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A. Ali

Publications and source records attributed to A. Ali.

At least 127 records · Page 7Linked to original sources
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

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arXiv2003

The $η^\prime g^* g^{(*)}$ Vertex Including the $η^\prime$-Meson Mass

The $η^\prime g^* g^{(*)}$ effective vertex function is calculated in the QCD hard-scattering approach, taking into account the $η^\prime$-meson mass. We work in the approximation in which only one non-leading Gegenbauer moment for both the quark-antiquark and the gluonic light-cone distribution amplitudes for the $η^\prime$-meson is kept. The vertex function with one off-shell gluon is shown to have the form (valid for $| q_1^2 | > m_{η^\prime}^2$) $F_{η^\prime g^* g} (q_1^2, 0, m_{η^\prime}^2) = m_{η^\prime}^2 H(q_1^2)/(q_1^2 - m_{η^\prime}^2)$, where $H(q_1^2)$ is a slowly varying function, derived analytically in this paper. The resulting vertex function is in agreement with the phenomenologically inferred form of this vertex obtained from an analysis of the CLEO data on the $η^\prime$-meson energy spectrum in the decay $Υ(1S) \to η^\prime X$. We also present an interpolating formula for the vertex function $F_{η^\prime g^* g} (q_1^2, 0, m_{η^\prime}^2)$ for the space-like region of the virtuality $q_1^2$, which satisfies the QCD anomaly normalization for on-shell gluons and the perturbative-QCD result for the gluon virtuality $| q_1^2| \gtrsim 2$ GeV$^2$.

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arXiv2003

An Analysis of the Inclusive Decay $Υ(1S) \to η^\prime X$ and Constraints on the $η^\prime$-Meson Distribution Amplitudes

We calculate the $η^\prime$-meson energy spectrum in the decay $Υ(1S) \to η^\prime g g g \to η^\prime X$ in the leading-order perturbative QCD in the static quark limit for the Orthoquarkonium. Our principal result is the extraction of parameters of the $η^\prime g^* g$ effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the $η^\prime$-meson energy spectrum. The perturbative QCD based framework provides a good description of the available CLEO data, allowing to constrain the lowest Gegenbauer coefficients $B^{(q)}_2$ and $B^{(g)}_2$ of the quark-antiquark and gluonic distribution amplitudes of the $η^\prime$-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the $η-γ$ and $η^\prime-γ$ transition form factors and the requirement of positivity of the EVF, yielding $B^{(q)}_2(μ_0^2) = -0.008 \pm 0.054$ and $B^{(g)}_2(μ_0^2) = 4.6 \pm 2.5$ for $μ_0^2 = 2$ GeV$^2$. This reduces significantly the current uncertainty on these coefficients. The resulting EFV $F_{η^\prime g^* g} (p^2, 0, m_{η^\prime}^2)$, including the $η^\prime$-meson mass effects, is presented.

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arXiv2002

Next-to-leading Order Calculations of the Radiative and Semileptonic Rare B Decays in the Standard Model and Comparison with Data

We review some selected rare B decays calculated in next-to-leading order accuracy in the Standard Model (SM). These include the radiative decays $B \to (X_s,K^*,ρ)γ$ and the semileptonic decays $B \to (X_s,K,K^*) \ell^+ \ell^-$, for which new data from the BABAR and BELLE collaborations have been presented at this conference. SM is in agreement with the current measurements within the theoretical and experimental errors. The impact of rare B-decays on the CKM phenomenology is quantitatively discussed.

