What lowenergy betabeams can tell about supernova physics

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What low-energy beta-beams can tell about
supernova physics

• N. Jachowicz, G.C. McLaughlin and C. Volpe
• Ghent University, Department of Subatomic and
  Radiation Physics, Proeftuinstraat 86, 9000 Gent,
  Belgium
• natalie.jachowicz_at_UGent.be

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What low-energy beta beams can tell about
supernova physics

• Introduction

• In a type II supernova, a massive star at the end
  of its life
• -undergoes gravitational collapse
• - a shockwave develops
• - travels outward, and the shock wave blows
  away the outer layers of the star
• . ?

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
In the supernova process

• weak interactions are important
• neutrinos are produced in the neutronization
  processes characterizing the gravitational
  collapse
• neutrinos are responsible for the cooling of the
  proto-neutron star
• neutrinos might reheat the stalled shock wave
  and cause a delayed explosion

Observing the neutrinos from a future (Galactic)
supernova explosion might learn a lot about the
processes going on in the center of the star and
the dynamics of the supernova imexplosion
H.-T. Janka astro-ph/0008432
Natalie Jachowicz

ECT,
Trento, June 28 2007
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Terrestrial detection of supernova neutrinos
What low-energy beta beams can tell about
supernova physics

• neutrinos are escaping from the center of the
  star
• carrying away the largest part of the energy
• Superkamiokande, SNO, OMNIS, LAND, LENA
• Target material e-, 16O, D, 56Fe, 208Pb, 12C

Neutrino-nucleus reactions provide an interesting
detection mechanism
SuperKamiokande
SNO

• relatively large cross sections
• thresholds in supernova-neutrino energy-region

Natalie Jachowicz

ECT,
Trento, June 28 2007
5

What low-energy beta beams can tell about
supernova physics
From the signal in the detector, one can learn
about

• arrival times
• neutrino flavor
• neutrinos vs antineutrinos
• energy information

• black hole formation
• neutrino masses
• charge-exchange vs neutral-current reactions
• charge of the outgoing lepton in charged-current
  reactions
• spin of the outgoing nucleon in neutral-current
• nucleon-knockout reactions
• threshold differences between different nuclei
• 1 nucleon vs 2 nucleon knockout

Natalie Jachowicz

ECT,
Trento, June 28 2007
6

What low-energy beta beams can tell about
supernova physics
The interpretation of the supernova signal can
only be as good as the understanding of
the neutrino-nucleus reaction that occurs in the
detector

• little experimental data is available
• very small cross sections
• no monochromatic neutrino beams

Uncertainties

• one has to rely on theoretical predictions,
• uncertainties induced by model dependence

Natalie Jachowicz

ECT,
Trento, June 28 2007
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Supernova neutrino spectra
What low-energy beta beams can tell about
supernova physics
Experimentally
Michel spectra
Natalie Jachowicz

ECT,
Trento, June 28 2007
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Beta-beam neutrino spectra
What low-energy beta beams can tell about
supernova physics
18Ne

• ß-decay of a primary boosted nuclear beam
  generates intense neutrino beams,
• with average energy and precise shape of the
  spectrum determined by the boost factor ? of the
  primary beam

• First proposed to produce high energy neutrinos
  in oscillation experiments
• (P.Zuchelli, Phys.Lett.B 532, 166 (2002).
• At lower gamma factor, the neutrino energy
  becomes very suitable for neutrino-nucleus
• scattering investigations
• (C. Volpe, J.Phys. G30, 1 (2004).

