LAr-tracker feasibility study Chris Marshall Lawrence Berkeley - - PowerPoint PPT Presentation

LAr-tracker feasibility study

Chris Marshall Lawrence Berkeley National Laboratory DUNE ND workshop 22 January, 2017

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Motivation

• LAr near detector ideal for cancelling systematics in
• scillation 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?

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Basic idea of this study

• Combine O(10s ton) non-magnetized LAr detector

with a magnetized tracking detector with fast timing

• Could be FGT-like, MINOS-like, etc.

LAr detector ~few m no B field Tracking detector Fast timing B field Passive material?

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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

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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

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Example: π+ energy profile

• Better to do this in 3D, but too slow
• Basically averages over transverse energy loss

KE = 50 MeV KE = 300 MeV

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Example: π+ containment

• Interpolate between

longitudinal profiles for different initial energy samples

• Containment

fraction = energy deposited in first X cm / total energy deposited

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FHC muon efficiency

• Numerator is muons that exit the rear of the LAr volume
• No passive material, and assumes all rear-exiting muons

have charge reconstructed

Right-sign (μ-) Wrong-sign (μ+)

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FHC muon efficiency

• Including LAr-contained muons
• Charge can be identified by decay with no B field

Right-sign (μ-) Wrong-sign (μ+)

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RHC muon efficiency

• Numerator is muons that exit the rear of the LAr volume
• No passive material, and assumes all rear-exiting muons

have charge reconstructed

Wrong-sign (μ-) Right-sign (μ+)

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RHC muon efficiency

• Including LAr-contained muons
• Can select μ→e events to get antineutrino CC, as long

as you can distinguish π→μ→e Wrong-sign (μ-) Right-sign (μ+)

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Contained hadronic energy

• 1x1x1m detector
• Ehad = sum of all meson total energy + proton kinetic energy
• Neutrons are excluded from both numerator and denominator

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Contained hadronic energy

• 3x3x3m detector
• Ehad = sum of all meson total energy + proton kinetic energy
• Neutrons are excluded from both numerator and denominator

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Interior vertices

• 3x3x3m detector
• Only events with vertices in upstream 50% of detector,

and middle half transverse directions

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Average hadronic containment

• Profile of previous 2D plots
• Does not include neutrons

FHC RHC

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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

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Average hadronic containment: with the neutrons

• Reduces “contained” energy due to invisible neutrons
• Especially for RHC at low hadronic energy, where μn

final states are common FHC RHC

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Hadron containment vs. neutrino energy (without neutrons)

• Typical hadronic energy containment is ~80-90% for a

2m detector in the 1-4 GeV region FHC RHC

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Hadron containment vs. neutrino energy (with neutrons)

• With neutrons it's more like 70% in FHC and 50% in

RHC at low neutrino energy FHC RHC

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Efficiency vs. neutrino energy: FHC muons

• 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 Right-sign (μ-) Wrong-sign (μ+)

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Efficiency vs. neutrino energy: RHC muons

• 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 Wrong-sign (μ-) Right-sign (μ+)

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FHC Efficiency vs. Q2

• Including LAr stoppers, inefficiency is due to side-exiting

muons, which will sculpt the Q2 distribution

• ND constraint would be flux * (XS skewed toward low Q2)

while FD would measure all Q2

Right-sign (μ-) Wrong-sign (μ+)

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RHC Efficiency vs. Q2

• Including LAr stoppers, inefficiency is due to side-exiting

muons, which will sculpt the Q2 distribution

• ND constraint would be flux * (XS skewed toward low Q2)

while FD would measure all Q2

Wrong-sign (μ-) Right-sign (μ+)

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A few drawbacks

• ND has acceptance holes, for example in (Ev, Q2), 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 νe / νμ ratio with charge ID

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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