APS/JPS Joint Meeting Kapalua, Maui, September 2005 Michael Smy UC Irvine Relic Neutrino Detection in Large Water Cherenkov Detectors

SK-ISK-II Time Period Apr  Jul Dec  Oct Live time1496 days791 days # of PMTs11146 PMTs5182 PMTs Fid.volume22.5 kt Energy Range MeV Michael Smy, UC Irvine Relic in Super-K atm.  → stealth  ± →e ± relic ’s spallation products from cosmic  ’s

Spectrum fitting in SK-I free parameter  = 0.0 : factor of SRN  = 1.30±0.2 : factor of ν e  = 0.45 ±0.1 : factor of ν μ  2 = 7.2 / 13 d.o.f Visible energy [MeV] SK-I preliminary Courtesy Iida, ICRR

Spectrum fitting in SK-II Visible energy [MeV] SK-II free parameter  = 0.0 : factor of SRN  = 0.76±0.2 : factor of ν e  = 0.51 ±0.1 : factor of ν μ  2 = 10.4 / 13 d.o.f ※ In SK-II, spallation BG is remaining in the first energy bin due to worse energy resolution. Number of remaining spallation is estimated from quality of rejected spallation events. preliminary Courtesy Iida, ICRR

Current SK Flux Limit SK-II limit: < 3.68 /cm 2 /sec SK-I limit: <1.25 /cm 2 /sec SK-I/II Limit: < 1.08 /cm 2 /sec preliminary revised in NNN05 Courtesy Iida, ICRR

Possible Improvements Enlarge Exposure: Increase Fiducial Volume; add SK-III, IV Reduce Deadtime and Efficiency of Nuclear Spallation Tagging Lower Analysis Threshold Detect Neutrons

Preliminary E-Scale correction D inc [cm] E corr / E true  Energy scale correction done using the `D inc ’ variable F(x) = P 1 e P 2 x + P 3 P 1 = ± P 2 = ± P 3 = ± X 2 = 1.1, 19 d.o.f Fitting function θ inc D inc E recon D wall Inner Detector wall E corr / E true 100 < wallsk < 200: mean  500 < wallsk < 1000: mean  After Corr: D wall Before Correction: D inc Courtesy Iida, ICRR

Position Resolution vs. D wall Fid V D wall [cm] Position resolution [cm] Red : 20MeV Green: 30MeV Blue : 50MeV ・ Resolution means 68% in  r distribution. ・ 50-70cm resolution for all energies. ・ Good position resolution out of fid V!! SK-II MC, 20MeV, 10000events Courtesy Iida, ICRR

Result after effwall cut After various cut, event rate becomes flat in D wall After various cut, event rate becomes flat in D wall Energy spectrum is consistent with expected Michel spectrum Energy spectrum is consistent with expected Michel spectrum Signal increase 15.6% (volume increase is 21%) Signal increase 15.6% (volume increase is 21%) After various cut, event rate becomes flat in D wall After various cut, event rate becomes flat in D wall Energy spectrum is consistent with expected Michel spectrum Energy spectrum is consistent with expected Michel spectrum Signal increase 15.6% (volume increase is 21%) Signal increase 15.6% (volume increase is 21%) D wall [m] Event rate [event / m 3 / 2.5y] Effwall cut efficiency is corrected. Visible Energy [MeV] Data Decay-e MC E correction is applied. F(x) is tuned for 20MeV Courtesy Iida, ICRR

The Best Way to Cut Spallation Events From MACRO 23rd International Cosmic Ray Conference, Vol. 4, Edited by D.A. Leahy, R.B. Hickws, and D. Venkatesan. Invited, Rapporteur, and Highlight Papers. Singapore: World Scientific, 1993., p.391 Vertical muon intensity (cm -2 s -1 sr -1 ) standard rock h gcm -2 Go Deep!