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arXiv2002

Improved Model-Independent Analysis of Semileptonic and Radiative Rare B Decays

We update the branching ratios for the inclusive decays $B\to X_s \ell^+ \ell^-$ and the exclusive decays $B\to (K,K^*) \ell^+ \ell^-$, with $\ell=e, \m$, in the standard model by including the explicit $O(\a_s)$ and $Λ_{\hbox{\tiny QCD}} / m_b$ corrections. This framework is used in conjunction with the current measurements of the branching ratios for $B\to X_s \g$ and $B\to K \ell^+ \ell^-$ decays and upper limits on the branching ratios for the decays $B\to (K^*,X_s) \ell^+ \ell^-$ to work out bounds on the Wilson coefficients $C_7$, $C_8$, $C_9$ and $C_{10}$ appearing in the effective Hamiltonian formalism. The resulting bounds are found to be consistent with the predictions of the standard model and some variants of supersymmetric theories. We illustrate the constraints on supersymmetric parameters that the current data on rare B decays implies in the context of minimal flavor violating model and in more general scenarios admitting additional flavor changing mechanisms. Precise measurements of the dilepton invariant mass distributions in the decays $B \to (X_s,K^*,K) \ell^+ \ell^-$, in particular in the lower dilepton mass region, and the forward-backward asymmetry in the decays $B \to (X_s,K^*) \ell^+ \ell^-$, will greatly help in discriminating among the SM and various supersymmetric theories.

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arXiv2002

Signatures of Supersymmetry in B Decays - A Theoretical Perspective

We discuss precision tests of the standard model in radiative and semileptonic rare B-decays and CP-violating asymmetries, and possible signatures of supersymmetry in these processes. Motivated by current data, and with an eye on the forthcoming measurements, we restrict ourselves to the processes in which the bench marks set by the standard model have either been met by ongoing experiments or are expected to be met shortly. This includes the mixing-induced CP asymmetry, measured through $\sin 2 β$, and branching ratios for the radiative and semileptonic rare decays $B \to X_s γ$, $B \to K^* γ$, $B \to X_s \ell^+ \ell^-$ and $B \to (K,K^*) \ell^+ \ell^-$, where $\ell^\pm =e^\pm, μ^\pm$.

hep-ph↗
arXiv2001

Same-Sign Dilepton Production via Heavy Majorana Neutrinos in Proton-Proton Collisions

We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton-proton collisions $pp\ra \ell^+ \ell^{\prime +}X$ for $\ell,~ \ell^\prime = e,~ μ,~ τ$ at the LHC energy $\sqrt{s}=14$ TeV. Assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $(m_{N},|U_{\ell N}U_{\ell^\prime N}|)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low energy experiments, we show that at LHC one has sensitivity to heavy Majorana neutrinos up to a mass $m_{N}\leq 2$ -- 5 TeV in the dilepton channels $μμ,~ ττ$, and $μτ$, but the dilepton states $e\ell$ will not be detectable due to the already existing constraints from neutrinoless double beta decay.

hep-ph↗
arXiv2001

The Effective $η^\prime g^* g^*$ Vertex at Arbitrary Gluon Virtualities

The effective $η^\prime g^* g^*$ vertex is studied in the standard (Brodsky-Lepage) and modified hard scattering approaches for arbitrary gluon virtualities in the time-like and space-like regions. The contribution of the gluons in the $η^\prime$-meson is taken into account, and the wave-function is constrained using data on the electromagnetic transition form factor of the $η^\prime$ meson. Our results have implications for the inclusive decay $B \to η^\prime X$ and exclusive decays, such as $B \to η^\prime (K, K^*)$, and in hadronic production processes $N + N (\bar N) \to η^\prime X$.

hep-ph↗
arXiv2001

The $η^\prime g^* g^*$ vertex with arbitrary gluon virtualities in the perturbative QCD hard scattering approach

We study the $η^\prime g^* g^*$ vertex for arbitrary gluon virtualities in the time-like and space-like regions, using the perturbative QCD hard scattering approach and an input wave-function of the $η^\prime$-meson consistent with the measured $η^\prime γ^* γ$ transition form factor. The contribution of the gluonic content of the $η^\prime$-meson is taken into account, enhancing the form factor over the entire virtuality considered. However, data on the electromagnetic transition form factor of the $η^\prime$-meson is not sufficient to quantify the gluonic enhancement. We also study the effect of the transverse momenta of the partons in the $η^\prime$-meson on the $η^\prime g^* g^*$ vertex, using the modified hard scattering approach based on Sudakov formalism. Analytic expressions for the $η^\prime g^* g^*$ vertex are presented in limiting kinematic regions and parametrizations are given satisfying the QCD anomaly, for real gluons, and perturbative QCD behavior for large gluon virtualities, in both the time-like and space-like regions. Our results have implications for the inclusive decay $B \to η^\prime X$ and exclusive decays, such as $B \to η^\prime (K,K^*)$, and in hadronic production processes $N + N (\bar N) \to η^\prime X$.

