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Rahul Sinha

Publications and source records attributed to Rahul Sinha.

At least 37 records · Page 2Linked to original sources
arXiv2015

Probing Higgs couplings at LHC and beyond

The study of the Higgs couplings following its discovery is the priority of future LHC runs. A hint of anomalous nature will be exhibited via its coupling to the Standard Model(SM) particles and open up new domain of phenomenological study of physics beyond the Standard Model. The enhanced statistics from next LHC runs will enable entry into the precision era to study the properties of Higgs with greater details. In this paper we present how one can extract Higgs couplings in future LHC runs at 14 TeV via $H \rightarrow Z Z^* \rightarrow 4 \ell$, using observables constructed from angular distributions for the Standard Model Higgs and Higgs with mixed CP configuration. We show how angular asymmetries can be used to measure the ratios of the couplings and the relative phases at LHC. We benchmark our analysis finding out the angular asymmetries and the best fit values of the ratios of the couplings for SM Higgs, CP-odd admixture, CP-even higher derivative contribution and when CP-even higher derivative contribution and CP-odd admixture are both present. In the Standard Model, $HZZ$ couplings have no momentum dependence. It is thus essential to demonstrate the momentum independence of the couplings to establish the couplings are SM like in nature. In this work we show how one can test the momentum independence of the Standard Model like coupling using angular asymmetries. We develop the necessary tools and demonstrate how to study the momentum dependence can be studied at future LHC runs.

hep-ph↗
arXiv2015

A model independent method for quantitative estimation of $SU(3)$ flavor symmetry breaking using Dalitz plot

The light hadron states are satisfactorily described in the quark model using $SU(3)$ flavor symmetry. If the $SU(3)$ flavor symmetry relating the light hadrons were exact, one would have an exchange symmetry between these hadrons arising out of the exchange of the up, down and strange quarks. This aspect of $SU(3)$ symmetry is used extensively to relate many decay modes of heavy quarks. However, the nature of the effects of $SU(3)$ breaking in such decays is not well understood and hence, a reliable estimate of $SU(3)$ breaking effects is missing. In this work we propose a new method to quantitatively estimate the extent of flavor symmetry breaking and better understand the nature of such breaking using Dalitz plot. We study the three non-commuting $SU(2)$ symmetries (subsumed in $SU(3)$ flavor symmetry): isospin (or $T$-spin), $U$-spin and $V$-spin, using the Dalitz plots of some three-body meson decays. We look at the Dalitz plot distributions of decays in which pairs of the final three particles are related by two distinct $SU(2)$ symmetries. We show that such decay modes have characteristic distributions that enable the measurement of violation of each of the three $SU(2)$ symmetries via Dalitz plot asymmetries in a single decay mode. Experimental estimates of these easily measurable asymmetries would help in better understanding the weak decays of heavy mesons into both two and three light mesons.

hep-ph↗
arXiv2014

On testing violations of Bose and $CPT$ symmetries via Dalitz plots and Dalitz `prism'

Bose symmetry and $CPT$ symmetry are two very fundamental symmetries of Nature. However, the validity of these symmetries in diverse phenomena must be verified by experiments. We propose new techniques to probe these two fundamental symmetries in the realm of mesons by using the Dalitz plot of a few three-body meson decays. Since these symmetries are very fundamental in nature, their violations, if any, are expected to be extremely small. Hence observing their violations requires study of a huge data sample. In this context we introduce a new three-dimensional plot which we refer to as the Dalitz 'prism'. This provides an innovative means for acquiring the huge statistics required for such studies. Using the Dalitz plots and the Dalitz prisms we chart out the way to probe the violations of Bose and $CPT$ symmetries in a significant manner. Since mesons are unstable and composite particles, testing the validity of Bose symmetry and the $CPT$ symmetry in these cases are of paramount importance for fundamental physics.

hep-ph↗
arXiv2014

Testing New Physics Effects in $B \to K^*\ell^+\ell^-$

It is generally believed that the decay mode $B\to K^*\ell^+\ell^-$ is one of the best modes to search for physics beyond the standard model. The angular distribution enables the independent measurement of several observables as a function of the dilepton invariant mass. The plethora of observables so obtained enable unique tests of the standard model contributions. We start by writing the most general parametric form of the standard model amplitude for $B\to K^*\ell^+\ell^-$ taking into account comprehensively all contributions within SM. These include all short-distance and long-distance effects, factorizable and non-factorizable contributions, complete electromagnetic corrections to hadronic operators up to all orders, resonance contributions and the finite lepton and quark masses. The parametric form of the amplitude in the standard model results a new relation involving all the $CP$ conserving observables. The derivation of this relation only needs the parametric form of the amplitude and not a detailed calculation of it. Hence, we make no approximations, however, innocuous. The violation of this relation will provide a smoking gun signal of new physics. We use the $1 \text{fb}^{-1}$ LHC$b$ data to explicitly show how our relation can be used to test standard model and search for new physics that might contribute to this decay.

