arXiv subjects

Alakabha Datta

Publications and source records attributed to Alakabha Datta.

At least 91 records · Page 5Linked to original sources

arXiv2008

Study of Polarization in B -> VT Decays

In this paper, we examine B -> VT decays (V is a vector and T is a tensor meson), whose final-state particles can have transverse or longitudinal polarization. Measurements have been made of B -> ϕK_2^*, and it is found that fT/fL is small, where fT (fL) is the fraction of transverse (longitudinal) decays. We find that the standard model (SM) naively predicts that fT/fL << 1. The two extensions of the naive SM which have been proposed to explain the large fT/fL in B -> ϕK^* -- penguin annihilation and rescattering -- make no firm predictions for the polarization in B -> ϕK_2^*. The two new-physics scenarios, which explain the data in B -> πK and the ϕ(ρ) K^* polarization measurements, can reproduce the fT/fL data in B -> ϕK_2^* only if the B -> T form factors obey a certain hierarchy. Finally, we present the general angular analysis which can be used to get helicity information using two- and three-body decays.

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arXiv2007

Testing Explanations of the $B\toϕK^*$ Polarization Puzzle

$B\toϕK^*$ ($\btos$) is three separate decays, one for each polarization of the final-state vector mesons (one longitudinal, two transverse). It is observed that the fraction of transverse decays, $\fT$, and the fraction of longitudinal decays, $\fL$, are roughly equal: $\fTfL \simeq 1$, in opposition to the naive expectation that $\fT \ll \fL$. If one requires a single explanation of all polarization puzzles, two possibilities remain within the standard model: penguin annihilation and rescattering. In this paper we examine the predictions of these two explanations for $\fTfL$ in $\btod$ decays. In $B \to ρρ$ decays, only $\bd \to ρ^0ρ^0$ can possibly exhibit a large $\fTfL$. In B decays related by U-spin, we find two promising possibilities: (i) $B^+ \to K^{*0} ρ^+$ ($\btos$) and $B^+ \to \Kbar^{*0} K^{*+}$ ($\btod$) and (ii) $\bs \to K^{*0} \Kbar^{*0}$ ($\btos$) and $\bd \to \Kbar^{*0} K^{*0}$ ($\btod$). The measurement of $\fTfL$ in these pairs of decays will allow us to test penguin annihilation and rescattering. Finally, it is possible to distinguish penguin annihilation from rescattering by performing a time-dependent angular analysis of $\bd \to \Kbar^{*0} K^{*0}$.

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arXiv2007

Extracting alpha from B0(d) --> K0 anti-K0 Decays

We propose a new method for obtaining the CP phase alpha, based on measurements of B0(d) --> K0 anti-K0, along with theoretical input. Due to the similarities of QCD factorization (QCDf) and perturbative QCD (pQCD), this input is basically the same for each of these models. Although the theoretical error is large at present, many of the contributing quantities will be better known in the future, leading to a smaller error. One outstanding question is the extent to which the precision on quark masses, especially m_c/m_b, can be improved. If one assumes that new physics is not present, the method can be used to predict the values of CP asymmetries in B0(d) --> K0 anti-K0: 0.02 <= A_{dir}^2 + A_{mix}^2 <= 0.125. A result outside this range would signal the existence of long-distance effects beyond those included in models of nonleptonic decays based on factorization (such as QCDf and pQCD), or the presence of new physics.

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arXiv2007

$β(ϕ_1)$ from $ B $ Decays to Charm

The measurement of $\sin {2β}$ from $B_d \to J/ψK_s$ does not resolve the discrete ambiguities in the angle $β$. A measurement of $\cos {2β}$ is therefore desirable.This talk is about measuring the CKM angle $β(ϕ_1)$ from various B decays to charm final states which also allow us a measurement of $\cos {2β}$.

