arXiv subjects
Publications and source records attributed to Amarjit Soni.
We discuss the determination of the CKM phase gamma through the decay B- -> K- D0 and related processes. In particular, we consider the use of this methods when the D0 subsequently decays to an inclusive state. We emphasize that strong phase information obtained at a psi(3770) charm factory can provide additional information which will be helpful in determining gamma.
Status of lattice calculations of hadron matrix elements along with CP violation in B and in K systems is reviewed. Lattice has provided useful input which, in conjunction with experimenatl data, leads to the conclusion that CP-odd phase in the CKM matrix plays the dominant role in the observed asymmetry in $B \to ψK_s$. It is now quite likely that any beyond the SM, CP-odd, phase will cause only small deviations in B-physics. Search for the effects of the new phase(s) will consequently require very large data samples as well as very precise theoretical predictions. Clean determination of {\it all} the angles of the unitarity triangle therefore becomes essential. In this regard $B \to K D^0$ processes play a unique role. Regarding K-decays, remarkable progress made by theory with regard to maintenance of chiral symmetry on the lattice is briefly discussed. First application already provide quantitaive information on $B_K$ and the $ΔI=1/2$ rule. The enhancement in $Re A_0$ appears to arise solely from tree operators, esp. $Q_2$; penguin contribution to $Re A_0$ appears to be very small. However, improved calculations are necessary for $ε^'/epsilon$ as there the contributions of QCD penguins and electroweak penguins largely seem to cancel. There are good reasons, though, to believe that these cancellations will not survive improvements that are now underway. Importance of determining the unitarity triangle purely from K-decays is also emphasized.
There is no good reason to think that BSM-CP-odd phases(s) will necessarily cause large deviations in B-physics from predictions of the SM. Therefore, residual theory error in extraction of the unitarity triangle can undermine experimental efforts to search for BSM phase(s). We stress that final states containing D0 or D0-bar in decays of charged and neutral B's can yield all the angles of the unitarity triangle with negligble theory error (i.e. O(0.1%)).
Oscillation effects in B0 -> Ks D0 and related processes are considered to determine delta=beta-alpha+pi. We suggest that D0 decays to CP eigenstates used in concert with inclusive D0 decays provide a powerful method for determining delta cleanly i.e. without any complication from penguin processes. The CP asymmetry is expected to be <=40% for D0 decays to non-CP eigenstates and <=80% for decays to CP eigenstates. This method can lead to a fairly accurate determination of delta with O(10^8-10^9) B-mesons.
We show that lattice calculation of K --> pi pi and $epe$ amplitudes for (8,1) and (27,1) operators to O(p^4) in chiral perturbation theory is feasible when one uses K --> pi pi computations at the two unphysical kinematics allowed by the Maiani-Testa theorem, along with the usual (computable) two and three point functions, namely K --> 0, K --> pi (with momentum) and K - bar{K}. Explicit expressions for the finite logarithms emerging from our O(p^4) analysis to the above amplitudes are also given.
The flavor changing decay Z -> d_I \bar{d}_J is investigated with special emphasis on the b \bar{s} final state. Various models for flavor violation are considered: two Higgs doublet models (2HDM's), supersymmetry (SUSY) with flavor violation in the up and down-type squark mass matrices and SUSY with flavor violation mediated by R-parity-violating interaction. We find that, within the SUSY scenarios for flavor violation, the branching ratio for the decay Z -> b \bar{s} can reach 10^{-6} for large \tanβvalues, while the typical size for this branching ratio in the 2HDM's considered is about two orders of magnitudes smaller at best. Thus, flavor changing SUSY signatures in radiative Z decays such as Z -> b \bar{s} may be accessible to future ``Z factories'' such as a Giga-Z version of the TESLA design.
We explore CP violation in a Left-Right Model that reproduces the quark mass and CKM rotation angle hierarchies in a relatively natural way by fixing the bidoublet Higgs VEVs to be in the ratio m_b:m_t. Our model is quite general and allows for CP to be broken by both the Higgs VEVs and the Yukawa couplings. Despite this generality, CP violation may be parameterized in terms of two basic phases. A very interesting feature of the model is that the mixing angles in the right-handed sector are found to be equal to their left-handed counterparts to a very good approximation. Furthermore, the right-handed analogue of the usual CKM phase delta_L is found to satisfy the relation delta_R \approx delta_L. The parameter space of the model is explored by using an adaptive Monte Carlo algorithm and the allowed regions in parameter space are determined by enforcing experimental constraints from the K and B systems. This method of solution allows us to evaluate the left- and right-handed CKM matrices numerically for various combinations of the two fundamental CP-odd phases in the model. We find that all experimental constraints may be satisfied with right-handed W and Flavour Changing Neutral Higgs masses as low as about 2 TeV and 7 TeV, respectively.
