Excited Muons Research Articles

Excited muon production in muon colliders via contact interaction

In recent years, with the enlightenment of some issues encountered in muon colliders, muon colliders have become more feasible for the high-energy physics community. For this reason, we studied the single production of an excited muon in muon colliders via contact interactions. In addition, we assumed that the excited muon decayed into a photon and muon through gauge interactions. Then, signal and background analyses were performed in muon–antimuon collider options with center-of-mass energies of 6, 14, and 100 TeV. The attainable mass and compositeness scale limits were calculated for the excited muon in these collider options. Based on the calculations, it was concluded that muon–antimuon colliders would be a perfect collider option for excited muon investigations.

Search for excited leptons in \u2113\u2113\u03b3 final states in proton-proton collisions at sqrt{mathrm{s}}=13 TeV

A search is presented for excited electrons and muons in ℓℓγ final states at the LHC. The search is based on a data sample corresponding to an integrated luminosity of 35.9 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector in 2016. This is the first search for excited leptons at sqrt{s} = 13 TeV. The observation is consistent with the standard model background prediction, and the most stringent exclusion limits to date are set on the excited lepton mass and the compositeness scale, at 95% confidence level. Excited electrons and muons are excluded for masses below 3.9 and 3.8 TeV, respectively, under the assumption that the excited lepton mass equals the compositeness scale. The best observed limit on the compositeness scale is obtained with an excited lepton mass of around 1.0 TeV, excluding values below 25 TeV for both excited electrons and muons.

Search for Excited Muons at the Future SPPC-based Muon--Proton Colliders

We have investigated the production potential of the spin-1/2 excited muons, predicted by the preonic models, at the four SPPC (Super Proton-Proton Collider)-based muon-proton colliders in different center-of-mass energies. For the signal process \mu p\rightarrow\mu^{\star}X\rightarrow\mu\gamma X, the production cross-section and the decay width values of the excited muons have been calculated. The pseudorapidity and transverse momentum distributions of the final state particles of muons and photons have been obtained to be determine the kinematical cuts best suited for discovery of the excited muons. By applying these cuts we have gotten the discovery, observation and exclusion mass limits of the excited muons for two compositeness scale values. It is shown that the discovery limits on the excited muons in case the compositeness scale equals to 100 TeV are 2.7, 3.9, 3.1 and 6.7 TeV for center-of-mass energies of 10.3, 14.2, 14.6 and 20.2 TeV, respectively.

Single production of the excited muons at the SPPC-based ultimate p collider

Single production potential of the excited muons at the SPPC-based ultimate muon-proton collider with center-of-mass energy of 116.6 TeV was analyzed. We calculated the production cross-sections and the decay widths of the excited muons with the process of µp → µ*X → γµX . We obtained the normalized transverse momentum and pseudorapidity distributions of the final-state particles to attain the kinematical cuts for the discovery of the excited muons. With these cuts, we determined the mass limits. It was shown that the discovery limits on the mass of the excited muons are 19.6 and 10.1 TeV for λ = mµ* and λ = 50 TeV, respectively.

Excited Muon Searches at the FCC-Based Muon-Hadron Colliders

We study the excited muon production at the FCC-based muon-hadron colliders. We give the excited muon decay widths and production cross-sections. We deal with the μp→μ⋆q→μγq process and plot the transverse momentum and normalized pseudorapidity distributions of final state particles to define the kinematical cuts best suited for discovery. By using these cuts, we get the mass limits for excited muons. It is shown that the discovery limits obtained on the mass of μ⋆ are 2.2, 5.8, and 7.5 TeV for muon energies of 63, 750, and 1500 GeV, respectively.

A search for an excited muon decaying to a muon and two jets in pp collisions at with the ATLAS detectoratlas.publications@cern.ch

A new search signature for excited leptons is explored. Excited muons are sought in the channel , assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb−1 of pp collision data at a centre-of-mass energy of taken with the ATLAS detector at the large hadron collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass . For between 1.3 and 3.0 TeV, the upper limit on ) is between 0.6 and 1 fb. Limits on are converted to lower bounds on the compositeness scale Λ. In the limiting case , excited muons with a mass below 2.8 TeV are excluded. With the same model assumptions, these limits at larger masses improve upon previous limits from traditional searches based on the gauge-mediated decay .

