Recent results on strangeness,charm and beauty production at HERA

Based on the data collected with the H1 and ZEUS detectors at HERA,recent results on strangeness,charm and beauty production in ep collision are presented.     

Recent results from fixed target charm and beauty experiments

In the last year there have been new observations of beauty by two fixed target experiments (E672/706 and E653). A few new results on charm have recently been presented by the photoproduction experiment E687 and by E789 and E769. An intriguing result on the purely muonic decay of charm comes from the CERN experiment WA75. These results are summarized and we conclude with a hint of the promise of E791, the very high statistics charm experiment, which is beginning to produce physics results     

Open charm production at RHIC: Recent results from STAR

We report recent measurements on the open charm production in d+Au and p+p collisions at $\sqrt {s_{NN} } = 200$ GeV from the STAR detector at RHIC. The two independent measurements — direct open charm hadron (D⁰, D^* etc.) reconstruction and non-photonic single electron spectrum — provide consistent results. The mid-rapidity charm differential cross section per nucleon-nucleon collision from d+Au collisions at RHIC is $d\sigma _{c\bar c}^{NN} /dy = 0.30 \pm 0.04(stat.) \pm 0.09(syst.)$ mb, which is higher than predictions from most of the NLO pQCD calculations. Implications for charmonium production in Au+Au collisions will also be discussed.     

Diffractive open charm production in deep-inelastic scattering and photoproduction at HERA

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D^*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.     

Measuring beauty production in Pb-Pb collisions at the LHC via single electrons in ALICE

We present the expected ALICE performance for the measurement of the p _t-differential cross section of electrons from beauty decays in central Pb-Pb collisions at the LHC. for the ALICE Collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.     

Measurement of beauty production at HERA using events with muons and jets

A measurement of the beauty production cross section in ep collisions at a centre-of-mass energy of 319 GeV is presented. The data were collected with the H1 detector at the HERA collider in the years 1999-2000. Events are selected by requiring the presence of jets and muons in the final state. Both the long lifetime and the large mass of b-flavoured hadrons are exploited to identify events containing beauty quarks. Differential cross sections are measured in photoproduction, with photon virtualities Q² < 1 GeV², and in deep inelastic scattering, where 2 < Q² < 100 GeV². The results are compared with perturbative QCD calculations to leading and next-to-leading order. The predictions are found to be somewhat lower than the data.Received: 7 February 2005, Revised: 26 April 2005, Published online: 31 May 2005     

Measurement of charm and beauty dijet cross sections in photoproduction at HERA using the H1 vertex detector

A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum p_t ^jet1(2)>11(8) GeV in the central range of pseudo-rapidity -0.9<η^jet1(2)<1.3. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable x_γ ^obs. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.     

Next-to-Leading order QCD corrections to charged current charm production and the unpolarized and polarized strange sea at HERA

We discuss fixed target and ISR inclusive photon production and attempt a comparison between theory and experiments. The dependence of the theoretical predictions on the structure functions, and on the renormalization and factorization scales is investigated. The main result of this study is that the data cannot be simultaneously fitted with a single set of scales and structure functions. On the other hand, there is no need for an additional primordial to force the agreement between QCD predictions and experiments, with the possible exception of one data set. Since the data cover almost overlapping kinematical ranges this raises the question of consistency among data sets. A comparative discussion of some possible sources of experimental uncertainties is sketched. Received: 23 November 1998 / Published online: 22 March 1999     

A study of charm and anti-charm production in beauty decays with the OPAL detector at LEP

The branching ratio of beauty hadrons to final states containing two charm hadrons, Br(b , has been measured using an inclusive method in hadronic Z⁰ decays with the OPAL detector at LEP. The impact parameter significance of tracks opposite tagged b-jets is used to differentiate b decays from other decays. The result is where det. is the systematic uncertainty due to the modelling of the detector, and is the systematic uncertainty due to the modelling of the underlying physics. Using this result, the average number of charm plus anti-charm quarks produced in a beauty quark decay, n_c, is found to be 1.12 ^{+ 0.11}_-0.10.Received: 11 July 2003, Published online: 18 May 2004     

