SN Physics Workshop September 17 th 2009 Michael Smy UC Irvine SN Relic Neutrinos in Large Water Cherenkov Detectors Chandra/Hubble View of E

Outline Super-Kamiokande SearchSuper-Kamiokande Search –Published Analysis using SK-I Data –Analysis Improvements & Data Update: increase sensitivity by ~factor two –Search with Neutron Tagging SN Relic Prospects with a DUSEL Water Cherenkov DetectorSN Relic Prospects with a DUSEL Water Cherenkov Detector –Without Neutron Tagging –With Neutron Tagging Chandra/Optical/Radio View of SN1006

Super-Kamiokande

PeriodLive time# ID PMTs / % coverageComment SK-I1496 days11146 / 40%Experiment start SK-II791 days5182 / 19 %After accident SK-III days11129/ 40%After repair SK-IVrunning now11129/ 40%New electronics Electron energy [MeV] SK Event Rate [/year /MeV] ν e + 16 O  16 N + e + ν e + 16 O  16 F + e - ν e + e  ν e + e - ν e + p  e + + n The main interaction mode for SRN’s in SK is charged current quasi- elastic interaction (inverse  decay) Courtesy K. Bays, UC Irvine

oxgen spallation products from cosmic  ’s (~600/day) atmospheric ’s –CC e ’s –sub-Cherenkov  production:  →stealth  →e radioactivity solar ’s reactor ’s spallation limits the energy threshold & cuts to reduce it causes greatest signal loss sub-Cherenkov threshold muons from atmospheric neutrinos are irreducible without neutron tagging SK Main Backgrounds atm.  → stealth  ± →e ± relic ’s spallation products from cosmic  ’s μ O e γ X X e Michael Smy, UC Irvine

Spallation Products 11 Be 11 Li 12 N 14 B energy resolution 8B8B 9 Li 8 Li 12 B 13 B 13 O 12 Be 12 C 8 He 9C9C 15 C 16 N Energy in MeV half life in s Courtesy K. Bays, UC Irvine

Spallation Products IsotopeHalflifeDecayKinetic Energy 16 6 C0.7478s -n-n ~4 MeV 15 6 C2.449s  MeV 16 7 N7.134s  MeV 11 4 Be13.8s - MeV 8 2 He0.122s  n/  -  MeV 12 4 Be0.0114s - MeV 96C96C0.127s +p+p 3~13 MeV 8 3 Li0.84s -- 12.5~13 MeV 12 5 B0.0204s - MeV 13 5 B0.0173s - MeV 9 3 Li0.178s  n/  -  ~10,13.5 MeV 85B85B0.77s + MeV 13 8 O0.0090s +p+p 8~14 MeV 12 7 N0.0110s + MeV 14 5 B0.0161s -- MeV 11 3 Li0.0085s  -  - n ~16/20.77MeV

form time diff.  t between muon and relic candidate reconstruct muon track calculate residual charge ResQ: total light minus charge expect. from length find distance of closest approach  l Transverse of muon to relic candidate use arrival time of each hit to calculate emission point along track:  l Longitudinal is difference of point of max. light emission and relic candidate projection peak light emission Q Peak Tagging Spallation Events μ entry point μ track  l Transverse maximum light emission  l Longitudinal Relic Candidate K. Bays, UC Irvine

Example of a dE/dx Plot distance along muon track (50 cm bins) p.e.’s Q Peak = sum of charge in window spallation expected here Courtesy K. Bays, UC Irvine

A Simple Example of Spallation Removal L TRAN (cm) L LONG (cm) L TRAN (cm) L LONG (cm) Spallation Courtesy K. Bays, UC Irvine entry point muon peak of dE/dx relic candidate L TRAN L LONG

Previous and Improved Spallation Tag three-variable likelihood cut for successful single track fits –  t –  l Transverse – ResQ two-variable likelihood cut for unsuccessful single track fits –  t – ResQ 150ms cut on  t 18 < E < 34: 36 % signal inefficiency for each muon type (single ,  bundle, stopping  ): four-variable likelihood cut if single, well-fit track –  t –  l Transverse –  l Longitudinal – Q Peak three-variable likelihood otherwise –  t –  l Transverse – Q total 18 < E < 24 MeV: 18.5 % ineff. 16 < E < 18 MeV: 22.5 % ineff. PreviousImproved Michael Smy, UC Irvine

Removal of Spallation 12 black – before likelihood cut, red – after likelihood cut dt (seconds) L TRAN (cm) (dt < 10 s) stopping muons single muons Courtesy K. Bays, UC Irvine Deadtime 18% (Improved from 36%) Increase in Exposure of 28% Further Tuning may be possible…

