arXiv subjects

Nita Sinha

Publications and source records attributed to Nita Sinha.

At least 19 recordsLinked to original sources

arXiv2026

Implications of the evidence for direct $\mathbf{CP}$ violation in $D\to π^+π^-$ decays

The observation of $CP$ violation in the difference of $CP$ asymmetries between $D\to K^+K^-$ and $D\to π^+π^-$ has raised a debate whether the observed asymmetries can be regarded as a signal of physics beyond the standard model (SM). In this paper we obtain all the topological amplitudes and isospin amplitudes directly from measured observables for $D\to ππ$. These results unambiguously imply a very large penguin contribution, having a central value $4.74$ times the magnitude of the amplitude for $D^0\toπ^+ π^-$. This fitted central value differs from a reasonable SM estimate of $10\%$ with a significance greater than $3.3σ$. In contrast to previous studies, we present model-independent arguments based only on unitarity of re-scattering amplitudes to show that large penguins cannot arise from re-scattering alone and likely indicate physics beyond the SM. In a model-independent approach we show how a very small contribution from physics beyond the SM with a large weak phase alleviates the problem.

hep-ph↗

arXiv2022

ALP-portal majorana dark matter

Axion like particles(ALPs) and right handed neutrinos~(RHNs) are two well-motivated dark matter(DM) candidates. However, these two particles have a completely different origin. Axion was proposed to solve the Strong CP problem, whereas RHNs were introduced to explain light neutrino masses through seesaw mechanisms. We study the case of ALP portal RHN DM taking into account existing constraints on ALPs. We consider the leading effective operators mediating interactions between the ALP and SM particles and three RHNs to generate light neutrino masses through type-I seesaw. Further, ALP-RHN neutrino coupling is introduced to generalize the model which is restricted by the relic density and indirect detection constraint.

hep-ph↗

arXiv2022

Two-component scalar and fermionic dark matter candidates in a generic U$(1)_X$ model

We consider a $U(1)_X\otimes \mathbb{Z}_2\otimes \mathbb{Z}'_2$ extension of the Standard Model (SM), where the $U(1)_X$ charge of an SM field is given by a linear combination of its hypercharge and B$-$L number. Apart from the SM particle content, the model contains three right-handed neutrinos (RHNs) $N_R^i$ and two scalars $Φ$, $χ$, all singlets under the SM gauge group but charged under $U(1)_X$ gauge group. Two of these additional fields, fermion $N_R^3$ is odd under $\mathbb{Z}_2$ and scalar $χ$ is odd under $\mathbb{Z}'_2$ symmetry. Thus both $χ$ and $N_R^3$ contribute to the observed dark matter relic density, leading to two-component dark matter candidates. We study in detail its dark matter properties such as relic density and direct detection taking into account the constraints coming from collider studies. We find that in our model, there can be possible annihilation of one Dark Matter (DM) into the other, which may potentially alter the relic density in a significant way.

hep-ph↗

arXiv2021

Interference effect in lepton number violating and conserving meson decays for a left-right symmetric model

We study the effect of interference on the lepton number violating~(LNV) and lepton number conserving~(LNC) three-body meson decays $M_1^{+}\to l_i^{+} l_j^{\pm}π^{\mp}$, that arise in a TeV scale Left Right Symmetric model~(LRSM) with degenerate or nearly degenerate right handed~(RH) neutrinos. LRSM contains three RH neutrinos and a RH gauge boson. The RH neutrinos with masses in the range of $M_N \sim$ (MeV - few GeV) can give resonant enhancement in the semi-leptonic LNV and LNC meson decays. In the case, where only one RH neutrino contributes to these decays, the predicted new physics branching ratio of semi-leptonic LNV and LNC meson decays $M_1^{+}\to l_i^{+} l_j^{+}π^{-}$ and $M_1^{+}\to l_i^{+} l_j^{-}π^{+}$ are equal. We find that with at least two RH neutrinos contributing to the process, the LNV and LNC decay rates can differ. Depending on the neutrino mixing angles and $CP$ violating phases, the branching ratios of LNV and LNC decay channels mediated by the heavy neutrinos can be either enhanced or suppressed, and the ratio of these two rates can differ from unity.

