arXiv subjects

Monojit Ghosh

Publications and source records attributed to Monojit Ghosh.

65 records · Page 4Linked to original sources

arXiv2016

Reason for T2K to run in dominant neutrino mode for detecting CP violation

The long-baseline experiment T2K in Japan has collected data in the neutrino mode corresponding to an exposure of $6.57 \times 10^{20}$ POT (Protons on Target) and currently it is running in the antineutrino mode. The main aim of the antineutrino run is to measure the leptonic phase $δ_{CP}$ which may help to understand the matter-antimatter asymmetry of the universe. In this work we show that in T2K, antineutrinos are required only for removing the wrong octant solutions which in turn improves the CP sensitivity. If however the octant is known then pure neutrino run is capable of giving the maximum CP sensitivity. If we divide the total true parameter space into eight sets, then we find that T2K antineutrino run helps in improving the CP sensitivity for only two sets while for the remaining six combinations pure neutrino run gives the best CP sensitivity. Thus if the neutrino run is replaced by the antineutrino run then it causes a reduction in the CP sensitivity in 75$\%$ of the true parameter space due to lesser statistics. Thus it is worthwhile to study if the T2K antineutrino run can be reduced by the antineutrino runs of the other experiments, so that T2K can run in dominant neutrino mode to extract the best CP sensitivity. In this work we explore the possibility of the antineutrino component of NO$ν$A and the atmospheric neutrino experiment ICAL@INO for compensating the antineutrino run of T2K.

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arXiv2016

Present Aspects and Future Prospects of Neutrino Mass and Oscillation

Neutrinos are neutral, spin-$\frac{1}{2}$ particles which undergo only weak interactions. The experimentally observed phenomenon of neutrino oscillation establishes the fact that neutrinos are massive and there is mixing between different neutrino flavours. This constitutes the first unambiguous hint towards the physics Beyond Standard Model (BSM). In the BSM theories, the neutrino mass terms in the Lagrangian lead to the non-diagonal neutrino mass matrix in the flavour basis which depends on neutrino mass and mixing parameters. Thus knowledge of the neutrino oscillation parameters and understanding the underlying symmetries of the neutrino mass matrix are very important as they can give an insight to the new physics beyond Standard Model. Therefore the measurement of different oscillation parameters and studying the structure of the neutrino mass matrix are some of the main goals in neutrino physics at present. In this thesis we have studied the potential of present/future neutrino oscillation experiments and synergy between them to determine the unknown parameters in the neutrino sector in the light of current experimental results. We have also studied the phenomenological consequences of texture zeros in the neutrino mass matrices in the presence of a sterile neutrino.

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arXiv2016

Maximising the DUNE early physics output with current experiments

The Deep Underground Neutrino Experiment (DUNE) is a proposed next generation superbeam experiment at Fermilab. Its aims include measuring the unknown neutrino oscillation parameters -- the neutrino mass hierarchy, the octant of the mixing angle $θ_{23}$ and the CP violating phase $δ_{CP}$. The current and upcoming experiments T2K, NOvA and ICAL@INO will also be collecting data for the same measurements. In this paper, we explore the sensitivity reach of DUNE in combination with these other experiments. We evaluate the least exposure required by DUNE to determine the above three unknown parameters with reasonable confidence. We find that for each case, the inclusion of data from T2K, NOvA and ICAL@INO help to achieve the same sensitivity with a reduced exposure from DUNE thereby helping to economize the configuration. Further, we quantify the effect of the proposed near detector on systematic errors and study the consequent improvement in sensitivity. We also examine the role played by the second oscillation cycle in furthering the physics reach of DUNE. Finally, we present an optimization study of the neutrino-antineutrino running of DUNE.

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arXiv2016

New look at the degeneracies in the neutrino oscillation parameters, and their resolution by T2K, NO$ν$A and ICAL

At present the three major unknowns in neutrino oscillation parameters are the mass hierarchy, the octant of $θ_{23}$ and the CP phase $δ_{CP}$. It is well known that the presence of hierarchy$-δ_{CP}$ and octant degeneracies affects the unambiguous determination of these parameters. In this paper we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy-$θ_{23}$ - $δ_{CP}$ degeneracy. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of $δ_{CP}$. These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if $θ_{13}$ is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of $δ_{CP}$. We identify which of these eight different degenerate solutions can occur in the test ($θ_{23} - δ_{CP}$) parameter space, taking the long-baseline experiment NO$ν$A running in the neutrino mode as an example. The inclusion of the NO$ν$A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy -- right octant solutions to a large extent. The remaining wrong hierarchy solutions can be removed by combining NO$ν$A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the $2σ$ level by the combined data set, for the true parameter space considered in the study.

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arXiv2015

Can the hint of $δ_{CP}$ from T2K also indicate the hierarchy and octant ?

The T2K neutrino data has already given a hint for the best-fit value of the leptonic CP phase $δ_{CP}$ as $-90^\circ$. In this paper we ask the question that if this hint is confirmed by the subsequent neutrino and anti-neutrino runs of T2K, then can it also give any information about the other two remaining unknown oscillation parameters - the neutrino mass hierarchy and octant of $θ_{23}$. We find that if T2K runs in only neutrino mode with its full targeted exposure, then $δ_{CP} = -90^\circ$ would indicate the true hierarchy as normal and the true octant as higher. On the other hand if T2K runs in equal neutrino and anti-neutrino mode then the true hierarchy can be confirmed as normal but the octant will remain undetermined. We have also studied the effect of anti-neutrino runs on CP sensitivity of T2K.

