Diffuse supernova neutrinos Cecilia Lunardini Arizona State University And RIKEN BNL Research Center

What can we learn (and how)? Generalities & motivation Future detectors: potential –Water Cherenkov –Water + Gd –Liquid scintillator –Liquid Argon Ideas for R&D Perspective for the future

The feeble signal of all SNe Sum over the whole universe: Supernovae S. Ando and K. Sato, New J.Phys.6:170,2004.

Probes deep in star’s 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, …

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

…and deep in space (and time!) ~40 % of ’s above 19.3 MeV are from z>0.5! S. Ando and K. Sato, New J.Phys.6:170,2004

Test cosmological rate of Sne Probe history of star formation –Short lived stars  SN rate traces star formation rate: R SF / R SN Reveal the first stars (Population III, z ~ )

Predicting the DF At E >~ MeV: Cosmological supernova rate from individual SN with oscillations From original neutrino spectrum (  ~ 5-7 MeV, depending on oscillations, etc.)  dependence C.L., PRD75,2007

Status of theory: anti- e flux Differences due to different inputs/methods C.L., Astropart.Phys.26: ,2006

Experimental status (new!) Species (experiment) Previous best (cm -2 s -1 ) 90%CL (direct limits only) New from SK (cm -2 s -1 ) 90% CL Anti- e (SK coll.) 1.2 (E/MeV>19.3) (E/MeV>19.3) e (SNO) 70, (22.9<E/MeV<36.9) 42-54, (22.9<E/MeV<36.9)  +   (LSD) (E/MeV>20) ( ) 10 3 (E/MeV>19.3) Anti-  + anti-  (LSD) (E/MeV>20) ( ) 10 3 (E/MeV>19.3) C. L. and O.L.G. Peres, JCAP08(2008)033

The future: what can we learn? Potential of next generation detectors

Pure water: anti- e anti- e + p ! n + e + Zhang et al. (Kamiokande) PRL61, 1988; Malek et al. (SuperK), PRL90, 2003; Aharmim et al., (SNO), PRD70, 2004; D. Autiero et al. (MEMPHYS, HyperK), arXiv:

Pros and Cons Well studied Scalable Background- dominated –invisible , atm. –Cut at E thr ~19.3 MeV (anti- e energy) Fogli et al. JCAP 0504:002,2005

(10-20) £ SK : event rate Exposure 1.6 Mton £ year –e.g., 0.2 Mt for 8 years –Threshold 19.3 MeV, 100% efficiency SN1987A- motivated (conservative) Model- motivated (generic) Max. allowed by SK limit 7-60~80-100~ C.L., Astropart.Phys.26: ,2006, Fogli et al. JCAP 0504:002,2005, Volpe & Welzel, 2007, C. L. and O.L.G. Peres, JCAP08(2008)033

Spectral sensitivity: limited by background needs N ~ – larger than typical, (incompatible with SN1987A) Useful: ~ Normalized to 60 events,  =3.28 Subtracted signal + total error C.L., Phys.Rev.D75:073022,2007 Error bars from Fogli et al, JCAP 0504:002,2005 N(18-23 MeV) N(23-28 MeV)

Normalized to 60 events, E 0 /MeV=15,  =2.6  =2  =3.28  =5 Testing  not realistic Good to learn about original spectrum –No degeneracy! C.L., Phys.Rev.D75:073022,2007

Most likely scenario: rate only 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 Reminds me of Ray Davis’ Homestake!

SNR/SNR 0 L /L 0 From diffuse flux From astro surveys (SNAP, JWST) From SN codes Room for suprises: invisible Supernovae?

Example from the present: SK bound constraining SN rate normalization –Spectrum dependent! Beacom et al., JCAP 0504:017,2005

Water + Gadolinium Anti- e + p ! n + e + Beacom & Vagins, Phys.Rev.Lett.93:171101,2004

Pros and cons Solution of water + GdCl 3 (0.2%) –n capture on Gd: e+ and n in coincidence –Filters spallation and invisible muons –Higher risk (new technique) –Cheap, safe, easy (SK tank can be used) GADZOOKS: Beacom and Vagins, PRL93, 2004

Major improvement with background –E th ~ 11.3 MeV (limited by reactors) Fogli et al. JCAP 0504:002,2005

