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Stellar Neutrino Studies at the Spallation Neutron Source (Oak Ridge)

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Or study of neutrino nucleus cross sections at veeery low energy. Pre supernovae ... Shock stalls due to neutrino escape & nuclear dissociation ... – PowerPoint PPT presentation

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Title: Stellar Neutrino Studies at the Spallation Neutron Source (Oak Ridge)


1
Stellar Neutrino Studies at the Spallation
Neutron Source(Oak Ridge)
(SNS)2
Or study of neutrino nucleus cross sections at
veeery low energy
NuFact 03 - June 10th
2
Pre supernovae
Evolutionary stages of a 25 MSUN star
Stage Temperature (K) Duration of
stage Hydrogen burning 4 x 107
7 x 106 years Helium burning 2 x
108 5 x 105years Carbon burning
6 x 108 600 years
Neon burning 1.2 x 109
1 year Oxygen burning 1.5 x 109
6 months Silicon burning
2.7 x 109 1 day Core
collapse 5.4 x 109 1/4
second
3
Supernovae
Recorded explosions visible to naked eye
Year (A.D.) Where observed
Brightness 185
Chinese
Brighter than Venus
369 Chinese
Brighter than Mars or Jupiter
1006 China, Japan, Korea,
Europe, Arabia Brighter than Venus
1054 China, SW India,
Arabia Brighter than Venus
1572
Tycho Nearly as bright as
Venus 1604
Kepler
Brighter than Jupiter 1987
Ian Shelton (Chile)
4
Explosion
  • Collapse and re-bound(1-4) creates a shock
    wave(5) propagating outward from center of
    core(6) , meeting in falling outer core material
  • Shock stalls due to neutrino escape nuclear
    dissociation
  • Deleptonisation of the core creates intensive
    neutrino flux (99 of energy)
  • Neutrino interactions behind the shock reheat the
    shock and drive it outwards(7)
  • Measuring 56Fe(ne ,e- ) 56Co provides valuable
    data to guide shock formation models.
  • Other cross sections, 28Si, should also play an
    important role.

5
5
Energy in supernovae
Total energy 1053 erg
98 of the energy is emitted by neutrinos !!!!
6
n-Process Nucleosynthesis in Supernovae
  • n process nucleosynthesis could be an
    important new dramatically altering the
    r-process (push through waiting nuclei)
  • n process nucleosynthesis can produce
  • rare isotopes - 180Ta, 138La, 19F, 10,11B
  • These isotopes cannot be produced at other
  • sites and thus form fingerprints
  • 181Ta(n, n n) 180Ta
  • 138Ba(ne ,e- ) 138La
  • 20Ne(n, n n) 19Ne 19F
  • 12C(n, n p)11B , 12C(n, n pn)10B

7
ConclusionNeutrinos are important
For Super Novae explosion mechanism SN
dynamics Nucleosynthesis of heavy elements.
To understand those we need to know Neutrino
oscillations parameters. Neutrino interactions
in the range of SN energies The last one is
important contribution to the nuclear theory
8
SN neutrino energies
Core collapse of 25 solar mass star
In this region of energy only three nucleus has
been measured d(40), C(10), and Fe(50), and
only carbon published.
9
The Spallation Neutron SourceORNL
1.3 GeV proton accelerator
Accumulator ring
2 MW Mercury target
10
SNS parameters
Primary proton beam energy - 1.3 GeV Intensity -
9.6 ? 1015 protons/sec Pulse duration -
380ns(FWHM) Repetition rate - 60Hz Total power -
2 MW Liquid Mercury target Number of neutrino
produced 3?1022/year
This is a neutrino factory already under
construction !!!
11
Present status
First beam - 2006, full power - 2008
12
Neutrino Production at SNS
??
??
?
?
Hg
e
0.13
?e
??
0.09
?-
p
?-
e-
94
99.6
??
13
Actual spectra of neutrinos from SNS
Energy Time
Short pulses with the energy similar to SN
neutrino spectra
14
SNS is a Unique Neutrino Source
  • The SNS will produce 3.2x1015 neutrinos/sec in
    60Hz pulses
  • It will be the most intense, pulsed, low energy
    neutrino source in the world!
  • The pulsed source drastically reduces backgrounds
    from cosmic rays. Reduction is equivalent to 1 km
    of rock overburden.
  • Beam time structure allows separation of ?m from
    ?m and ?e
  • Spectra of ?m, ?m and ?e are well known
  • ?e is highly suppressed

