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p( g ,n p + g / ) reaction measured with the Crystal Ball at MAMI

p( g ,n p + g / ) reaction measured with the Crystal Ball at MAMI. Dan Watts, Derek Glazier University of Edinburgh Richard Codling, John Annand University of Glasgow. Crystal Ball Collaboration meeting, Mainz, 2007. Why measure p( g ,n p + g ’ ) ??. Independent test of

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p( g ,n p + g / ) reaction measured with the Crystal Ball at MAMI

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  1. p(g,np+g/) reaction measured with the Crystal Ball at MAMI Dan Watts, Derek Glazier University of Edinburgh Richard Codling, John Annand University of Glasgow Crystal Ball Collaboration meeting, Mainz, 2007

  2. Why measurep(g,np+g’) ?? • Independent test of • theoretical treatment of • reaction amplitudes and • rescattering effects in • radiative p photoproduction • g radiated from • p+ lines (rather than proton • lines as in pp0g’) – brem • production has different • strength/angular behaviour • Give additional • sensitivity to MDM? Black lines : g + p →p + p0 + g' Blue lines : g + p →n + p+ + g'

  3. Theoretical predictions p(g,np+g’) • Predictions presently available • in unitary model (and cEFT presently in development) • Main features: • 1) Cross sections ~5x larger than • p(g,pp0g’) • 2) Linear asymmetries large and • positive • 3) Sensitivity to MDM marginal • (in sampled kinematics) • 4) But helicity asymmetry shows • promise as complimentary • determination of MDM Tree level Unitary model

  4. p+ detection in the Crystal Ball: Achieving good energy determination Utility of Crystal Ball for p0 detection well understood but p+energy determination unexplored Expect some challenges: 1) Separation from proton/electron events 2) Hadronic/nuclear interactions 3) Unstable decay products Particle-ID detector } GEANT simulation to indicate CB response Michel spectrum of e+ energies • p+m+ + nm(~26 ns) e+ne nm(~2 ms)

  5. Geantsimulation: p+ shower shapes Good Event • Use shower shape to help identify event types • Reject many of m, NI events with simple restriction on Ncryst<=4 Muon decay event Nuclear interaction

  6. Geant simulation: 150 MeV p+ signals in the CB No shower size restriction <=4 crystals in the shower Counts Counts Muon decay Split off clusters Hadronic interactions Energy contained in cluster (GeV) Energy contained in cluster (GeV)

  7. p(g,np+g’) : Outline of data analysis Accept events with: 1p+, 2 neutral clusters in CB/TAPS 1p+, 1 neutron TAPS, 1 other neutral p(g,np+g’) total 4-mom kinematic fit (CL>10-1) If two neutrals assume either is photon or neutron, analyse both combinations Reject events with: 2 neutrals pass Mp0 kinematic fit (CL>10-3) - pp0,np+p0 Mp+miss = Mn Kin. Fit(CL>10-3) - np+ np+ Total 4 momentum fit(CL>10-2) - np+ p+ shower condition <=4 crystals Data used in next plots: all MDM data at Ee=885 MeV July/Sep/Jan Total p(g,np+g’) events – 70,000

  8. p(g,np+g’) : Simulation data • Run event generators through Monte Carlo of CB/TAPS • Predicted energy deposits smeared according to observed experimental energy resolutions • Event generators: • p(g,np+g) • p(g,np+) - split off clusters from n/p+ • p(g,np+p0) – Missed/combined g from p0 decay • All phase space distributions at the moment!’) :

  9. p(g,np+g’) : Analysis results Mgp - mass of the system recoiling from the pion minus the neutron mass Experiment Simulated np+g Simulated np+ Simulated npop Mgp Mgp N.B. Kinematic cuts to reject background relaxed in these plots!! Mgp Mgp

  10. p(g,np+g’) : Analysis results Experiment Simulated np+g Simulated np+ Simulated npop

  11. p(g,np+g’) : Linear asymmetry Eg= 360 ± 20 MeV Eg/ = 50-80 MeV Eg/ = 80-110 MeV Eg/ = 110-140 MeV qp(CM) = 0o-70o qp(CM) = 70o-110o qp(CM) = 110o-180o S fp

  12. p(g,np+g’) : Linear asymmetry Eg=420 ± 20 MeV Eg/ = 50-80 MeV Eg/ = 80-110 MeV Eg/ = 110-140 MeV qp(CM) = 0o-70o qp(CM) = 70o-110o qp(CM) = 110o-180o S fp