Search for new phenomena in events with three or more charged leptons in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

A generic search for anomalous production of events with at least three charged leptons is presented. The data sample consists of $pp$ collisions at $\sqrt{s}=8$ TeV collected in 2012 by the ATLAS experiment at the CERN Large Hadron Collider, and corresponds to an integrated luminosity of 20.3 fb$^{-1}$. Events are required to have at least three selected lepton candidates, at least two of which must be electrons or muons, while the third may be a hadronically decaying tau. Selected events are categorized based on their lepton flavour content and signal regions are constructed using several kinematic variables of interest. No significant deviations from Standard Model predictions are observed. Model-independent upper limits on contributions from beyond the Standard Model phenomena are provided for each signal region, along with prescription to re-interpret the limits for any model. Constraints are also placed on models predicting doubly charged Higgs bosons and excited leptons. For doubly charged Higgs bosons decaying to $e\tau$ or $\mu\tau$, lower limits on the mass are set at 400 GeV at 95% confidence level. For excited leptons, constraints are provided as functions of both the mass of the excited state and the compositeness scale $\Lambda$, with the strongest mass constraints arising in regions where the mass equals $\Lambda$. In such scenarios, lower mass limits are set at 3.0 TeV for excited electrons and muons, 2.5 TeV for excited taus, and 1.6 TeV for every excited-neutrino flavour.

Search for excited electrons and muons in TeV proton–proton collisions with the ATLAS detector

The ATLAS detector at the Large Hadron Collider is used to search for excited electrons and excited muons in the channel pp → ℓℓ* → ℓℓγ, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb−1 of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass mℓ*. For mℓ* ⩾ 0.8 TeV, the respective upper limits on σB(ℓ* → ℓγ) are 0.75 and 0.90 fb for the e* and μ* searches. Limits on σB are converted into lower bounds on the compositeness scale Λ. In the special case where Λ = mℓ*, excited-electron and excited-muon masses below 2.2 TeV are excluded.

Search for Excited and Exotic Muons in theμγDecay Channel inpp¯Collisions ats=1.96 TeV

We search for excited and exotic muon states mu* using an integrated luminosity of 371 pb(-1) of p[over]p collision data at sqrt[s]=1.96 TeV. We search for associated production of mumu* followed by the decay mu*-->mugamma. We compare the data to model predictions as a function of the mass of the excited muon M(mu*), the compositeness energy scale Lambda, and the gauge coupling factor f. No signal above the standard model expectation is observed. We exclude 107<M(mu*)<853 GeV/c(2) for Lambda=M(mu*) in the contact interaction model, and 100<M(mu*)<410 GeV/c(2) for f/Lambda=10(-2) GeV-1 in the gauge-mediated model, both at the 95% confidence level.

Search for excited muons inpp¯collisions ats=1.96 TeV

We present the results of a search for the production of an excited state of the muon, mu(*), in proton antiproton collisions at root s =1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb(-1). We search for mu(*) in the process p (p) over bar ->mu(*)mu, with the mu(*) subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu(*) production by four-fermion contact interactions and mu(*) decay via electroweak processes, we set a 95% confidence level production cross section upper limit ranging from 0.057 to 0.112 pb, depending on the mass of the excited muon. Choosing the scale for contact interactions to be Lambda=1 TeV, excited muon masses below 618 GeV are excluded.

Search for excited leptons at LEP

A search for charged and neutral excited leptons is performed in 217 pb−1 of e+e− collision data collected with the L3 detector at LEP at centre-of-mass energies from 202 up to 209 GeV. The pair- and single-production mechanisms of excited electrons, muons and taus, as well as of excited electron-, muon- and tau-neutrinos, are investigated and no signals are detected. Combining with L3 results from searches at lower centre-of-mass energies, gives improved limits on the masses and couplings of excited leptons.

