arXiv subjects

Suprabh Prakash

Publications and source records attributed to Suprabh Prakash.

At least 19 recordsLinked to original sources

arXiv2023

Neutrino oscillation measurements with KamLAND and JUNO in the presence of scalar NSI

Determination of neutrino mass ordering and precision measurement of neutrino oscillation parameters are the foremost goals of the JUNO experiment. Here, we explore the effects of scalar non-standard interactions (sNSI) on the electron anti-neutrino survival probability measured by JUNO. sNSI appear as corrections to the neutrino mass term in the Hamiltonian. We have considered the simplest scenario where there is only one NSI ($\eta_{ee}$) present in the theory. Our results show that sNSI can have a significant effect on neutrino oscillation probabilities at the medium- and long-baseline reactor experiments. We fit KamLAND data assuming non-zero sNSI in theory and find that {\it estimates of $\Delta m^2_{21}$ and $\theta_{12}$ from KamLAND deviate significantly from their standard best-fit values} if one assumes sNSI in the theory. $\eta_{ee} \in [-1.0, 1.0]$ is allowed by KamLAND. JUNO cannot constrain sNSI but it can robustly measure $\Delta m^2_{21}$ and $\theta_{12}$ even when they differ widely from their current best-fit values. {\it Our work highlights the necessity of global analysis of constraints on sNSI and standard two-flavour oscillation parameters before arduous three-flavour questions such as neutrino mass ordering or CP violation in their presence are attempted.

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arXiv2021

A close look on 2-3 mixing angle with DUNE in light of current neutrino oscillation data

Recent global fit analyses of oscillation data show a preference for normal mass ordering (NMO) at 2.5$σ$ and provide 1.6$σ$ indications for lower $θ_{23}$ octant and leptonic CP violation. A high-precision measurement of $θ_{23}$ is pivotal to convert these hints into discoveries. In this work, we study in detail the capabilities of DUNE to establish the deviation from maximal $θ_{23}$ and to resolve its octant at high confidence levels. We exhibit the possible correlations and degeneracies among $\sin^2θ_{23}$, $Δm^2_{31}$, and $δ_{CP}$ in disappearance and appearance oscillation channels at the probability and event levels. Introducing for the first time, a bi-events plot in the plane of total $ν$ and $\barν$ disappearance events, we discuss the impact of $\sin^2θ_{23}$ - $Δm^2_{31}$ degeneracy in establishing non-maximal $θ_{23}$ and show how this degeneracy can be resolved by exploiting the spectral shape information in $ν$ and $\barν$ disappearance events. A 3$σ$ (5$σ$) determination of non-maximal $θ_{23}$ is possible in DUNE in total 7 years if $\sin^2θ_{23} \lesssim 0.465~(0.450)$ or $\sin^2θ_{23} \gtrsim 0.554~(0.572)$ for any value of $δ_{CP}$ and NMO. We study the individual contributions from appearance and disappearance channels, impact of systematic uncertainties and marginalization over oscillation parameters, importance of spectral analysis and data from both $ν$ and $\barν$ runs, while analyzing DUNE's sensitivity to establish non-maximal $θ_{23}$. DUNE can resolve the octant of $θ_{23}$ at 4.2$σ$ (5$σ$) using 7 (10) years of run assuming $\sin^2θ_{23}$ = 0.455, $δ_{CP}$ = $223^\circ$, and NMO. DUNE can improve the current relative 1$σ$ precision on $\sin^2θ_{23}$ ($Δm^2_{31}$) by a factor of 4.4 (2.8) using 7 years of run.

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arXiv2020

Constraining visible neutrino decay at KamLAND and JUNO

We study visible neutrino decay at the reactor neutrino experiments KamLAND and, JUNO. Assuming the Majoron model of neutrino decay, we obtain constraints on the couplings between Majoron and neutrino as well as on the lifetime/mass of the most massive neutrino state i.e., $τ_{3} / m_{3}$ or $τ_{2} / m_{2}$, respectively, for the normal or the inverted mass orderings. We obtain the constraints on the lifetime $τ_{2} / m_{2} \geq 1.4 \times 10^{-9}~\rm{s/eV}$ in the inverted mass ordering for both KamLAND and JUNO at 90% CL. In the normal ordering in which the bound can be obtained for JUNO only, the constraint is milder than the inverted ordering case, $τ_{3} / m_{3} \geq 1.0 \times 10^{-10}~\rm{s/eV}$ at 90% CL. We find that the dependence of lightest neutrino mass ($=m_{\rm{lightest}}$), $m_1 (m_3)$ for the normal (inverted) mass ordering, on the constraints for the different types of couplings (scalar or pseudo-scalar) is rather strong, but the $m_{\rm{lightest}}$ dependence on the lifetime/mass bound is only modest.

