19/04/23 Giuseppe Ruggiero - CERN 1

Background rejection in P326

(NA48/3)Giuseppe Ruggiero

CERNK-Rare 2005 WorkshopFrascati 26 / 05 / 2005

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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)