Tau Factories Research Articles

Collimated muon beam proposal for probing neutrino charge-parity violation

AbstractThe phenomenon of neutrino oscillation is of great theoretical and experimental interest for our understand of the nature of the neutrino and its implication for physics beyond the standard Model. Currently available neutrino oscillation experiments can already constrain neutrino mixing parameters with a confidence level up to 3 standard deviations (σ). However, it remains challenging to provide a deterministic constraint on the Charge-Parity (CP) violation phase of the neutrino mixing matrix. Here, we propose an experimental setup that exploits collimated muon beams to probe neutrino CP-violation. In our proposed acceleration experiment, a 45 GeV positron source with additional muon collimation, interfaces with near-future neutrino detectors like DUNE and T2K, to probe neutrino CP-violation phase with a significantly higher sensitivity than obtained with the neutrino detectors alone, and to determine tau neutrino properties. Simulations estimate the collection of 104 tau (anti-) neutrino in 5 years, and a sensitivity of over 7 standard deviations for δCP = ∣π/2∣ in 5 years. Collecting ντ appearance events from μ− and μ+ beams over 10 years can attain a 3-4 standard deviation sensitivity. This proposal may serve as a tau factory.

Touschek lifetime and luminosity optimization for Russian Super Charm Tau factory

Electron-positron collider Super Charm Tau factory is planned to be built in the National center for physics and mathematics, Sarov. It is a double ring collider with crab waist collision scheme operating in wide beam energy range from 1.5 GeV to 3.5 GeV with peak luminosity of 1035 cm-2s-1. The polarized electron source and three Siberian Snakes provide 80% longitudinally polarized electron beam at 2 GeV. Superconducting wigglers decrease damping times, effects of intra-beam scattering and increase Touschek beam lifetime, particularly at low energy. The paper presents the status of collider design and optimization of luminosity and beam lifetime.

Measurement of the Weinberg Angle in an Experiment at the Super Charm Tau Factory with a Polarized Beam

Measurement of the Weinberg Angle in an Experiment at the Super Charm Tau Factory with a Polarized Beam

DIRC options for the Super Charm Tau Factory

The Super Charm Tau Factory (SCTF) is a future facility to be built in Novosibirsk (Russia). It mainly addresses unanswered questions regarding the Standard Model (SM) of particle physics such as flavor violating decays and charmonium states beyond the open-charm threshold. SCTF is going to provide a luminosity up to 1035 cm−2s−1 with a center of mass (CMS) energy between 2 and 6 GeV . The physics programs studied in SCTF require excellent particle identification of muons and charged pions especially in the low momentum regime. In particular, the accurate separation of both particle species at momenta between 0.2 and 1.5 GeV is very important. Two Cherenkov detectors, based on the principle of detection of internally reflected Cherenkov radiation (DIRC), are proposed to cover the desired phase space over the full solid angle. Both detectors, the Endcap Disc DIRC (EDD) and the Barrel DIRC, have been originally designed for pion/kaon separation in the future PANDA detector at FAIR in Germany and need to be adapted and optimized for the SCTF detector in order to achieve the desired Cherenkov angle resolution of less than 1 mrad for particle momenta around 1 GeV/c.

Exploring CP-violating heavy neutrino oscillations in rare tau decays at Belle II

In this work, we study the lepton number violating tau decays via two intermediate on-shell Majorana neutrinos Nj into two charged pions and a charged lepton τ±→π±Nj→π±π±ℓ∓. We consider the scenario where the heavy neutrino masses are within 0.5 GeV≤MN≤1.5 GeV. We evaluated the possibility to measure the modulation of the decay width along the detector length for these processes at tau factories, such as Belle II. We study some realistic conditions which could lead to the observation of this phenomenon at futures τ factories.

Search for the Electric Dipole Moment and anomalous magnetic moment of the tau lepton at tau factories

Precise measurement of the Electric Dipole Moment (EDM) and anomalous magnetic moment (g-2) of particles are important tests of Beyond Standard Model (BSM) physics. It is generally believed that the tau lepton couples more strongly to BSM due to its large mass, and can be searched for at collider experiments. A new method to ap- proximately reconstruct the neutrinos from the hadronic decays of τ−τ+ pairs produced at e−e+ tau factories is proposed. With all final state particle momenta available, observables based on matrix elements and sensitive to BSM are calculated. It is estimated that with 50 ab−1 of data to be delivered by the Belle-II experiment, a tau EDM search with a 1-σ level precision of left|{d}_{tau}^{NP}right|<2.04times {10}^{-19} 10 e·cm, and g-2 search with left|{alpha}_{tau}^{NP}right|<1.75times {10}^{-5} (1.5% of the SM prediction), can be expected when systematics are not considered. The new precision can effectively constrain BSM models with heavy mirror neutrinos. It can also constrain models containing a light scalar with mass at O(1 GeV), which can explain the current muon g-2 anomaly as well. The method in this work offers a new opportunity to search for BSM at current and future tau factories with high precision.

