General Review of GRAAL physics : Achievements and Future

General Review of GRAAL physics :Achievements and Future

D. Rebreyend LPSC Grenoble

(GRAAL Collaboration)

MENU04, 30 August ’04

D. Rebreyend, MENU04 2

Outline

GRAAL set-up Meson photoproduction on the proton Eta photoproduction on the neutron HYDILE polarized HD target


Compton Beam

(nm) E(MeV)

514 1100

351 1483

300 1660

Energy Spectrum Polarisation

Simulation

Experiment

EeESRF = 6027.6 0.6

MeV

Linear

Circular

tag~ 10 6 /s

FWHM=16 MeV

Tagged

region


LAGRANE Detector

1: Compton beam 2: Liquid H2/D2 target

3: BGO Calorimeter 4: Cylindrical MWPC’s

5: Plastic Barrel 6: Plastic Wall

7: Plane MWPC’s 8: Shower Wall

Shower Wall

• neutron efficiency 20 %

• / neutron PID

ToF

E

250


GRAAL Domain

• E = .6-1.6 GeV/ W=1.4-2 GeV

• Region of second and third resonance

• , K, ’ thresholds

• Complementary of LEGS and LEPS

’ threshold

threshold

K threshold

LEGS/BNL LEPS/SPRING8

E (GeV)

(

b)

threshold

Meson Photoproduction on the proton


Survey of GRAAL Results Published

+n: from 700 to 1500 MeV (PLB ’00 and ’02) p : and d/d from threshold to 1100 MeV (PRL ’98, PLB ’02)

00p: and d/d from 700 to 1500 MeV (PRL ’03)

Close to completion 0p: and d/d from 700 to 1500 MeV p : extension to 1500 MeV

In progress p : comparison neutral (0 ) / charged decay (+0) K and K

K AnalysisChannel selection

• 3 tracks in MWPC’s

• 2-body kinematical constraints calculation of 3 momenta

• PID by combining calculated momenta with E and/or ToF

important check: vertex reconstruction

p + - K

Distance (primary-secondary) vertices

(No efficiency correction)

Distance (primary-secondary) vertices

(No efficiency correction)

c = 7.6 cm

(PDG: 7.89 cm)

Azi

muth

al dis

trib

uti

on

NH+NV NV-NH/NH+NV

P

Beam Asymmetry

Recoil Polarization (linear polar.)

Px = P Ox sin21 - Pcos2

Py = P - P T cos2/ 1 -

Pcos2

Pz = P Oz sin21 - Pcos2

1.2 GeV

1.4 GeV

1.05 GeV

1.2 GeV

1.4 GeV

1.05 GeV

angular distributionangular distribution

P angular distributionP angular distribution

Good agreement with LEPS

PRL ‘03

d/d = (d/d)0{1 – P cos(2) }

Cross SectionC

ount

s/do

se (

a.u.

)C

ount

s/do

se (

a.u.

)

p K+ p K+

p K+ p K+

SAPHIR data (EPJ ’04)

Eta photoproduction on the neutron


• SAID analysis : Possible narrow N* at 1680 and/or 1730 MeV

• Polyakov & Rathke (EPJ A18 (03)) :Dominance of photoproduction on the neutron for N10

look for reactions : n N10 n, K0 , K+ -

Recent Motivation Soliton Model anti-decuplet

Non-exotic resonance with a narrow width 10 MeV


Preliminary Remarks Grenoble analysis (A. Lleres) Studied channels :

d +

n K0 n K+ -

n n (“ easy channel ”) cross section Comparison p p proton target / deuteron target Preliminary results (error bars only statistical) No Fermi momentum correction:

width structure (E)100-130 MeV

No evidence but statistics is too poor for

definite conclusion


n(p) n(p) Event Selection

• Identical geometrical acceptances for n and p

• Selection of “Quasi-Free kinematics” ??

