NonleptonicΛ b decays at colliders

We discuss nonleptonic two-body decays of _b baryons, which may be studied in the near future at colliders.     

Higgs boson physics in the s-channel at μ+μ− colliders

Techniques and strategies for discovering and measuring the properties of Higgs bosons via s-channel production at a μ⁺μ⁻ collider, and the associated requirements for the machine and detector, are discussed in detail. The unique feature of s-channel production is that, with good energy resolution, the mass, total width and partial widths of a Higgs boson can be directly measured with remarkable accuracy in most cases. For the expected machine parameters and luminosity the standard model (SM) Higgs boson h_SM, with mass ≲ 2m_W, the light h⁰ of the minimal supersymmetric standard model (MSSM), and the heavier MSSM Higgs bosons (the CP-odd A⁰ and the CP-even H⁰) can all be studied in the s-channel, with the heavier states accessible up to the maximal √s over a large fraction of the MSSM parameter space. In addition, it may be possible to discover the A⁰ and H⁰ by running the collider at full energy and observing excess events in the bremsstrahlung tail at lower energy. The integrated luminosity, beam resolution and machine/detector features required to distinguish between the h_SM and h⁰ are delineated.     

Searches for the decay D 0 → µ+µ− at hadron colliders

Investigations of rare charmed-meson decays are used to test the Standard Model and to perform searches for new physics beyond it. Advances made in searches for the rare decay D ⁰ → µ⁺µ^? in experiments at the HERA and Tevatron hadron colliders and at the LHC over the last few years are considered.     

The search for D 0 → μ+μ− decay

Studies of rare decays of charmed mesons are used to test the Standard Model and search for new physics. In the present paper we review the progress in the experimental methods of searching for the D ⁰→μ⁺μ^? rare decay in recent studies of proton-nuclear and hadron-hadron interactions.     

Leptonic decays of vector mesons and a possible μ+μ− resonance

The possible existence of a vector leptonic resonance (⁰) in the ^+– system is considered. We discuss the effect such a resonance would have on the g factor of the muon and also on the ratio of the partial widths of the muonic and electronic decay modes (R_V = (V ^+–)/G (V e⁺ e^–)) of the neutral vector mesons ⁰,,,, and. From the experimental values of R and R, the following values are obtained for the mass, coupling constant, and partial decay widths of the resonance: M = 872 ± 60 MeV, f²/4 = 4 ± 2) ·10^–4, ( ^{0 + –}) = 0.12±0.06 MeV, and (^{0 0 +–}) = 0.13±0.06 MeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 39–43, May, 1977.     

Search for lepton number violating decays B+ → π- μ+ μ+ and B+ → K- μ+ μ+

A search is performed for the lepton number violating decay B+ → h- μ+ μ+, where h- represents a K- or a π-, using an integrated luminosity of 36 pb(-1) of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B+ → K- μ+ μ+) < 5.4×10(-8) and B(B+ → π- μ+ μ+) < 5.8×10(-8) are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

Search for B(s)(0) → μ+ μ- and B(0) → μ+ μ- decays in pp collisions at sqrt[s] = 7 TeV

A search for the rare decays B(s)(0) → μ+ μ- and B(0) → μ+ μ- is performed in pp collisions at sqrt[s] = 7 TeV, with a data sample corresponding to an integrated luminosity of 1.14 fb(-1), collected by the CMS experiment at the LHC. In both cases, the number of events observed after all selection requirements is consistent with expectations from background and standard-model signal predictions. The resulting upper limits on the branching fractions are B(B(s)(0) → μ+ μ-) < 1.9 × 10(-8) and B(B(0) → μ+ μ-)<4.6 × 10(-9), at 95% confidence level.     

Comparison ofW ±+jet andZ 0+jet production at hadron colliders

We analyse the lowest-order QCD production mechanisms forp \(\bar p\) →W ^±+jet andp \(\bar p\) →Z ⁰+jet to find possible differences in jet properties for the two processes.     

The Z′→WW→ℓ+ν+jet+jet signal at hadron colliders

We investigate the prospect of using the lepton-neutrino-jet-jet final state to examine Z′→WW production at high energy hadron colliders. We find that with a judicious selection of events the signal for a new (E₆) gauge boson is comparable to the ordinary QCD background and that, in spite of the small Z′ cross section, detection at a large luminosity super collider might be possible.     

