Proton Decay: A Giant Orphan in Particle Physics

Transcription

1 Proton Decay: A Giant Orphan in Particle Physics Stony Brook University and Universitat Autonoma de Barcelona SLAC Summer Institute August 1, 2005

2 A Long Time Ago 1929: Weyl suggests absolute stability of proton 1938: Stuckelberg and 1949: Wigner postulate existence and conservation of a heavy charge (baryon number) associated w/ heavy particles 1954: M. Goldhaber (w/ Reines and Cowan, Jr.) publishes the first experimental result on proton lifetime inspired by Continuous Creation theory using a liquid scintillator detector (shielded w/ paraffin+lead) containing ~3x10 28 protons, he obtains lower limits on τ p τ p > years (for free protons) τ p > years (for bound nucleons)

3 M. Goldhaber and W. Pauli (1958 at BNL) Mr. Radioactive, I think protons decay. You cannot be serious! You must be more desperate than I was.

4 Reines-Cowan Experiment

5 Sometime in Early 1970 s Pati-Salam Model of Grand Unification I don t think so. Experimental results Prof. Salam, Indicate otherwise. my GUT feeling is that Let me think about it protons must decay. Some months later My GUT feels the same. Let s publish it.

6 Electricity Magnetism} Terrestrial Celestial } Einstein s s Dream: Unification of All Particle Interactions QED }Unified (EM Interaction) Electro-weak }Grand Unification Weak theory theory Theories Can all (GUTs) the + Supersymmetry QCD forces in } (Strong Interaction) nature be Gravitation form? Standard Model (SM) = Unified Electro-weak theory + QCD (not a truly unified theory) Super- String/M unified in one To realize this dream we need experimental breakthroughs such as: Proton decay SUSY particles Extras dimensions Theory (?)

7 Search for Proton Decay Quest for Grand Unification the next step In SM, protons (practically) do not decay ==> Baryon number conservation law -->Accidental or approximate GUT models (SU(5), SO(10), E 6...) ==> Quark-Lepton unification ==> Color-charge quantization ==> Coupling constant Unification (SUSY GUTs) ==> predict decay of protons (generic prediction) Proton decay - only direct experimental access to GeV (10-30 cm) scale ==> Truly an energy frontier experiment ==> identified as one of the most important issues to be resolved Many national committees

8 SU(5) by Georgi and Glashow (1974)

9 matter p Decay mechanisms { dominated by the dimension=6 op. gauge boson mediated decays d u u u d u Predictions Proton Decay in SU(5) By Georgi and Glashow (1974) X Y anti-matter e + u u e + u u } π0 u u X d u d Y u (X ±4 / 3, Y ±1/ 3 : new gauge bosons) e + d d e + u u " (p # e + $ 0 ) B = 4 x 10 29±1.7 years, B (p # e + $ 0 ) % 40 ~ 60 % " B (p # e + $ 0 ) > 1.2 x yrs (IMB (+Frejus) Lower C.L.) 5.4 x yrs (current SuperK Lower C.L.) ==> Complete exclusion of minimal SU(5) model

10 Proton Decay Detectors IMB Kamiokande Super-Kamiokande Soudan

11 Current Status So far, no evidence for proton decay However, there are tantalizing hints for unification Small but finite neutrino mass see-saw mechanism? Convergence of the running coupling constants Especially with supersymmetry SUSY Breaking SM MSSM M GUT = ~ 2x10 16 GeV (?)

12 SUSY GUTs Unification scale higher than non-susy-guts (M x ~ 2 x GeV) suppression of gauge boson mediated decay! (p " e + # 0 % ) $ ' M X (* 4 B & 2x10 16 x 10 36±1 years GeV) dominated by the D=5 op. (color Higgs triplet, q=1/3) mediated decays µ u! { p d W s K u c } + u! 3 M3 ~ 3 x GeV, M susy ~ 1 TeV " (p # K + ' * $ ) % ' M * ) ~q, ), B ( &H + ) ( 1TeV, + x9x10 31 years (& H : hadronic matrix element in GeV 3 ) highly model dependent 2 2 ' M * 3 ' ) ( 10 16, 2tan& * ), GeV+ ( + 2

13 continue: SUSY GUTs Recent Developments β H = ± (10-20%) GeV 3 (New lattice QCD calculation) α s (M Z ) = ± (PDG 2000) smaller than before (smaller M x ) Limit on tanβ (> ~3-4, most recent results) all make the proton lifetime shorter! (p " e + # 0 % ) $ ' 2.5 (* 2 %' 0.04 (* 2 %' M X (* 4 B & A R ) & +GUT ) & x years GeV) within experimental reach (Marciano) " B (p # K + & $ )% M 2 & 2 ( q ( M3 ( 1TeV ( x10 30 years GeV ( ' ) *, years The current SuperK limit: τ (ν K) > 2.3 x yrs (new) ' ) + + *

