K*0 and φ meson production in proton–nucleus interactions at ?s=41.6\textGeV\sqrt{s}=41.6\text{GeV}

The inclusive production cross sections of the strange vector mesons K^*0, K̄^*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to p_T = 3.5 GeV/c. The atomic number dependence is parametrised as σ_pA=σ_pN*A^α, where σ_pN is the proton–nucleon cross section. Within the phase space accessible, α(K^*0)=0.86±0.03, α(K̄^*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σ_pN→K*0=(5.06±0.54) mb, σ_pN→K̄*0=(4.02±0.45) mb, and σ_pN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K^± mesons, the measured values of α for φ mesons coincide with those of K⁺ mesons for all transverse momenta, while the enhancement for K^*0/K̄^*0 mesons is smaller.     

B* production in Z decays

The decayB ^*B has been observed with the DELPHI detector at LEP, where theB ^* meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB ^*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c². 95% confidence level upper limits at 6 MeV/c² are placed on both the isospin (i.e.B ⁺-B ⁰) and theB _s -B _ud splitting of the mass difference. The production ratio ofB ^* toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB ^* cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB ^* energy of x _E =0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB ^* polarisation states is measured to be _L/(_L + _T) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).CICYT_AEN93-0832     

Inclusive D*± meson cross sections and D*±-jet correlations in photoproduction at HERA

Differential photoproduction cross sections are measured for events containing D^*± mesons. The data were taken with the H1 detector at the ep collider HERA and correspond to an integrated luminosity of 51.1 pb^-1. The kinematic region covers small photon virtualities Q² < 0.01 GeV² and photon–proton centre-of-mass energies of 171 < W_γ p < 256 GeV. The details of the heavy quark production process are further investigated in events with one or two jets in addition to the D^*± meson. Differential cross sections for D^*+jet production are determined and the correlations between the D^*± meson and the jet(s) are studied. The results are compared with perturbative QCD predictions applying collinear- or k_t-factorisation.     

Nuclear matter properties in relativistic mean-field model with σ- ω coupling

The σ-ω coupling is introduced phenomenologically in the linear σ-ω model to study the nuclear matter properties. It is shown that not only the effective nucleon mass M^* but also the effective σ meson mass m _σ ^* and the effective ω meson mass m _ω ^* are nucleon-density-dependent. When the model parameters are fitted to the nuclear saturation point, with the nuclear radius constant r ₀ = 1.14 fm and volume energy a ₁ = 16.0 MeV, as well as to the effective nucleon mass M ^* = 0.85M, the model yields m _σ ^* = 1.09m _σ and m _ω ^* = 0.90m _ω at the saturation point, and the nuclear incompressibility K ₀ = 501 MeV. The lowest value of K₀ given by this model by adjusting the model parameters is around 227 MeV. Received: 23 March 2001 / Accepted: 8 June 2001     

Search for and study of low-mass scalar mesons in reaction np → npπ+π? at neutron beam momentum Pn = (5.20 ± 0.12) GeV/c

We present the results of a search for and study of the resonance effects in the system of π⁺π⁻ from the reaction np → npπ⁺π⁻ at the momentum of quasi-monochromatic neutrons P _n = (5.20 ± 0.12) GeV/c from the data obtained in an exposure of the 1-m hydrogen bubble chamber of Veksler and Baldin Laboratory of High Energies, Joint Institute for Nuclear Research (VBLHE JINR). After the supplementary selection of the events where a secondary proton was emitted in the forward hemisphere in the general c.m.s. of the reaction (cosθ* _p > 0) in the effective mass spectrum of π⁺π⁻ combinations, we found nine peculiarities at the masses (350 ± 3), (408 ± 3), (489 ± 3), (579 ± 5), (676 ± 7), (762 ± 11), (878 ± 7), (1036 ±13), and (1170 ± 11) MeV/c ² with experimental widths of no more than several tens of MeV/c ². We carried out a direct measurement of the spins of resonances and also obtained other quantum numbers. All of these peculiarities have a similar set of quantum numbers I ^G (J ^PC ) = 0⁺ (0⁺⁺). We investigated a sequence of scalar-isoscalar resonances f ₀(σ₀) with masses in the range M ≤ 1200 MeV/c ². We found a phenomenological dependence of the resonance mass on its number. This dependence covered not only the resonances shown in this paper, but also those present in PDG tables with quantum numbers of f ₀(σ₀) mesons.     

B* production in Z0 decays

The process B*→Bγ has been observed in a sample of approximately 4.1 million hadronic Z⁰ decays collected by the OPAL detector at LEP in the years 1991–1995. Inclusively reconstructed B mesons have been combined with converted photons to reconstruct approximately 1900 B* mesons. The B*–B mass difference is found to be ΔM(B* ?B) = 46.2 ± 0.3 ± 0.8 MeV/c ², and the rate of B* meson production relative to that of B mesons is found to be σ _B*/σ _B = 0.760 ± 0.036 ± 0.083, where the first errors are statistical and the second systematic. The angular distribution of the transition photon in the B* rest frame has been measured and the relative contribution of longitudinal B* polarization states found to be σ _l/(σ _l + σ _t ) = 0.36 ± 0.06 ± 0.07, consistent with a simple spin counting picture. These results average over B⁰, B± and B _s ⁰ mesons.     

