arXiv subjects
Publications and source records attributed to Zhiqing Zhang.
The LHeC is a proposed upgrade of the LHC to study $ep/eA$ collisions in the TeV regime, by adding a 60 GeV electron beam through an energy recovery linac. In $ep$, high precision top and electroweak physics can be performed, such as measurements of anomalous top couplings, light quark couplings to the $Z$ boson and the energy dependence of the weak mixing angle $\sin^2\!θ_W$, for which simulation studies are presented.
In this talk, I present the brand new results from the H1 and ZEUS Collaborations on the combination of all previously published inclusive deep inelastic cross sections at HERA for neutral and charged current $e^\pm p$ scattering for zero beam polarisation and the corresponding parton distributions functions, HERAPDF 2.0, at up to next-to-next-to-leading order (NNLO). The results also include a new precise determination at next-to-leading order (NLO) of the strong coupling constant $α_s(M^2_Z)=0.1184\pm 0.0016$ (excluding scale uncertainties) based on a simultaneous fit to the combined inclusive cross section data and jet production data.
Recent calculations of the hadronic vacuum polarisation contribution are reviewed. The focus is put on the leading-order contribution to the muon magnetic anomaly involving $e^+e^-$ annihilation cross section data as input to a dispersion relation approach. Alternative calculation including tau data is also discussed. The $τ$ data are corrected for various isospin-breaking sources which are explicitly shown source by source.
The evolution of the determination of the strong coupling constant $α_s$ from the leptonic branching ratios, the lifetime, and the invariant mass distributions of the hadronic final state of the $τ$ lepton over the last two decades is briefly reviewed. The improvements in the latest ALEPH update are described in some detail. Currently this is one of the most precise $α_s$ determinations. Together with the other determination at the $Z$ boson mass pole, they constitutes the most accurate test of the asymptotic freedom in QCD.
This contribution covers three recent results on deep-inelastic scattering at HERA: (i) new measurements of the proton longitudinal structure function $F_L$ from H1 and ZEUS experiments, (ii) a dedicated NC cross section measurement from ZEUS in the region of high Bjorken $x$, and (iii) preliminary combination results of all HERA inclusive data published up to now by H1 and ZEUS, taking into account the experimental correlations between measurements.
The leading-order hadronic contribution to the muon magnetic moment anomaly $a_μ\equiv (g_μ-2)/2$, calculated using a dispersion integral of $e^+e^-$ annihilation data and $τ$ data, is briefly reviewed. This contribution has the largest uncertainty to the predicted value of $a_μ$, which differs from the direct measurement by $\sim 3.6 (2.4)$ standard deviations for the $e^+e^- (τ)$ based analysis. Recent results and main open issues on the subject are discussed.
Inclusive e^\pm p single and double differential cross sections for neutral (NC) and charged current (CC) deep inelastic scattering processes are measured with the H1 detector at HERA. The data were taken at a centre-of-mass energy of \sqrt{s} = 319 GeV with a total integrated luminosity of 327.8 pb^{-1} shared between two lepton beam charges and two longitudinal lepton polarisation modes. The differential cross sections are measured in the range of negative four-momentum transfer squared, Q2, between 60 and 50 000 GeV2, and Bjorken x between 0.0008 and 0.65. The measurements are combined with earlier published unpolarised H1 data to improve statistical precision and used to determine the structure function xF_3^{γZ}. A measurement of the structure function F_2^{γZ}, sensitive to parity violating effects in NC, is presented for the first time. The polarisation dependence of the CC total cross section is also measured. The new measurements are well described by a next-to-leading order QCD fit based on all published H1 inclusive cross section data which are used to extract the parton distribution functions of the proton.
This talk covers three contributions from H1: "Measurement of the inclusive e^\pm p scattering cross section at high inelasticity y and of the structure function F_L", "Determination of the integrated luminosity at HERA using elastic QED Compton events" and "Inclusive deep inelastic scattering at high Q2 with longitudinally polarized lepton beams at HERA". These are new measurements mainly based on the full HREA-II data but include also those from HERA-I in the combination whenever it is relevant. The main results of these measurements are briefly summarized here.
The leading-order hadronic contribution to the muon magnetic anomaly a_μ = (g_μ - 2)/2, calculated using a dispersion integral of e+e- annihilation data and tau decay data, is briefly reviewed. This contribution has the largest uncertainty to the predicted value of a_μ, which differs from the experimental value by ~3.6 (2.4) standard deviations for the e+e- (tau) based analysis. New results since the last workshop and main open issues on the subject are discussed.