We consider the possibility of studying the CP properties of various B(s) decays at an electro-positron machine tuned to the Upsilon(5s). Since decay modes of the B(s) with definite CP are relatively rare, we suggest that the use of more common modes which are not pure CP eigenstates may allow the determination of the CKM phase gamma. By studying the degree of correlation between different decay modes at a Upsilon(5s) it is possible to determine the degree of affinity of each decay mode to a CP eigenstate. Once this is known, the correlation between a decay mode with a greater affinity to a particular CP eigenstate with a mode such as D(s) + K- gives a determination of the phase gamma.
A method is proposed for the determination of the unitarity angle alpha through tree penguin interference. The modes needed would be of the form B0/B0-bar -> rho0 M and B0/B0-bar -> omega M where M is spin-0 uu-bar/dd-bar meson, for instance M=pi0, eta, eta',a0 or f0. An analogous method can also determine gamma using M=KS or K_L. The validity of the theoretical approximations used may be tested by over determining alpha with several modes. If two or more modes are used, the determination has a four-fold ambiguity but additional information from pure penguin decays or theoretical estimates may be used to reduce the ambiguity to alpha, alpha+pi. The method as applied to determining gamma is probably less promising.
A method for clean determination of the unitarity angles alpha and gamma is proposed that uses only direct CP violation and does not require any time dependent measurements. The method takes advantage of helicity amplitudes for B_u, B_d and B_s decay to two vector mesons and can be used, at any B-facility, in conjunction with a large number of modes. It also allows for experimental tests of theoretical approximations involved.
We have systematically investigated the semi-inclusive B decays B->MX, which are manifestations of the quark decay b->Mq, within the framework of QCD-improved factorization. These decays are theoretically clean and have distinctive experimental signatures. We focus on a class of these that do not require any form factor information and therefore may be especially suitable for extracting information on the angles $α$ and $γ$ of the unitarity triangle. The nonfactorizable effects, such as vertex-type and penguin-type corrections to the two-body b decay and hard spectator corrections to the 3-body decay are calculable in the heavy quark limit. QCD factorization is applicable when the emitted meson is a light meson or a charmonium. We discuss the issue of the CPT constraint on partial rate asymmetries. The strong phase coming from final-state rescattering due to hard gluon exchange between the final states can induce large rate asymmetries for tree-dominated color-suppressed modes $(π^0,ρ^0,ω)X_{\bar s}$. The nonfactorizable hard spectator interactions in the 3-body decay, though phase-space suppressed, are extremely important for the tree-dominated modes $(π^0,ρ^0,ω)X_{\bar s}, ϕX$, $J X_s,J X$ and the penguin-dominated mode $ωX_{s\bar s}$. In fact, they are dominated by the hard spectator corrections. Our result for ${\cal B} (B\to J/ψX_s)$ is in agreement with experiment. The semi-inclusive decay modes: $B^0_s\to (π^0,ρ^0,ω)X_{\bar s}$, $ρ^0X_{s\bar s}$, $B^0\to(K^-X,K^{*-}X)$ and $B^-\to (K^0X_s,K^{*0}X_s)$ are the most promising ones in searching for direct CP violation. In fact, they have branching ratios of order $10^{-6}-10^{-4}$ and CP rate asymmetries of order $(10-40)%$.
Recent experimental observations of CP asymmetry in B0 -> psi K0 constitute the first significant signal of CP violation outside the neutral kaon system; thus they represent an important milestone to test the CKM paradigm. We, therefore, undertake a critical appraisal of the existing experimental and theoretical inputs used to deduce constraints on sin(2 beta) and other important parameters and thus find, in particular, sin(2 beta) > 0.50 at 95% CL which is completely compatible with the combined experimental result: sin(2 beta) = 0.46 +- 0.17, representing an important success of the CKM model of CP violation. Searches for new physics in B decays to psi+K0 like final states will require improved precision; we make some suggestions to facilitate these. We also present a global fit including the new CP asymmetry measurements in B->psi+K0 as an additional input yielding e.g. gamma =29-56 degrees, eta-bar = >.19-.36, rho-bar=.15-.37, Jcp=(1.8 - 3.0) X 10^(-5), $Br(K+ -> pi+ nu nu-bar)=(0.51 - 0.90) X 10^(-10) and Br(KL -> pi0 nu nu-bar) = (0.11 - 0.31) X 10^(-10) at 95% CL.
