Search for Proton Decay in Super-Kamiokande...2017/11/24 · Search for Proton Decay in...
Transcript of Search for Proton Decay in Super-Kamiokande...2017/11/24 · Search for Proton Decay in...
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Search for Proton Decay in Super-Kamiokande
Yusuke SudaMini-Workshop for High Energy Gamma Ray Astrophysics
Max-Planck-Institute for Physics, Nov. 24, 2017
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Who am I• I am Yusuke Suda from Univ. of Tokyo, Japan
• Master of Science (Mar. 2014)
• “Research and Development of Large-Aperture Hybrid Photo-Detectors for Hyper-Kamiokande”
• Doctor of Philosophy (Sep. 2017)
• “Search for Proton Decay Using an Improved Event Reconstruction Algorithm in Super-Kamiokande”
• Postdoc at Center for High Energy gEophysics Research (CHEER), Earthquake Research Institute (ERI), UTokyo
• Muon radiography (Muography) for geoscience
2
First
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What is Proton Decay• Phenomena predicted by Grand Unified Theories (GUTs) of
elementary particles
• Unification of three fundamental forces (EM, Weak, Strong)
• Very high energy scale ( ≧1015 GeV)
• Solve electromagnetic charge quantization, etc.
• Mixture between quarks and leptons → Proton decay
• Proton decay is the best tool to test GUTs!
3
Accelerators
Prot
on
⇡0
↵↵
Predicted Proton lifetime:1032 - 1039 years
⌧ ⇠ M4X
↵2m5p
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Year1940 1960 1980 2000 2020 2040
Life
time
Lim
it (y
ears
)
2110
2510
2910
3310
3710 0π+ e→Minimal SU(5), p0π+ e→Minimal SO(10), p
Goldhaberet alFlerov
Evans & SteinbergFiremanBennett
(1954)et alReines (1958)et alReines
et alBackenstoss Giamati & ReinesKropp & Reines
et alGurr Bergamasco & PicchiReines & Crouch
et alLearned (NUSEX)et alBattistoni
(KGF)et alKrishnaswamy (Soudan)et alBartelt (Frejus)et alBerger (Homestake)et alCherry
(Kamiokande)et alHirata (IMB)et alMcGrew
(Super-K I)et alShiozawa (Super-K I-II)et alNishino
(Super-K I-IV)et alAbe
Proton Decay So Far
4
SO(10) GUT
SU(5) GUT
Water Cherenkov
Iron Calorimeter
Liquid Scintillator
Geochemical Radiochemical
(1954)
• Long history of over 60 years. No significant candidate
• Super-Kamiokande (SK) is the top and still in predictions
• Proton decay may happen at any time
• Let’s search proton decay in SK!
Baryon number conservation
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Super-KamiokaNDE• 50kton water Cherenkov detector
• 1000m underground, Kamioka, JPN
• Record Č light (Q・T) by 20-inch PMTs
• PID by Č ring pattern
SK1 SK2 SK3 SK4
Period 1996-2001 2002-2005 2006-2008 2008-
Live time 1489.2 798.6 518.1 2650.4(~Sep. 2016)
Photocoverage(# of PMTs)
40%(11,146)
19%(5,182)
40%(11,129)
40%(11,129)
Outer Detector
(veto)
InnerDetector
50kton Tank
ucleonecay
xperiment
39.3 m
41.4
m
Half of the all data
e, γ
Fuzzy
μ
Sharp
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6
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1033 protons in inner detector
10 years null observation of proton decay→ Proton lifetime > 1034 years
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My target decay mode: p→e+π0 ・Most dominant in non-SUSY GUTs ・Most sensitive for SK
Decay time of π0: 8×10-17 s Gamma conversion length: ~40cm
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Back-to-back topology→ Easily distinguish from
atmospheric neutrinos
e+
γ
γ
Proton Decay Simulation
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Elec.
Cable hole μ
Invisible μ
Stopping μ
Through-going μ
Radioactive BG
FC neutrino
VETO
Rock
PC neutrino
UPMU neutrino
Flasher
Proton decay
Michel e
Michel e
Data Flow
10
106 events/day
8 events/day
Reconstruction
Proton decay search
Fully contained reduction(no OD activity, no flasher
PMT etc.)
Mostly atmospheric neutrino events
(BG for proton decay)
Vertex, #rings, PID, momentum etc.
Cut-based analysis
I was an expert of fully contained reduction(trouble shooting, preparation for data set etc.)
