arXiv subjects

Gad Eilam

Publications and source records attributed to Gad Eilam.

32 records · Page 2Linked to original sources

arXiv2004

Three heavy jet events at hadron colliders as a sensitive probe of the Higgs sector

Assuming that a non-standard neutral Higgs with an enhanced Yukawa coupling to a bottom quark is observed at future hadron experiments, we propose a method for a better understanding of the Higgs sector. Our procedure is based on "counting" the number of events with heavy jets (where "heavy" stands for a c or b jet) versus b jets, in the final state of processes in which the Higgs is produced in association with a single high p_T c or b jet. We show that an observed signal of the type proposed, at either the Tevatron or the LHC, will rule out the popular two Higgs doublet model of type II as well as its supersymmetric version - the Minimal Supersymmetric Standard Model (MSSM), and may provide new evidence in favor of some more exotic multi Higgs scenarios. As an example, we show that in a version of a two Higgs doublet model which naturally accounts for the large mass of the top quark, our signal can be easily detected at the LHC within that framework. We also find that such a signal may be observable at the upgraded Tevatron RunIII, if the neutral Higgs in this model has a mass around 100 GeV and \tanβ> 50 and if the efficiency for distinguishing a c jet from a light jet will reach the level of 50%.

hep-ph↗

arXiv2003

Lepton-flavor-violating decays L->l gamma gamma as a new probe of supersymmetry with broken R-parity

Lepton-flavor-violating decays of the type L->l gamma gamma (mu->e gamma gamma, tau->e gamma gamma, and tau->mu gamma gamma) are proposed as new probes of R-parity-violating supersymmetry. Non-penguin diagrams with a sneutrino that decays into two photons via a triangle graph might trigger such decays even in the absence of the corresponding radiative decays into one photon only, e.g. mu->e gamma. Thus, processes of the type L->l gamma gamma may provide an independent probe of new flavor physics.

hep-ph↗

arXiv2002

Rare Z Decays

Motivated by the well known impact of rare decays of hadrons and leptons on the evolution of the Standard Model and on limits for new physics, as well as by the proposal for Giga-Z option at TESLA, we investigate the rare decay Z -> b s-bar in various extensions of the Standard Model.

hep-ph↗

arXiv2002

Flavor changing Z-decays from scalar interactions at a Giga-Z Linear Collider

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.

hep-ph↗

arXiv2002

Semi-inclusive Decay $B\to ϕX_s$: Rate and Momentum Spectrum of $ϕ$

We study the rate and $ϕ$ momentum distribution in semi-inclusive decays $B \toϕX_s $ induced by the quark level processes $b\toϕs$ and $b\toϕs g$, in which the gluon is radiated from the internal charm quark loop or emitted from the virtual gluon of the strong penguin (inner bremsstrahlung). We find ${\cal B}(b\toϕs)=6.7\times 10^{-5}$ and ${\cal B}(b\toϕs g)=3.8\times 10^{-5}$. The momentum spectrum of $ϕ$ produced by $b\toϕs g $ is very broad. With the cut $|{\bf k}_ϕ|\geq 2.0$ GeV, ${\cal B}(b\toϕs)=6.1\times 10^{-5}$ (where the Fermi motion of the $b$-quark in the $B$-meson is described by a Gaussian), and ${\cal B}(b\toϕs g)=1.0\times 10^{-5}$. Due to the special nature of $ϕ$, many difficulties which hindered a reliable theoretical prediction for $B\to η' X_s$ decay are absent in the process $B\to ϕX_s$. Therefore, theoretical predictions for $B\to ϕX_s$ are relatively clean. Moreover, the clear experimental signature of the $ϕ$ is of great help. Data for $B\toϕX_s$, both the branching ratio and the $ϕ$ momentum distribution, would teach us about the strength of strong penguins which might be of great importance in the search for CP violation and for new physics at $B$ factories.

hep-ph↗

arXiv2002

$B\to ϕπ$ and $B^0 \to ϕϕ$ in the Standard Model and new bounds on R parity violation

