carolina neutrino workshop 20041 prospects for neutrino physics at the spallation neutron source...
TRANSCRIPT
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
+
-
~99%
+
ee+
p
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
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!
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51
Energy, MeV
Neu
trin
o F
lux
e
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51
Energy, MeV
Neu
trin
o F
lux
e
SNS neutrino spectra
Supernova neutrino spectra, 100 ms post-bounce
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
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.
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.
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!
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.
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.
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
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
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.
Carolina Neutrino Workshop 2004 14
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.
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.
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.