Search for <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript> → <Emphasis Type="Italic">ϕ</Emphasis>µµ decay at the Large Hadron Collider

As B _s -mesons will be produced abundantly at the LHC, the observability of the flavour-changing-neutral-current decay mode B _s → ϕμ⁺μ⁻ has been studied in CMS at the LHC centre-of-mass energy of 10 TeV. With an integrated luminosity of 100 pb⁻¹, an upper limit of 6.7 × 10⁻⁶ on the branching ratio is expected to be obtained. The potential at 7 TeV with a luminosity of 1 fb⁻¹ is expected to be better.     

Analysis of Bs→φ?+?? decay with new-physics effects

The rare B _s →φ ℓ ⁺ ℓ ⁻decay is investigated by using the most general model-independent effective Hamiltonian for ℓ=μ,τ. The calculated value of Br(B _s →φ μ ⁺ μ ⁻)=1.92×10⁻⁶ is consistent with the experimental upper bound. The dependencies of the branching ratios and polarization asymmetries of leptons and combined lepton–antilepton asymmetries on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton-polarization asymmetries are very sensitive to scalar- and tensor-type interactions. The results obtained in this work will be very useful in searching new physics beyond the standard model.     

Search for <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript> → µµ<Emphasis Type="Italic">γ</Emphasis> at large hadron collider

The branching ratio for B _s → ℓ⁺ℓ⁻ γ mode is of the same order as B _s → ℓ⁺ℓ⁻, since there is no helicity suppression in the 3-body decay mode. New Physics beyond Standard Model may affect these rates favourably for experimental observation at LHC and simultaneous measurements of the modes B _s → μ⁺μ⁻ and B _s → μ⁺μ⁻ γ at LHC experiment will indicate the basic nature of the interaction at play. A simulation study has been performed to evaluate the potential of CMS detector to observe the more difficult mode of B _s → μ⁺μ⁻γ. An upper limit of 2.08 × 10⁻⁷ on the branching ratio is expected to be achieved corresponding to an integrated luminosity of 10 fb⁻¹.     

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     

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     

Rescattering and electroweak penguin effects in strategies to constrain and determine the CKM angle γ from B → πK decays

A general parametrization of the B ⁺ → π ⁺ K ⁰ and B _d ⁰ → π ⁻ K ⁺ decay amplitudes is presented. It relies only on the isospin symmetry of strong interactions and the phase structure of the Standard Model and involves no approximations. In particular, this parametrization takes into account both rescattering and electroweak penguin effects, which limit the theoretical accuracy of bounds on γ arising from the combined B ^+- → π ^+- K, B _d → π ^∓ K ^± branching ratios. Generalized bounds making also use of the CP asymmetry in the latter decay are derived, and their sensitivity to possible rescattering and electroweak penguin effects is investigated. It is pointed out that experimental data on B ^± → K ^± K allow us to include rescattering processes in these bounds completely, and an improved theoretical treatment of electroweak penguins is presented. It is argued that rescattering effects may enhance the combined B ^± → K ^± K branching ratio by a factor of O(10) to the 10⁻⁵ level, and that they may be responsible for the small present central value of the ratio of the combined B _d → π ^∓ K ^± and B ^± → π ^± K branching ratios, which has recently been reported by the CLEO collaboration and, if confirmed, would exclude values of γ within a large region around 90°.     

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.     

Strange hadron production in Σ-<Emphasis Type="Italic">A</Emphasis> interactions in the SELEX experiment

We report our observations on the resonance signals of masses of 1520, 1670, 1810 (1 820), and 2100 MeV c ⁻², produced inclusively in the reaction Σ⁻ + C(Cu) → p + K⁻ + X, and the signals of masses of 1020 and 1525 MeV c ⁻², produced inclusively in the reaction Σ⁻ + C(Cu) → K⁺ + K⁻ + X, with a 600-GeV c ⁻¹- momentum hyperon beam in the SELEX experiment at the Fermilab. The masses, widths, and branching ratios were measured. The resonance signal of mass of 1520 MeV c ⁻² correspond to the known Λ(1520) hyperon. The signals of masses of 1020 and 1525 MeV c ⁻² in the K⁺K⁻ system correspond to the φ⁰(1020)- and f ₂′(1525) mesons, respectively. The branching ratio of the resonance of mass of 1670 MeV c ⁻² relative to Λ(1520) is (24.92 ± 0.45 ± 0.48)%, while that of the resonance of mass of 1810 (or 1 820) MeV c ⁻² relative to Λ(1520) is (16.13 ± 0.38 ± 0.45)%. The branching ratio of the f ₂′(1525) resonance relative to φ⁰(1020) is (10.75 ± 0.25 ± 0.45)%. Data analysis was performed over 6 × 10⁷ trigger events registered by the SELEX setup on the FNAL Tevatron.     

