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Experimental Review of Supernova Relic Neutrinos

Experimental Review of Supernova Relic Neutrinos. (Diffuse Supernova Neutrino Background : DSNB). Takashi Iida (Queen’s University, Canada) Mar. 21 st , 2011. Seminar @Gran Sasso National Laboratory. About me!!. Ciao !! Thank you for the invite. Takashi Iida

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Experimental Review of Supernova Relic Neutrinos

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  1. Experimental Review of Supernova Relic Neutrinos (Diffuse Supernova Neutrino Background : DSNB) Takashi Iida (Queen’s University, Canada) Mar. 21st, 2011 Seminar @Gran Sasso National Laboratory

  2. About me!! Ciao !! Thank you for the invite • Takashi Iida • Ph.D with SRN search in Super-K • Posdoc for SNO+ in Queen’s university, Canada

  3. Outline • Introduction • Supernova and Supernova relic • Experiments review • LSD, Super-K, SNO, KamLAND • Future experiments • Gadzooks!, SNO+, LENA • Summary

  4. Supernovae have a history Astronomy is one of the oldest study SN 1006 remnant People have been looking for Supernovae for more than 1000 years. But,,, Supernovae have been happening since the Big bang! The history of SN is about 14 billion years!!

  5. What can we learn from SN?? • Neutrino oscillation • Neutrino mass hierarchy • MSW effect Particle physics Supernova!! • Nucleosynthesis • R-process • Neutrino process Nuclear physics Astrophysics • Cosmic rays • Gamma ray burst • Gravitational wave • Neutron stars, blackhole Understanding SN is Very important !!

  6. 24 years from SN1987A Feb. 23rd 1987 First neutrino detection from Supernova!! We learned from SN1987A • Neutrinos are emitted from SN. • Luminosity.  Order of 10^53 erg • Average E of neutrinos.  ~10MeV • Duration of the burst.  ~10sec the dawn of a new era in ”Neutrino astronomy”

  7. It’s been two decades since 1989. This decade will be a great time for “Neutrino Astronomy”!!

  8. We are all waiting for SN • Understanding supernova burst is important for particle physics, nuclear physics and astrophysics. • Neutrino is the best tool for observing SN • RealtimeSN is rare: < 1SN / 30y / galaxy • Supernova Relic Neutrino is stable and promising source • Useful for studying SN mechanisms and evolution of the universe • No experiments has succeeded to detect SRN!!

  9. Classic papers on SRN Bisnovatyi-Kogan, Seidov, Sov. Astron. 26, 132 (1982) Krauss, Glashow, Schramm, Nature 310, 191 (1984)

  10. Supernova Relic Neutrinos（SRN） • There exist 10＾9 Galaxies and each has 10＾11stars!! • ~0.3% of them are big enough to make a Supernova explosion. • In other words, 10＾17 Supernovae happened in our universe since Big ban. • Each Supernova release 10^53 [erg]and 99% are emitted as neutrinos. Supernova Relic Neutrinos(SRN) are the Diffuse Neutrino Background originate all the past supernovae. past present Red shift effect for Neutrino spectrum Star formation rate measured by optics Hopkins and Beacom, Astrophys. J. 651, 142(2006) S.Ando, Astrophys.J.607:20-31,2004. • SRN shows us integrated SN neutrino from past to present.

  11. Supernova Relic Neutrinos （SRN） C: Speed of light Z: Red shift parameter Fn: Flux of SRN En: Energy of SRN Constant SN (Totani et al., 1996) Totani et al., 1997 Hartmann, Woosley, 1997 Malaney, 1997 Kaplinghat et al., 2000 Ando et al., 2005 Lunardini, 2006 (dash) Fukugita, Kawasaki, 2003 What can we learn from SRN?? • The mechanism of Supernova • (Total/Average n energy, spectrum) • The history of Universe • The history of heavy nucleosystheis. • Invisible SN exist? and so on…

