LAr-tracker feasibility study Chris Marshall Lawrence Berkeley National Laboratory DUNE ND workshop 22 January, 2017
Motivation ● LAr near detector ideal for cancelling systematics in oscillation analysis ● Same target nucleus as FD ● Same or very similar reconstruction techniques ● ND rate is ~0.08 events per ton per spill at 1 MW, so a many-ton magnet will create a lot of pile-up in detector with O(ms) drift times ● Can we reconstruct LAr events with O(10s) of side-entering particles? 2 Chris Marshall
Basic idea of this study Passive material? LAr detector Tracking detector ~few m Fast timing no B field B field ● Combine O(10s ton) non-magnetized LAr detector with a magnetized tracking detector with fast timing ● Could be FGT-like, MINOS-like, etc. 3 Chris Marshall
Key questions ● What fraction of muons enter magnetized region? ● What fraction of hadron energy is contained in LAr? ● As a function of LAr volume ● vs. various kinematic variables 4 Chris Marshall
Method details ● Generate events using GENIE 2.12 + MEC ● Events distributed randomly within FV of cubic LAr detector, with 20cm between edge of FV and detector ● Assume 2.3 MeV/cm for muons ● Assume 14 cm radiation length for electrons, photons ● Hadrons: ● Generate particle gun events with Geant4 in LAr at various initial momenta ● Fill histograms of energy vs. distance in particle direction, including all interaction products 5 Chris Marshall
Example: π + energy profile KE = 300 MeV KE = 50 MeV ● Better to do this in 3D, but too slow ● Basically averages over transverse energy loss 6 Chris Marshall
Example: π + containment ● Interpolate between longitudinal profiles for different initial energy samples ● Containment fraction = energy deposited in first X cm / total energy deposited 7 Chris Marshall
FHC muon efficiency Wrong-sign (μ + ) Right-sign (μ - ) ● Numerator is muons that exit the rear of the LAr volume ● No passive material, and assumes all rear-exiting muons have charge reconstructed 8 Chris Marshall
FHC muon efficiency Wrong-sign (μ + ) Right-sign (μ - ) ● Including LAr-contained muons ● Charge can be identified by decay with no B field 9 Chris Marshall
RHC muon efficiency Right-sign (μ + ) Wrong-sign (μ - ) ● Numerator is muons that exit the rear of the LAr volume ● No passive material, and assumes all rear-exiting muons have charge reconstructed 10 Chris Marshall
RHC muon efficiency Right-sign (μ + ) Wrong-sign (μ - ) ● Including LAr-contained muons ● Can select μ→e events to get antineutrino CC, as long as you can distinguish π→μ→e 11 Chris Marshall
Contained hadronic energy ● 1x1x1m detector ● E had = sum of all meson total energy + proton kinetic energy ● Neutrons are excluded from both numerator and denominator 12 Chris Marshall
Contained hadronic energy ● 3x3x3m detector ● E had = sum of all meson total energy + proton kinetic energy ● Neutrons are excluded from both numerator and denominator 13 Chris Marshall
Interior vertices ● 3x3x3m detector ● Only events with vertices in upstream 50% of detector, and middle half transverse directions 14 Chris Marshall
Average hadronic containment RHC FHC ● Profile of previous 2D plots ● Does not include neutrons 15 Chris Marshall
Add in neutrons ● For neutrons only, containment fraction is energy deposited in first X cm / true kinetic energy ● Gives estimate for visible energy from neutrons 16 Chris Marshall
Average hadronic containment: with the neutrons RHC FHC ● Reduces “contained” energy due to invisible neutrons ● Especially for RHC at low hadronic energy, where μn final states are common 17 Chris Marshall
Hadron containment vs. neutrino energy (without neutrons) RHC FHC ● Typical hadronic energy containment is ~80-90% for a 2m detector in the 1-4 GeV region 18 Chris Marshall
Hadron containment vs. neutrino energy (with neutrons) RHC FHC ● With neutrons it's more like 70% in FHC and 50% in RHC at low neutrino energy 19 Chris Marshall
Efficiency vs. neutrino energy: FHC muons Wrong-sign (μ + ) Right-sign (μ - ) ● y distribution smears out the features ● First oscillation peak is 2.56 GeV, second oscillation peak is 0.85 GeV near the minimum of efficiency 20 Chris Marshall
Efficiency vs. neutrino energy: RHC muons Right-sign (μ + ) Wrong-sign (μ - ) ● y distribution smears out the features ● First oscillation peak is 2.56 GeV, second oscillation peak is 0.85 GeV near the minimum of efficiency 21 Chris Marshall
FHC Efficiency vs. Q 2 Wrong-sign (μ + ) Right-sign (μ - ) ● Including LAr stoppers, inefficiency is due to side-exiting muons, which will sculpt the Q 2 distribution ● ND constraint would be flux * (XS skewed toward low Q 2 ) while FD would measure all Q 2 22 Chris Marshall
RHC Efficiency vs. Q 2 Right-sign (μ + ) Wrong-sign (μ - ) ● Including LAr stoppers, inefficiency is due to side-exiting muons, which will sculpt the Q 2 distribution ● ND constraint would be flux * (XS skewed toward low Q 2 ) while FD would measure all Q 2 23 Chris Marshall
A few drawbacks ● ND has acceptance holes, for example in (E v , Q 2 ), so some cross section shape uncertainties may not cancel in FD/ND ratio ● Some reliance on MC to correct for escaping hadronic energy ● Can be constrained with data by using “interior” events with very good containment ● No electron charge discrimination for Ar events ● If magnetized detector were sufficiently fine-grained, could measure ν e / ν μ ratio with charge ID 24 Chris Marshall
Conclusions ● LAr-tracker hybrid could work with LAr not magnetized ● Could greatly reduce mass around LAr and reduce pile- up, preserving a O(10 ton) Ar ND target ● Worth pursuing further 25 Chris Marshall
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