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Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly
Sam HomillerYITP, Stony Brook
Light Scalars and the KOTO Anomaly
1
arXiv:1911.10203 (accepted in PRL)
In collaboration with D. Egaña-Ugrinovic and Patrick Meade
APS April Meeting, April 21, 2020
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 2
KOTO Measures Rare Kaon DecaysKOTO is an experiment at J-PARC searching for the rare decay of a neutral Kaon into a pion + neutrinos
K ⇡
Br(KL ! ⇡0⌫⌫)SM = (3.4± 0.6)⇥ 10�11
Buras et al., arXiv:1503.02693
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 3
K0L
Collimators, Sweeping Magnet, etc…
π0γ
γ
νν
Hermetic Veto System
Cal
orim
eter
s
Charged Particles Deflected
Target
Proton beam
KOTO Measures Rare Kaon Decays
zRe
cons
truct
edπ0
p T
Reconstructed π0 vertex (z)
Signal events
Measure angle between photons and their energies
Demand no other activity in the detector
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly
SM Signal + Background expectation: events
4
Shinohara, KAON 2019
The KOTO “Anomaly” As of Fall 2019
Single Event Sensitivity: 6.9⇥ 10�10
?
0.1± 0.02
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly
SM Signal + Background expectation: events
5
Shinohara, KAON 2019
The KOTO “Anomaly” As of Early 2020
Single Event Sensitivity: 7.1⇥ 10�10
0.39± 0.08Including preliminary estimate of charged Kaon contamination
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 6
Confronting the Anomaly
Theoretical perspective: are there simple & motivated ways of explaining this result with new physics?
The 2 events are consistent with:
The absolute simplest: add a scalar singlet to the SM
Yes!
Br(KL ! ⇡0 + inv.)KOTO = 1.4+1.8(3.7)�0.9(1.2) ⇥ 10�9
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 7
Higgs Portal Explanation of KOTO
⇣(H†H') ! ⇣ (vh') ! sin ✓ ⇠ ⇣v/m
2h
Add to the SM a scalar singlet, mixing with the Higgs:
s d
W±
qjgj
qj
'
K ⇡
All couplings dictated by the mixing angle
escapes KOTO undetected, mimicking the neutrinos
Scalar is long lived
Egana-Ugrinovic, SH, Meade [1911.10203]
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 8
Higgs Portal Explanation of KOTOEgana-Ugrinovic, SH, Meade [1911.10203]
Blue: preferred KOTO region
Dashed-gray: scalar lifetime
(2 events)
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 9
Higgs Portal Explanation of KOTOEgana-Ugrinovic, SH, Meade [1911.10203]
Consistent with all other bounds and explains the 2 events!
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 10
Bounds: Charged Kaon DecaysThe same diagram also leads to charged Kaon decays:
K+ ! ⇡+⌫⌫(model-independent relationship: Grossman, Nir, Phys. Lett B398, 1997, 163-168)
Constrained by NA62 and E949
s d
W±
qjgj
qj
'
For charged pions, can reconstruct the missing mass
Large background when m' ⇠ m⇡=)(“predicted” by Hou et al., 1412.4397, 1611.09673)
“‘Blessed are the Blind, for they shall see the Heavens open’ .… … So, please: Analyze, KOTO, Analyze!”
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 11
Bounds: Proton Beam DumpsCHARM: 400 GeV (SPS) proton beam dump
400 GeV beam
35 m
5 m480 m
Cu
' ! e+e�K ! ⇡'
⌘ ! ⇡'
Bergsma et.al., Phys. Lett., 157B, 5,6, p. 458
Bounds cover a large portion of the window left open by NA62
Beam Dumps lead to tension with “intermediate lifetime” explanations of the KOTO events
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 12
What if we change the scalar couplings?Different Flavor textures let us investigate alternative solutions to KOTO
cuij
M'H Qiuj !
8><
>:
gu'uu
gc'cc
gt'tt
s d
W±
qjgj
qj
'
Coupling predominantly to charm leads to intermediate-lifetime scalars
' gc
�
�c
c
c
Similar to Minimal Higgs Portal!
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 13
Different Flavor textures let us investigate alternative solutions to KOTO
cuij
M'H Qiuj !
8><
>:
gu'uu
gc'cc
gt'tt
Coupling predominantly to charm leads to intermediate-lifetime scalars
' gc
�
�c
c
c
What if we change the scalar couplings?
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly
• There’s a large anomaly in rare Kaon decays
• Events can be explained by the simplest extension of the SM
• Strongest constraints come from beam-dumps and charged Kaons
• Non-minimal solutions using a shorter lifetime can work, but are in tension with beam dump constraints
14
Summary
What’s Next?• Look out for KOTO final analysis (expected to finish this Summer)
• More data from 2019 KOTO Run
• New NA62 results?(Volpe, Tues. Flavor Session)
• Future LLP Experiments? (See PBC Summary: 1901.09966)
DM Implications: Pospelov, Ritz, Voloshin 0711.4866, Krnjaic, 1512.04119
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 15
Backup
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 16
2 Events vs. 3 Events
3 events 2 events
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 17
2 Events vs. 3 Events
3 events 2 events
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 18
Future Constraints (PBC)
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 19
2016-2018 Background Estimationfrom Satoshi Shinohara, KAON 2019
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 20
Updated Background EstimatesAs of January, 2020 from T. Nomura, J-PARC Meeting
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 21
Updated Background EstimatesAs of January, 2020 from T. Nomura, J-PARC Meeting
(Jan. 17, 2020)
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 22
KOTO 2015 Result
BR < 3.0 × 10−9
(90% C.L.)
PRL 122, 021802 (2019)
Samuel Homiller — shomiller@gmail.com | Light Scalars and the KOTO Anomaly 23
KOTO RunsFrom Taku Yamanaka, KAON2019
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