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
Cross section as a function of the boost factor
? of the beam
Natalie Jachowicz

ECT,
Trento, June 28 2007
10

What low-energy beta beams can tell about
supernova physics
Procedure

• linear combinations of normalized beta-beam
  spectra
• fitting the constructed energy distribution to
  the supernova-neutrino spectrum by minimizing the
  expression,
• varying the expansion parameters ai and the boost
  factors ?i

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
Total folded cross sections

• 16O CRPA calculation
• deuteron S. Nakamura, T. Sato, S. Ando et al.,
• Nucl. Phys. A 707 (2002)

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics

• Differential folded cross section
• determines signal in the detector energy
  transfer and excitation energy of the target
  nucleus indicate the decay products that will be
  observed in the detector

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
16O
differential folded cross sections
Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
2D
differential folded cross sections
Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
208Pb
differential folded cross sections
Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
16O
differential folded cross sections
multipole contributions
Natalie Jachowicz

ECT,
Trento, June 28 2007
17

What low-energy beta beams can tell about
supernova physics
This very satisfying agreement suggests that it
is possible to reconstruct supernova-neutrino
signal using the results of the beta-beam
measurement without going through the
intermediate step of using a nuclear structure
calculation

• For each set of beta-beam data at a given g,
  there will be a measured response in the detector
• Taking appropriate linear combinations of the
  measured response provides a very accurate
  picture of the response of the detector to an
  incoming supernova-neutrino spectrum

Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
Energy resolution
Width resolution
Natalie Jachowicz

ECT,
Trento, June 28 2007
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What low-energy beta beams can tell about
supernova physics
Reconstructing the supernova neutrino
spectrum ?
Natalie Jachowicz

ECT,
Trento, June 28 2007
20

What low-energy beta beams can tell about
supernova physics
Inversion of the method reconstructing the
supernova neutrino energy spectrum
Supernova neutrino signal in a terrestrial
detector
Fit with linear combination of beta beam
responses
a?i, ?i
Natalie Jachowicz

ECT,
Trento, June 28 2007
21
What low-energy beta beams can tell about
supernova physics
Inversion of the method - test
Starting from a power-law supernova neutrino
spectrum , we determine the best
fit to this spectrum
Adding noise to the expansion parameters mimicks
the effect of various sources of uncertainties

0.05 0.10
Noise ai? (1 ) ai
We than check wich power law spectrum yields the
best fit to
Natalie Jachowicz

ECT,
Trento, June 28 2007
22
What low-energy beta beams can tell about
supernova physics
Inversion of the method reconstruction in terms
of average energy and width of the spectrum
curves 90 confidence levels for spectra with
5 and 10 uncertainty on the expansion
parameters
Natalie Jachowicz

ECT,
Trento, June 28 2007
23
What low-energy beta beams can tell about
supernova physics
Neutrinos are oscillating !
Very schematically, the emitted supernova
neutrino spectrum can be written as a combination
of a low energy and a high energy component
In a terrestrial detector, neutral current
reactions are accessible for both components, the
neutral current signal looks like
In a terrestrial detector, only supernova
electron neutrinos can produce a massive lepton,
the charged current signal looks like
Natalie Jachowicz

ECT,
Trento, June 28 2007
24
What low-energy beta beams can tell about
supernova physics
In a first step the 2 combinations of beta-beam
data that produce the best fit to the neutral
current signal are determined
are selected to minimize the difference between
and
In a second step these synthetic spectra are used
to determine the oscillation parameters Rfit and
Ifit that yield the best agreement with the
charged current signal
Rfit and Ifit are selected to minimize the
difference between
and
Natalie Jachowicz

ECT,
Trento, June 28 2007
25
What low-energy beta beams can tell about
supernova physics
Neutrinos are oscillating determining
Rfit and Ifit
Natalie Jachowicz

ECT,
Trento, June 28 2007
26

What low-energy beta beams can tell about
supernova physics

• Conclusions

• We take linear combinations of low-energy
  beta-beam spectra,
• and fit those to supernova-neutrino
  energy-spectra , thus building synthetic
  supernova spectra
• the corresponding differential cross sections are
  in very good agreement
• This technique can be inverted to reconstruct
  the parameters of the supernova neutrino spectrum
• and learn about the oscillation characteristics
  of supernova neutrinos
• The agreement is so good, we propose low-energy
  beta-beams as a direct way to measure the
  nuclear response to a supernova neutrino signal
  and obtain information about the supernova
  neutrino spectrum and supernova neutrino
  oscillations

Natalie Jachowicz

ECT,
Trento, June 28 2007