Measurement of ω/? → e+e? in proton + proton collisions at ?s \sqrt s = 200 GeV at RHIC-PHENIX

The PHENIX experiment at RHIC has measured ω and ϕ meson production using di-electron decay mode over a psude-rapidity range of |η| ≤ 0.35 and a transverse momentum range of 0 < p _T < 5 GeV/c in proton + proton collisions at $ \sqrt s $ \sqrt s = 200 GeV. The spectra of production cross section as a function of p _T for ω and ϕ → e ⁺ e ⁻ show good agreement with other hadornic decay channels ω → π ⁰ γ, ω ⁰ π ⁺ π ⁻ and ϕ → K ⁺ K ⁻, respectively.     

Phenomenological applications of<Emphasis Type="Italic">k</Emphasis><Subscript>T</Subscript>factorization

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-bodyB-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct CP asymmetry in B⁰ → π⁺π⁻ (23 +7%) and B⁰ →K ⁺π⁻ (− 17 ± 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiativeB →(K*/ρ)γ decays.     

Comments on preliminary data on the reactions e + e −→φ→γ f 0(980)→γπ0π0

Preliminary data on the reactions e ⁺ e ⁻→φ→γ f ₀(980)→γπ⁰π⁰ together with data on ππ scattering and the reactions J/ψ→φπ⁺π⁻ and K ⁻ p→π ⁺π⁻(Λ,Σ) are analyzed. The analysis shows that the mass of the f ₀(980) meson is = 950 MeV, and BR(φ→γf ₀→γπ⁰π⁰)≃ 1× 10⁻⁴, indicating that the f ₀(980) resonance is of a four-quark nature. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 445–449 (10 April 1998)     

Radiative kaon decay in the chiral perturbation theory

We analyze the possibility of experimental investigation of new low-energy relations between the values of resonance masses in the meson form factors and the differential rate of radiative kaon decay K ⁺ → π⁺ e ⁺ e ⁻(μ⁺μ⁻) at the current level of the experimental precision. A set of arguments is listed in favor that these relations can be a consequence of weak static interactions in the Standard Model. The results were presented at the 5th NA48 Mini-Workshop on Kaon Physics, CERN, Dec. 12, 2006. The text was submitted by the authors in English.     

Experimental study of direct photon emission in K/it− → π−π0γ decay using ISTRA+ detector

The branching ratio in the charged-pion-kinetic-energy region of 55 to 90 MeV for the direct photon emission in the K ⁻ → π⁻π⁰γ decay has been measured using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV/c negative secondary beam of the U-70 PS. The value Br(DE)=[0.37±0.39(stat.)±0.10(syst.)]×10⁻⁵ obtained from the analysis of 930 completely reconstructed events is consistent with the average value of two stopped-kaon experiments, but it differs by 2.5 standard deviations from the average value of three in-flight-kaon experiments. The result is also compared with recent theoretical predictions. The text was submitted by the authors in English.     

An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane ⁺ e ⁻ pair in the decay of the 3.68 MeV (3/2) state in¹³C, whose decay is predominantly M1, are presented. An upper limit of 7 × 10⁻⁵ has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c². This leads to an upper limit of 10⁻⁶ for the coupling of such a particle to nucleons. Such a limit rules out the explanation of thee ⁺ ande ⁻ peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.     

Scalar mesons in the decays η′ → 3π0 and η′ → π0π+π?

The decays η → 3π ⁰ and η → π ⁰ π ⁺ π ⁻ are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz plot for the decay η′ → 3π ⁰, it is sufficient to take into account the contributions of the σ and a ₀ mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay η′ → π ⁰ π ⁺ π ⁻ is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend strongly on model parameters.     

