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Background rejection in P326 (NA48/3)

Background rejection in P326 (NA48/3). Giuseppe Ruggiero CERN K-Rare 2005 Workshop Frascati 26 / 05 / 2005. Overview. Characterization of the background Kinematics and background rejection capability Muon rejection and Muon ID Requirements and results from simulations Photon rejection

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Background rejection in P326 (NA48/3)

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  1. Background rejection in P326 (NA48/3) Giuseppe Ruggiero CERN K-Rare 2005 Workshop Frascati 26 / 05 / 2005 Giuseppe Ruggiero - CERN

  2. Overview • Characterization of the background • Kinematics and background rejection capability • Muon rejection and Muon ID • Requirements and results from simulations • Photon rejection • Requirements and results from simulations • Electron ID • Results from NA48 studies on data • Results about background rejection • Some thoughts about Charged Veto • Conclusions Giuseppe Ruggiero - CERN

  3. Background rejection • Main task of a pnn experiment • All the K+ decay modes are potentially dangerous • Goal of P326: S/B = 10~10-12 rejection • 2-Steps: • Kinematic rejection • Veto and Particle ID • g, m, charged particles • m – p - e separation As better as possible resolution in charged particle reconstruction High hermeticity Giuseppe Ruggiero - CERN

  4. Background kinematically constrained Pion track hyp. 92% of total background Allows us to define the signal region Giuseppe Ruggiero - CERN

  5. Background not kinematically constrained Pion track hyp. 8% of total background Spoils the signal region Giuseppe Ruggiero - CERN

  6. Kinematics: Gigatracker + Double Spectrometer • Tracking systems operating in vacuum • Gigatracker: pixels • Spectrometer: Straw tubes • Gigatracker: • 4x10-3 X0 per station • PK measurement • qK measurement • Spectrometer: • 5x10-3 X0 per chamber • 2 Ptrack measurements • qtrack measurement • Resolution limited by MS Giuseppe Ruggiero - CERN

  7. Kinematic reconstruction Total qpK qp PK Ptrack qK Two independent measurements of the downstream track momentum m2miss resolution ~1.1×10-3 GeV2/c4 Main contribution from QpK measurement Giuseppe Ruggiero - CERN

  8. Kinematic rejection CUTS: Against Km2, p+p0 and p+p+p- Gaussian background < 10-6 Against Km2 RICH operational reasons Simulation and results p+p0 • Simulation of the tracking systems • GEANT - based • Accidental PileUp in Gigatracker • (150 ps resolution per station) • Kinematic rejection inefficiency: • (Limited by non gaussian tails from MS) • Km2~5 x 10-6(Region I mainly) • p+p0~2 x 10-4 • Reconstruction: • Room for ×3 gain in rejection power • (loss in signal acceptance) Cuts on Ptrack Giuseppe Ruggiero - CERN

  9. Sources of m rejection inefficiency: “Catastrophic” m energy losses m bremsstrahlung e+e- pair production high Q2m+ e- scattering m decay in flight Deep inelastic m – nucleon scattering m+ + N  m+ + hadrons (<10-6) electromagnetic shower(10-5) Muon rejection: Physics EM showers (from ICARUS) Hadronic shower (from ICARUS) Giuseppe Ruggiero - CERN

  10. Muon rejection: MAMUD • Detector: Sampling Calorimeter (m rejection) + Magnet (beam deflection) • Goal: m rejection inefficiency < 10-5 • Sensitivity to minimum ionizing particles (MIP) • Distinguishhadronic and electromagneticshowers (longitudinal segmentation) • Bending power:5 Tm 75 GeV/c beam deflected by ~18 mrad Giuseppe Ruggiero - CERN

  11. Simulation of muon rejection: results • Complete GEANT simulation of MAMUD • Rejection: • MAMUD + LKr calorimeter • Rejected events: • MIP deposition in last section only • EM cluster shape • Inefficiency ~10-5 (>90% signal acceptance) • (Inefficiency ~10-6with50% signal acceptance) Giuseppe Ruggiero - CERN

  12. Muon – Pion ID Detector: RICH Goal: Muon – Pion separation with 10-2 ineff. over a wide momentum range As low X0 as possible (RICH before LKr) 1st option:P.S. Cooper – FERMILAB-CONF-05-015-CD Some Brain – Storming : O. Ullaland (CERN) 0.1 ~1 in 2 m Ar : ~22 pe and c=23.7 mrad Argon 0.01 Helium Dq m / p (rad) 0.001 ~1 in 15 m He : ~21 pe and c=8.2 mrad 0.0001 5 10 15 20 25 30 35 40 Giuseppe Ruggiero - CERN Momentum (GeV/c)

  13. Photon Rejection • Detectors: lead-scint sandwich (ANTI), LKr, lead-scint sandwich (IRC, SAC) • Goal: 10-8 level of veto inefficiency on p0 (requirement from p+p0) • Decays with p0: energy correlation between gs’ from p0 decay • Decays with single photon (radiative): hermeticity (0 - 50 mr coverage) Energy of photons from p0 in p+p0 events ANTI LKr Eg > 1 GeV IRC / SAC Eg > 6 GeV 0 1 2 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9 10 Eg (GeV) Eg (GeV) Eg (GeV) Giuseppe Ruggiero - CERN

  14. Simulation of photon rejection: results • Simulation of geometrical layout • Parametrization of the g inefficiencies • Inefficiency: 2 x 10-8 on p0 from p+p0 • 5 x 10-8 on p0 from Kl3 • 10-3 on g from radiative • GEANT simulation of each • device started • Simulation results validating on • existing detector configurations • where data are available 2mm lead / 6mm Scintillator DATA: S. Ajimura et al., NIM A435 (1999) 408 MC: Our GEANT4 simulation Inefficiency 10-4 10-5 200 400 600 800 1000 Giuseppe Ruggiero - CERN Photon Energy (MeV)

  15. Electron ID • Detector: LKr • Inefficiency of e ID studied in • NA48 with e from p0 Dalitz decay. • Background from hadronic • showers • hID = 1% for E/p < 0.9. • Improvement of a factor 10 if • E/p < 0.85 (about 2% signal lost) • Room for improvements using • E/p + other informations about • clusterization (NN technique). • We assume hID = 10-3 Giuseppe Ruggiero - CERN

  16. Signal acceptance and Kaon flux • Fast simulation of the complete layout • Signal acceptance(Geometry, kinematic cuts, FF): • Region I: 4.5% • Region II: 14.5% • Assumed signal BR = 10-10 • Detailed simulation of the beam line • Expected kaon decays in fiducial region per year: 4.8 x 1012 Giuseppe Ruggiero - CERN

  17. RESULTS: Events collected per year Without Form Factor Giuseppe Ruggiero - CERN

  18. Thoughts about Charged Vetoes • Goal:at least 5 x 10-3 on a single track • Reject Ke4, Km4, p+p+p- • The most dangerous one: Ke4 Task at high angle 2 Gigatracker stations Giuseppe Ruggiero - CERN

  19. Conclusions • The experimental layout is being finalised • Background estimation almost complete • Region I: well understood, a RICH is needed for m background rejection. • S/B = ~5, but room for improvements. • Region II: • S/B > 10, (but with Ke4 and Kp3 contributions missing) • Charged vetoes to be optimised • Once dead-time and selection cuts are taken into account, a 10% signal acceptance is plausible (i.e. 40 events/year for Br~10-10) Giuseppe Ruggiero - CERN

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