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arXiv2020

On The Decaying-Sterile Neutrino Solution to the Electron (Anti)Neutrino Appearance Anomalies

We explore the hypothesis that the unexplained data from LSND and MiniBooNE are evidence for a new, heavy neutrino mass-eigenstate that mixes with the muon-type neutrino and decays into an electron-type neutrino and a new, very light scalar particle. We consider two different decay scenarios, one with Majorana neutrinos, one with Dirac neutrinos; both fit the data equally well. We find a reasonable, albeit not excellent, fit to the data of MiniBooNE and LSND. The decaying-sterile-neutrino hypothesis, however, cleanly evades constraints from disappearance searches and precision measurements of leptonic meson decays, as long as $1~{\rm MeV}\gtrsim m_4\gtrsim 10$~keV. The SBN program at Fermilab should be able to definitively test the decaying-sterile-neutrino hypothesis.

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arXiv2020

Tensions between the appearance data of T2K and NOvA

The long baseline neutrino experiments, T2K and NOvA, have taken significant amount of data in each of the four channels: (a) $ν_μ$ disappearance, (b) $\barν_μ$ disappearance (c) $ν_e$ appearance and (d) $\barν_e$ appearance. There is a mild tension between the disappearance and the appearance data sets of T2K. A more serious tension exists between the $ν_e$ appearance data of T2K and the $ν_e / \barν_e$ appearance data of NOvA. This tension is significant enough that T2K rules out the best-fit point of NOvA at $95\%$ confidence level whereas NOvA rules out T2K best-fit point at $90\%$ confidence level. We explain the reason why these tensions arise. We also do a combined fit of T2K and NOvA data and comment on the results of this fit.

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arXiv2018

Understanding the degeneracies in NO$ν$A data

The combined analysis of $ν_μ$ disappearance and $ν_e$ appearance data of NO$ν$A experiment leads to three nearly degenerate solutions. This degeneracy can be understood in terms of deviations in $ν_e$ appearance signal, caused by unknown effects, with respect to the signal expected for a reference set of oscillations parameters. We define the reference set to be vacuum oscillations in the limit of maximal $θ_{23}$ and no CP-violation. We then calculate the deviations induced in the $ν_e$ appearance signal event rate by three unknown effects: (a) matter effects, due to normal or inverted hierarchy (b) octant effects, due to $θ_{23}$ being in higher or lower octant and (c) CP-violation, whether $δ_{CP} \sim - π/2$ or $δ_{CP} \sim π/2$. We find that the deviation caused by each of these effects is the same for NO$ν$A. The observed number of $ν_e$ events in NO$ν$A is equivalent to the increase caused by one of the effects. Therefore, the observed number of $ν_e$ appearance events of NO$ν$A is the net result of the increase caused by two of the unknown effects and the decrease caused by the third. Thus we get the three degenerate solutions. We also find that further data by NO$ν$A can not distinguish between these degenerate solutions but addition of one year of neutrino run of DUNE can make a distinction between all three solutions. The distinction between the two NH solutions and the IH solution becomes possible because of the larger matter effect in DUNE. The distinction between the two NH solutions with different octants is a result of the synergy between the anti-neutrino data of NO$ν$A and the neutrino data of DUNE.

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arXiv2017

What measurements of neutrino neutral current events can reveal

We show that neutral current (NC) measurements at neutrino detectors can play a valuable role in the search for new physics. Such measurements have certain intrinsic features and advantages that can fruitfully be combined with the usual well-studied charged lepton detection channels in order to probe the presence of new interactions or new light states. In addition to the fact that NC events are immune to uncertainties in standard model neutrino mixing and mass parameters, they can have small matter effects and superior rates since all three flavours participate. We also show, as a general feature, that NC measurements provide access to different combinations of CP phases and mixing parameters compared to CC measurements at both long and short baseline experiments. Using the Deep Underground Neutrino Experiment (DUNE) as an illustrative setting, we demonstrate the capability of NC measurements to break degeneracies arising in CC measurements, allowing us, in principle, to distinguish between new physics that violates three flavour unitarity and that which does not. Finally, we show that NC measurements can enable us to restrict new physics parameters that are not easily constrained by CC measurements.