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arXiv2014

Probing CP violation with the three years ultra-high energy neutrinos from IceCube

The IceCube collaboration has recently announced the discovery of ultra-high energy neutrino events. These neutrinos can be used to probe their production source, as well as leptonic mixing parameters. In this work, we have used the first IceCube data to constrain the leptonic CP violating phase $δ_{cp}$. For this, we have analyzed the data in the form of flux ratios. We find that the fit to $δ_{cp}$ depends on the assumptions made on the production mechanism of these astrophyscial neutrinos. Consequently, we also use this data to impose constraints on the sources of the neutrinos.

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arXiv2014

Evidence for leptonic CP phase from NO$ν$A, T2K and ICAL: A chronological progression

We study the synergy between the long-baseline (LBL) experiments NO$ν$A and T2K and the atmospheric neutrino experiment ICAL@INO for obtaining the first hint of CP violation in the lepton sector. We also discuss how precisely the leptonic CP phase ($δ_{CP}$) can be measured by these experiments. The CP sensitivity is first described at the level of oscillation probabilities, discussing its dependence on the parameters -- $θ_{13}$, mass hierarchy and $θ_{23}$. In particular, we discuss how the precise knowledge or lack thereof of these parameters can affect the CP sensitivity of LBL experiments. We follow a staged approach and analyze the $δ_{CP}$ sensitivity that can be achieved at different points of time over the next 15 years from these LBL experiments alone and/or in conjunction with ICAL@INO. We find that the CP sensitivity of NO$ν$A/T2K is enhanced due to the synergies between the different channels and between the two experiments. On the other hand the lack of knowledge of hierarchy and octant makes the CP sensitivity poorer for some parameter ranges. Addition of ICAL data to T2K and NO$ν$A can exclude these spurious wrong-hierarchy and/or wrong-octant solutions and cause a significant increase in the range of $δ_{CP}$ values for which a hint of CP violation can be achieved. In fact in parameter regions unfavourable for NO$ν$A/T2K, we may get the first evidence of CP violation by adding the ICAL data to these. Similarly the precision with which $δ_{CP}$ can be measured also improves with inclusion of ICAL data.

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arXiv2014

Synergies between neutrino oscillation experiments: An `adequate' configuration for LBNO

Determination of the neutrino mass hierarchy, octant of the mixing angle theta_{23} and the CP violating phase delta_{CP} are the unsolved problems in neutrino oscillation physics today. In this paper our aim is to obtain the minimum exposure required for the proposed Long Baseline Neutrino Oscillation (LBNO) experiment to determine the above unknowns. We emphasize on the advantage of exploiting the synergies offered by the existing and upcoming long-baseline and atmospheric neutrino experiments in economising the LBNO configuration. In particular, we do a combined analysis for LBNO, T2K, NOvA and INO. We consider three prospective LBNO setups -- CERN-Pyhasalmi (2290 km), CERN-Slanic (1500 km) and CERN-Frejus (130 km) and evaluate the adequate exposure required in each case. Our analysis shows that the exposure required from LBNO can be reduced considerably due to the synergies arising from the inclusion of the other experiments.

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arXiv2013

Can atmospheric neutrino experiments provide the first hint of leptonic CP violation?

The measurement of a non-zero value of the 1-3 mixing angle has paved the way for the determination of leptonic CP violation. However the current generation long-baseline experiments T2K and NOvA have limited sensitivity to delta_{CP}. In this paper we show for the first time, the significance of that atmospheric neutrino experiments in providing the first hint of CP violation in conjunction with T2K and NOvA. In particular, we find that adding atmospheric neutrino data from the ICAL detector at the India-based Neutrino Observatory (INO) to T2K and NOvA results in a two-fold increase in the range of delta_{CP} values for which a 2 sigma hint of CP violation can be obtained. In fact in the parameter region unfavorable for the latter experiments, the first signature of CP violation may well come from the inclusion of atmospheric neutrino data.

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arXiv2013

Implication of a vanishing element in 3+1 Scenario

In this paper we study the phenomenological implications of the one zero textures of low energy neutrino mass matrices in presence of a sterile neutrino. We consider the 3+1 scheme and use the results from global fit for short baseline neutrino oscillation data which provides the bounds on the three additional mixing angles. We find that the mass matrix elements $m_{αβ}$ ($α, β= e, μ, τ$) involving only the active states can assume vanishing values in the allowed parameter space for all the mass spectrum. Among the mass matrix elements connecting the active and sterile states, $m_{es}$ and $m_{μs}$ can become small only for the quasi-degenerate neutrinos. The element $m_{τs}$ on the other hand can vanish even for lower values of masses since the 3-4 mixing angle only has an upper bound from current data. The mass matrix element ($m_{ss}$) involving only the sterile state stays $\sim$ $\mathcal{O}$(1) eV in the whole parameter region. We study the possible correlations between the sterile mixing angles and the Majorana phases to give a zero element in the mass matrix.

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arXiv2012

Two Zero Mass Matrices and Sterile Neutrinos

Recent experimental data is indicative of the existence of sterile neutrinos. The minimal scheme that can account for the data and is consistent with cosmological observations is the 3+1 picture which consists of three predominantly active and one predominantly sterile neutrino with the fourth neutrino being heavier than the other three. Within this scheme there are two possibilities depending on whether the three light states obey normal or inverted hierarchy. In this paper we consider the two zero textures of the low energy neutrino mass matrix in presence of one additional sterile neutrino. We find that among 45 possible two zero textures for this case, 15 are consistent with all current observations. Remarkably, these correspond to the two-zero textures of a three active neutrino mass matrix. We discuss the mass spectrum and the parameter correlations that we find in the various textures. We also present the effective mass governing neutrinoless double beta decay as a function of the lowest mass.

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