Improvement of Spallation Tagging PMT entry position muon photons from muon interaction spallation occurs here Qpeak sum of 10 bins around peak projected position of spallation product distance along muon track in m 11 new 3D tag: predict spallation point along  track PMT times &  track fit to reconstruct point of emission Q histogram of such points, peak predicts point of spallation Courtesy K. Bays, UC Irvine

This Really Works: A Simple Example 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

13 L LONG (random,red) L LONG (spallation,black) L TRAN (spallation,black) L TRAN (random,red) dt (spallation,black) dt (random,flat,red) Q PEAK (spallation,black) Q PEAK (random,red) Likelihood Method x10 pe Courtesy K. Bays, UC Irvine

Removal of Spallation Deadtime 18% (Compared to 37% in Publication) Further Tuning in Progress… 14 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

Current SK Flux Limit SK-II limit: < 3.68 /cm 2 /sec SK-I limit: <1.25 /cm 2 /sec SK-I/II Limit: < 1.08 /cm 2 /sec preliminary revised in NNN05 Courtesy Iida, ICRR

Future SK Flux Limit SK-II limit: ≈ 2.9 /cm 2 /sec SK-I limit: ≈ 1 /cm 2 /sec SK-I-III Limit: ≈ 0.75 /cm 2 /sec revised in NNN05 Courtesy Iida, ICRR SK-III limit: ≈ 1.6 /cm 2 /sec

Neutron Tagging (with Gd) e

Mimic ν e +p→e + +n with α+ 9 Be→ 12 C * +n n+p→…→n+Gd→Gd+γ’s(Σ=8 MeV) 12 C * → 12 C+γ(4.4 MeV) 0.2% GdCl 3 Sol. in Source:  n =28% 0.2% GdCl 3 Sol. in all SK:  n =90% Am/Be/GdCl 3 -Sol. n Correlation Source detect by BGO Φ=13 cm Φ=18 cm 18 cm 5 cm BGO 0.2 % GdCl 3 Solution Am/Be Courtesy Watanabe, ICRR

Preliminary Results dR < 2m yields 90 % efficiency 2-component t-fit: f(t) = p 1 e -t/p 2 +p 3 e -t/p 4 +p 5 (Ther. n’s leave source, return & capture on Gd. with τ =20μs) dR [cm] Number of Events 91.9% 95.1% Data MC dT [μs]dT [×10-3 sec] Data MC Courtesy Watanabe, ICRR

Energy Spectrum of n Capture Mean Value ~ 4.7 MeV in Data & MC Number of Events Energy [MeV] MC Data Red: Trig. Eff. Included. Red: E > 4 MeV Courtesy Watanabe, ICRR

Measure Water Transparency Michael Smy, UC Irvine

GdCl 3 Solution pure H 2 O0.2%GdCl 3 pure H 2 O0.8%GdCl 3 337nm(~67m)125.8±5.9m27.74±0.26m 360nm(~90m)210±21m33.00±0.23m 405nm140.0±4.8m106.5±3.3m134.2±6.6m66.8±0.9m 478nm107.4±7.9m94.4±8.0m65.1±5.6m69.8±3.2m 532nm26.01±0.74m26.60±0.81m21.54±0.63m21.08±0.51m 595nm6.253±0.021m6.242±0.027m6.402±0.015m6.422±0.014m 650nm2.840±0.012m2.853±0.002m2.821±0.007m2.864±0.004m Michael Smy, UC Irvine

Super-Kamiokande: Reach down to 3MeV! Online Vertex Fitting + Prefilter: Need ~50 CPU’s Michael Smy, UC Irvine Intelligent Very Low E Trigger PMT photons from vertex 4-hit Combin. Vertex

4.4MeV LINAC threshold>9 4.4MeV LINAC threshold>9 Michael Smy, UC Irvine

Lessons from SK for a 100kton Detector go deep! spallation background best removed by depth as much photocathode coverage as possible: energy resolution is crucial need good calibration system for energy scale design detector with neutron tagging to distinguish stealth muon decays from signal don’t choose exact cylinder; flat surfaces are bad for low energy event reconstruction sophisticated trigger with very low threshold needed Michael Smy, UC Irvine