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Alakabha Datta

Publications and source records attributed to Alakabha Datta.

125 records · Page 7Linked to original sources
arXiv2001

Measuring sin 2βin Bs(t) -> phi K_s

We show that, unlike other pure b -> d penguin processes, the decay Bs(t) -> phi K_s is dominated by a single amplitude, that of the internal t-quark. The contributions of the u- and c-quark operators each vanish due to a cancellation between the (V-A) \otimes (V-A) and (V-A) \otimes (V+A) matrix elements. Thus, the indirect CP asymmetry in this decay probes sin 2β. Although this cancellation is complete only for certain values of the s- and b-quark masses, the theoretical uncertainty on sin 2βis still less than 10% over most (~80%) of the parameter space. By measuring the direct CP asymmetry, one can get a better idea of the probable error on sin 2β.

hep-ph↗
arXiv2001

Weak decays to final states with Radial Excitation Admixtures

We consider the weak decays of a B meson to final states that are mixtures of S-wave radially excited components. We consider non leptonic decays of the type $B \to ρ' π/B \to ρπ$, $B \to ω' π/B \to ωπ$ and $B \to ϕ' π/B \to ϕπ$ where $ρ'$, $ω'$ and $ϕ'$ are higher $ρ$, $ω$ and $ϕ$ resonances. We find such decays to have larger or similar branching ratios compared to decays where the final state $ρ$, $ω$ and $ϕ$ are in the ground state. We also study the effect of radial mixing in the vector and the pseudoscalar systems generated from hyperfine interaction and the annihilation term. We find the effects of radial mixing to be small and generally negligible for all practical purposes in the vector system. However, in the $η-η^{\prime}$ system the effects of radial mixing are appreciable and seriously affect decay branching ratios for $B \to η(η')K(K^*)$. In particular we find that nonstandard $η(η')$ mixing can resolve the puzzles in $B \to η(η')K$ decays.

hep-ph↗
arXiv2000

Vacuum Stability Higgs Mass Bound Revisited with Implications for Extra Dimension Theories

We take the standard model to be an effective theory including higher dimensional operators suppressed by scale $Λ$ and re-examine the higgs mass bounds from the requirements of vacuum stability. Our results show that the effects of the higher dimensional operators on the higgs mass limits are significant. As an implication of our results, we study the vacuum stability higgs mass bounds in theories with extra dimensions.

hep-ph↗
arXiv1999

Flavor Changing Decays of $Υ$ and $J/ψ$

We study flavor changing processes $Υ\to B/{\bar B} X_s$ and $J/ψ\to D/{\bar D} X_u$ in the B factories and the Tau-Charm factories. In the standard model, these processes are predicted to be unobservable, so they serve as a probe of the new physics. We first perform a model independent analysis, then examine the predictions of models; such as top color models and MSSM with R-parity violation ; for the branching ratios of $Υ\to B/{\bar B} X_s$ and $J/ψ\to D/{\bar D} X_u$ . We find that these branching ratios could be as large as $10^{-6}$ and $10^{-5}$ in the presence of new physics.

hep-ph↗
arXiv1999

Flavor Changing processes in Quarkonium Decays

We study flavor changing processes $Υ\to B/{\bar B} X_s$ and $J/ψ\to D/{\bar D} X_u$ in the B factories and the Tau-Charm factories. In the standard model, these processes are predicted to be unobservable, so they serve as a probe of the new physics. We first perform a model independent analysis, then examine the predictions of models; such as TopColor models, MSSM with R-parity violation and the two Higgs doublet model; for the branching ratios of $Υ\to B/{\bar B} X_s$ and $J/ψ\to D/{\bar D} X_u$ . We find that these branching ratios could be as large as $10^{-6}$ and $10^{-5}$ in the presence of new physics.

hep-ph↗
arXiv1999

Implications of Isospin Conservation in $Λ_b$ Decays and Lifetime

We consider isospin predictions for the semi-leptonic and non-leptonic decays of the $Λ_b$ baryon. Isospin conservation of the strong interactions constrains the possible final states in $Λ_b$ decays. Since the baryon hyperfine splittings depend upon light quark dynamics and do not decrease with increasing heavy quark mass, this leads in general to to phase space enhancements in $Λ_b$ decays relative to $B$ meson decays for the same underlying quark transitions. Consequently the $Λ_b$ lifetime is smaller than the $B$ lifetime. Phase space enhancements in $Λ_b$ decays relative to $B$ decays can be understood in terms of hyperfine interactions in the heavy quark system.

hep-ph↗
arXiv1998

Large CP Violation in $B\to K^{(*)} X$ Decays

We consider the possibility of observing CP violation in quasi-inclusive decays of the type $B^-\to K^- X$, $B^-\to K^{*-} X$, $\bar B^0\to K^- X$ and $\bar B^0\to K^{*-} X$, where $X$ does not contain strange quarks. We present estimates of rates and asymmetries for these decays in the Standard Model and comment on the experimental feasibility of observing CP violation in these decays at future $B$ factories. We find the rate asymmetries can be quite sizeable.

hep-ph↗
arXiv1997

Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar B} \to D^* l {\barν} $ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l {\barν} $ decays. The form factors are then used to obtain non-leptonic decay partial widths for $ B\to D π(K) $ and $B \to D D (D_s) $ in the factorization approximation.