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arXiv2007

CP Violation in Hadronic tau Decays

We re-examine CP violation in the Delta S = 0 decays tau -> N pi nu_tau (N=2,3,4). We assume that the new physics (NP) is a charged Higgs. We show that there is no NP contribution to tau -> pi pi nu_tau, which means that no CP violation is expected in this decay. On the other hand, NP can contribute to tau -> N pi nu_tau (N=3,4). These are dominated by the intermediate resonant decays tau -> omega pi nu_tau, tau -> rho pi nu_tau and tau -> a_1 pi nu_tau. We show that the only sizeable CP-violating effects which are possible are in tau -> a_1 pi nu_tau -> 4 pi nu_tau (polarization-dependent rate asymmetry) and tau -> omega pi nu_tau (triple-product asymmetry).

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arXiv2007

Is there New Physics in B Decays ?

Rare decays of the $B$ meson are sensitive to new physics effects. Several experimental results on these decays have been difficult to understand within the standard model (SM) though more precise measurements and a better understanding of SM theory predictions are needed before any firm conclusions can be drawn. In this talk we try to understand the present data assuming the presence of new physics. We find that the data points to new physics of an extended Higgs sector and we present a two higgs doublet model with a 2-3 flavor symmetry in the down type quark sector that can explain the deviations from standard model reported in several rare B decays.

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arXiv2006

$B_s$ Mixing and New Physics in hadronic $b \to s \bar{q} q$ transitions

We study the implication of the recent $Δm_s$ measurement on $ b \to s \bar{q} q$ transitions. We show that it is possible, in the presence of a flavour symmetry, that the phase in $B_s$ mixing may be unobservable even with new CP odd phases in $b \to s$ transitions. These phases may then produce new CP odd effects in certain $b \to s \bar{q} q $ transitions like $ B \to K π$ but not in others like $ B_d \to ϕK_s$. Working in a two higgs doublet model of new physics we discuss the allowed NP contribution to $B \to K π$ and $ B_d \to ϕK_s$ decays with the new $ Delta m_s$ measurement.

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arXiv2006

Hadronic B Decays: A General Approach

In this paper, we propose a general approach for describing hadronic B decays. Using this method, all amplitudes for such decays can be expressed in terms of contractions, though the matrix elements are not evaluated. Many years ago, Buras and Silvestrini proposed a similar approach. However, our technique goes beyond theirs in several ways. First, we include recent theoretical and experimental developments which indicate which contractions are negligible, and which are expected to be smaller than others. Second, we show that all B-decay diagrams can be simply expressed in terms of contractions. This constitutes a formal proof that the diagrammatic method is rigourous. Third, we show that one reproduces the relations between tree and electroweak-penguin diagrams described by Neubert and Rosner, and by Gronau, Pirjol and Yan. Fourth, although the previous results hold to all orders in alpha_s, we show that it is also possible to work order-by-order in this approach. In this way it is possible to make a connection with the matrix-element evaluation methods of QCD factorization (QCDfac) and perturbative QCD (pQCD). Finally, using the contractions approach, we re-evaluate the question of whether there is a ``B -> pi K puzzle.'' At O(alpha_s^0), we find that the diagram ratio |C'/T| is about 0.17, a factor of 10 too small to explain all the B -> pi K data. Both QCDfac and pQCD find that, at O(α_s^1), the value of |C'/T'| may be raised to only about 2-3 times its lowest-order value. We therefore conclude that, assuming the effect is not a statistical fluctuation, it is likely that the value of |C'/T'| is similar to its O(α_s^0) result, and that there really is a B -> pi K puzzle.

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arXiv2006

Vacuum Stability in Split Susy and Little Higgs Models

We study the stability of the effective higgs potential in the split supersymmetry and Little Higgs models. In particular, we study the effects of higher dimensional operators in the effective potential on the higgs mass predictions. We find that the size and sign of the higher dimensional operators can significantly change the higgs mass required to maintain vacuum stability in Split Susy models. In the Little Higgs models the effects of higher dimensional operators can be large because of a relatively lower cut-off scale. Working with a specific model we find that a contribution from the higher dimensional operator with coefficient of O(1) can destabilize the vacuum.

