General Review of GRAAL physics :Achievements and Future

D. Rebreyend LPSC Grenoble

(GRAAL Collaboration)

MENU04, 30 August ’04

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Outline

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

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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

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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

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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

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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

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• 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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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)

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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!!

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Proton Beam Asymmetry

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Neutron Beam Asymmetry

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K0 Analysis

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K0results

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European Synchrotron Radiation Facility

• Circumference : 844 m

• 40 beamlines

• Ee = 6.03 GeV

• Ie = 200 mA

• Bunch structure = 2.8 ns

ESRF parameters

GRENOBLE