Solar 8 B and hep neutrino are a SRN background (hep at 18 MeV, and both at 16 MeV, because of energy resolution) Cut criteria is optimized using 8 B /hep MC improved cut is energy dependent, tuned in 1 MeV bins hep 8B8B pep pp e recoil energy (total) (MeV) energy resolution for an event of energy: 16 MeV 18 MeV Solar ν Events 7 Be 1618 Courtesy K. Bays, UC Irvine

Solar cut MeV ε = 86.5% MeV ε = 72.5% MeV ε = 95.5% Inefficiency: Previous: 7% for 18-34MeV Improved: 4.5% for 18-19MeV, 0% above 19MeV solar candidates Courtesy K. Bays, UC Irvine

External Backgrounds Energy in MeV remove events with small effective wall to kill radioactive decays originating outside the detector but reconstructing within the fiducial volume of SK : Signal Inefficiency: Previous: 7% Improved: 2.5% : Signal Inefficiency: Previous: 7% Improved: 2.5% reconstructed event vertex reconstructed event direction effective wall Inner detector wall Effective Wall in cm Courtesy K. Bays, UC Irvine

Efficiency Improvement new cuts more efficient AND at least as effective > 34MeV, efficiency increase < 1.0 due to new background reducing cuts (new pion cut especially) 18 – 34 MeV, large efficiency increase due mostly to new spallation and solar cuts MeV region is now usable as well! efficiency increase > 18 MeV: (# events new/previous) Energy [MeV] unnormalized relic (Ando) unnormalized stealth  Michels new! Courtesy K. Bays, UC Irvine

Future of this Search New cuts improve efficiency, re-analyzing now More planned improvements: –Fiducial volume enlargement –Finalizing event selection Combine SK-I, SK-II and SK-III data. Extract new combined limit. Hope to publish result within 1 year. Future phase: neutron tagging with Gd. Courtesy K. Bays, UC Irvine

Possibilities of e tagging 2.2MeV  -ray  T = ~ 200  sec Possibility 1 n+Gd → ~8MeV   T = ~30  sec Possibility 2 (ref. Vagins and Beacom) e could be identified by delayed coincidence. e could be identified by delayed coincidence. Positron and gamma ray vertices are within ~50cm. n+p →d +  Number of hit PMT is about 6 in SK-IV e e+e+ p n   p Gd Add 0.2% Gd 2 (SO 4 ) 3 in water GADZOOKS! ν e + p  e + + n Inverse beta decay Courtesy Iida, ICRR

Gadzooks! dissolve Gd salts into SK water to detect gamma by neutron capture need to investigate –water transparency –water recirculation –material effects test tank for Gadzooks! is now being constructed!! Measured Gd n capture Spectrum in SK Astrophys. J. 697, (2009) Michael Smy, UC Irvine

GdCl 3 Source in Super-Kamiokande measure Gd n capture gamma cascades: –Spectrum –Vertex Resolution –Capture Time Michael Smy, UC Irvine

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 Assuming invisible muon B.G. can be reduced by a factor of 5 by neutron tagging. With 10 yrs SK data, Signal: 33, B.G. 27 (E vis =10-30 MeV) SK10 years (  =67%) Assuming 67% detection efficiency. Courtesy Iida, ICRR

Gadolinium Water “Band-Pass” Filter UltrafilterNanofilter De-Ioniziation/ Reverse Osmosis pure water plus Gd from tank Gd plus smaller impurities (UF product) Gd-sized impurities only (NF reject) impurities smaller than Gd (NF product) impurities bigger than Gd (UF reject) impurities to drain (DI/RO reject) pure water (DI/RO product) M. Vagins, ICMU

Filtration/Transparency Studies in Irvine IDEAL “band pass” water system IDEAL pure H 2 O System “band pass” System Extra DI Michael Smy, UC Irvine usual style water filtration system Simple Filter DI

Measuring Water Transparency Michael Smy, UC Irvine idea based on a IMB device measure light intensity continuously as a function of light travel distance vertical pipe for quick & easy change of distance pipe is necessarily short (< height of lab) look for changes when GdCl 3 / Gd 2 (SO 4 ) 3 is introduced plastic pipe and tank (no metal effects) use integrating spheres and a focal lens to stabilize intensity measurements of Si photodiodes use laser pointers (small, cheap & good beam quality)

Pulsed Laser Pointers Experimental Setup Beam Splitter & Steerer Integrating Sphere & Photodiode Adjustable Mirrors Michael Smy, UC Irvine

