arXiv subjects

Kamales Kar

Publications and source records attributed to Kamales Kar.

33 records · Page 2Linked to original sources

arXiv2003

Prospects of probing $θ_{13}$ and neutrino mass hierarchy by Supernova Neutrinos in KamLAND

In this paper we study the physics potential of the KamLAND detector in probing neutrino oscillation parameters through observation of supernova neutrinos. In particular, we discuss the possibilities of probing the mixing angle $θ_{13}$ and determining the sign of $Δm^2_{32}$ from the total charged current(CC) event rates on the proton and $^{12}{C}$ target, as well as from the CC spectra. We discuss the chances of probing the earth matter effect induced modulations from the observation of CC spectra in the different CC reactions in KamLAND and find the volume required to get a statistically significant signature of the earth matter effect in different energy bins. We also calculate the event rates expected in the neutral current (NC) reactions on Carbon and free proton and investigate if the charged current to neutral current ratios, which are free of the absolute luminosity uncertainty in the supernova neutrino fluxes, can be useful in probing the oscillation parameters.

hep-ph↗

arXiv2002

Neutrinos from Supernovae

In this review, the effect of flavor oscillations on the neutrinos released during supernova explosion after core collapse is described. In some scenarios there are large enhancement of the number of events compared to the no oscillation case. Various other features associated with supernova neutrinos are also discussed.

hep-ph↗

arXiv2002

Half lives and Rates for Electron Capture on Drip Line Nuclei and for Beta Decay with 65 < A <100

The half lives are calculated for the process of $β^\pm$ decay and electron capture for nuclei in mass range $\sim$ 65 - 100 relevant for the core of a massive star at late burning stage of steller evolution that leads to supernova explosion. The rates of electron capture process are also computed for nuclei relevant during presupernova stage of massive stars. These half lives and rates are calculated by expressing $β^\pm$ Gamow-Teller decay strengths in terms of smoothed bivariate strength densities. These strength densities are constructed in the framework of spectral averaging theory for two body nuclear Hamiltonian in a large nuclear shell model space. The method has a natural extension to weak interaction rates for r and rp-processes.

astro-ph↗

arXiv2002

Three Generation Neutrino Oscillation Parameters after SNO

We examine the solar neutrino problem in the context of the realistic three neutrino mixing scenario including the SNO charged current (CC) rate. The two independent mass squared differences $Δm^2_{21}$ and $Δm^2_{31} \approx Δm^2_{32}$ are taken to be in the solar and atmospheric ranges respectively. We incorporate the constraints on $Δ$m$^2_{31}$ as obtained by the SuperKamiokande atmospheric neutrino data and determine the allowed values of $Δm^2_{21}$, $θ_{12}$ and $θ_{13}$ from a combined analysis of solar and CHOOZ data. Our aim is to probe the changes in the values of the mass and mixing parameters with the inclusion of the SNO data as well as the changes in the two-generation parameter region obtained from the solar neutrino analysis with the inclusion of the third generation. We find that the inclusion of the SNO CC rate in the combined solar + CHOOZ analysis puts a more restrictive bound on $θ_{13}$. Since the allowed values of $θ_{13}$ are constrained to very small values by the CHOOZ experiment there is no qualitative change over the two generation allowed regions in the $Δm^2_{21} - \tan^2 θ_{12}$ plane. The best-fit comes in the LMA region and no allowed area is obtained in the SMA region at 3$σ$ level from combined solar and CHOOZ analysis.

hep-ph↗

arXiv2001

Global oscillation analysis of solar neutrino data with helioseismically constrained fluxes

A seismic model for the Sun calculated using the accurate helioseismic data predicts a lower $^{8}{B}$ neutrino flux as compared to the standard solar model (SSM). However, there persists a discrepancy between the predicted and measured neutrino fluxes and it seems necessary to invoke neutrino oscillations to explain the measurements. In this work, we have performed a global, unified oscillation analysis of the latest solar neutrino data (including the results of SNO charged current rate) using the seismic model fluxes as theoretical predictions. We determine the best-fit values of the neutrino oscillation parameters and the $χ^2_{\mathrm min}$ for both $ν_e-ν_{\mathrm active}$ and $ν_e -ν_{\mathrm sterile}$ cases and present the allowed parameter regions in the $Δm^2 - \tan^2 θ$ plane for $ν_e-ν_{\mathrm active}$ transition. The results are compared with those obtained using the latest SSM by Bahcall and his collaborators.