hep-ph↗

arXiv2020

Signatures of $\tilde{R}_2$ class of Leptoquarks at the upcoming $ep$ colliders

We explore the signatures of the $\tilde{R}_2$ class of leptoquark (LQ) models at the proposed $e^- p$ and $e^+p$ colliders. We carry out an analysis for the proposed colliders LHeC and FCC-eh with center of mass (c.m.) energy 1.3 TeV and 3.46 TeV, respectively. For $\tilde{R}_2$ class of LQ models, there are a number of final states that can arise from LQ production and its subsequent decay. In this report we do a detailed cut-based analysis for the $l^{\pm}j$ final state. We also discuss the effect of polarized electron and positron beams on LQ production and in turn on $l^{\pm}j$ production. At LHeC, the final state $l^+j$ has very good discovery prospect. We find that, only 100 $\text{fb}^{-1}$ of data can probe LQ mass upto 1.2 TeV with $5σ$ significance, even with a generic set of cuts. On the contrary, at FCC-eh, one can probe LQ masses upto 2.2 TeV (for $e^-$ beam) and 3 TeV (for $e^+$ beam), at more than $5σ$ significance with luminosity $1000\,\text{fb}^{-1}$ and $500\,\text{fb}^{-1}$, respectively.

hep-ph↗

arXiv2020

Probing muonic charged current nonstandard interactions at decay-at-rest facilities in conjunction with T2HK

The muon decay-at-rest ($μ$-DAR) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $μ$-DAR source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton Hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $μ$-DAR and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic considerations reveal that the oscillation probability is most sensitive to the NSI parameter in the $μ$-e sector. For this parameter, we show that the $μ$-DAR setup can improve on the existing bounds down to around 0.01, especially when the data are combined with neutrino data from T2HK experiment due to the lifting of parameter degeneracies. The high precision with which $μ$-DAR can measure $δ_{\rm{CP}}$ is shown to be robust even in the presence of the considered NSIs. Finally, we show that the combination of $μ$-DAR along with T2HK can also be used to put mild constraints on the NSI phase in the vicinity of the maximal CP-violating value for the chosen benchmark value of $\varepsilon^{μe}_{μe}=0.01$.

hep-ph↗

arXiv2019

Sensitivity of Lepton Number Violating Meson Decays in Different Experiments

We study the discovery prospect of different three body lepton number violating~(LNV) meson decays $M_{1}^{-}\to\ell_{1}^{-}\ell_{2}^{-}M_{2}^{+}$ in the framework of right handed~(RH) neutrino extended Standard Model~(SM). We consider a number of ongoing experiments, such as, NA62 and LHCb at CERN, Belle II at SuperKEK, as well as at the proposed future experiments, SHiP, MATHUSLA and FCC-ee. The RH Majorana neutrino $N$ mediating these meson decays provides a resonant enhancement of the rates, if the mass of $N$ lies in the range $(100\, \text{MeV}-6\, \text{GeV})$. We consider the effect of parent mesons velocity, as well as, the effect of finite detector size. Using the expected upper limits on the number of events for the LNV decay modes, $M_{1}^{-} \to\ell_1^{-}\ell_2^{-}π^{+}$~($M_{1}=B, B_c,D, D_{s}\,\text{and}\,K$), we analyze the sensitivity reach of the mixing angles $|V_{e N}|^{2}$, $|V_{μN}|^{2}$, $|V_{τN}|^{2}$, $|V_{e N}V_{μN}|$, $|V_{e N}V_{τN}|$ and $|V_{μN}V_{τN}|$ as a function of heavy neutrino mass $M_{N}$. We show that, inclusion of parent meson velocity can account to a large difference for active-sterile mixing, specially for $D$, $D_s$ meson decay at SHiP and $K$ meson decay at NA62. Taking into account the velocity of the $D_s$ meson, the future beam dump experiment SHiP can probe $|V_{eN}|^2 \sim 10^{-9}$. For RH neutrino mass in between 2 - 5 GeV, MATHUSLA can provide best sensitivity reach of active-sterile mixings.

