Proton Decay searches -- sensitivity, BG and photo-coverage. Univ. of Tokyo, Kamioka Observatory Masato Shiozawa

Transcription

1 Proton Decay searches -- sensitivity, BG and photo-coverage -- Univ. of Tokyo, Kamioka Observatory Masato Shiozawa

2 NNN5 Water as a proton decay detector Source H 2 O 2/1 free proton no nuclear effect, accurate&high detection efficiency no Fermi motion, good momentum valance.54megaton(hyper-k) ~ protons Good detector performance Vertex resolution: 3 cm (1-ring) :~2 cm(p e + π ) Trigger threshold: 5 MeV electrons trigger ε=1% for most of nucleon decay modes Energy resolution: 3~4% for e, μ Particle ID : 99% 1-ring 1 μ,, e : ~95% p e + π,p μ + π These performance is achieved in Super-K-I, 4% photocoverage. Question: can we reduce photo-coverage? Keeping the excellent performance?

3 NNN5 Large water Cherenkov detectors Super-K 22kton Simulation was done. SK-I: 4% coverage SK-II:19% coverage UNO 44kton Hyper-K 54kton

4 p e + NNN5 p e + π MC Super-Kamiokande Run Event ::6:35 Inner: 3849 hits, 8189 pe Outer: 4 hits, 2 pe (in-time) Trigger ID: x3 D wall: cm FC, mass = 99. MeV/c^2 Charge(pe) > <.1 e + γ γ Times (ns)

5 p e + NNN5 Total momentum (MeV/c) p e + π MC Super-Kamiokande Preliminary p e + π MC Invariant proton mass (MeV/c 2 ) Criteria for p e + π 2 or 3 Cherenkov rings All rings are showering 85 < Mπ M < 185MeV/c 2 (3-ring) No decay electron 8 < M proton < 15 MeV/c 2 total < 25 MeV/c P total ε = 4 % in SK-I

6 NNN5 Tight momentum cut for p e p + π Total momentum (MeV/c) P tot < 25 MeV/c, BG2.2ev/Mtyr, eff=44% P tot < 1 MeV/c, BG.15ev/Mtyr, eff=17.4% atmν MC Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) Total momentum (MeV/c) Mtonyr Main target Invariant proton is free mass (MeV/c proton 2 ) decays for the tight cut bind bound proton decay free free proton decay Invariant proton mass (MeV/c 2 )

7 Lifetime sensitivity for p e p + π NNN p e+π sensitivity p eπ sensitivity (9%, 3σ CL) Partial Lifetime (years) HK 1years SK-I limit 92ktyr 5.4 x 1 33 yrs (9%CL) Normal cut, 9%CL 3σ CL Tight cut, 9%CL 3σ CL Exposure (kton year) Hyper-K 1yrs ~1 35 years@9%cl ~4x1 34 years@3σcl

8 Reduce photo-sensor cost? NNN5 sensor cost is a significant part of total cost. in case of Hyper-K 1$(1/3xSK) x 2,(4% coverage) = 2M$ important to understand minimum requirement of photo- coverage from each physics topics (p e+ e+π in my talk) SK-II (19% coverage SK-I I 4%) ) is a good opportunity to investigate physics sensitivity with reduced photo- coverage well tuned SK-II detector simulation fitters (vertex,ring#,particle( ID,momentum ) ) are also well tuned and calibrated. reliable study is possible.

9 Number of events Number of events % NNN5 (1)vertex fitter and (2)ring fitter % H2O free proton dist. btw reconstructed and true vertex (m) p e+π Monte Carlo SK-I(4%c) SK-II(19%c) Number of events Number of events SK-I 38% 6% 2% % 57% 2% Number of rings SK-II 19.7cm(68%) 21.8cm(68%) Almost same performance Efficiency(74% for 2-3rings) doesn t change Fraction of 3ring slightly decrease

10 Number of events Number of events (3)Particle ID and (4)π mass 4 35 showering type non-showering type SK-I showering type non-showering type SK-II Particle ID likelihood p e+π Monte Carlo Number of events Number of events NNN π invariant mass SK-I SK-II PID performance; 94-95% 96% for free proton decay π mass resolution; 22.1MeV 24.MeV free proton 2.2MeV 28.5MeV

