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Status of analysis of leptonic decays

Status of analysis of leptonic decays. By Marcin Berłowski The Andrzej Soltan Institute for Nuclear Studies , Warsaw Collaboration & Analysis Meeting, Juelich 8-10.VI.2009. Outline. Apr07 pp  pp  at 1.4 GeV PT29 numbers Decay channel    and some expectations

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Status of analysis of leptonic decays

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  1. Status of analysis of leptonic decays By Marcin Berłowski The Andrzej Soltan Institute for Nuclear Studies, Warsaw Collaboration & Analysis Meeting, Juelich 8-10.VI.2009

  2. Outline • Apr07 pppp at 1.4 GeV PT29 numbers • Decay channel  and some expectations • Selection of e+e- and results • In search of e+e-, background, conclusions • Future plans and final conclusions

  3. Data from April 2007 runs • Reaction: pp→pp at 1.4 GeV • Three triggers for charged decays (8, 29, 31) PT29 trigger • Trigger definition - [frha2*frhb2*ecrl*Vfvh] • Prescaled by factor 5 • High energy deposited in both sides of SEC • It didn't choose between  decays: →e+e-e+e-, →e+e-, →e+e-, → • ~300 runs each around 100k of events • 2 weeks of data taking (with PT29) around 100h of stable conditions All results below based on 40% of above

  4. → Data IMgg [GeV] Cut: 0.5 < MMpp < 0.6 GeV 2 most energetic photons

  5. → CDN=2, E > 50 MeV Data Data

  6. Expectations • We see 349k ev with at least 2 (E>50MeV)‏ • Raw estimation of number of eta's from IM pick (gaussian fit) ~ 10630 ev • After reconstruction efficiency & detector acceptance for e+e- we expect ~ 126 ev • We know from previous CELSIUS/WASA analysis that we have from  conversion, background in ratio ~1:2 in respect toe+e- channel. Finally ~ 190 ev

  7. Selection of →e+e- events • Particle selection: - Two charged from FD closest in time, within 3°-18°, edep>0.1 GeV - Two oppositely charged tracks giving lowest IMee - Photon of energy > 50 MeV, giving greatest angle to e+e- pair on a XY plane, also most energetic gamma • Time cuts: - Coincidence between FDC, CDC, CDN (every combination of them in [-25,+35]ns bounds) - At least one PS hit in the proper time interval - For each of FDC, CDC: (max_time – min_time) in 20 and 50 ns respectively

  8. Indication of e+e- pair(s) MC Data Data IMee < 0.125 GeV 0.5 GeV <MMpp< 0.6 GeV

  9. →e+e- in data IMeeg MMpp • Cuts: cdn=1, cdc=2 • IMee<0.125, E>50 MeV • For IMeeg plot cut on MMpp 0.52-0.58 GeV Data Data

  10. Conclusions from →e+e- • We see agreement with expectations from → channel in number of events in pick • Dailtz decay (and conversion of photon in detector material) clearly visible • This channel gives us an opportunity to study the response of our detector for low energetic electrons • In later stage single Dalitz decay can be used as normalization to another, less probable decays

  11. →e+e-

  12. Selection of →e+e- events • Particle selection: - Two charged from FD closest in time, within 3°-18°, edep>0.1 GeV - Two oppositely charged tracks giving greatest opening angle on a XY plane • Time cuts: - Coincidence between FDC, CDC (every combination of them in [-25,+35]ns bounds) - At least one PS hit in the proper time interval - For each of FDC, CDC: (max_time – min_time) in 20 and 50 ns respectively • Particle identification: - Ratio between momentum and deposited energy 0.7<R<1.65 - Energy deposit > 200 MeV, total momentum > 200 MeV/c • Kinematical cuts: - Opening angle in e-p pair in bounds: 70°<θee<140° - Missing mass of e-p pair: 1.7< MMee < 2 GeV - Missing mass of two protons: 0.52 < MMpp < 0.58 GeV

  13. Particle identification • Edep CDC > 0.2 GeV • Mom CDC > 0.2 GeV/c MC Pions MC Data

  14. Opening angle • Opening angle: 70° <ANGee< 140° Pions MC MC Data

  15. Problems with low IMee tail MC →e+e- MC →e+e- MC →e+e- MC →e+e-

  16. Conclusions from →e+e- • After applying all above cuts we see no events from 1M pp→pp+- MC and 10 events in data (in 0.5<IMee<0.6 GeV) • The background reduction for direct 2 pions is on the level of 10-4 • As for data we still see events on the level of 10-4 • The invariant mass precision is still not enough (vertex inclusion to reconstruction?) • Particle identification on dE/E maybe can help in background reduction

  17. Final conclusions and „to do” list • Only 40% of all data collected with trigger PT29 was allready analyzed • Sep08 pp 2 weeks with unprescaled „energetic” trigger analysis will be started soon. Delay was related to computer problems (solved hopefully last week) and low disk space (new 1TB HD was installed in Juelich) • Background for →e+e- must be studied more carefully (we see that two pion production and eta decays are not the only source)

  18. Thank you for your attention

  19. Backup slides

  20. Missing mass of e-p pair • 1.7< MMee < 2 GeV Pions MC Data

  21. Particle identification MC Pions Data • Ratio mom/edep: 0.7< R <1.65

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