Photoproduction of h and h ‘ Mesons on the Nucleon
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Transcript of Photoproduction of h and h ‘ Mesons on the Nucleon
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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
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threshold threshold threshold
nonresonant background:
large very small large
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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)
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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
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ETA-MAIDETA-MAID
uses a simpler approachuses a simpler approachwithout additional unitarization:without additional unitarization:
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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
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Background
Born Terms
very small coupling constant:
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Vector Meson Exchanges
22 2
2hadronic form factor ( ) V V
VV
mF t
t
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This description for vector meson exchanges
works fine in the resonance region (W < 2
GeV)
but cannot be extended to high energies
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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
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Vector Meson Exchanges inpp
Fit high-s, low-t data
to determine the
vector meson couplings
gVNN and VNN
Data from DESY (1970)
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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
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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
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Eta-Maid 2001 compared to data from TAPS@Mainz and GRAAL
differential cross section photon beam asymmetry
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Comparison with the Eta-Maid 2003Comparison with the Eta-Maid 2003
Reggeized ModelReggeized Model
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with std. vector meson polesand hadronic form factors
with reggeized vector mesons
both models describe very well the proton data
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standard resonances
reggeized + resonancesreggeized only
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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
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! almost afactor 10
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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
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Comparison with preliminary data from CB-ELSAtotal c.s. on proton and neutron (I. Jaegle, priv. comm. 2006)
Maid 2001
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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
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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
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effect of a non-strange pentaquark in
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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)
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pentaquark solution
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D15 resonance versus PentaquarkD15 resonance versus Pentaquark in angular distribution on the neutron
both models cannot really describe the differential cross section
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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
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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
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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)
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pp Total Cross Sections
total: Regge + S11
Regge trajectories
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comparison of old ‘-Maid with SAPHIR(98) data
only S11 resonance requiredP11 or even higher resonancesare not really necessary
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fit to preliminary JLab/CLAS data (M. Dugger, N*2005 and private comm.)
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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