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Reconstruction Algorithm• Conventional: APfit
• Determine reconstruction params. step-by-step (vertex → #rings → PID → momentum)
• Use charge&time information of “hit” PMT only
• Momentum determination by using observed charge inside Č-cone w/ a half angle of 70° → Bias
• Developed 20 years ago and written by Fortran (hard to maintain)
• New: fiTQun
• Determine all params simultaneously by a maximum likelihood method
• Use not only hit PMT information but also “unhit” PMT information
• Initial development by the T2K experiment, written by C++ 11
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fiTQun
Charge PDF Time PDFUnhit PDF
Distance btw. true/recon. vertex (cm)0 10 20 30 40 50 60 70 80 90 100
Num
ber o
f Eve
nts
0
500
1000
1500
2000
2500
3000
3500
4000
): σResolution (1: 19.6 cm (Dwall>1.5m)fiTQun: 19.5 cm (Dwall>2.0m)fiTQun
: 29.6 cm (Dwall>2.0m)APfit
True Momentum (MeV/c)0 200 400 600 800 1000 1200 1400
Mom
entu
m R
esol
utio
n (%
)
0123456789
10
(Dwall>1.5m)fiTQun (Dwall>2.0m)fiTQun
(Dwall>2.0m)APfit
Hit PDF
Vertex Resolution Momentum ResolutionEx) Atm.-νe CCQE MC
(Poisson w/ correction)
• Fit params. x = {x, y, z, t, θ, φ, p} × (# of rings)• Construct likelihood function for given ring(s) hypotheses• Maximize likelihood for each event
(Poisson) (Gaussian)
Observed Q&T
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)µLe/Lln(-3000 -2000 -1000 0 1000 2000 3000
Num
ber o
f Eve
nts
0
100
200
300
400
500
600
700
800 SK-IV DataπCC w/o eν
oth.0πCC w/ 0eν 0πCC w/ eνπCC w/o µν
oth.0πCC w/ 0µν0πCC w/ µν
NC
Validation of fiTQun• Performance in MC was well examined, but treatment of real
data was not enough to physics analysis
• I did
• Check in data/MC likelihood distributions
• Correction of time dependent detector params.
• Estimation of energy scale uncertainty
• Uncertainty 2.1%, same as APfit
• Tuning of ring counting parameter
• Finally, fiTQun has been verified for SK-IV data/MC
• Then, T2K experiment employed fiTQun for their analysis and announced a new hint for leptonic CP violation in summer 2017
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PID μ←→e
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Elapsed Years0 1 2 3 4 5 6 7 8
PMT
Gai
n (a
.u.)
0.95
1
1.05
1.1
1.15
1.2
Calibration of fiTQun
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Date1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018
Wat
er A
ttenu
atio
n Le
ngth
(m)
50
60
70
80
90
100
110
120
130
PMT gain corr. Water Atten. corr.w/o corr.
Mom
entu
m/R
ange
(M
eV/c
/cm
)
Ex) SK1
RMS/Mean=2.2% RMS/Mean=1.0% RMS/Mean=0.6%
SK1SK2SK3SK4
Year
+2%/year
• PMT gain and water attenuation length vary with time
PMT Gain Water Attenuation Length
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Search for Proton Decay• First application of fiTQun to proton decay
• First time of changing SK proton decay analysis framework
• Target decay mode: p→e+π0
• Hybrid search: APfit (SK1-3, null observation) + fiTQun (SK4)
• Selection criteria
15
1. Fiducial volume
2. Number of rings (2 or 3)
3. PID (all shower ring, no Micheal-e)
4. π0 mass (for 3-ring events)
5. No gamma-ray from neutron capture
6. Total invariant mass and momentum cut
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Distance from the wall to the true vertex (cm)0 200 400 600 800 1000 1200 1400 1600 1800
Effic
ienc
y in
eac
h bi
n
0
0.2
0.4
0.6
0.8
1
1.2
16
• By changing selection criteria for fiTQun, I did
• Expand fiducial volume by 10%
• Reduce # of BG events by arrpox. 30%
• Tighter total invariant mass cut is applied
• While keeping similar level of signal efficiency as APfit
fiTQun free-pAPfit free-p
fiTQun all-pAPfit all-p
APfitfiTQun
Chance of discovery!(22.5 kton → 24.7kton)
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fiTQun APfitLower box Upper box Lower box Upper box
Eff. (all) (%) 20.0±0.3 18.1±0.3 19.0±0.3 19.0±0.3BG (/Mt/yr) 0.028±0.019 0.778±0.102 0.030±0.021 1.116±0.132
*stat. error only
Bound-pFree-p
Signal MC Atm-ν MC (500 years)
• To enhance sensitivity, signal region is divided by two
• Lower box: less BGs & systematics error (Fermi motion)
• #total BG in SK4: ~0.14 (0.19) events for fiTQun (APfit)
Upper boxLower box
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Result
18
)2Total Invariant Mass (MeV/c0 200 400 600 800 1000 1200
Tota
l Mom
entu
m (M
eV/c
)
0
100
200
300
400
500
600
700
800
900
1000
)2Total Invariant Mass (MeV/c0 200 400 600 800 1000 1200
Tota
l Mom
entu
m (M
eV/c
)
0
100
200
300
400
500
600
700
800
900
1000
APfit (163.0 kton*years)fiTQun (179.5 kton*years)
SK-IV SK-IV
• No candidate was found in SK-IV data for both fitters
• Combine with the other SK data (APfit, no candidates) and calculate lower lifetime limit by Bayes’ theorem
• Lifetime limit: τ/B(p→e+π0) > 1.88×1034 years @ 90% C.L.
