Measurement of charm fragmentation ratios and fractionsin photoproduction at HERA

The production of , D⁰, D ⁺ , D_s ⁺ and charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of . The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality and for photon-proton centre-of-mass energies in the range . The charm hadrons were reconstructed in the range of transverse momentum and pseudorapidity . The production cross sections were used to determine the ratio of neutral and charged D-meson production rates, , the strangeness-suppression factor, , and the fraction of charged D mesons produced in a vector state, . The measured and values agree with those obtained in deep inelastic scattering and in e ⁺ e^- annihilations. The measured value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, , were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured is smaller and is larger than those obtained in e ⁺ e^- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process. Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005     

Search for lepton-flavor violation at HERA

A search for lepton-flavor-violating interactions and has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of . The data were taken at center-of-mass energies, , of 300 and . No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below , limits were set on , where is the coupling of the LQ to an electron and a first-generation quark q₁, and is the branching ratio of the LQ to the final-state lepton (μ or ) and a quark q. For LQ masses much larger than , limits were set on the four-fermion interaction term for LQs that couple to an electron and a quark and to a lepton and a quark , where and are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process , the ZEUS limits are the most stringent to date. Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005     

Neutral pion production in d-Au collisions at \sqrt{s_{NN}} = 200 GeV

In this paper, preliminary results are presented on high inclusive neutral pion measurements in d-Au collisions at GeV in the pseudo-rapidity range . Photons from the decay are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations. Arrival of the final proofs: 4 July 2005 PACS: 25.75.-q     

Twist-3 distribution amplitudes of the pion and kaon from the QCD sum rules

Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes ( and ) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of and the first two moments of and of the pion and kaon can be obtained with 30 uncertainty; (ii) the fourth moment of the and the second moment of the can be obtained when the uncertainty are relaxed to 35 ; (iii) the fourth moment of the can be obtained only when the uncertainty are relaxed to 40 ; (iv) we have and after including the -corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.Received: 6 January 2005, Revised: 29 March 2005, Published online: 22 June 2005PACS: 13.20.He, 11.55.Hx     

Renormalization-group improved calculation of the $B\to X_s\gamma$ branching ratio

Using results on soft-collinear factorization for inclusive B-meson decay distributions, a systematic study of the partial decay rate with a cut on photon energy is performed. For values of E ₀ below about 1.9 GeV, the rate can be calculated without reference to shape functions using a multi-scale operator product expansion (MSOPE). The transition from the shape-function region to the MSOPE region is studied analytically. The resulting prediction for the branching ratio depends on three large scales: m _b , , and . Logarithms associated with these scales are resummed at next-to-next-to-leading logarithmic order. While power corrections in turn out to be small, the sensitivity to the scale GeV (for GeV) introduces significant perturbative uncertainties, which so far have been ignored. The new theoretical prediction for the branching ratio with GeV is , where the first error is an estimate of perturbative uncertainties and the second one reflects uncertainties in input parameters. With this cut of all events are contained. When this fraction is combined with the previously best prediction for the total decay rate, one obtains , with a somewhat less conservative estimate of parametric uncertainties. The implications of larger theory uncertainties for new physics searches are briefly explored with the example of the type-II two-Higgs-doublet model, for which the lower bound on the charged-Higgs mass is reduced compared with previous estimates to approximately 200 GeV at 95% confidence level.Received: 18 September 2004, Revised: 18 January 2005, Published online: 21 February 2005     

Multijet production in neutral current deep inelastic scattering at HERA and determination of $\alpha_s$

Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities . The data were taken at the ep collider HERA with centre-of-mass energy using the ZEUS detector and correspond to an integrated luminosity of . Jets were identified in the Breit frame using the k_T cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections are presented as functions of jet transverse energy ( ), pseudorapidity ( ) and Q² with and . Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant , determined from the ratio of the trijet to dijet cross sections, is . Received: 1 April 2005, Revised: 28 June 2005, Published online: 30 August 2005     