We reevaluate the hadronic contributions to the muon magnetic anomaly, and to the running of the electromagnetic coupling constant at the Z-boson mass. We include new pi+pi- cross-section data from KLOE, all available multi-hadron data from BABAR, a reestimation of missing low-energy contributions using results on cross sections and process dynamics from BABAR, a reevaluation of all experimental contributions using the software package HVPTools, together with a reanalysis of inter-experiment and inter-channel correlations, and a reevaluation of the continuum contributions from perturbative QCD at four loops. These improvements lead to a decrease in the hadronic contributions with respect to earlier evaluations. For the muon g-2 we find lowest-order hadronic contributions of (692.3 +- 4.2) 10^-10 and (701.5 +- 4.7) 10^-10 for the e+e- based and tau-based analyses, respectively, and full Standard Model predictions that differ by 3.6 sigma and 2.4 sigma from the experimental value. For the e+e- based five-quark hadronic contribution to alpha(MZ) we find Delta_alpha_had[5](MZ)=(275.7 +- 1.0) 10^-4. The reduced electromagnetic coupling strength at MZ leads to an increase by 7 GeV in the most probable Higgs boson mass obtained by the standard Gfitter fit to electroweak precision data.
A summary of recent results reported in the Structure Functions and Low-x working group at the DIS 2009 Workshop is given. Recent measurements of deep inelastic scattering cross sections and structure functions at HERA and of proton anti-proton collisions at Tevatron are presented. New developments of the extraction of parton distribution functions and of new theoretical developments are discussed.
Precision measurements of SM Higgs recoil mass and cross-section are performed with the Higgs-Strahlung process ee -> Zh, with Z -> mumu and Z -> ee at 230 GeV and 250 GeV center of mass energies, presuming Mh=120GeV, assuming the integrated luminosity is 500 1/fb, based on full simulations of several detector models for the ILC. Results are given and compared in this article, of the two center of mass energies, and of several detector models. According to the studies, the Higgs mass can be determined with a statistical error of 39 MeV and 3.6% statistical error for the cross-section.
The latest results from the ep HERA collider both within the Standard (electroweak) Model and beyond are reviewed. Most of the results are based on the full HERA data sample, which corresponds to an integrated luminosity of about 0.5 fb-1 per experiment (H1 or ZEUS).
Results on multi-lepton events at high transverse momenta, isolated lepton events with large missing transverse energy and single W production reported to this conference are based for the first time on the full data samples taken by two colliding experiments, H1 and ZEUS, at HERA. The data correspond to an integrated luminosity of about 1fb-1 from both experiments.
Applying realistic veto efficiencies for the low angle electromagnetic calorimeter located in the very forward direction of the future international linear collider, we revisited the Standard Model background contributions studied previously in stau analyses with supersymmetrical dark matter scenarios.
The current status of the experimental measurements and theoretical predictions of the anomalous magnetic moment of the muon $a_μ$ is briefly reviewed. The emphasis is put on the evaluation of the hadronic contribution to $a_μ$ as it has the largest uncertainty among all Standard Model contributions. The precision of the hadronic contribution is driven by the input e+e- data predominantly from the π+pi- channel. Including the latest experimental data on e+e- annihilation into hadronsfrom CMD2 and SND for the π+π- channel and BaBar for multihadron final states, the updated Standard Model prediction disagrees with the measurement dominated by BNL by 3.3 standard deviations, with the theoretical precision exceeding the experimental one.
The inclusive neutral and charged current deep inelastic scattering processes at high Q2 provide the main basis for electroweak studies at HERA. These studies include the determination of the W boson propagator mass and weak neutral current couplings of light quarks to the Z0 boson. The polarised electron or positron beam at HERA II gives rise to additional sensitivities for these studies. Exceptions also exist; this is the case for the single W production.
Hadronic $τ$ decays provide a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables based on the spectral functions of hadronic $τ$ decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, quark and gluon condensates. Using the ALEPH spectral functions and branching ratios, complemented by some other available measurements, and a revisited analysis of the theoretical framework, the value $\asm = 0.345 \pm 0.004_{\rm exp} \pm 0.009_{\rm th}$ is obtained. Taken together with the determination of \asZ from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of $α_s^{-1}(s)$ is found to agree with QCD at a precision of 4%. The value of \asZ obtained from $τ$ decays is $\asZ = 0.1215 \pm 0.0004_{\rm exp} \pm 0.0010_{\rm th} \pm 0.0005_{\rm evol} = 0.1215 \pm 0.0012$.