(10-20) £ SK : event rate Exposure 1.6 Mton £ year –e.g., 0.2 Mt for 8 years –Threshold 11.3 MeV, 100% efficiency SN1987A- motivated (conservative) Model- motivated (generic) Max. allowed by SK limit ~22-128~ C.L., Astropart.Phys.26: ,2006, Fogli et al. JCAP 0504:002,2005, Volpe & Welzel, 2007, C. L. and O.L.G. Peres, JCAP08(2008)033

Spectral sensitivity! Normalized to 150 events,  =3.28 C.L., Phys.Rev.D75:073022,2007

A step beyond SN1987A! Test SN codes of spectra formation, some oscillation effects, etc. 0.1 Mt £ yr : –Tests part of parameter space –May not reach SN1987A region 0.1 Mt £ yr Yuksel, Ando and Beacom, Phys.Rev.C74:015803,2006

Chance to test  ! r ~ 0.6 – 0.9 Normalized to 150 events C.L., Phys.Rev.D75:073022,2007

C.L., Astropart.Phys.26: ,2006 Direct supernova observations Diffuse neutrinos

Liquid scintillator Anti- e + p ! n + e + Eguchi et al. (KamLAND), PRL92, 2004; Aglietta et al.(LSD), Astrop. Phys. 1, 1992; Wurm et al. (LENA), Phys.Rev.D75:023007,2007

Pyhäsalmi (Finland), 50 Kt dependent on SN model (CSFR assumed, f*=2.5) LL:120 KRJ:105 TBP:68 dependent on SFR f*=0.720 CSFR105 f*= event rate in 10 yrs: inside the energy window from 9.7 to 25 MeV background events: 12 From: M. Wurm, talk at NNN06

Avoid nulear powerplants! Wurm et al., PRD75, 2007 For LENA :

Probing the neutrino spectrum:

Liquid argon e + Ar ! K + e - D. Cline et al. (LANNDD), Nucl.Instrum.Meth.A503: ,2003; B Fleming (ArgoNEUT), Nucl.Phys.Proc.Suppl.155: ,2006; Baibussinov et al. (MODULAr), Astropart.Phys.29: ,2008 ; Autiero et al. (GLACIER, LAGUNA), JCAP 0711:011,2007

Cocco et al., JCAP 0412:002,2004 Background: –Solar –Atmospheric –Energy window: MeV (normalization- dependent) 0.5 Mt £ year: –N » 60

Best e detector! With both e and anti- e physics potential at least doubles! Volpe & Welzel, arXiv:

Ideas for R&D A theorist’s perspective

Oscillations reduce reactor background Five reactors closest to Homestake If all reactors were at 510 Km (optimal distance for suppression at 11 MeV: D/Km= 170,510,850, …) C.L., in preparation Energy window can be ~1 MeV lower

Directional detection for signal separation Only way to fully separate backgrounds (solar, reactor) –Open energy window 1 – 10 MeV : cold neutrinos from Pop III stars, neutron stars, geoneutrinos, … Necessary for truly multi-purpose facility! F. Iocco et al, Astropart. Phys. 23 (2005 )

Gd- or Li-loaded liquid scintillator –e - scattering in LAr Kinematic reconstruction of CC reactions in LAr Hochmuth et. al., Astropart. Phys. 27 (2007), Shimizu, Nucl. Phys. Proc. Suppl. 168 (2007) Shimizu, Nucl. Phys. Proc. Suppl. 168 (2007)

Perspectives for the future

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

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)

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

Talk in one slide 0.1 Mt £ yr Direct supernova observations Diffuse neutrinos Background separation at low energy is key!

Backup slides

Literature –Bisnovatyi-Kogan & Seidov, 1982 ; Krauss,Glashow & Schramm, 1984 ; Woosley, Wilson &Mayle, 1986 ; Totani & Sato, 1995 ; Totani, Sato& Yoshii, 1995 ; Malaney 1997; Hartmann &Woosley 1997; Kaplinghat, Steigman & Walker,2000 ; Ando, Sato & Totani, 2003 ; Ando &Sato, 2003 ; Strigari, Kaplinghat, Steigman&Walker, 2000 ; Ando, 2004 ; Iocco et al.,2004; Lunardini 2005 ; Daigne, Olive, Sandick & Vangioni, 2005; Lunardini, 2006; Wurm et al., 2007; Yuksel & Beacom, 2007; Volpe & Welzel, 2007; Chakraborty et al., 2008; Lunardini & Peres, 2008

Sensitivity to SN rate