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arXiv2001

Extended Minimal Flavour Violating MSSM and Implications for B Physics

The recently reported measurements of the CP asymmetry a(psi K) by the BABAR and BELLE collaborations are in good agreement with the standard model (SM) prediction, resulting from the unitarity of the CKM matrix. The so-called minimal flavour violating (MFV) supersymmetric extensions of the standard model, in which the CKM matrix remains the only flavour changing structure, predict a(psi K) similar to the one in the SM. With the anticipated precision in a(psi K) and other CP asymmetries at the B factories and hadron colliders, one hopes to pin down any possible deviation from the SM. We discuss an extension of the MFV-supersymmetric models which comfortably accommodates the current measurements of the CP asymmetry a(psi K), but differs from the SM and the MFV-supersymmetric models due to an additional flavour changing structure beyond the CKM matrix. We suggest specific tests in forthcoming experiments in B physics. In addition to the CP-asymmetries in B-meson decays, such as a(psi K) and a(pi pi), and the mass difference Delta M_s in the Bs-bar(Bs) system, we emphasize measurements of the radiative transition b -> d gamma as sensitive probes of the postulated flavour changing structure. Interestingly, the CKM-unitarity analysis in the Extended-MFV model also allows solutions rho < 0, as opposed to the SM and the MFV models for which only rho > 0 solutions are now admissible, implying gamma > pi/2, where gamma=- arg (Vub). Such large values of gamma are hinted by the current measurements of the branching ratios for the decays B -> pi pi and B -> K pi.

hep-ph↗
arXiv2001

Photonic and Leptonic Rare B Decays

Some selected topics involving photonic and leptonic rare B decays are reviewed. The interest in their measurement for the CKM phenomenology is underlined. They are also potentially interesting in searching for physics beyond the standard model. This is illustrated on the examples of the decays $B \to (K,K^*) \ell^+ \ell^-$ and $B \to (ρ, ω) γ$ by contrasting their anticipated phenomenological profiles in the standard model and some variants of supersymmetric models.

hep-ph↗
arXiv2000

What if the Mass Difference $ΔM_s$ is around 18 Inverse Picoseconds?

Present experiments in pursuit of the mass difference in the Bs-Bs(bar) system have put a lower bound on this quantity of $ΔM_s > 14.9 ps^{-1}$ (at 95% C.L.). The same experiments also yield a local minimum in the log-likelihood function around $ΔM_s = 17.7 ps^{-1}$, which is $2.5σ$ away from being zero. Motivated by these observations, we investigate the consequences of a possible measurement of $ΔM_s = 17.7 \pm 1.4 ps^{-1}$, in the context of both the standard model and supersymmetric models with minimal flavor violation. We perform a fit of the quark mixing parameters in these theories and estimate the expected ranges of the CP asymmetries in B decays, characterized by $α$, $β$ and $γ$, the interior angles of the CKM-unitarity triangle. Based on this study, we argue that, if indeed $ΔM_s$ turns out to be in its currently-favored range, this would disfavor a large class of supersymmetric models. Indeed, of all the models examined here, the best fit to the data occurs for the standard model.

hep-ph↗
arXiv2000

b Quark Physics with 2 .10^9 Z Bosons

It has been suggested to realize a factory for 10^9 Z^0 through a linear e^+e^- collider with polarized beams. Very likely the relevant CP studies for B mesons will already have been performed at the B factories by that time, hence GIGA-Z will be a third generation b physics experiment. Yet such a facility would provide us with unique opportunities in the domain of beauty physics that would be of essential significance even in 2010: (1) Production and decay of polarized beauty baryons; (2) searching for and probing transitions driven by b --> q ν\barν; (3) detailed and comprehensive studies of inclusive semileptonic B_s decays.

