arXiv subjects

Bhubanjyoti Bhattacharya

Publications and source records attributed to Bhubanjyoti Bhattacharya.

At least 55 records · Page 3Linked to original sources

arXiv2015

Simultaneous Explanation of the $R_K$ and $R(D^{(*)})$ Puzzles

At present, there are several hints of lepton flavor non-universality. The LHCb Collaboration has measured $R_K\equiv{\cal B}(B^+ \to K^+ μ^+ μ^-)/{\cal B}(B^+ \to K^+ e^+ e^-)$, and the BaBar Collaboration has measured $R(D^{(*)}) \equiv {\cal B}({\bar B} \to D^{(*)+} τ^- {\barν}_τ) / {\cal B}({\bar B} \to D^{(*)+} \ell^- {\barν}_\ell)$ ($\ell = e,μ$). In all cases, the experimental results differ from the standard model predictions by 2-3$σ$. Recently, an explanation of the $R_K$ puzzle was proposed in which new physics (NP) generates a neutral-current operator involving only third-generation particles. Now, assuming the scale of NP is much larger than the weak scale, this NP operator must be made invariant under the full $SU(3)_C \times SU(2)_L \times U(1)_Y$ gauge group. In this Letter, we note that, when this is done, a new charged-current operator can appear, and this can explain the $R(D^{(*)})$ puzzle. A more precise measurement of the double ratio $R(D)/R(D^*)$ can rule out this model.

hep-ph↗

arXiv2014

Probing New Physics in Higgs Couplings to Fermions using an Angular Analysis

The standard-model Higgs boson couples to quarks through a parity-even scalar $Hq{\bar q}$ coupling. We show that the rare Higgs decay $H\to VZ$, where $V$ is a vector quarkonium state such as $J/ψ$ ($c{\bar c}$) or $Υ(1S)$ ($b{\bar b}$), can be used to search for the presence of a parity-odd pseudoscalar $Hq{\bar q}$ coupling. Since both $V$ and $Z$ can decay to a pair of charged leptons, this presents an experimentally-clean channel that can be observed at the high-luminosity LHC or a future hadron collider. The P-even and P-odd $Hq{\bar q}$ couplings can be measured by analyzing the angular distribution of the final-state leptons.

hep-ph↗

arXiv2014

Charmless B -> PPP Decays: the Fully-Symmetric Final State

In charmless B -> PPP decays, where P is a pseudoscalar meson, there are six possibilities for the symmetry of the final state. In this paper, for P=pi,K, we examine the properties of the fully-symmetric final state. We present expressions for all 32 B -> PPP decay amplitudes as a function of both SU(3) reduced matrix elements and diagrams, demonstrating the equivalence of diagrams and SU(3). We also give 25 relations among the amplitudes in the SU(3) limit, as well as those that appear when the diagrams E/A/PA are neglected. In the SU(3) limit, one has the equalities \sqrt{2} A(B+ -> K+ pi+ pi-)_{FS} = A(B+ -> K+ K+ K-)_{FS} and \sqrt{2} A(B+ -> pi+ K+ K-)_{FS} = A(B+ -> pi+ pi+ pi-)_{FS}, where FS denotes the fully-symmetric final state. These provide good tests of the standard model that can be carried out now by the LHCb Collaboration.

hep-ph↗

arXiv2013

Extraction of the CP-violating phase $γ$ using $B \to K ππ$ and $B \to K K {\bar K}$ decays

Using the B{\sc a}B{\sc ar}\ measurements of the Dalitz plots for $B^0 \to K^+π^0π^-$, $B^0 \to K^0π^+π^-$, $B^+ \to K^+π^+π^-$, $B^0 \to K^+ K^0 K^-$, and $B^0 \to K^0 K^0 {\bar K}^0$ decays, we demonstrate that it is possible to cleanly extract the weak phase $γ$. We find four possible solutions. Three of these -- $32^\circ$, $259^\circ$, and $315^\circ$ -- are in disagreement with the SM, while one -- $77^\circ$ -- is consistent with the SM. An advantage of this Dalitz-plot method is that one can obtain many independent measurements of $γ$, thereby reducing its statistical error. An accurate determination of the errors, however, requires detailed knowledge of the data.

hep-ph↗

arXiv2013

Measurement of $γ$ from three-body B decays

Using the BaBar measurements of the Dalitz plots for the decays $B^0 \to K^+π^0π^-$, $B^0 \to K^0π^+π^-$, $B^+ \to K^+π^+π^-$, $B^0 \to K^+ K^0 K^-$, and $B^0 \to K^0 K^0 \bar K^0$, we demonstrate that it is possible to cleanly extract the weak phase $γ$. An advantage of this Dalitz-plot method is that one can obtain many independent measurements of $γ$, thereby reducing its statistical error. An accurate determination of the errors, however, requires detailed knowledge of the data. Hopefully, an experimental group will repeat the analysis, and obtain precise values of the errors.