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arXiv2005

The 2-3 symmetry: Flavour Changing $b$, $τ$ Decays and Neutrino Mixing

The observed pattern of neutrino mixing may be the result of a 2-3($ μ- τ$) symmetry in the leptonic sector. We consider a two Higgs doublet model with a 2-3 symmetry in the down type quark and the charged lepton sector. The breaking of the 2-3 symmetry by the strange quark mass and the muon mass leads to FCNC in the quark sector and the charged lepton sector that are suppressed by ${m_s \over m_b}$ and ${m_μ \over m_τ}$ in addition to the mass of the heavy Higgs boson of the second Higgs doublet. A Higgs boson mass of $ m_H \sim 600 - 900$ GeV can explain the deviation from standard model reported in several rare B decays. Predictions for other B decays are made and a new CP phase is predicted in $B_{s}-{\bar{B}_{s}}$ mixing. The lepton flavour violating decays $ τ\to μ\bar{l}(\bar{q}) l(q)$ are below the experimental limits. The breaking of 2-3 symmetry in the lepton sector can lead to deviations of the atmospheric neutrino mixing angle from the maximal value by $ \sim 2$ degrees.

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arXiv2005

Polarization States in B -> rho K* and New Physics

The standard-model explanations of the anomalously-large transverse polarization fraction fT in B -> phi K* can be tested by measuring the polarizations of the two decays B+ -> rho+ K*0 and B+ -> rho0 K*+. For the scenario in which the transverse polarizations of both B -> rho K* decays are predicted to be large, we derive a simple relation between the fT's of these decays. If this relation is not confirmed experimentally, this would yield an unambiguous signal for new physics. The new-physics operators which can account for the discrepancy in B -> pi K decays will also contribute to the polarization states of B -> rho K*. We compute these contributions and show that there are only two operators which can simultaneously account for the present B -> pi K and B -> rho K* data. If the new physics obeys an approximate U-spin symmetry, the B -> phi K* measurements can also be explained.

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arXiv2005

Methods for Measuring New-Physics Parameters in B Decays

Recently, it was argued that new-physics (NP) effects in B decays can be approximately parametrized in terms of a few quantities. As a result, CP violation in the $B$ system allows one not only to detect the presence of new physics (NP), but also to measure its parameters. This will allow a partial identification of the NP, before its production at high-energy colliders. In this paper, we examine three methods for measuring NP parameters. The first uses a technique involving both $\btos$ and $\btod$ penguin B decays. Depending on which pair of decays is used, the theoretical error is in the range 5--15%. The second involves a comparison of $B\to πK$ and $B\toππ$ decays. Although the theoretical error is large ($\gsim 25%$), the method can be performed now, with presently-available data. The third is via a time-dependent angular analysis of $\bvv$ decays. In this case, there is no theoretical error, but the technique is experimentally challenging, and the method applies only to those NP models whose weak phase is universal to all NP operators. A reliable identification of the NP will involve the measurement of the NP parameters in many different ways, and with as many B decay modes as possible, so that it will be important to use all of these methods.

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arXiv2004

The B -> pi K Puzzle and New Physics

The present B -> pi K data is studied in the context of the standard model (SM) and with new physics (NP). We confirm that the SM has difficulties explaining the B -> pi K measurements. By adopting an effective-lagrangian parametrization of NP effects, we are able to rule out several classes of NP. Our model-independent analysis shows that the B -> pi K data can be accommodated by NP in the electroweak penguin sector.