Open charm mesons and charmonia in magnetized strange hadronic matter

We investigate the in-medium masses of open charm mesons (D(\begin{document}$ D^0 $\end{document}, \begin{document}$ D^+ $\end{document}), \begin{document}$ \bar{D} $\end{document}(\begin{document}$ \bar{D^0} $\end{document}, \begin{document}$ D^- $\end{document}), \begin{document}$ D_s $\end{document}(\begin{document}$ {D_{s}}^+ $\end{document}, \begin{document}$ {D_{s}}^- $\end{document})) and charmonium states (\begin{document}$ J/\psi $\end{document}, \begin{document}$ \psi(3686) $\end{document}, \begin{document}$ \psi(3770) $\end{document}, \begin{document}$ \chi_{c0} $\end{document}, \begin{document}$ \chi_{c2} $\end{document}) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of a magnetic field, the number and scalar densities of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons result from their interactions with nucleons, hyperons, and the scalar fields (the non-strange field σ, strange field ζ, and isovector field δ) in the presence of a magnetic field. The mass modifications of the charmonium states result from the modification of gluon condensates in a medium simulated by the variation in the dilaton field (χ) in the chiral effective model. The effects of finite quark masses are also incorporated in the trace of the energy-momentum tensor in quantum chromodynamics to investigate the mass shifts of charmonium states. The in-medium masses of open charm mesons and charmonia are observed to decrease with an increase in baryon density. The charged \begin{document}$ D^+ $\end{document}, \begin{document}$ D^- $\end{document}, \begin{document}$ {D_{s}}^+ $\end{document}, and \begin{document}$ {D_{s}}^- $\end{document} mesons have additional positive mass shifts due to Landau quantization in the presence of a magnetic field. The effects of the strangeness fraction are observed to be more dominant for \begin{document}$ \bar{D} $\end{document} mesons compared with D mesons. The mass shifts of charmonia are observed to be larger in hyperonic media compared with nuclear media when the effect of the finite quark mass term is neglected. These medium mass modifications can have observable consequences on the production of the open charm mesons and charmonia in high-energy asymmetric heavy-ion collision experiments.     

Recent results on hadron spectroscopy from BES

The BES-Ⅲ Detector is a very versatile multipurpose device located at the Institute of High Energy Physics(IHEP) in Beijing,China.Concerning the physics program it ties stringently up to the past BES and BES-Ⅱ experiments.Since start of the data taking in the middle of 2008 the accumulated dataset of 200·106 J/ψ events and 100·106 ψ events already exceeds the world data on these resonances.In addition to studies of the charmonium systems the data offers great opportunity for investigations in the light hadron sector.In detail it will be reported about the confirmation of the enhancement in p invariant mass in radiative J/ψ decays,the search for decays Y(2175) → K0 K0,observation of a charged κ± in K±π0 and observation of a new excited baryon N(2065) decaying to pπ0 and charged conjugate.The first result is based on data taken by BES-Ⅱ and BES-Ⅲ,the latter three on data collected by BES-Ⅱ only.     