  12. We have two possible choices!! Now we understand SRN is important!But how to detect SRN?? Scintillator Water Low Background Large light yield (×100) Neutron tagging No inv-m Lower E threshold Reactor n (<10MeV) Atmospheric n Large volume Cheap and easy Direction information Spallation (<18MeV) Invisible m-e decay from atmospheric n (>18MeV)

  13. So, what’s presented today? • This is the most important plot in this talk !! • Solid line shows the SRN flux upper limit from each experiment. • Dashed line shows expected sensitivity for future experiments. • What they have already done? • What limited the sensitivity so far? • Can we improve more for future? • are presented!! SNO+ LENA GADZOOKS! (Ando model)

  14. SRN search so far • Kamiokande (1988) • LSD (1992) • Super-K (2003) • SNO (2007) • KamLAND (2008) Kamiokande detector and analysis are similar to Super-K. So please let me skip Kamiokande and explain detail for Super-K.

  15. in Mont-Blanc Laboratory LSD

  16. Detection of SRN in LSD ne via Inverse beta decay (IBD) 2.2MeV ne and ne via CC All fravor via NC

  17. SRN search in LSD • The energy threshold is set at 5MeV for inner 16 counters and 7MeV for external ones. • After each trigger the energy threshold is lowered to 0.8MeV for 500 msec to detect gamma ray. • Detection efficiency of delayed gamma is 50%.

  18. Energy spectrum of IBD like event • Energy spectrum. • One event between 12-25MeV.  Nlimit = 3.8 @90% C.L. All events Followed by 2.2MeV

  19. Result in LSD • This is the first result for all flavor neutrinos. • Although worse than Kamiokande.

  20. Mont-Blanc LSD result (1992) ne (Ando model)

  21. 42 m 39.3 m Super-K detector Super-K is a large water Cherenkov detector for n detection experiment. It is located at Kamioka mine in Japan. • 50,000 ton total mass • 22,500 ton fiducial volume • 11,146 50 cm PMTs Inner • 1,885 20 cm PMTs Outer • 40% photocathode coverage • 1000 m minimum depth • 4.5 MeV Trigger threshold • E Res. 16%/E1/2 @ 10 MeV • Position ~50 cm @ 10 MeV • Angular ~30° @10 MeV SK-I SK-II SK-III Reconstruction Accident Full reconstruct

  22. νe+ 16O  16N + e+ SRN detection in Super-k Inverse beta decay is dominant reaction in Super-K 10 νe+ p  e+ + n νe+ p  e+ + n 0.1 Enent Rate [/year /MeV/22.5kt] Ee = En - 1.3 [MeV] 10-3 νe+ 16O  16F + e- 10-5 νe+ e  νe + e- Expected number SRN events 0.3 -1.9 events/year/22.5kton (Ee=18-30MeV) 10-7 0 10 20 30 40 50 Electron energy [MeV]

  23. Background Sources 1, Cosmic ray muon 2, Spallation induced by cosmic ray muon 3, Solar neutrino 4, 「Visible」m-e decay from atmospheric nm 5, 「Imvisible」m-e decay from atmospheric nm 6, Atmospheric ne cf. 「visible」 means that muon E is over the Cherenkov threshold （１）ー（４） is rejected by data analysis （ Next page） （５）、（６） is considered by spectrum fitting ( later)

  24. Normal Spallation cut The spallation BGis reduced by a likelihood method that uses timing and track information of the muons preceding the candidate events. Cherenkov angle cut Positrons with E>18MeV have a Cherenkov angle of qC ~ 42 degrees. To remove muons and multiple gamma-rays, remove events with 38° < qCor 50°> qC. Solar direction cut To remevesolar neutrino events, the events in the direction of the sun are removed. (E<25MeV && Cosqsun>0.75) Tight Spallation cut In addition to the normal spallation cut, tighter criteria is applied in order to enhance the rejection efficiency of spallation BG. So, we remove events which occur within 0.15 sec. Gamma ray cut Some g ray events originating from outside of fiducial volume have possibility of being reconstructed within fiducial volume of SK. We remove the events whose expected travel distance of g ray is < 450cm.