14 SUSY GUTs Current SuperK limit τ/b (p ν K) > 2.3 x yrs (new) Many models may have been already ruled out! Discovery is around the corner! Especially MSSM SU(5) is considered to be ruled out (See: H. Murayama & A. Pierce, Phys.Rev.D65:055009,2002, hep-ph/ )) proton decay limits provide most stringent restrictions to SUSY (recall R-parity conservation) Some say SUSY-SO(10) models are also in trouble. But

15 Proton Decay in non-gut Models Proton Decay in Intersecting D-brane Models, I. Klebanov and E. Witten, hep-th/ one of the first few testable calculations/predictions based on string theory τ/β predicted (D=6 operators) = ~10 36 years (assuming M GUT = 2x10 16 GeV) Probing the Plank Scale with Proton Decay, R. Harnik,, D. T. Larson, H. Murayama,, and M. Thormeier,, hep- ph/ Proton decays in models with a string-inspired anomalous U(1) X family symmetry Proton decays probes Plank scale rather than GUT scale Predicted proton lifetimes similar to the GUT model predictions Proton decay on the Top Ten most important issues listed by string theorists

16 Super-Kamiokande Kamiokande-I Experiment 50 kton Water Cherenkov Detector -- Inner Detector (ID) w/ 11, PMTs -- Outer Detector (OD) w/ 1,840 8 PMTs -- 40% Photocathode coverage Super-Kamiokande Detector (built for proton decay searches) Electronics Hut Research Goals Proton decay searches Solar neutrinos Atmospheric neutrinos Astrophysical neutrinos ==> neutrino oscillations 41.4 m OD ID 39.4 m Kamioka Mine in Japan The Collaboration ~120 physicists 23 institutions from Japan and US

17 SuperK Photos SuperK Inner Detector Half Filled with Water ~Feb Outer Detector ~October 1995

18 Water Cherenkov Detector Technique cosθ = 1/nβ, n(water) = 1.33 β(threshold) = 1/n, θ(max)= 42 o P(threshold) ~ 1.14 mc p--> e + π 0 Photo-cathode Dinode Anode Q, t Photo-electron Cherenkov Photon

19 PMT Glass Blowing

20 p e + π 0 Decay Event Signature selection criteria 2,3-ring, all e-like no Michel electron 85<m π <185MeV/c 2 ( 3-ring) p p <250MeV/c 800<m p <1050MeV/c 2

21 p e+ π0 search in SuperK p e+ π0 MC 41% Signal efficiency atm ν BG MC 0.3 expected Background data 0 candidate in Data τ/b(p e+π0)䠐 years 䟺90%CL, w/ SK-I 1489 days data) τ/b(p e+π0)䠐 years 䟺90%CL, w/ SK-II 421 days data)

22 p K + ν Decay Event Signature 16 O νk +15 Nγ,, K + µ + ν search (SK-I) selection criteria 1 µ-like ring 1 Michel electron 210 < p µ +< 260MeV/c proton rejection cut 7<N hitγ <60

23 p K + ν search in SuperK efficiency = 8.6% 0.7 exp d BKG 0 candidate Other K + decay modes searhes: p νk +, K + π + π 0 p νk +, K + µ + ν (no γ tagging) three searches combine τ/b(p νk + ) years 90%CL

24 Summary Proton Decay Search Results

25 Why a Next generation Nucleon decay and Neutrino (NNN) Experiment? Non-zero Neutrino Masses In SM, neutrino masses are assumed to be zero In many of the GUT Models (especially in SO(10)), small neutrino masses are predicted through Seesaw Mechanism 2 m(! i ) = m Di M m Di : M : (M >> m Di ) Dirac mass of charged fermion Majorana mass of ν R depends on the mass scale of the models Thus, observation of small non-zero neutrino mass could lead us to the physics of very high mass scale, which in turn could lead us to proton decays Super-Kamiokande observation of the non-zero neutrino mass ==> could be the first evidence for Grand Unification ==> Motivation for renewed effort for proton decay searches

