In this paper, we indicate the theoretical possibility of using the decay of polarized muons at rest as a source of the transversely polarized electron antineutrino beam. Such a beam can be used to probe new effects beyond standard model. We mean here new tests concerning CP violation, Lorentz structure and chirality structure of the charged current weak interactions. The main goal is to show how the energy and angular distribution of the electron antineutrinos in the muon rest frame depends on the transverse components of the antineutrino beam polarization. Our analysis is model-independent and consistent with the current upper limits on the non-standard couplings. The results are presented in a limit of infinitesimally small mass for all particles produced in the decay.
The first order QED corrections to the polarized muon decay spectrum are considered. The exact dependence on electron and muon masses is kept. Numerical results are presented.
Generation of arbitrarily spin polarized muon pairs is investigated via polarized $e^-e^+$ collision. We calculate the fully spin-resolved cross section ${\rm d}σ_{e^-e^+\rightarrow μ^-μ^+}$ and utilize the Monte Carlo method of binary collision to describe the production and polarization processes of muon pairs. We find that, due to the dependence of mixed helicities on the scattering angle, arbitrarily polarized muon pairs with both of the longitudinal and transverse spin components can be produced. The collision of tightly collimated electron and positron beams with highly longitudinal pola…
The fermion lifetime was usually calculated in terms of spin states. However, after comparing spin states with helicity states and chirality states, it is pointed out that a spin state is helicity degenerate, and so it can not be used for discussion of the dependence of lifetime on the polarization of an initial-state fermion. Using helicity states, we calculate the lifetime of polarized muons. The result shows that the lifetime of right-handed polarized muons is always greater than that of left-handed polarized muons with the same speed in flight.
In a previous paper, we showed that the decay rate of a muon is only slightly affected by the presence of a circularly polarized laser and we gave an analytic expression for the correction. In this paper, we present the analytical result for the case of a linearly polarized laser. Again the effect of the laser is small.
Based on the parity violation in Standard Model, we study the dependence of the lifetime on the polarization of an initial-state fermion in weak interactions. The fermion lifetime was usually calculated in terms of spin states. However, after comparing spin states with helicity states and chirality states, it is pointed out that a spin state is helicity degenerate, and the spin state and the helicity state are entirely different. Using helicity states, we calculate the lifetime of polarized muons. The result shows that the lifetime of right-handed polarized muons is always greater than that of…
A theoretical description of elastic polarized muon-electron scattering is presented. Complete one-loop electroweak radiative corrections are calculated with taking into account the exact dependence on the muon mass. The effects due to some higher order corrections and the electroweak scheme dependence are analyzed. The case of longitudinally polarized fermions in the initial state is investigated. Analytical results are derived with the help of the SANC system. Numerical results are presented for unpolarized and polarized cross sections. Calculations are realized in the Monte Carlo integrator…
In this paper, we analyze the polarized muon decay at rest (PMDaR) and elastic neutrino-electron scattering (ENES) admitting the non-standard V+A interaction in addition to standard V-A interaction. Considerations are made for Dirac massive muon neutrino and electron antineutrino. Moreover, muon neutrinos are transversely polarized. It means that the outgoing muon-neutrino beam is a mixture of the left- and right-chirality muon neutrinos and has a fixed direction of transverse spin polarization with respect to production plane. We show that the angle-energy distribution of muon neutrinos conta…
A search for the lepton-flavor violating $μ^{+}\rightarrow e^{+}γ$ decay using polarized muons is proposed. By measuring the angular distribution of $e^{+}$s with respect to the muon spin direction, in particular antiparallel $e^{+}$s, the serious physics background from $μ^{+}\rightarrow e^{+}ν\overlineνγ$ as well as accidental background from normal muon decay accompanied by a high-energy photon can be suppressed significantly. In addition to the enhancement of the sensitivity, the angular distribution would discriminate among different extensions to the Standard Model, once the signal is ob…
A search for the lepton-flavor violating $μ^{+}\rightarrow e^{+}γ$ decay using polarized muons is revisited in terms of suppression of the serious background arising from an accidental coincidence between a $e^{+}$ in the normal muon decay and a high energy photon in the radiative muon decay, $μ^{+} \rightarrow e^{+} ν\overlineν γ$. It is found that a high energy photon in $μ^{+} \rightarrow e^{+} ν\overlineν γ$ decay is preferentially emitted parallel to the muon spin direction, similarly to $e^{+}$ in the normal muon decay. The selective measurements of either $e^{+}$s or photons moving anti…
Top quark pair production is presented at a polarized Muon Collider above the threshold region. The off-diagonal spin basis is the natural basis for this discussion as the top quark pairs are produced in an essentially unique spin configuration for 100% polarization. Modest polarization, say 30%, can lead to 90% of all top quark pair events being in one spin configuration. This will lead to sensitive tests on anomalous top quark couplings.
