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Z. J. Ajaltouni

Publications and source records attributed to Z. J. Ajaltouni.

16 recordsLinked to original sources
arXiv2023

Searching for New Physics in the Differential Decay Width of a Lambda_b Semi-leptonic Decay

We propose to investigate the effects of new physics in the semi-leptonic sequential decay $Λ_b \to Λ_c (\to Λπ) τ{\bar ν}_τ$. Firstly, we write the general, model independent, non-covariant expression of the differential decay width of the process. Then, we calculate that observable according to three different types of new physics interactions, which might explain the tension of data with the standard model predictions. We find that some coefficients of the differential decay width are sensitive to the kind of interaction that is assumed. The measurements that we suggest seem to be feasible.

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arXiv2019

Polarization in (quasi-)two-body decays and new physics

We consider two-body and quasi-two-body decays of the type $f_1 \to f_2 B$, where $f_1$ and $f_2$ are spin-1/2 fermions and $B$ a spin-0 or spin-1 boson. After recalling the non-covariant formalism for decay amplitudes, we derive the expression of the differential decay width and of the polarizations of the final spinning particles, both on- and off-shell. We find an intriguing geometrical interpretation of the results about the polarization. We also illustrate some methods for measuring the polarizations of the resonances and for optimizing data analysis. Then we propose applications to semi-leptonic weak decays, with a major attention to the $T$-odd component of the polarization; this may help to find, simultaneously, possible time-reversal violations and hints to physics beyond the standard model. We suggest also a $CPT$ test. Last, we discuss some $T$-odd observables for the production process of $f_1$ and for the study of the strong final state interactions of non-leptonic decays.

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arXiv2018

Detailed Study of the Decay Lambda_b --> Lambda_c tau {\bar ν}_τ

We examine in detail the semi-leptonic decay $Λ_b \to Λ_c τ{\bar ν}_τ$, which may confirm previous hints, from the analogous $B$ decay, of a new physics beyond the standard model. First of all, starting from rather general assumptions, we predict the partial width of the decay. Then we analyze the effects of five possible new physics interactions, adopting in each case five different form factors. In particular, for each term beyond the standard model, we find some constraints on the strength and phase of the coupling, which we combine with those found by other authors in analyzing the analogous semi-leptonic decays of $B$. Our analysis involves some dimensionless quantities, substantially independent of the form factor, but which, owing to the constraints, turn out to be strongly sensitive to the kind of non-standard interaction. We also introduce a criterion thanks to which one can discriminate among the various new physics terms: the left-handed current and the two-higgs-doublet model appear privileged, with a neat preference for the former interaction. Lastly, we suggest a differential observable that could, in principle, help to distinguish between the two cases.

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arXiv2012

Interference Effects, Time Reversal Violation and Search for New Physics in Hadronic Weak Decays

We propose some methods for studying hadronic sequential two-body decays involving more spinning particles. It relies on the analysis of T-odd and T-even asymmetries, which are related to interference terms. The latter asymmetries turn out to be as useful as the former ones in inferring time reversal violating observables; these in turn may be sensitive, under some particular conditions, to possible contributions beyond the standard model. Our main result is that one can extract such observables even after integrating the differential decay width over almost all of the available angles. Moreover we find that the correlations based exclusively on momenta are quite general, since they provide as much information as those involving one or more spins. We generalize some methods already proposed in the literature for particular decay channels, but we also pick out a new kind of time reversal violating observables. Our analysis could be applied, for example, to data of LHCb experiment.

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arXiv2008

Model Independent Tests for Time Reversal and CP Violations and for CPT Theorem in Λ_b and \barΛ_b Two Body Decays

Weak decays of beauty baryons like Λ_b (\barΛ_b) into Λ(\barΛ) and V (J^P = 1^-), where both decay products are polarized, offer interesting opportunities to perform tests of time reversal and CP violations and of CPT invariance. We propose a model independent parametrization of the angular distribution and of the polarization of the final resonances, by means of the spin density matrix. The transverse component of the polarization is sensitive to time reversal violations, moreover CP-and CPT-sensitive observables are defined.

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arXiv2007

Testing Time-Reversal: Lambda_b Decays into Polarized Resonances

Weak decays of beauty baryons like Lambda_b into Lambda V(J^P=1^-), where the produced resonances are polarized, offer interesting opportunity to perform tests of Time-Reversal Invariance. This paper emphasizes the particular role of the resonance polarization-vectors and their physical properties by symmetry transformations. In particular, it is shown that the normal component of a polarization-vector, as defined in the Jackson's frame, is Lorentz invariant and could get large values, notably in the case of J/psi production.

