arXiv subjects

Sandhya Choubey

Publications and source records attributed to Sandhya Choubey.

At least 109 records · Page 6Linked to original sources

arXiv2004

Update of the solar neutrino oscillation analysis with the 766 Ty KamLAND spectrum

We investigate the impact of the 766.3 Ty KamLAND spectrum data on the determination of the solar neutrino oscillation parameters. We show that the observed spectrum distortion in the KamLAND experiment firmly establishes $Δm^2_{21}$ to lie in the low-LMA solution region. The high-LMA solution is excluded at more than 4$σ$ by the global solar neutrino and KamLAND spectrum data. The maximal solar neutrino mixing is ruled out at $6σ$ level. The $3σ$ allowed region in the $Δm^2_{21}-\sin^2θ_{12}$ plane is found to be remarkably stable with respect to leaving out the data from one of the solar neutrino experiments from the global analysis. We perform a three flavor neutrino oscillation analysis of the global solar neutrino and KamLAND spectrum data as well. The $3σ$ upper limit on $\sin^2θ_{13}$ is found to be $ \sin^2θ_{13} <0.055$. We derive predictions for the CC to NC event rate ratio and day-night (D-N) asymmetry in the CC event rate, measured in the SNO experiment, and for the suppression of the event rate in the BOREXINO and LowNu experiments. Prospective high precision measurements of the solar neutrino oscillation parameters are also discussed.

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arXiv2004

Global Analysis of Neutrino Oscillation

We present the constraints on neutrino oscillation parameters $Δm^2_{\odot}$ and $θ_{\odot}$ governing the solar neutrino oscillations from two generation analysis of solar and KamLAND data. We include the latest 766.3 ton year KamLAND data in our analysis. We also present the allowed values of parameters $Δm^2_{atm}$ and $\sin^2θ_{atm}$ from two generation oscillation analysis of SuperKamiokande atmospheric and K2K data. For both cases we discuss the precision achieved in the present set of experiments and also how the precision can be improved in future. We also obtain the bounds on $θ_{13}$ from three generation analysis of global oscillation data. We emphasise on the roles played by different data sets in constraining the allowed parameter ranges.

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arXiv2004

Reactor Anti-Neutrino Oscillations and Gadolinium Loaded Super-Kamiokande Detector

We explore the potential of measuring the solar neutrino oscillation parameters in the proposed gadolinium loaded Super-Kamiokande (SK-Gd) detector. Gadolinium dissolved in water can detect neutrons much more efficiently than pure water. This imparts the detector the ability to observe electron type antineutrinos, transforming Super-Kamiokande into a huge reactor antineutrino detector with an event rate approximately 43 times higher than that observed in KamLAND. We simulate the reactor antineutrino data expected in this high statistics detector. We use these prospective data to study the precision with which the solar neutrino oscillation parameters, $Δm^2_{\odot}$ and $\sin^2θ_{\odot}$, can be determined i) with the SK-Gd detector, and ii) by combining the SK-Gd data with the global data on solar neutrino oscillations. For comparison and completeness the allowed regions of $Δm^2_{\odot}$ and $\sin^2θ_{\odot}$, expected to be obtained from the data of the solar neutrino and KamLAND experiments, are also presented.

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arXiv2004

Testing whether muon neutrino flavor mixing is maximal

The small difference between the survival probabilities of muon neutrino and antineutrino beams, traveling through earth matter in a long baseline experiment such as MINOS, is shown to be an important measure of any possible deviation from maximality in the flavor mixing of those states.

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arXiv2004

Solar Neutrino Oscillation Parameters in Experiments with Reactor Anti-Neutrinos

We review the current status of the solar neutrino oscillation parameters. We discuss the conditions under which measurements from future solar neutrino experiments would determine the oscillation parameters precisely. Finally we expound the potential of long baseline reactor anti-neutrino experiments in measuring the solar neutrino oscillation parameters.

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arXiv2004

Electrophobic Lorentz invariance violation for neutrinos and the see-saw mechanism

We show how Lorentz invariance violation (LIV) can occur for Majorana neutrinos, without inducing LIV in the charged leptons via radiative corrections. Such ``electrophobic'' LIV is due to the Majorana nature of the LIV operator together with electric charge conservation. Being free from the strong constraints coming from the charged lepton sector, electrophobic LIV can in principle be as large as current neutrino experiments permit. On the other hand electrophobic LIV could be naturally small if it originates from LIV in some singlet ``right-handed neutrino'' sector, and is felt in the physical left-handed neutrinos via a see-saw mechanism. We develop the formalism appropriate to electrophobic LIV for Majorana neutrinos, and discuss experimental constraints at current and future neutrino experiments.

