Beijing, Sept 2nd 2004 Rachele Di Salvo Beam asymmetry in meson photoproduction on deuteron targets at GRAAL MENU2004 Meson-Nucleon Physics and the Structure

Beijing, Sept 2nd 2004 Rachele Di Salvo

Beam asymmetry in meson photoproduction on deuteron targets at

GRAAL

MENU2004Meson-Nucleon Physics and the Structure of the Nucleon

August 29th - Sep 4th 2004, Beijing (China)

presented by

Rachele Di SalvoRachele Di SalvoOn behalf of the GRAAL Collaboration

I.N.F.N. – Sezione Roma2


Outline

The GRAAL experimental set-up

Physics motivations Preliminary results for:

in , 0 photoproduction on q.f. proton and q.f.neutron in deuteron

Update on search on pentaquark in: n n (P11) d

Summary and Conclusions


The Graal facility is a backscattering photon facility located at the E.S.R.F. (Grenoble, France)


Main GRAAL features

• Production technique: Compton backscattering of laser light on electrons •Energy range: 0.5 1.5

GeV

e-

e-Ee,me

E’e, me

E

EL

L

•Energy resolution: 1.1% (FWHM)

•High polarization degree

( 100% for the higher energies)

Photon beam

1ch=50 ps

=147ps

•Monitoring of the flux


Photon detection (energy resolution 3% FWHM at 1 GeV)

Charged particle identification and reconstruction (proton - pions)

Energy measurement for protons

Neutron detection (and energy measurement in forward direction)

Experimental Apparatus


The Graal detector: Lagrane

Large Acceptance Graal Apparatus for Nuclear Experiments


Physics motivationsIn the resonance region perturbative QCD cannot be applied.

The processes can be described in terms of effective theories based on a certain number of experimental constraints for the determination of static and dynamical properties of N* resonances: mass M, width , helicity amplitudes A1/2 and A3/2 ,

partial decay widths n , n , YK .

1) Precise measurements of differential cross sections and asymmetries in meson photoproduction on the nucleon are necessary

2) Measurements in neutron targets (deuteron) are necessary for a study of the isospin structure of photoexcitation amplitudes.


+p+(n) -> +p+(n)

To be compared with photoproduction on free proton

+n+(p) -> +n+(p)

p -> +p

photo-production on quasi-free nucleons

from Deuteron


+p+(n)->+p+(n) 2

Events selection (1)

•1 neutron incentral or forward direction

•NO charged particle (the proton is spectator)

•1 proton incentral or forward direction

•NO other neutral particle (the neutron is spectator)

•2 in BGO ( invariant mass)

+n+(p)->+n+(p) 2


• Invariant mass of 2 in BGO 0.45 M 0.65

GeV

•Bidimensional cut on -nucleon coplanarity vs. miss= Polar angle of the particle missing from in 2-body kinematicsN = Nucleon polar angle

= miss-N

Bidimensional cut on (Mmiss,-MN ) vs. (Mmiss,N-M )

Mmiss,N= Mass of missing particle from

(Nucleon)

N.B. For the central neutron: Mmiss n obtained by the |pn| extracted by

two body kinematics + n and n measured in the BGO detector



Events selection (2): Two body reaction

Proton

miss-p(deg)

-

p (deg)

miss-n(deg)

-

n (deg)

Neutron


Mmiss (GeV)

Mmiss N (GeV)

Forward nucleon

Mmiss N (GeV) Mmiss (G

eV)

Proton

Neutron

Central nucleon



Invariant Mass

Before cuts

After cuts

Mass (GeV) Mass (GeV)

Proton

Neutron


Azimuthal Distribution: ))cos(2P(121

/KN/KN/KN

2211

11

Proton

Neutron


firstresults on q.f.proton+p+(n)->+p+(n) Green Laser LineUV Laser Line

Said- BO12

N.B. Error bars: statistical errors only

Maid

Preliminary

Preliminary


Preliminary

Said- BO12 (free proton)Maid (free proton)

Comparison photoproduction on

+ p -> + p Free proton

Quasi free proton

+ p (n) -> + p (n)


Maid (free proton)Maid (free neutron)

firstresults on q.f.neutron+n+(p)->+n+(p) Green LineUV Line

N.B. Error bars: statistical errors only

Preliminary

Preliminary


Quasi free neutron

Quasi free proton

+ p (n) -> + p (n)

+ n (p) -> + n (p)

Comparison photoproduction on

Preliminary


+p+(n) -> 0+p+(n)

To be compared with 0 photoproduction on free proton

+n+(p) -> 0+n+(p)

p -> 0+p

0 photo-production on quasi-free nucleons

from Deuteron


+p+(n)->0+p+(n)2


•1 neutron incentral or forward direction

•NO charged particle (the proton is spectator)

•1 proton incentral or forward direction

•NO other neutral particle (the neutron is spectator)

•2 in BGO (0 invariant mass)

+n+(p)->0+n+(p)2


• Invariant mass of 2 in BGO M 0.25 GeV

• Bidimensional cut on -nucleon coplanarity vs.