We present a new study of polarized elastic muon-electron scattering. The Born cross-section is calculated for arbitrary polarization of muon and electron. The complete photonic O(alpha) radiative corrections are determined for the case of longitudinally polarized muons and electrons. All calculations are done by two methods: semianalytic, which allows an implementation of the experimental cuts used for the analysis of MU-E scattering data from the beam polarimeter of the SMC experiment at CERN and completely analytic, which is used for cross checks The FORTRAN code MUELA realizes formulae of …
The pure lepton decay of the polarized muon is considered, accounting for a new tensor interaction which is outside of the Michel local interactions. This interaction leads to new energy distribution and polarization of the final charged lepton. The presence of such a type of interaction is strongly required for the description of the latest experimental results on the weak radiative pion decay in the full kinematic region. Assuming quark--lepton universality, predictions for a deviation from the Standard Model are made using only one new parameter. They do not contradict the present experimen…
Lepton flavor violating processes $μ\to e γ$ and $μ\to 3e$ with polarized muons are studied in the supersymmetric grand unified theory (SUSY GUT). As a result of a detailed numerical calculation, it is shown that the P- and T-odd asymmetries defined with the help of the muon polarization and the ratio of two branching fractions make a good contrast between the SU(5) and SO(10) SUSY GUT. These observables are useful to extract differences of the two theories. In particular, the P-odd asymmetry of $μ\to e γ$ varies 100%--100% in SO(10) whereas it is 100% in SU(5) and the T-odd asymmetry of $μ\to…
Within the framework of electroweak theory, we investigate the elastic scattering process $ e^{-} + ν_μ \rightarrow e^{-} + ν_μ$ in the presence of an intense elliptically polarized laser field. We derive an analytical expression for the spin-unpolarized differential cross section using the first Born approximation and the Dirac-Volkov states to describe the incident and scattered electrons. Our results generalize those found for the linearly polarized field by Bai \textit{et al.} [Phys. Rev. A \textbf{85}, 013402 (2012)] and for the circularly polarized field by El Asri \textit{et al.} [Phys.…
In this paper, we have investigated the elementary particle reaction ${e}^{+} {e}^{-} \rightarrowμ^{+} μ^{-}$ that results from the electron-positron interaction, at the leading order, with an intense laser wave of circular polarization. We have derived, by annalytical means, the laser-assisted differential cross section expression by using the scattering matrix approach. We have analyzed the energy and the number of exchanged photons dependence of muon pair production in electron-positron annihilation at different centre of mass energies including the $Z$-boson peak. For this reason, a wide r…
In view of the great contribution of neutrino-electron scattering to the deep understanding of electroweak interactions, we focus in this paper on the study of elastic scattering of a muon neutrino by an electron $(e^{-}ν_μ\rightarrow e^{-}ν_μ)$ in the presence of a circularly polarized electromagnetic field. We perform our theoretical calculation within the framework of Fermi theory using the exact wave functions of charged particles in an electromagnetic field. The expression of the differential cross section (DCS) for this process is obtained analytically in the absence and presence of the …
The $μ^-e^-\to e^-e^-$ process in a muonic atom is one of the promising probes to study the charged lepton flavor violation (CLFV). We have investigated the angular distribution of electrons from the polarized muon of the atomic bound state. The parity violating asymmetric distribution of electrons is analyzed by using lepton wave functions under the Coulomb interaction of a finite nuclear charge distribution. It is found that the asymmetry parameters of electrons are very sensitive to the chiral structure of the CLFV interaction and the contact/photonic interaction. Therefore, together with t…