All final state particles detected: 2 + n (p) proton/neutron detected at forward

angles : lab 250

2 detected in BGO : lab 250

Selection by invariant mass and

2-body kinematical angular correlations no recoil proton/neutron

n / p


Invariant Mass

p : 0.6 % (taking p= n ) n : 0.3 %

N N : 1-3 %

1.2 % 0.9 %

n n n n p p p p

Simulation

Data

Small background

Background

estimates


p p Differential Cross Section : Free/Quasi-free

d/

d

(b

/sr)

CM = 1620

Distributions at fixed CM (backward) angles versus E

CM = 1480

CM = 1390

CM = 1230 CM

= 1170

CM = 1300 CM

= 1100 CM = 1040

Clear Discrepancy below 1100 : Data Analysis / Physics ?

not quasi-free reaction close to 1000


n n Differential Cross Section

• No prominent peak

• Structure at E 1.05 GeV (W 1.7GeV)

• Marked Angular Dependence

d/d (b/sr) at fixed CMd/d (b/sr) at fixed CM

CM = 1540 CM

= 1340

CM = 1200 CM

= 1070


Comparison QF neutron vs QF proton (1)Ratio QF neutron/QF proton

R=dn/dp at fixed CMR=dn/dp at fixed CM

• Ratio 0.6-0.5 below 900 MeV

(Bonn, R=0.68 PRL ’97)

• Sudden rise around 1 GeV resonance

(Kouznetsov, Moscow seminar, April ’03)

CM = 1540 CM

= 1340

CM = 1200 CM

= 1070


Comparison QF neutron vs QF proton (2)Integrated Cross Section (p,n 250)

• No “narrow” peak observed in neutron cross section but

shoulder for neutron above 900 MeV

• Rise in difference (neutron-proton) compatible with “narrow” structure

neutron

normalized QFproton

neutron

normalized QFproton*

neutron – C x protonneutron – C x proton

Simulated peak :

W=1.68 GeV, = 10 MeV

Because of Fermi motion :

FWHM = 127 MeV


Comparison QF neutron/QF proton (3)Integrated ( n) Invariant Mass (p,n 250)

• No peak : compatible with behaviour of d/d

• Spreading due to Fermi motion Resolution

( n) Invariant Mass (GeV)

neutron

normalized proton

neutron

normalized proton*

neutron – C x protonneutron – C x proton

Simulated peak :

W=1.68 GeV, = 10 MeV

Because of resolution :

FWHM = 96 MeV

Num

ber

of e

vent

s


Beam Asymmetry

See R. Di Salvo’s talk in Parallel Session for more details

n n n n p p p p

Bea

m A

sym

met

ry

HYDILE target


Operating Principle & Performances Pure HD

good dilution factor (15 % Al)

n and p are polarized

“Relaxation Magnetic Switch” principle (Hoenig ’67)

o-H2 impurities used to polarize (HD weakly coupled to lattice)

o-H2 decays to p-H2 in a few days HD spins decoupled from lattice

relaxation time / 1/ o-H2 concentration

Fabrication process

polarization of HD with static method in a Dilution Refrigerator (17 T, 10 mK)

at Orsay

aging process in DR for 2-3 months 1 T, 1 K

transport from Orsay to Grenoble

Expected performances

polarization : 80 % for p and 20 % for d (50 % with FAP)

relaxation time : 1-2 weeks

Dilution Refrigerator (Orsay)

In-beam + transfert cryostats (Grenoble)


First run with polarized HD in November 2004

Recent achievements

• Installation of Transfer (TC) and In-beam cryostats (IBC) in Grenoble (10/03)

• Running of IBC during 3 days at 1.5K (11/03)

• First complete and successful transfer of an unpolarized HD sample from Orsay to Grenoble (April 2004)


Summary

p and K, : results will be released in a “near” future

n n : preliminary results on d/d have been obtained at neutron forward angles ( 250) No prominent peak but structure is observed around W=1.7 GeV

not seen on the proton Extension to all angles foreseen

First data with HYDILE target scheduled in November!!


Proton Beam Asymmetry


Neutron Beam Asymmetry


K0 Analysis


K0results


European Synchrotron Radiation Facility

• Circumference : 844 m

• 40 beamlines

• Ee = 6.03 GeV

• Ie = 200 mA

• Bunch structure = 2.8 ns

ESRF parameters

GRENOBLE

General Review of GRAAL physics : Achievements and Future

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