Recent progress in N* physics from Kaon photoproduction experiments at CLAS using polarization observabes. The Rutherford Centennial Conference on Nuclear Physics. The University of Manchester on 8-12 August 2011 Ken Livingston, University of Glasgow Motivation Missing resonances 1 st complete measurement in pseudoscalar meson production Polarization observables at CLAS Progress towards a complete measurement in K + photoproduction on p Measurements on the neutron Summary

Missing resonances Clear indication of resonances in γp cross section for many channels Constituent quark models predict many resonances, but several missing Mostly from πN scattering and single π photoproduction Really missing or undetected since weak coupling to these channels Try other channels. Eg. K photoproduction Eg. Cross sections show some hints of new D 13. Better to look at angular distributions and polarization observables. With D 13 Without D 13 Mart & Benhold, Phys. Rev. C (R) (1999)

Polarization observables in pseudoscalar meson production 4 Complex amplitudes: 16 real polarization observables. Complete measurement from 8 carefully chosen observables. πN has high statistics but in KY recoil is self-analysing I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B (1975). πNπNKY recoil targ γγ targ recoil ☻☻☻ ☻ linearly polarized photons ☻☻☻ longitudinally polarized target ☻☻☻ transversely polarized target circ polarized photons ☻☻☻ Complete, and over-determined

A B C Continuous Electron Beam Accelerator Facility  E: 0.75 –6 GeV  I max : 200A  RF: 1499 MHz  Duty Cycle:  100%  (E)/E: 2.5x10 -5  Polarization: 80%  Simultaneous distribution to 3 experimental Halls Injector LINAC Experimental Halls Jefferson Lab Hall B

Polarization observables at CLAS  + N →  m Linear Polarisation Circular polarisation Nucleon recoil polarimiter x → Y  Hyperons are “self analysing” Transverse polarized nucleon targets Longitudinally polarized nucleon targets

Polarization observables - a simple example,  Systematics of detector acceptance cancel out. “Only” need to know P lin, the degree of linear polarization. }

g8b preliminary results -    and     Craig Paterson, Glasgow  p     p    p         p      Single polarization observables  Photon asymmetry P Recoil polarization (induced pol. along y) T Target asymmetry Double polarization observables O x Polarization transfer along x O z Polarization transfer along z figure by R.Schumacher, CMU

g8b preliminary results -    Results compared with previous results from LEPS 6, 100MeV Energy bins > 2050MeV More bins for our data Increase the angular coverage to backward angles LEPS also recently have some consistent, new points at backward angles. Hicks et al., PRC 76, (R) (2007). PRELIMINARY

g8b preliminary results -    Double polarization ovservable O x Results compared with Regge-Plus-Resonance model from Gent group Large Polarizations Some evidence for an important role for missing D 13 (1900) state Poor agreement at low energy PRELIMINARY Status of CLAS measurements of         on proton (from g1c and g8b) Single polarization observables  Photon asymmetry (lin pol) P Recoil polarization (induced pol. along y) T Target asymmetry (lin pol) Double polarization observables O x Polarization transfer along x (lin pol) O z Polarization transfer along z (lin pol) C x Polarization transfer along x (circ pol) C z Polarization transfer along z (circ pol) R. Bradford et al., Phys. Rev. C 75, (2007).

Meson photoproduction with linearly and circularly polarized photons on polarized target E02-112: γp→KY (K + Λ, K + Σ 0, K 0 Σ + )‏ E03-105/E04-102: γp→π 0 p, π + n E05-012: γp→ηp E06-013: γp→π + π - p g9a running conditions November 3, 2007– February 12, 2008 Longitudianally polarized target Circularly and linearly polarized photon beam GeV Trigger: at least one charged particle in CLAS Target Pol > 80%, Relaxation time > 1600hrs – better that design goals g9 FROST – FROzen Spin Target (butanol = C4H9OH) g9b March – July 2010 Transversely polarized target Racetrack coils for transverse polarization

butanol 12 CCH 2 g9aFROST beam target observables G,E Stuart Fegan, Glasgow Liam Casey, CUA Based on ~2% of statistics butanol 12 CCH 2 Measurement of G, E (Double pol. Observable (lin and circ pol. on long. targ)  p     p    and  p         p      Butanol is not a pure proton target. Background from 12 C butanol Subtract events from 12 C Pol observables corrected by dilution factor. 12 C CH 2 PRELIMINARY

G10. Unpolarized photons on Deuterium 1 st measurement of σ for the γ n → K + Σ - Measurements on n (Deuterium) target Detect  - n, K + Σ from  - n inv. mass Circularly and linearly polarized photons on n (g13, Deuterium target) γ n → K + Σ - analysis for polarization observables underway. Edwin Munevar, GWU Sergio Anefalos Pereira, INFN. Phys. Lett. B 688 (2010) CLAS Data ▲ LEPS _____ Gent RPR model Edwin Munevar, GWU PRELIMINARY

K production on n. Deuterium target PRELIMINARY G13 1 st measurement of Beam Asymmetry  n (p)   s     p  Neil Hassall, Glasgow Single, and double polarization observables in progress

Measurements on n (Deuterium) target HDIce Solid Deuterium-Hydride (HD) – a new class of polarized target A. Sandorfi. Spin can be moved between H and D with RF transitions All material can be polarized with almost no background Run in November 2011

Summary  Huge effort on N*, missing baryon resonances  We are close to an answer.  Complete measurements on p and n soon (K , K  ) Some related talks given in Parallel Session 1b: The complete photoproduction measurement what is needed from the experimental point of view, W Briscoe Measurement of the double polarisation observable 'F' in pion photoproduction with the crystal ball at MAMI P Hall Barrientos The use of nested sampling in the extraction of polarisation observables at CLAS S Lewis The Regge-plus-Resonance model for kaon production on the nucleon J Ryckebusch