Search for B(s)(0) → μ+ μ- and B(0) → μ+ μ- decays with CDF II

A search has been performed for B(s)(0) → μ+ μ- and B(0) → μ+ μ- decays using 7 fb(-1) of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of B(0) candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of B(B(0) → μ+ μ-) < 6.0 × 10(-9) at 95% confidence level. We observe an excess of B(s)(0) candidates. The probability that the background processes alone could produce such an excess or larger is 0.27%. The probability that the combination of background and the expected standard model rate of B(s)(0) → μ+ μ- could produce such an excess or larger is 1.9%. These data are used to determine B(B(s)(0)→ μ+ μ-) = (1.8(-0.9) (+1.1)) × 10(-8) and provide an upper limit of B(B(s)(0) → μ+ μ-) < 4.0 × 10(-8) at 95% confidence level.     

J/ψ production at large transverse momentum at hadron colliders

We calculateJ/ψ hadroproduction and emphasize the importance of theJ/ψ signal as a measure ofb \(\bar b\) production via the decayB→ψX and of the gluon structure function at lowx via χ hadroproduction followed by χ→ψγ decay. We compare with UA1 data and data at ISR energies and make predictions for ψ production at TEVATRON energies.     

Aspects of two-photon physics at lineare + e − colliders

We discuss various reactions at futuree ⁺ e ^– and colliders involving real (beamstrahlung or backscattered laser) or quasi-real (bremsstrahlung) photons in the initial state and hadrons in the final state. The production of two central jets with large transverse momentump _T is described in some detail; we give distributions for the rapidity andp _T of the jets as well as the di-jet invariant mass, and discuss the relative importance of various initial state configurations and the uncertainties that arise from the at present rather poor knowledge of the parton content of the photon. We also present results for mono-jet production where one jet goes down a beam pipe, for the production of charm, bottom and top quarks, and for single production ofW andZ bosons. Where appropriate, the two-photon processes are compared with annihilation reactions leading to similar final states. We also argue that the behaviour of the total inelastic cross section at high energies will probably have little impact on the severity of background problems caused by soft and semi-hard (minijet) two-photon reactions. We find very large differences in cross sections for all two-photon processes between existing desings for futuree ⁺ e ^– colliders, due to the different beamstrahlung spectra; in particular, both designs with 1 and 1 events per bunch crossing exist. The number of hadronic two-photon events is expected to rise quickly with the beam energy. Hadronic backgrounds will be even worse if thee ⁺ e ^– collider is converted into a collider.     

Detecting Rare J/ψ → μ+μ− Events in the CBM Experiment

Physics of Particles and Nuclei Letters - A simple and efficient trigger for selecting the rare $${J mathord{left/ {vphantom {J psi }} right. kern-0em} psi } to {{mu }^{ + }}{{mu }^{ -...     

Light charged Higgs scalars at high-energy e+e− colliders

We study the prospects for detecting light charged Higgs scalars (H^±) at future e⁺e⁻ colliders. Various two-Higgs-doublet models (2HDM) and a general multi-Higgs-doublet model (MHDM) are considered, all of which may contain a H^± in the discovery range of LEP2. The potentially troublesome cases of M_H^± ∼ M_W and M_H^± ∼ M_Z are discussed, as well as ways of distinguishing the different models.     

Bs,d → μ+μ- decays in a flavor changing Z' model decays in a flavor changing Z' model

We study the pure leptonic decays Bs,d→μ+μ- in a Flavor Changing Z' Model. Prom the recent measurements of the branching ratios β(Bs,d →μ+μ-).we have derived the bounds on the effective μ-μ-Z' lepton coupling BμμL. We find that, (i) if neglecting the contribution from the right-handed lepton coupling BμμR, we obtain 1.32 < BμμL < 3.32; (ii) if considering the contribution from the right-handed lepton coupling BμμR and setting BμμL = BμμR, we obtain 0.99 < BμμL < 2.19. Our results could be useful for researching Z' effects.     

Radiative corrections for associatedZH production at futuree + e − colliders

The \(ZHf\bar f\) four-point function is calculated in the one-loop approximation of the Standard Model and full analytic results are presented. The loop contributions due to both light and new heavy fermions are inspected in detail. The dominant mechanisms of Higgs-boson production from fermions are compared. The effect of radiative corrections on the cross section of \(f\bar f \to ZH\) including bremsstrahlung is studied. The spectrum of hard bremsstrahlung is integrated analytically. The implications for Higgs-boson searches at futuree ⁺ e ^? colliders in the energy range 200 \(200GeV \le \sqrt s \le 1.5TeV\) , which includes both LEP 2 and the Next Linear Collider, are analyzed. ForM _H <2m _t weak corrections in the modified on-mass-shell scheme are generally negative and feebly vary withM _H , while forM _H >2m _t , they strongly increase withM _H and may take large positive values. Electromagnetic corrections dramatically reduce the cross section close to theZH-production threshold, while they may considerably enhance it far above this threshold.