hep-ph↗

arXiv2018

Probing Leptoquark and Heavy Neutrino at LHeC

We explore leptoquark production and decay for the $\tilde{R}_{2}$ class of models at the proposed $e^{-} p$ collider LHeC, planned to operate with 150 GeV electron and 7 TeV proton beams. In addition to the coupling of leptoquark with the lepton and jet, the model also has right handed neutrinos, coupled to the leptoquark. We analyse the collider signatures of a number of final states, that can originate from leptoquark decay into the standard model particles, as well as, the final states that originate from further decay of the heavy neutrinos, produced from leptoquark. We find that the final state $\ell^{-}+\text{n-jets}\,(1\leq\text{n} \leq 2)$ has the largest discovery prospect, more than $5σ$ with only few fb of data to probe a leptoquark of mass 1.1 TeV, even with a generic set of cuts. The significance falls sharply with increasing leptoquark mass. However, with 100\,$\rm{fb}^{-1}$ of data, a 5$σ$ discovery for leptoquarks of mass upto 1.4 TeV is still achieveable. Also for the same luminosity, final state $\bar{b}\ell^{+}τ^{-}+\text{n-jets}\,(\text{n}\geq 2)+\text{MET}$, resulting from the cascade decay of the leptoquark to an $\bar{t}$ and right handed neutrino, followed by further decays of $\bar{t}$ and the neutrino, is expected to yield a rather large number of events~($\approx 180$).

hep-ph↗

arXiv2017

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

physics.ins-det↗

arXiv2017

Constraining Right Handed Gauge Boson Mass from Lepton Number Violating Meson Decays in a Low Scale Left Right Model

We analyze the lepton number violating (LNV) meson decays that arise in a TeV scale Left Right Symmetry model. The right handed Majorana neutrino $N$ along with the right handed or Standard Model gauge bosons mediate the meson decays and provide a resonant enhancement of the rates if the mass of $N$ ($M_N$) lies in the range $\sim (100\, \rm{MeV}-5\, \rm{GeV})$. Using the expected upper limits on the number of events for the LNV decay modes $M_{1}^{+} \to\ell^{+}\ell^{+}π^{-}$~($M_{1}=B, D, D_{s}, K$), we derive constraints plausible on the mass of the right handed charged gauge boson by future searches at the ongoing NA62 and LHCb experiments at CERN, the upcoming Belle II at SuperKEK, as well as at the proposed future experiments, SHiP and FCC-ee. These bounds are complimentary to the limits from same-sign dilepton search at Large Hadron Collider (LHC). The very high intensity of Charmed mesons expected to be produced at SHiP will result in a far more stringent bound, $M_{W_R}>18.4$~TeV (corresponding to $M_N=1.46$~GeV), than the other existing bounds from collider and neutrinoless double beta decay searches.

hep-ph↗

arXiv2017

Searching for New physics in Charm Radiative decays

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for $c\rightarrow uγ$ decay is enhanced by more than $\mathcal{O}(10^2)$ as compared to that in the Standard model when QCD corrections to next-to-leading order are incorporated. In a left-right symmetric model (LRSM) along with a heavy vector-like fermion, enhancement of this order can be achieved at the bare (QCD uncorrected) level itself. We propose that a measurement of the photon polarization could be used to signal the presence of such new physics inspite of the large long distance effects. We find that there is a large region within the allowed parameter space of model with vector-like quark with additional left-right symmetry, where depending on the exact size of the long distance contribution, the photon polarization can be dominantly right-handed.