Particle identification system for the Super Charm–Tau Factory at Novosibirsk

The Super Charm–Tau (SCT) Factory is a proposed electron–positron collider in Novosibirsk with a peak luminosity of 1035cm−1s−1 operating in the energy range between 2and 6 GeV. The interaction region should be equipped by an excellent universal particle detector meeting the requirements of broad physics program of the experiment. Research and development for all detector subsystems is currently underway. Particle identification (PID) system of the detector is required to provide the state-of-the-art level of μ/π separation for the particle momenta up to 1.2GeV∕c. The following options for the PID system are considered in this paper: focusing aerogel ring imaging Cherenkov (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel shifter photomultiplier (ASHIPH), and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30ps. Assessment of the charged particle separation performance for these options based on simulation and prototype tests results is presented.

Project for a Super Charm–Tau Factory at BINP

The construction of an electron–positron collider of the megascience class, referred to as the Super Charm–Tau Factory, is envisaged at the Budker Institute of Nuclear Physics (Novosibirsk). The beam energy will vary between 1 and 2.5 GeV, and the peak luminosity of the machine will reach 1035 cm–2 s–1 owing to the Crab-Waist collision scheme and to high beam currents (up to 2 A). The project provides for a longitudinal polarization of the electron beam in the collision region. The physics agenda includes in-depth studies of the c-quark and tau-lepton properties and a search for beyond-SM physics.

Resonant CP violation in rare \u03c4\xb1 decays

In this work, we study the lepton number violating tau decays via intermediate on-shell Majorana neutrinos Nj into two scalar mesons and a lepton τ± → M1±Nj → M1±M2±ℓ∓. We calculate the Branching ratios Br(τ±) and the CP asymmetry (Γ(τ+) − Γ(τ−))/(Γ(τ+) + Γ(τ−)) for such decays, in a scenario that contains at least two heavy Majorana neutrinos. The results show that the CP asymmetry is small, but becomes comparable with the branching ratio Br(τ±) when their mass difference is similar with their decay width ΔMN ∼ ΓN. We also present regions of the heavy-light neutrino mixing elements, in which the CP asymmetry could be explored in future tau factories.

Lepton flavour violation in a left-right symmetric model

We consider in this paper a Left-Right symmetric gauge model in which a global lepton-number-like symmetry is introduced and broken spontaneously at a scale that could be as low as 10^4 GeV or so. The corresponding physical Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level flavour-violating couplings to the charged fermions, leading to sizeable majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a leptonic variant of the model and show that the branching ratios for \mu -> e+J, \tau -> e + J and \tau -> \mu + J decays can be large enough to fall within the sensitivities of future \mu and \tau factories. On the other hand the left-right gauge symmetry breaking scale may be as low as few TeV.

Physics at new accelerators: Looking beyond the standard model

Neutrino masses can have important implications in nuclear and particle physics, astrophysics and cosmology. Apart from the effects related to solar neutrinos, neutrino oscillations, dark matter, beta and double beta decays, massive neutrinos can also produce signals in the new accelerators. Here I focus on μ and τ number violating processes, very promising for muon and tau factories, as well as on the signatures associated with spontaneously broken R parity supersymmetry and neutral heavy leptons. These include the possibility of high rates for single chargino and neutralino production at LEP, LHC/SSC, as well as new signatures involving invisibly decaying Higgs bosons.

Neutrino masses in supersymmetry with spontaneously broken R-parity

The neutrino mass spectrum that arises in supersymmetry models with spontaneously broken R-parity is studied in detail. We analyse the attainable values for m ν e , m ν μ and m ν τ , once all observational constraints have been incorporated, including both those that arise from collider experiments such as LEP, as well as weak interaction constraints, such as the non-observation of neutrinoless double-β decay, the limits from neutrino oscillation searches, etc. For natural choices of the parameters neutrino masses arise in a very striking pattern: while ν e and ν μ have masses lying in the adequate range for the explanation of the observed deficit in the solar neutrino flux via the MSW effect, the ν τ mass is large enough to lead to novel signatures associated with the τ-lepton that could be seen both a LEP as well as at a tau factory. These provide an additional tool to probe the parameters characterizing the solar neutrino conversions in conventional accelerator experiments. The related processes include the single-chargino Z-decay branching ratio BR( Z → χτ) as large as ∼ 6 × 10 −5 and single-majoron emission τ-decay branching ratios τ → μ + J as large as ∼ 10 −4 corresponding to solar neutrino oscillation parameters in the non-adiabatic branch favoured by present solar neutrino data. The τ-neutrino is naturally much heavier than ν μ and decays to it via majoron emission, with a lifetime short enough to obey cosmological limits.

The electric dipole moment of the tau

Although stringent limits exist on the electric dipole moments of the neutron, electron and muon, there is very little information on the electric dipole moment of the tau. Such a dipole moment would be observable in the angular distribution of the tau pairs in electron-position annihilation. We calculate the effects of an electric dipole moment on this angular distribution, and show that the current upper bound on the electric dipole moment is 1.4 × 10 16 e cm. This bound could be improved significantly at a tau factory. The electric dipole moment of neutrinos is also discussed.