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

https://arxiv.org/abs/2107.07487

Introduction


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


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)


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


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 ?


Introduction ● Introduction

Electron Beam Dump Experiment


Overview𝑒! Beam Dump Experiment


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


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


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



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



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



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


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


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


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


(# of events) = (# of produced 𝑍′) × (Acceptance)

※ We use Weizsäcker-Williams approximation :

● 𝑒! beam dump

Result


Constraint on LFV couplingResult


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


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


Appendix

Constraint on LFV couplingAppendix


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


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


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

electron beam dump constraints on light bosons with lepton

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