• 5% improvement from APfit-based analysis
Not official yetNot official yet
Signal box
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Summary• Proton decay is a smoking gun for GUTs
• Developed and validated the new event reconstruction algorithm, fiTQun
• Improved search for p→e+π0 with fiTQun was conducted
• Same efficiency but fiducial volume +10%, #BGs -30%
• No candidate was found
• World leading proton lifetime limit: 1.88×1034 years @ 90% C.L.
• Most stringent constraint for non-SUSY GUT
19
Detail information can be found in Suda’s thesis http://www-sk.icrr.u-tokyo.ac.jp/sk/publications/index-e.html#doctor
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20Let’s go as much as we can!
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74 m
60 m
Think Bigger
• Hyper-Kamiokande project (~10 times bigger than SK)
• Search region of proton decay will reach 1035 years
• Many rich physics: CP violation, ν mass hierarchy, SN relic etc.
• FiTQun is compatible with HK
• Photosensor is a key to success21
Hyper-K
Super-K
KAMIOKANDE 1983
1996
2026 (expected)
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/ ndf 2χ 473.8 / 161Prob 1.465e-32p0 6.4± 375.9 p1 0.057± 9.577 p2 0.064± 2.133 p3 7.0± 587.1 p4 0.1± 18.8 p5 0.122± 3.304 p6 14.7± 652.2 p7 0.1± 27.8 p8 0.149± 3.082 p9 39.8± 510.5 p10 0.20± 36.37 p11 0.285± 3.413 p12 8.2± 389.9 p13 0.45± 46.07 p14 0.634± 5.003
Charge [pC]0 20 40 60 80 1000
100
200
300
400
500
600
700 / ndf 2χ 473.8 / 161
Prob 1.465e-32p0 6.4± 375.9 p1 0.057± 9.577 p2 0.064± 2.133 p3 7.0± 587.1 p4 0.1± 18.8 p5 0.122± 3.304 p6 14.7± 652.2 p7 0.1± 27.8 p8 0.149± 3.082 p9 39.8± 510.5 p10 0.20± 36.37 p11 0.285± 3.413 p12 8.2± 389.9 p13 0.45± 46.07 p14 0.634± 5.003
Multi-photoelectron distribution
Avalanche Diode
8-inch
200ton tank
Cosmic-ray μInstall
R&D of Hybrid Photo-Detector• One of candidates. Better performance than SK PMT
• Hope to use in HK (20-inch HPD is testing in water tank)
22
SudaHPD
Photon counting!
1PE
Photon counting!
2PE 3PE4PE
5PE
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Current Research
23
↑ Satsuma-Iwojima Volcano, Japan
H. Tanaka, 2009
2m
3m2mScintillation detector →
μ
Magma
• Muon radiography (Muography) @ Earthquake research institute, Japan
• Explore inner structure of volcanos and active fault by measuring cosmic-ray muon flux through target
• Commit to geophysics and disaster prevention
• One of the few applications of high energy physics
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Active Fault
24
• Muography of Atotsugawa fault (near Super-K)
• Estimation of 3D density profile of the fault by measuring muon flux (θ, φ) at each depth (Data taking is ongoing)
• I will evaluate expected muon flux at detector by GEANT4
• Working hard to publish the world’s first result
Borehole
Fractured zone(low density)
Rock
Detector
μTerrain @ GEANT4
Scintillation muon detector
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Transition of My Research
25
Past
Now
Future?
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Expected Future Work
26
• Gamma-ray burst search @ CTA LST
• GRB is the brightest explosion in the universe
• Explore mechanisms of jet formation and particle acceleration especially for long GRBs with LST’s high statistics data
• I would like to contribute to
• Low energy threshold (20GeV or less) in order to detect GRBs
• PMT calibration and analysis tool development utilizing my experience (fiTQun, HPD, etc.)
• Pointing calibration in order to not miss GRBs
• Eager to accomplish the first measurement of a GRB by the ground based telescope