11 Number of events Number of events (5)Proton mass and (6)proton momentum SK-I SK-II proton invariant mass (MeV/c 2 ) p e+π Monte Carlo Number of events Number of events NNN5 SK-I SK-II total proton momentum proton mass resolution; 33.8MeV 42.3 free proton 28.5MeV 35.2 proton mom. resolution; 177MeV(68%) 171 free proton 81MeV(68%) 83

12 Efficiency in each step p e+π Monte Carlo NNN5 1 detection efficiency DST 2,3ring combined free proton PID π combined free proton decay-e M tot P tot Detection eff. = ( )% -- SK-I ( )% -- SK-II SK-I SK-II Same efficiency within 1% level A B C D E selection criteria Slightly worse resolution of π and proton mass

13 Total momentum (MeV/c) Total momentum (MeV/c) Proton mass vs momentum p e+π Monte Carlo SK-I SK-II Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) Total momentum (MeV/c) NNN5 atmν(bg) Monte Carlo SK-I 2.2Mtyr SK-II.45Mtyr Invariant proton mass (MeV/c 2 ) ( )% ( )% 8ev/2.2Mtonyr 2ev/.45Mtonyr ~1+-7ev/2.2Mtyr Same BG level within 7%

14 Conclusion NNN5 Water Cherenkov detector is a excellent detector for p e + π searches. detailed comparison btw 4% and 2% coverage same p e p + π efficiency even with 2% coverage slightly worse mass resolution 1% coverage maybe acceptable need further studies on other decay modes, like p ν+k +, e + +K,

15 supplements

16 p e + NNN5 Total momentum (MeV/c) AtmνBG MC Super-Kamiokande Preliminary 1 years atmν MC Invariant proton mass (MeV/c 2 ).3 exp d BG Total momentum (MeV/c) data Super-Kamiokande Preliminary 1489 days data Invariant proton mass (MeV/c 2 ) candidate τ p/b(p e + π ) > years (9% CL)

17 Comparison of data and MC in NNN5 p e + π search total momentum (MeV/c) L (938,2) total mass (MeV/c 2 ) Super-Kamiokande Preliminary days total invariant mass (MeV/c 2 ) Super-Kamiokande Preliminary days distance L in mass v.s. momentum plot Super-Kamiokande Preliminary days total momentum (MeV/c)

18 NNN5 Backgrounds for p e + π search (2) Tight momentum cut to reduce BG Total momentum (MeV/c) atmν MC Invariant proton mass (MeV/c 2 ) P tot < 25 MeV/c P tot < 1 MeV/c BG events in signal box 3 events/2 Mton yr ~.15 events/mton yr

19 Total momentum (MeV/c) Analysis for discovery of p e + π Tight momentum cut target is mainly free protons efficiency=17.4%,.15bg/mtyr free proton free proton Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) NNN5 bind proton bound proton Invariant proton mass (MeV/c 2 ) No Fermi momentum No binding energy No nuclear effect Small systematic uncertainty of effici High detection efficiency Perfectly known proton mass and moment

20 partial nucleon life time (year) Lifetime prediction NNN5 p p Dimension=6 (2 fermion 2 fermion) + e 4 5 u u d g m Γ = p M 4 X : τ ( p e+ π ) = 1 ~35? years Dimension=5 (2 fermion - 2 sfermion) q ~ ν h 4 m 5 u u d w ~ X q ~ H ~ C d d s d π Κ + Γ = p M 2 M 2 Hc X : τ ( p νk + ) = 1 29~39? years minimal SU(5) minimal SUSY SU(5) Super-K SUSY SO(1)

21 energy reconstruction NNN5 μ momentum/track e momentum Full Super-K-I period cosmic ray mu Elapsed days from Apr decay electrons Elapsed days from Apr % ±1% ±1% +-1% Corrected for light attenuation length in water Time variation of E scale ~.9% Number of events π invariant mass MeV/c 2 E scale difference < 1.8% (decaye, pi, cosmic mu) energy scale uncertainty of neutrino detection < 2.%