Transcript Neutrinos from stars & stellar explosions

Supper Neutrino Source
Neutrinos at the SNS (Spallation Neutron Source)
Yu.Efremenko
ORNL
0. A little bit of Modern Neutrino History
1. Why Low Energy Neutrinos are Good
2. Some Proposed Neutrino Experiments at SNS
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Lets Look Back in Time
The Earliest Neutrino Conference that has Transparencies posted on
the WEB is Neutrino 1998
From the opening talk by
P.Ramond(Florida)
Ten Years later
dm122 = 7.58·10-5 eV2 sin2(2θ12)=0.87
SNO & KamLAND
Yes !!!
Yes !!!
dm322 = 2.4·10-3 eV2 sin2 (2θ23)=1.00
SuperK, K2K, MINOS
MiniBoone left door open for some
exotic scenarios
Two out of three done!!!!!
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Now We Have New Set of Experimental Challenges
We have a long list of neutrino properties to study.
Neutrino Mass –> KATRIN + Set of Double Beta Experiments
θ13 -> DoubleChooz, Daya Bay, T2K, NOVA
CP phase–> Long Baseline experiments
At the same time we have to look at what role neutrinos are playing in
our Universe.
To do so we have to better understand neutrino interactions with
nuclei!
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Man Made Neutrino Sources
Nuclear reactors
En<10 MeV
Stop Pion Facilities
10<En<53 MeV
Very interesting region. It is
nicely coincides with
neutrino energies produced
during the
Super Novae Explosion
H.E. “accelerators”
En >100 MeV
In E-M
LSN~L galaxy
In Neutrinos
LSN~ 3000 L galaxy
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Core-collapse supernovae
SN 1987a
Anglo-Australian Observatory
•
Destruction of massive star initiated by the Fe core collapse
1053 ergs of energy released
99% carried by neutrinos
•
A few should happen every century in our Galaxy, but the
last one observed was over 300 years ago (recently
discovered ~150 years old remnants of SN in M.W. G1.9+0.3)
•
Dominant contributor to Galactic nucleosynthesis
•
Neutrinos and the weak interaction play a crucial role in the
mechanism, which is not well understood
SN neutrino spectra,
0.1 s post-bounce
Neutrinos and Core Collapse SN
n opacities
Electron capture and
core collapse
•
Electron capture and the
charged-current ne reaction
are governed by the same
nuclear matrix element:
ne + A(Z,N)  A(Z+1,N-1) + e-
•
New calculations using a
hybrid model of SMMC and
RPA predict significantly
higher rates for N>40
•
Supernovae models w/ new
rates:
shock starts deeper and
weaker but less
impedance
n reactions and
•
•
Neutrinos interactions are
believed to be crucial in
the delayed mechanism
•
Realistic treatment of n
opacities is required for
supernova models
Many ingredients
• Charged-current
reactions on free
nucleons (and nuclei)
• Neutral-current
scattering
• nA coherent scattering
• ne-e scattering
• nn scattering
• nn annihilation
nucleosynthesis
•
Neutrino reactions with
nuclei ahead of the shock
may alter the entropy &
composition of in fall
[Bruenn & Haxton (1991)].
•
Neutrino reactions may
have an important
influence on
nucleosynthesis in the r
process: setting the
neutron-to-proton ratio
and altering the
abundance pattern
[Haxton et al. (1997)].
The weak interaction plays a crucial role in supernova !
We need good understanding of neutrino interactions !
Supernova Neutrino Observations
SN 1987A
High statistic measurement of
neutrino signal from SN
will provide wealth of
information about SN
dynamics
•
•
An accurate understanding of
neutrino cross sections is
important for SN neutrino
detectors.
ADONIS
Nuclei of interest: C, O, Fe, Pb
HALO
or
Diffuse Supernovae Neutrino (DSN) Detection
While waiting for SN to
happen in the Milky Way we
can search for diffuse SN flux
From: C.Lunardini, astro-ph/0610534
Several proposals are aiming
to be sensitive enough to see
DSN:
•GADZOOKS
•HyperKamiokande
•UNO
•MEMHYS
•LENA
•LANNDD
•GLACIER
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Atmospheric Neutrino Background for DSN
Water Cherenkov detectors:
Irreducible background from
atmospheric neutrino interactions:
SuperK
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kton·y
n  16O    X
limit discovery potential.