We study the pure penguin decays $B \to ϕπ$ and $B^0 \to ϕϕ$. Using QCD factorization, we find ${\cal B}(B^\pm \toϕπ^{\pm} )=2.0^{+0.3}_{-0.1}\times 10^{-8}$. For the pure penguin annihilation process $B^0 \to ϕϕ$, analyzed here for the first time, ${\cal B}(B^0 \toϕϕ)=2.1^{+1.6}_{-0.3}\times 10^{-9}$. The smallness of these decays in the Standard Model makes them sensitive probes for new physics. From the upper limit of $B\to ϕπ$,we find constraints on R parity violating couplings, $| λ{''}_{i23}λ{''}_{i21}|<6\times10^{-5}$, $| λ'_{i23}λ'_{i21}|<4\times10^{-4}$ and $| λ'_{i32}λ'_{i12}|<4\times10^{-4}$ for $i=1,2,3$. Our new bounds on $|λ{''}_{i23}λ{''}_{i21}|$ are one order of magnitude stronger than before. Within the available upper bounds for $| λ{''}_{i23}λ{''}_{i21}|$, $|λ'_{i23}λ'_{i21}|$ and $|λ'_{i32}λ'_{i12}|$, we find that ${\cal B}(B\toϕϕ)$ could be enhanced to $10^{-8}\sim 10^{-7}$. Experimental searches for these decays are strongly urged.

hep-ph↗

arXiv2001

Study of B0-->J/Psi D() and etac D() in Perturbative QCD

Motivated by recent interest in soft $J/Ψ$ production in B decays, we investigate ${B}^0 \to J/ΨD^{(\star)}$ and $η_c D^{(\star)}$ decays in perturbative QCD. We find that, within that framework, these decays are calculable since the heavy $c\bar{c}$ pair in the final states is created by a hard gluon. The branching ratios are estimated to be around $10^{-7}\sim 10^{-8}$, too small to be consistent with the data, suggesting that other mechanism(s) contribute to the observed excess of soft $J/Ψ$ in ${B}^0 \to J/Ψ+ X$ decays. The possibility of the production of a hybrid $s{\bar d}g$ meson with mass about 2 GeV is briefly entertained.

hep-ph↗

arXiv2000

Determining the quantum numbers of excited heavy mesons

We discuss the decays X^* -> Xe^+e^- (``Dalitz decays'') of excited heavy mesons into their ground states and an electron-positron pair. We argue that the measurement of the invariant mass spectrum of the lepton pair gives clear indication on the quantum numbers of the excited meson and thus provides an experimental test of the quark model predictions.

hep-ph↗

arXiv2000

CP Violation in Top Physics

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.

hep-ph↗

arXiv1996

Radiative Dileptonic Decays of B Mesons

We investigate the radiative dileptonic decays $B_s(B_d)\toγl^+l^-$ within the standard model. Using the constituent quark model, the branching ratios turn out to be around $5\times 10^{-9}$ for $B_s\to γμ^+μ^- $ and around $6\times 10^{-10}$ for $B_d \to γμ^+μ^- $, with slightly larger values for $B_s(B_d) \to γe^+e^- $. The differential rate as a function of the dilepton invariant mass is given. The possibility of using these processes to determine the decay constants of $B_s$ or $B_d$ is discussed.

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↗

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↗

arXiv1995

Large CP Asymmetries in $B^{\pm}\toη_c(χ_{c0})π^{\pm}$ from $η_c(χ_{c0})$ Width

We study CP asymmetries in $B^{\pm}\to hπ^{\pm}$ decays, where the hadronic states $h=ρρ, K\Kbarπ$, $π^+π^-K^+K^-$, etc., and $h=π^+π^-, K^+K^-, 2(π^+π^-)$, etc., are taken on the resonances $η_c$ and $χ_{c0}$, respectively. The relatively large $η_c$ and $χ_{c0}$ decay widths, of about 10$-$15 MeV, provide the necessary absorptive phase in the interference between the resonance (going through $b\to c\cbar d$) and the background (through $b\to u\ubar d$) contributions to the amplitude. Large asymmetries of order 10$\%$ or more are likely in some modes.

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↗