1

Study of N* excitations in 2-pion production

2

Analysis of +-p single differential cross-sections.

p-++

p+0

pp

p-P++33(1600)

p+F015(1685)

direct 2production

p+D13(1520)

Isobar Model JM05

JM06

V. Mokeev

3

Test of JM05 program on well known states.

D13(1520)

ep → ep (A1/22+S1/2

2)1/2, GeV-1/2 A3/2, GeV-1/2

Q2 GeV2Q2 GeV2

→ JM05 works well for states with significant N couplings.

4

P11(1440) and D13(1520) electrocouplings from N and pπ+π-

from analysis of CLAS 2data within JM06

from analysis of 1 CLAS data

combined analysis of 1 CLAS data

• 2 data show clear evidence for sign flip of P11(1440) A1/2

electrocoupling. • Electrocouplings obtained in two independent analyses of 1 and 2 channels are in reasonable agreement.

D13(1520)P11(1440)

5

First consistent amplitudes for A1/2(Q2), A3/2(Q2) of D33(1700)

D33(1700)ep → ep State has dominant coupling to N : PDG:80-90%Np

Many of the higher mass states have significant coupling to Nππ.

6

Search for New Baryon States

7

|q3>

|q2q>

Possible reason: they have small coupling to N-channel.

Possible solutions: 1. States don’t exist, e.g. di-quark model predicts fewer states, with different underlying symmetry group

2. States exist but have not been found.

Model expectations: Hadronic couplings to N(, N) much larger, while photocouplings are more comparable to those for observed states. Other channels that may be sensitive to “missing” states are: K, K, p

“Missing” Baryon States

Quark models with underlying SU(6)xO(3) symmetry predict many states, not observed in either hadronic experiments or in meson photo- and electro-production.

8

9

10

- Is the P33(1600)*** is really there?

- One more 3/2+(1720) state ?

- New resonances in KY ?

Evidence for new baryon states?

11

Search for Baryon States in p p

Two methods:

Isobar models (similar approach as in single pion analysis): energy-dependences of amplitudes are parameterized. fits to several (or all) one-dimensional projections.

Event-by event analysis: fit partial-wave content independently for every energy bin. makes maximum use of all correlations in the multi-dimensional phase space. ambiguities can give multiple solutions.

12

SU(6)xO(3) Classification of Baryons

P(1600)

13

Evidence for P33(1600) *** state

W=1.59 GeV

no P33(1600)

with P33(1600)

Fit to high statistics photoproduction datarequires inclusion ofP33(1600) state.

Sample datap p

14

P33(1600) state parameters

Mass, MeV 1686 ± 10 1550 - 1700 PDG1687 ± 44 Dytman1706 ± 10 Manley

Total decaywidth, MeV

338 ± 100 250 - 450 PDG493 ± 75 Dytman430 ± 75 Manley

BF ( 65 ± 6 40 -70 PDG59 ± 10 Dytman67 ± 5 Manley

A1/2 -30 ± 10 - 29 ± 20 PDG

A3/2 -17 ± 10 -19 ± 20 PDG

this analysis world

15

A new 3/2+(1720) baryon state?

M.Ripani et. al. Phys. Rev. Lett.91, 022002 (2003)

Difference between curves due to signal from possible 3/2+(1720) state

Fit with new 3/2+(1720) state

Contributions from conventional states only

JM03 Isobar Model Analysis

→ epep

16

Photo- and electroproduction comparsion

photoproductionelectroproductionp

Q2=0

W(GeV) W(GeV)

Q2=0

17

Total p p cross-section off protons.

Signal from 3/2+(1720) state present, but masked by large background and destructive N*/background interference.

Hadronic couplings and mass derived from the fit of virtual photon data, and 3/2+(1720) photocouplings fitted to the real photon data.

Background

Resonances

Interference

full calculation

no 3/2+

18

Parameters derived from combined analysis

Mass,MeV

Total width,MeV

BF(),%

BF(P),%

“New 3/2+

State” 1722 92 50 11

PDGP13(1720)

1650-1750 100-200 not observed

70 – 85

Mass and decays

19

– To reduce ambiguities, the search for new excited states aims at “complete” or nearly complete measurements in γp→πN, ηN, K+Y and γn→πN, K0Y and using combinations of beam, target, and recoil polarizations:

• differential cross sections with unpolarized, circularly polarized, and linearly polarized photon beams,

• recoil polarizations for hyperons,

• longitudinally or transversely polarized proton and neutron (deuteron) targets.

– Other reactions include γp → ρN, ωp, ππN with linearly polarized beams, and with polarized beam and polarized targets.

