arXiv subjects

A. Rubbia

Publications and source records attributed to A. Rubbia.

120 records · Page 7Linked to original sources

arXiv2002

Search for an exotic three-body decay of orthopositronium

We report on a direct search for a three-body decay of the orthopositronium into a photon and two penetrating particles, o-Ps -> gamma + X1 + X2. The existence of this decay could explain the discrepancy between the measured and the predicted values of the orthopositronium decay rate. From the analysis of the collected data a single candidate event is found, consistent with the expected background. This allows to set an upper limit on the branching ratio < 4.4 \times 10^{-5} (at the 90% confidence level), for the photon energy in the range from 40 keV < E_gamma< 400 keV and for mass values in the kinematical range 0 < mX1+mX2 <900 keV. This result unambiguously excludes the o-Ps -> gamma + X1 + X2 decay mode as the origin of the discrepancy.

hep-ex↗

arXiv2002

Invisible decay of orthopositronium vs extra dimensions

In models of Randall-Sundrum type orthopositronium (o-Ps) can disappear due to tunnelling into additional dimension(s). The experimental signature of this effect is the invisible decay of orthopositronium. We point out that this process may occur at a rate within two or three orders of magnitude of the present experimental upper limit. We discuss this in details and stress that the existence of invisible decay of orthopositronium in vacuum could explain the o-Ps decay rate puzzle. Thus, our result enhances the existing motivation and justifies efforts for a more sensitive search for o-Ps->invisible decay in a near future experiment. Possible manifestations of new physics in other rare (exotic) decays of orthopositronium are also discussed.

hep-ph↗

arXiv2001

On the energy and baseline optimization to study effects related to the $δ$-phase (CP-/T-violation) in neutrino oscillations at a Neutrino Factory

In this paper we discuss the detection of CP and T-violation effects in the framework of a neutrino factory. We introduce three quantities, which are good discriminants for a non vanishing complex phase ($δ$) in the $3\times 3$ neutrino mixing matrix. We find that these three discriminants (in vacuum) all scale with $L/E_ν$. Matter effects modify the scaling, but these effects are large enough to spoil the sensitivity only for baselines larger than 5000 km. So, in the hypothesis of constant neutrino factory power, the sensitivity on the $δ$-phase is independent of the baseline chosen. Specially interesting is the direct measurement of T-violation from the ``wrong-sign'' electron channel, which involves a comparison of the $\nue\ra\numu$ and $\numu\ra\nue$ oscillation rates. However, the $\numu\ra\nue$ measurement requires magnetic discrimination of the electron charge, experimentally very challenging in a neutrino detector: low-energy neutrino beams and hence short baselines, are preferred. In this paper we show the exclusion regions in the $Δm^2_{12} - δ$ plane for two concrete cases. We obtain a similar excluded region provided that the electron detection efficiency is $\sim$20% and the charge confusion 0.1%. The $Δm^2_{12}$ compatible with the LMA solar data can be tested with a flux of 5$\times 10^{21}$ muons. We compare these results with the fit of the visible energy distributions.

hep-ph↗

arXiv2001

Neutrino cross-section measurement with neutrinos from muon decay

In this paper we stress the idea that new, more precise neutrino cross-sections measurements at low energies will be necessary to improve the results of future big neutrino detectors, which will be dominated by the contribution of the systematic errors. The use of a muon beam instead of the traditional pion beams is proposed. This choice allows the simultaneous measurement of both, numu and nue interactions and the two helicities, in a clean environment and with a precise knowledge of the beam flux. We show that with approx 10^{15} mu's/year and a moderate mass detector (approx 100 tons) placed close to the muon storage ring, precisions of the order of 10% in sigma(nu) (E_nu bin size of 100 MeV) can be reached for neutrino energies below 2 GeV.

hep-ph↗

arXiv2000

The flavor of neutrinos in muon decays at a neutrino factory and the LSND puzzle

The accurate prediction of the neutrino beam produced in muon decays and the absence of opposite helicity contamination for a particular neutrino flavor make a future neutrino factory the ideal place to look for the lepton flavor violating (LFV) decays of the kind $μ^+\ra e^+\nuebar\numu$ and lepton number violating (LNV) processes like $μ^-\ra e^-\nue\numu$. Excellent sensitivities can be achieved using a detector capable of muon and/or electron identification with charge discrimination. This would allow to set experimental limits that improve current ones by more than two orders of magnitude and test the hypothesis that the LSND excess is due to such anomalous decays, rather than neutrino flavor oscillations in vacuum.

hep-ph↗

arXiv2000

Physics at a Neutrino Factory

In response to the growing interest in building a Neutrino Factory to produce high intensity beams of electron- and muon-neutrinos and antineutrinos, in October 1999 the Fermilab Directorate initiated two six-month studies. The first study, organized by N. Holtkamp and D. Finley, was to investigate the technical feasibility of an intense neutrino source based on a muon storage ring. This design study has produced a report in which the basic conclusion is that a Neutrino Factory is technically feasible, although it requires an aggressive R&D program. The second study, which is the subject of this report, was to explore the physics potential of a Neutrino Factory as a function of the muon beam energy and intensity, and for oscillation physics, the potential as a function of baseline.

hep-ex↗

arXiv2000

Physics potential at a neutrino factory: can we benefit from more than just detecting muons?