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arXiv2016

Capabilities of long-baseline experiments in the presence of a sterile neutrino

Assuming that there is a sterile neutrino, we ask what then is the ability of long-baseline experiments to i) establish that neutrino oscillation violates CP, ii) determine the three-neutrino mass ordering, and iii) determine which CP-violating phase or phases are the cause of any CP violation that may be observed. We find that the ability to establish CP violation and to determine the mass ordering could be very substantial. However, the effects of the sterile neutrino could be quite large, and it might prove very difficult to determine which phase is responsible for an observed CP violation. We explain why a sterile neutrino changes the long-baseline sensitivities to CP violation and to the mass ordering in the ways that it does. We note that long-baseline experiments can probe the presence of sterile neutrinos in a way that is different from, and complementary to, the probes of short-baseline experiments. We explore the question of how large sterile-active mixing angles need to be before long-baseline experiments can detect their effects, or how small they need to be before the interpretation of these experiments can safely disregard the possible existence of sterile neutrinos.

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arXiv2016

Analysis of four-zero textures in $3+1$ framework

The presence of a zero texture in the neutrino mass matrix can indicate the presence of an underlying symmetry which can generate neutrino mass and mixing. In this paper, for the first time we study the four-zero textures of the low energy neutrino mass matrix in the presence of an extra light-sterile neutrino i.e., the 3+1 neutrino scheme. In our analysis we find that out of the 210 possible four-zero textures only 15 textures are allowed. We divide the allowed four-zero textures into two classes -- class $A$ in which the value of mass matrix element $M_{ee}$ is zero and class $B$ in which $M_{ee}$ is non-zero. In this way we obtain ten possible four-zero textures in class $A$ and five possible four-zero textures in class $B$. In our analysis we find that, for normal hierarchy the allowed number of textures in class $A$ ($B$) is nine (three). For the case of inverted hierarchy we find that, two textures in class $A$ are disallowed and these textures are different from the disallowed textures for normal hierarchy in class $A$. However, we find that all the five textures in class $B$ are allowed for the inverted hierarchy. Based on analytic expressions for the elements $M_{αβ}$, we discuss the reasons for certain textures being disallowed. We also discuss the correlations between the different parameters of the allowed textures. Finally, we present the implications of our study on experimental searches for neutrinoless double beta decay.

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arXiv2016

Hierarchy sensitivity of NO$ν$A in light of T2K $ν_e$ appearance data

The $ν_e$ appearance data of T2K experiment has given a glimpse of the allowed parameters in the hierarchy-$δ_{CP}$ parameter space. In this paper, we explore how this data affects our expectations regarding the hierarchy sensitivity of the NO$ν$A experiment. For the favourable combinations of hierarchy and $δ_{CP}$, the hierarchy sensitivity of NO$ν$A is unaffected by the addition of T2K data. For the unfavourable combinations, NO$ν$A data gives degenerate solutions. Among these degenerate solutions, T2K data prefers IH and $δ_{CP}$ in the lower half plane over NH and $δ_{CP}$ in the upper half plane. Hence, addition of the T2K data to NO$ν$A creates a bias towards IH and $δ_{CP}$ in the lower half plane irrespective of what the true combination is.

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arXiv2015

The impact of sterile neutrinos on CP measurements at long baselines

With the Deep Underground Neutrino Experiment (DUNE) as an example, we show that the presence of even one sterile neutrino of mass $\sim$1 eV can significantly impact the measurements of CP violation in long baseline experiments. Using a probability level analysis and neutrino-antineutrino asymmetry calculations, we discuss the large magnitude of these effects, and show how they translate into significant event rate deviations at DUNE. Our results demonstrate that measurements which, when interpreted in the context of the standard three family paradigm, indicate CP conservation at long baselines, may, in fact hide large CP violation if there is a sterile state. Similarly, any data indicating the violation of CP cannot be properly interpreted within the standard paradigm unless the presence of sterile states of mass O(1 eV) can be conclusively ruled out. Our work underscores the need for a parallel and linked short baseline oscillation program and a highly capable near detector for DUNE, in order that its highly anticipated results on CP violation in the lepton sector may be correctly interpreted.