hep-ph↗

arXiv2013

CP asymmetries in three-body B+- decays to charged pions and kaons

CP asymmetries have been measured recently by the LHCb collaboration in three-body $B^+$ decays to final states involving charged pions and kaons. Large asymmetries with opposite signs at a level of about 60% have been observed in $B^\pm\to π^\pm({\rm or} K^\pm)π^+π^-$ and $B^\pm \to π^\pm K^+K^-$ for restricted regions in the Dalitz plots involving $π^+π^-$ and $K^+K^-$ with low invariant mass. U-spin is shown to predict corresponding $ΔS=0$ and $ΔS=1$ asymmetries with opposite signs and inversely proportional to their branching ratios, in analogy with a successful relation predicted thirteen years ago between asymmetries in $B_s\to K^-π^+$ and $B^0 \to K^+ π^-$. We compare these predictions with the measured integrated asymmetries. Effects of specific resonant or non-resonant partial waves on enhanced asymmetries for low-pair-mass regions of the Dalitz plot are studied in $B^\pm \to π^\pm π^+π^-$. The closure of low-mass $π^+π^-$ and $K^+K^-$ channels involving only $ππ\leftrightarrow K\bar K$ rescattering may explain by CPT approximately equal magnitudes and opposite signs measured in $B^\pm\to π^\pmπ^+π^-$ and $B^\pm \to π^\pm K^+K^-$.

hep-ph↗

arXiv2013

Measurement of gamma using B -> K pi pi and B -> K K Kbar decays

The BaBar measurements of the Dalitz plots for B0 -> K+ pi0 pi-, B0 -> K0 pi+ pi-, B+ -> K+ pi+ pi-, B0 -> K+ K0 K-, and B0 -> K0 K0 Kbar0 decays are used to cleanly extract the weak phase gamma. We find four possible solutions: $(31^{+2}_{-3})^\circ$, $(77 \pm 3)^\circ$, $(258^{+4}_{-3})^\circ$, and $(315^{+3}_{-2})^\circ$. One solution -- $(77 \pm 3)^\circ$ -- is consistent with the SM. Its error, which includes leading-order flavor-SU(3) breaking, is far smaller than that obtained using two-body B decays.

hep-ph↗

arXiv2013

Searching for New Physics with bbar -> sbar Bs -> V_1 V_2 Penguin Decays

We present the most general (six-helicity) angular analysis of Bs -> V_1 (-> P_1P'_1) V_2 (-> P_2P'_2) (V_i is a vector meson, and P_i, P'_i are pseudoscalars). We focus on final states accessible to both Bs and Bsbar -- these are mainly bbar -> sbar penguin decays. We also derive the most general decay amplitude, and discuss the differences between it and that used by LHCb in its analysis of Bs -> phi phi. In the standard model, all CP violation is predicted to be small, so that the simple measurement of a sizeable CP-violating observable indicates the presence of new physics. A full fit to the data is not necessary. By determining which of the CP-violating observables are nonzero, one can learn about the structure of the underlying NP. Finally, we apply the angular analysis to Bs -> K^{*0} Kbar^{*0}, and show that there are numerous CP-violating observables that remain in the untagged data sample.

hep-ph↗

arXiv2013

Reducing Penguin Pollution

The most common decay used for measuring 2beta_s, the phase of Bs-Bsbar mixing, is Bs -> J/psi phi. This decay is dominated by the colour-suppressed tree diagram, but there are other contributions due to gluonic and electroweak penguin diagrams. These are often referred to as "penguin pollution" (PP) because their inclusion in the amplitude leads to a theoretical error in the extraction of 2beta_s from the data. In the standard model (SM), it is estimated that the PP is negligible, but there is some uncertainty as to its exact size. Now, phi_s^{c\bar{c}s} (the measured value of 2beta_s) is small, in agreement with the SM, but still has significant experimental errors. When these are reduced, if one hopes to be able to see clear evidence of new physics (NP), it is crucial to have the theoretical error under control. In this paper, we show that, using a modification of the angular analysis currently used to measure phi_s^{c\bar{c}s} in Bs -> J/psi phi, one can reduce the theoretical error due to PP. Theoretical input is still required, but it is much more modest than entirely neglecting the PP. If phi_s^{c\bar{c}s} differs from the SM prediction, this points to NP in the mixing. There is also enough information to test for NP in the decay. This method can be applied to all Bs/Bsbar -> V1 V2 decays.

hep-ph↗

arXiv2013

Shift in weak phase $γ$ due to CP asymmetries in $D$ decays to two pseudoscalar mesons

