arXiv subjects

Amarjit Soni

Publications and source records attributed to Amarjit Soni.

197 records · Page 11Linked to original sources

arXiv1996

Enhanced CP Violation with $B\to K D^0 (\overline D^0)$ Modes and Extraction of the CKM Angle gamma

The Gronau-London-Wyler (GLW) method extracts the CKM angle $γ$ by measuring $B^\pm$ decay rates involving $D^0/\overline D^0$ mesons. Since that method necessitates the interference between two amplitudes that are significantly different in magnitude, the resulting asymmetries tend to be small. CP violation can be greatly enhanced for decays to final states that are common to both D^0 and $\overline D^0$ and that are not CP eigenstates. In particular, large asymmetries are possible for final states f such that $D^0\to f$ is doubly Cabibbo suppressed while $\overline D^0\to f$ is Cabibbo allowed. The measurement of interference effects in two such modes allows the extraction of $γ$ without prior knowledge of $Br(B^-\to K^- \overline D^0)$, which may be difficult to determine due to backgrounds.

hep-ph↗

arXiv1996

Signals from Flavor Changing Scalar Currents at the Future Colliders

We present a general phenomenological analysis of a class of Two Higgs Doublet Models with Flavor Changing Neutral Currents arising at the tree level. The existing constraints mainly affect the couplings of the first two generations of quarks, leaving the possibility for non negligible Flavor Changing couplings of the top quark open. The next generation of lepton and hadron colliders will offer the right environment to study the physics of the top quark and to unravel the presence of new physics beyond the Standar Model. In this context we discuss some interesting signals from Flavor Changing Scalar Neutral Currents.

hep-ph↗

arXiv1996

The B -> X_s gamma gamma rare decay

The rare decay B -> X_s gamma gamma is studied in the Standard Model (SM) and in two different versions (Model I and Model II) of the Two Higgs Doublet Model (2HDM). In the SM the branching ratio into ``hard photons'' is about 10^(-7) and can be appreciably different in the 2HDM. We also introduce a forward-backward asymmetry which gives an additional handle to discriminate different models.

hep-ph↗

arXiv1996

Phenomenology of Two Higgs Doublet Models with Flavor Changing Neutral Currents

A comprehensive phenomenological analysis of a two Higgs doublet model, with flavor changing scalar currents at the tree level, called model III, is presented. Constraints from existing experimental information especially on (Delta F)=2 processes are systematically incorporated. Constraints emerging from rare B-decays, Z-->b\bar b, and the ρparameter are also examined. Experimental implications for e^+e^- (μ^+μ^-)-->t\bar c+\bar t c, t-->cγ(Z,g), D^0-\bar D^0, and B^0_s-\bar B^0_s oscillations, and for e^+e^-(Z)-->b\bar s+s\bar b are investigated and experimental effort towards these is stressed. We also emphasize the importance of clarifying the experimental issues pertaining to Z-->b\bar b.

hep-ph↗

arXiv1996

CP Conserving and CP Violating Asymmetries in $e^+e^-\to t\bar tν_e\barν_e$} at the NLC: Application to Determining the Higgs Width

The polarization asymmetries of $t$, $\bar t$ quarks can be used in the reaction $e^+e^-\to t\bar tν_e\barν_e$ to measure the Higgs width, in the Standard Model or in its extensions, and to search for non-standard CP violating phases. As an application of the CPT theorem the Higgs width is monitored through a CP-even, $T_N$-odd, polarization asymmetry, $B_y$. CP violation manifests through interference at tree graph level with the resonant Higgs amplitude. Consequently, the asymmetries are all quite sizable and can be in the range of 10--50\% for a wide choice of the Higgs mass.

hep-ph↗

arXiv1996

CP Nonconservation in $p\bar p\to t\bar b X$ at the Tevatron

The reaction $p\bar p\to t\bar bX$ is found to be rather rich in exhibiting several different types of CP asymmetries. The spin of the top quark plays an important role. Asymmetries are related to form factors arising from radiative corrections of the $tbW$ production vertex due to non-standard physics. As illustrations, effects are studied in two Higgs Doublet Models and in Supersymmetric Models; asymmetries up to a few percent may be possible.

