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A Highly Selective Dilepton Trigger System Based on Ring Recognition

A Highly Selective Dilepton Trigger System Based on Ring Recognition. Alberica Toia II Physikalisches Institut Justus-Liebig-Universität Gießen, Germany for the HADES Collaboration. Overview HADES dilepton second level trigger: The Matching Unit

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A Highly Selective Dilepton Trigger System Based on Ring Recognition

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  1. A Highly Selective Dilepton Trigger System Based on Ring Recognition Alberica Toia II Physikalisches Institut Justus-Liebig-Universität Gießen, Germany for the HADES Collaboration • Overview • HADES dilepton second level trigger: • The Matching Unit • Performances of the Ring Recognition algorithm (J.Lehnert) • Identification of pair(investigation of close pairs) • Opening angle distribution • Properties of rings • Ratios online/offline

  2. Lepton selection Df Dq p (MeV/c) Lepton Signatures The Matching Unit • Combines electron signatures • Determines p from Dq The HADES magnet Momentum

  3. Trigger condition % evts >= 1 online ring 10.5% >= 1 online lepton 2.9% >= 2 online rings 4.6% >= 2 online leptons 1.7% >= 1 online dilepton 0.3% Dilepton Selection Data: Nov01C-C 1.5AGeV full field Opening Angle • Combines leptons into un-like sign pairs with a given opening angle and invariant mass range Opening angle (°) Invariant Mass No Shower IPU included -> higher lepton reduction -> different acceptance for e+ and e- -> RICH is the most selective element of the second level trigger m (MeV/c2)

  4. Analysis Strategy Which leptons are lost with a given trigger condition? Comparison of candidates found by online hardware algorithms with results from full offline analysis real leptons ??? Offline analysis SHOWER Offline LEPTONS RICH TOF MDC • Correlation of electron signatures from different detectors • More complex algorithms than online are possible Found by online ??? -> need for a calibration reaction pp -> pph

  5. x x x x x x x x x x Pairs of Rings • Opening angle of online pairs • Correlation with Mini Drift Chambers (MDC) • fakes suppression • position resolution xx x Fakes accompanying real rings All rings found by online Correlated with MDC • local maximum needs to be extended to the 8 neighbouring pads ??? • real rings main source of fake rings (~ 1 ring diameter)-> hint for smeared out rings (conversion pairs ???) • unphysical distribution at large opening angle (phase space) IPU opening angle

  6. META Matching Rings Further coincidence with TOF / Shower („META“ - MultiplicityElectronTriggerArray) magnet coils low B field Analysis steps: • Before B field: - DqRICH-MDC < 2° - DfRICH-MDC < 5° • After B field: - DqMDC-META no cut - DfMDC-META < 5° - 5 ns < tof < 8 ns -> best candidate selected MDC RICH high B field electrons p ~ 1/DqMETA - MDC e+ e- positrons DqMETA - MDC MDC opening angle

  7. all doubles singles MDC opening angle doubles singles # pads per ring Properties of Rings 2 rings match 2 MDC („singles“) 1 ring matches 2 MDC („double“) 1 ring matches 1 MDC cluster: unresolved close pair • „Singles“ still contaminated by unresolved close pairs • Different behaviour of „singles“ and „doubles“ • No clean discriminating criteria

  8. Online Ring correlated with MDC correlated with META Online Ring correlated with MDC correlated with META Offline Ring correlated with MDC correlated with META Correlated Online Ring Correlated Online Ring Correlated Offline Ring Comparison Online - Offline Online Pairs Offline Ring correlated with MDC correlated with META Correlated Offline Ring Offline Pairs • PAIRS RATIO e(ePAIR~ eSINGLE LEPTON2) : • (Online AND Offline)/Online • (Offline AND Online)/Offline • as a function of opening angle in MDC

  9. Doubles found by offline Correlated with online 72% Rings found by offline Correlated with online 66% Singles found by offline Correlated with online 52% Ratio of Pairs: online/offline Pair Ratio (ePAIR~ eSINGLE LEPTON2) as a function of opening angle in MDC opening angle opening angle Loss of pairs at ~ 4° < a < 10° (destructive interference of ring and veto region) opening angle

  10. Rings found by online Doubles found by online Singles found by online Correlated with offline 66% Correlated with offline 53% Correlated with offline 78% Ratio of Pairs: offline/online Pair Ratio (ePAIR~ eSINGLE LEPTON2) as a function of opening angle in MDC opening angle opening angle eonline / offline ~ eoffline / online -> need for an absolute reference system, i.e.: pp -> pph as a calibration reaction opening angle

  11. Offline AND online / online Rings found by offline Doubles found by offline Singles found by offline Singles found by online Doubles found by online Rings found by online Correlated with offline 78% Correlated with offline 66% Correlated with online 52% Correlated with online 66% Correlated with offline 53% Correlated with online 72% Online AND offline / offline opening angle opening angle opening angle opening angle opening angle opening angle

  12. Simulation of Lepton Pairs • 2 leptons per event shot from target • 100 < p < 1000 MeV • 25° < q < 40° • 65° < q < 80° • noise 1% Single lepton efficiency --- strongerdrop at 1° < a < 3° due to higher photon multiplicity (veto) ---lower saturation efficiency due to lower photon multiplicity eASYMPTOTIC ~ 98% eASYMPTOTIC ~ 90% opening angle a (deg)

  13. Summary and Outlook Alberica Toia Ingo Fröhlich, Adrian Gabriel, Daniel Kirschner, Wolfgang Kühn, Jörg Lehnert, Erik Lins, Markus Petri, Jim Ritman, Daniel Schäfer, Michael Traxler II. Physikalisches Institut Justus-Liebig-Universität Gießen, Germany • Low magnetic field: • possibility of resolving close pairs (conversion) • better understanding of the ring properties • Characterization of relevant figures of the online Ring Recognition Estimation and methods for: • Single lepton efficiency • Pair ratios online/offline and viceversa • Reduction factor • Characterization for different thresholds • Full analysis of simulated data • Lower limit for ring recognition efficiency • Need for a calibration reaction

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