Sampling Detectors for ne Detection and Identification Interest de jour: what is sin22q13 • oscillations nm -> ne • ‘superbeams’ • ‘Current’ generation of experiments • How can we do better • Sampling detectors for ne detection Adam Para, Fermilab NuFact02 Imperial College Different baselines: where the oscillation peaks are ? L(km)/n 1 2 3 300 0.73 GeV 0.24 GeV 0.15 GeV 750 1.82 GeV 0.60 GeV 0.36 GeV 1500 3.64 GeV 1.21 GeV 0.73 GeV Flux/rates drop En < 1 GeV (KEK/JHF to SuperK, CERN to Frejus 0.3 < En < 3 GeV (NuMI) 0.5< En < 6 GeV (CERN to Taranto, BNL to ?) Neutrino Cross Sections N+lepton N+l+p Many particles What will MINOS do? Two functionally identical neutrino detectors " Det. 1 Det. 2 ne Interactions in MINOS? NC interactions: NC, Eobs = 3 GeV Energy distributed over ‘large’ volume ne CC interactions (low y) : •Electromagnetic shower: •Short •Narrow •Most of the energy in a narrow cluster Detector Granularity: •Longitudinal: 1.5X0 energy •Transverse: ~RM ne CC, Etot = 3 GeV Needle in a Haystack ? NC Background n spectrum ne (|Ue3|2 = 0.001) NC (visible energy), no rejection ne background Spectrum mismatch: These neutrinos contribute to background, but no signal MINOS Limits on nm to ne Oscillations 10 kton-yr exposure, Dm2=0.003 eV2, |Ue3|2=0.01: Signal (e = 25%) - 8.5 ev ne background - 5.6 ev Other (NC,CC,nt) – 34.1 ev M. Diwan,M. Mesier, B. Viren, L. Wai, NuMI-L-714 90% CL: | Ue3|2< 0.01 Limit comparable to a far superior detector (ICARUS) in CNGS beam Sample of ne candidates defined using topological cuts Receipe for a Better Experiment More neutrinos in a signal region Less background Better detector (improved efficiency, improved rejection against background) Bigger detector Lucky coincidences: • distance to Soudan = 735 km, Dm2=0.025-0.035 eV2 1.27Dm2 L p E 2 E 2.54Dm2 L p 1.6 2.2 GeV • Below the tau threshold! (BR(t->e)=17%) Two body decay kinematics At this angle, 15 mrad, energy of produced neutrinos is 1.5-2 GeV for all pion energies very intense, narrow band beam ‘On axis’: En=0.43Ep pL ( p* cosq * E* ) pT p* sin q * Off-axis ‘magic’ ( D.Beavis at al. BNL Proposal E-889) 1-3 GeV intense beams with well defined energy in a cone around the nominal beam direction 2 2 A Flux 2 2 1 q 4pz 2 NC/ ne /p0 detectors CHARM II (nme scattering) Challenges: Identify electrons Small cross section, large background from NC interactions Solution: •Low Z, fine grained calorimeter Detector(s) Challenge Surface (or light overburden) High rate of cosmic m’s Cosmic-induced neutrons But: Duty cycle 0.5x10-5 Known direction Observed energy > 1 GeV Principal focus: electron neutrinos identification • Good sampling (in terms of radiation/Moliere length) Large mass: • maximize mass/radiation length • cheap A possible detector: an example Cheap low z absorber: recycled plastic pellets Cheapest detector: glass RPC (?) Constructing the detector ‘wall’ Containment issue: need very large detector Engineering/assembly/practical issues On the Importance of the Energy Resolution Cut around the expected signal region too improve signal/background ratio M. Messier, Harvard U. Energy resolution vis-à-vis oscillation pattern First oscillation minimum: energy resolution/beam spectrum ~ 20% well matched to the width of the structure Second maximum: 20% beam width broader than the oscillation minimum, need energy resolution <10%. Tails?? Energy Resolution of Digital Sampling Calorimeter Digital sampling calorimeter: 1/3 X0 longitudinal 3 cm transverse Energy = Cx(# of hits) DE ~ 15% @ 2 GeV DE ~ 10% 4-10 GeV ~15% non-linearity @ 8 GeV, no significant nongaussian tails Improve energy resolution? Total Absorption Calorimeter: HPWF Energy resolution limited by fluctuations of the undetected energy: nuclear binding energy, neutrinos and not by sampling fluctuations ‘Crude’ sampling calorimeter (CITFR), 10 cm steel, better energy resolution than total absorption one (HPWF) Neutrino energy, Quasi-elastics ? m nm + n → m + p (Em , pm) n En mN Em mm2 2 mN Em pm cos q m En(reconstruct) p m events s=80MeV En(reconstruct) – En (True) (MeV) ~ 2 GeV: CC ne / NC interactions ~ 2 GeV: nm CC interaction ~ 7 GeV: CC ne / NC interactions CC ne vs NC events: example Electron candidate: Long track ‘showering’ I.e. multiple hits in a road around the track Large fraction of the event energy ‘Small’ angle w.r.t. beam NC background sample reduced to 0.3% of the final electron neutrino sample (for 100% oscillation probability) 35% efficiency for detection/identification of electron neutrinos Detector questions/issues What is the optimal absorber material (mostly an engineering/cost question, if DX0 kept constant) What longitudinal sampling (DX0)? What is the desired density of the detector? (containment/engineering/transverse segmentation) Containment issues: fiducial volume vs total volume, engineering issues: what is the practical detector size? What is the detector technology (engineering/cost issue if transverse segmentation kept constant) What is the optimal transverse segmentation (e/p0, saturation,…) Can a detector cope with cosmic ray background? What is the necessary timing resolution?