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arXiv2015

Probing Neutrino Oscillation Parameters using High Power Superbeam from ESS

A high-power neutrino superbeam experiment at the ESS facility has been proposed such that the source-detector distance falls at the second oscillation maximum, giving very good sensitivity towards establishing CP violation. In this work, we explore the comparative physics reach of the experiment in terms of leptonic CP-violation, precision on atmospheric parameters, non-maximal theta23, and its octant for a variety of choices for the baselines. We also vary the neutrino vs. the anti-neutrino running time for the beam, and study its impact on the physics goals of the experiment. We find that for the determination of CP violation, 540 km baseline with 7 years of neutrino and 3 years of anti-neutrino (7nu+3nubar) run-plan performs the best and one expects a 5sigma sensitivity to CP violation for 48% of true values of deltaCP. The projected reach for the 200 km baseline with 7nu+3nubar run-plan is somewhat worse with 5sigma sensitivity for 34% of true values of deltaCP. On the other hand, for the discovery of a non-maximal theta23 and its octant, the 200 km baseline option with 7nu+3nubar run-plan performs significantly better than the other baselines. A 5sigma determination of a non-maximal theta23 can be made if the true value of sin^2theta23 lesssim 0.45 or sin^2theta23 gtrsim 0.57. The octant of theta23 could be resolved at 5sigma if the true value of sin^2theta23 lesssim 0.43 or gtrsim 0.59, irrespective of deltaCP.

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arXiv2014

The need for an early anti-neutrino run of NOvA

The moderately large value of $\ty$, measured recently by reactor experiments, is very welcome news for the future neutrino experiments. In particular, the \nova experiment, with 3 years each of $ν$ and $\anu$ runs, will be able to determine the mass hierarchy if one of the following two favourable combinations is true: normal hierarchy with $-180^\circ \leq \dcp \leq 0$ or inverted hierarchy with $0\leq \dcp \leq 180^\circ$. In this report, we study the hierarchy reach of the first 3 years of \nova data. Since $\sin^2 2 \tz$ is measured to be non-maximal, $\tz$ can be either in the lower or higher octant. Pure $ν$ data is affected by $\ty$-hierarchy and octant-hierarchy degeneracies, which limit the hierarchy sensitivity of such data. A combination of $ν$ and $\anu$ data is not subject to these degeneracies and hence has much better hierarchy discrimination capability. We find that, with a 3 year $ν$ run, hierarchy determination is possible for only two of the four octant-hierarchy combinations. Equal 1.5 year runs in $ν$ and $\anu$ modes give good hierarchy sensitivity for all the four combinations.

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arXiv2013

Exploring the three flavor effects with future superbeams using liquid argon detectors

Recent measurement of a moderately large value of theta13 signifies an important breakthrough in establishing the standard three flavor oscillation picture of neutrinos. It has provided an opportunity to explore the sub-dominant three flavor effects in present and future long-baseline experiments. In this paper, we perform a comparative study of the physics reach of two future superbeam facilities, LBNE and LBNO in their first phases of run, to resolve the issues of neutrino mass hierarchy, octant of theta23, and leptonic CP violation. We also find that the sensitivity of these future facilities can be improved significantly by adding the projected data from T2K and NOvA. Stand-alone LBNO setup with a 10 kt detector has a mass hierarchy discovery reach of more than 7 sigma, for the lowest allowed value of sin^2theta23(true) = 0.34. This result is valid for any choice of true deltaCP and hierarchy. LBNE10, in combination with T2K and NOvA, can achieve 3 sigma hierarchy discrimination for any choice of deltaCP, sin^2theta23, and hierarchy. The same combination can provide a 3 sigma octant resolution for sin^2theta23(true) leq 0.44 or for sin^2theta23(true) geq 0.58 for all values of deltaCP(true). LBNO can give similar results with 10 kt detector mass. In their first phases, both LBNE10 and LBNO with 20 kt detector can establish leptonic CP violation for around 50% values of true deltaCP at 2 sigma confidence level. In case of LBNE10, CP coverage at 3 sigma can be enhanced from 3% to 43% by combining T2K and NOvA data, assuming sin^2theta23(true) = 0.5. For LBNO setup, CP violation discovery at 3 sigma is possible for 46% values of true deltaCP if we add the data from T2K and NOvA.

