Latest results from GRAAL collaboration presented by Valentina Vegna

Beijing, 19-22 April 2009 NSTAR 2009 Valentina Vegna

Latest results from GRAAL collaborationpresented by

Valentina Vegnaon behalf of the GRAAL Collaboration

Università degli Studi di Roma “Tor Vergata” and INFN Sezione di Roma Tor Vergata

Workshop on the Physics of Excited Nucleon – NSTAR 2009, Beijing

the GRAAL experimental set-up; and 0 photoproduction on quasi-free neutron; K+ and K+0 photoproduction on free proton; in memoriam of Eid Hourany.


Meson Photoproduction at GRAAL

(b

)

GRAAL/ESRF

E (GeV)

threshold

K threshold

’ threshold

Beam Asymmetry Measurements for accessible

reactions:

• polarized photon beam;

• large acceptance apparatus;

• tagged photon beam.


GRAAL Polarized and Tagged Photon Beam

e-

e-

Ee,me

E’e, me

E

EL

L

16 MeV FWHM

Ee= 6 GeV

EL= 2.41 eV (green line, = 514 nm)

EL= 3.53 eV (U.V. line, = 351 nm)

Emax= 1.1 GeV

Emax= 1.5 GeV

green line

UV line

Tagger Energy Spectrum Energy Resolution


GRAAL Detector

Photon detection (energy resolution 3% FWHM at 1 GeV); Charged particle identification (protons - pions); Energy measurement for protons; Neutron detection (and energy measurement in forward direction).

NOT IN SCALE


Measurement at GRAAL

))cos(2P(121

/KN/KN/KN

HHVV

VV

Experimental Distribution at fixed E and m

CM: )cos(2 PΣ 1ε kN VH,VH,

pnpn

kp pnpn 0

deg0


Photoproduction on Quasi-Free Nucleon in Deuteron npnp

pnpn

Preselection:

2 neutral cluster detected in BGO (invariant mass (0.35-0.7) GeV/c2);

1 neutron or 1 proton (in the central or in the forward detectors);

no other particles.

1

Kinematic Analysis:

• Two-body nature of each reaction step:

2

miss

calc

calcN

measN

measN

measmeasmeas

M

EE

E

Selection cuts:

•

•

3

180 measmeasN

calcN

measN vs

Nmissmeascalc MMvsEE

A.Fantini et al., Phys.Rev.C 78, 015203 (2008)


in Photoproduction on qfp and fp

qfp

fp

MAID2001 - fp

reggeized model - qfp

MAID2001 - qfp

• at low energies: dependence

• with increasing energy: forward-backward asymmetry

CM

2sin 152013D

167015F



in Photoproduction on qfn

qfn

reggeized model

MAID2001

GeVE 9.0

GeVEGeV 25.19.0

EGeV 25.1

: symmetric behaviour

: symmetric behaviour

: peak in forward direction

167515D



up to 1.05 GeV: qfn quite close to qfn;

above 1.05 GeV:• P11(1670);• S11(1650)-P11(1710).

qfnqfp

in Photoproduction on qfp and qfnA.Fantini et al., Phys.Rev.C 78, 015203 (2008)


0 Photoproduction on Quasi-Free Nucleon in Deuteron npnp 0

pnpn 0

Pre-selection:

2 neutral cluster detected in BGO (invariant mass (0.09-0.20) GeV/c2);

1 neutron or 1 proton (in the central or in the forward detectors);

no other particles (quasi-free kine).

1

Kinematical Analysis:

• Two-body nature of each reaction step:

2

miss

calc

calcN

measN

measN

measmeasmeas

M

EE

E

0

0000

Selection cuts:

•

•

3

180 0measmeas

NcalcN

measN vs

000 miss to π

meascalc MvsEE

R. Di Salvo, to be submitted


in 0 Photoproduction on qfp and fpR. Di Salvo, to be submitted

fpqfp


in 0 Photoproduction on qfnR. Di Salvo, to be submitted

qfn

MAID2007

MAID2007 new


in 0 Photoproduction on qfnMultipole extraction in MAID2007

MAID2007 qfn

mod MAID2007 qfn

170011P

1.0

70

MeVtot

172013P

Real partImmaginary part


in 0 Photoproduction on qfp and qfnR. Di Salvo, to be submitted

qfnqfp

MAID2007 “new” for neutron

MAID2007 “new” for proton


K+ and K+0 Photoproduction on Free Proton pKKp

pKKKp 0

Kinematic Analysis:

• Three-body kinematics;

• Two-body nature of each reaction step;

Check: decay length

Preselection:

3 tracks + at most 1 neutral cluster detected in BGO (no neutral particle: K+; 1 neutral particle: K+0)

Kp

p

0 Kp

0

p

Selection cuts:

• Energy balance;

• Charged particles mass;

• Missing mass ;

• Energy of the from decay.

