Photoproduction of Photoproduction of and and ‘ Mesons ‘ Mesons on the Nucleonon the Nucleon

introduction

the MAID project

t-channel exchanges: poles vs. Regge trajectories

D15(1675) resonance vs. P11(1675) pentaquark

summary and conclusion

L. Tiator, Institut für Kernphysik, Universität Mainz

threshold threshold threshold

nonresonant background:

large very small large

motivation for and ‘

• missing or misidentified resonances

• qqq resonances vs. dynamically generated resonances

with N or with , e.g. S11(1535)

• exotic resonances: Does the + pentaquark exist?

if so, it should have a non-strange partner

P11(~1700)

MAIDMAID

the Mainz-Dubna Unitary Isobar the Mainz-Dubna Unitary Isobar ModelModel

K-matrix unitarization

unitarization phasedetermined by the Watson theorem, below 2 threshold

relaxed above 2 threshold

ETA-MAIDETA-MAID

uses a simpler approachuses a simpler approachwithout additional unitarization:without additional unitarization:

Resonances Breit-Wigner form

8 resonances are included in -MAID :

D13(1520) very important for

S11(1535) most important

S11(1650) very important

D15(1675) very important for

F15(1680) less important

D13(1700) unimportant

P11(1710) important

P13(1720) unimportant

Background

Born Terms

very small coupling constant:

Vector Meson Exchanges

22 2

2hadronic form factor ( ) V V

VV

mF t

t

This description for vector meson exchanges

works fine in the resonance region (W < 2

GeV)

but cannot be extended to high energies

t =

Regge Trajectory Exchanges

0( )t t At high s and low t, it is known that meson photoproduction can be well described by Regge trajectories in the t-channel.

( ) 1 ( )

Regge0

1

sin( ( )) 2 ( ( ))

VV

t i tV V V

V V

es

s t t

SP

pole 2

1V

Vt m

P

Replace pole-like propagator

With Regge propagator

Vector Meson Exchanges inpp

Fit high-s, low-t data

to determine the

vector meson couplings

gVNN and VNN

Data from DESY (1970)

Cross sections

• MAMI in MainzKrusche et al., Phys. Lett. B358, 40 (1995)

MAMI 95

• ELSA in BonnPrice et al., Phys. Rev. C 51, 2283 (1995)

ELSA 95

• GRAAL, ESRF in GrenobleRenard et al., Phys. Lett. B528, 215 (2002)

GRAAL 02

Beam asymmetry

• GRAAL, ESRF in GrenobleAjaka et al., Phys. Rev. Lett. 81, 1797 (1998)

GRAAL 98Kouznetsov (SAID database)

GRAAL 01

Target asymmetry

• PHOENICS, ELSA in BonnBock et al., Phys. Rev. Lett. 81, 534 (1998)

ELSA 98

Photoproduction Data available in 2001

Cross sections

• GRAAL, ESRF in GrenobleRenard et al., Phys. Lett. B528, 215 (2002)

GRAAL 02

• CLAS, Jefferson LabDugger et al., Phys. Rev. Lett. 89, 222002 (2002)

CLAS 02

• CB-ELSA in BonnCrede et al., Phys. Rev. Lett. 94, 012004 (2005)

BONN 05

Photoproduction Data after 2001

preliminary data 2005/06

Cross sections and Beam Asymmetry• GRAAL (d/d and for proton and neutron)

Kouznetsov et al., N*2005

GRAAL 05

• CB-ELSA ( and d/d for proton and neutron) Jaegle et al. N*2005

BONN 05

Eta-Maid 2001 compared to data from TAPS@Mainz and GRAAL

differential cross section photon beam asymmetry

Comparison with the Eta-Maid 2003Comparison with the Eta-Maid 2003

Reggeized ModelReggeized Model

with std. vector meson polesand hadronic form factors

with reggeized vector mesons

both models describe very well the proton data

standard resonances

reggeized + resonancesreggeized only

The role of the The role of the

DD1515(1675) resonance(1675) resonance

N branching ratios in our 2 models:

17 % for the EtaMaid with v.m. poles0.7 % for the reggeized model

! almost afactor 10

Comparison with preliminary data from GRAALdiff. c.s. and beam asymm. on neutron (priv. comm. S. Kouznetsov, 2006)

-Maid 2001-Maidwithout D15

bump observed around 1650 MeV

Comparison with preliminary data from CB-ELSAtotal c.s. on proton and neutron (I. Jaegle, priv. comm. 2006)

Maid 2001

ETA - MAID 2003

isobar model (update of Eta-Maid2001)

reggeized isobar model ( Regge trajectories)

(preliminary data from CB-ELSA, I. Jaegle, priv. comm. 2006)

only the model with the strong D15 can describe the neutron data

problems with the D15(1675) resonance:

1) in the std EtaMaid model it fits the neutron data very well

but needs a large branching ratio of N = 17 %

SU(3)fl for baryon octett

gives a prediction of N= 2.5 %

(Guzey and Polyakov, hep-ph/0512355)

2) in the Regge model the D15(1675) does not play any

important role

effect of a non-strange pentaquark in

quasifree eta photoproduction on the deuteronin collaboration with Alexander Fix

( e.g. A. Fix and H. Arenhövel, Z. Phys. A 359 (1997) 427 )

in impulse approximation:

NN fsi is negligible

NN fsi is larger but only important near threshold

input: EtaMaid with additional pentaquark state P11(1675)

pentaquark solution

D15 resonance versus PentaquarkD15 resonance versus Pentaquark in angular distribution on the neutron

both models cannot really describe the differential cross section

Summary on Summary on production production

The old EtaMaid 2001 describes new data > 2002 very well

D15 resonance needs a very large N branching ratio,

to describe the photon asymmetry on the proton

this leads to the peak in (n)/(p)

a non-strange narrow pentaquark state P11(1675)

Fermi averaged in the deuteron would also produce such a

peak

angular distributions are not yet conclusive

total cross sections• DESY

ABBHHM collaboration, PRC 175 (1968) 1669 AHHM collaboration, 1976, Nucl. Phys. B108 (1976) 45

• SAPHIR in BonnR. Ploetzke et al., PL B444, 555 (1998)

differential cross sections

• SAPHIR in BonnR. Ploetzke et al., PL B444, 555 (1998)

• JLAB/CLASM. Dugger et al., preliminary (2005-2006)

N*2005 Tallahassee and private communication

’ ’ Photoproduction DataPhotoproduction Data

photoproduction

pp

Born terms are small

and can be neglected

t-channel vector meson

Regge trajectories are

fixed from pp

the sharp rise of the total cross section near threshold is similar to pp and suggests

an S11 resonance threshold

(98)(76)(68)

pp Total Cross Sections

total: Regge + S11

Regge trajectories

comparison of old ‘-Maid with SAPHIR(98) data

only S11 resonance requiredP11 or even higher resonancesare not really necessary

fit to preliminary JLab/CLAS data (M. Dugger, N*2005 and private comm.)

Summary on Summary on ‘ production‘ production

The new JLab/CLAS data are very accurate and cover a large kinematical rangeand allow to draw more reliable conclusions

Born terms are negligible, g‘NN /4 << 0.1

a reggeization of the t-channel is clearly necessaryin this energy region of E > 1.7 GeV

an S11 resonance at W=1904 MeV (only 8 MeV above threshold)plays the dominant role, similar as in production

further resonances are needed in order to describe the data:mainly D13(2080) found at W = 2100 MeV, weakly P11 (2100) found at 2083 MeVand P13(1900) found at 1926 MeV

2