Transversal Target Asymmetries in Threshold p0 Photoproduction Peter-Bernd Otte, Annual SFB School Boppard, October 2014

Photoinduced Reactions on Protons Introduction Photoinduced Reactions on Protons Produktion verstehen von \gamma p  X oder \pi+ oder \pi0:  Meine Analyse: „Bereich der Schwelle ganz genau untersuchen“ MAMI geht bis sqrt(s) = 2,09 GeV, d.h. alles wird abgedeckt. s = 2*m_p+E_g+m_p**2 Schwelle bei (ein- und auslaufendes Proton hat Impuls = 0): 2E_Schwelle*m_p = m_pi^2 + 2*m_p*m_pi Ethr = 145MeV (Eg) MAMI energy range

Pion Photoproduction Introduction S- und P-wave multipole amplitudes Models: large differences, although they all describe the existing (published) data Determination of multipole amplitudes  model independent

Mainz Microtron 1) Experimental Setup cw electron accelerator sources: 100% duty factor sources: unpol.: Imax = 100µA pol.: Imax = 20µA with Pe≈80% MAMI-B/C: 180-883MeV DE = 13keV 900-1604MeV DE = 110keV RTM = Race Track Mikrotron (Mehrfaches Durchlaufen einer Beschleunigungseinheit) HDSM = Harmonic double sided Mikrotron MAMI C seit 2006

Photon beam 1) Experimental Setup Photon tagging spectrometer („Glasgow-Mainz-Tagger“): e- Bremsstrahlung momentum determination of scattered e- Eg = E0-Ee coverage: 7..93% E0 DE ≈ 1MeV (@E0=450MeV) flux: 4*105 g/s/MeV Polarised photons e- long. pol.  circ. pol. Crystal  lin. pol. Helicity transfer e- -> g Rückstoß auf Atomkern vernachlässigbar. lin. pol. e-: 100µm Diamant electrons E0 g beam

Target Cell 1) Experimental Setup Target cell Butanol C4H9OH 2 cm long and 2 cm diameter or Carbon foam / LH2 Rückstoß auf Atomkern vernachlässigbar. lin. pol. e-: 100µm Diamant electrons E0 g beam

Detector System 1) Experimental Setup Target cell Butanol C4H9OH 4π photon spectrometer (n and charged particles as well) Target cell Butanol C4H9OH 2 cm long and 2 cm diameter or Carbon foam / LH2 g beam

Detector System 1) Experimental Setup Particle ID (DE/E) 4π photon spectrometer (n and charged particles as well) Particle ID (DE/E) with thin plastic scintilators 20°<q<160° : barrel of 24x 2°<q<20° : 384x g beam

Detector System 1) Experimental Setup optional: Threshold C Detector 4π photon spectrometer (n and charged particles as well) optional: Threshold C Detector MWPC 2 cylindrical chambers charged particles only g beam

Detector System 1) Experimental Setup TAPS 366 BaF2 crystals (PMTs) 4π photon spectrometer (n and charged particles as well) TAPS 366 BaF2 crystals (PMTs) 12 radiation lengths 1°<q<20° (3%) self triggering Crystal Ball 672 NaI(Tl) crystals (PMTs) 16 radiation lengths 20°<q<160° (94%) s ≈ 2-3° self triggering g beam

1) Experimental Setup Detector System photons TAPS CB

Target: Mainz-Dubna Pol. Frozen Spin Target 1) Experimental Setup Target: Mainz-Dubna Pol. Frozen Spin Target Target: See talk J. Linturi tomorrow! „Dynamic Nucleon Polarisation“ polarise free electrons (radical) transfer pol. to protons P0 ≈ 90% (only H), P=P0e-t/t 3He/4He dilution cryostat T = 26mK & B = 0.44T for t≈2*10³h H spin: transversal or longitudinal super conducting saddle coil DNP: Dynamic Nucleon Polarisation („70GHz Mikrowellen System“): Electrons polarised by microwaves and transfer their polarisation to the protons. Polarising field B = 2.5 T spin of nuclei = 0 background = quasi free and coherent \pi0 production