hep-ph↗
arXiv2000

Supersymmetric Effects on Isospin Symmetry Breaking and Direct CP Violation in $B \to ργ$

We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity $Δ^{-0} \equiv Γ(B^- \to ρ^- γ)/2Γ(B^0 \to ρ^0 γ)-1$, its charge conjugate $Δ^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to ρ^\pm γ$. We illustrate this by working out theoretical profiles of the charge-conjugate averaged ratio $Δ\equiv {1 \over 2}(Δ^{+0} +Δ^{-0})$ and the CP asymmetry $A_{CP}(B^\pm \to ρ^\pm γ)$ in the standard model and in some variants of the minimal supersymmetric standard model. We find that chargino contributions in the large $\tan β$ region may modify the magnitudes and flip the signs of $Δ$ and $A_{CP}(B^\pm \to ρ^\pm γ)$ compared to their standard-model values, providing an unmistakeable signature of supersymmetry.

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arXiv1999

A Comparative Study of the Decays $B \to (K,K^*) \ell^+ \ell^-$ in Standard Model and Supersymmetric Theories

Using improved theoretical calculations of the decay form factors in the Light Cone-QCD sum rule approach, we investigate the decay rates, dilepton invariant mass spectra and the forward-backward (FB) asymmetry in the decays $B \to (K,K^*) \ell^+ \ell^-$ ($\ell^\pm =e^\pm,μ^\pm,τ^\pm$) in the standard model (SM) and a number of popular variants of the supersymmetric (SUSY) models. Theoretical precision on the differential decay rates and FB-asymmetry is estimated in these theories taking into account various parametric uncertainties. We show that existing data on $B \to X_s γ$ and the experimental upper limit on the branching ratio ${\cal B}(B \to K^* μ^+ μ^-)$ provide interesting bounds on the coefficients of the underlying effective theory. We argue that the FB-asymmetry in $B \to K^* \ell^+ \ell^-$ constitutes a precision test of the SM and its measurement in forthcoming experiments may reveal new physics. In particular, the presently allowed large-$\tan β$ solutions in SUGRA models, as well as more general flavor-violating SUSY models, yield FB-asymmetries which are characteristically different from the corresponding ones in the SM.

hep-ph↗
arXiv1999

CP Violation and Prospects at B Factories and Hadron Colliders

We review the information on the CKM matrix elements, unitarity triangle and CP-violating phases $α, β$ and $γ$ in the standard model which will be measured in the forthcoming experiments at B factories, HERA-B and hadron colliders. We also discuss two-body non-leptonic decays $B \to h_1 h_2$, with $h_i$ being light mesons, which are interesting from the point of view of CP violation and measurements of these phases. Partial rate CP asymmetries are presented in a number of decay modes using factorization for the matrix elements of the operators in the effective weak Hamiltonian. Estimates of the branching ratios in this framework are compared with existing data on $B \to Kπ,η' K, K^{*}π,ρπ$ decays from the CLEO collaboration.

hep-ph↗
arXiv1999

Profiles of the Unitarity Triangle and CP-Violating Phases in the Standard Model and Supersymmetric Theories

We report on a comparative study of the profile of the CKM unitarity triangle, and the resulting CP asymmetries in B decays, in the standard model and in several variants of the minimal supersymmetric standard model (MSSM), characterized by a single phase in the quark flavour mixing matrix. The supersymmetric contributions to the mass differences ΔM_d, ΔM_s and to the CP-violating quantity |ε| are, to an excellent approximation, equal to each other in these theories, allowing for a particularly simple way of implementing the resulting constraints on the elements of V_{CKM} from the present knowledge of these quantities. Incorporating the next-to-leading-order corrections and applying the current direct and indirect constraints on the supersymmetric parameters, we find that the predicted ranges of \sin 2 βin the standard model and in MSSM models are very similar. However, precise measurements at B-factories and hadron machines may be able to distinguish these theories in terms of the other two CP-violating phases αand γ. This is illustrated for some representative values of the supersymmetric contributions in ΔM_d, ΔM_s and |ε|.

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