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arXiv2013

High-precision measurement of atmospheric mass-squared splitting with T2K and NOvA

A precise measurement of the atmospheric mass-squared splitting |Δm^2_{μμ}| is crucial to establish the three-flavor paradigm and to constrain the neutrino mass models. In addition, a precise value of |Δm^2_{μμ}| will significantly enhance the hierarchy reach of future medium-baseline reactor experiments like JUNO and RENO-50. In this work, we explore the precision in |Δm^2_{μμ}| that will be available after the full runs of T2K and NOvA. We find that the combined data will be able to improve the precision in |Δm^2_{μμ}| to sub-percent level for maximal 2-3 mixing. Depending on the true value of \sin^2θ_{23} in the currently-allowed 3 sigma range, the precision in |Δm^2_{μμ}| will vary from 0.87% to 1.24%. We further demonstrate that this is a robust measurement as it remains almost unaffected by the present uncertainties in θ_{13}, δ_{CP}, the choice of mass hierarchy, and the systematic errors.

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arXiv2013

Resolving the octant of theta23 with T2K and NOvA

Preliminary results of MINOS experiment indicate that theta23 is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for theta23: one in the lower octant (LO: theta23 < 45 degree) and the other in the higher octant (HO: theta23 > 45 degree). numu to nue oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOvA experiments. Because of the hierarchy-deltacp degeneracy and the octant-deltacp degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of deltacp for which octant resolution is easy (challenging). However, for octant resolution the unfavorable deltacp values of the neutrino data are favorable for the anti-neutrino data and vice-verse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NOvA to resolve the octant ambiguity. If sin^2\theta23 =0.41, then NOvA can rule out all the values of theta23 in HO at 2 sigma C.L., irrespective of the hierarchy and deltacp. Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and anti-neutrino runs of 2.5 years each, a 2 sigma resolution of the octant becomes possible provided sin^2\theta23 \leq 0.43 or \geq 0.58 for any value of deltacp.

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arXiv2012

Potential of optimized NOvA for large theta(13) & combined performance with a LArTPC & T2K

NOvA experiment has reoptimized its event selection criteria in light of the recently measured moderately large value of theta(13). We study the improvement in the sensitivity to the neutrino mass hierarchy and to leptonic CP violation due to these new features. For favourable values of deltacp, NOvA sensitivity to mass hierarchy and leptonic CP violation is increased by 20%. Addition of 5 years of neutrino data from T2K to NOvA more than doubles the range of deltacp for which the leptonic CP violation can be discovered, compared to stand alone NOvA. But for unfavourable values of deltacp, the combination of NOvA and T2K are not enough to provide even a 90% C.L. hint of hierarchy discovery. Therefore, we further explore the improvement in the hierarchy and CP violation sensitivities due to the addition of a 10 kt liquid argon detector placed close to NOvA site. The capabilities of such a detector are equivalent to those of NOvA in all respects. We find that combined data from 10 kt liquid argon detector (3 years of nu + 3 years of nubar run), NOvA (6 years of nu + 6 years of nubar run) and T2K (5 years of nu run) can give a close to 2 sigma hint of hierarchy discovery for all values of deltacp. With this combined data, we can achieve CP violation discovery at 95% C.L. for roughly 60% values of deltacp.

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arXiv2012

Getting the best out of T2K and NOvA

We explore the combined physics potential of T2K and NOvA in light of the moderately large measured value of theta13. For sin^2 2*theta13 = 0.1, which is close to the best fit value, a 90% C.L. evidence for the hierarchy can be obtained only for the combinations (Normal hierarchy, -170 <= deltaCP <= 0) and (Inverted hierarchy, 0 <= deltaCP <= 170), with the currently planned runs of NOvA and T2K. However, the hierarchy can essentially be determined for any value of deltaCP, if the statistics of NOvA are increased by 50% and those of T2K are doubled. Such an increase will also give an allowed region of deltaCP around its true value, except for the CP conserving cases deltaCP = 0 or 180. We demonstrate that any measurement of deltaCP is not possible without first determining hierarchy. We find that comparable data from a shorter baseline (L ~ 130 km) experiment will not lead to any significant improvement.

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