Prospects for Neutrino Physics at the Spallation Neutron Source

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Prospects for Neutrino Physics at the Spallation
Neutron Source

• Vince Cianciolo, ORNL
• for the nSNS Collaboration

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The Spallation Neutron Source

• Proton beam current 1 mA
• Proton beam energy 1 GeV
• Protons/pulse 1.6?1014
• Pulse rate 60 Hz
• Pulse length 380 ns (FWHM)
• Operating hours/year 5000
• Proton target material Mercury
• Neutrinos/pulse/flavor 1.6?1013
• Neutrino-target interactions/year few thousand

Repeat 60/sec.
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Time Structure

• Next pulse arrives in 16,000,000 ns!
• Turning the detector on for only a few ms after
  each pulse reduces cosmic-ray background by
  x2,500.
• 2.3 km water-equivalent.
• Leaving the detector off for the first ms after a
  pulse effectively eliminates machine-related
  backgrounds.
• Also eliminates clean neutral-current events.
• Whether sufficient background rejection can be
  achieved w/o this cut (through shielding and
  detector techniques) is under study.

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Energy Spectra

• Neutrino spectra at stopped-pion facilities have
  significant overlap with the spectra of neutrinos
  generated in a supernova explosion!

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Scientific Motivation

• Core-collapse supernovae.
• Neutrino detector calibration.
• Nuclear structure (complement to RIA).

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Core Collapse Supernovae

• Most spectacular explosions in the universe. (R.
  Hix)
• Birthplace of most heavy elements we are
  stardust.
• The core of a supernova is so dense it is black
  to neutrinos. Since there are so many of them
  they play a crucial role in the explosion and the
  accompanying nucleosynthesis.
• Knowledge of nA cross-sections for Alt120 is
  crucial when attempting to make accurate
  supernova models.

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Neutrino Detector Calibration

• Large-scale detectors exist or are proposed to
  measure supernovae neutrinos.
• In order to make full use of their data,
  calibrations of neutrino interactions in the
  detector materials are required.
• Integral cross-sections insufficient.
• Differential cross-sections (vs. energy, angle)
  are crucial.
• Neutral-current interactions also very important.

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Nuclear Structure

• nA cross section measurements provide important
  information to constrain nuclear structure
  models.
• Reasonable extrapolations away from measured
  nuclei can be made for DNlt8, DPlt8 (up to shell
  boundaries).
• The plot shows extrapolation regions relative to
  8 of the 36 feasible target materials.
• Rather complete coverage in a few years!

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nSNS GoalPrecision nA Cross Section Measurements

• Build a facility that will allow a total cross
  section measurement with slt10 in one year.

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Feasibility

• A suitable location has been identified.
• Floor-loading calculations have been performed.
• Total capacity 545 tons.
• Allows for 1 meter ceiling, ½ meter walls.
• Together with SNS time structure, active veto
  provides sufficient rejection of cosmic-ray
  background.
• SNS management has provided encouraging response
  and is empanelling a review committee.

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Bunker, Active Veto

• Active veto (e gt 99) required to reduce cosmic
  muons.
• Time structure plus passive shield reduces
  cosmogenic and machine-related neutron
  backgrounds sufficiently.
• 1m thick ceiling½-m thick walls
• 4.5 x 4.5 x 6.5 m3 total vol. ? 3.5 x 3.5 x 5.5
  m3 inside shield.
• Remaining volume large enough to house two 10-ton
  fiducial target/detectors.

S
Shielding
Veto
Detector 2 20 t
Detector 1 20 t

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Segmented Detector

• Designed to handle metals or other solid targets.
• Targets thin wall pipes, easily replaced.
• Active detector straw gas tubes.
• Mass of the sensitive part of the detector is
  less than target mass.
• Reconstruct tracks and count of fired tubes
• sE 30
• sQ 15 degrees
• Particle ID through e.g., of fired tubes, track
  linearity, energy deposition.

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Homogeneous Detector

• Standard technology
• mBoone
• Suitable for transparent liquid targets, e.g., d,
  C, N, O, I, Br, Pb
• Light detection by PMT or PD
• 38 PMT coverage allows for either scintillator
  or Cerenkov detection.

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Timescale

• Commissioning could reasonably begin when machine
  power approaches design value (end of CY08).

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Collaboration

• Robust collaboration.
• gt30 members, more welcome!
• Next collaboration meeting to be held June 11-12
  at ORNL.
• Assembled study report that discusses all
  elements of this talk in greater detail.
• Will form the basis for input to the APS Neutrino
  Working Group
• Copies available at back of room, on the web.

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Conclusions

• The SNS provides a unique opportunity to study
  low-energy (10s of MeV) nA interactions.
• Pulsed time structure.
• Intensity.
• Building a nA facility at the SNS is feasible.
• Sufficient intensity.
• Suitable location.
• SNS Management encouragement.
• Addresses broad range of physics interests.
• Understanding the supernova explosion mechanism.
• Calibration of neutrino detectors.
• Nuclear structure complementary to RIA.

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Neutrino oscillations at the SNSORLAND Redux

• If MiniBoone confirms LSND result, the SNS would
  be a logical place to follow up.
• Low backgrounds due to absorption of the vast
  majority of nes in mercury target.
• If nSNS goes forward there will already be a near
  detector to quantify the remaining backgrounds.
• Very precise measurement of oscillation
  parameters possible.