Carolina Neutrino Workshop 2004 1

Prospects for Neutrino Physics at the Spallation Neutron Source

Vince Cianciolo, ORNLfor the SNS Collaboration

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%

+

ee+

p

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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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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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Energy, MeV

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SNS neutrino spectra

Supernova neutrino spectra, 100 ms post-bounce

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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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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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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

• 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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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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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 ( > 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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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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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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Timescale• Commissioning could

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

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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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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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.