26 1998 Neutrino Revolution and Physics Goals for NNN Experiments Neutrino Oscillations Super-Kamiokande+Atm exps +SNO+Solar exps Non-zero Neutrino Mass See-saw Mechanism Non-zero Neutrino Mixing Grand Unification Proton Decay Large Underground Detectors Lepton Mixing Matrix K2K, MINOS, CNGS, T2K Superbeams, (Betabeams) LMA solution, sinθ 13 0 Supernova CP Violation in Lepton Sector Superbeam, Neutrino Factories Lepto-Genesis Matter-antimatter Asymmetry Majorana Phase CPV? in the Universe

27 NNN Underground Detector Current Proposals and Ideas Water Cherenchov Detectors 3-M, Hyper-Kamiokande, Mton-Frejus, UNO Liquid Argon Detectors 100kton-Europe, LANDD Liquid Scintilator Detectors LENA (a la SciPIO) Magnetized Iron Detectors INO (India-based Neutrino Observatory: a la MONOLITH) Focused on atmospheric neutrinos detection

28 Future Large Water Cherenkov Detectors

29 Design Considerations Goal: physics capability detector cost Topology and Size Light attenuation length limit in pure water: ~80 m at 400 nm PMT pressure limit: ~6 atm (60 m of water) Largest possible width of underground cavity: ~60 m Single largest active module size: ~60m x 60m x 60m PMT (photocathode) coverage Need relatively high coverage (~ 40%) for low energy physics (solar and SRN), and 6 MeV γ detection from p K + ν in oxygen Need fine granularity for LBL ν e appearance experiments to reject π 0 background

30 Continue: Design Considerations Number and size of the modules for a fixed fiducial volume Module size detector cost Larger surface area to fiducial volume ratio Requires more PMTs Smaller fiducial to total volume ratio Need more drifts and auxiliary/service space typically excavation costs for drifts are more expensive than for large volume excavation Module size Energy Containment especially crucial in atm nu studies, such as L/E study Module size Pattern Recognition Capability (with same photocathode coverage) Keep the module size as large as possible

31 Depth cosmogenic background Detector Site Issues rock instability rock temperature detector cost Optimal Depth ~4000 mwe (~5000 ft) Driven by the SRN search and Solar nu study Reduce spallation background also reduce the risk of possible unknown B.G. to PDK searches at shallow depths minimize detector dead time keep some amount of cosmic rays for calibration purposes Distances from Major Proton Accelerator Labs Different baselines present vastly different physics potential

32 UNO Detector Conceptual Design A Water Cherenkov Detector optimized for: Light attenuation length limit PMT pressure limit Cost (built-in staging) UNO Collaboration 99 Physicists 40 Institutions 7 Countries 40% 10% Only optical separation 60x60x60m 3 x3 Total Vol: 650 kton Fid. Vol: 440 kton (20xSuperK) # of 20 PMTs: 56,000 # of 8 PMTs: 14,900

33 US DUSEL Candidate Sites and Potential Superbeam Experiments Icicle Creek Henderson Homestake 1720 km San Jacinto 1315 km 1500 km 2760 km Soudan 730 km 2875 km 1720 km 2560 km FNAL BNL Kimballton WIPP

34 Henderson Mine Location (Empire, Colorado) Henderson Mine Airport ~60 miles Denver

35 Vast Infrastructure #2 shaft Red Mt. Mill Site ~10 miles Existing tailing site and all necessary environmental permits Henderson 2000 modernization project: ~$150M

36 Vast Infrastructure High speed conveyor Harrison Mt. ~12,300 ~1,800 ft Mining Area

37 Henderson Conveyor and Rock Crusher

38 Henderson DUSEL Conceptual Design Harrison Mountain Elev. 12,300 ft Red Mountain Elev. 12,300 ft Central Campus Elev ft, (4200 mwe) Midway Campus Elev ft, (5100 mwe) Lower Campus Elev ft. (6000 mwe) Shaft pristine rock Silver Plume Granite Internal Shaft Urad Porphyry Upper Campus 1&2 Elev ft, (2500 mwe) Elev ft, (3100 mwe) Access Ramps Primos Porphyry Henderson Granite Red Mountain Porphyry Henderson Orebody Silver Plume Granite perturbed rock 7500 Level 7065 Level EarthLab/ Geoscience Area

39 Hyper-Kamiokande Current Design 2 detectors with 5 modules each 2 X (48m 50m 250m), Total (Fiducial) vol. = 1 (0.54) Mton 20% photocathode coverage DOS?

