PROTON DECAY - University of Tennessee
Transcript of PROTON DECAY - University of Tennessee
PROTON DECAY P627 Experimental Particle Physics
Final Project Presentation
Kübra Yeter
The University of Tennessee, Knoxville
04/25/2012
Outline
• Theory
• Experiments
• Future plans
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.
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.
Proton Decay in Standard Model
• The probability of this process to happen is suppressed
~𝑒−(4𝜋
𝛼𝑊 )~10−150.
Grand Unification and Proton Decay
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.
SU(5)
Minimal SUSY SU(5)
(SU(5)+ Low energy Supersymmetry) • Low energy SUSY would allow baryon and lepton number
violating interactions of type 𝑄𝐿𝐷𝑐, 𝑈𝑐𝐷𝑐𝐷𝑐, L𝐿𝐸𝑐 in the
super potential.
• Strong, weak and electromagnetic
gauge couplings are found to unify
nicely at a scale 𝑀𝑋 ≈ 2 × 1016 GeV
the scale of interest for proton decay.
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+)~4 × 1033yrs
𝜏(𝑝 → 𝜇+ + 𝐾0)~6 × 1033yrs
𝜏(𝑝 → 𝜇+ + 𝜋0)~1 × 1034yrs.
Can be tested by increasing the
current sensitivity by a factor of
10.
SO(10) Unification:
• Attractive since quarks, leptons, anti-quarks and anti-
leptons 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 𝑀𝑋 ≈ 2 × 1016 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 1033-1036 years.
Experiments:
Experiment:
Super KamiokaNDE: • SK-I: 1996 – 2001
• 11146 50-cm inward facing PMTs,
• 7.5 × 1033 protons, 6.0 × 1033 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,
• 1885 20-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 2003 - Oct 2005
Recovery from accident
5182 50-cm inner PMTs
Acrylic + FRP protective
Outer detector fully restored
Super KamiokaNDE:
Super KamiokaNDE:
• SK-III: May 2006 - August 2008
Restored 40% coverage
Outer detector segmented (top | barrel |
bottom)
• SK-IV: September 2008 -
SK-IV Replace all electronics – 2008
T2K beam – late 2009
Decay modes:
• 𝑝 → 𝑒+ + 𝜋0 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.
“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 →? > 1.3 × 1023 yrs. It was assumed that the parent
𝑇ℎ232 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 →? > 3 × 1023 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 > 7.4 × 1024 yrs was determined on the basis of
geochamical measurements with Te or by looking for the possible
daughter nuclides.
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 𝜋0’s search on top of a
background consisting mostly of neutral-current
atmospheric neutrino events with single 𝜋0 in n→ υ + 𝜋0
decay.
• Combination of first two techniques + tagging the mono-
energetic low energy photon from the de-excitation of the
excited nucleus that is left after the decay of a proton in
𝑂16 .(e.g. 𝑝 → υ + 𝐾+ decay)
(1) proton decay MC (2) atmospheric neutrino MC
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.
Background:
Selection criteria for 𝑝 → 𝑒+ +𝜋0 (𝑝 → 𝜇+ +𝜋0) • (A) # of rings 2 or 3,
• (B) one of the rings is e-like (𝜇-like) for 𝑝 → 𝑒+ + 𝜋0
(𝑝 → 𝜇+ + 𝜋0) and all other rings are e-like.
• (C) For 3 ring events, 𝜋0 invariant mass is reconstructed
between 85 and 185 MeV/𝑐2
• (D) The # of 𝑒−’s from muon decay is 0(1) for 𝑝 → 𝑒+ + 𝜋0
(𝑝 → 𝜇+ + 𝜋0)
• (E) The reconstructed total momentum is less than 250
MeV/c, and the reconstructed total invariant mass is
between 800 and 1050 MeV/𝑐2.
Bayes Theorem:
Future Collaborations:
Long Baseline Neutrino Experiment
(LBNE)
200kt
Water Cherenkov
Detector
34kt
Liquid Argon TPC
Long Baseline Neutrino Experiment
(LBNE) (Liquid Ar TPC) • Largest 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.
Bibliography
• Experimental limits on the proton life-time from the
neutrino experiments with heavy water (Tretyak and
Zdesenko, 2001) http://arxiv.org/pdf/nucl-ex/0104011.pdf
• The Super Kamiokande Detector (S. Fukuda, et.al.)
• Particle Data Group http://pdg.lbl.gov/
• 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)