Form factors and branching ratio for the B→lνγ decay

Form factors parameterizing radiative leptonic decays of heavy mesons (B⁺→γl⁺ν_l) against photon energy are computed in the language of dispersion relations. The states contributing to the absorptive part in the dispersion relation are the multiparticle continuum, estimated by the quark triangle graph, and resonances with quantum numbers 1^- and 1⁺, which includes B^* and B_A ^* and their radial excitations, which model the higher state contributions. Constraints provided by the asymptotic behavior of the structure dependent amplitude, Ward identities and gauge invariance are used to provide useful information for the parameters needed. The couplings g_BB*γ and f_BBA*γ are predicted as we restrict ourselves to the first radial excitation; otherwise using these as an input the radiative decay coupling constants for the radial excitations are predicted. The value of the branching ratio for the process B⁺→γμ⁺ν_μ is found to be in the range 0.5×10^-6. A detailed comparison is given with other approaches.     

B→K1?+?? decays in a family non-universal Z′ model

The implications of the family non-universal Z′ model in the B→K ₁(1270,1400)ℓ ⁺ ℓ ⁻(ℓ=e ,μ ,τ) decays are explored, where the mass eigenstates K ₁(1270, 1400) are the mixtures of ¹ P ₁ and ³ P ₁ states with the mixing angle θ. In this work, considering the Z′ boson and setting the mixing angle θ=(−34±13)^○, we analyze the branching ratio, the dilepton invariant mass spectrum, the normalized forward–backward asymmetry and lepton polarization asymmetries of each decay mode. We find that all observables of B→K ₁(1270)μ ⁺ μ ⁻ are sensitive to the Z′ contribution. Moreover, the observables of B→K ₁(1400)μ ⁺ μ ⁻ have a relatively strong θ-dependence; thus, the Z′ contribution will be buried by the uncertainty of the mixing angle θ. Furthermore, the zero crossing position in the FBA spectrum of B→K ₁(1270)μ ⁺ μ ⁻ at low dilepton mass will move to the positive direction with Z′ contribution. For the tau modes, the effects of Z′ are not remarkable due to the small phase space. These results could be tested in the running LHC-b experiment and Super-B factory.     

Study of Bs→φ?+?? decay in a single universal extra dimension model

Using form factors derived from the light-cone sum rules, we investigate B _s →φℓ ⁺ ℓ ⁻ (ℓ=e,μ,τ) in a single universal extra dimension model (UED). In UED, there is only one new parameter with respect to the Standard Model (SM), which is the inverse of the compactification radius R of the extra dimension. In this work, the branching ratios, the dilepton invariant mass spectra, the forward–backward asymmetries, and the lepton polarization asymmetries of B _s →φℓ ⁺ ℓ ⁻ are calculated. For a lower value of 1/R, there are some considerable discrepancies between the UED and SM. However, with the increase of 1/R, the effect of UED tends to diminish; in particular for 1/R≥1000 GeV, two models have approximately the same predictions. Compared with data from CDF for B _s →φμ ⁺ μ ⁻, we find that the 1/R tends to be larger than 350 GeV. We also find that the zero crossing point of the forward–backward asymmetry of B _s →φμ ⁺ μ ⁻ becomes smaller, which would be an important platform for probing the UED effect. These results could be tested in the Large Hadron Collider (LHC) at CERN and the future super-B factory.     

Production of electron-positron pairs by a photon propagating in a strongly magnetized thermal bath

The production of electron-positron pairs by a photon propagating in a thermal bath in both zero and strong (B ≫ 4.41 × 10¹³ G) magnetic fields has been considered. The mean free path has been calculated for the high-energy photon propagating through a thermodynamically equilibrium photon gas along the magnetic field lines so that the γ → e ⁻ e ⁺ decay is kinematically forbidden. It has been shown that the strong magnetic field suppresses the probability of the γγ′ → e ⁻ e ⁺ process. The analyzed process can be useful for analysis of possible mechanisms of the generation of the e ⁻ e ⁺ plasma in the regions of the polar caps of magnetars.     

Search for low-mass exotic mesonic structures: II. Attempts to understand the results

Our previous paper, part I of the same study, shows the different experimental spectra used to draw a conclusion on the genuine existence of narrow, weakly excited mesonic structures having masses below and a little above the pion (M = 139.56 MeV) mass. This study [1] was instigated by the observation, in the Σ⁺ disintegration—Σ⁺ → pP ⁰, P ⁰ → μ⁻μ⁺ [2]—of a narrow range of dimuon masses. The authors make a conclusion on the existence of a neutral intermediate state P ₀ with a mass M = (214.3 ± 0.5) MeV. We present here some attempts to understand the possible nature of the structures observed in part I. The text was submitted by the authors in English.