Recent results on Atomospheric Neutrino Oscillation from SuperKamiokande

Recent results on Atomospheric Neutrino Oscillation from Super-Kamiokande Yoshihisa Obayashi Kamioka Observatory, ICRR, Univ. of Tokyo for the Super-Kamiokande Collaboration

Super-Kamiokande Imaging Water Cherenkov detector � 50 kt Pure Water � 32 kt Inner Detector viewed by 20 inch PMTs. Num of tubes: � 42 m 11146(SK-I), 5200(-II), 11129(-III, IV) � t~2 m Outer Detector viewed by 1885 8 inch PMTs 1996 - 2002 - 2006 - 2008 - 39. 3 m Mt. Ikenoyama (1396 m) Kamioka, Japan 1000 m (2700 m. w. e. ) SK Jul. 24, 2010 Acrylic (front) + FRP (back) Elec. Upgrade SK-II Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K SK-III SK-IV 2

proton Atmospheric Neutrino p, K, … cosq=1(downgoing) L~15 km cosq=0 m nm cosq=-1(upgoing) L~13000 km nm e ne nm/ne ~ 2 @En<a few Ge. V Jul. 24, 2010 Zenith angle distribution ~Up/Down symmetric (In the case of NO oscillation) Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 3

Event Topology FC � Energy Jul. 24, 2010 PC UP-Stopmu spectrum of neutrino UP-Thrumu Up-going Muons Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 4

Particle Identification Muon Decay Electron � Identify Electron-like(Showering) particles and Muon-like particles using Cherenkov ring Pattern and Angle likelihood Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K DATA MC(ALL) MC(nm CCQE) 5

Zenith angle & lepton momentum distributions n –nt oscillation (best fit) null oscillation momentum e-like SK-I+II+III Preliminary Live time: SK-I 1489 d (FCPC) 1646 d (Upmu) SK-II 799 d (FCPC) 827 d (Upmu) SK-III 518 d (FCPC) 636 d (Upmu) Sub-Ge. V samples are divided to improve sensitivity to lowenergy oscillation effects 6 Jul. 24, 2010

2 -flavor oscillation analysis results SK-I+II+III Preliminary Zenith Physical Region (1 s) m 232=2. 11+0. 11/-0. 19 x 10 -3 sin 22 23>0. 96 (90%C. L. ) L/E Physical Region (1 s) m 232=2. 19+0. 14/-0. 13 x 10 -3 sin 22 23>0. 96 (90%C. L. ) n Results of both zenith angle analysis and L/E analysis are consistent. n SK provides the most stringent limit for sin 2(2θ 23). Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 7

Full 3 -flavor oscillation analysis n. Consider both matter effect and solar term simultaneously. n Matter effect: possible enhancement of ne is expected in several Ge. V energy region and in Earth core 13 and mass hierarchy could be studied. n Solar term: possible enhancement of ne in sub-Ge. V region 23 octant degeneracy could be studied. n Interference: CP phase could be studied. (when sin 2 13 >~0. 05). Difference in # of electron events: Matter effect Solar term Interference (The n flux difference is also expected. ) Full 3 -f osc. analysis: all parameters are considered simultaneously. PRD 81, 092004: either matter effect or solar term is considered with approximations (cannot test the interference part) Jul. 24, 2010 Interference Solar term Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Matter 8

Full 3 -flavor oscillation results - Normal hierarchy. 0035 SK-I+II+III Preliminary 0. 4 . 0035 99% C. L. 90% C. L. 68% C. L. best Excluded by CHOOZ at 90% C. L. . 0015 -. 0035 Inverted hierarchy - . 0035 0. 4 . 0015 1 0 0 . 0015 0. 84 9 0 0. 4 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 0 300 Jul. 24, 2010

Full 3 -flavor oscillation results - Normal hierarchy 2 min = 469. 94 /416 dof SK-I+II+III Preliminary Parameter Best point 90% C. L. allowed 68% C. L. allowed ∆m 223 (x 103) 2. 11 e. V 2 1. 88 - 2. 75 e. V 2 1. 99 - 2. 54 e. V 2 sin 2 23 0. 525 0. 406 - 0. 629 0. 441 - 0. 597 sin 2 13 0. 006 < 0. 066 < 0. 036 CP- 220º - 140. 8 - 297. 3º Parameter Best point 90% C. L. allowed 68% C. L. allowed ∆m 223 (x 103) 2. 51 e. V 2 1. 98 - 2. 81 e. V 2 2. 09 - 2. 64 e. V 2 sin 2 23 0. 575 0. 426 - 0. 644 0. 501 - 0. 623 sin 2 13 0. 044 < 0. 122 0. 0122 - 0. 0850 CP- 220º 121. 4 - 319. 1º 165. 6 - 280. 4º - Inverted hierarchy 2 min = 468. 34 /416 dof n. No significant preference on hierarchy. n. No significant constraint on CP phase at 90% C. L. 10 (sin 2 12 , m 212) are fixed at (0. 304, 7. 66 x 10 -5 e. V 2) Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

Comparison with 2 -flavor analysis Full 3 -flavor (90%) 99% C. L. 90% C. L. 68% C. L. best 2 - 2 min distributions 2 -flavor Full 3 -flavor 2 -flavor (90%) 99%C. L. 90%C. L. 68%C. L. Consistent results are obtained. No deviation of sin 2 23 from 0. 5. Allowed region of m 223 is a bit larger than that of the 2 -flavor analysis as the effect of CP phase is also taken into account. 11 90%C. L. allowed region (1 dof, 2= 2 min+2. 71) Full 3 -flavor (NH) Global-best (1. 88< m 223 <2. 75) e-3 (2. 22< m 223<2. 60) e-3 0. 406 < sin 2 23< 0. 629 0. 401 < sin 2 23< 0. 615 (0. 93 < sin 22 23 ) Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K (0. 95 < sin 22 23 ) Jul. 24, 2010