  25. M.Malek et.al. Phys. Rev. Lett. 90, 061101,2003 Signal extraction Data Chi2 fitting using energy spectrum was done for extracting signal. SK1 1496days Invisible m-e decay ( ) Atmospheric ne Flux limit @90%C.L. < 1.2 /cm2/sec (>19.3MeV) World best limit so far!!

  26. Latest official result Minor improvement of BG reduction & SK-II data added in 2007 preliminary preliminary SK-II SK-I (1496day) (791day) DATA DATA Imvisiblem-e decay Imvisiblem-e decay Atmospheric ne Atmospheric ne Spallation BG Visible energy [MeV] Visible energy [MeV] 90% C.L. Flux limit (preliminary) SK-I : < 1.25 /cm2 /sec SK-II : < 3.68 /cm2/sec SK-I + SK-II : < 1.08 /cm2 /sec

  27. Super-K result ne ne (Ando model)

  28. SNO 306 days’ 1st phase data was used for this search

  29. ne search

  30. SRN analysis in SNO • From1999 Nov. 2 until 2001 May 28 (306.4 days) corresponding to an exposure of 0.65 ktons yr • Only single electron events are selected  CC • 94% efficiency for SRN signal

  31. SNO analysis 8B BG are estimated by atmospheric n MC (Bartol04 flux and NUANCE package). 0.18 +/- 0.04 BGs are expected. Mainly atmospheric NC. No BG observed in Evis = 21 – 35MeV!! hep Atmn SRN 2.3 ev upper limit is set at the 90% CL. Flimit < 70 /cm2/sec (En = 22.9 – 36.9MeV)

  32. SNO result (2005) ne ne (Ando model)

  33. The KamLAND Detector O.Perevozchikov Balloon & support ropes calibration device & operator Target LS Volume (1 kton, 13m diameter) 80% Dodecane(C12H26) 20% Pseudocumene(C3H9) PPO 1.36g/l Glovebox Chimney (access point) Buffer Oil Zone PMT (225 20” in OD + 1879 17” and 20” in ID) (34% coverage of ID) Outer Detector (3.2 kton Water Cherenkov) Stainless Steel Inner Vessel (18m diameter) νe+ p  e+ + n ne search as like LSD and Super-K.

  34. High Energy Candidates 6.0m fiducial volume 7.5->15MeV: 10 candidates has been selected + 2 triple coincidence: multiple neutrons capture Run# 1824, Prompt# 13658585 Delayed# 13658586, 13658587 Run# 5941, Prompt# 4644789 Delayed# 4644790, 4644791 + 1 muon decay (triple coincidence) Run# 5380 Prompt_1# 41470(muon, E=15.5MeV) Prompt_2# 41471(positron, E=13.6MeV) Delayed# 41472 dT1-2=1.23μsec dR1-2=6.4 cm solar antineutrino energy range Eprompt Edelayed ▬ solar candidates ▬ multiple n-capture ▬ μ - decay ▬ solar candidates ▬ multiple n-capture ▬ μ - decay 10 events 6 events ΔR ΔT ▬ solar candidates ▬ multiple n-capture ▬ μ - decay ▬ solar candidates ▬ multiple n-capture ▬ μ - decay 10 events in 6.0m volume, 6 events in 5.5m volume.

