσγσ

∫∫ ≤

2

n2He

pp

][

MeV/c 100p ][

3

dψ

ψ

Is it SRC ? Does this talk being given in the correct section?

Preliminary Results

p

n

dF (p)

F (n)

F (p)

F (n)

RNA (Reduced Nuclear Amplitude)

Experimental nucleon FF gluon exchanges within the nucleons

Neglect diagrams with gluon exchanges between the nucleons

Photon can interacts with any quarks

)(p

1 (n)F (p)F

)m-(s

1 2

2t

2222

dcmf

dt

d θσ∝

Brodsky , Hiller PRC 28, 475 (1983)

p

n

dF (p)

F (n)

F (p)

F (n)

TQC (Two - Quark Coupling)

gluon exchanges within the nucleons Experimental nucleon FF

Photon interacts with the exchange pair of quarks

)()(

1 (n)F (p)F

)m-(s

1 2

222

22d

cmfsdt

d θσΛ−

∝

Radyushkin

gluon exchanges between the nucleons neglected

p

n

d

HRM (Hard rescattering Model)

p) (2 lowdψ

qTγ

NNNNT →

Convolution of large angle pn scattering amplitude , hard photon – quark interaction vertex, and low momentum nuclear wave function

The pn scattering amplitude is obtained from large angle pn data

Frankfurt, Miller, Sargsian, Strikman PRL 84, 3045 (2000).

Quark – Gluon String model (QGS)

3 q exchange with an arbitrary number of gluon exchanges

Regge theory - nonlinear trajectory

Grishina et al. EUR. J. Phys. A 10, 355 (2000)