Crystal Ball at MAMI Daniel Watts, Univ. of Edinburgh (UK) For the Collaboration

(mainly involving low cross sections and/or precision measurements) Precision spectroscopy of low lying baryon states:   (1232)) from  p    ’  p and    ’  n   (S 11 (1535)) from  p  ’  p reaction Threshold meson production: (test of LET/ ChPT): Strangeness (  N →  K)  0 photoproduction at threshold Ambiguity free amplitude analysis of meson photoproduction Requires Double polarization measurements:  N → N  (  ); N  ( ,…) channels Tests of fundamental symmetries (C,CP,CPT…) Rare  / decays In medium properties of hadrons & nuclear physics: Meson photo production on nuclei Main physics objectives

100% duty factor electron microtron MAMI-C 1.5 GeV upgrade (2006) (MAMI-B 0.85 GeV) Crystal Ball - A2 hall (tagged photon beam) The MAMI facility One of the MAMI-C magnets  e

Photon Tagger upgrade

E  max (GeV) I  max (s -1 MeV -1 ) Δ E  (FWHM  (MeV) Pol  lin (%) Pol  circ (%) 3.5 ≈ ≈ ≈ ≈ ≈ ≈ Photon beam facilities Legs B C

 1976 Conceived SPEAR (E cm = GeV) DORIS (Ecm = GeV) BNL-AGS (E cm = 1.2 – 1.53 GeV) 2002 MAMI (E cm = GeV) Crystal Ball history

Crystal Ball arrives at Frankfurt

Good angular and energy resolution, close to 4  acceptance Setup at MAMI Tracker & Particle-ID

 ~ 1.5 o  ~ 1.3 o Two cylindrical wire chambers 480 anode wires, 320 strips Adapted from DAPHNE New MWPC tracker under construction (2006) 2mm thick EJ204 scintillator 320mm

MWPC & Particle-ID in situ

Good angular and energy resolution, close to 4  acceptance Setup at MAMI Tracker & Particle-ID

MAMI Photo Gallery CB with PMTs CB Panoramic view of MAMI setup  TAPS CB TAPS

Targets at MAMI Liquid hydrogen (deuterium) target Liquid 3 He target (2006) Polarised 3 He gas target (~2008) Frozen spin Target butanol / deuterated butanol (~2007)

Apr '05-Jan'06 : MAMI-C upgrade, photon tagger upgrade '06 onwards : Second production runs E  = GeV: unpolarized, polarised, nuclear targets Nov '02: Crystal Ball moved to Mainz Nov '03: Crystal Ball installed at photon beam at MAMI Mar '04: TAPS installed Apr '04: MWPC and PID installed May '04: First test run tests with the complete setup Jun'04-Apr '05 : First production runs – timetable E  = GeV: unpolarized H 2 or D 2 targets, nuclear targets

Selection of preliminary spectra from first round of experiments E  = 0.1 – 0.8 GeV

Preliminary analyses:    identification   →   MeV   →   MeV   →    →   MeV

Preliminary analyses: A gs (  0 )A gs coherent  0 photoproduction from nuclei 208 Pb 33 o sin  ~ 1.22 /D R m ~ 5.75 fm (R c ~ 5.50 fm) E  =220 MeV 16 O 12 C 40 Ca 4.4 MeV 3.7MeV 6.1 MeV Also see coincident low energy Nuclear Decay Photons !! Clear diffraction patterns for 208 Pb, 40 Ca, 16 O, 12 C d  /d  A 2 (q/k  )P 3 2 |F m (q)| 2 sin 2   Matter form factor,  properties in the medium C. Tarbert, D. Watts

Photon Asymmetry  : Preliminary analyses: ( , p)  0 A. Starostin

High statistics measurement With  beam polarisation → ,  circ ~5% of total statistics Preliminary analyses: p( ,p)      dependence of     yield (not acc. corrected) F.Zehr

Preliminary analyses: p( ,p)    to measure    p p   ´´  p   p ´´ p p  ´´  + + coherent addition... small dominant    MAMI pilot measurement with TAPS only M. Kotulla et al., PRL 89 (2002)

 100 in statistics measure  beam polarisation observables Both p  0 and n  + decay of  +   =5  p   =3  p   =1  p   = 0.79  p   =3  p p( ,p)    to measure   

Future plans with MAMI-C E  = 0.1 – 1.5 GeV

Double-polarisation in pseudo-scalar meson photoproduction Polarisation of  target recoil Observable

 p → p  0  p → p   n → n  0  n → n  Circularly polarised photons + longitudinally polarised protons (or neutrons) Deuterated butanol frozen spin target Butanol frozen spin target Beam-target observable: E Previous E measurement for  p → p  0 led to significant revision of helicity amplitudes for D 13 (1520) [ PRL 88, (2002)] Neutron targets: different resonance contributions, isospin structure Also get  channels – mechanisms, contributions to GDH integrand Expected data accuracy    10 o E  ±10 MeV 250 hrs  p → p  0   =90 o  n → n  0   =90 o E E  (MeV)

