Proton Decay searches -- sensitivity, BG and photo-coverage -- Univ. of Tokyo, Kamioka Observatory Masato Shiozawa
April-25 @ 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) ~2 1 35 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?
April-25 @ NNN5 Large water Cherenkov detectors Super-K 22kton Simulation was done. SK-I: 4% coverage SK-II:19% coverage UNO 44kton Hyper-K 54kton
p e + π @Super-K April-25 @ NNN5 p e + π MC Super-Kamiokande Run 999999 Event 294 12-11-6::6:35 Inner: 3849 hits, 8189 pe Outer: 4 hits, 2 pe (in-time) Trigger ID: x3 D wall: 946.1 cm FC, mass = 99. MeV/c^2 Charge(pe) >15. 13.1-15. 11.4-13.1 9.8-11.4 8.2-9.8 6.9-8.2 5.6-6.9 4.5-5.6 3.5-4.5 2.6-3.5 1.9-2.6 1.2-1.9.8-1.2.4-.8.1-.4 <.1 e + γ γ 91 728 546 364 182 5 1 15 2 Times (ns)
p e + π @Super-K April-25 @ NNN5 Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 p e + π MC Super-Kamiokande Preliminary p e + π MC 2 4 6 8 1 12 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
April-25 @ 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% 1 9 8 7 6 5 4 3 2 1 atmν MC 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 2Mtonyr 2 4 6 8 1 12 Main target Invariant proton is free mass (MeV/c proton 2 ) decays for the tight cut. 1 9 8 7 6 5 4 3 2 1 bind bound proton decay free free proton decay 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 )
Lifetime sensitivity for p e p + π April-25 @ NNN5 1 37 p e+π sensitivity p eπ sensitivity (9%, 3σ CL) Partial Lifetime (years) 1 36 1 35 1 34 1 33 1 32 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 1 2 1 3 1 4 1 5 1 6 Exposure (kton year) Hyper-K 1yrs ~1 35 years@9%cl ~4x1 34 years@3σcl
Reduce photo-sensor cost? April-25 @ 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.
Number of events Number of events 3 25 2 15 1 5 3 25 2 15 1 5 68% April-25 @ NNN5 (1)vertex fitter and (2)ring fitter.1.2.3.4.5.6.7.8.9 1 68% H2O free proton.1.2.3.4.5.6.7.8.9 1 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 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 SK-I 38% 6% 2% 1 2 3 4 5 41% 57% 2% 1 2 3 4 5 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
Number of events Number of events (3)Particle ID and (4)π mass 4 35 showering type non-showering type 3 25 2 15 1 5 SK-I -4-2 2 4 4 35 showering type non-showering type 3 25 2 15 1 5 SK-II -2-1 1 2 Particle ID likelihood p e+π Monte Carlo Number of events Number of events 6 5 4 3 2 1 6 5 4 3 2 1 April-25 @ NNN5 1 2 3 1 2 3 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
Number of events Number of events (5)Proton mass and (6)proton momentum 1 9 8 7 6 5 4 3 2 1 SK-I 6 8 1 12 1 9 8 7 6 5 4 3 2 1 SK-II 6 8 1 12 proton invariant mass (MeV/c 2 ) p e+π Monte Carlo Number of events Number of events 1 9 8 7 6 5 4 3 2 1 1 9 8 7 6 5 4 3 2 1 April-25 @ NNN5 SK-I 2 4 6 SK-II 2 4 6 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
Efficiency in each step p e+π Monte Carlo April-25 @ NNN5 1 detection efficiency.8.6.4.2 DST 2,3ring combined free proton PID π combined free proton decay-e M tot P tot Detection eff. = (4.1+-1.5)% -- SK-I (41.1+-1.5)% -- 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
Total momentum (MeV/c) Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 1 9 8 7 6 5 4 3 2 1 Proton mass vs momentum p e+π Monte Carlo SK-I 2 4 6 8 1 12 SK-II 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 1 9 8 7 6 5 4 3 2 1 April-25 @ NNN5 atmν(bg) Monte Carlo SK-I 2.2Mtyr 2 4 6 8 1 12 SK-II.45Mtyr 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ) (4.1+-1.5)% (41.1+-1.5)% 8ev/2.2Mtonyr 2ev/.45Mtonyr ~1+-7ev/2.2Mtyr Same BG level within 7%
Conclusion April-25 @ 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,
supplements
p e + π @Super-K-I April-25 @ NNN5 Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 AtmνBG MC Super-Kamiokande Preliminary 1 years atmν MC 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ).3 exp d BG Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 data Super-Kamiokande Preliminary 1489 days data 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ) candidate τ p/b(p e + π ) > 5.4 1 33 years (9% CL)
Comparison of data and MC in April-25 @ NNN5 p e + π search 1 5 1 4 1 3 1 2 total momentum (MeV/c) L (938,2) total mass (MeV/c 2 ) 1 2 1 1 Super-Kamiokande Preliminary 1489.2 days 1-1 2 4 6 8 1 12 total invariant mass (MeV/c 2 ) 1 1 1-1 Super-Kamiokande Preliminary 1489.2 days 2 4 6 8 1 12 distance L in mass v.s. momentum plot 16 14 12 1 8 6 4 2 Super-Kamiokande Preliminary 1489.2 days 5 1 15 2 25 3 total momentum (MeV/c)
April-25 @ NNN5 Backgrounds for p e + π search (2) Tight momentum cut to reduce BG Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 atmν MC 2 4 6 8 1 12 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
Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 Analysis for discovery of p e + π Tight momentum cut target is mainly free protons efficiency=17.4%,.15bg/mtyr free proton free proton 2 4 6 8 1 12 Invariant proton mass (MeV/c 2 ) Total momentum (MeV/c) 1 9 8 7 6 5 4 3 2 1 April-25 @ NNN5 bind proton bound proton 2 4 6 8 1 12 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
1 3 1 31 1 32 1 33 1 34 1 35 partial nucleon life time (year) Lifetime prediction April-25 @ 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)
energy reconstruction April-25 @ NNN5 μ momentum/track e momentum 1.5 1.4 1.3 1.2 1.1.99 1.98.97.96.95 1.5 1.4 1.3 1.2 1.1 1.99.98.97.96.95 Full Super-K-I period cosmic ray mu 25 5 75 1 125 15 175 2 Elapsed days from Apr.-1-1996 decay electrons 25 5 75 1 125 15 175 2 Elapsed days from Apr.-1-1996 +-1% ±1% ±1% +-1% Corrected for light attenuation length in water Time variation of E scale ~.9% Number of events 14 12 1 8 6 4 2 π invariant mass 5 1 15 2 25 3 MeV/c 2 E scale difference < 1.8% (decaye, pi, cosmic mu) energy scale uncertainty of neutrino detection < 2.%