Search for charged excited leptons in e+e− collisions at [formula omitted]–209 GeV

A search for charged excited leptons decaying into a lepton and a photon has been performed using approximately 680 pb−1 of e+e− collision data collected by the OPAL detector at LEP at centre-of-mass energies between 183 and 209 GeV. No evidence for their existence was found. Upper limits on the product of the cross-section and the branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

New physics potential with a neutrino telescope

Active Galactic Nuclei are considered as sources of neutrinos, with neutrino energies extending up to 10^{18} eV. It is expected that these highly energetic cosmic neutrinos will be detected by the neutrino telescopes, presently under construction. The detection process is very sensitive to the total muon neutrino cross-section. We examine how the total cross section changes at high energies, by the single production of excited fermions (excited muon and muon-neutrino). For parameters (masses, couplings) of the excited fermions allowed by the experimental constraints, we find that for energies of the incoming muon-neutrino above 100 TeV the cross-section for single production of (excited muon and muon-neutrino) supersedes the standard total cross-section.

High-pressure μSR studies of ferro- and antiferromagnetic metals

High‐pressure μSR experiments on ferromagnetic nickel and \alpha‐iron and antiferromagnetic chromium are reported. In Ni above 260 K BFermi was found to be proportional to the saturation magnetization, whereas at lower temperatures it is temperature independent apart from a small anomaly below 30 K which is presumably caused by a magnetoelastic interaction. There was no evidence for an occupation of metastable sites by the μ+ below the Curie temperature. By contrast, in \alpha‐Fe the temperature dependence of \curpartialBμ/\curpartialp shows a structure which might be attributed to the occupation of excited muon states at elevated temperatures.

Mass limits for excited electrons and muons from Z 0 decay

We searched for excited electrons and muons from Z 0 decay in the channels ee→eeγ, ee→eeγγ, ee→(e)eγ, ee→μμγ, ee→μμγγ. using the L3 detector at LEP. The lower mass limit for e ∗ is 45.0 GeV and for μ ∗ 45.3 GeV. The upper limits of ℓℓ ∗Z 0 and ℓℓ ∗γ couplings at 95% CL have been determined up to m ℓ∗ close to the Z 0 mass.

Search for the substructure of leptons in high energy QED processes at tristan

QED processes up to O(α 4) have been studied at center-of-mass energies between 50 and 57 GeV using the AMY detector at TRISTAN. A possible substructure of the electron and muon is investigated in terms of chiral invariant contact interactions and also in terms of excited lepton production. The differential cross section data for e +e −→e +e − are consistent with the standard model at a confidence level of only 3.5%. From the absence of excited lepton production, we establish new upper limits on the coupling to excited electrons of mass up to 56 GeV/ c 2 and on the coupling to excited muons of mass up to 52 GeV/ c 2.

Effects of an excited muon on μ+μ−γ final states

We investigate the experimental consequences of the existence of an excited muon which couples to a photon and a Z 0. Postulating a μ ∗ interaction langrarian, we present complete lowest order calculations of the matrix element squared which describes μ + μ − γ production in electron-positron collisions.

Limits on masses of excited electrons and muons from neutrino scattering off electrons

The data on ν ω e → ν ω e and ν ωe → ν ωe from the CHARM Collaboration are used to set new and interesting bounds on the masses of hypothetical excited electrons and muons. In particular, it turns out that excited electrons cannot exist with masses below a couple of hundred GeV.

Experimental Test of Higher-Order QED and a Search for Excited Muon States

The reactions e+e−→μ+μ−γγ and e+e−→μ+μ−γ have been studied at s=29 GeV with the MAC detector at the SLAC storage ring PEP. The measured cross sections, charge asymmetry, and invariant-mass distributions are in good agreement with the predictions of QED theory. Limits are derived for the production of excited muon states.Received 6 December 1982DOI:https://doi.org/10.1103/PhysRevLett.51.257©1983 American Physical Society

Limits on masses and couplings of excited electrons and muons

We compute the effect of excited leptons on the electron and muon anomalous magnetic moments. We compare the limits given by g - 2 measurements with those obtained recently in e +e − collisions and with future possibilities offered by high energy projects.