The effect of the Gaussian profile of the new Higgs doublet on the radiative lepton flavor violating decay

We study the branching ratios of the lepton flavor violating processes μ→eγ, τ→eγ and τ→μγ by considering that the new Higgs scalars localize with Gaussian profile in the extra dimension. We see that the BRs of the LFV decays μ→eγ, τ→eγ and τ→μγ are at the order of magnitude of 10^-12, 10^-16 and 10^-12 in the considered range of the free parameters. These numerical values are slightly suppressed in the case that the localization points of new Higgs scalars are different from the origin.     

The effect of the location of the new Higgs doublet on the radiative lepton flavor violating decays in the split fermion scenario

We study the branching ratios of the lepton flavor violating processes μ→eγ, τ→eγ and τ→μγ in the split fermion scenario, with the assumption that the new Higgs doublet is restricted to the 4D brane (thin bulk) in one and two extra dimensions, in the framework of the two Higgs doublet model. We observe that the branching ratios are sensitive to the location of the 4D brane and, in the second case, the width of the thin bulk, especially for the μ→eγ decay.     

Higgs and Z<Superscript>′</Superscript> phenomenology in B–L extension of the standard model at LHC

The phenomenology of the low scale U(1)_B–L extension of the standard model and its implications at LHC energies is presented. In this model, an extra gauge boson corresponding to B–L gauge symmetry and an extra SM singlet scalar (heavy Higgs boson) are predicted. We show a detailed analysis of both heavy and light Higgs bosons decay and production in addition to the possible decay channels of the new gauge boson. We find that the cross sections of the SM-like Higgs production are reduced by ∼20–30%, while its decay branching ratios remain intact. The extra Higgs boson has relatively small cross sections and the branching ratios of Z^′→l⁺l^- are of order ∼20% to be compared to ∼3% of the SM results. Hence, the search for Z^′ is accessible via a clean dilepton signal at LHC.     

Study of ATLAS sensitivity to FCNC top decays

The ATLAS experiment sensitivity to top quark flavour changing neutral current (FCNC) decays was studied at LHC using tt̄ events. While one of the top quarks is expected to follow the dominant Standard Model decay t→bW, the other decays through a FCNC channel, i.e. t→Zu(c), t→γu(c) or t→gu(c). Different types of analyses, applied to each FCNC decay mode, were compared. The FCNC branching ratio sensitivity (assuming a 5σ signal significance) and 95% confidence level limits on the branching ratios (in the hypothesis of signal absence) were obtained.     

Some properties of the newly observed X(1835) state at BES

Recently the BES collaboration has announced the observation of a resonant state in the π⁺π^-η’ spectrum in J/ψ→γπ⁺π^-η’ decay. Fitting the data with a 0^-+ state, the mass is determined to be 1833.7 MeV with 7.7σ statistic significance. This state is consistent with the one extracted from previously reported pp̄ threshold enhancement data in J/ψ→γpp̄. We study the properties of this state using QCD anomaly and QCD sum rules, assuming X(1835) to be a pseudoscalar, and we show that it is consistent with the data. We find that this state has a sizeable matrix element , leading to branching ratios of (2.61–7.37)×10^-3 and (2.21–10.61)×10^-2 for J/ψ→γG_p and for G_p→π⁺π^-η^′, respectively. Combining the calculated branching ratio of J/ψ→γG_p and data on threshold enhancement in J/ψ→γpp̄, we determine the coupling for the G_p–p–p̄ interaction. We finally study the branching ratios of the other J/ψ→γ+three mesons decay modes. We find that J/ψ→γG_p→γ(π⁺π^-η,KKπ⁰) can provide useful tests for the mechanism proposed. PACS 11.55.Hx; 12.39.Fe; 12.39.Mk; 13.25.Gv     

Branching ratio and CP-asymmetry of B<Subscript>s</Subscript>→ρ(ω)K decays in the perturbative QCD approach

In this paper, we calculate the branching ratios and CP-violating asymmetries for B_s→ρ^±K^∓, ρ⁰K̄⁰ and ωK̄⁰ decays in the perturbative QCD factorization approach. The theoretical predictions for the CP-averaged branching ratios of the considered decays are Br(B_s→ρ^±K^∓)≈24.7×10^-6, Br(B_s→ρ⁰K̄⁰)≈1.2×10^-7 and Br(B_s→ωK̄⁰)≈1.7×10^-7; and we also predict large CP-violating asymmetries for the considered decay modes. Specifically, the large A_CP ^dir(B_s→ρ^±K^∓) at -12% level plus large branching ratio at 10^-5 level are measurable in the forthcoming LHC-b experiments. PACS 13.25.Hw; 12.38.Bx; 14.40.Nd     