hep-ph↗
arXiv2014

Inferring the nature of the boson at 125-126 GeV

The presence of a bosonic resonance near 125 GeV has been firmly established at the Large Hadron Collider. Understanding the exact nature of this boson is a priority. The task now is to verify whether the boson is indeed the scalar Higgs as proposed in the Standard Model of particle physics, or something more esoteric as proposed in the plethora of extensions to the Standard Model. This requires a verification that the boson is a $J^{PC}=0^{++}$ state with couplings precisely as predicted by the Standard Model. Since a non Standard Model boson can in some cases mimic the Standard Model Higgs in its couplings to gauge bosons, it is essential to rule out any anomalous behavior in its gauge couplings. We present a step by step methodology to determine the properties of this resonance without making any assumptions about its couplings. We present the analysis in terms of uni-angular distributions which lead to angular asymmetries that allow for the extraction of the couplings of the 125-126 GeV resonance to Z bosons. We show analytically and numerically, that these asymmetries can unambiguously confirm whether the new boson is indeed the Standard Model Higgs boson.

hep-ph↗
arXiv2013

A new technique to observe direct CP Violation in D mesons using Bose Symmetry and Dalitz Plot

We present a new and sensitive method to observe direct CP violation in $D$ mesons using Bose symmetry and Dalitz plot. We apply the method to processes such as $B \to D^0\bar{D}^0 P$, where $P$ is either a $K$ or a $π$. By choosing to reconstruct $D$ mesons only through their decays into CP eigenstates, we show that any asymmetry in the Dalitz plot can arise only through direct CP violation. We further show how CP violation parameters can be determined. Since the approach involves only Bose symmetry, the method is applicable to any multi-body process that involves $D^0\bar{D}^0$ in the final state. We briefly discuss how $B\to D^* \bar{D}^* P$ can also be used in a similar way.

hep-ph↗
arXiv2012

Design & Simulation of 128x Interpolator Filter

This paper presents the design consideration and simulation of interpolator of OSR 128. The proposed structure uses the half band filers & Comb/Sinc filter. Experimental result shows that proposed interpolator achieves the design specification, and also has good noise rejection capabilities. The interpolator accepts the input at 44.1 kHz for applications like CD & DVD audio. The interpolation filter can be applied to the delta sigma DAC. The related work is done with the MATLAB & XILINX ISE simulators. The maximum operating frequency is achieved as 34.584 MHz.

cs.ET↗
arXiv2012

New Physics Effects and Hadronic Form Factor Uncertainties in B -> K^* l^+ l^-

It is well known that New Physics can contribute to weak decays of heavy mesons via virtual processes during its decays. The discovery of New Physics, using such decays is made difficult due to intractable strong interaction effects needed to describe it. Modes such as B -> K^* l^+ l^- offer an advantage as they provide a multitude of observables via angular analysis. We show how the multitude of "related observables" obtained from B -> K^* l^+ l^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown universal form factors in heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We show how form factor ratios can be measured directly from helicity fraction with out any assumptions what so ever. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. We examine both the large-recoil and low-recoil regions of the K^* meson and point out special features and derive relations between observables valid in the two limits. In the large-recoil regions several of the relations are unaffected by corrections to all orders in α_s. We present yet another new relation involving only observables that would verify the validity of the relations between form-factors assumed in the low-recoil region. The several relations and constraints derived will provide unambiguous signals of New Physics if it contributes to these decays.

hep-ph↗
arXiv2012

Isolating New Physics Effects from Hadronic Form Factor Uncertainties in B\to K^* \ell^+\ell^-

The discovery of New Physics, using weak decays of mesons is difficult due to intractable strong interaction effects needed to describe it. We show how the multitude of "related observables" obtained from B\to K^* \ell^+\ell^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown form factors required to describe the decay using heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive other relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. The relations derived will provide unambiguous signals of New Physics if it contributes to these decays.

hep-ph↗
arXiv2011

Determination of Weak Amplitudes using Bose Symmetry and Dalitz Plots

We present a new method using Dalitz plot and Bose symmetry of pions that allows the complete determination of the magnitudes and phases of weak decay amplitudes. We apply the method to process like B->K^* pi, with the subsequent decay of K^* -> K pi. Our approach enables the additional measurement of an isospin amplitude without any theoretical assumption. This advance will help in measuring weak phase and probing for new physics beyond standard model with fewer assumptions.

hep-ph↗
arXiv2010

Measuring the Magnitude of the Fourth-Generation CKM4 Matrix Element V_{t'b'}

We study the decays of heavy chiral (t', b') quarks in a four-generation extension of the Standard Model. If the difference between the t' and b' masses is smaller than the W mass, as favored by precision electroweak measurements, then the Cabibbo-Kobayashi-Maskawa favored, on-shell decay t'-->b'W is forbidden. As a result, other t' decays have substantial branching fractions, which are highly sensitive to the magnitude of the diagonal CKM matrix element V_{t'b'}. We show that |V_{t'b'}| can be determined from the ratio of the two-body and three-body t'-decay branching fractions and estimate the precision of such a measurement at the LHC. We discuss the hadronization of a t' for large enough values of |V_{t'b'}|.