40 Hyper-K Candidate Site: Tochibora Mine -60M-130M-200M-250M-300M-370M?BŒû180M40M4?BŒû80M4?BŒû ª?BŒû?BŒû O??Î?BHW?Î?BFW?Î?B4?Î 1??Î?B3??Î?B-340M?H?ìƒsƒbƒg j?ó?º Eƒuƒ?ƒbƒN32??BOP10M Ê?BŒû 1,156 m Super-K (Depth:2700mwe) 480 m Hyper-K 295km JHF Hyper-K (Depth: mwe, not decided yet ) (Tochibora-mine of the Kamioka mining company) Physics focus: CPV, proton decay, supernova burst

41 1Mton Class WC Detector at Fréjus 130 km TRES? Fréjus New safety tunnel Current tunnel Considered in conjunction w/ an ambitious CERN Physics with a MMW proton source initiative Window of opportunity with the planned new safety tunnel construction Variety of detector design is considered: 3 detectors, UNOlike detector, etc.

42 No proposals for Cuatro Nueve Detectors, yet! However

43 3M Detector at Homestake Mine 10 cylindrical detectors (50m x 50mφ), 100 kton each Total (Fiducial) vol.: 1 (0.8) Mton No veto region 10% photocathode coverage 3M at 6950 level DIEZ?

44 UNO Physics Goals Nucleon decay Supernova Neutrinos Atmospheric Neutrinos Supernova Relic Neutrinos Super-beam (+Beta-beam) Solar Neutrinos Astrophysical Neutrino sources Multi-purpose detector with comprehensive physics programs for astrophysics, nuclear physics and particle physics Synergy between accelerator physics and non-accelerator physics

45 p --> e + π 0 Search Background 20 Mton-yr Atm nu Background MC SuperK Standard Cuts ==> 2.2 events/mton-yr ==> signal eff.: 43.0% Tighter Momentum Cut ==> 0.15 events/mton-yr ==> signal eff.: 17.4%

46 p --> e + π 0 Search Signal Signal Events w/ Tighter Momentum Cut No Fermi Momentum No Binding energy No Nuclear effect (π 0 scattering, absorption and charge exchange) Important to have a medium with free protons

47 Comparison of the Standard SuperK Analysis and the HyperK/UNO Analysis SuperK cut Tight cut

48 Reconstructed Mass Peak from p e + π 0 τ/b(p e + π 0 ) = 5x10 34 years 1 candidate event/~1.5 yrs τ/b(p e + π 0 ) = 1x10 35 years 1 candidate event/~3 yrs

49 UNO Sensitivity for p K + ν Prompt γ coincidence method most powerful: most backgrounds are mis-fitted vertex events can be rejected by improved fitter Limiting background from νp νλk + 1 event/mt-yr

50 UNO Proton Decay Sensitivity and Updated Theoretical Predictions (e + π 0 )

51 UNO Proton Decay Sensitivity and Updated Theoretical Predictions (K + ν)?

52 Andromeda Galaxy Supernova Reach ~ 1 Mpc (local group of galaxies) Supernova Rate ~ 1/10 or 15 yrs

53 Galactic Supernova Beacom, Boyd and Mezzacappa PRL 85, 3568 (2000) ~140,000 events in UNO, ~1/30 years msec timing structure of the flux An example of unstable Eq. Of State Determination of core collapse mechanism Pons et al., PRL 86, 5223 (2001) Possible Observation of Birth of a Black Hole!

54 Through-going Muon Event in UNO Can look for astrophysical neutrino sources w/ energy range ~10 GeV ~100 GeV Complementary to ICECUBE

55 Conclusions Proton decays provide unique signature for Unification Physics Perhaps the only direct probe of the Unification Scale (~10 16 GeV) Experimental search for proton decays resulted so far no evidence, but set stringent limits Many theoretical models ruled out However, large detectors inspired by the GUT models and built for proton decay searches resulted in major discoveries Lesson learned: if we make good instrument, good things can happen Unexpected discoveries are often more revolutionary than the expected Importance of theorists role in realization of an experiment Observation of neutrino oscillations (mass) Observation of neutrinos from SN1987A First real time and directional observation of solar neutrinos Confirmation of the solar neutrino flux deficit

56 Continue: Conclusions UNO tackles some of the most important physics questions today w/ potential of major discoveries An excellent site exists at the Henderson mine NSF s DUSEL process progressing well If built, it will provide a comprehensive nucleon decay and neutrino physics program for the US and world science community for the 21th century Intersection of interests from HEP, NP and AP communities; and international community (Japan: Hyper-Kamiokande, Europe: CERN/Fréjus (133 km) initiatives) We are one step closer to a realization of the Einstein s dream with the discovery of the neutrino oscillations. Hopefully more forward steps can be taken in the near future with major new discoveries.

57 The End