Towards a measurement of the two-photon decay width of the Standard Model Higgs boson at a Photon Collider

A study of the measurement of the two photon decay width times the branching ratio of the Standard Model Higgs boson with a mass of 120 GeV in photon–photon collisions is presented, assuming a γ γ integrated luminosity of 80 fb⁻¹ in the high energy part of the spectrum. The analysis is based on the reconstruction of the Higgs events produced in the γ γ→H process, followed by the decay of the Higgs into a pair. A statistical error of the measurement of the two-photon width, Γ(H→γ γ), times the branching ratio of the Higgs boson, BR is found to be 2.1% for one year of data taking.     

Study of J/ψ decaying into ωpp?

The decay J/ψ→ωpp̄ is studied using a 5.8×10⁷ J/ψ event sample accumulated with the BES II detector at the Beijing Electron–Positron Collider. The decay branching fraction is measured to be B(J/ψ→ωpp̄)=(9.8±0.3±1.4)×10^-4. No significant enhancement near the pp̄ mass threshold is observed, and an upper limit of B(J/ψ→ωX(1860))B(X(1860)→pp̄)<1.5×10^-5 is determined at the 95% confidence level, where X(1860) designates the near-threshold enhancement seen in the pp̄ mass spectrum in J/ψ→γpp̄ decays.     

Lepton flavor violating Z→l1 +l2 - decay in the split fermion scenario in the two Higgs doublet model

We predict the branching ratios of the Z→e^±μ^±, Z→e^±τ^± and Z→μ^±τ^± decays in the framework of the 2HDM, in the split fermion scenario. We observe that the branching ratios are not sensitive to a single extra dimension; however, this sensitivity is considerably large for two extra dimensions.     

Λ<Subscript>b</Subscript>→Λℓ<Superscript>+</Superscript>ℓ<Superscript>-</Superscript> decay in universal extra dimensions

We study the exclusive Λ_b→Λℓ⁺ℓ^- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λ_b→Λℓ⁺ℓ^- (ℓ=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λ_b→Λℓ⁺ℓ^- decay and determination of the zero position of are very useful in looking for new physics in the framework of the UED models. PACS 12.60.-i; 13.30.-a; 14.20.Mr     

Rare decays of Λ b → Λ γ and Λ b → Λ l + l ? in universal extra-dimension model

The exclusive weak decay of Λ _b →Λ γ and Λ _b →Λ l ⁺ l ⁻ are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the branching ratio of Λ _b →Λ γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ _b →Λ l ⁺ l ⁻. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ _b →Λ μ ⁺ μ ⁻ is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ _b decays are not a useful tool to provide any valuable information for the universal extra-dimension model.     

Isospin symmetry breaking in ρ→πγ decay

In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10^-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10^-4 and one of charged mode, B(ρ^±→π^±γ) = (4.5±0.5)×10^-4. Received: 7 January 2002 / Accepted: 2 April 2002     

MSSM Higgs sector CP violation at photon colliders: revisited

The CP violating phases in soft SUSY breaking terms may induce indirect CP violation in the neutral Higgs boson sector through SUSY particle loops as well as direct CP violation in the γγ→H_i (i=1,2,3) through CP violating vertices. We present a complete analysis of the MSSM Higgs sector CP violation at photon colliders including the chargino loop contributions in the regime , where the CP violating mixing in the neutral Higgs sector is very strongly influenced by the scalar top loop, more so than the chargino and neutralino ones. However, the CP violating phases of the higgsino and wino mass parameters may still generate direct CP violation in γγ→H_i. In this process, the CP violating phenomena become very rich, and thus we study the production rates and polarization asymmetries in the Higgs production in detail. Photon colliders with high luminosity and well controlled polarized initial photon beams are indispensable in determining the CP properties of neutral Higgs bosons. PACS 14.80.Cp; 12.60.Jv; 11.30.Er     

Designing Klod detector prototypes and results of their experimental tests

The projected KLOD facility is intended for finding and investigating the ultrarare decay K _L ⁰ → π⁰ν$ \bar \nu $ \bar \nu ; its branching ratio predicted by the Standard Model is Br = (3.0 ± 0.6) × 10⁻¹¹. Designing and testing the prototype of the decay-volume veto system and beam veto calorimeter, which are the most important detectors of the facility, are considered. It is shown that the proposed beam veto calorimeter is able to detect γ rays with a high efficiency at the neutron flux of 300 MHz.     

