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Prospects for Neutrino Physics at the Spallation Neutron Source
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Carolina Neutrino Workshop 2004 1
Prospects for Neutrino Physics at the Spallation Neutron Source
Vince Cianciolo, ORNLfor the SNS Collaboration
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Carolina Neutrino Workshop 2004 2
The Spallation Neutron Source
• Proton beam current: 1 mA• Proton beam energy: 1 GeV• Protons/pulse: ~1.61014
• Pulse rate: 60 Hz• Pulse length: 380 ns (FWHM)• Operating hours/year: 5000• Proton target material: Mercury• Neutrinos/pulse/flavor: ~1.61013
• Neutrino-target interactions/year: few thousand
Neutrino!
Repeat 60/sec.
x ~1000
LINAC:
Accumulator Ring:
A
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~99%
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ee+
p
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Carolina Neutrino Workshop 2004 3
Time Structure
Decays with t1/2 = t1/2 = 26 ns
• Next pulse arrives in 16,000,000 ns!• Turning the detector on for only a few
s after each pulse reduces cosmic-ray background by ~ x2,500.
• 2.3 km water-equivalent.• Leaving the detector off for the first
s 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.
Decays with t1/2 = t1/2 = 2.2 s
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Carolina Neutrino Workshop 2004 4
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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SNS neutrino spectra
Supernova neutrino spectra, 100 ms post-bounce
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Carolina Neutrino Workshop 2004 5
Scientific Motivation• Core-collapse supernovae.• Neutrino detector calibration.• Nuclear structure
(complement to RIA).
National Research Council Report by the Committee on the Physics of the Universe
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Carolina Neutrino Workshop 2004 6
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 A cross-sections for A<120 is crucial when attempting to make accurate supernova models.
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Carolina Neutrino Workshop 2004 7
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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Carolina Neutrino Workshop 2004 8
Nuclear Structure
• A cross section measurements provide important information to constrain nuclear structure models.
• Reasonable extrapolations away from measured nuclei can be made for ~N<8, P<8 (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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Carolina Neutrino Workshop 2004 9
SNS Goal:Precision A Cross Section
Measurements
• Build a facility that will allow a total cross section measurement with <10% in one year.
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Carolina Neutrino Workshop 2004 10
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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Carolina Neutrino Workshop 2004 11
Bunker, Active Veto• Active veto ( > 99%) required
to reduce cosmic muons.• Time structure plus passive
shield reduces cosmogenic and machine-related neutron backgrounds sufficiently.– 1m thick ceiling;½-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
Detector 120 t
Detector 220 t
Shielding
Veto
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Carolina Neutrino Workshop 2004 12
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:– E ~ 30%
– ~ 15 degrees
• Particle ID through e.g., # of fired tubes, track linearity, energy deposition.
e
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Carolina Neutrino Workshop 2004 13
Homogeneous Detector
• “Standard” technology– Boone
• 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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Carolina Neutrino Workshop 2004 14
Timescale• Commissioning could
reasonably begin when machine power approaches design value (end of CY08).
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Carolina Neutrino Workshop 2004 15http://www.phy.ornl.gov/workshops/nusns/vSNSstudy.pdf
Collaboration• Robust collaboration.
– >30 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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Carolina Neutrino Workshop 2004 16
Conclusions• The SNS provides a unique opportunity to study
low-energy (10’s of MeV) A interactions.– Pulsed time structure.– Intensity.
• Building a A 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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Carolina Neutrino Workshop 2004 17
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 es 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.