• Bidimensional cut on (Mmiss,-MN ) vs. (Mmiss,N-M )

for forward nucleons

• Bidimensional cut on (Ecalc,N-Ecalc’,N ) vs. (Mmiss,-MN

)

for central nucleons

Ecalc,N = Nucleon energy extracted from energy

conservation

Ecalc,N = E + MN - E

Ecalc’,N = Nucleon energy extracted from 2-body kinematics

Ecalc’,N (E, N, N )



Events selection (2): Two body kinematics

miss-N (deg)

-

N (deg)

-

N (deg)

Before cut After cut

miss-N (deg)

alessia

neutron dtheta 8 deg coplan 16 deg



Mmiss N-M ° G

eV)

Mm

iss ° -MN (Gev)

Forward proton/neutron


Mm

iss ° -MN (Gev)

MmissN-M ° G

eV)

alessia

neutron missmpio-mn 100 MeV missmn-mpio 160 MeVproton missmpio-mp 140 MeV missmp-mpio 180 MeV


Events selection (2) Central proton/neutron


Ecalc N – Ecalc’

N (GeV) Mmiss °-MN

(Gev)

Ecalc N – Ecalc’

N (GeV)Mmiss °

-MN(Gev)

alessia

neutron dEcalc 80 MeV missm-m 120 MeVproton dEcalc 60 MeV missm-m 120 MeV


Green Line Said- SM02UV Line Mai

d

Preliminary

Preliminary

N.B. Error bars: statistical errors onlySistematic errors 1.5%

firstresults on q.f.proton+p+(n)->0+p+(n)


Said- FA01 (free proton) GRAAL data included up to 1.1 GeV

Said - WI00 (free proton)GRAAL data NOT included

Comparison 0 photoproduction

on

+ p -> 0 + p

Free proton

Quasi free proton

+ p (n) -> + p (n) (uv data)

(green data)

Preliminary


firstresults on q.f.neutron+n+(p)->0+n+(p)

Green LineUV Line

Said (free neutron)Maid (free neutron)

N.B. Error bars: statistical errors onlySistematic errors 1.5%

Preliminary

Preliminary



onQuasi free proton

+ p (n) -> + p (n)

Quasi free neutron

+ p (n) -> + p (n)

Low energy bins

Preliminary



onQuasi free proton

+ p (n) -> + p (n)

Quasi free neutron

+ p (n) -> + p (n)

High energy bins

Preliminary


Conclusions (1)First results have been obtained on the analysis of the ando photoproduction on the quasi-free proton and neutron on a deuteron target:Asymmetry results show:

photoproduction: qfp and free proton similar behavior

qfn and qfp similar behavior o photoproduction: qfp and free proton similar behavior

qfn and qfp different behaviour at higher energy bins: NO change of sign for neutron


+ n + vs + d +

REACTION 1 Threshold 1738 MeV REACTION 2 Threshold 941 MeV

+

+

+

+

+

+

It is accessible at lower incoming energies


Photo-production Decays

+ d +

K° p - p

+

dp


° Invariant Masses + d +

VERYPRELIMINARY

°1 Invariant Mass GeV

°2 Invariant Mass GeV


X-Y Vertex + d

VERYPRELIMINARY

y (cm)

x (cm)


VERYPRELIMINARY

cm

Z Vertex + d


theta vs. phi + d

VERYPRELIMINARY


M vs MK° + d VERY

PRELIMINARY


VERYPRELIMINARY

1531 Mev

invariant mass from enlarged statistics

Very Preliminary


N5(1710) or P11(1710)

From a recent paper of Polyakov

“On photoexcitation of baryon antidecuplet”

HEP-PH/0303138;

Eur. Phys.J. A18,691-695(2003))

the photoexcitation of the P11 in the -channel should be much more strongly pronounced on the neutron than on the proton:

+ n (p) -> + n (p)

+ p (n) -> + p (n)


The -nucleon invariant mass in the final state of the reactions:

+ d -> + n + (p)

+ d -> + p + (n)

Data Simulation

The N5 (1715) dduuu Final State

VERY PRELIMINARYDo not quote

Very Preliminary


The -nucleon invariant mass calculated from the energy of the incoming gamma ray:

+ d -> + n + (p)

+ d -> + p + (n)

Data Simulation

The N5 (1715) dduuu Initial State

VERY PRELIMINARYDo not quote

Very Preliminary


ConclusionsWORK IN PROGRESS on the two promising channels:

+ d

+ n (p) N5 n (p)

•More results are expected in the near future from new data taking

•Future: Data taking with a polarized HD target

Documents

Beijing, Sept 2nd 2004 Rachele Di Salvo Beam asymmetry in meson photoproduction on deuteron targets at GRAAL MENU2004 Meson-Nucleon Physics and the Structure