Detectors with Neutron Detection Capabilities:
Antineutrino Channel with neutron detection will
eliminate such a background n e  p  n  e
From LENA proposal: Phys.Rev.D75:023007 there is
claim of background free window from 10 till 25 MeV
However background from neutral current reactions
n e, 12C  n11C n e,
have not been considered yet.
We need good understanding of neutrino Carbon and
neutrino Oxygen interactions!!!
Neutrino Nuclear Interactions at Low MeV Range are:
Important for understanding of supernovae mechanism
Important for neutrino detection from SN
Important for Calculations of backgrounds for DSN
Have a general interest for the nuclear theory
So far it is a green field. Only
n-C interactions have been
accurately studied
experimentally.
There are ~ 40% accurate data
for d,Fe,I
v-d is well
understood
theoretically and
indirectly has been
measured by SNO
It is important to provide accurate v-A measurements for wide range of isotopes
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Early interest in low energy neutrino nucleus cross
sections:
Twenty five years later, same scientist is still
interested in neutrino-nucleus cross sections
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Neutrino Coherent Scattering
Z0
Detectable only via very low
energy (~10keV) nuclear recoil
A
D.Z. Freedman PRD 9 (1974)
A. Drukier & L. Stodolsky, PRD 30, 2295 (1984)
Horowitz et al. astro-ph/0302071
Straight-forward to calculate
“Huge” cross section > 10-39 cm2
Never observed
Important for supernova dynamics (neutrino opacity)
What Physics Could be Learned From Neutrino
Coherent Scattering?
K. Scholberg, Phys. Rev D 73 (2006) 033005
Basically, any deviation from SM is interesting...
- Weak mixing angle:
could measure to ~few % (new channel)
- Non Standard Interactions (NSI) of neutrinos:
could significantly improve constraints
- Neutrino magnetic moment:
hard, but conceivable
It is difficult to do it on Nuclear Reactors because of the continues flux
and very low recoil energies
New Facility -SNS
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SNS
LINAC:
 x ~1000 
Accumulator Ring:
Repeat 60/sec.
1 GeV
Similar pulse structure to ISIS  greatly suppressed backgrounds
Eventual operation > 1 MW (~FY09)
Presently being commissioned.
0.5 MW power has been achieved last week
~7x1012 p / spill
(~10x ISIS)
Accelerator
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Target
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Neutrino Production at SNS
pA
~99%
+
DAR
p+
ne
CAPTURE
  2200 nsec
  26 nsec
p
n
Specific benefits of neutrinos at SNS
•Well known neutrino spectra (DAR)
•Separate neutrinos of different flavors by time cut
•Very high neutrino intensities ~ 1015 n/sec
•Pulsed Structure
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e+
n
Potential Locations for Neutrino Experiments at the
Spallation Neutron Source
proposed site inside target building
protons
20 m2 x 6.5 m (high)
Close to target ~ 20 m
 2x107 n/cm2/s
q=165 to protons
 lower backgrounds
The SNS
Target hall
There are multiple sites available outside of target building.