Exclusive semileptonic rare decays $B \to K^{(*)} l^ + l^-$ in a SUSY SO(10) GUT

In the SUSY SO(10) GUT context, we study the exclusive processes . Using the Wilson coefficients of the relevant operators including the new operators which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients , among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA, , and of decay, which are expected to be measured in B factories, the deviation of in can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization can reach several percent for and it is 0.05 or so for , which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005     

An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment

The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e ⁺ and e^- beams, together with differential cross-section data on inclusive jet production in e ⁺ p scattering and dijet production in scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of at NLO; An additional uncertainty from the choice of scales is estimated as . This is the first extraction of from HERA data alone.     

Isospin constraints from/on $B \to \pi\pi$

The Standard Model constraints on which can be derived from the decays are revisited in some depth. As experimental inputs, the , decays complemented by the decays, the CP parameters and , and/or the value of as determined by the global CKM fit are used. The constraints discussed here are model independent in the sense that they rely only on Isospin symmetry, following the Gronau-London proposal. A new bound on and the function are introduced. While another bound applied to BABAR results is shown to imply that is negative. The Grossman-Quinn bound is rediscussed. A close form expression is given for as a function of the measurements. Various scenarios for the future of the isospin analysis are explored. To probe the Standard Model the plane is introduced.Received: 17 December 2004, Published online: 25 January 2005     

Probing the light neutral Higgs boson scenario of the <Emphasis Type="Italic">CP</Emphasis>-violating MSSM Higgs sector at the LHC

In the CP-violating minimal supersymmetric standard model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings (A_t, A_b) and the gluino mass , e.g., or , for GeV and -5, the lightest Higgs boson mass ( ) is GeV. This mass interval is still allowed by results of standard LEP Higgs searches because of a strongly suppressed H₁ZZ coupling. However, in the same region of parameter space in which these two conditions occur, the coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying associate production, leading to a signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the standard model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields -45 signal events, completely free of SM background, for - 30 fb^-1 of accumulated luminosity, after taking into account the overall efficiency for tagging four b-jets.Received: 21 February 2005, Published online: 6 July 2005     

Study of spin and decay-plane correlations of W bosons in the e + e$^-\rightarrow$ W + W- process at LEP

Data collected at LEP at centre-of-mass energies GeV are used to study correlations of the spin of W bosons using events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in and events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.Received: 26 October 2004, Revised: 15 January 2005, Published online: 3 March 2005     

Impact of four-quark shape functions on inclusive B decay spectra

It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order to decay distributions in the endpoint region. The corresponding functions and are estimated using the vacuum-insertion approximation. A numerical analysis of various decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other subleading shape-function contributions. Received: 29 June 2005, Published online: 13 September 2005     

Measurement of inclusive jet cross sections in photoproduction at HERA

Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of events in the kinematic range of photon virtualities and photon-proton centre-of-mass energies represents an integrated luminosity of . Jets are defined using the inclusive algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E_T ^jet and pseudorapidity in the domain and . The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in E_T ^jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003     

e<Superscript> + </Superscript>e<Superscript>-</Superscript>-pair production in Pb-Au collisions at 158 GeV per nucleon

We present the combined results on electron-pair production in 158 GeV/n Pb-Au ( = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 for semi-central collisions (28 ) when yields are integrated over m > 200 MeV/c² in invariant mass. The measured yield, its stronger-than-linear scaling with , and the dominance of low pair p_t strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at 500 MeV/c², however, cannot be described without strong medium modifications of the meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.Received: 2 March 2005, Published online: 8 June 2005     

Di-jet production in photon-photon collisionsat $\sqrt{s_{\protect\bf\mathrm{ee}}}$ from 189 to 209 GeV

Di-jet production is studied in collisions of quasi-real photons at e ⁺ e^- centre-of-mass energies from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive -clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy of the two leading jets, and as a function of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, , for different regions of . Angular distributions in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of and is presented, where is the jet pseudo-rapidity. Different regions of the - -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.Received: 20 December 2002, Published online: 17 October 2003     