Kpm

1

2

3

4

A.Lleres et al., EPJ A 31, 79-93 (2007)


in K+ and K+0 Photoproduction

GRAALGhent Isobar

SaclayBonn coupled

channel

GRAAL

Published Bonn coupled channel

New Bonn coupled channel



GRAAL

CLAS

Ghent Isobar

Saclay

Bonn coupled

channel

P in K+ PhotoproductionA.Lleres et al., EPJ A 31, 79-93 (2007)

0cos0cos

0cos0cos2

pp

pp

NN

NNP

013.0642.0

• Saclay Model:

170011S 180013P 185013D

• Ghent Isobar Model: 190013D

• Reggeized Model:

190013P 190013D

• Bonn Coupled Channel Model:

187513D

From and P measurements:

pp PW cos12

1cos


Formalism for Recoil Observables in K+ Photoproduction

]2sin2cos2sin2cos1[2

1'''

0 zzyxxf OPTPPOPP

d

d

d

d

2cos1

2sin,','

P

OPP zxzx

2cos1

2cos'

P

TPPP y

S1

S1

S2S2 S4

S4 S3

S3

<Py’

>S1 S2

lab=0°

lab=90°

P

TPP

2

2

P

TPP

2

2

P

TPP

2

2

P

TPP

2

2

<Px’,z’

>S3 S4

lab=0°

lab=90°

zxOP ,2

zxOP ,2

zxOP ,2

zxOP ,2

',',',' cos2

12

1cos zx

pzxzx

p

OPW

',',','','0

',' cos2

1cos2

1 zxp

zxzxp

zxzx OPNN

'''

0' cos

2

21cos

2

1 yp

yp

yy

P

TPPNN

pp PW cos12

1cos

'' cos

2

21

2

1cos y

pyp P

TPPW


Double Polarization Observables in K+ PhotoproductionA.Lleres et al., EPJ A 39, 149-161 (2009)

GRAALGI RPRBonn Gatchina


'''

'

cos2

12 x

px

xx

x OP

NN

N

'''

'

cos2

12 z

pz

zz

z OP

NN

N


T in K+ Photoproduction


From Ox, Oz and T extractions:

• Ghent Isobar RPR Model:

165011S 171011P 172013P

190013P 190013D

• Bonn Gatchina Model:

153511S 165011S 172013P 184011P

190013P

'

'

''

'

cos1

cos2

21

21

2yp

yp

yy

y

P

P

TPP

P

NN

N



Comparison with CLAS

PTOCOC zxxz

22222221 zxzx CCPOOT A.Lleres et al., EPJ A 39, 149-161 (2009)


Conclusions• photoproduction on nucleon:

measurement of in the energy range from 0.7 to 1.5 GeV;

qfp is similar to fp: it suggests that qfn is similar to fn;

the energy dependence of qfp and qfn is very similar up to 1.05 GeV;

above 1.05 GeV, qfp is forward peaked while qfn looks more symmetric around CM = 90°;

above 1.05 GeV and backward angles, qfn is substantially higher than qfp;

• 0 photoproduction on nucleon:

measurement of in the energy range from 0.5 to 1.5 GeV;

qfpis similar to fp : it suggests that qfn is similar to fn;

qfp and qfn are very similar for low values of 0* but differ a lot with increasing of

0*;

• K+ photoproduction:

systematic measurements of , P, Ox, Oz and T in the energy range from 0.9 to 1.5 GeV;

comparisons with 4 different models confirm the necessity to introduce new or poorly known resonances in the 1900 MeV mass region: P13and/or D13;

we need only one additional double-polarization observable to extract helicity amplitudes.


In memory of Dr. Eid Hourany

Dr Eid HOURANY died in October 2008 at the age of 67.

He had been involved as the leader of the Orsay team in the GRAAL venture since the beginning and constructed the scintillating wall of the GRAAL detection system.

He has been a talented experimentalist able to analyse complex data. In the last few years, he has analyzed almost alone, « exotic » final states as: Nπ0π0, Nπ0η, Nω and extracted from the GRAAL data very innovative information.

The quality of the GRAAL physics production is largely indebted to his constantly demanding attitude.


Double 0 photoproduction

P.R.L. 90 (2003) Phys.Lett.B 651 (2007)

...on the proton ...on the neutron

1520D

1440P

13

11

1700D

1710P

13

11


photoproduction on the proton

P.R.L. 96 (2006)

1680F 1720P 1520D 151313


Simultaneous and 0 photoproduction

P.R.L. 100 (2008)

3-body phase space

Döring, Oset,Strottman (2006)

ηpS ,Sπpγ 11110

pπΔ ηΔ,pγ 0


Thanks a lotfor your attention


0 Photoproduction: Re-calculation of 0 C.M.

R. Di Salvo, to be submitted

FPP

Deviation of the Lorentz Boost Axis

PPPP extr

NF 0 Re-calculation of 0 C.M.

EMEE NextrN

22

NextrN

extrN MEP


Photoproduction: Selected EventsFantini et al., Phys.Rev.C 78, 015203 (2008)

proton neutronce

ntr

al re

gio

nfo

rward

regio

n

Proton Neutron

Centre 2.4% 3.9%

Forward 0.9% 1.4%

Total exstimated background


Photoproduction: CheckFantini et al., Phys.Rev.C 78, 015203 (2008)

Check on the validity of:

3-parameters fit:

Similiar results for beam asymmetry;

Higer 2;

The quality of fits gets worse.


P0 in K+0 Photoproduction

pKKKp 0

uuPP

0

u , unity vector along the direction of emission in the 0 rest frame

0

3

1 PP


K+ Photoproduction : Efficiency Dependence for N+ and N-

Lleres et al., EPJ A 31, 79-93 (2007)

via Monte Carlo simulation

'' coscos xp

xp

sel

xx

x

gen

xx

x

NNN

NNN

Cor

''

'

''

' 22

Detection efficiencies and correction factors depend on the input values of Ox , Oz and T: iterative method (3 iterations).


Internal Check

1PT

11

1

1

2222

222

222

zx

zx

zx

OOPT

OO

OOPA.Lleres et al., EPJ A 39, 149-161 (2009)


Photoproduction: theoretical models for comparisonsFantini et al., Phys.Rev.C 78, 015203 (2008)


Models in K photoproduction off free protonsSACLAY G.I.

GRPR

BCC

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Latest results from GRAAL collaboration presented by Valentina Vegna