hep-ph↗

arXiv2016

Favoured $B_c$ Decay modes to search for a Majorana neutrino

Recently, the LHCb collaboration reported the observation of the decay mode $B_{c}^{-}\rightarrow\overline{B}_{s}^{0}π^{-}$ with the largest exclusive branching fraction amongst the known decay modes of all the $B$ mesons. Here we propose a search for a few lepton-number violating decay modes of $B_c$ which can only be induced by Majorana neutrinos. Distinguishing between Dirac and Majorana nature of neutrinos is an outstanding problem and hence, all possible searches for Majorana neutrinos need to be carried out. Since the lepton number violating modes are expected to be rare, when using meson decay modes for these searches one expects CKM favoured modes to be the preferred ones; $B_{c}\rightarrow B_{s}$ is one such transition. With a resonance enhancement of the Majorana neutrino mediating the $B_{c}^{-}\rightarrow\overline{B}_{s}^{0}\ell_{1}{-}\ell_{2}^{-}π^{+}$ modes one can hope to observe these rare modes, or, even their non-observation can be used to obtain constraints on the mixing angles of the heavy Majorana singlet with the light flavour neutrinos from upper limits of the branching fractions which are tighter or compatible with results from earlier studies. Also, we find that the relatively suppressed mode $B_{c}^{-}\rightarrow J/ψ\ell_{1}^{-}\ell_{2}^{-}π^{+}$ can provide even tighter constraints on $\mid V_{e N}\mid^2$, $\mid V_{μN}\mid^2$, $\mid V_{e N} V_{μN}\mid$, and in a larger range of the heavy neutrino mass. Further, exclusion regions for $\mid V_{e N} V_{τN}\mid$, $\mid V_{μN} V_{τN}\mid$ can also be obtained for masses larger than those accessible in tau decays. Upper limits on $\mathscr{B}\left(B_{c}^{-}\rightarrowπ^{+}\ell_{1}^{-}\ell_{2}^{-}\right)$ can also result in stringent exclusion curves for all the mixing elements, including that for $\mid V_{τN}\mid^2$ in a mass range where it is unconstrained thus far.

hep-ph↗

arXiv2015

Schottky Anomaly and Hadronic Spectrum

We show that the hadronic "heat capacity" calculated as a function of temperature may be used to infer the possible presence of different scales underlying the dynamical structure of hadronic resonances using the phenomenon of Schottky anomaly. We first demonstrate this possibility with well known meson spectrum in various channels and comment on the possibility of using this method as a diagnostic to distinguish the exotic states.

hep-ph↗

arXiv2015

Non-leptonic decays of Charmed mesons into two Pseudoscalars

We examine the role of resonant coupled channel final state interactions (FSI), as well as weak annihilation and exchange contributions in explaining all the two body hadronic $D\rightarrow PP$ decay modes data. In the un-unitarized amplitudes we include modified Wilson coefficients with non-factorizable corrections as parameters. For the hadronic form factors, the z-series expansion method is used to get the $q^2$ dependence. The FSI effects are incorporated via a phenomenological approach with widths of resonances to various channels taken from observations where available, and others as additional parameters to be determined from fits of all the theoretical rates to the measured ones. Our results for the rather hard to explain $D^0\rightarrow K^+K^-, π^+π^- $ are in agreement with measured values. We demonstrate that both weak exchange as well as FSI effects are required to get the correct branching ratio for the $D^ \rightarrow K^0\bar{K^0}$ mode. Using our unitarized amplitudes we evaluate the strong phase difference between the amplitudes for $D^0\rightarrow K^-π^+$ and $D^0\rightarrow K^+π^-$ and find it to be in complete agreement with the recent BES III result.

hep-ph↗

arXiv2015

Simulations Study of Muon Response in the Peripheral Regions of the Iron Calorimeter Detector at the India-based Neutrino Observatory