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2.8·1020 protons delivered on
target in two week period
1020 neutrino produced
Background Studies
Space for prototype development
Neutron detectors
Power ~ 0.4 MW
60 tons of steel
Now: Background, shielding & protoype studies
Counts
Particle id
p~2 C
-2
0
2
Time (s)
4
6
neutrons
gammas
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Pulse height
protons
Possible Concept of Shielded Enclosure for
Neutrino Experiments
•
Total volume = 130 m3
4.5m x 4.5m x 6.5m (high)
•
Heavily-shielded
•
60 m3 steel ~ 470 tons
1 m thick on top
0.5 m thick on sides
•
Active veto
•
~70 m3 instrumentable
•
Configured to allow 2 simultaneously
operating detectors of up to 40 tons
nA coherent scattering
43 m3 liquid detector
Segmented detector for solids
Prototypes for SN detectors
nSNS
BL18
ARCS
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Proton beam
(RTBT)
Cosmic Ray Veto
Sensitive to cosmic muons
Blind for gammas from
(n , gamma) capture
Bunker
wave-length shifting fibers
read out by multi-anode PMT
1.5 cm iron
extruded scintillator
1 cm x 10 cm x 4.5 m
• Efficiencies
muons ~99% muons
7.6 MeV gamma = 0.005%
neutron =0.07%
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Veto R&D
• In collaboration with MECO
100 x 4.5-m planks extruded for nSNS
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Homogeneous Experiment
• 3.5m x 3.5m x 3.5m steel vessel (43 m3)
• 600 PMT’s (8” Hamamatsu R5912)
 Fiducial volume 15.5 m3 w/ 41%
coverage
• Robust well-understood design
•
•
•
dE/E ~ 6%
dx ~ 15-20 cm
dq ~ 5 - 7
First experiments:
1300 events/yr ne+12C12N+e- (mineral oil)
450 events/yr ne+16O 16F+e- (water)
1000 events/yr nx+2H  p+n+ nx (heavy water)
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Performance
Geant4 Monte Carlo simulations ongoing
• dE/E ~ 6%
• dx ~ 15-20 cm
• dq ~ 5 - 7
• Neutron discrimination?
• Layout and coverage
• More compact photosensors
60% of mass lost to fiducial cut
dE/E = 6.8% at 50 MeV
less if corrected for position
Standard Model Tests
• Shape of the ne spectrum from  decay is sensitive to scalar and
tensor components of the weak interaction
μ+  e+ + ne + nμ .
ne + 12C  e- + 12N g.s.
nSNS expected
1-yr operation
L=0.11 KARMEN upper limit
Armbruster et al., PRL81 (1998)
L=0
• We could substantially
improve the limit on L with
only 1 year of data
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Segmented Experiment
corrugated
metal target
straw tube
16 mm
anode wire
Target - thin corrugated metal sheet (e.g. 0.75 mm-thick iron)
Total mass ~14 tons, 10 tons fiducial
Other good metal targets: Al, Ta, Pb
Detector
1.4x104 gas proportional counters (straw tube)
3m long x 16mm diameter
3D position by Cell ID & charge division
PID and Energy by track reconstruction
Expected Statistic
1100 events/yr ne+FeCo+e1100 events/yr ne+AlSi+e4900 events/yr ne+Pb Bi+e-
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Straw tube R&D
•
Currently testing prototypes
Diameters between 10-16 mm
Lengths ranging up to 2 m
Gases (Ar-CO2, Isobutene, CF4)
•
Measure resolution with cosmic muons
Energy, position, time
•
•
How much can time resolution be
improved using pulse shape information?
Simulations to improve the fast neutron
discrimination.
Slow charge collection
broad
e
timing
problematic
narrow
time (s)
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The CLEAR (Coherent Low Energy A Recoils) Experiment
CLEAR
A. Curioni
Background for CLEAR
Expect ~190 events/year in 20 kg of xenon >3 keVr
SNS neutronics group calculation of neutron spectrum
+ Fluka sim through shielding (T. Empl)
+ Xe detector sim (J. Nikkel)
+ scaling using measured fluxes
Sterile Neutrinos
Neutrino Oscillations
Test CP Violation
Osc-SNS
•MiniBooNE/LSND-type detector
•Higher PMT coverage (25% vs 10%)
•Mineral oil + scintillator (vs pure oil)
•Faster electronics (200 MHz vs 10 MHz)
•Located ~60m upstream of the beam
dump/target, this location reduces DIF
background
~ 60m
Oscillation Event Rates
LSND
Beam
Width
600 s
S:B
1:1
n  ne
FNAL
Osc.
Candidates
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(observed R > 10)
600 ns
1:3
~400
695 ns
5:1
~448/year
n  ne
SNS
n  ne
Expected for LSND
best fit point of :
sin22q =0.004 dm2 =
1
Summary & Outlook
• Understanding of neutrino interactions are
important for:
– Physics of Supernova
– Calculation of response of Large Neutrino Detectors to Milky
Way Supernova
– Calculation of backgrounds from DSN
• The combination of high flux and favorable time structure at
the SNS is very attractive for diverse program of neutrino
studies
• New Proposals like CLEAR and Osc-SNS appeared recently
• We welcome new ideas and participation
• See http://www.phy.ornl.gov/nusns
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