hep-ph↗

arXiv2001

Impact of the first SNO results on Neutrino Mass and Mixing

We investigate the implications of the SNO charged-current (CC) and electron scattering (ES) measurements of solar \br neutrino fluxes for neutrino mass and mixing parameters by performing a global and unified $χ^2$ analysis of the solar neutrino data in the framework of two neutrino mixing. We consider both $ν_e -ν_{active}$ and $ν_e -ν_{sterile}$ solutions and perform (i) analysis of the total rates data of Cl, Ga, SK and SNO experiments and (ii) global analysis including the total rates data, the recoil electron spectrum data of SK and the CC spectrum observed at SNO. For the $ν_e-ν_{active}$ case the inclusion of the SNO results in the analysis of the total rates reduces(enhances) the goodness-of-fit (GOF) of the SMA(LMA) solution. The flat spectrum observed at SK further favours the LMA solution over the SMA solution and no allowed area is obtained in the SMA region at 3$σ$ level from the global analysis. For the $ν_e -ν_{sterile}$ case, with the inclusion of the SNO results, all the solutions are disfavoured with a probability of more than 99% from the total rates analysis while for the global analysis the GOF of these become much worse.

hep-ph↗

arXiv2001

A three generation oscillation analysis of the Super-Kamiokande atmospheric neutrino data beyond one mass scale dominance approximation

In this paper we do a three-generation oscillation analysis of the latest (848 days) Super-Kamiokande (SK) atmospheric neutrino data going beyond the one mass scale dominance (OMSD) approximation. We fix $Δ_{12} = Δ_{13}$ ($Δ_{LSND}$) in the range 0.5 - 2 eV$^2$ as allowed by the results from LSND and other accelerator and reactor experiments on neutrino oscillation and keep $Δ_{23}$ ($Δ_{ATM}$) and the three mixing angles as free parameters. In such a scenario, the oscillation probabilities for the accelerator and reactor neutrinos involve only two of the mixing angles $θ_{12}$ and $θ_{13}$ and one mass scale. But the atmospheric neutrino oscillation is in general governed by both mass scales and all the three mixing angles. The higher mass scale gives rise to $Δm^2$ independent average oscillations for atmospheric neutrinos and does not enter the $χ^2$ analysis as an independent parameter. The $Δ_{23}$ and the three mixing angles on the other hand appear as independent parameters in the $χ^2$ analysis and the best-fit values of these are determined from an analysis of a) the SK data, b) the SK and CHOOZ data. The allowed values of the mixing angles $θ_{12}$ and $θ_{13}$ from the above analysis are compared with the constraints from LSND and other accelerator and reactor experiments. Implications for future long baseline experiments are discussed.

hep-ph↗

arXiv2000

Effect of flavor mixing on the time delay of massive supernova neutrinos

The neutrinos and antineutrinos of all the three flavors released from a galactic supernova will be detected in the water Cerenkov detectors. We show that even though the neutral current interaction is flavor blind, and hence neutrino flavor mixing cannot alter the total neutral current signal in the detector, it can have a non-trivial impact on the delay of massive neutrinos and alters the neutral current event rate as a function of time. We have suggested various variables of the neutral and charged current events that can be used to study this effect. In particular the ratio of charged to neutral current events can be used at early times while the ratio of the energy moments for the charged to the neutral current events can form useful diagnostic tools even at late times to study neutrino mass and mixing.

hep-ph↗

arXiv1999

Flavor mixing and time of flight delay of supernova neutrinos

The neutrinos from galactic supernovae can be detected by the Sudbury Neutrino Observatory and the Super-Kamiokande. The effect of neutrino mass can show up in the observed neutrino signal by (i) delay in the time of flight and (ii) distortion of the neutrino energy spectrum due to flavor mixing. We discuss a combination of the two effects for both charged and neutral current processes in the detectors for realistic three flavor scenarios and show that neutrino flavor mixing can lead to non-trivial changes in the event rate as a function of time.

hep-ph↗

arXiv1999

How degenerate can cosmological neutrinos be?