We consider the partial rate asymmetry in the inclusive decay modes b to s gamma and b to d gamma, concentrating on non-standard models with new charged Higgs interactions. We find that the charged Higgs contribution to the asymmetry for b to s gamma is small in such models due to a universal cancellation mechanism. The asymmetry is therefore difficult to distinguish experimentally from the Standard Model (SM) value, which is also small. The cancellation mechanism is found to be rendered inoperative in supersymmetry due to the presence of chargino loops. Unlike b to s gamma, the rate asymmetry for b to d gamma in Higgs models can be quite different from its SM value, generally ranging from -20% to +20%. Specific model calculations are performed for the Three-Higgs Doublet Model and the ``Top'' Two-Higgs Doublet Model to serve as illustrations. We also offer some suggestions that may be helpful to experimentalists in the detection of the inclusive mode b to d gamma.
We present a first calculation of the strange quark mass using domain wall fermions. This paper contains an overview of the domain wall discretization and a pedagogical presentation of the perturbative calculation necessary for computing the mass renormalization. We combine the latter with numerical simulations to estimate the strange quark mass. Our final result in the quenched approximation is 95(26) MeV in the ${\bar{MS}}$ scheme at a scale of 2 GeV. We find that domain wall fermions have a small perturbative mass renormalization, similar to Wilson quarks, and exhibit good scaling behavior.
Various methods are discussed for obtaining the CKM angle gamma through the interference of the charged B-meson decay channels B- -> K- D0 and B- -> K- D0-bar where the D0 and D0-bar decay to common final states. It is found that choosing final states which are not CP eigenstates can lead to large direct CP violation which can give significant bounds on gamma without any theoretical assumptions. If two or more modes are studied, gamma may be extracted with a precision on the order of +/-15 degrees given about 10^8 B-mesons. We also discuss the case of three body decays of the D0 where additional information may be obtained from the distribution of the D0 decay products and consider the impact of D-D-bar oscillations.
We explore charged-Higgs cp-violating effects in a specific type III two-Higgs doublet model which is theoretically attractive as it accommodates the large mass of the top quark in a natural fashion. Two new CP-violating phases arise from the right-handed up quark sector. We consider CP violation in both neutral and charged B decays. Some of the important findings are as follows. 1) Large direct-CP asymmetry is found to be possible for B+- to psi/J K+-. 2) Sizable D-anti-D mixing effect at the percent level is found to be admissible despite the stringent constraints from the data on K-anti-K mixing, b to s gamma and B to tau nu decays. 3) A simple but distinctive CP asymmetry pattern emerges in decays of B_d and B_s mesons, including B_d to psi/J K_S, D+ D-, and B_s to D_s+ D_s-, psi eta/eta^prime, psi/J K_S. 4) The effect of D-anti-D mixing on the CP asymmetry in B+- to D/anti-D K+- and on the extraction of the angle gamma of the unitarity triangle from such decays can be significant.
CP violation in top physics is reviewed. The Standard Model has negligible effects, consequently CP violation searches involving the top quark may constitute the best way to look for physics beyond the Standard Model. Non-standard sources of CP violation due to an extended Higgs sector with and without natural flavor conservation and supersymmetric theories are discussed. Experimental feasibility of detecting CP violation effects in top quark production and decays in high energy e+ e-, gamma-gamma, mu+ mu-, pp and p-bar p colliders are surveyed. Searches for the electric, electro-weak and the chromo-electric dipole moments of the top quark in e+ e- -> t-bar t and in p p -> t-bar t X are descibed. In addition, other mechanisms that appear promising for experiments, e.g., tree-level CP violation in e+ e- -> t-bar t h, t-bar t Z, t-bar t nu_e-bar nu_e and in the top decay t -> b tau nu_tau and CP violation driven by s-channel Higgs exchanges in p p, gamma gamma, mu+ mu- -> t-bar t etc., are also discussed.
Lattice matrix elements are briefly reviewed. In the quenched approximation $f_B$, $B_B$ and $B_K$ are now under good control. Experimental hints for $f^{\rm expt}_{D_S}> f^{\rm QQCD}_{D_S}$ are noted; precise determination of $f_{D_S}$ from experiment as well as from the lattice is strongly advocated. Lattice calculations of the form factor for $B\toπ\ellν$ at relatively large value of $q^2$ have made good progress and should be useful in conjunction with precise measurement of the differential spectra expected from $B$-factories. Recent attempt at $K\to ππ$ using staggered quarks is briefly discussed; use of non-perturbative renormalization, improved actions and operators with staggered quarks is emphasized. Due to the good chiral behavior of domain wall quarks it would be useful to study $K\to ππ$ with this discretization.