Diffraction at HERA, Color Opacity and Nuclear Shadowing in DIS off nuclei

The QCD factorization theorem for diffractive processes in DIS is used to derive formulae for the leading twist contribution to the nuclear shadowing of parton distributions in the low thickness limit (due to the coherent projectile (photon) interactions with two nucleons). Based on the current analyzes of diffraction at HERA we find that the average strength of the interactions which govern diffraction in the gluon sector at x≤ 10⁻³, Q ₀= 2 GeV is ∼50mb. This is three times larger than in the quark sector and suggests that applicability of DGLAP approximation requires significantly larger Q ₀ in the gluon sector. We use this information on diffraction to estimate the higher order shadowing terms due to the photon interactions with N≥ 3 nucleons which are important for the scattering of heavy nuclei and to calculate nuclear shadowing and Q ² dependence of gluon densities. For the heavy nuclei the amount of the gluon shadowing: G _A(x,Q ₀ ²) /AG _N(x,Q ₀ ²)_{|x ≤ 10−3}∼ 0.25–0.4 is sensitive to the probability of the small size configurations within wave function of the gluon “partonometer” at the Q ₀ scale. At this scale for A∼ 200 the nonperturbative contribution to the gluon density is reduced by a factor of 4–5 at x≤ 10⁻³ unmasking PQCD physics in the gluon distribution of heavy nuclei. We point out that the shadowing of this magnitude would strongly modify the first stage of the heavy ion collisions at the LHC energies, and also would lead to large color opacity effects in eA collisions at HERA energies. In particular, the leading twist contribution to the cross section of the coherent J/ψ production off A≥ 12 nuclei at s ⁻²≥ 70 GeV is strongly reduced as compared to the naive color transparency expectations. The Gribov black body limit for F _2A(x,Q ²) is extended to the case of the gluon distributions in nuclei and shown to be relevant for the HERA kinematics of eA collisions. Properties of the final states are also briefly discussed. Received: 12 March 1999     

Charm, beauty and charmonium production at HERA-B

is a fixed target experiment working on the 920 GeV proton beam of the HERA accelerator at the DESY laboratory in Hamburg. During the last data taking period (2002-2003), about 150 million dilepton triggers, 220 million minimum bias events and 35 million hard photon triggers were acquired. These large statistics allow detailed studies on the production of charmonium states in proton-nucleus p-A collisions, which extend for the first time into the negative Feynman-x () region. Measurements of the inclusive , and open charm cross sections are also ongoing. After a brief discussion of the detector and of the data samples, we report on preliminary results obtained on these physics topics. Arrival of the final proofs: 18 July 2005 PACS: 24.85.p, 13.85.Ni     

Recent results on hadron spectroscopy from BES

The BES-Ⅲ Detector is a very versatile multipurpose device located at the Institute of High Energy Physics （IHEP） in Beijing, China. Concerning the physics program it ties stringently up to the past BES and BES-Ⅱ experiments. Since start of the data taking in the middle of 2008 the accumulated dataset of 200.10^6 J/ψ events and 100.10^6 ψ＇ events already exceeds the world data on these resonances. In addition to studies of the charmonium systems the data offers great opportunity for investigations in the light hadron sector. In detail it will be reported about the confirmation of the enhancement in pp invariant mass in radiative J/ψ decays, the search for decays Y（2175） → K＊0K＊0, observation of a charged K^± in K^±π^0 and observation of a new excited baryon N＊（2065） decaying to pπ^0 and charged onjugate. The first result is based on data taken by BES-Ⅱ and BES-Ⅲ, the latter three on data collected by BES-Ⅱ only.     

Excited state mass spectra,decay properties and Regge trajectories of charm and charm-strange mesons

The framework of a phenomenological quark-antiquark potential(Coulomb plus linear confinement)model with a Gaussian wave function is used for detailed study of masses of the ground, orbitally and radially excited states of heavy-light Qq,(Q=c,q=u/d,s) mesons. We incorporate a O(1/m) correction to the potential energy term and relativistic corrections to the kinetic energy term of the Hamiltonian. The spin-hyperfine, spin-orbit and tensor interactions incorporating the effect of mixing are employed to obtain the pseudoscalar, vector, radially and orbitally excited state meson masses. The Regge trajectories in the(J,M~2) and(nr,M~2) planes for heavy-light mesons are investigated with their corresponding parameters. Leptonic and radiative leptonic decay widths and corresponding branching ratios are computed. The mixing parameters are also estimated. Our predictions are in good agreement with experimental results as well as lattice and other theoretical models.