hep-ph↗
arXiv1997

Pion-Nucleon Phase Shifts in Heavy Baryon Chiral Perturbation Theory

We calculate the phase shifts in the pion-nucleon scattering using the heavy baryon formalism. We consider phase shifts for the pion energy range of 140 to $200 $ MeV. We employ two different methods for calculating the phase shifts - the first using the full third order calculation of the pion-nucleon scattering amplitude and the second by including the resonances $Δ$ and $N^*$ as explicit degrees of freedom in the Lagrangian. We compare the results of the two methods with phase shifts extracted from fits to the pion-nucleon scattering data. We find good to fair agreement between the calculations and the phase shifts from scattering data.

hep-ph↗
arXiv1996

B --> D(D^*) Form Factors in a Bethe-Salpeter model

We calculate the form factors for the semileptonic decays of the $B$ meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. We show that our model is consistent with the constraints of Heavy Quark Effective Theory (HQET) and we extract the matrix elements that represent the $1/m_Q$ corrections to the form factors in HQET. With available data, we obtain $V_{cb} $=$ (31.9 \pm 1.4)\times10^{-3}$.

hep-ph↗
arXiv1995

Non-Leptonic two body decays of Charmed and Λ_b Baryons

We calculate the two body Cabibbo allowed non-leptonic decays of charmed baryons $Λ_c$ and $Ξ_c$ which involve transitions of a heavy quark to a light quark. We use data on the Cabbibo favoured non-leptonic decays $Λ_c \rightarrow Λπ^{+}$ and $Λ_c \rightarrow Σ^{+} π^{0 }$ to obtain information on the form factors in the $c \rightarrow s $ transition. We also calculate the decay $Λ_c \rightarrow p ϕ$. Using HQET the information on form factors from the $c \rightarrow s $ transition is used to model the form factors in $b \rightarrow s $ transition which are then used in the study of $Λ_b \rightarrow J/ ψΛ$ decay.

hep-ph↗
arXiv1995

Semi-Leptonic Decays of Λ_c and Λ_b Baryons involving Heavy to Light Transitions and the determination of V_{ub}

We calculate the semi-leptonic decays of $Λ_c$ and $Λ_b$ baryons which involve transitions of a heavy quark to a light quark. In a previous work we used data on the Cabibbo favoured non-leptonic decays of charmed baryons $Λ_c \rightarrow Λπ^{+}$ and $Λ_c \rightarrow Σ^{+} π^{0 }$ to obtain information on the form factors in the $c \rightarrow s $ transition. This form factor informations is used to study the semi-leptonic decay $Λ_c \rightarrow Λl ν$. Using SU(3) symmetry and HQET it is shown how a knowledge of form factors in $Λ_c \rightarrow Λl ν$ can be applied to $Λ_b \rightarrow p l ν$ decay and used to measure $|V_{ub}/V_{cs}|^{2} $.

hep-ph↗
arXiv1994

Form factors for Charmed Baryon Decays at order 1/m_c in the HQET limit

We study the vector and axial vector form factors in the heavy to light transitions in charmed baryon decays using HQET. We calculate the 1/m_c corrections to the form factors and show that these corrections can be significant. We also consider applications to semi-leptonic and hadronic decays of charmed baryons.

hep-ph↗
arXiv1994

S-wave phase shift in Lambda-pi scattering

We calculate the s-wave strong interaction $Λ$$π$ phase shift at the $Ξ$ mass taking into account contributions from the ${{\frac{1}{2}}}^{-}$ and ${{\frac{3}{2}}}^{-}$ $Σ$ resonances. We find the S-wave phase shift to be small, of the order of 0.3 degrees and bounded by 0.5 degrees.

hep-ph↗
arXiv1994

Corrections to mass scale predictions in SO(10) GUT with higher dimensional operators

We calculate the two loop contribution to the predictions of the mass scales in an SO(10) grand unified theory. We consider the modified unification scale boundary conditions due to the non-renormalizable higher dimensional terms arising from quantum gravity or spontaneous compactification of extra dimensions in Kaluza-Klein type theory. We find the range of these couplings which allows left-right symmetry to survive till very low energy (as low as $\sim$ TeV) and still be compatible with the latest values of $\sin^2 θ_W$ and $α_s$ derived from LEP. We consider both the situation when the left-right parity is broken and conserved.We consider both supersymmetric and non-supersymmertic versions of the SO(10) theory.Taking the D-conserved non-susy case as an example we calculate the effects of moderate threshold uncertainties at the heavy scale, due to the unknown higgs masses,on the gravity induced couplings.

hep-ph↗
arXiv1993

Higher Dimensional Operators and Low Energy Left-Right Symmetry

We consider higher dimensional operators due to quantum gravity or spontaneous compactification of extra dimensions in Kaluza-Klein type theory and their effect in the $SO(10)$ Lagrangian. These operators change the boundary conditions at the unification scale. As a result one can allow left-right symmetry to survive till very low energy (as low as $\sim$ TeV) for a wide range of values for the coupling of these higher dimensional operators and still make the theory compatible with the latest values of $\sin^2 θ_W$ and $α_s$ derived from LEP. We consider both non-supersymmetric and supersymmetric cases with standard higgses. Proton lifetime is very large in these theories.

hep-ph↗