Variable well suited to studies of Roper resonance ( P 11 (1440) )  p → p  0  p → n  + linearly polarised photons + longitudinally polarised protons Beam-target observable: G Expected Data accuracy    10 o E  ±10 MeV 600 hrs

Beam-Recoil Observables: C x, O X, T, P Graphite sheet (~7cm thick) TAPS Crystal Ball  beam Hydrogen target cell Initial path of proton Polarimeter acceptance : ±20 o polar angle (target at centre) Most events suffer only coulomb scattering Useful scattered event Select events with scattering angles larger than ~10 degrees : arising from nuclear interaction n() =n o (){1+A()[P y cos()–P x sin()]

Beam-Recoil Observables- p(   )p 300 hrs E e =0.85 GeV 500 hrs E e =1.5 GeV   (cm)=130 o

~4  detector system Very good neutral (and charged) particle detection capabilities Excellent properties of MAMI beam Availability of polarized targets Recoil nucleon polarimetry possibilities High quality data for meson photoproduction for E  up to ~1.5 GeV can be expected Summary

J.Brudvik, J. Goetz, B.M.K.Nefkens, S.N.Prakhov, A.Starostin, I. Saurez, University of California, Los Angeles, CA, USA J.Ahrens, H.J.Arends, D.Drechsel, D.Krambrich, M.Rost, S.Scherer, A.Thomas, L.Tiator, D. von Harrach and Th.Walcher Institut fur Kernphysik, University of Mainz, Germany R. Beck, M. Lang, A. Nikolaev, S. Schumann, M. unverzagt, Helmholtz-Institut fur strahlen und Kernphysik, Universitat Bonn, Germany S.Altieri, A.Braghieri, P.Pedroni, A.Panzeri and T.Pinelli INFN Sezione di Pavia and DFNT University of Pavia, Italy J.R.M.Annand, R.Codling, E.Downie, D.Glazier, J. Kellie, K.Livingston, J.McGeorge, I.J.D.MacGregor, R. Owens D.Protopopescu and G.Rosner Department of Physics and Astronomy, University of Glasgow, Glasgow, UK C.Bennhold and W.Briscoe George Washington University, Washington, USA S.Cherepnya, L.Fil'kov, and V.Kashevarow Lebedev Physical Institute, Moscow, Russia V.Bekrenev, S.Kruglov, A.Koulbardis, and N.Kozlenko Petersburg Nuclear Physics Institute, Gatchina, Russia B.Boillat, B.Krusche and F.Zehr, Institut fur Physik University of Basel, Basel, Ch P. Drexler, F. Hjelm, M. Kotulla, K. Makonoyi, R.Novotny, M. Thiel and D. Trnka II. Phys. Institut, University of Giessen, Germany D.Branford, K.Foehl, C.M.Tarbert and D.P.Watts School of Physics, University of Edinburgh, Edinburgh, UK V.Lisin, R.Kondratiev and A.Polonski Institute for Nuclear Research, Moscow, Russia J.W. Price California State University, Dominguez hills, CA, USA D.Hornidge Mount Allison University, Sackville, Canada P. Grabmayr and T. Hehl Physikalisches Institut Universitat Tubingen, Tubingen, Germany D.M. Manley Kent State University, Kent, USA M. Korolija and I. Supek Rudjer Boskovic Institute, Zagreb, Croatia D. Sober Catholic Catholic University, Washington DC M. Vanderhaeghen, College of William and Mary, Williamsburg, USA

(mainly involving low cross sections and/or precision measurements) Precision spectroscopy of low lying baryon states:   (1232)) from  p    ’  p and    ’  n  m(S 11 (1535)) from  p  ’  p reaction Threshold meson production: (test of LET/ ChPT): Strangeness (  N →  K)  0 photoproduction at threshold Ambiguity free amplitude analysis of meson photoproduction Requires Double polarization measurements:  N → N  (  ); N  ( ,…) channels Tests of fundamental symmetries (C,CP,CPT…) Rare  decays In medium properties of hadrons: Meson photo production on nuclei Main physics objectives

 100 in statistics measure  beam polarisation observables Both p  0 and n  + decay of  +   =5  p   =3  p   =1  p   = 0.79  p   =3  p p( ,p)    to measure   

4 complex amplitudes – 16 observables in meson photoproduction Each double polarisation observable gives different combination of amplitudes To fix the 4 amplitudes unambiguously → 8 real quantities Cannot choose from the same set Polarisation of  target recoil Double-polarisation: theory background Observable

Predicted sensitivity to poorly established resonances Resonance parameters from quark model (Capstick and Roberts) Solid – SAID Dashed – background + **** Dotdash- background + **** +N - 3/2 (1960) Dutta, Gao and Lee, PRC 65, (2002) Cx’ (  + recoil) – theoretical predictions

