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)