Target Material 1) Experimental Setup Unpolarised Polarisable Material unpol. liquid Hydrogen (lH2) @ low T: parahydrogen (spins: ) not polarisable Polarisable Material Butanol (advantages: DNP, high P, large t, radiation hard, large d, high f) only H polarised unpol. BG I(12C) = I(16O) = 0 DNP: Dynamic Nucleon Polarisation („70GHz Mikrowellen System“): Electrons polarised by microwaves and transfer their polarisation to the protons. Polarising field B = 2.5 T spin of nuclei = 0 background = quasi free and coherent \pi0 production

Butanol Target: important properties 1) Experimental Setup Butanol Target: important properties Dilution Factor Filling Factor not trivial! Best mess. method: melting  f=60(3)% for butanol butanol balls Effective d(q,E) necessary Mandatory: decent statistics  Does not work in threshold region

Photoinduced Reactions on Protons 2) Photo p Production Photoinduced Reactions on Protons D region 2nd and 3rd resonant region threshold Produktion verstehen von \gamma p  X oder \pi+ oder \pi0:  Meine Analyse: „Bereich der Schwelle ganz genau untersuchen“ MAMI geht bis sqrt(s) = 2,09 GeV, d.h. alles wird abgedeckt. s = 2*m_p+E_g+m_p**2 Schwelle bei (ein- und auslaufendes Proton hat Impuls = 0): 2E_Schwelle*m_p = m_pi^2 + 2*m_p*m_pi Für die 2. und 3. Resonanz-Region werden bis hin zu F-Wellen von Relevanz. Ethr = 145MeV (Eg) MAMI energy range

Amplitudes in Pion Photo Production 2) Photo p Production Amplitudes in Pion Photo Production Spin observables Oi (q, W) Legendre expansion up to Lmax Legendre coefficients Aik bilinear combinations of multipoles, e.g.: Omelaenko (1981): 5 observables necessary for complete experiment Talk from Y. Wunderlich tomorrow

Threshold p0 production 2) Photo p Production Threshold p0 production Beam / Target Polarisation: In threshold region (Eg=144-180MeV): PWA (L=1): only S- and P-wave amplitudes E0+ & M1+, M1-, E1+ near threshold assumption: E0+ complex, all other real but Im(E0+) is fixed by Fermi Watson theorem (unitarity): necessary: determine 4 real numbers from experiment independent. meas. of Im(E0+) requires add. observable  “complete data base” E0+ etc. are multipoles \beta = cusp parameter, real value around 3 a = exchange scattering length Q = Pion momentum

p0 threshold production 2) Photo p Production p0 threshold production 2001: First measurements with TAPS (A. Schmidt et al., PRL2001, 87.232501) lin. pol. photons unpol. H target s0, but only one S point Physical Review Letters expand Observable in a cos(\theta) series for energy-angle separation direct access to real part / imaginary part of E0+ also possible in treshold region: test dominance at D-Waves with F

p0 threshold production 2) Photo p Production p0 threshold production 2001: First measurements with TAPS (A. Schmidt et al., PRL2001, 87.232501) lin. pol. photons unpol. H target s0, but only one S point 2008: high precision measurement s0, S with CB/TAPS (D. Hornidge et al., PRL2013, 111.062004)  Re(E0+, M1+, M1-, E1+) example: Physical Review Letters expand Observable in a cos(\theta) series for energy-angle separation direct access to real part / imaginary part of E0+ also possible in treshold region: test dominance at D-Waves with F

P-Waves Amplitudes 2) Photo p Production deviations for large E  D res. Messung stimmt überall gut mit der Theorie überein! Geringer stat. Fehler Lediglich für große E stimmt die Näherung für M1+ nicht mehr, da hier die Ausläufer der Delta-Res. greifen.

