Proton Decay Physics Poten/al

Transcription

1 Proton Decay Physics Poten/al Can a discovery s/ll be made? What size would be needed to make a reasonably sensi/ve experiment? Why this experiment? R.Svoboda, LBNL, May

2 Proton Decay: Is Normal Ma+er Stable? LHC unifica/on energy Three of the four forces of nature are thought to become similar in strength at very high energies far above any conceivable accelerator Simple unifica/on theory ruled out by data proton decay is an effec/ve way to test such theories >1.4x10 34 years (TAUP 2013)

3 New theories (e.g. SUSY) can push up unifica/on scale But new decay modes now predicted Example of a possible proton decay through supersymmetric par/cles. Observa/on of virtual processes like proton decay is our only known way to access physics at these energies

4 Current Limits

5 The Stability of the Proton con$nues to be one of the biggest ques/ons in Par/cle Physics Tests a fundamental, but unexplained conserva/on law Hallmark of Grand Unified Theories Extension of the idea of running coupling constants Broad connec/on with theory at many levels: strings, extra dimensions, etc. Explores a region forever inaccessible to accelerators If SUSY is not found at LHC, may be only way to search for it for foreseeable future What are limifng factors?

6 63% E.Kearns, ISOUP MeV KAON IS INVISIBLE! Hyper- K PMT coverage 108 MeV, β=0.82 (C threshold is 0.75) 21%

7 LENA Low Energy Neutrino Astronomy 152 MeV τ(k+) = 12.8 ns 108 MeV 18 ns no problem! 5 ns a problem ε = 0.65

8 Background from atmospheric neutrinos background in vicinity of ROI Use of PSD to separate muons from Kaons can we do this beger (or at least as good) with Cherenkov/scin/lla/on? Along with ~100% efficient energy cut you get a background of 0.064/yr/50kT

9 pg νk + in WbLS 105 MeV K+ energy does not require very much light, however picking out the muon decay at short /mes must improve with more scin/lla/on K+/µ separa/on from PSD will depend on amount of light and /ming (worse than LENA) Cherenkov/scin/lla/on light could be a powerful handle (~zero for K+, ~2-3 for muon?)

10 Only a small amount of WbLS is needed to see the 105 MeV K+

11 WATCHMAN compeffve with other direct K+ detecfon experiments WbLS 60 kt 10 yr

12 50 kt Consistent with plot from LENA paper

13 Pà e + π 0 in Water Cherenkov Mton- years exposure (M.Shiozawa, TAUP2013) Atmospheric Neutrino Background SIGNAL but expected atmospheric neutrino background is 0.7 events measurements done by the K2K experiment. This mode will be background limited in future detectors.

14 Neutron Tagging It is expected that proton decay will not produce neutrons in the final state WbLS would give neutron tagging, maybe not necessary to load with Gd?

15 Note: Proton Decay in water makes No Neutrons 2/10 of protons are free protons. No neutrons. 2/10 of protons are in P 1/2 shell. If they decay nucleus is already in the ground state. No neutrons 4/10 of protons are in P 3/2 shell. If they decay then a P 1/2 proton will drop down, giving a 6 MeV gamma. No neutrons. ~80% of proton decays should give neutrons only indirectly from FSI. Detailed calcula/on gives 81% (Eijiri, PRC 48, 1993) ATMOSPHERIC NEUTRINO EVENTS THAT MIMIC PROTON DECAY CAN BE REJECTED BY NEUTRON TAGGING

16 Will Proton Decay Result in Neutrons?

17 Theory predicts inclusive neutron de- excita/on branching ra/o of ~8%. Most proton decays should not have neutrons. (0.08*0.8 = 6.4% in water) H.Ejiri PRC 48 (1993)

18 Effects of Atmospheric Neutrino Background RejecFon on pg e + π 0 sensifvity 0.5 Megaton with neutron tagging (rejects 90% of atmospheric neutrinos) 0.5 Megaton with background Super- K with background 60 kton detector will not do much here year

19 R.Svoboda, 17 May 2014

20 Conclusions KT per KT, in principle WbLS should have similar efficiency and background for LS when it comes to K +ν mode Many caveats What about other modes with neutron tagging? For neutron detec/on, WbLS would mean that Gd- loading not necessary. This would help to reject background For modes like e+ π0, beger to do HK

21 Backup

22 "Texas" PMT's ü Currently, only Hamamatsu produces PMT's for use in physics experiments. Lack of compe//on results in higher costs, dependence on yen/dollar ra/o, and necessity to send HEP$ overseas for in many experiments ü NSF S4 program includes development of alterna/ve domes/c supplier of PMTs. This program will end next year auer delivery and tes/ng of ~20 11" prototype PMT's from ADIT/ETL, in Sweetwater Texas. This same company owns Ludlum Instruments and Eljen and has purchased Electron Tubes, Limited.