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arXiv2006

Testing CP and Time Reversal Symmetries with $Λ_b \to ΛV(1-)$ Decays

In this letter, an overview is given for interesting tests of both CP and Time Reversal symmetries with the beauty baryon $Λ_b $. Extensive use of the helicity formalism and HQET is done for all calculations. Then, emphasis is put on sophisticated methods like analysis of resonance polarizations and particular angle distributions which can exhibit a clear signal of TR violation.

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arXiv2004

An angular distribution analysis of $Λ_b$ decays

A study of the angular distributions of the processes $Λ_b \to Λ V(1^-)$ with $V ({J/Ψ,ρ}^0)$ is performed. Emphasis is put on the initial $Λ_b$ polarization and the polarization density-matrices are derived to perform tests of both Time-Reversal (TR) and CP violation.

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arXiv2004

$Λ_b$ Decays into $Λ$-Vector

A complete study of the angular distributions of the processes, $Λ_b \to Λ V(1^-)$, with $Λ\to p π^-$ and $V (J/Ψ) \to {\ell}^+ {\ell}^-$ or $V (ρ^0,ω) \to π^+ π^-,$ is performed. Emphasis is put on the initial $Λ_b$ polarization produced in the proton-proton collisions. The polarization density-matrices as well as angular distributions are derived and help to construct T-odd observables which allow us to perform tests of both Time-Reversal and CP violation.

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arXiv2004

Direct CP Violation in B decays with rho0-omega Mixing

A complete study of the process B to pi+ pi- V(V=1--) is performed both in the framework of the helicity formalism and the effective lagrangian approach. Emphasis is put on the factorization hypothesis and the importance of the rho0- omega mixing in enhancing the direct CP violation. New results involving some branching ratios and the ratio of the Penguin/Tree amplitude are given in details.

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arXiv2004

Angular Analysis of Lambda_b Decays into Lambda v(1-) Applications to Time-Odd Observables and CP violation in Lambda_b Decays (I)

A complete study of teh angualr distributions of the process Lambda_b to Lambda V(1-) with lambda to p pi- and V(J/Psi) to l+l- or V(rho0,omega, phi) to pi+ pi-, K+K- is performed. Emphasis is put on the initial Lambda-b polarization produced in the proton-proton collisions and, without any dynamical assumption, polarized density-matrices of the vector-mesons V are derived and help to construct T-odd observables which allow us to perform tests of both Time-Reversal and CP violation.

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arXiv2003

Simulation Methods of the Processes $B \to π^+ π^- V$ including $ρ^0-ω$ Mixing Effects

Simulation methods for the decays $ B \to π^+ π^- V$, where $V$ is a $1^{--}$ vector-meson, are presented in detail. Emphasis is put on the use of the helicity formalism and the use of effective Lagrangians. We show the importance of ${ρ^{0}}-ω$ mixing in enhancing the direct $CP$ violation (DCPV) when the pion-pion invariant mass is near the mass of the $ω$.

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arXiv2003

Direct CP Violation In B --> pi^+ pi^- V With rho^0--omega Mixing Effects: Phenomenological Approach

We present a detailed study of direct CP violation and branching ratios in the channels $B^{0,\pm} \to π^{+}π^{-} V^{0,\pm}$, where $V$ is a vector meson ($K^{* 0,\pm}$ or $ρ^{\pm}$). Emphasis is placed upon the important role played by ${ρ^{0}}-ω$ mixing effects in the estimation of the CP-violating asymmetry parameter, $a_{cp}$, associated with the difference of $B$ and $\bar B$ decay amplitudes. A thorough study of the helicity amplitudes is presented as a function of the pion-pion invariant mass. All of the calculations and simulations considered correspond to channels which will be analyzed at the LHCb facility.

hep-ph↗
arXiv2003

$B^0(\pm)$ decays into two vector mesons. Physical motivations and a general method for simulations

In this paper, a complete description of the channels $B \to V_1 V_2$ is given. Emphasis is put on the determination of the dynamical density matrix which elements are computed according to the Wilson operator product expansions entering into the formulation of the weak effective hamiltonian. \vskip 0.3cm Kinematical consequences related to the particular channel $B \to K^* ρ^0 (ω)$ are described in details.

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