hep-ph↗

arXiv1996

$R_b$ and $R_c$ in the Two Higgs Doublet Model with Flavor Changing Neutral Currents

A study of $R_b$ and $R_c$ is presented in the context of a Two Higgs Doublet Model (2HDM) with flavor changing scalar currents (FCSC). Implications of the model for the $ρ$-parameter and for $b\to sγ$ are also considered. The experimental data on $R_b$ places stringent constraints on the model parameters. The configuration of the model needed to account for $R_b$ is found to be irreconcilable with constraints from $b\to sγ$ and $ρ$. In particular, if $R^{\rm exp}_b>R^{\sss{\rm SM}}_b$ persists then this version of 2HDM will be ruled out or require significant modifications. Noting that aspects of the experimental analysis for $R_b$ and $R_c$ may be of some concern, we also disregard $R^{\rm exp}_b$ and $R^{\rm exp}_c$ and give predictions for these using constraints from $b\to sγ$ and $ρ$ parameter only. We emphasize the theoretical and experimental advantages of the observable $R_{b+c}\equiv Γ(Z\to b\bar b\mbox{ or } c\bar c)/Γ(Z\to\mbox{hadrons})$. We also stress the role of $R_\ell\equiv Γ(Z\to\mbox{hadrons})/Γ(Z\to \ell^+\ell^-)$ in testing the Standard Model (SM) despite its dependence on QCD corrections. Noting that in models with FCNC the amplitude for $Z\to c\bar c$ receives a contribution which grows with $m^2_t$, the importance and uniqueness of precision $Z\to c\bar c$ measurements for constraining flavor changing $t\bar c$ currents is underscored.

hep-ph↗

arXiv1995

Flavor Changing Neutral Scalar Currents at $μ^+μ^-$ Colliders

The prospect of observing the flavor changing decay $\fH\to t\bar c$ of a neutral Higgs boson produced via $s$-channel and its subsequent decay into $t\bar c$ is considered at a $μ^+μ^-$ collider. Numerical estimates are given in the context of a two Higgs doublet model with flavor changing couplings. It is found that for many values of the model parameters such {\it tree-level} flavor changing decays will be produced at an observable level. In addition studies of the helicity of the top will allow the determination of the relative strengths of the flavor changing Higgs couplings and these may be measured with about $10^3$ events.

hep-ph↗

arXiv1995

Probing flavor changing top-charm-scalar interactions in $e^+e^-$ collisions

Due to the very large mass of the top-quark, probing the flavor changing top-charm-scalar vertex is clearly very important. Fortunately the largeness of $m_t$ endows a unique signature to the resulting reaction i.e., $e^+e^-\to t\bar c (\bar t c)$ that should be helpful in identification of such events. A two Higgs doublet model, without natural flavor conservation, is used to give an illustrative estimate for the rate for these reactions.

hep-ph↗

arXiv1995

Neutral Higgs CP Violation at $μ^+μ^-$ colliders

CP violating asymmetries in both the production and the decays of $s$-channel neutral Higgs bosons at $μ^+μ^-$ colliders can be large. If the CP violation occurs in the muon-Higgs coupling, one observes a production asymmetry with transversely polarized $μ^+μ^-$ beams. Likewise if the CP violation occurs in the top-Higgs or $τ$-Higgs coupling, one observes an azimuthal decay asymmetry in $μ^+μ-\to t\bar t$ (or $τ^+τ^-$). CP studies at such colliders allow a uniquely clean way of deducing the underlying CP phases; in turn these parameters would significantly improve our understanding of baryogenesis.

hep-ph↗

arXiv1995

CP Nonconservation in $e^+e^-\to t\bar tg$

CP violation effects in $e^+ e^- \to t\bar tg$ are examined. CP-odd, $T_n$-odd and $T_n$-even observables can both be used to extract information on the real and imaginary parts of Feynman amplitudes. Two Higgs doublet model with CP violating phase from neutral Higgs exchange is used to estimate possible effects.