Search for CQM predicted states.CLAS

20

New Results in γp→pπ0CLASFA06 solutionof SAID analysis

A1/2 from Nπ analysis for S11(1535) now agrees with Nη results as was found earlier in electro-production.

Strong excitation of P13(1720) is consistent with earlier analysis of pπ+π- electro-couplings.

21

Photoproduction of K+Λ, K+Σ0

Fit: Bonn-Gatchina group, Anisovich et al., 2007

CLAS

P13

P13P11 K exchange

22

Photoproduction of K+Λ/Σ0

Fit: Bonn-Gatchina group, Anisovich et al., 2007

KΛ KΣ

Fit with P13(1900)

23

γp—>K+Λ Polarization transfer

w/o P13(1900) with P13(1900)

CLAS

Fit shows strong preference for second P13 state. Existence of this state would be evidence against the quark-diquark model.

Includes *** / **** states

(E. Santopinto, 2005)

Quark-Diquark Model

Coupled channel fit: Bonn-Gatchina group, Anisovich et al, 2007

24

Excited Cascades Ξ*

• Advantage over search for N*’s and Y*’s is narrow widths of Ξ’s• Possible production mechanism through decay of excited

hyperons – requires large acceptance and high luminosity experiments

CLAS

Ξ(1320)

Ξ(1530)

Missing mass MM(K+K+) works for narrow states, but higher energy and higher statistics are needed.

Possible production mechanism

25

Search in γp―>π-K+K+Ξ*CLAS

A Ξ state at 1.62GeV and 50 MeV width could be the 1* candidate in PDG. Such a state would be consistent with a dynamically generated Ξπ state. It would contradict quark models. Requires more statistics and PWA.

Ξ(1530)

New high statististics run in 2008!

26

Reaction Diffcrs

Lin. beam

Circ. beam

Long.Target

Trans. Target

Recoil Group Publication/Status/Schedule

γp→pπ0 x G1 arXiv:0705.0816

γp→nπ+ x G1 analysis

γp→pη x G1, G10 PRL89, 222002, 2002

γp→pη’ x G1, G10 PRL96, 062001, 2006

γp→K+Λ, K+Σ x x x G1, G10 PRC69 042201, 2004; PRC73, 035202, 2006; PRC75 035205, 2007

γp→K0*Σ+ x G1 PRC75 042201, 2007

γp→pπ-π+ x x G1 PRL95 162003, 2006, analysis

γp→pω, pρ0, nρ+ x x G8 2005 / Analysis

γn→ K0Λ, K0Σ, K+Σ-, K-Σ+

x x x x G13 2007 / Analysis

γp→pπ0, nπ+, pη x x x x G9-FROST 2007/2009

γp→K+Λ, K+Σ x x x x x G9-FROST 2007/2009

γp→pπ-π+ x x x x G9-FROST 2007/2009

γn→ K0Λ, K0Σ, K+Σ-, K-Σ+

x x x x x G14-HD 2010

γn→pπ-,nπ+π- x x x x G14-HD 2010

Experiment Status & Plans of Search for New N* StatesCLAS

27

CLAS γd→K0Λ, π-p, (ps)

Eγ=1.5 – 1.7

Online beam asymmetry for γn→π-p

Photons produced coherently from aligned diamond crystals are linearly polarized.

Identify: Ks →π+π- Λ→pπ-

Eγ=1.1-1.3 GeVAll polar angles

< 0.1% of all data

Ks

M(π+π-), GeV

Λ

M(pπ-), GeV

• Plots show a 5 GeV run with the coherent edge at 1.9 GeV

28

γp →K+ΛProjected Accuracy of Data (4 of over 100 bins)

→→ →

29

γn →K0Λ Projected Accuracy of Data (4 of over 100 bins)

→→ →

30

Conclusions

• The study of N* excitations in photo- and electroproduction of mesons from nucleons is key for the understanding of the strong force that confines the quarks into nucleons.

• The experimental and theoretical analysis we are all engaged in will make gigantic contributions towards that goal.

31

N*’s ARE FUN !

32

Fit of CLAS 2 data on 3 invariant masses and - angular distributions within the framework of JM05.

, mcbn

W, GeV

Q2=0.65 Gev2

Q2=0.95 Gev2

Q2=1.30 Gev2

Reasonable description of invariant mass and p- angular distributions was achieved in entire kinematics area covered by CLAS data.

33

Diquark-Quark Model

Includes all observed *** & **** states

(E. Santopinto, 2005)

Spectrum predicted for masses below 2 GeV.