Improved measurement of theB0 andB+ meson lifetimes

The lifetimes of theB ⁰ andB ⁺ mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB ⁰ andB ⁺ mesons were partially reconstructed by identifying events containing a lepton with an associatedD*⁻ or meson. The second method used fully reconstructedB ⁰ andB ⁺ mesons. The third method, used to measure theB ⁰ lifetime, employed a partial reconstruction technique to identifyB ⁰→D*⁻ π ⁺ X decays.     

Calculation of the photoionization with deexcitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li⁺ and B³⁺ at high but nonrelativistic photon energies θ. Several lower ¹ S and ³ S states are considered. We present and analyze the ratios R _d ⁺ * of the cross sections of photoionization with deexcitation, σ _(d) ⁺ *(θ), and of the photoionization with excitation, σ⁺*(θ). The dependence of R _d ⁺ * on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest, the results obtained can be verified using long-lived excited states such as 2³ S of He. The text was submitted by authors in English.     

Measurement of D* mesons in jets from p + p collisions at ?s \sqrt s = 200 GeV

We report the measurement of charged D* mesons in jets produced in proton-proton collisions at a center of mass energy $ \sqrt s $ \sqrt s = 200 GeV with the STAR experiment at RHIC. The production rate is found to be N(D*⁺ + D*⁻)/N (jet) = 0.015 ± 0.008 (stat) ± 0.007 (sys) for D* mesons with fractional momenta 0.2 < z < 0.5 in jets with 11.5 GeV mean transverse energy. This rate is consistent with perturbative QCD evalulation of gluon splitting into a pair of charm quarks and subsequent hadronization.     

Probing meson spectral functions with double differential dilepton spectra in heavy-ion collisions

The double differential dilepton spectrum d/(d ² d _⊥ ²) at fixed transverse mass M _⊥ allows a direct access to the vector meson spectral functions. Within a fireball model the sensitivity of d/(d ² d _⊥ ²) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum d/d ², in the spectrum d/(d ² d _⊥ ²) with fixed M _⊥ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.[3mm] Received: 16 November 2000 / Accepted: 16 January 2001     

The strong coupling constants of excited positive parity heavy mesons in light-cone QCD

We calculate the strong coupling constants g_p^**p^*π, where P^** (D^**, B^**) is the 1⁺ p-wave state, in the framework of the light-cone QCD sum rules, and using these values ofg_p^**p^*π , we compute the hadronic decay widths forD^** → D^* π and B^** → B^* π.     

Diffractive S and D wave vector mesons in deep inelastic scattering

Helicity amplitudes for diffractive leptoproduction of the S and D wave states of vector mesons are derived. A dramatically different spin dependence for production of the S and D wave vector mesons is predicted. It is found that R=σ_L/σ_T is very small and that the higher twist effects in the production of longitudinally polarized D wave vector mesons are abnormally large. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 268–273 (25 February 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

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.     

Predictions for the forward cone in diffractive deep inelastic scattering

We calculate the diffraction slope B _D for diffractive deep inelastic scattering. We find a counterintuitive rise of B _D in going from exclusive diffractive excitation of vector mesons to excitation of continuum states with M ²∼Q ². For the small-mass continuum we predict a rapid variation of B _D with M ² on a scale of m _V ² and a sharp drop of B _D for a small-mass continuum above the vector meson excitation. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 604–609 (25 October 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Scalar σ meson at a finite temperature in a nonlocal quark model

The properties and temperature behavior of the π and σ bound states are studied in the framework of the nonlocal model with a separable interaction kernel, based on the quark Dyson-Schwinger and meson Bethe-Salpeter equations. M _π(T), f _π(T), M _σ(T), and Γ_{σ → ππ}(T) are considered above and below the deconfinement and chiral restoration transitions. Talk at the Round-Table Discussion “Searching for a Mixed Phase of Strongly Interacting Matter at the JINR Nuclotron,” Dubna, July 7–9, 2005. The text was submitted by the authors in English.     