hep-ph↗

arXiv1994

Enhancement of CP Violation in B^+- to K_i^+- D^0 By Resonant Effects

Resonance width effects in charged $B$ decays to neutral $D$ mesons and excited kaon states $K_i$ around 1400 MeV are shown to lead to large calculable final state phases. $CP$ asymmetries are defined for any charged $B$ decay to three pseudoscalar mesons involving intermediate overlapping resonance states. Asymmetries up to about 10$\%$ are found in $B^+\to K^+_i D^0\to (Kπ)^+ D^0$. Decay distributions can be used to determine the weak phase $γ$ of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. No separation of the contributions from individual resonances is required.

hep-ph↗

arXiv1993

Isgur-Wise Function on the Lattice

We review our method and numerical results for calculation of the Isgur-Wise function on the lattice. We present a discussion of the systematic errors. Using recent experimental results, we find $V_{cb} = 0.044\pm 0.005\pm .007$. Contribution to Lattice '93 proceedings. Needs espcrc2.sty file (included after \end{document}). Search Figure1.ps for postscript files.

hep-lat↗

arXiv1993

A Lattice Computation of the Decay Constants of $B$ and $D$ Mesons

A lattice calculation of the pseudoscalar decay constant of heavy-light mesons is reported. Results are obtained (in the quenched approximation) from lattices at $β=6.3$ through a procedure that interpolates between the static approximation of Eichten and the conventional ("heavy" Wilson fermion) method. The previously observed discrepancy between these two approaches has been resolved: we find the scaling quantity $f\sqrt{M}$ to be significantly smaller than previous calculations had indicated ({\it e.g.} at $β=6.0$); in addition, we discuss a modification which is required in normalizing the conventional amplitude to correct for large-$am$ lattice errors. This change guarantees that $f\sqrt{M}$ will smoothly approach its value in the static limit. From the numerical interpolation of the static and intermediate-mass results, we find, in units of MeV, $f_B=187(10)\pm34\pm15$, $f_{B_s}=207(9)\pm34\pm22$, $f_D=208(9)\pm35\pm12$ and $f_{D_s}=230(7)\pm30\pm18$, where the first error is statistical and the second two are estimates of systematics due to 1) fitting and large-$am$ effects and 2) scaling. In addition, using lattices at $β=6.3$, $β=6.0$ and $β=5.7$ and extrapolating to the limit of zero lattice spacing, we have computed $f_K/f_π= 1.08\pm.03\pm.08$ in the quenched approximation.

hep-lat↗

arXiv1992

Calculating the Isgur-Wise Function on the Lattice

We calculate the Isgur-Wise function by measuring the heavy-heavy meson transition matrix element on the lattice. The standard Wilson action is used for both the heavy and light quarks. Our first numerical results are presented.

hep-lat↗

arXiv1992

Quenched Lattice Results for $f_B$ and $f_D$

We have computed the decay constants for the $B$ and $D$ mesons, using quenched lattices at $β=6.3$, by interpolating between the static approximation of Eichten and the conventional (``heavy'' Wilson fermion) method. A more careful treatment of the static result using better sources with longer time-displacements and a modification to the Wilson quark normalization to correct approximately for lattice effects in the large-$am$ regime have led to the elimination of the large discrepancy between the two methods which had been previously observed. We report final results, with estimates of various systematic errors.

hep-lat↗

arXiv1992

Introduction to Lattice Gaugefixing and Effective Quark and Gluon Masses

This talk was presented to a non-lattice audience at the June, 1992 Paris Workshop on QCD Vacuum Structure. We report on the status of quark and gluon propagators in quenched, gaugefixed lattice QCD. In Landau gauge we find that the effective quark mass in the chiral limit is $M_q \sim 350(40)MeV$. Quark and gluon propagators, the slope of the quark dispersion relation, and effective masses all appear to depend on gauge. A link-chain picture of lattice gaugefixing in the color $N\to\infty$ and strong coupling limit, where the system becomes almost solvable, supports the gauge variance of these numerical results. Subscribers will be given one Postscript file, the Figure included. Latex and Axis versions available from KY at kyee@rouge.phys.lsu.edu on request.

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