$μ^{+} \to e^{+} γ$ and $μ^{+} \to e^{+}e^{+}e^{-}$ processes are analyzed in detail with polarized muons in supersymmetric grand unified theories. We first present Dalitz plot distribution for $μ^{+} \to e^{+}e^{+}e^{-}$ decay based on effective Lagrangian with general lepton-flavor-violating couplings and define various P- and T-odd asymmetries. We calculate branching ratios and asymmetries in supersymmetric SU(5) and SO(10) models taking into account complex soft supersymmetry breaking terms. Imposing constraints from experimental bounds on the electron, neutron and atomic electric dipole m…
Axion-Like Particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global $U(1)$ symmetries. Such particles can have lepton-flavor-violating (LFV) couplings to the SM charged leptons. LFV ALPs provide the possibility to address some of the SM long-lasting problems. We investigate the sensitivity of a future muon collider suggested by the Muon Accelerator Program (MAP) to the production of LFV ALPs in the ALP mass range $m_a\leq1$ MeV. ALPs are assumed to be produced through the LFV decay $τ\ra\ell a$ ($\ell=e,μ$) of one of the tau leptons produced in the muon-an…
The constructions of the new high-intensity muon beamlines are progressing in facilities around the world, and new physics searches related to the muons are expected. The facilities can observe the transverse positron polarization of the polarized $μ^+$ decay to test the standard model. The transition of muonium into antimuonium (Mu-to-$\bar{\text{Mu}}$ transition), which is one of the interesting possibilities in the models beyond the standard model, can be also tested. The near-future observation of the transition gives us a great impact since it indicates that there is an approximate discre…
We discuss the measurement of polarized photons arising from radiative muon capture. The spectrum of left circularly polarized photons or equivalently the circular polarization of the photons emitted in radiative muon capture on hydrogen is quite sensitive to the strength of the induced pseudoscalar coupling constant $g_P$. A measurement of either of these quantities, although very difficult, might be sufficient to resolve the present puzzle resulting from the disagreement between the theoretical prediction for $g_P$ and the results of a recent experiment. This sensitivity results from the abs…
Measuring longitudinally polarized vector boson scattering in, e.g., the ZZ channel is a promising way to investigate the unitarization scheme from the Higgs and possible new physics beyond the Standard Model. However, at the LHC, it demands the end of the HL-LHC lifetime luminosity, 3000/fb, and advanced data analysis technique to reach the discovery threshold due to its small production rates. Instead, there could be great potential for future colliders. In this paper, we perform a Monte Carlo study and examine the projected sensitivity of longitudinally polarized ZZ scattering at a TeV scal…
We present a comprehensive phenomenological study of heavy flavor distributions and correlations in longitudinally polarized proton-proton collisions at BNL-RHIC. All results are obtained with a flexible parton-level Monte Carlo program at next-to-leading order accuracy and include the fragmentation into heavy mesons, their subsequent semi-leptonic decays, and experimental cuts. Next-to-leading order QCD corrections are found to be significant for both cross sections and double-spin asymmetries. The sensitivity of heavy flavor measurements at BNL-RHIC to the gluon polarization of the nucleon i…
We consider the production of muon pairs from the scattering of pions on longitudinally polarized protons. We calculate the cross section and the single spin asymmetry for this process, taking into account pion bound state effects. We work in the kinematic region where the photon has a large longitudinal momentum fraction, which allows us to treat the bound state problem perturbatively. Our predictions are directly proportional to the pion distribution amplitude. A measurement of the polarized Drell-Yan cross section thus allows the determination of the shape of the pion distribution amplitude…
Several parity violating left-right asymmetries in Møller electron-electron and muon-muon scattering are considered in the context of the electroweak standard model at tree level in fixed target and collider experiences. We show that in colliders the asymmetry with only one of the beam polarized is large enough to compensate the smaller cross section at high energies. We also show that these asymmetries are very sensitive to a doubly charged vector bilepton resonance but they are insensitive to scalar ones.