P T Previous experimental data – SAID database Data for all CM breakup angles O x’ C x’ Recent JLAB data not in database

First determination p(,p) 0 in 2002 Hall A JLab MAID & SAID poor description of new data Recent C x’ measurement at JLab Polarisation transfer C x’ Photon energy (MeV)

The proposed experimental setup Graphite sheet TAPS Crystal Ball  beam Hydrogen target cell Initial path of proton Polarimeter acceptance : ±20 o polar angle (target at centre) Most events suffer only coulomb scattering Useful scattered event Select events with scattering angles larger than ~10 degrees : arising from nuclear interaction n() =n o (){1+A()[P y cos()–P x sin()]

GEANT simulation of polarimeter No Graphite With Graphite scatterer Simulation includes realistic smearing of energy deposits due to experimental energy resolution and proper cluster finding algorithms Finite target size and E  resolution included Angle between  N (E ,   ) and TAPS hit

   CM) >~130 o E=150 MeV E=200 Eg=300 E=500 E=750 E=1000 E=1500 Polarimeter acceptance Nucleon angle in lab (deg) Pion angle in CM (deg) Kinematic acceptance of polarimeter p(  )N

More forward recoils than for pion production. Almost all recoils are incident on polarimeter up to ~0.8 GeV Eg=720 Eg=820 Eg=920 Eg=1520 Lab nucleon angle (degrees) CM  angle (degrees) Polarimeter acceptance Kinematic acceptance of polarimeter p(  )N

Cx’ – Extraction and expected accuracy Plot difference in  distributions for two helicity states (cut on region of  with reasonable A()) Left with simple sin() Dependence. Extract Px Photon energy (MeV) Cx’  P  =0.7, E=±25MeV,   =130±10  ~ 1 b/sr → Cx ~  ~ 0.1 b/sr → Cx ~0.05  Greatly improved data quality

Measure direction of nucleon before and after the scatterer with sufficient accuracy to determine an analysing reaction has taken place. Polarimetry basics For incident protons also have multiple (coulomb) scattering  scat =5-20 o  scat

Magnetic dipole moments:   (1232) from  p    ’  p and    ’  n  S 11 (1535) from  p  ’  p) reaction Threshold meson production: (test of LET/ ChPT): Strangeness (  N →  K)  0 photoproduction at threshold Double polarization measurements: (properties of baryon resonances/GDH)  N → N  (  ); N  ( ,…) channels Mass of  - meson and rare  decays Meson photo production on nuclei: medium mod., nuclear properties Future programme

4 complex amplitudes →16 observables in meson photoproduction → need 8 well chosen measurements to fix the 4 amplitudes Each double polarisation observable gives a different combination of amplitudes Polarisation of  target recoil Double- polarisation in pseudo-scalar meson photoproduction Observable

MWPC tracker  ~ 1.5 o  ~ 1.3 o Adapted from MWPCs used with the DAPHNE detector New dedicated MWPC tracker under construction (Complete early 2006)

Scattered nucleon detection in TAPS 1 TAPS block ~ position resolution for hit TAPS~0.9m from scatterer N  Straight through 10 o scatter 20 o scatter

Detrimental side-effects of scatterer material To hit polarimeter T N >100 MeV in  (p,  )N above the  Proton energy loss 100 MeV. Multiple scattering 100 MeV 0.37 radiation lengths  conversion ~ 30% T p incident proton (MeV) T p exit proton (MeV) T p after graphite Energy loss Coulomb scattering Proton energy (MeV) FWHM scattering angle (deg)

 1976 Conceived SPEAR (E cm = GeV)  spectroscopy radiative  decays  decays D decays,  →   f DORIS (Ecm = GeV) Y spectroscopy radiative  decays BNL-AGS (E cm = 1.2 – 1.53 GeV)   decays, medium. mod 2002 MAMI (E cm = GeV) Crystal Ball history

24 of 2x10x320mm EJ204 scintillator 24 Hamamatsu  =10mm PMT Particle-ID detector Small light attenuation Good separation of p,  with little overhead in material before MWPC and CB detectors

Hadron Structure:  + Magnetic Moment recent calculation: W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D. Drechsel, PRC 71, (04) includes  N rescattering loops

Hadron Structure:  + Magnetic Moment Connection between  N  ’ N and  N  N pp   n

Hadron Structure:  + Magnetic Moment M. Kotulla et al., PRL 89 (2002) TAPS – first   p →   p  ’ data   =1   =7 (units:  N )

Hadron Structure:  + Magnetic Moment sensitivity to angular differential cross section with cut on  ´ energy sensitivity to beam asymmetry (linearly polarized photon beam)

Good angular and energy resolution, close to 4  acceptance for charged and neutral final states Setup at MAMI