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L. Reina

Publications and source records attributed to L. Reina.

69 records · Page 4Linked to original sources
arXiv1999

Measuring the Higgs Yukawa Couplings at a Next Linear Collider

We investigate the inclusive production of a Higgs boson with a pair of heavy quarks (t-tbar b-bbar), in e^+e^- collisions at high energies, sqrt(s)=500 GeV and sqrt(s)=1 TeV. We consider both the Standard Model and the supersymmetric case. In both cases O(alpha_s) QCD corrections are included. The associated production of a Higgs boson with a t-tbar pair is extremely sensitive to the top-Higgs Yukawa coupling and may allow the precision measurement of this coupling. In some regions of the supersymmetric parameter space the associated production of a Higgs boson with a b-bbar pair receives large resonant contributions and can have a significant rate.

hep-ph↗
arXiv1999

NLO QCD predictions for internal jet shapes in DIS at HERA

The transverse momentum flow inside jets is a sensitive measure of internal jet structure. For the current jets in deep inelastic scattering this jet shape measure is determined at order alpha_s^2, i.e. with up to three partons inside a single jet. The scale dependence of jet shapes in various jet algorithms is discussed. Results agree well with recent measurements by the ZEUS Collaboration, without introducing the hadronization parameter R_sep.

hep-ph↗
arXiv1999

Associated Higgs Production in the MSSM

We investigate the inclusive production of the Higgs bosons of the minimal supersymmetric model with a heavy quark pair, ($t {\bar t}$ and $b {\bar b}$), in e^+e^- collisions at high energies, $\sqrt{s}=500 GeV$ and $\sqrt{s}=1 TeV$. The ${\cal O}(α_s)$ QCD radiative corrections are included and the dependence of the production rates on the parameters of the MSSM is explored. The associated production of a Higgs boson with a $b {\bar b}$ pair receives large resonant contributions and can have a significant rate.

hep-ph↗
arXiv1997

QCD Corrections to Associated Higgs Boson Production

We compute QCD corrections to the processes $e^+e^-\to t \bar t h^0$ and $pp\to t \bar t h^0$ by treating the Higgs boson as a parton which radiates off a heavy quark. This approximatiion is valid in the limits $M_h<<M_t$ and $M_h, M_t<<\sqrt{s}$. The corrections increase the rate for $pp\to t \bar t h^0$ at the LHC by a factor of 1.2 to 1.5 over the lowest order rate for an intermediate mass Higgs boson, $M_h < 180 GeV$. The QCD corrections are small for $e^+e^-\to t \bar t h^0$ at $\sqrt{s}=1 TeV$.

hep-ph↗
arXiv1995

Estimates of $ε\prime/ε$

We review the latest calculations of the next-to-leading $\DSone$ effective Hamiltonian, relevant for $K\to ππ$ transitions. Numerical results for the Wilson coefficients are given for different regularization schemes. Predictions of $\epse$, obtained using different approaches to evaluate the relevant hadronic matrix elements, are compared. Given the present value of the top mass, $m_t=(174\pm 17)$ GeV, all the analyses, in spite of the large theoretical uncertainties, indicate that the value of $\epse$ is smaller than $1\times 10^{-3}$.

hep-ph↗
arXiv1995

An Upgraded Analysis of $ε\prime/ε$ at the Next-to-Leading Order

An upgraded analysis of $\ep$, $x_d$ and $\epp/\ep$, using the latest determinations of the relevant experimental and theoretical parameters, is presented. Using the recent determination of the top quark mass, $m_t=(174 \pm 17)$ GeV, our best estimate is $\epp/\ep= 3.1 \pm 2.5 $, which lies in the range given by E731. We describe our determination of $\epp/\ep$ and make a comparison with other similar studies. A detailed discussion of the matching of the full theory to the effective Hamiltonian, written in terms of lattice operators, is also given.

hep-ph↗
arXiv1994

$b \rightarrow s γ$ AND $b \rightarrow s g$: A THEORETICAL REAPPRAISAL

We present upgraded theoretical predictions for inclusive and exclusive radiative decays of {\it B} mesons. Our results include those next-to-leading order corrections that have already been computed. Our best estimates in the Standard Model are $BR(B \rightarrow K^* γ)=(4.3 \pm 0.9^{ +1.4}_{-1.0}) \times 10^{-5}$, $BR(B \rightarrow X_s γ) =(1.9 \pm 0.2\pm 0.5) \times 10^{-4}$, $Γ(B \rightarrow K^* γ)/ Γ(B \rightarrow X_s γ)=0.23 \pm 0.09$ and $BR(B \rightarrow X_s g)= (1.57 \pm 0.15 ^{+0.86}_{-0.59} \pm 0.23) \times 10^{-3}$. We also consider limits found with two-Higgs-doublet models.

