Electron Beam Dump Constraints on Light Bosons with Lepton ...
Transcript of Electron Beam Dump Constraints on Light Bosons with Lepton ...
Kento Asai (Saitama Univ.)
Electron Beam Dump Constraintson Light Bosons
with Lepton Flavor Violating Couplings
Summer camp on ILC accelerator, physics and detectors 2021
22 Sep. 2021 (online)Based on T. Araki, KA, T. Shimomura, arXiv : 2107.07487 [hep-ph]
1/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Introduction
2/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Charged Lepton Flavor Violation (cLFV)
● Introduction
Neutrino OscillationcLFV is violating
In the SM
Prediction : ~10!"#
Experiements : < 10!$%
It is impossible to detect cLFV process
Beyond the SM
≪
・Leptophilic scalar・Extra gauge boson (ex: U(1)!!"!")
・Dark Photon w/ dipole LFV coupling
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Introduction
Charged lepton flavor violation process is a smoking gun signal of new physics
Constraints on cLFVcLFV process Exp. limit on BR Future prospect
SINDRUM Collaboration (1988)
PDG (2020)
MEG Collaboration (2016)
PDG (2020)
TWIST Collaboration (2015)
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Introduction ● Introduction
Constraints on cLFVEx) Leptophilic scalar model
In light-mass & small-coupling region (𝑚&~0.01 − 1 GeV & 𝑦'~10!( − 10!")
2, New particles with CLFV coupling are long-lived
1, CLFV coupling can be as large as CLFC one
5/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Introduction
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● Introduction
Constraints on cLFV
・CLFV interactions affect results of long-lived particle search experiments?
・Long-lived particle search experiments can detect CLFV decays ?
6/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Introduction ● Introduction
Electron Beam Dump Experiment
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Overview𝑒! Beam Dump Experiment
8/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)Beam of high-energy 𝑒" is dumped into dense target
High intensity- Production of large number of
new particles
Detector is placed behind long shieldLow background- Most of background events are
removed by shield Sensitive to small coupling region- New particles should be long-lived
to reach detector
● 𝑒! beam dump
E137 experiment𝑒! Beam Dump Experiment
9/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)Experiment parametersBeam : 20 GeV 𝑒! beam
≅ 2×10%) EOTTarget : Aluminum beam dumpShielding : 179m ground (hill)Decay volume : 204m open airDetector : EM calorimeter + MWPC
● 𝑒! beam dump
New particle production𝑒! Beam Dump Experiment
10/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)
Lagrangian
Target
Coupling with electronsBremsstrahlungproduction
New particles are produced through bremsstrahlung process
● 𝑒! beam dump
New particle detection𝑒! Beam Dump Experiment
11/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)
Lagrangian
Detector
Coupling with electrons
After passing through shield, new particles decay into 𝑒*𝑒! pair in decay volume and are detected
Decay into 𝑒*𝑒! pair Detection
Detection
● 𝑒! beam dump
𝑒! Beam Dump Experiment
12/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)
Lagrangian
Target
Coupling with 𝑒 & 𝜇Bremsstrahlungproduction
Possibly LFV interactions contribute to bremsstrahlung production
New particle production with LFV coupling
● 𝑒! beam dump
New particle detection𝑒! Beam Dump Experiment
13/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Batell, Essig, Surujon, PRL113 (2014)
Lagrangian
Target
Coupling with 𝑒 & 𝜇
LFV decay can be searched by beam dump experiment
with LFV coupling
Decay into 𝜇*𝑒! pair Detection
Detection
● 𝑒! beam dump
E137 experiment𝑒! Beam Dump Experiment
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with LFV coupling
Unfortunately, E137 experiment can detect only electron
We have explored constraints on LFV couplings of new particles by E137 experiment
● 𝑒! beam dump
Benchmark model𝑒! Beam Dump Experiment
15/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Ex) U(1)!!"!" model
○ 𝜇- (𝜏-) leptons have U(1)+!!+" charge +1 (-1)
○ Additional gauge symmetry : U(1)+!!+"
○ U(1)+!!+"-charged scalar breaks U(1)+!!+" gauge symmetryEx) SU(2)! doublet scalar (U(1)!!"!"-charge : +1) :
Mass term is not diagonal
● 𝑒! beam dump
Benchmark model𝑒! Beam Dump Experiment
16/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Ex) U(1)!!"!" model
in flavor basis
in mass basis
LFV couplings of 𝑍! appear naturally
● 𝑒! beam dump
Number of signal events𝑒! Beam Dump Experiment
17/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
(# of events) = (# of produced 𝑍′) × (Acceptance)
※ We use Weizsäcker-Williams approximation :
● 𝑒! beam dump
Result
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Constraint on LFV couplingResult
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U(1)"!#"" model
○ Large mixing angleLarger 𝑒$𝑒" coupling
(More 𝑍′ production & signals)Larger 𝜇$𝑒" coupling
(More 𝑍′ production ?& Stronger constraint from 𝜇 → 𝑒𝑒𝑒)
● Result
○ For , E137 experiment can give stronger bound on LFV coupling than 𝜇 → 𝑒𝑒𝑒
Production through LFV couplingResult
20/23Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Production cross section
: LFC : LFV
For ,
LFC
LFV
𝑍! production through LFV coupling is negligible
● Result
Summary○ Electron beam dump experiments have sensitivity to light new
physics interacting very weakly
○ In such small coupling regions, LFV couplings can be as large as LFC ones without conflicting with current LFV constraints
○ We considered scalar-, (pseudoscalar-), vector-, and dipole-type LFV interactions and studied effects on 𝑒!BD
21/23浅井健⼈ (埼⽟⼤学) ⽇本物理学会2021秋季⼤会 (2021/09/15) @ オンラインILC陽電⼦・電⼦ビームダンプ実験による新物理探索
・vector (𝑈(1)+!!+"model) 𝑒!BD can constraint on large unexplored region
・others For large LFV couplings, explorable region by 𝑒!BD is covered with constraints from 𝜇 → 𝑒𝑋
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Appendix
Constraint on LFV couplingAppendix
25/27Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Scalar-type int.
○ Larger LFV/LFC ratioLarger 𝜇$𝑒" coupling
Shorter decay length for & smaller Sensitivity region is covered with constraints from
● Appendix
Constraint on LFV coupling
26/27Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
dipole-type int.
○ Larger LFV/LFC ratioLarger 𝜇$𝑒" coupling
Shorter decay length for & smaller Sensitivity region is covered with constraints from
● Appendix
Appendix
Constraint on LFV coupling
27/27Kento Asai (Saitama Univ.) Summer camp on ILC 2021 (2021/09/22) @ onlineElectron Beam Dump Constraints on Light Bosons with LFV Couplings
Scalar-type int.
If E137 experiment can detect muon,signal :
𝑒! beam dump with muon detector can search unexplored LFV coupling and perhaps detect LFV decay
● Appendix
Appendix