Comparison of Hierarchies Best fit is in the inverted hierarchy case Normal hierarchy (NH): 2 min= 469. 94/416 dof Inverted hierarchy (IH): 2 min= 468. 34/416 dof ∆ 2 = 1. 6 No significant difference Multi-Ge. V samples tend to favor inverted hierarchy. • NH • IH There also some contributions from Multi-Ge. V like samples favoring IH to NH. 12 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

Search for CPT violation in atm. n � Under the CPT theorem, P(n n) and P(n n) should be same. � Test n oscillation or n oscillation separately. SK-I+II+III Preliminary Neutrino: m 232=2. 2 x 10 -3 e. V 2 sin 22 23=1. 0 Anti-neutrino: m 232=2. 0 x 10 -3 e. V 2 sin 22 23=1. 0 No evidence for CPT violating oscillations is found Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 13

Improvements of the DAQ system IEEE Trans. Nucl. Sci. 57 (2010) 428 SK-I, III: partial data above threshold (Num. of hits) were read (1. 3 sec window x 3 k. Hz) SK-IV: All hits above pulse height threshold are read, then apply complex triggers by software. Periodic trigger PMT signals New Electronics (60 k. Hz) Clock Collect all hits every 17 sec. Event build Precise analysis with variable in parallel in real time windows -time (QBEE) Readout (Ethernet) T 2 K GPS from J-PARC Typical event time windows: Super-Low-Energy (SLE) events (<~6. 5 Me. V): -0. 5/+1. 0 sec high rate (~3 k. Hz) decay electrons Normal events(>~6. 5 Me. V): -5/+35 sec Supernova Relic n (SRN) candidates(>~10 Me. V, No OD): -5/+535 sec neutrons T 2 K events: -512/+512 sec at T 2 K beam spill timing x 5 Wider dynamic range for charge measurement of each channel (>2000 p. C) x 100 No dead time up to ~6 MHz/10 sec for Supernova burst neutrinos Apply precise event reconstruction to remove more low-e BG events in real-time 14 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

Muon Decay Electron Tagging Parent muon t~2 us Decay Electron SK-III (1. 3 us gate width) Expected decay curve Identified data Detection Efficiency = 72. 6% 15 SK-IV (40 us gate width) Expected decay curve Identified data Wider gate width of SK-IV enables detection of muon decay electrons at T~1 us efficiently Detection Efficiency = 88. 4% Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

Zenith angle distributions of SK-IV atm. n SK-IV -like e-like Sub. Ge. V Sub-Ge. V SK-IV 449 days data n –nt oscillation null oscillation Multi-Ge. V PC Stable Data taking! 16 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

SUMMARY � Recent update on Atmospheric neutrino oscillation from SK-I, III 2 Flavor nm-nt oscillation result � Full 3 Flavor including Solar term & CP, Mass Hierarchy “Consistent with 2 flavor result, No preference of Hierarchy � CPT violations search “No evidence” � � Electronics Upgrade (SK-IV) Improvement on Decay-electron tagging efficiency � Stable Atmospheric neutrino data taking � � Super-Kamiokande Talk/Posters M. Miura(Nucleon decay) 24 -Jul-2010 09: 20; BSM Session � H. Sekiya(Solar neutrino) Poster � M. Smy (Low-energy anti neutrino detection) Poster � Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 17

BACKUP SLIDES

nt appearance search Likelihood variables (Downward going) Data BKG MC Tau MC PRL 97, 171801 (2006) t-like selection; efft=43%, S/N=5% multi ring t nt decay-e (a) Visible Energy (b) Max. decay-e distance from vertex (c) Ring Candidates (d) Sphericity in the lab frame (e) Clustered sphericity in COM frame Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 19

nt appearance search PRL 97, 171801 (2006) zenith angle distribution of tau enrich sample � Best-fit tau excess: 138+/-48(stat. )+15/-32(syst. ) � Expected: 78+/-26(syst. ) (Likelihood) tau enrich sample is consistent with n -nt oscillation Jul. 24, 2010 Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 20

Kamiokande History � 1983 � 1987 1991 1996 1998 � � 1999 2001 2002 � 2006 � 2008 � � � 21 2009 Kamiokande started observation to search for Proton decay Kamiokande observed SN 1987 a Construction of SK started observation “Evidence for oscillation of atmospheric neutrinos” K 2 K started Accident Partial reconstruction SK-II started K 2 K-II started (-2004) Full reconstruction SK-III started Replacement of DAQ electronics SK-IV Started T 2 K started SK hall excavation(1994) Filling water (1996) “Evidence…”(1998) Accident(2001) SK-II starts soon(2002) SK-III starts soon(2006) Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K Jul. 24, 2010

Kamioka Underground Site Kam. LAND (Tohoku Univ. ) XMASS (Mar. 2008~) CANDLES (Mar. 2008~) Super-Kamiokande 40 m Atotsu Entrance IPMU APIMS GC Ge det. Rn det. … (Mar. 08~) Jul. 24, 2010 Gadolinium project R&D (10 mx 15 mx 8~9 mh, March 2010~) CLIO (Gravitational Wave) Laser extensometer (Geophysics) NEWAGE Superconductive gravimeter Yoshihisa OBAYASHI, Atmospheric Neutrino from Super. K 22