hep-ph↗
arXiv1994

$ε^\prime/ε$: theoretical results and updated phenomenological analysis

We present the results for the Next-to-Leading Order effective hamiltonian for $ΔS\!=\! 1$ decays, in presence of both QCD and QED corrections, and update the existing theoretical predictions for $ε^\prime/ε$. To appear on the Proceedings of the Third KEK Topical Conference on CP Violation, its Implications to Particle Physics and Cosmology, Tsukuba, 16-18 November 1993

hep-ph↗
arXiv1993

Leading Order QCD Corrections to $b\rightarrow s \, γ$ and $b \rightarrow s \, g$ Decays in Three Regularization Schemes

We discuss in detail the calculation of the leading order QCD corrections to the Effective Hamiltonian which governs $b \rightarrow s\, γ$ and $b \rightarrow s \, g$ transitions in three different regularization schemes (HV, NDR and DRED). We show that intermediate stages of the calculation do depend on the regularization, but the same scheme independent coefficients can be obtained in all the considered schemes. A detailed discussion of the results already present in the literature is also given.

hep-ph↗
arXiv1993

Scheme Independence of the Effective Hamiltonian for $b \rightarrow s \, γ$ and $b \rightarrow s \, g$ Decays

We present a calculation of the effective weak Hamiltonian which governs $b \rightarrow s\, γ$ and $b \rightarrow s \, g$ transitions in two different renormalization schemes (NDR and HV). In the leading logarithmic approximation, we show that the coefficients of the effective Hamiltonian are scheme independent only when one takes correctly into account the scheme dependence of one- and two- loop diagrams. We demonstrate that in NDR there are contributions which were missed in previous calculations. These contributions are necessary to obtain scheme independent coefficients in the final results.

hep-ph↗
arXiv1993

Spontaneous Baryogenesis with Observable CP Violation

Using a left-right symmetric model with Spontaneous CP Violation and the hypothesis of a weakly first order electroweak phase transition we derive a relation between the produced baryon asymmetry and the observed parameter $\varepsilon$, describing CP violation in the $K$ system.

hep-ph↗
arXiv1993

NLO calculation of $ε^{\prime}/ε$ in QCD and QED within the lattice QCD framework

We present the results of our recent calculation of $ε^{\prime}/ ε$ at the Next-to-Leading (NLO) order in QCD and QED, in the framework of $\DSone$ Effective Hamiltonians. The operator matrix elements are taken from lattice QCD, at a scale $μ=2\,\,\mbox{GeV}$. NLO corrections seem to lower the value of $ε^{\prime}/ε$, favouring the experimental result of E731. Contributions from different operators are analyzed and dependence on $\mt$, $μ$ and $Λ_{\sss QCD}$ discussed. (Talk given at the XXVIIIth Rencontres de Moriond, ``Electro-Weak Interactions and Unified Theories'', March 13-19 1993).

hep-ph↗
arXiv1993

The $ΔS=1$ Effective Hamiltonian Including Next-to-Leading Order QCD and QED Corrections

In this paper we present a calculation of the $ΔS=1$ effective weak Hamiltonian including next-to-leading order QCD and QED corrections. At a scale $μ$ of the order of few GeV, the Wilson coefficients of the operators are given in terms of the renormalization group evolution matrix and of the coefficients computed at a large scale $\sim M_W$. The expression of the evolution matrix is derived from the two-loop anomalous dimension matrix which governs the mixing of the relevant current-current and penguin operators, renormalized in some given regularization scheme. We have computed the anomalous dimension matrix up to and including order $\alphas^2$ and $\alphae \alphas$ in two different renormalization schemes, NDR and HV, with consistent results. We give many details on the calculation of the anomalous dimension matrix at two loops, on the determination of the Wilson coefficients at the scale $M_W$ and of their evolution from $M_W$ to $μ$. We also discuss the dependence of the Wilson coefficients/operators on the regularization scheme.

hep-ph↗
arXiv1992

$ε^{\prime}/ε$ at the next-to-leading order in QCD and QED

We present a new calculation of the CP violation parameter $ε^{\prime}/ ε$. The results reported in this paper have been obtained by using the $ΔS=1$ effective Hamiltonian computed at the next-to-leading order, including QCD and QED penguins. The matrix elements of the relevant operators have been taken from lattice QCD, at a scale $μ=2$ GeV. At this relatively large scale, the perturbative matching between the relevant operators and the corresponding coefficients is quite reliable. The effect of the next-to-leading corrections is to lower the prediction obtained at the leading order, thus favouring the experimental result of E731. We analyze different contributions to the final result and compare the leading and next-to-leading cases.

hep-ph↗