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D. Meloni

Publications and source records attributed to D. Meloni.

At least 55 records · Page 3Linked to original sources
arXiv2010

Atmospheric lepton fluxes at very high energy

The observation of astrophysical neutrinos requires a detailed understanding of the atmospheric neutrino background. Since neutrinos are produced in meson decays together with a charged lepton, important constraints on this background can be obtained from the measurement of the atmospheric muon flux. Muons, however, can also be produced as mu+ mu- pairs by purely electromagnetic processes. We use the Z-moment method to study and compare the contributions to the atmospheric muon and neutrino fluxes from different sources (pi/K decay, charmed and unflavored hadron decay, and photon conversion into a muon pair). We pay special attention to the contribution from unflavored mesons (eta, eta', rho0, omega and phi). These mesons are abundant in air showers, their lifetimes are much shorter than those of charged pions or kaons, and they have decay branching ratios of order 10^-4 into final states containing a muon pair. We show that they may be the dominant source of muons at E_mu >10^3 TeV.

astro-ph.HE↗
arXiv2009

Atmospheric lepton fluxes at ultrahigh energies

In order to estimate the possibility to observe exotic physics in a neutrino telescope, it is essential to first understand the flux of atmospheric neutrinos, muons and dimuons. We study the production of these leptons by high-energy cosmic rays. We identify three main sources of muons of energy E > 10^6 GeV: the weak decay of charm and bottom mesons and the electromagnetic decay of unflavored mesons. Contrary to the standard assumption, we find that eta mesons, not the prompt decay of charm hadrons, are the dominant source of atmospheric muons at these energies. We show that, as a consequence, the ratio between the neutrino and muon fluxes is significantly reduced. For dimuons, which may be a background for long-lived staus produced near a neutrino telescope, we find that pairs of E ~ 10^7 GeV forming an angle above 10^-6 rad are produced through D (80%) or B (10%) meson decay and through Drell-Yan proceses (10%). The frequency of all these processes has been evaluated using the jet code PYTHIA.

hep-ph↗
arXiv2008

Solving the octant degeneracy with the Silver channel

We study the potential of the combination of the golden ($ν_e \to ν_μ$) and silver ($ν_e \to ν_τ$) channels to solve the octant degeneracy affecting the measurement of $θ_{13}$ and $δ$ at future neutrino factories. To search for $τ$ leptons produced in $ν_τ$ charged-current interactions, we consider two different detectors: the Emulsion Cloud Chamber detector (ECC) and the Liquid Argon Time Projection Chamber (LAr TPC). We show that, when using similar detector masses, the upgraded version of the ECC detector (sensitive also to hadronic $τ$ decay modes) and the LAr TPC detector have comparable sensitivities to the octant of $θ_{23}$, being able to discriminate the two solutions for $\sin^2 (2θ_{13}) \gtrsim 10^{-3}$ at 3$σ$ level if $θ_{23}=40^\circ$. We also show that the same setups are able to see deviation from maximal mixing as small as $\sim$ (4-6)% (at 3$σ$) if $θ_{13}$ is close to its upper bound.

hep-ph↗
arXiv2007

Sterile neutrinos at the CNGS

We study the potential of the CNGS beam in constraining the parameter space of a model with one sterile neutrino separated from three active ones by an $\mathcal{O}(\eVq)$ mass-squared difference, $\Dmq_\Sbl$. We perform our analysis using the OPERA detector as a reference (our analysis can be upgraded including a detailed simulation of the ICARUS detector). We point out that the channel with the largest potential to constrain the sterile neutrino parameter space at the CNGS beam is $ν_μ\to ν_τ$. The reason for that is twofold: first, the active-sterile mixing angle that governs this oscillation is the less constrained by present experiments; second, this is the signal for which both OPERA and ICARUS have been designed, and thus benefits from an extremely low background. In our analysis we also took into account $ν_μ\to ν_e$ oscillations. We find that the CNGS potential to look for sterile neutrinos is limited with nominal intensity of the beam, but it is significantly enhanced with a factor 2 to 10 increase in the neutrino flux. Data from both channels allow us, in this case, to constrain further the four-neutrino model parameter space. Our results hold for any value of $\Dmq_\Sbl \gtrsim 0.1 \eVq$, \textit{i.e.} when oscillations driven by this mass-squared difference are averaged. We have also checked that the bound on $θ_{13}$ that can be put at the CNGS is not affected by the possible existence of sterile neutrinos.

