Background rejection in P326 (NA48/3)
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Transcript of Background rejection in P326 (NA48/3)
19/04/23 Giuseppe Ruggiero - CERN 1
Background rejection in P326
(NA48/3)Giuseppe Ruggiero
CERNK-Rare 2005 WorkshopFrascati 26 / 05 / 2005
19/04/23 Giuseppe Ruggiero - CERN 2
OverviewCharacterization of the background
Kinematics and background rejection capabilityMuon rejection and Muon ID
Requirements and results from simulations
Photon rejectionRequirements and results from simulations
Electron IDResults from NA48 studies on data
Results about background rejection
Some thoughts about Charged VetoConclusions
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Background rejectionMain task of a Main task of a experiment experiment
All the K+ decay modes are potentially All the K+ decay modes are potentially dangerousdangerous
Goal of P326: Goal of P326: S/B = 10S/B = 10 ~~101012 12
rejectionrejection
2-Steps:Kinematic rejection
Veto and Particle ID, , charged particles – e separation
As better as possible resolutionin charged particle reconstruction
High hermeticity
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Background kinematically constrained
Decay BR
K2 0.634
+0 0.211
++- (00)
0.070
92% of total background Allows us to define the signal region
Pion track hyp.
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Background not kinematically constrainedDecay BR
KKe3e3 0.049
KK33 0.033
KK22 0.006
++00 0.001KKe4e4 4 x
10-5
KK44 1 x 10-5
8% of total background Spoils the signal region
Pion track hyp.
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Kinematics: Gigatracker + Double
Spectrometer Tracking systems operating in
vacuum
Gigatracker: pixels Spectrometer: Straw tubes
Gigatracker: 4x10-3 X0 per station PK measurement K measurement
Spectrometer: 5x10-3 X0 per chamber 2 Ptrack measurements
track measurement
Resolution limited by MS
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Kinematic reconstruction
Two independent measurements of the downstream track
momentum
m2miss resolution ~1.1×103 GeV2/c4
Main contribution from K measurement
PtrackPK
K
Total
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Kinematic rejection2 2 4miss
2 2 4miss
Region I: 0 < m 0.01 /
Region II: 0.026 < m 0.068 /
GeV c
GeV c
Cuts on Ptrack
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) K2 ~5 x 106 (Region I mainly)
+0 ~2 x 104
Reconstruction: Room for ×3 gain in rejection power
(loss in signal acceptance)
track15 < P 35 /GeV c
CUTS:
Simulation and results
Against , and
Gaussian background < 106
Against RICH operational reasons
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Muon rejection: PhysicsSources of Sources of rejection inefficiency: rejection inefficiency: “Catastrophic” “Catastrophic” energy lossesenergy losses
bremsstrahlung e+e- pair production high Q2 + e- scattering decay in flight
Deep inelastic – nucleon scattering + + N + + hadrons (<106)
electromagnetic shower (105)
EM showers (from ICARUS)
Hadronic shower (from ICARUS)
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Muon rejection: MAMUD Detector: Sampling Calorimeter ( rejection) + Magnet (beam
deflection) Goal: rejection inefficiency < 105
Sensitivity to minimum ionizing particles (MIP)
Distinguish hadronic and electromagnetic showers (longitudinal segmentation)
Bending power: 5 Tm 75 GeV/c beam deflected by ~18 mrad
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Simulation of muon rejection: results
Complete GEANT simulation of MAMUD
Rejection: MAMUD + LKr calorimeter
Rejected events: MIP deposition in last section onlyEM cluster shape
Inefficiency ~105 (>90% signal acceptance)
(Inefficiency ~106 with 50% signal acceptance)
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0.0001
0.001
0.01
0.1
0 5 10 15 20 25 30 35 40
Momentum (GeV/c)
Delta_Theta muon/pion (rad)
Muon – Pion ID
~1 in 15 m He : ~21 pe and c=8.2 mrad
~1 in 2 m Ar : ~22 pe and c=23.7
mrad
Detector: RICHRICH
Goal: Muon – Pion separation with 102 ineff. over a wide momentum range As low X0 as possible (RICH before LKr)
1st option: P.S. Cooper – FERMILAB-CONF-05-015-CDSome Brain – Storming : O. Ullaland (CERN)
(
rad
)
0.1
0.01
0.001
0.0001
Momentum (GeV/c)
5 10 15 20 25 30 35 40
Argon
Helium
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Photon Rejection
E (GeV)E (GeV) E (GeV)10 2 1 60 2 3 4 5 60 123 4 5 7 8 910
ANTI LKr E > 1 GeV IRC / SACE > 6 GeV
Detectors: lead-scint sandwich (ANTI), LKr, lead-scint sandwich (IRC, SAC)
Goal: 108 level of veto inefficiency on 0 (requirement from +0) Decays with 0: energy correlation between s’ from 0 decay Decays with single photon (radiative): hermeticity (0 - 50 mr coverage)
Energy of photons from 0 in +0 events
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Simulation of photon rejection: resultsSimulation of geometrical layout
Parametrization of the inefficiencies Inefficiency: 2 x 108 on 0 from +0
5 x 108 on 0 from Kl3
103 on from radiativeDetector E range Inefficien
cy
ANTI< 50 MeV 1
(0.5, 1) GeV 104
> 1 GeV 105
LKR
< 1 GeV 1
(1,3) GeV 104
(3,5) GeV 104 105
> 5 GeV 105
IRCs, SAC
All 106
GEANT simulation of each device started Simulation results
validating on existing detector configurations where data are available
DATA: S. Ajimura et al., NIM A435 (1999) 408
MC: Our GEANT4 simulation
Photon Energy (MeV)200 400 600 800 1000
Ineff
icie
ncy
10-4
10-5
2mm lead / 6mm Scintillator
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Electron IDDetector: LKr
Inefficiency of e ID studied in NA48 with e from 0 Dalitz decay.
Background from hadronic showers
ID = 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 ID = 103
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Signal acceptance and Kaon flux
Fast simulation of the complete layoutSignal acceptance (Geometry, kinematic cuts,
FF):Region I: 4.5%Region II: 14.5%
Assumed signal BR = 10-10
Detailed simulation of the beam lineExpected kaon decays in fiducial region per year: 4.8 x 1012
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TotalTotal Region IRegion I Region IIRegion II
SignalSignal 91.2 21.6 69.6
KK22 1.6 1.4 0.1
++00 4.4 2.3 2.1
KKe3e3 1.6 0.2 1.4
KK33 <0.1 0 <0.1
KK22 0.4 0.1 0.3
++00 <0.1 0 <0.1
++++ In progress 0 In progress
KKe4e4In progress 0 In progress
KK44< 102 ×Ke4 0 < 102 ×Ke4
BackgrouBackgroundnd
8 + charged
4 4 + charged
RESULTS: Events collected per year
Wit
hou
t F
orm
Facto
r
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Thoughts about Charged VetoesGoal: at least 5 x 10-3 on a
single track Reject Ke4, K4, ++-
The most dangerous one: Ke4
2 Gigatracker stations
Task at high angle
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ConclusionsThe experimental layout is being finalisedBackground estimation almost completeRegion I: well understood, a RICH is needed for background rejection.
S/B = ~5, but room for improvements.
Region II:S/B > 10, (but with Ke4 and K3 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)