  13. p(g,np+g’) : Analysis results (Linear Asymmetry) Unitary model (kD+=2) Linear Asymmetry Linear Asymmetry Eg = 320 ±20 MeV Eg = 360 ±20 MeV 70o < qp(CM) < 110o Linear Asymmetry Unitary model normalised to agree in soft photon limit Rescattering not included Eg = 420 ±20 MeV

  14. p(g,np+g’) : Analysis results (Linear Asymmetry) Unitary model (kD+=2) Linear Asymmetry Linear Asymmetry Eg = 320 ±20 MeV Eg = 360 ±20 MeV 0o < qp(CM) < 70o Linear Asymmetry Unitary model normalised to agree in soft photon limit Rescattering not included Eg = 420 ±20 MeV

  15. p(g,np+g’) : Analysis results (Linear Asymmetry) Unitary model (kD+=2) Linear Asymmetry Linear Asymmetry Eg = 320 ±20 MeV Eg = 360 ±20 MeV 110o < qp(CM) < 180o Linear Asymmetry Unitary model normalised to agree in soft photon limit Rescattering not included Eg = 420 ±20 MeV

  16. p(g,np+g’) : Helicity dependence Eg=420 ± 20 MeV Eg/ = 50-90 MeV Eg/ = 90-130 MeV Eg/ = 130-170 MeV qg/(CM) = 0o-70o qg/(CM) = 70o-110o qg/(CM) = 110o-180o f in CM frame z = gbeam y = p x gbeam

  17. p(g,np+g’) : Helicity dependence Eg=460 ± 20 MeV Eg/ = 50-90 MeV Eg/ = 90-130 MeV Eg/ = 130-170 MeV qg/(CM) = 0o-70o qg/(CM) = 70o-110o qg/(CM) = 110o-180o

  18. p(g,np+g’) : Helicity dependence Eg=620 ± 20 MeV Eg/ = 50-90 MeV Eg/ = 90-130 MeV Eg/ = 130-170 MeV qg/(CM) = 0o-70o qg/(CM) = 70o-110o qg/(CM) = 110o-180o

  19. p(g,np+g’) : Analysis results (Helicity dependence) Helicity shows sin (f) dependence Assumption: Fit distributions with sin(f) - extract amplitude to give helicity asymmetry at phi =90o

  20. p(g,np+g’) : Analysis results (Helicity dependence) qg(CM) = 70o-110o qg(CM) = 0o-70o Experimental data: Eg = 420±20 MeV All qp(CM) fg (CM) = 90o Scirc Scirc Eg/ Eg/ qg(CM) = 110o-180o Unitary model kD = 1 kD = 3 kD = 5 Unitary model integrated over appropriate qg(CM) ranges (at fixed qp(CM) = 90o) Scirc Eg/

  21. p(g,np+g’) : Analysis results (Helicity dependence) qg(CM) = 70o-110o qg(CM) = 0o-70o Experimental data: Eg = 470±20 MeV All qp(CM) fg (CM) = 90o Scirc Scirc Eg/ Eg/ qg(CM) = 110o-180o Unitary model kD = 1 kD = 3 kD = 5 Unitary model integrated over appropriate qg(CM) ranges (at fixed qp(CM) = 90o) Scirc Eg/

  22. Summary • We see a promisingly clean p(g,np+g’) signal • Extracted linear polarisation observables will give important • constraints on the theoretical modelling of radiative pion • photoproduction • Helicity asymmetry may show promising additional route to • gain sensitivity to MDM - future dedicated beamtime ? • Need to pass theoretical predictions through detector • acceptance before publication (Unitary, CEFT?)

  23. p(g,np+g’) : Analysis results qg(CM) = 70o-110o qg(CM) = 0o-70o Eg = 470±20 MeV qp(CM) = 90±??o fg (CM) = 90o Unitary model kD = 1 kD = 3 kD = 5 qg(CM) = 110o-180o Unitary model integrated over appropriate qg(CM) ranges

  24. p(g,np+g’) : Analysis results All plots: Eg = 400 ± 20 MeV Only keep data which have overall p(g,np+g’) 4-momentum with confidence level > 0.1

  25. Importance of MDM determination of D+(1232) Present knowledge

  26. CB@MAMI

  27. Outline • Motivation • Count rate estimate • g n  (Deuterium data) • p+ detection – preliminary analysis of experimental data