The magnetized Iron CALorimeter detector (ICAL) which is proposed to be built in the India-based Neutrino Observatory (INO) laboratory, aims to study atmospheric neutrino oscillations primarily through charged current interactions of muon neutrinos and anti-neutrinos with the detector. The response of muons and charge identification efficiency, angle and energy resolution as a function of muon momentum and direction are studied from GEANT4-based simulations in the peripheral regions of the detector. This completes the characterisation of ICAL with respect to muons over the entire detector and has implications for the sensitivity of ICAL to the oscillation parameters and mass hierarchy compared to the studies where only the resolutions and efficiencies of the central region of ICAL were assumed for the entire detector. Selection criteria for track reconstruction in the peripheral region of the detector were determined from the detector response. On applying these, for the 1--20 GeV energy region of interest for mass hierarchy studies, an average angle-dependent momentum resolution of 15--24%, reconstruction efficiency of about 60--70% and a correct charge identification of about 97% of the reconstructed muons were obtained. In addition, muon response at higher energies upto 50 GeV was studied as relevant for understanding the response to so-called rock muons and cosmic ray muons. An angular resolution of better than a degree for muon energies greater than 4 GeV was obtained in the peripheral regions, which is the same as that in the central region.

physics.ins-det↗

arXiv2014

Can the observed CP asymmetry in tau --> K pi nu_tau be due to Non-Standard Tensor interactions?

An intriguing opposite sign of the CP violating asymmetry was recently measured in the tau decay modes tau -> Ks pi nutau by the BaBar collaboration, than that expected within the Standard Model. If this result is confirmed with higher precision, the observed decay rate asymmetry ACP, can only arise from some Non-Standard Interactions(NSI) occurring possibly in both the hadronic as well as in the leptonic sectors. We illustrate that while a simple charged scalar interaction cannot yield this rate asymmetry, it will be possible to generate this in the presence of a tensor interaction. Parameterizing the strength and weak phase of this NSI contribution, the observed branching ratio and the decay rate CP asymmetry for the particular mode tau -> Ks pi nutau, are used to determine the CP violating weak phase and the coupling of a tensorial interaction that can give a consistent sign and magnitude of the asymmetry.

hep-ph↗

arXiv2014

A Simulations Study of the Muon Response of the Iron Calorimeter Detector at the India-based Neutrino Observatory

The magnetised Iron CALorimeter detector (ICAL), proposed to be built at the India-based Neutrino Observatory (INO), is designed to study atmospheric neutrino oscillations. The ICAL detector is optimized to measure the muon momentum, its direction and charge. A GEANT4-based package has been developed by the INO collaboration to simulate the ICAL geometry and propagation of particles through the detector. The simulated muon tracks are reconstructed using the Kalman Filter algorithm. Here we present the first study of the response of the ICAL detector to muons using this simulations package to determine the muon momentum and direction resolutions as well as their reconstruction and charge identification efficiencies. For 1-20 GeV/c muons in the central region of the detector, we obtain an average angle-dependent momentum resolution of 9-14%, an angular resolution of about a degree, reconstruction efficiency of about 80% and a correct charge identification of about 98%.

physics.ins-det↗

arXiv2012

Determining neutrino mass hierarchy from electron disappearance at a Low energy neutrino factory

Recent measurements of large theta_{13} by Daya Bay and RENO reactor experiments have opened up the possibility of determining the neutrino mass hierarchy, i.e. the sign of the mass squared splitting Delta m_{31}^2, the CP-violating phase delta_{CP} and the octant of theta_{23}. In the light of this result, we study the performance of a low energy neutrino factory (LENF) for determination of the mass hierarchy. In particular, we explore the potential of the nu_e$ and barν_e disappearance channels at LENF to determine the neutrino mass hierarchy, that is free from the uncertainties arising from the unknown delta_{CP} phase and the theta_{23} octant. We find that using these electron neutrino (antineutrino) disappearance channels with a standard LENF, it is possible to exclude the wrong hierarchy at 5 sigma with only 2 years of running.

hep-ph↗