hep-ph↗
arXiv2007

Exotic physics with ultrahigh energy cosmic rays

Ultrahigh energy cosmic rays provide a unique ground for probing new physics. In this talk we review the possibility of testing TeV gravity in interactions of cosmogenic neutrinos and the potential to discover long-lived exotic particles in nucleon-produced air showers, such as gluinos of split-SUSY models or staus of supersymmetric models with a gravitino LSP.

hep-ph↗
arXiv2007

New physics from ultrahigh energy cosmic rays

Cosmic rays from outer space enter the atmosphere with energies of up to 10^{11} GeV. The initial particle or a secondary hadron inside the shower may then interact with an air nucleon to produce nonstandard particles. In this article we study the production of new physics by high energy cosmic rays, focusing on the long-lived gluino of split-SUSY models and a WIMP working as dark matter. We first deduce the total flux of hadron events at any depth in the atmosphere, showing that secondary hadrons can not be neglected. Then we use these results to find the flux of gluinos and WIMPs that reach the ground after being produced inside air showers. We also evaluate the probability of producing these exotic particles in a single proton shower of ultrahigh energy. Finally we discuss the possible signal in current and projected experiments. While the tiny flux of WIMPs does not seem to have any phenomenological consequences, we show that the gluinos could modify substantially the profile of a small fraction of extensive air showers. In particular, they could produce a distinct signal observable at AUGER in showers of large zenith angle.

hep-ph↗
arXiv2006

Probing TeV gravity at neutrino telescopes

Models with extra dimensions and the fundamental scale at the TeV could imply sign als in large neutrino telescopes due to gravitational scattering of cosmogenic neu trinos in the detection volume. Apart from the production of microscopic black hol es, extensively studied in the literature, we present gravity-mediated interactions at larger distances, that can be calculated in the e ikonal approximation. In these elastic processes the neutrino loses a small fracti on of energy to a hadronic shower and keeps going. The event rate of these events is higher than that of black hole formation and the signal is distinct: no charged leptons and possibly multiple-bang events.

hep-ph↗
arXiv2006

$ν_μ$ disappearance at the SPL, T2K-I, NO$ν$A and the Neutrino Factory

We study the measurement of the atmospheric neutrino oscillation parameters, $θ_{23}$ and $Δm^2_{23}$, at the $ν_μ$ disappearance channel at three conventional beam facilities, the SPL, T2K-phase I and NO$ν$A. These two parameters have been shown to be of crucial importance in the measurement of two of the unknowns of the PMNS mixing matrix, $θ_{13}$ and the leptonic CP-violating phase $δ$. In our analyis, the effect of the two discrete ambiguities, ${\rm sign}(Δm^2_{23})$ and ${\rm sign}(\tan 2 θ_{23})$, is explicitly taken into account. We analyse also the $ν_μ$ disappearance channel at the Neutrino Factory, and combine it with the ``golden'' $ν_e \to ν_μ$ and ``silver'' $ν_e \to ν_τ$ appearance channels to study its impact on the measurement of $θ_{13}$ and $δ$. Eventually, we present the sensitivity of the four facilities to different observables: $θ_{13}$, $δ$, maximal $θ_{23}$, the sign of the atmospheric mass difference, $s_{atm}$, and the $θ_{23}$-octant, $s_{oct}$.