There are well-known bounds on light neutrino masses from cosmological energy density arguments. These arguments assume the neutrinos to be non-degenerate. We show how these bounds are affected if the neutrinos are degenerate. In this case, we obtain correlated bounds between neutrino mass and degeneracy.

hep-ph↗

arXiv1998

Effect of Flavour Oscillations on the Detection of Supernova Neutrinos

Neutrinos and antineutrinos of all three flavours are emitted during the post bounce phase of a core collapse supernova with $\numu/\nutau (\anumu/\anutau)$ having average energies more than that of $\nue(\anue)$. They can be detected by the new earth bound detector like SNO and Super-Kamiokande which are sensitive to neutrinos of all three flavours. In this letter we consider the effect of flavour oscillations on the neutrino flux and their expected number of events at the detector. We do a three-generation analysis and for the mass and mixing schemes we first consider the threefold maximal mixing model consistent with the solar and the atmospheric neutrino data and next a scenario with one $Δm^2 \sim 10^{-11} eV^2$ (solar range) and the other $Δm^2 \sim 10^{-18} eV^2$, for which the oscillation length is of the order of the supernova distance. In both these scenarios there are no matter effects in the resultant neutrino spectrum and one is concerned with vacuum oscillations. We find that though neutrino oscillations result in a depletion in the number of $\nue$ and $\anue$ coming from the supernova, the actual signals at the detectors are appreciable enhanced.

hep-ph↗

arXiv1998

Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova

Neutrinos emitted during stellar core collapse leading to a supernova are primarily of the electron neutrino type at source which may undergo oscillation between flavor eigenstates during propagation to an earth-bound detector. Although the number of neutrinos emitted during the pre-bounce collapse phase is much smaller than that emitted in the post-bounce phase (in which all flavors of neutrinos are emitted), a nearby supernova event may nevertheless register a substantial number of detections from the pre-bounce phase at SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The calorimetric measurement of the supernova neutrino fluence from this stage via the charge current and neutral current detection channels in SNO and the corresponding distortion of detected spectrum in SK over the no-oscillation spectrum, can probe information about neutrino mass difference and mixing which are illustrated here in terms of two- and three-flavor oscillation models.

astro-ph↗

arXiv1997

Excited States of 71Ge above the Neutron Emission Threshold and Solar Neutrino Capture rates for Ga Detectors

In Gallium detectors for solar neutrinos, the capture rate due to Gamow-Teller transitions to excited states of 71Ge beyond the neutron emission threshold is usually neglected. We make a model calculation to estimate its effect and find that this yields an additional contribution which may be as much as 0.4 SNU, even larger than that from the Isobaric Analog State in 71Ge reached by Fermi transitions, which is normally included in the standard predictions.

astro-ph↗

arXiv1995

Accelerator, reactor and atmospheric neutrino data: a three flavour oscillation analysis

We perform a three flavour analysis of the atmospheric, accelerator and reactor neutrino data from the Kamiokande, LSND and Bugey experiments respectively. Choosing the values of ${Δ{m}}^2$ obtained from two flavour fits of the first two experiments, the allowed ranges of the three generation mixing angles are determined. The accelerator experiments CHORUS and NOMAD are found to be most sensitive to regions of the allowed parameter space which correspond to genuine three generation solutions for the atmospheric neutrino anomaly.

hep-ph↗

arXiv1995

Resonant neutrino oscillations and shock revival in type-II supernovae

The role of matter enhanced resonant neutrino oscillations in reviving a stalled shock in a type-II supernova through delayed neutrino heating is investigated. The extent of neutrino heating is estimated for the allowed possibility of complete flavour conversion self-consistently with the changes in nuclear equilibrium. The average internal energy per nucleon is substantially increased indicating the possiblty of a robust explosion.

hep-ph↗