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arXiv2004

A Measurement of gamma from the Decays Bd(t) -> D()+ D()- and Bd -> Ds()+ D()-

Recently, it was proposed to use measurements of Bd(t) -> D(*)+ D(*)- and Bd -> Ds(*)+ D(*)- decays to measure the CP phase gamma. In this paper, we present the extraction of gamma using this method. We find that gamma is favored to lie in one of the ranges [19.4o - 80.6o] (+ 0o or 180o), [120o - 147o] (+ 0o or 180o), or [160o - 174o] (+ 0o or 180o) at 68% confidence level (the (+ 0o or 180o) represents an additional ambiguity for each range). These constraints come principally from the vector-vector final states; the vector-pseudoscalar decays improve the results only slightly. Although, with present data, the constraints disappear for larger confidence levels, this study does demonstrate the feasibility of the method. Strong constraints on gamma can be obtained with more data.

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arXiv2004

Getting SM and New Physics CP phases from $B$ Decays

A method to extract Standard Model(SM) CP phases involving B decays is presented. The method involves a pair of decays where one decay receives a significant $b \to d$ penguin contribution while the second has a significant $b \to s$ penguin contribution, but is dominated by a single amplitude. SM CP phase information is obtained using the fact that the $b \to s$ transition amplitude is related by SU(3) to a piece of the amplitude with the $b \to d$ transition. If there is significant new physics only in $b \to s$ transitions and not in $b \to d$ transitions then this method can be used to measure new physics(NP) phases.

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arXiv2004

Extracting beta and the new D_{sJ} resonances

The three body decays $B \to D^{(*)} \bar{D}^{(*)} K_s$ may be used to measure both $\sin{2β}$ and $\cos{2β}$. Crucial to the $\cos{2β}$ measurement is the resonant contribution to the three body decay from p-wave excited $D_s$ states. If these p-wave states are the newly discovered $D_s(2317)$ and $D_s(2460)$ then they are below the $D^{(*)} K$ threshold and hence do not contribute to $B \to D^{(*)} \bar{D}^{(*)} K_s$. The three body decays can then be used to measure $\sin{2β}$ without resonant dilution and to look for new physics in $ b \to c \bar{c} s $ transition.

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arXiv2004

Measuring New-Physics Parameters in B Penguin Decays

We examine new-physics (NP) effects in B decays with large b -> s penguin amplitudes. Decays involving b -> d penguins are assumed to be unaffected. We consider a model-independent parametrization of such NP. We argue that NP strong phases are negligible relative to those of the standard model. This allows us to describe the NP effects in terms of a small number of effective amplitudes A_NP^q (q=u,d,s,c) and corresponding weak phases Phi_q. We then consider pairs of neutral B decays which are related by flavour SU(3) in the standard model. One receives a large b -> s penguin component and has a NP contribution; the other has a b -> d penguin amplitude and is unaffected by NP. The time-dependent measurement of these two decays allows the {\it measurement} of the NP parameters A_NP^q and Phi_q. The knowledge of these parameters allows us to rule out many NP models and thus partially identify the new physics.

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arXiv2004

Obtaining CKM Phase Information from B Penguin Decays

We discuss a method for extracting CP phases from pairs of B decays which are related by flavor SU(3). One decay (B0 -> M1 M2) receives a significant bbar -> dbar penguin contribution. The second (B' -> M1' M2') has a significant bbar -> sbar penguin contribution, but is dominated by a single amplitude. CP phase information is obtained using the fact that the B' -> M1' M2' amplitude is related by SU(3) to a piece of the B0 -> M1 M2 amplitude. The leading-order SU(3)-breaking effect (~25%) responsible for the main theoretical error can be removed. For some decay pairs, it can be written in terms of known decay constants. In other cases, it involves a ratio of form factors. However, this form-factor ratio can either be measured experimentally, or eliminated by considering a double ratio of amplitudes. In all cases, one is left only with a second-order effect, ~5%. We find twelve pairs of B decays to which this method can be applied. Depending on the decay pair, we estimate the total theoretical error in relating the B' -> M1' M2' and B0 -> M1 M2 amplitudes to be between 5% and 15%. The most promising decay pairs are Bd -> pi+ pi- and Bu+ -> K0 pi+, and Bd -> D+ D- and Bd -> Ds+ D- or Bu+ -> Ds+ D0bar.

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