In this paper, we analyze the polarized muon decay at rest (PMDaR) admitting the non-standard V+A interaction in addition to the standard V-A interaction. We show that the angle-energy distribution of Dirac muon neutrinos is sensitive to the interference terms between the standard V-A coupling of left-chirality muon neutrino and exotic V+A coupling of right-chirality one, which are proportional to the transverse components of muon neutrino spin polarization. The interferences do not vanish in a massless limit and include the relative phases to test the CP violation (CPV). It allows to calculat…
QED radiative corrections to polarized muon decay spectrum are considered. Leading and next--to--leading logarithmic approximations are used. Exponentiation of soft radiation is discussed. The present theoretical uncertainty of the spectrum description is estimated.
Although the Lepton Flavor Violating (LFV) decay $μ^+\to e^+ γ$ is forbidden in the Standard Model (SM), it can take place within various theories beyond the SM. If the branching ratio of this decay saturates its present bound [{\it i.e.,} Br$(μ^+ \to e^+γ)\sim 10^{-11}$], the forthcoming experiments can measure the branching ratio with high precision and consequently yield information on the sources of LFV. In this letter, we show that for polarized $μ^+$, by studying the angular distribution of the transversely polarized positron and linearly polarized photon we can derive information on the…
A major part of the future COMPASS program is dedicated to the investigation of the nucleon structure through Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP). COMPASS will measure DVCS and DVMP reactions with a high intensity muon beam of 160 GeV and a 2.5 m-long liquid hydrogen target surrounded by a new TOF system. The availability of muon beams with high energy and opposite charge and polarization will allow to access the Compton form factor related to the dominant GPD $H$ and to study the $x_{B}$-dependence of the $t$-slope of the pure DVCS cross section…
Positronium decay into a muon-antimuon pair by virtue of the interaction with a superintense laser field of linear polarization is considered. The minimum laser intensity required amounts to a few 10^22 W/cm^2 in the near-infrared frequency range. Within the framework of laser-dressed quantum electrodynamics, the total reaction rate is calculated and related to the cross section for field-free electron-positron annihilation into muons. The muons are created with ultrarelativistic energies and emitted under narrow angles along the laser propagation direction. The dynamical properties of the muo…
Predictions for the muon decay spectrum are usually derived from the derivative-free Hamiltonian. However, it is not the most general form of the possible interactions. Additional simple terms with derivatives can be introduced. In this work the distortion of the standard energy and angular distribution of the electrons in polarized muon decay caused by these terms is presented.
Search for azimuthal asymmetries in semi-inclusive production of charged hadrons by 160 GeV muons on the longitudinally polarized deuterium target, has been performed using the 2002- 2004 COMPASS data. The observed asymmetries integrated over the kinematical variables do not depend on the azimuthal angle of produced hadrons and are consistent with the ratio $g_1^d(x)/f_1^d(x)$. The asymmetries are parameterized taking into account possible contributions from different parton distribution functions and parton fragmentation functions depending on the transverse spin of quarks.They can be modulat…
The Michel parameter xi" has been determined from a measurement of the longitudinal polarization of positrons emitted in the decay of polarized and depolarized muons. The result, xi" = 0.981 +- 0.045stat +- 0.003syst, is consistent with the Standard Model prediction of unity, and provides an order of magnitude improvement in the relative precision of this parameter. This value sets new constraints on exotic couplings beyond the dominant V-A description of the leptonic weak interaction.
It is known that the linearly polarized photons can partly transform to circularly polarized ones via forward Compton scattering in a background such as the external magnetic field or noncommutative space time. Based on this fact we explore the effects of the NC-background on the scattering of a linearly polarized laser beam from an intense beam of charged leptons. We show that for a muon/electron beam flux $\bar\varepsilon_{μ,e}\sim 10^{12}/10^{10}\,{\rm TeV}\,{\rm cm}^{-2}\,{\rm sec}^{-1}$ and a linearly polarized laser beam with energy $k^0\sim $1 eV and average power $\bar{P}_{\rm laser}\s…
We examine the utility of employing polarized lepton (electron and muon) beams to perform indirect searches for scalar leptoquarks. We find that polarization can extend the reach in excluding leptoquark masses for both $e^+e^-$ and $μ^+μ^-$ machines. Polarization can also provide a diagnostic tool for determining leptoquark couplings.