A difference of several tenths of a percent has been observed between the direct CP asymmetries of $D^0\to K^+K^-$ and $D^0\to π^+π^-$. It has been noted recently that CP asymmetries in such singly-Cabibbo-suppressed (SCS) decays can affect the determination of the weak phase $γ$ using the Gronau-London-Wyler method of comparing rates for $B^+ \to D K^+$ and $B^- \to D K^-$, where $D$ is a superposition of $D^0$ and $\od$ decaying to a CP eigenstate. Using an analysis of the CP asymmetries in SCS decays based on a $c \to u$ penguin amplitude with standard model weak phase but enhanced by CP-conserving strong interactions, we estimate typical shifts in $γ$ of several degrees and pinpoint measurements which would reduce uncertainties to an acceptable level.

hep-ph↗

arXiv2013

Direct CP Violation in Nonleptonic Charm Decays

LHCb, CDF and most recently Belle have observed a large difference between direct CP asymmetries in $D^0\to K^+K^-$ and $D^0\toπ^+π^-$. We use the measured value of $ΔA_{CP}$ to constrain the magnitude and strong phase of a QCD-enhanced standard model penguin and predict its effects on direct CP asymmetry in $D^0\toπ^0π^0$ and $D^+\to K^+\bar{K}^0$.

hep-ph↗

arXiv2012

Extraction of $γ$ from three-body B decays

The conventional use of two-body B decays to extract $γ$, although theoretically clean, is currently statistics-limited. On the other hand, a bulk of data on three-body B decays is available from $B$ factories. Applying the flavor-SU(3)-symmetric approach proposed in Ref.\ \cite{ReyLeLorier:2011ww} to \babar data, we find the highly promising result $γ= (81^{+4}_{-5} ({\rm avg.}) \pm 5 ({\rm std.\ dev.}))^\circ$. This establishes the use of three-body B decays as a viable alternative for the extraction of weak phases. In this preliminary analysis we have neglected several sources of uncertainties such as the effect of flavor-SU(3) breaking due to meson masses, and error correlations between input experimental parameters. A better understanding of these will improve the viability of this method.

hep-ph↗

arXiv2012

Nonleptonic Charm Decays and CP Violation

In this talk we briefly present a flavor-SU(3) technique to study branching ratios and direct CP asymmetries $D$-meson decays. The first part of the talk is meant to set up a foundation, based on previous work, to deal with flavor-SU(3) amplitudes and relative strong phases. In addition, we present a model for dealing with SU(3)-breaking in branching ratio measurements of SCS $D^0$ decays. In the second part of the talk we make use of a proposal for an enhanced CP-violating penguin in the SM, to explain the recent LHCb and CDF observations of CP violation in SCS $D^0$ decays. Furthermore, we use our model to predict CP violation in $π^0π^0$ and $K^+\bar{K}^0$ final states. Large experimental bounds on individual CP asymmetries give rise to a large allowed range of $δ$, the strong phase of the CP-violating penguin. We also briefly discuss future prospects.

hep-ph↗

arXiv2012

Direct CP Violation in D Decays in view of LHCb and CDF Results

The LHCb and CDF Collaborations have recently reported evidence for a CP asymmetry around -0.7% in $ΔA_{CP}$, the difference between $A_{CP}(D^0 \to K^+ K^-)$ and $A_{CP}(D^0 \to π^+π^-)$. In the Standard Model this effect may be accounted for by enhanced $1/m_c$ corrections in a CP-violating penguin amplitude governed by a Cabibbo-Kobayashi-Maskawa (CKM) factor $V^*_{cb}V_{ub}$. A consistent scheme based on broken flavor SU(3) is presented relating Cabibbo-favored (CF) and singly-Cabibbo-suppressed (SCS) $D$ meson decay rates into two pseudoscalars. Two important ingredients supporting the above interpretation for $ΔA_{CP}$ are a large exchange amplitude in CF decays which is formally $1/m_c$-suppressed, and a pure $ΔU=0$ U-spin breaking CP-conserving penguin amplitude involving $V^*_{cs}V_{us}$ and $V^*_{cd}V_{ud}$ which accounts for the difference between the $D^0\to K^+K^-$ and $D^0\to π^+π^-$ decay rates. The magnitudes of the CP conserving and CP violating penguin amplitudes, where the former involves U-spin breaking at a level of 10%, are shown to be related to each other by the magnitudes of corresponding CKM factors. This simple scheme leads to preferable sign predictions for CP asymmetries in charmed meson decays into two pseudoscalars and to correlations between asymmetries in two pairs of these processes.

hep-ph↗

arXiv2012

Flavor-SU(3) tests from $D^0 \to K^0 K^- π^+$ and $D^0 \to \bar K^0 K^+ π^-$ Dalitz plots