S wave amplitude 2) Photo p Production direct measurement via: Fermi Watson theorem or measurement (p+n thr.) Direkte Messung von ImE0+ ab \pi+ Schwelle unitarity cusp

Threshold p production 2) Photo p Production Threshold p production add measurement with unpol. photons & trans. pol. target: (2010, 2011) Measurement of with T  b and known E0+ Direct measurement of Im(E0+) Check consistency with S measurements (2008) Physics Review Letters Ladungsaustausch messbar expand Observable in a cos(\theta) series for energy-angle separation direct access to real part / imaginary part of E0+ also possible in treshold region: test dominance at D-Waves with F ?  Test strong isospin breaking

Analysis: Definitions 2) Photo p Production Analysis: Definitions Relevant: Determination of Obs.: asymmetry Event by event selection into 2 bins: „+“ and „-“ for T: for F: p spin (incoming) p0 g Was ist der T? „Target Asymmetrie“  Wie wird T gemessen? Erklären! Wechsel von pT (10-5Hz) nicht zwingend notwendig, nur zur Reduktion von falschen Asymmetrien durch eine unterschiedliche Detektor-Akzeptanz (T & F gleichzeitig bestimmbar) p for T’: Physical results <>0 expected =0 expected

Analysis: 3 Methods 2) Photo p Production Objective: get T of pure pol. hydrogen Diluted asymmetry on butanol target: Methods: determine (works only >220MeV) denominator  normalise with simulation & f denominator  normalise with unpol. Measurement & f “Ingredients:” butanol + carbon meas. butanol + simulation butanol + hydrogen Dilution Factor: Fermi motion and FSI  need for eff. Dilution factor  Same results expected…

Analysis details 3) Results Butanol Signal missing mass /MeV 2g  p0 reconstruction (no problem) proton detection (problematic, does not emerge the target)  Technique: Missing Mass (half of the total data set, all energies and q) Signal Um zu zeigen, dass die Analyse die Reaktion identifizieren kann. Kombinatorischer Untergrund bei der 2g-Masse zu sehen. missing mass /MeV

Photoinduced Reactions on Protons: Measured 3) Results Photoinduced Reactions on Protons: Measured Threshold & D region 2nd and 3rd resonant region Produktion verstehen von \gamma p  X oder \pi+ oder \pi0:  Meine Analyse: „Bereich der Schwelle ganz genau untersuchen“ MAMI geht bis sqrt(s) = 2,09 GeV, d.h. alles wird abgedeckt. s = 2*m_p+E_g+m_p**2 Schwelle bei (ein- und auslaufendes Proton hat Impuls = 0): 2E_Schwelle*m_p = m_pi^2 + 2*m_p*m_pi S. Schumann P. Barrientos P. Otte Analysis by: V. Kashevarov MAMI energy range

Status & Results for T and F Black = But/Sim red = But/H green = But/C Blue = MAID All analyses completed possible overview via Legendre Polynoms F @ 330MeV T @ 330MeV 𝐴⋅𝜎=𝜌⋅sin⁡(𝜃) 𝑝 0 + 𝑝 1 cos 𝜃 + 𝑝 2 3 cos 2 𝜃 −1 2 +…

Systematic uncertainties 3) Results Systematic uncertainties Sources, O(~%) different analysis techniques (e.g. carbon subtraction) Helicity dep. photon flux (A=0,005) Detector asymmetries Goodness of detectors maintenance butanol target, contribution of I=1/2 atoms C13 (1,1%) and O17 isotopes. F4 in container (He3 for cooling) limits resolution future investigations Hierzu beantworte ich gerne am Ende Fragen.

3) Results Systematic Errors ssys(T) = global Difference between analyses T’ ssys(F) = global Difference between analyses DA(beam flux) % Error in g flux (tagger poblems) 3,0 Unstable detectors and electronics f 2,0 (?) P(target) 2,0 P(beam) 2,7 total global sys. Error (indep. of q, E) 5,1 (T) 5,8 (F) depends on q, E

Thank you Summary / Outlook 4) Outlook Goal: model independent PWA from threshold up to W=2GeV Using techniques from Stahov?  talk tomorrow Measured & analysed Pion photoproduction: S, T, F Actual work in group measurements with “n” longitudinal pol.: G, E (in analysis) ditto: other channels Ideal: remeasure T with all improvements we learned Thank you More channels like \eta 2\pi_0 werden untersucht