hep-ph↗
arXiv2005

The impact of solar and atmospheric parameter uncertainties on the measurement of $θ_{13}$ and $δ$

We present in this paper the analysis of the measurement of the unknown PMNS parameters $θ_{13}$ and $δ$ at future LBL facilities performing complete three parameters fits, each time fully including in the fit one of the atmospheric and solar oscillation parameters within its present (future) error. We show that, due to the presence of degeneracies, present uncertainties on $θ_{23}$ and $Δm^2_{23}$ worsen significantly the precision on ($θ_{13}$,$δ$) at future LBL experiments. Only if a precision on the atmospheric parameters at least similar to what expected at T2K-I is reached, then the sensitivities to $θ_{13}$ and $δ$ that have been presented in the literature for many facilities (where $θ_{23}$ and $Δm^2_{23}$ are generally considered as fixed external inputs) can indeed be almost recovered.On the other hand, the impact on this measurement of the uncertainties on the solar parameters, $θ_{12}$ and $Δm^2_{12}$ is already negligible. Our analysis has been performed using three reference setups: the SPL Super-Beam and the standard low-$γ$ $β$-Beam, both aiming toward a Mton Water Čerenkov detector located at L=130 km; the 50 GeV Neutrino Factory with a 40 kton Magnetized Iron Detector to look for the ``golden channel'' $ν_e \to ν_μ$ with baseline L=3000 km and a 4 kton Emulsion Cloud Chamber to look for the ``silver channel'' $ν_e \to ν_τ$ with baseline L=732 km.

hep-ph↗
arXiv2005

The measurement of $θ_{13}$ and $δ$: the role of the uncertainties on the solar and atmospheric parameters

In this talk we show how the errors on solar and atmospheric parameters affect the measurement of the unknown PMNS parameters $θ_{13}$ and $δ$ at future LBL facilities. Performing three parameters fits in $θ_{13}$, $δ$ and, in turn, one of the atmospheric or solar parameters, we show that present uncertainties on $θ_{23}$ and $Δm^2_{23}$ worsen significantly the precision on ($θ_{13}$,$δ$) whereas the solar sector does not introduce further uncertainties. A precision on the atmospheric parameters similar to what expected at T2K-I is necessary to improve the sensitivities to $θ_{13}$ and $δ$.

hep-ph↗
arXiv2005

TeV gravity at neutrino telescopes

Cosmogenic neutrinos reach the Earth with energies around 10^9 GeV, and their interactions with matter will be measured in upcoming experiments (Auger, IceCube). Models with extra dimensions and the fundamental scale at the TeV could imply signals in these experiments. In particular, the production of microscopic black holes by cosmogenic neutrinos has been extensively studied in the literature. Here we make a complete analysis of gravity-mediated interactions at larger distances, where they can be calculated in the eikonal approximation. In these processes a neutrino of energy E_νinteracts elastically with a parton inside a nucleon, loses a small fraction y of its energy, and starts a hadronic shower of energy y E_ν<< E_ν. We analyze the ultraviolet dependence and the relevance of graviton emission in these processes, and show that they are negligible. We also study the energy distribution of cosmogenic events in AMANDA and IceCube and the possibility of multiple-bang events. For any neutrino flux, the observation of an enhanced rate of neutral current events above 100 TeV in neutrino telescopes could be explained by TeV-gravity interactions. The values of the fundamental scale of gravity that IceCube could reach are comparable to those to be explored at the LHC.

hep-ph↗
arXiv2005

Flavour and polarisation in heavy neutrino production at e+ e- colliders

We analyse l W nu production at ILC, paying special attention to the role of the final lepton flavour and beam polarisation in the search for a new heavy neutrino N. We show that a sizeable coupling to the electron V_eN ~ 10^-2 is necessary to have an observable signal in any of the channels, despite the fact that the signal may be more visible in muon or tau final states. The non-observation of a heavy neutrino at ILC will improve the present upper bound on its mixing with the electron by more than one order of magnitude, V_eN < 0.007 for m_N between 200 and 400 GeV.

