Meson Photoproduction with Polarized Targets

Meson Photoproduction Meson Photoproduction with with

Polarized TargetsPolarized Targets

production

a) 0 at threshold

b) Roper and P11(1710)

production

a) S11-D13 phase rotation in threshold region

b) Neutron bump at W = 1680 MeV

’production

a) separation of S and P wave multipoles close at threshold

b) ’ on the deuteron

L. Tiator, Mainz

if the amplitudes (multipoles) are real or if the Watson theorem can be appliedwe only needs to measure a real number for each partial wave

if we can neglect all D- and higher partial waveswe only have to deal with 4 real quantities:

E0+, E1+, M1+, M1- or E0, P1, P2, P3

and we are done with d/d and without worrying about target or recoil polarization

2 very famous examples, both from MAMI:0 p partial waves at threshold0 p, + n with full isospin separation in the region

IntroductionIntroduction

But for all other cases, where the imaginary parts are unknownwe need nucleon polarizations,

either polarized targets or

recoil polarization measurements

Pion photoproductionPion photoproduction

• at threshold

• P11(1440) and P11(1710)

the photon asymmetry at from threshold to 200 MeV is very important

from all calculations and partial wave analyses up to now,

only ChPT is able to describe it (by fitting LECs)

most other calculations get even an opposite sign near threshold

the P11 resonances are partially hidden states

they are very difficult to isolate

and are most debated among all resonances

the photon asymmetry at from threshold to 200 MeV is very important

for all calculations and partial wave analyses up to now, only ChPT is able to describe it (by fitting LECs)

also dispersion relations can not describe the asymmetry

the M1- multipole is only poorly known

because most observables are very insensitive on this multipole

but it is very important because of our interest in the Roper resonance

with MAMI B we had already started to measure the G observable,

which gives the most direct access to M1- (pending proposal)

now in the same channel we can further look into the second P11,which could be a verry narrow state and is currently debated

P11 resonances

• S11(1535) plays an outstanding role in and e,e‘ and and dominates the total cross section completely

• at higher energies: S11(1650), P11(1710), P13(1720) play some role

• around E=1 GeV or W=1670 MeV a surprising structure appears in on the neutron (quasi-free) which is still not fully explained speculations about narrow P11(1680) (pentaquark)

or strong D15(1675) (EtaMaid)

or P11(1710) in coupled-channels approach (Gießen model)

• small resonance contributions can be observed with polarization observables as interferences with the large S wave, e.g. D13(1520) is clearly visible in ,

even with a branching of only / total = 0.0006

Eta photoproductionEta photoproduction

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eta photoproduction near thresholdeta photoproduction near threshold

main multipoles in the threshold regionmain multipoles in the threshold region

Wthreshold = 1487 MeV < Wcm < 1600 MeV

Ethresh=709 MeV < Elab < 900 MeV

E0+ S11(1535) dominated

E2- , M2- D13(1520) dominated

E1+ , M1+ background (Born,

)here we will use the helicity multipoles A,B:

A0+ = E0+

A2- = (3 M2- - E2- ) / 2

B2- = E2- + M2-

B1+ = E1+ - M1+

fit to the data

no additional information in these „exotic“ observables

only only TT, , GG and and Ox‘Ox‘ are sensitive are sensitiveto the phase rotationto the phase rotation

T around 30°-60° and 120°-150°

Ox‘ between 30°- 150°

G between 45°- 135°

Beam-Recoil Double Polarization Beam-Recoil Double Polarization Experiment in 2007 at MAMI-A1Experiment in 2007 at MAMI-A1

pp ( e, e´p )( e, e´p )

in search for the phase rotation in search for the phase rotation in eta electroproductionin eta electroproduction

Recoil Polarization in plane: =or

single polarization:

double polarization:

confirms the phase rotation

The question remains: The question remains:

Is the phase rotationIs the phase rotationof of hadronichadronic or or electromagneticelectromagnetic origin? origin?

This can be answered inThis can be answered in

quasi-free quasi-free production on the deuteron production on the deuteron

the neutron bumpthe neutron bump

in eta photoproductionin eta photoproduction

at W=1670-1680 MeVat W=1670-1680 MeV

schematic view of schematic view of on the neutron on the neutron

Photoproduction of Photoproduction of mesons on the mesons on the deuterondeuteron

in the presence of a narrow in the presence of a narrow PP1111(1670)(1670) resonanceresonance

resonance parameters for the pentaquark in our calculations:

( A. Fix, L.T., M.V. Polyakov, EPJ A in print )

model with a strong D15 :

model with a narrow P11 :

GRAAL measurements

of the beam asymmetry

on the proton and on the neutron

Photon Beam AsymmetryPhoton Beam Asymmetryon the Protonon the Proton

data: Bartalini et al., GRAAL 2007

EtaMaid

CQM, Saghai, Li

Bonn pw analysis,Sarantsev et al.

comparison of GRAAL proton data comparison of GRAAL proton data with pentaquark solutionswith pentaquark solutions

data: Bartalini et al. GRAAL 2007

EtaMaid

ReggeMaid + P11(1670)

Bonn pw analysisSarantsev et al.

ReggeMaid - P11(1670)

the proton data does not show any pentaquark signature !!

can we do something to solve this can we do something to solve this puzzle?puzzle?

also here the target polarization can very well distiguishbetween different models, see SFB-MAMI proposal 2007

Etaprime photoproductionEtaprime photoproduction

misplaced or missing resonances dominate already at threshold

the current situation with the existing models is very unsatisfactory

nowbody knows which resonances play the dominant role

the reason for this is: we have only unpolarized diff. c.s.

and no polarization observables

the same polarization observables, already discussed in eta production

are also helpful here: T (and E)

other observables will need higher energies

‘ photoproduction on the proton

3 comparable fits with EtaprimeMaid to JLab/CLAS data of:

JLab data 2006 fit I : B+++S11(2120)

+P13(1960)+D13(2140)

fit II : B+++S11(1905)+P11(2080)

+P13(1925)+D13(2100)

fit III : B+++S11(1960)+P11(2080)

+P13(2060)+D13(2100)

with polarized targets and linearly and circularly polarized photons

we can measure up to 8 polarization observables

4 with circular polarization up the maximum beam energy of 1.5 GeV:

d, T, E and F

4 with linear polarization are possible up to approximately 1 GeV:

, G, H and P

SummarySummary

The following top priority problems can be attacked:The following top priority problems can be attacked:

at 0 threshold: Re E0+, Im E0+ , T, F

Roper P11(1440) and second P11(1710) G

S11-D13 phase rotation in T, G

neutron bumb in production G, T, E

‘ partial waves at threshold T

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Meson Photoproduction with Polarized Targets