hep-ph↗
arXiv2007

Accurate measurement of the D0-D0bar mixing parameters

We propose a new method to determine the mass and width differences of the two D meson mass-eigenstates as well as the CP violating parameters associated with D^0-\bar{D}^0 mixing. We show that an accurate measurement of all the mixing parameters is possible for an arbitrary CP violating phase, by combining observables from a time dependent study of D decays to a doubly Cabibbo suppressed mode with information from a CP eigenstate. As an example we consider D^0-> K^{*0} π^0 decays where the K^{*0} is reconstructed in both K^+π^- and K_Sπ^0. We also show that decays to the CP eigenstate D-> K^+K^- together with D-> K^+π^- can be used to extract all the mixing parameters. A combined analysis using D^0-> K^{*0} π^0 and D-> K^+K^- can also be used to reduce the ambiguity in the determination of parameters.

hep-ph↗
arXiv2007

Generalized analysis on $B\to K^* ρ$ within and beyond the Standard Model $-$ Can it help understand the $B \to K π$ puzzle?

We study $B \to K^* ρ$ modes that are analogues of the much studied $B\to K π$ modes with B decaying to two vector mesons instead of pseudoscalar mesons, using topological amplitudes in the quark diagram approach. We show how $B \to K^*ρ$ modes can be used to obtain many more observables than those for $B \to K π$ modes, even though the quark level subprocesses of both modes are exactly the same. All the theoretical parameters (except for the weak phase $γ$), such as the magnitudes of the topological amplitudes and their strong phases, can be determined in terms of the observables without any model-dependent assumption. We demonstrate how $B\to K^*ρ$ can also be used to verify if there exist any relations between theoretical parameters, such as the hierarchy relations between the topological amplitudes and possible relations between the strong phases. Conversely, if there exist reliable theoretical estimates of amplitudes and strong phases, the presence of New physics could be probed. We show that if the tree and color-supressed tree are related to the electroweak penguins and color-supressed electroweak penguins, it is not only possible to verify the validity of such relations but also to have a clean measurement of New Physics parameters. We also present a numerical study to examine which of the observables are more sensitive to New Physics.

hep-ph↗
arXiv2006

Patterns of New Physics in B Decays

We show that any new physics (NP) which affects B decays with penguin contributions can be absorbed by redefinitions of the standard-model (SM) diagrammatic amplitudes. Hence, there are no clean signals of NP in such decays unless there is an accurate theoretical estimate of parameters or a justifiable approximation can be made. In all decays with penguin contributions, NP simultaneously affects pairs of diagrams. The evidence for a large C' from fits to B-> pi K data is naturally explained if NP contributes to P_EW, since NP affects the P_EW and C' diagrams as a pair. The weak phase gamma measured in B-> pi K decays will always agree with its SM value even in the presence of NP, if the NP contributes in such a way that the amplitudes retain the SM form after suitable redefinitions.

hep-ph↗
arXiv2006

Has New Physics already been seen in B_d meson decays?

We show using a model independent approach that the deviation in measured B_d^0-\bar{B}_d^0 mixing phase caused by pollution from another amplitude, within the Standard Model, is always less in magnitude, and has the same sign as the weak phase of the polluting amplitude. The exception is to have large destructive interference between the two amplitudes. We demonstrate that any deviation larger than a few degrees is only possible if the observed decay rate results from fine tuned cancellations between significantly larger quark level amplitudes. These simple observations have very significant consequences for signals of New Physics.

hep-ph↗
arXiv2005

Improved measurement of (2 beta+gamma)

We propose to measure the Cabibbo-Kobayashi-Maskawa parameter (2 beta+gamma) using B^0 decays involving several intermediate states, and describe a general formalism that applies to a broad class of decays. The main advantage of this method is that the ratios between the interfering amplitudes can be measured without requiring external input. In addition, discrete ambiguities are resolved.

hep-ph↗
arXiv2005

Angular analysis of B decaying into J/psi Tensor, J/psi Vector and J/psi Scalar

The analysis of $B \to \jpsi K^{\star}_{2}(1430)$ decay mode is complicated by the fact that close to the $J^{PC}=2^{++}$ meson $\Kstart(1430)$, there lie other $J^{PC}=1^{--}$ and $J^{PC}=0^{++}$ resonances, $K^{\star}(1410)$ and $K^{\star}_{0}(1430)$ respectively. We show how an angular analysis can be used to isolate the contributions from the different resonances and partial waves contributing to the final state $B\to \jpsi K_X$, where $K_X$ could be any of the resonance $K^{\star}_{2}(1430)$, $K^{\star}(1410)$ or $K^{\star}_{0}(1430)$. For this purpose we study the time integrated differential decay rate. We also construct a time dependent angular asymmetry that enables a clean measurement of the mixing phase $β$ in the mode $B\to \jpsi \Kstart(1430)$ alone, without contributions from the decay modes $B\to\jpsi\Kstarsz(1430)$ or $B\to\jpsi\Kstar(1410)$.

hep-ph↗