In order to fully address the oscillation processes at a neutrino factory, a detector should be capable of identifying and measuring all three charged lepton flavors produced in charged current interactions {\it and} of measuring their charges to discriminate the incoming neutrino helicity. This is an experimentally challenging task, given the required detector mass for long-baseline experiments. We address the benefit of a high-granularity, excellent-calorimetry non-magnetized target-detector, which provides a background-free identification of electron neutrino charged current and a kinematical selection of tau neutrino charged current interactions. We assume that charge discrimination is only available for muons reaching an external magnetized-Fe spectrometer. This allows the clean classification of events into electron, right-sign muon, wrong-sign muon and no-lepton categories. In addition, high granularity permits a clean detection of quasi-elastic events, which by detecting the final state proton, provide a selection of the neutrino electron helicity without the need of an electron charge measurement. From quantitative analyses of neutrino oscillation scenarios, we conclude that in many cases the discovery sensitivities and the measurements of the oscillation parameters are dominated by the ability to measure the muon charge. However, we identify cases where identification of electron and tau samples contributes significantly.

hep-ph↗

arXiv2000

ICANOE - Imaging and Calorimetric Neutrino Oscillation Experiment

The main scientific goal of the ICANOE detector is the one of elucidating in a comprehensive way the pattern of neutrino masses and mixings, following the SuperKamiokande results and the observed solar neutrinos deficit. To achieve these goals, the experimental method is based upon the complementary and simultaneous detection of CERN beam (CNGS) and cosmic ray (CR) events. For the currently allowed values of the SuperKamiokande results, both CNGS and cosmic ray data will give independent measurements and provide a precise determination of the oscillation parameters.

hep-ex↗

arXiv1999

Three-family oscillations using neutrinos from muon beams at very long baseline

The planned LBL experiments will be able to prove the hypothesis of flavor oscillation between muon and tau neutrinos. We explore the possibility of a second generation long baseline experiment at very long baseline, i.e. L in the range 5000-7000 km. This distance requires intense neutrino beams that could be available from very intense muon beams as those needed for $μ$ colliders. Such baselines allow the study of neutrino oscillations with $E/L \approx 2\times 10^{-3} eV^2$ with neutrinos of energy $E_ν\approx 10 GeV$, i.e. above tau threshold. Moreover, matter effects inside the Earth could lead to observable effects in $ν_e \to ν_μ$ oscillations. These effects are interchanged between neutrinos and antineutrinos, and therefore they can be tested by comparing the oscillated spectra obtained running the storage ring with positive and negative muons.

hep-ph↗

arXiv1998

A medium baseline search for $ν_μ\toν_e$ oscillations at a $ν$ beam from muon decays

The accurate knowledge of the $\barν_e (ν_μ)$ beam produced in $μ^-$ decays and the absence of $ν_e (\barν_μ)$ contamination, make a future muon storage ring the ideal place to look for $\numunue$ ($\numubarnuebar$) oscillations. Using a detector capable of electron and muon identification with charge discrimination (e.g., the presently running NOMAD experiment), good sensitivities to $\numunue (\numubarnuebar)$ oscillations could be achieved. With the CERN-PS as a proton driver for a muon storage ring of the kind envisaged for a $μ$-collider, the LSND claim would be confirmed or disproved in a few years of running.

hep-ph↗

arXiv1998

Long baseline neutrino oscillation disappearance search using a $ν$ beam from muon decays

We study the feasibility of performing a $ν_μ$ disappearance long-baseline experiment using a neutrino beam coming from muon decays. The advantage of such a technique with respect to the production of neutrino beams from pions is that in a muon decay both muon and electron neutrinos are produced in the same quantity. In case of $ν_μ\toν_{τ,s}$ oscillations, the $ν_e$ charged current (CC) events can be used as a control sample, to predict in situ the $ν_μ$ rates, thus reducing the systematics due to the knowledge of the neutrino flux, which is the main source of uncertainties for disappearance experiments. We consider as our neutrino target, the ICARUS detector in its final mass configuration of 4.8 kton.

hep-ph↗

arXiv1998

A Test of $\numunux$ Oscillations and determination of the $Δm^2$ parameter of Atmospheric Neutrinos using the $L/E$ method

We point out that the measurement of the $L/E$ distribution of atmospheric neutrino events with sufficient resolution in order to observe the characteristic modulations of neutrino oscillations would provide a unique way to test the $\numunux$ oscillations nature of the atmospheric neutrino anomaly in the parameter range $5\times 10^{-4} < Δm^2 < 2\times 10^{-3}\rm\ eV^2$. With an integrated exposure of a few tens of kiloton-year, this method can cover the lower part of the $Δm^2$ region of the currently allowed atmospheric neutrino solution and is therefore complementary to the one explorable with planned long-baseline neutrino beam experiments. We stress that experimentally this method relies on the ability to measure high energy muons ($E_μ>5\rm GeV$). A large magnetized calorimeter of several kilotons would be ideally suited for this measurement. The existing LEP detectors augmented with atmospheric neutrino triggers could also be used to perform such a study.

hep-ph↗