hep-ph↗
arXiv2004

Cosmogenic neutrinos and signals of TeV gravity in air showers and neutrino telescopes

The existence of extra dimensions allows the possibility that the fundamental scale of gravity is at the TeV. If that is the case, gravity could dominate the interactions of ultra-high energy cosmic rays. In particular, the production of microscopic black holes by cosmogenic neutrinos has been estimated in a number of papers. We consider here gravity-mediated interactions at larger distances, where they can be calculated in the eikonal approximation. We show that for the expected flux of cosmogenic neutrinos these elastic processes give a stronger signal than black hole production in neutrino telescopes. Taking the bounds on the higher dimensional Planck mass M_D (D=4+n) from current air shower experiments, for n=2 (6) elastic collisions could produce up to 118 (34) events per year at IceCube. On the other hand, the absence of any signal would imply a bound of M_D>~5 TeV.

hep-ph↗
arXiv2003

Clone flow analysis for a theory inspired Neutrino Experiment planning

The presence of several clone solutions in the simultaneous measurement of ($θ_{13},δ$) has been widely discussed in literature. In this letter we write the analytical formulae of the clones location in the ($θ_{13},δ$) plane as a function of the physical input pair ($\barθ_{13},\barδ$). We show how the clones move with changing $\barθ_{13}$. The "clone flow" can be significantly different if computed (naively) from the oscillation probabilities or (exactly) from the probabilities integrated over the neutrino flux and cross-section. Using our complete computation we compare the clone flow of a set of possible future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory proposals. We show that the combination of these specific BetaBeam and SuperBeam does not help in solving the degeneracies. On the contrary, the combination of one of them with the Neutrino Factory Golden and Silver channel can be used, from a theoretical point of view, to solve completely the eightfold degeneracy.

hep-ph↗
arXiv2003

The synergy of the golden and silver channels at the Neutrino Factory

We deepen the study of the so-called ``silver channel'' $ν_e \to ν_τ$ \cite{Donini:2002rm} and of its relevance to solve some of the ambiguities that can arise in the simultaneous measurement of $(θ_{13},δ)$ at the Neutrino Factory by presenting in full detail the characteristics of the considered OPERA-like detector and the experimental treatment of the different backgrounds and signals. Furthermore, we perform a detailed study of the systematic errors associated both with the OPERA-like and the magnetized-iron detectors and their effects on the sensitivity. Finally, we also apply a refined statistical analysis of the simulated events based on the frequentist approach.

hep-ph↗
arXiv2002

The silver channel at the Neutrino Factory

We notice that looking for $ν_e \to ν_τ$ at the same time as $ν_e \to ν_μ$ oscillations could significantly help to reduce the errors in the leptonic CP-violating phase $δ$ measurement. We show how the $ν_e \to ν_μ$ (``golden'') and $ν_e \to ν_τ$ (``silver'') transitions observed at an OPERA-like 2 Kton lead-emulsion detector at L = 732 Km, in combination with the $ν_e \to ν_μ$ transitions observed at a 40 Kton magnetized iron detector with a baseline of L = 3000 Km, strongly reduce the so-called $(θ_{13}, δ)$ ambiguity. We also show how a moderate increase in the OPERA-like detector mass (4 Kton instead of 2 Kton) completely eliminates the clone regions even for small values of $θ_{13}$.

hep-ph↗
arXiv2002

Telling three from four neutrino scenarios

In this talk I will consider the possibility of distinguish the usual three neutrino model from scenarios in which a light sterile neutrino is also present. I will show that the confusion with the so-called 3+1 scheme can arise in some particular region of the parameter space whereas it is essentially absent for the 2+2 scheme. Then I will discuss the ambiguities in the determination of the CP-violating phase $δ$.

hep-ph↗