PROTON DECAY. P627 Experimental Particle Physics Final Project Presentation Kübra Yeter The University of Tennessee, Knoxville 04/25/2012

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1 PROTON DECAY P627 Experimental Particle Physics Final Project Presentation Kübra Yeter The University of Tennessee, Knoxville 04/25/2012

2 Outline Theory Experiments Future plans

3 Unsolved Problems in High Energy Physics: Higgs mechanism, Hierarchy problem, Magnetic monopoles, Proton decay and spin crisis, Super symmetry, Generations of matter, Electroweak symmetry breaking, Neutrino mass, Confinement, Strong CP problem, etc.

4 Proton Decay in Standard Model In SM proton is a stable particle. The possible BNV process in SM is non-perturbative sphaleron process. BNV in SM is associated with the vacuum structure of SU(N) gauge theories with spontaneously broken symmetry. In electroweak gauge theory, the vacuum state is infinitely degenerate, and the different substates are separated by energy barriers. Through a quantum tunneling process, the system can move to a different vacuum substate which has nonzero baryon number.

5 Proton Decay in Standard Model The probability of this process to happen is suppressed ~e (4π α W ) ~

6 Grand Unification and Proton Decay

7 SU(5) SU 5 SU 3 strong SU 2 weak U 1 (electromagnetic) by spontaneous symmetry breaking. Mismatch of the 3 gauge couplings when extrapolated to high energies.

8 SU(5)

9 Minimal SUSY SU(5) (SU(5)+ Low energy Supersymmetry) Low energy SUSY would allow baryon and lepton number violating interactions of type QLD c, U c D c D c, LLE c in the super potential. Strong, weak and electromagnetic gauge couplings are found to unify nicely at a scale M X GeV the scale of interest for proton decay.

10 Minimal SUSY SU(5) (SU(5)+ Low energy Supersymmetry) Low energy SUSY brings in a new twist to proton decay, however, as it predicts a new decay mode which would be mediated by the colored Higgsino, the GUT/SUSY partners of the Higgs doublets. May be saved by some modifications. Then, τ(p υ + K + )~ yrs τ(p μ + + K 0 )~ yrs τ(p μ + + π 0 )~ yrs. Can be tested by increasing the current sensitivity by a factor of 10.

11 SO(10) Unification: Attractive since quarks, leptons, anti-quarks and antileptons of a family are unified in a single 16-dimensional spinor representation. When embedded with low energy SUSY so that the mass of the Higgs boson is stabilized, the three gauge coupling nearly unified at the energy scale of M X GeV. Even without SUSY SO(10) models are consistent with experimental limits and unification. SO(10) can break to SM via an indermediate symmetry such as SU(4) SU(2)l SU(2)r. Lifetime limit is in the range years.

12 Experiments:

13 Experiment:

14 Super KamiokaNDE: SK-I: cm inward facing PMTs, protons, neutrons 40% photocathode coverage, detects low energy e - s down to ~5MeV, sensitive to nucleon decay ID s fiducial volume is 22.5 kton OD surrounds ID, cm outward facing PMTs equipped with 60 cm 60 cm wavelength shifter plates to increase efficiency. OD tags incoming cosmic ray muons and exciting muons induced by atmospheric neutrinos. SK-II: Jan Oct 2005 Recovery from accident cm inner PMTs Acrylic + FRP protective Outer detector fully restored

15 Super KamiokaNDE:

16 Super KamiokaNDE: SK-III: May August 2008 Restored 40% coverage Outer detector segmented (top barrel bottom) SK-IV: September SK-IV Replace all electronics 2008 T2K beam late 2009

17 Decay modes: p e + + π 0 and p υ + K + => dominant decay modes Different GUTs predict different modes to have the dominant branching fraction, making it critical for experiments to search in every mode that is accessible to their respective detectors. The observation of differing rates in more than one channel could provide enough extra information to allow distinction among various models of grand unification theories.

18 Independent on channel decay It is not known a priori which mode of proton decay is preferable so the limits on proton decay independent on the channel are very important. The bound τ p? > yrs. It was assumed that the parent 232 Th nucleus is destroyed by the strongly or electromagnetically interacting particles emitted in the proton decay or in case of proton s disappearance (or proton decay into neutrinos) by the subsequent nuclear deexcitation process. The limit τ p? > yrs was established by searching for neutrons born in liquid scintillator, enriched in deuterium, as result of proton decay in deterium. The limit τ p 3υ > yrs was determined on the basis of geochamical measurements with Te or by looking for the possible daughter nuclides.

19 Methods of searching for nucleon decay: Defining selection criteria that maximize the signal detection efficiency and minimize the background. Bump search method: For some decay modes in which low background cannot be achieved, e.g. one must look for mono-energetic peak of single π 0 s search on top of a background consisting mostly of neutral-current atmospheric neutrino events with single π 0 in n υ + π 0 decay. Combination of first two techniques + tagging the monoenergetic low energy photon from the de-excitation of the excited nucleus that is left after the decay of a proton in 16 O.(e.g. p υ + K + decay)

20 (1) proton decay MC (2) atmospheric neutrino MC

21 Systematic uncertainties: Imperfect knowledge of light scattering in water, energy scale and particle identification. In background estimation: imperfect knowledge of atmospheric neutrino flux, neutrino cross sections, energy scale, and particle identification.

22 Background:

24 Selection criteria for p e + + π 0 (p μ + + π 0 ) (A) # of rings 2 or 3, (B) one of the rings is e-like (μ-like) for p e + + π 0 (p μ + + π 0 ) and all other rings are e-like. (C) For 3 ring events, π 0 invariant mass is reconstructed between 85 and 185 MeV/c 2 (D) The # of e s from muon decay is 0(1) for p e + + π 0 (p μ + + π 0 ) (E) The reconstructed total momentum is less than 250 MeV/c, and the reconstructed total invariant mass is between 800 and 1050 MeV/c 2.

27 Bayes Theorem:

28 Future Collaborations:

29 Long Baseline Neutrino Experiment (LBNE) 200kt Water Cherenkov Detector 34kt Liquid Argon TPC

30 Long Baseline Neutrino Experiment (LBNE) Largest liquid Ar TPC, (Liquid Ar TPC) The ability to observe charged particle tracks below the Cherenkov threshold in water means that some modes poorly observed in Super-K would be much better measured in LBNE LAr. e.g. p υ + K + decay It doesn t contribute other modes sensitivities that much.

31 Bibliography Experimental limits on the proton life-time from the neutrino experiments with heavy water (Tretyak and Zdesenko, 2001) The Super Kamiokande Detector (S. Fukuda, et.al.) Particle Data Group FPIF Report on Proton Decay Presentation on Proton Decay and GUTs, Hitoshi Murayama (2005) Presentation on Grand Unified Theories and Proton Decay, Ed Kearns (2009)

Theoretical Particle Physics FYTN04: Oral Exam Questions, version ht15

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