15
Reaction Cross section for these energy is small
!!!
  • 0.297?10-43 cm2
  • 0.050?10-43 cm2
  • 0.92?10-41 cm2
  • 0.45?10-41 cm2
  • 0.27?10-41 cm2
  • 7.2?10-41 cm2
  • 2.5?10-40 cm2
  • ?ee- ? ?ee-
  • ??e- ? ??e-
  • ?e12C ? 12Ngs e-
  • ?e12C ? ?e 12C
  • ??12C ? ??12C
  • ?ep ? ne
  • ?e56Fe ? 56Co e-

However SNS will deliver 3 1022 neutrinos per
year At such flux Carbon at 20 meters yields
¼ interaction per kilogram per year
16
Location of detectors at SNS
Neutrino emission from the target is isotropic
Closer gt Smaller and Cheaper
Extra advantage for small detector less
background from cosmic rays. Not exceedingly
close to the target, as some shielding is
required to reduce flux of energetic neutrons
from spallation target.
17
SNS Target Building
  • Property of BES branch of DOE
  • Neutron beams and users have high priority

Our advantage we do not need beam line ! We do
not want beam line ! We need a spot on the floor
not far away from the target
18
What do we plan?
We propose to built protected enclosure At 20
meters from the SNS Bunker with active veto
large enough to have two 10-20 t detectors. 4.5 ?
4.5 ? 6.5 meter outside 2.5 ? 2.5 ? 5.5 meters
inside Two detectors placed one on the top of
other
First one Homogeneous Simple, light collection
technique. Liquid, transparent targets Second
Segmented More challenging, modular structure
with replaceable targets. Detector should have
enough mass to provide 1k events per year. Plan
is to run one new target every year. First target
will be Iron.
19
Concept of homogenous detector
Hermetic vessel with good PMT coverage
300, 8 PMTs 40 of photocathode coverage 15 t
fiducial mass
Liquid targets 2d, 12C, 16O, 127I
3 m
20
Concept of segmented detector
?
Metal or other solid targets 51V, 27Al, 9Be,
11B, 52Cr, 56Fe, 59Co, 209Bi, 181Ta
e
Active detector gas tubes Energy measurement -
by range
Expected resolution for tubes 10mm and 0.5 mm at
30 MeV is 25 Detector size for 20 t fiducial
mass is 3.0 ? 2.3 ? 2.3 Expected event rate
(for iron target)16/day Good separation from
neutrons
21
Background estimations
SNS neutrons. Extra shielding and absorbers will
eliminate low energy neutrons Time cut will
remove high energy neutrons Cosmic Ray
Background SNS duty factor is 4?10-4 Active
hermetic veto will cut another 99 1 meter of
steel overburden will kill hadronic
component Our estimations shows that expected
number of untagged neutrons events in the
detector is - 5 /day. This is already below
expected neutrino event rates Extra factor is
expected from PID in detectors.
22
(SNS)2 Schedule
Formal Proposal -January 2004 Detector RD and
design-2003-2006 (applying for ORNL LDRD money
right now) Detector Construction begins- FY
2006 Shielding Enclosure Erection-
2007 Detectors Installation Completed- January
2008 Detectors Commissioning- Summer 2008.
23
Conclusion
  • We have a unique opportunity to established
    program for neutrino- nucleus cross section at
    very lower energy
  • This will be modest by , long range program
  • This program will influence Cosmology, Nuclear
    Astrophysics, and Nuclear theory
  • This program should be done !!!
  • Ideas and collaborators are welcome
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