Reject 0.2% Gd(NO 3 ) 3 : UV (337nm) Pure Water MeasurementGd(NO 3 ) 3 Measurement linear scale log scale 125.8±5.9m 94.87±0.46cm Michael Smy, UC Irvine

Endorse GdCl 3 Solution Endorse GdCl 3 Solution 360nm337nm 650nm 595nm 532nm 478nm 405nm 0.8% Solution: 4xGadzooks! Concentration Michael Smy, UC Irvine 66.8±0.9m 69.8±3.2m 21.08±0.51m 6.422±0.014m 2.864±0.004m 33.00±0.23m 27.74±0.26m

Gadolinium Compound Selection GdCl 3 is considered too corrosive for stainless steel tank/PMT support structure Gd(NO 3 ) 3 is opaque in the UV Gd 2 (SO 4 ) 3 is not as corrosive and (from spectro-photometer measurements) should have good water transparency However, it dissolves not nearly as fast: must first solve selective water filtration Michael Smy, UC Irvine

Gd 2 (SO 4 ) 3 Filtering Progress took data with ultrafilter and two types of nanofilters basic principle is sound UF passed ~100% of Gd 2 (SO 4 ) 3 NF rejected ~100% of Gd 2 (SO 4 ) 3 actually use try multiple stages of NF; clean up product with DI & RO units so far, cannot reproduce transparency even without Gd; need to tune the bandpass; check for impurities from additional components when filtration is working, measure resulting water transparency of Gd 2 (SO 4 ) 3 solution M. Vagins, ICMU

Make 100 ton class test tank and demonstrate the GADZOOKS! Idea. 0.2%Gd water in 100 ton class water tank PMTs Water system Transparency measurement EGADS Evaluating Gadolinium’s Action on Detector Systems Figure by A.Kibayashi Courtesy A. Kibayshi, Okayama University

Current status of Gadzooks! Excavation has started Test tank is currently designed Construction will start soon Material compatibility test Study selective water filtration at Irvine transparency measurement at Irvine test a large-scale water system and measure the water transparency performance with EGADS soon Michael Smy, UC Irvine

Supernova Relic Neutrino Requirement of DUSEL Water Detector K. Bays, UC Irvine

Requirements sufficient depth to avoid being overwhelmed by spallation background need above about six photo-electrons/MeV for sufficient energy resolution (and threshold for Gd n capture events) need low PMT dark noise (same reason): cooling of the PMT environment good radiopurity Michael Smy, UC Irvine

Expected Threshold for DUSEL Detector at 4850ft Level assume spallation background is dominant issue assume spallation spectrum scales with muon rate when varying depth ignore correlation between spallation energy and lifetime keep signal/background ratio to the same level as SK Michael Smy, UC Irvine

I Relic Spectrum Increase in relic rate in water compared to present SK analysis as energy threshold changes Courtesy K. Bays, UC Irvine

II Muon Intensity as Function of Depth Courtesy K. Bays, UC Irvine

III Spallation Spectrum at SK The unnormalized spallation spectrum from SK data can be parameterized by a simple formula: The increase in spallation as the energy threshold is lowered can be calculated by: En (MeV) Courtesy K. Bays, UC Irvine

III Spallation Spectrum With Gd: Guess Spallation Rate with n shorter livetime, less products, less energy …but what are production rates? what if spallation list is not complete? if reduced by ~1 order of magnitude: shift spectrum by 2.6MeV (ln(10)MeV/0.894) Michael Smy, UC Irvine

Energy Threshold Results Some particular values: 4050 (4850 ft) = 15.5/12 MeV 2930 (3500 ft) = 17.5/15 MeV 2700 m.w.e. (SK) = 18/15.5 MeV 1680 (2000 ft) = 20.5/18 MeV 250 (300 ft) = 25/22.5 MeV since SK will lower the threshold, a DUSEL detector should be able to employ the same techniques, so this is very conservative Depth (m.w.e.) Energy Threshold (MeV) w/o Gd with Gd Courtesy K. Bays, UC Irvine

Conclusions SK is improving the sensitivity of the SN relic search spallation tagging is critical for this together with data update, sensitivity should improve by up to a factor of two SK will lower the energy threshold of the search to 16 MeV SK investigates introduction of Gd salt to detect anti-neutrinos via delayed coincidence using n capture on Gd: –water filtration system is currently designed in Irvine –large-scale test and material effects are studied soon in a especially built test tank next to SK with Gd, SK should see SN relics within ten years DUSEL detector has excellent prospects to measure and study the SN relic signal –must have sufficient photocathode coverage –must have cool enough PMT environment –must have radiopurity DUSEL depth is sufficient with or without Gd