  35. Background sources in KamLAND • Accidental Background • 9Li produced by cosmic muons • Reactor antineutrinos • Background from atmospheric neutrinos

  36. Background estimation KamLAND 5.5m analysis Total BG within 7.5-15MeV: 8.78 ± 2.16 events Total BG within 15-30MeV: 3.96 ± 1.04 events Nlimit : number of limit @95% CL by F-C. s : Averaged cross section e : Detection efficiency T : Livetime (1430d) Nprotons : Number of protons • NC cross-section uncertainty 18% • Atmospheric neutrino flux uncertainty 22% • Combined uncertainty 28.4% 120 /cm2 /sec (7.5-15MeV)  16/cm2 /sec /MeV Oleg Perevozchikov HEP Seminar at BNL, Sep. 2009

  37. KamLAND result (2008) (Ando model)

  38. Atmospheric neutrino BGs in KamLAND KamLAND analysis also showed the event rates in future LENA,50 kt liquid scintillator detector from the various neutrino sources (LENA proposal Phys.Rev.D75:023007) Is that true!? Can’t we detect SRN in future detector? Let me discuss about this! Our B.G. calculations They said: B.G. rate from NC interactions of the atmospheric neutrinos is significantly higher than expected SRN…

  39. Discussion • For a scintillator detector, atmospheric n is the largest BGs (n + 12C  n + n + 11C). • According to KamLAND analysis, this BGs are more significant than SRN flux. • The key of BG reduction is 11C (~20min half life) tagging!! Can we really defeat BG !?

  40. 11C tagging Enemy : n + 12C  n + n + 11C 11C rate in KamLAND ~1000 /day/kton ~1 [/day/m3] 11C search inside 1m sphere for 2hours after SRN candidate 15cm vertex resolution in LS detector @1MeV 20min half life of 11C Deeper than ~4000mwe is preferable  0.35 11C is expected in KamLAND  35% inefficiency for SRN If we want to tag 11C, one order lower muon rate is required!!

  41. Future experiments Gadzooks! / SNO+ / LENA

  42. Gadzooks! n ne p Gd e+ g 8MeV Gd in water • ne signal can be separated from BG by neutron tagging. • Load Gd into SK water to detect gamma by neutron capture.

  43. Possibility of SRN detection Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with NNN05 flux revision If invisible muon background can be reduced by neutron tagging SK10 years (e=67%) Assuming 67% detection efficiency. Test tank for feasibility study is now being constructed!! With 10 yrs SK data, Signal: 33, B.G. 27 (Evis =10-30 MeV) Assuming invisible muon B.G. can be reduced by a factor of 5 by neutron tagging. Slide by M.Nakahata

  44. L.Marti in NOW2010 Evaluating Gadolinium’s Action on Detector Systems

  45. L.Marti in NOW2010 Tank was constructed.Mounting PMTs and installing electronics and DAQ. Aim to start within 2011.

  46. SNO+

  47. SNO+ advantage • Size - SNO+ has 780 tons of scintillator,comparing to 300tons of Borexino. • Depth - SNO+ is at 6080 mwe, whileKamLAND is at 2700 mwe. • Light yield - ~9500 PMTs. ~500 pe / MeV - Without Nd loading 5% resolution @1MeV

  48. BG estimation KamLAND analysis Assuming… Reactor flux  1/4 9Li  negligible Atm n same rate (tag 11C) Total expected BG 1.07 BGs (1430d, 7.5-15MeV) Main BG source : n + 12C  n + n + 11C 20min life time Tagging 11C can reduce the atmospheric n BGs dramatically. SNO+ BG rate is less than 1/8 of KamLAND!!

  49. BG estimation KamLAND analysis Assuming… Reactor flux  1/4 9Li  negligible Atm n same rate (tag 11C) Total expected BG 0.3 BGs (1430d, 7.5-15MeV) Main BG source : n + 12C  n + n + 11C 20min life time 2nd BG source : Reactor n E threshold m detection eff 3rd BG source : nm+ p  m + n

  50. Flux limit on SRN Nlimit : number of limit @90% CL by F-C. s : Averaged cross section e : Detection efficiency (assume 90%) T : Livetime (5y) Nprotons : Number of protons in SNO+ (=7*10^31 protons) 26 /cm2 /sec (7.5-20MeV)  2.1 /cm2 /sec /MeV For 1.07 BG 18 /cm2 /sec (7.5-20MeV)  1.4 /cm2 /sec /MeV For 0.3 BG

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