Predictions are presented for the oscillation phase in neutrino oscillations following pion decay at rest and in flight, muon decay and nuclear $β-$decay at rest as well as for muon oscillations following pion decay at rest and in flight. The neutrino oscillation phases found disagree with the conventionally used value: $ϕ_{12} = Δm^2 L/(2P)$. The same oscillation phase is found for neutrino and muon oscillations following pion decay at rest. Shortcomings of previous treatments of the quantum mechanics of neutrino oscillations are commented on.
The angular asymmetry in decays of polarized muons and tau leptons is discussed. Both the standard $V-A$ Fermi model and the general parameterization via Michel parameters are considered. Numerical importance of contributions suppressed by charged lepton mass ratio is underlined. Contribution of the second order QED correction is estimated in the leading logarithm approximation.
Combining neutrino oscillations at T2K or T2HK with antineutrinos oscillations from muon decay at rest (DAR) allows a determination of the leptonic CP-violating phase delta. The degeneracies of this phase with theta13 and theta23 are broken and delta can be reliably distinguished from 180-delta. We present the sensitivity to delta of T2(H)K together with a muon DAR experiment using Super-K as a near detector and Hyper-K at the Tochibora site as a far detector.
We have measured the spin-dependent structure function $g_1^p$ in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range $0.003 < x < 0.7$ and $1 GeV^2 < Q^2 < 60 GeV^2$. A next-to-leading order QCD analysis is used to evolve the measured $g_1^p(x,Q^2)$ to a fixed $Q^2_0$. The first moment of $g_1^p$ at $Q^2_0 = 10 GeV^2$ is $Γ^p = 0.136\pm 0.013(stat.) \pm 0.009(syst.)\pm 0.005(evol.)$. This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge $a_0$ is found to be $0.28 \pm 0.16$…
Polarization of a vortex state fermion has rich structure due to the nontrivial momentum distribution of wave function. This larger freedom provides an unique opportunity to prepare fermions in exotic polarized states, which do not exist for plane-wave state fermions. Based on the so called spin-orbit state which was studied both theoretically and experimentally, we put forward a peculiar vortex muon whose polarization exhibits $Z_n$ symmetry and study its decay. We investigate the azimuthal distribution of the emitted electrons and find that it exhibits the same symmetry ($Z_n$) as the initia…
We study the possibility of measuring the muon Yukawa couplings in s-channel Higgs boson production at a muon collider with transversely polarized beams. We investigate sensitivity to the relative size of the CP-odd and CP-even muon Yukawa couplings. Provided the event rate observed justifies the operation of the mu+mu- Higgs boson factory, we find that 40% polarization for both beams is sufficient to resolve the CP nature of a single resonance as well as disentangle it from two overlapping CP conserving resonances.
We show theoretically that the angular distribution of decay rate of muon can be changed dramatically by embedding the decaying muon in a strong linearly polarized laser field. Evaluating the S-matrix elements taking all electronic multiphoton processes into account. The results suggest the muon may have internal structures instead structureless as in the standard model.