Electroproduction of <Emphasis Type="Italic">ρ</Emphasis><Superscript>0</Superscript> mesons on protons in quasielastic kinematics at intermediate energies and spin-flip mechanism of direct meson knockout

It is shown that the amplitude for the direct knockout of ρ ⁰ mesons plays an important role at energies W above the resonance region, W ≳ 2 GeV, and rather high values of Q ² ≳ 1.5−2 GeV²/c ² and that it corresponds to the t pole in the channel of the virtual decay p → p + π ⁰ accompanied by quark-spin flip upon momentum transfer to the meson, π ⁰ + γ* _T → ρ ⁰. The contributions of several scalar mesons (p → p + f ₀ channel), the contribution of the tensor meson f ₂, and effects of the interference between different contributions were taken into account in addition to the contribution of the π ⁰ meson. The vectorand tensor-meson-dominance models were used to estimate the respective vertex constants. Within the proposed mechanism, the differential cross sections dσ _L /dt and dσ _T /dt were calculated for several W and Q ² values at which the respective total cross sections were measured by the CLAS Collaboration. Agreement with data on the transverse part of the total cross section, σ _T , was attained, whereby the assumption of a dominant role of magnetic spin transitions in the meson skin of the nucleon under conditions of quasielastic-knockout kinematics is confirmed. At the same time, the contribution of spin-flip transitions is suppressed in the longitudinal part of the cross section, σ _L , and this is confirmed by the results of our calculations. The behavior of the differential cross section dσ _T /dt is predicted with an eye to future experiments.     

Effects of Final State Interactions in Pure Annihilation Decay of B+ → D+K0*

The decay of the B ⁺ meson to the D ⁺ and K ⁰* mesons is a pure annihilation decay. For this reason, in the framework of the quantum chromodynamics factorization (QCDF) approach, this decay has a small amplitude and a small branching ratio. In this research we find that, before the D ⁺ and K ⁰* mesons are produced in the final states, pair mesons such as D _s ⁺* and D _s ⁺ρ⁰ are produced. The intermediate-state mesons via the exchange of K ⁰(K ⁰*) and D ⁺(D ⁺*) go to the D ⁺ and K ⁰* final state mesons. However we calculate the B ₊ → D ⁺ K ⁰* decay in two different frameworks. The first framework is the QCDF method and the second one is final state interaction (FSI). The experimental branching ratio of B ₊ → D ₊ K ⁰* decay is less than 3 × 10^–6, and our results obtained by the QCDF method and FSI are (0.35 ± 0.04) × 10^–6 and (2.94 ± 0.10) × 10^–6, respectively.     

Composite-meson model and meson exchange currents

We study the meson exchange currents (MEC) mechanism for the pion double-charge exchange (DCX) reaction in a composite-meson model. The model assumes that the mesons are two-quark systems and can interact with each other only through quark loops. The contributions of the ρ, σ, and f₀ mesons, the four-quark box diagram as well as a contact diagram has been taken into account. It is shown that the contribution of the ρ, σ, and f₀ mesons increases the forward scattering cross-section in an average by 25% and decreases with energy.     

Bs,d→ππ,πK,KK: status and prospects

Several years ago, it was pointed out that the U-spin-related decays B_d→π⁺π^-, B_s→K⁺K^- and B_d→π^∓K^±, B_s→π^±K^∓ offer interesting strategies for the extraction of the angle γ of the unitarity triangle. Using the first results from the Tevatron on the B_s decays and the B-factory data on B_u,d modes, we compare the determinations of γ from both strategies, study the sensitivity on U-spin-breaking effects, discuss the resolution of discrete ambiguities, predict observables that were not yet measured but will be accessible at LHCb, explore the extraction of the width difference ΔΓ_s from untagged B_s→K⁺K^- rates, and address the impact of new physics. The data for the B_d→π⁺π^-, B_s→K⁺K^- system favour the BaBar measurement of direct CP violation in B_d→π⁺π^-, which will be used in the numerical analysis and result in a fortunate situation, yielding γ=(66.6^+4.3+4.0 _-5.0-3.0)^°, where the latter errors correspond to a generous estimate of U-spin-breaking effects. On the other hand, the B_d→π^∓K^±, B_s→π^±K^∓ analysis leaves us with 26°≤γ≤70°, and points to a value of the B_s→π^±K^∓ branching ratio that is larger than the current Tevatron result. An important further step will be the measurement of mixing-induced CP violation in B_s→K⁺K^-, which will also allow us to extract the B⁰ _s–B̄⁰ _s mixing phase unambiguously with the help of B_s→J/ψφ at the LHC. Finally, the measurement of direct CP violation in B_s→K⁺K^- will make the full exploitation of the physics potential of the B_s,d→ππ,πK,KK modes possible.     

Possible tetraquark states in the <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">χ</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis>1</Subscript> invariant-mass distribution

In this article, we assume that there exist hidden charmed tetraquark states with spin–parity J ^P=1⁻, and we calculate their masses with the QCD sum rules. The numerical result indicates that the masses of the vector hidden charmed tetraquark states are about M _Z =(5.12±0.15) GeV or M _Z =(5.16±0.16) GeV, which are inconsistent with the experimental data on the π ⁺ χ _c1 invariant-mass distribution. The hidden charmed mesons Z ₁, Z ₂ or Z may be scalar hidden charmed tetraquark states, hadro-charmonium resonances or molecular states.