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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.

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arXiv2003

Constraints on neutrino oscillation parameters from the SNO salt phase data

The physics implications of the just published salt phase data from the SNO experiment are examined. The effect of these data on the allowed ranges of the solar neutrino oscillation parameters, $Δ_m^2_{21}$ and $\sin^2θ_{12}$, are studied in the cases of two- and three- neutrino mixing. In the latter case we derive an upper limit on the angle $θ_{13}$. Constraints on the solar $ν_e$ transitions into a mixture of active and sterile neutrinos are also presented. Finally, we give predictions for the day-night asymmetry in the SNO experiment, for the event rate in the BOREXINO and LowNu experiments, and discuss briefly the constraints on the solar neutrino oscillation parameters which can be obtained with prospective KamLAND data.

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arXiv2003

Solar Neutrino Oscillation Parameters after KamLAND

We explore the impact of the data from the KamLAND experiment in constraining neutrino mass and mixing angles involved in solar neutrino oscillations. In particular we discuss the precision with which we can determine the the mass squared difference $Δm^2_{solar}$ and the mixing angle $θ_{solar}$ from combined solar and KamLAND data. We show that the precision with which $Δm^_{solar}$ can be determined improves drastically with the KamLAND data but the sensitivity of KamLAND to the mixing angle is not as good. We study the effect of enhanced statistics in KamLAND as well as reduced systematics in improving the precision. We also show the effect of the SNO salt data in improving the precision. Finally we discuss how a dedicated reactor experiment with a baseline of 70 km can improve the $θ_{solar}$ sensitivity by a large amount.

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arXiv2003

On the Measurement of Solar Neutrino Oscillation Parameters with KamLAND

A new reactor power plant Shika-2, with a power of approximately 4 GW and at a distance of about 88 km from the KamLAND detector is scheduled to start operating in March 2006. We study the impact of the $\barν_e$ flux from this reactor on the sensitivity of the KamLAND experiment to the solar neutrino oscillation parameters. We present results on prospective determination of $Δm^2_\odot$ and $\sin^2θ_\odot$ using the combined data from KamLAND and the solar neutrino experiments, including the effect of the Shika-2 contribution to the KamLAND signal and the latest data from the salt enriched phase of the SNO experiment. We find that contrary to the expectations, the addition of the Shika-2 reactor flux does not improve the $\sin^2θ_\odot$ sensitivity of KamLAND, while the ambiguity in $Δm^2_\odot$ measurement may even increase, as a result of the averaging effect between Kashiwazaki and the Shika-2 reactor contributions to the KamLAND signal.

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arXiv2003

Precision measurement of oscillation parameters with reactors

We review the potential of long and intermediate baseline reactor neutrino experiments in measuring the mass and mixing parameters. The KamLAND experiment can measure the solar mass squared difference very precisely. However it is not at the ideal baseline for measuring the solar neutrino mixing angle. If low-LMA is confirmed by the next results from KamLAND, a reactor experiment with a baseline of 70 km should be ideal to measure precisely the solar neutrino mixing angle. If on the contrary KamLAND re-establishes high-LMA as a viable solution, then a 20--30 km intermediate baseline reactor experiment could yield very rich phenomenology.

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arXiv2003

Testing the solar LMA region with KamLAND data

We investigate the potential of 3 kiloTon-years(kTy) of KamLAND data to further constrain the $Δm^2$ and $\tan^2θ$ values compared to those presently allowed by existing KamLAND and global solar data. We study the extent, dependence and characteristics of this sensitivity in and around the two parts of the LMA region that are currently allowed. Our analysis with 3 kTy simulated spectra shows that KamLAND spectrum data by itself can constrain $Δm^2$ with high precision. Combining the spectrum with global solar data further tightens the constraints on allowed values of $\tan^2θ$ and $Δm^2$. We also study the effects of future neutral current data with a total error of 7% from the Sudbury Neutrino Observatory. We find that these future measurements offer the potential of considerable precision in determining the oscillation parameters (specially the mass parameter).

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arXiv2003

CP violation and matter effect for a variable earth density in very long baseline experiments

The perturbative treatment of subdominant oscillation and the matter effect in neutrino beams/superbeams, propagating over long baselines and being used to look for CP violation, is studied here for a general matter density function varying with distance. New lowest order analytic expressions are given for different flavour transition and survival probabilities in a general neutrino mixing basis and a variable earth matter density profile. It is demonstrated that the matter effect in the muon neutrino (antineutrino) flavour survival probability vanishes to this order, provided the depletion, observed for atmospheric muon neutrinos and antineutrinos at super-Kamiokande, is strictly maximal. This result is independent of the earth density profile and the distance L between the source and the detector. In the general variable density case we show that one cannot separate the matter induced asymmetry from a genuine CP effect by keeping two detectors at distances $L_1$ and $L_2$ from the source while maintaining a fixed ratio $L_1/E_1 = L_2/E_2$. This needs to be done numerically and we estimate the asymmetry generated by the earth matter effect with particular density profiles and some chosen parameters for very long baseline neutrino oscillation experiments.