We study chargino production at a muon collider with longitudinally polarized beams and center of mass energies around the heavy neutral Higgs boson resonances. We show that the interference of the CP even and CP odd Higgs bosons can be analyzed using the energy distributions of the lepton or W boson from the chargino two-body decays \tildeχ^\pm_j\to\ell^\mp\tildeν_\ell or \tildeχ^\pm_j \to W^\pm \neutralino_1, respectively. The energy distributions depend on the longitudinal polarization of the decaying chargino, which are correlated to the muon beam polarizations. We define asymmetries in th…
Particle oscillations following neutrino production processes are analysed within Feynman's path amplitude formulation of quantum mechanics. Consideration of the temporal sequence of production and detection events reveals an important contribution to the oscillation phase from the space-time propagator of the decaying source particle. Formulae are derived for spatial neutrino oscillations following pion decay (at rest and in flight), muon decay and nuclear $β$-decay at rest, as well as for similar muon oscillations after pion decay at rest and in flight. In all cases studied, the neutrino osc…
Electron-positron pair production in combined laser and Coulomb fields is studied. To this end, the Feynman diagram for multiphoton pair creation by muon impact on a circularly polarized high-frequency laser beam is evaluated within the framework of laser-dressed quantum electrodynamics employing relativistic Volkov states. In the limit of low laser intensity, the result is shown to coincide with the known expression for multiphoton pair creation by a proton which is treated as an external Coulomb field. A scaling of the total pair creation rate is analyzed. The recoil distribution is calculat…
The cross sections for the reactions of muonium(anti-muonium) production in high energy electron(positron) scattering by nuclei e^-(e^+) + Z -> Z + M^0(anti-M^0) + mu^-(mu^+) are calculated in dependence on an energy and polarization of an initial electron(positron) and a polarization of a final mu^-(mu^+)-meson. Due to coherent phenomenon the cross sections are proportional to Z^2. For Z ~ 100 due to the factor Z^2 the cross sections are large enough to be measured at energies available at the HERA Collider in DESY. The results are discussed in connection with a test of CPT invariance.
We studied the radiative muon decay $μ^+ \to e^+ν\barνγ$ by using for the first time an almost fully polarized muon source. We identified a large sample (~13000) of these decays in a total sample of 1.8x10^14 positive muon decays collected in the MEG experiment in the years 2009--2010 and measured the branching ratio B($μ^+ \to e^+ν\barνγ$) = (6.03+-0.14(stat.)+-0.53(sys.))x10^-8 for E_e > 45 MeV and E_γ > 40 MeV, consistent with the Standard Model prediction. The precise measurement of this decay mode provides a basic tool for the timing calibration, a normalization channel, and a strong qual…
We systematically compute and discuss meson and muon polarized radiative decays. Doubly differential distributions in terms of momenta and helicities of the final lepton and photon are explicitly computed. The undergoing dynamics giving rise to lepton and photon polarizations is examined and analyzed in the soft and hard region of momenta. The particular configurations made by right-handed leptons with accompanying photons are investigated and interpreted as a manifestation of the axial anomaly. The photon polarization asymmetry is evaluated. Finiteness of polarized amplitudes against infrared…
The muon decay-at-rest ($μ$-DAR) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $μ$-DAR source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton Hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $μ$-DAR and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic consider…
We have performed a global analysis of muon decay measurements to establish model-independent limits on the space-time structure of the muon decay matrix element. We find limits on the scalar, vector and tensor coupling of right- and left-handed muons to right- and left-handed electrons. The limits on those terms that involve the decay of right-handed muons to left-handed electrons are more restrictive than in previous global analyses, while the limits on the other non-standard model interactions are comparable. The value of the Michel parameter eta found in the global analysis is -0.0036 \pm …
We consider, in the electroweak standard model context, several left-right asymmetries in $μe$ elastic scattering at fixed target and collider experiments. For the former case, we show that the muon mass effects are important in a wide energy range. We also show that these asymmetries are sensitive to the electroweak mixing angle $θ_W$. The effect of an extra $Z'$ neutral vector boson appearing in a 331 model is also considered. The capabilities of these asymmetries in the search of this extra $Z'$ are addressed.
We complement the results for the radiative corrections to the s2.l angular correlation of baryon semileptonic decays of Ref. [1] with the final results in the rest frame of the decaying baryon.
The phases of quantum interference effects in charged lepton production by neutrinos (neutrino oscillations) following pion decay at rest and in flight, muon decay and nuclear $β-$decay at rest as well as for `muon oscillations' following pion decay at rest and in flight are calculated. The same phase is found for neutrino and muon oscillations following pion decay at rest. The results found disagree with the conventionally used value: $ϕ_{12} = Δm^2 L/(2P)$. Differences to previous treatments are briefly commented on
We derive the corrections induced by the W-boson propagator to the differential rates of the leptonic decay of a polarized muon and tau lepton. Results are presented both for decays inclusive of inner bremsstrahlung as well as for radiative ones, when a photon emitted in the decay process is measured. The numerical effect of these corrections is discussed. The definition of the Fermi constant is briefly reviewed.
