Diffuse supernova neutrinos: what can we learn and how

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Diffuse supernova neutrinos what can we learn
(and how)?

• Cecilia Lunardini
• Arizona State University
• And RIKEN BNL Research Center

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The feeble signal of all SNe

• Sum over the whole universe

Supernovae
S. Ando and K. Sato, New J.Phys.6170,2004.
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Probes deep in stars interior

• physics near SN core
• Energetics of collapse (mass of core , eq. of
  state) ? spectra formation
• ? oscillations at extreme density
• ?-? refraction effects, ? mass spectrum, ?13
• new physics
• axions, majorons, sterile ?,
• ? decay,

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• Alternative to a galactic supernova!
• Lower statistics
• Continuous flux, no waiting time
• might be standard physics in future!
• 20 events/year at 20 SuperK
• A galactic supernova will always be once in a
  lifetime, the DF will be everyday stuff

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and deep in space (and time!)

• 40 of ?s above 19.3 MeV are from zgt0.5!

S. Ando and K. Sato, New J.Phys.6170,2004.
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• Test cosmological rate of Sne
• Probe history of star formation
• Short lived stars ? SN rate traces star formation
  rate RSF / RSN
• Reveal the first stars (Population III, z 13
  -20)

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Predicting the DF
Cosmological supernova rate
from individual SN with oscillations

• At E gt 10-15 MeV

From original neutrino spectrum ( ? 5-7 MeV,
depending on oscillations, etc.)
? dependence
C.L., PRD75,2007
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Status of theory anti-?e flux
C.L., Astropart.Phys.26190-201,2006

• Differences due to different inputs/methods

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Experimental status (new!)
C. L. and O.L.G. Peres (UniCamp, Brazil), in
preparation
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The future what can we learn?

• Potential of next generation detectors

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Pure water anti-?e

• anti-?e p ! n e

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Pros and Cons

• Well studied
• Scalable
• Background-dominated
• Cut at Ethr19.3 MeV (anti-?e energy)
• invisible ?, atm. ?

Fogli et al. JCAP 0504002,2005
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(10-20) SK event rate

• Exposure 1.6 Mton year
• e.g., 0.2 Mt for 8 years
• Threshold 19.3 MeV, 100 efficiency

C.L., Astropart.Phys.26190-201,2006, Fogli et
al. JCAP 0504002,2005, Volpe Welzel, 2007,
C.L. O.L.G. Peres, to appear soon.
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Spectral sensitivity limited by background

• needs N 100-200
• larger than typical, (incompatible with SN1987A)
• Useful
• N(18-23 MeV)/N(23-28 MeV) 0.6 - 3

Normalized to 60 events, b3.28
Subtracted signal total error
C.L., Phys.Rev.D75073022,2007 Error bars from
Fogli et al, JCAP 0504002,2005
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Normalized to 60 events, E0/MeV15, a2.6

• Testing b not realistic
• Good to learn about original spectrum
• No degeneracy!

b5
b3.28
b2
C.L., Phys.Rev.D75073022,2007
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Most likely scenario rate only
Reminds me of Ray Davis Homestake!

• Test of normalizations
• SN rate normalization
• SN neutrino flux luminosity
• Model-dependent (need to assume neutrino
  spectrum)
• Indirect sensitivity to energy spectrum
• Tested for fixed normalizations

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Room for suprises invisible Supernovae?
Artist's concept
From diffuse ? flux
SNR/SNR0
From astro surveys (SNAP, JWST)
L?/L0
http//snap.lbl.gov/ http//www.jwst.nasa.gov/,
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• Example from the present SK bound constraining
  SN rate normalization
• Spectrum dependent!

Beacom et al., JCAP 0504017,2005.
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Water Gadolinium

• Anti-?e p ! n e

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Pros and cons

• Solution of water GdCl3 (0.2)
• Higher risk (new technique)
• Cheap, safe, easy (SK tank can be used)
• n capture on Gd e and n in coincidence
• Filters spallation and invisible muons

GADZOOKS Beacom and Vagins, PRL93, 2004
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• Major improvement with background
• Eth 11.3 MeV (limited by reactors)

Fogli et al. JCAP 0504002,2005
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(10-20) SK event rate

• Exposure 1.6 Mton year
• e.g., 0.2 Mt for 8 years
• Threshold 11.3 MeV, 100 efficiency

C.L., Astropart.Phys.26190-201,2006, Fogli et
al. JCAP 0504002,2005, Volpe Welzel, 2007,
C.L. O.L.G. Peres, to appear soon.
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Spectral sensitivity!
Normalized to 150 events, b3.28
C.L., Phys.Rev.D75073022,2007
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A step beyond SN1987A!

• Test SN codes of spectra formation, some
  oscillation effects, etc.
• Probe part of the parameter space with 0.1 Mt
  yr
• Incompatible with SN1987A

0.1 Mt yr
Yuksel, Ando and Beacom, Phys.Rev.C74015803,2006
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Chance to test ? !
Normalized to 150 events
r 0.6 0.9
C.L., Phys.Rev.D75073022,2007
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Artist's concept
Direct supernova observations
Diffuse neutrinos
C.L., Astropart.Phys.26190-201,2006
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Liquid scintillator

• Anti-?e p ! n e

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LENA _at_ Pyhäsalmi (Finland), 50 Kt
event rate in 10 yrsinside the energy window
from 9.7 to 25 MeV
From M. Wurm, talk at NNN06
background events 12
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Avoid nuclear powerplants!
Wurm et al., PRD75, 2007
For LENA
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Probing the neutrino spectrum
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Sensitivity to SN rate
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Liquid argon

• ?e Ar ! K e-
• Best ?e detector!
• With both ?e and anti-?e physics potential at
  least doubles!

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• Background
• Solar
• Atmospheric
• Energy window 16-40 MeV (normalization-dependent)
  
• 0.5 Mt year
• N 60

Cocco et al., JCAP 0412002,2004
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Perspectives for the future
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Conservative scenario

• No galactic SN in the next 10 yrs
• The DF will be detected first data after
  SN1987A!
• WaterGd 20 kt ? indication
• Water 0.4 Mt ? evidence (rate
  only?)
• WaterGd 0.4 Mt ? measure spectrum
• or Liquid scintillator 50 kt

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• With spectral sensitivity beyond SN1987A
• Strong focus on original spectrum
• Some sensitivity to ?
• constraint on L? R(0)
• More precise ? from SN surveys (SNAP, JWST)

http//snap.lbl.gov/ http//www.jwst.nasa.gov/,
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Exciting scenario

• Precise L? and spectrum from Galactic supernova
• Precise ? from SN surveys
• DF will help measure
• R(0) (independent check)
• ? (independent check)
• fraction of stars that become SN (failed SN?)
• progenitor dependence of neutrino spectrum