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arXiv2003

Precision Neutrino Oscillation Physics with an Intermediate Baseline Reactor Neutrino Experiment

We discuss the physics potential of intermediate $L \sim 20 ÷30$ km baseline experiments at reactor facilities, assuming that the solar neutrino oscillation parameters $Δm^2_{\odot}$ and $θ_{\odot}$ lie in the high-LMA solution region. We show that such an intermediate baseline reactor experiment can determine both $Δm^2_{\odot}$ and $θ_{\odot}$ with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to $Δm^2_{\rm atm}$, which drives the dominant atmospheric $ν_μ$ ($\barν_μ$) oscillations, and to $θ$ - the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. We find that this experiment can improve the bounds on $\sin^2θ$. If the value of $\sin^2θ$ is large enough, $\sin^2θ\gtap 0.02$, the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of $Δm^2_{\rm atm}$. We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion.

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arXiv2003

Exploring the sensitivity of current and future experiments to $θ_{\odot}$

However the allowed range of $θ_{\odot}$ ($θ_{12}$) did not change much with the inclusion of the KamLAND results. In this paper we probe if future data from KamLAND can increase the accuracy of the allowed range in $θ_{\odot}$ and conclude that even after 3 kton-year of statistics and most optimistic error estimates, KamLAND {\it may} find it hard to significantly improve the bounds on the mixing angle obtained from the solar neutrino data. We discuss the $θ_{12}$ sensitivity of the survival probabilities in matter (vacuum) as is relevant for the solar (KamLAND) experiments. We find that the presence of matter effects in the survival probabilities for $^8B$ neutrinos give the solar neutrino experiments SK and SNO an edge over KamLAND, as far as $θ_{12}$ sensitivity is concerned, particularly near maximal mixing. Among solar neutrino experiments we identify SNO as the most promising candidate for constraining $θ_{12}$ and make a projected sensitivity test for the mixing angle by reducing the error in the neutral current measurement at SNO. Finally we argue that the most accurate bounds on $θ_{12}$ can be achieved in a reactor experiment, if the corresponding baseline and energy can be tuned to a minimum in the survival probability. We propose a new reactor experiment which can give the value of $\tan^2θ_{12}$ to within 14%. We also discuss the future Borexino and LowNu experiments.

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arXiv2003

The Solar Neutrino Problem after the first results from Kamland

The first results from the KamLAND experiment have provided confirmational evidence for the Large Mixing Angle (LMA) MSW solution to the solar neutrino problem. We do a global analysis of solar and the recently announced KamLAND data (both rate and spectrum) and investigate its effect on the allowed region in the $Δm^2-\tan^2θ$ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at $Δm^2 = 6.06 \times 10^{-5}$ eV $^2$ and $\tan^2θ=0.42$, very close to the global solar best-fit, leaving a large allowed region within the global solar LMA contour. The inclusion of the KamLAND spectral data in the global fit gives a best-fit $Δm^2 = 7.15 \times 10^{-5}$ eV $^2$ and $\tan^2θ=0.42$ and constrains the allowed areas within LMA, leaving essentially two allowed zones. Maximal mixing though allowed by the KamLAND data alone is disfavored by the global solar data and remains disallowed at about $3σ$. The LOW solution is now ruled out at about 5$σ$ w.r.t. the LMA solution.

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arXiv2003

Gamma ray bursts as probes of neutrino mass, quantum gravity and dark energy

We calculate the time delays of neutrinos emitted in gamma ray bursts due to the effects of neutrino mass and quantum gravity using a time dependent Hubble constant which can significantly change the naive results presented hitherto in the literature for large redshifts, and gives some sensitivity to the details of dark energy. We show that the effects of neutrino mass, quantum gravity and dark energy may be disentangled by using low energy neutrinos to study neutrino mass, high energy neutrinos to study quantum gravity, and large redshifts to study dark energy. From low energy neutrinos one may obtain direct limits on neutrino masses of order 10^{-3} eV, and distinguish a neutrino mass hierarchy from an inverted mass hierarchy. From ultra-high energy neutrinos the sensitivity to the scale of quantum gravity can be pushed up to E_{QG} ~ 5 times 10^{30} GeV. By studying neutrinos from GRBs at large redshifts a cosmological constant could be distinguished from quintessence.

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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.

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