Measurement of deeply virtual Compton scattering at HERA

A measurement is presented of elastic deeply virtual Compton scattering made using e ⁺ p collision data corresponding to a luminosity of 46.5 pb^-1, taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q ², the invariant mass of the p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range , and . QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.Received: 19 May 2005, Revised: 23 June 2005, Published online: 19 August 2005     

Large 2HDM(II) one-loop corrections in leptonic tau decays

The one-loop contributions to the branching ratios for leptonic decays are calculated in the CP-conserving 2HDM(II). The analysis is focused on large enhanced contributions. We found that these contributions, involving loops with both neutral and charged Higgs bosons, dominate over the tree-level exchange, the latter one being totally negligible for the decay into e. We derive a simple analytical expression for the one-loop contribution which holds in the large case. We show that the leptonic branching ratios of are complementary to the Higgsstrahlung processes for h(H) and have a large potential in constraining the parameters of the model. In this work we provide upper limits on the Yukawa couplings for both light h and light A scenarios, and we derive a new lower limit on the mass of as a function of which differs significantly from what was considered as a standard constraint based on the tree-level exchange only. Interestingly we also obtain an upper limit on . Received: 22 February 2005, Revised: 12 July 2005, Published online: 6 October 2005 D. Temes: ^* UMR 5108 du CNRS, associée á l'Université de Savoie.     

Tachyonic cyclotron radiation

We study superluminal cyclotron emission by electrons and muons in semiclassical orbits. The tachyonic line spectra of hydrogenic ions such as , , and , as well as their muonic counterparts , and are calculated, in particular the tachyonic power transversally and longitudinally radiated, the total intensity, and the power radiated in the individual harmonics. We also investigate tachyonic continuum radiation from electrons and protons cycling in the surface and light cylinder fields of -ray and millisecond pulsars, such as the Crab pulsar, PSR B1509-58, and PSR J0218 + 4232. The superluminal spectral densities generated by non-relativistic, mildly relativistic and ultra-relativistic source particles are derived. We study the parameters determining the global shape of the transversal and longitudinal densities and the energy scales of the broadband spectrum. The observed cutoff frequency in the -ray band of the pulsars is used to infer the upper edge of the orbital energy, and we conclude that electrons and nuclei cycling in the surface fields can reach energies beyond the "ankle" of the cosmic ray spectrum. This suggests -ray pulsars as sources of ultra-high energy cosmic rays. Arrival of the final proofs: 17 November 2005 PACS: 41.60.Ap, 11.10.Lm, 36.10.Dr, 98.70.Sa     

Heavy flavor production in PHENIX

The PHENIX experiment at RHIC measured single electron spectra in p + p, d + Au and Au + Au collisions at GeV, and in Au + Au collisions at GeV. In these spectra, electrons from semi-leptonic decays of charmed particles are the dominant contribution after subtraction of all 'photonic' sources (photon conversions, Dalitz decays, decays of light vector mesons). The p + p open charm production cross-section is found to be in good agreement with pQCD NLO calculations. The shape of the distributions obtained for p + p interactions is compared with those observed for nucleus-nucleus collisions. From p + p to d + Au and Au + Au interactions, open charm production is found to scale with the number of binary collisions . Au + Au data at GeV is compatible with the ISR p + p results scaled by . The elliptic flow parameter v₂ of heavy flavor electrons has also been measured, and is found to be non-zero in the intermediate p_T range. Arrival of the final proofs: 29 June 2005 PACS: . ^* Deceased Spokesperson     

Flavour-independent h<Superscript>0</Superscript>A<Superscript>0</Superscript> search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Upper limits on the cross-section of the pair-production process , assuming 100 branching fraction to hadrons, are derived from a new search for the hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the and decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ( and planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region GeV and GeV is excluded at 95 % CL, independently of and for selected values of which are representative of a complete -scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005