Multi-photon signatures at the Fermilab Tevatron

Fermiophobic Higgs bosons (h_f) exhibiting large branching ratios for decay to two photons can arise in models with two or more scalar doublets and/or triplets. In such models the conventional production mechanisms at hadron colliders, which rely on the h_fVV coupling (V=W,Z), may be rendered ineffective due to severe mixing angle suppression. In this scenario, double h_f production may proceed via the complementary mechanism qq’→H^±h_f with subsequent decay H^±→h_fW^*, leading to events with up to four photons. We perform a simulation of the detection prospects of h_f in the multi-photon (>3) channel at the Fermilab Tevatron and show that a sizeable region of the (m_H±,m_hf) parameter space can be probed during Run II.     

Search for Higgs bosons decaying to WW in e+e- collisions at LEP

A search for Higgs bosons produced in association with a fermion pair, and decaying to WW, is performed with the data collected by the ALEPH detector at centre-of-mass energies ranging from 191 to 209 GeV. The data correspond to an integrated luminosity of 453.2 pb^-1. Thirteen exclusive selections are developed according to the different final state topologies. No statistically significant evidence for a Higgs boson decaying into a WW pair has been found. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e⁺e^-→Hff̄ cross section and the H→WW branching ratio. The data on the search for H→WW are combined with previously published ALEPH results on the search for H→γγ, to significantly extend the limits on the mass of a fermiophobic Higgs boson.     

Quark-Antiquark states and their radiative transitions in terms of the spectral integral equation: Bottomonia

In the framework of the spectral integral equation, we consider the states and their radiative transitions. We reconstruct the interaction on the basis of data for the levels of the bottomonium states with J ^PC = 0⁻⁺, 1⁻⁻, 0⁺⁺, 1⁺⁺, 2⁺⁺ as well as the data for the radiative transitions γ (3S) → _γχbJ(2P) and γ(2S) → _γχbJ(1P) with J = 0, 1, 2. We calculate bottomonium levels with the radial quantum numbers n ≤ 6, their wave functions, and corresponding radiative transitions. The ratios Br[_χbJ(2P) → _γγ(2S)]/Br[_χbJ(2P) → _γγ(1S)] for J = 0, 1, 2 are found to be in agreement with data. We determine the component of the photon wave function using the data for the e ⁺ e ⁻ annihilation, e ⁺ e ⁻ → γ(9460), γ(10 023), γ(10 036), γ(10 580), γ(10 865), γ(11 019), and predict partial widths of the two-photon decays ηb0 → γγ, χb0 → γγ, χb2 → γγ for the radial excitation states below the threshold (n ≤ 3). The text was submitted by the authors in English.     

μ → <Emphasis Type="Italic">e</Emphasis>γ decay versus the μ → <Emphasis Type="Italic">eee</Emphasis> bound and lepton flavor violating processes in supernova

Even tiny lepton flavor violation (LFV) due to some New Physics is able to alter the conditions inside a collapsing supernova core and probably to facilitate the explosion. LFV emerges naturally in a see-saw type-II model of neutrino mass generation. Experimentally, the LFV beyond the Standard Model is constrained by rare lepton decay searches. In particular, strong bounds are imposed on the μ → eee branching ratio and on the μ-e conversion in muonic gold. Currently, the μ→eγ is under investigation in the MEG experiment that aims at a dramatic increase in sensitivity in the next three years. We seek a see-saw type-II LFV pattern that fits all the experimental constraints, leads to Br(μ →eγ) ≳ Br(μμ →eee), and ensures a rate of LFV processes in supernova high enough to modify the supernova physics. These requirements are sufficient to eliminate almost all freedom in the model. In particular, they lead to the prediction 0.4 × 10⁻¹² ≲ Br(μ → eγ) ≲ 6 × 10⁻¹², which will be testable by MEG in the nearest future. The considered scenario also constrains the neutrino mass-mixing pattern and provides lower and upper bounds on τ-lepton LFV decays. We also briefly discuss a model with a single bilepton in which the μ → eee decay is absent at the tree level.     

Exploring the di-photon decay of a light Higgs boson in the MSSM with explicit CP violation

The di-photon decay channel of the lightest Higgs boson is considered as a probe to explore CP violation in the minimal supersymmetric standard model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs–sfermion–sfermion couplings, with and without light sparticles. The impact of a light stop on the decay width and branching ratio (BR) is established through a detailed study of the amplitude of the process H₁→γγ. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM parameters, a light stop can change the BR by more than 50% with a CP-violating phase φ_μ∼90°, while the change is almost nil with a heavy stop.