The processes $D^0\to K^0 K^-π^+$ and $D^0\to\ok K^+π^-$ involve intermediate vector resonances whose amplitudes and phases are related to each other via flavor-SU(3) symmetry. Dalitz plots for these two processes can shed light on the usefulness of this symmetry in studying charm decays. Until this year the only available data on this process came from a conference report in 2002 by the BaBar Collaboration, but now an independent data sample of higher statistics has become available from the CLEO Collaboration. The goal is to predict Dalitz plot amplitudes and phases assuming flavor-SU(3) symmetry and compare them with experiment. An SU(3) fit can account for the relative magnitudes of the amplitudes for the decays $D^0 \to K^{*-}K^+$ and $D^0 \to K^{*+}K^-$, but neither the current BaBar sample (based on an integrated luminosity of 22 fb$^{-1}$) nor the CLEO analysis has significant evidence for the decays $D^0\to K^{*0}\ok$ and $D^0 \to \oks K^0$. At this level one is unable to compare magnitudes and phases with theoretical predictions. The purpose of this Letter is to advocate an analysis using the full BaBar sample (more than 20 times the 2002 value). It should definitively determine whether predicted magnitudes and phases agree with experiment. A similar analysis should be possible with an even larger sample of events collected by the Belle Collaboration at KEK-B.

hep-ph↗

arXiv2012

Implications of sterile neutrinos for medium/long-baseline neutrino experiments and the determination of $θ_{13}$

We revisit some of the recent neutrino observations and anomalies in the context of sterile neutrinos. Based on a general parametrization motivated in the presence of sterile neutrinos, the consistency of the MINOS disappearance data with additional sterile neutrinos is discussed. We also explore the implications of sterile neutrinos for the measurement of $|U_{\mu3}|$ in this case. Regarding the determination of $|U_{e3}|$, we observe that the existence of sterile neutrinos may induce a significant modification of the $θ_{13}$ angle in neutrino appearance experiments like T2K and MINOS, over and above the ambiguities and degeneracies that are already present in 3-neutrino parameter extractions. The modification is less significant in reactor neutrino experiments like Double-CHOOZ, Daya Bay and RENO and therefore the extracted $|U_{e3}|$ value when sterile neutrinos are present is close to the one that would be obtained in the 3-neutrino case. We also conclude that the results from T2K imply a 90% C.L. lower-bound on $|U_{e3}|$, in the "$\,3+2$" neutrino case, which is still within the sensitivity of future reactor neutrino experiments like Daya Bay, and consistent with the one-$σ$ range of $\sin^22θ_{13}$ recently reported by the Double-CHOOZ experiment. Finally, we argue that for the recently determined best-fit parameters, the results in the "$\,3+1$" scenario would be very close to the medium/long baseline results obtained in the "$\,3+2$" case analyzed in this work.

hep-ph↗

arXiv2012

Measuring beta_s with Bs -> K0() K0bar() -- a Reappraisal

The Bs-Bsbar mixing phase, beta_s, can be extracted from Bs -> K0(*) K0bar(*), but there is a theoretical error if the second amplitude, Vub* Vus P'uc, is non-negligible. Ciuchini, Pierini and Silvestrini (CPS) have suggested measuring Puc in Bd -> K0(*) K0bar(*), and relating it to P'uc using SU(3). For their choice of the direct and indirect CP asymmetries in Bd -> K0(*) K0bar(*), they find that the error on beta_s is very small, even allowing for 100% SU(3) breaking. In this paper, we re-examine the CPS method, allowing for a large range of the Bd -> K0(*) K0bar(*) observables. We find that the theoretical error in the extraction of beta_s can be quite large, up to 18 degrees. This problem can be ameliorated if the value of SU(3) breaking were known, and we discuss different ways, both experimental and theoretical, of determining this quantity.

hep-ph↗

arXiv2012

CP asymmetries in singly-Cabibbo-suppressed $D$ decays to two pseudoscalar mesons

The LHCb Collaboration has recently reported evidence for a CP asymmetry approaching the percent level in the difference between $D^0 \to π^+ π^-$ and $D^0 \to K^+ K^-$. We analyze this effect as if it is due to a penguin amplitude with the weak phase of the standard model $c \to b \to u$ loop diagram, but with a CP-conserving enhancement as if due to the strong interactions. In such a case the magnitude and strong phase of this amplitude $P_b$ are correlated in order to fit the observed CP asymmetry, and one may predict CP asymmetries for a number of other singly-Cabibbo-suppressed decays of charmed mesons to a pair of pseudoscalar mesons. Non-zero CP asymmetries are expected for $D^+ \to K^+ \ok$ (the most promising channel for which a non-zero CP asymmetry has not yet been reported), as well as $D^0 \to π^0 π^0$, $D_s^+ \to π^+ \ko$, and $D_s \to π^0 K^+$. No CP asymmetry is predicted for $D^+ \to π^+ π^0$ or $D^0 \to \ko \ok$ in this framework.

hep-ph↗