  28. Count rate estimate • Detection efficiencies ep+~25% en~30% eg~90% (pp0gep0~85% ep~70% eg~90% ) • Electron count rate 5x105 s-1MeV-1 • Tagging efficiency ~50% • Tagged photon flux 2.5x105 gs-1MeV-1 • 5cm long proton target 2.1x1023 cm-2 • Data acquisition live time ~70% • ds/dEg~0.5 nb/MeV • Total count rate ~0.7x105 events (with g'=30-150 MeV Eg=340-490 MeV)

  29. p(g,np+g’) : Analysis results (Helicity dependence) qg(CM) = 0o-70o qg(CM) = 70o-110o Eg = 420±20 MeV qp(CM) = 90 ±??o fg (CM) = 90o qg(CM) = 110o-180o Unitary model kD = 1 kD = 3 kD = 5 Unitary model integrated over appropriate qg(CM) ranges

  30. p+ detection in the Crystal Ball : Tracker & Particle-ID detector 2mm thick EJ204 scintillator 320mm s(q) ~ 1.5o s(f) ~ 1.3o • Two cylindrical wire chambers • 480 anode wires, 320 strips

  31. p(g,np+g’) : Analysis results s(barns)*10-6 Acceptance Eg(MeV) Eg(MeV) Acceptance x10-3 Acceptance x10-3 Eg(MeV) Eg(MeV)

  32. CB – data analysis parameters • Threshold for cluster finding = 5 MeV • Individual crystal threshold given by TDC (~1.5 MeV). • Do not include clusters near to edge of CB - qg= 30 - 150 deg • Require PID hit within Df=±10 deg of cluster centre • 2-D region cut on plot of PID energy versus CB cluster energy Protons Energy deposited in PID Pion cut Energy of cluster in CB(MeV)

  33. MWPC & Particle-ID in situ

  34. p(g,np+g’) : Analysis results qg(CM) = 70o-110o qg(CM) = 0o-70o Eg = 470±20 MeV qp(CM) = 90±??o fg (CM) = 90o Unitary model kD = 1 kD = 3 kD = 5 qg(CM) = 110o-180o Unitary model integrated over appropriate qg(CM) ranges

  35. p+ - Selection of energy tagged events • Use two-body kinematics g + p → n + p+ • Select n and p+ events back-to-back in phi plane • Calculate p+ energy from pion angleand Eg • Note that wire chamber tracking NOT included – uncertainty from reaction vertex

  36. Setup at MAMI ~41cm ~25cm s/Eg = 1.7% / Eg(GeV)0.4 sq = 2-3o sf = 2o / sin q Tracker & Particle-ID Good angular and energy resolution, close to 4p acceptance

  37. Preliminary p+ signals • Epcalculated – EpMeasured • No restriction on shower size 0-25 25-50 50-75 75-100 100-125 125-150 150-175 175-200

  38. Preliminary p+ signals • Epcalculated – EpMeasured • 4 or less crystals in the p+ shower 0-25 25-50 50-75 75-100 100-125 125-150 150-175 175-200

  39. Preliminary p+ signals • Epcalculated – EpMeasured • 2 or less crystals in the p+ shower 0-25 25-50 50-75 75-100 100-125 125-150 150-175 175-200

  40. Energy resolution • Includes uncertainties in reaction vertex, energy loss … as well as intrinsic CB resolution

  41. Fraction with good energy determination • Look at fraction of events within

  42. Conclusions • g + p → n + p+ eventsidentified • Energy tagged p+ events indicate CB gives reasonable energy signal • MWPC software now implemented – further studies • Develop improved shower shape algorithm which exploits correlation of energy deposits and shape in pion induced shower. • Look at sampling after pulse - see time dependence of positron decays?

  43. Magnetic moment of the D+ via the g + p n + p+ + g' reaction p+ n p Daniel Watts – University of Edinburgh Ph.D student Richard Codling – University of Glasgow

  44. Preliminary p+ signals in CB No. cryst <4 No. cryst < 16 • Plot Epcalculated - EpMeasured • Shift of peak - energy losses? • Simple shower shape restrictions give noticeable effect on response shape • Development of better shower algorithms underway Michel spectrum 0-25 25-50 50-75 75-100 100-125 125-150 150-175 175-200

  45. p+ - Comparison of calculated and measured energies • Rough tagger random subtraction included • All angles summed over

  46. Geant simulation: p+ signals in the CB Ncryst<3 & no neighbours No restriction on shower size m+ decay Highest cluster energy (GeV) Nuclear interaction Incident p+ energy (GeV)

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