arXiv subjects

H. Spiesberger

Publications and source records attributed to H. Spiesberger.

At least 37 records · Page 2Linked to original sources

arXiv2016

Quark-hadron duality: pinched kernel approch

Hadronic spectral functions measured by the ALEPH collaboration in the vector and axial-vector channels are used to study potential quark-hadron duality violations (DV). This is done entirely in the framework of pinched kernel finite energy sum rules (FESR), i.e. in a model independent fashion. The kinematical range of the ALEPH data is effectively extended up to $s = 10\; {\mbox{GeV}^2}$ by using an appropriate kernel, and assuming that in this region the spectral functions are given by perturbative QCD. Support for this assumption is obtained by using $e^+ e^-$ annihilation data in the vector channel. Results in both channels show a good saturation of the pinched FESR, without further need of explicit models of DV.

hep-ph↗

arXiv2016

Precision Measurement of sin2(theta_w) at MESA

A forthcoming experiment of low-energy elastic electron proton scattering at the new MESA facility in Mainz is planned to provide a high-precision measurement of the parity-violating polarisation asymmetry. This experiment is expected to lead to a precision determination of the weak mixing angle, competitive with Z-pole data. We discuss the challenges for theory to derive predictions with the required accuracy.

hep-ph↗

arXiv2016

Theoretical determination of the hadronic (g-2) of the muon

An approach is discussed on the determination of the leading order hadronic contribution to the muon anomaly, $a_μ^{HAD}$, based entirely on theory. This method makes no use of $e^+ e^-$ annihilation data, a likely source of the current discrepancy between theory and experiment beyond the $3\, σ$ level. What this method requires is essentially knowledge of the first derivative of the vector current correlator at zero-momentum. In the heavy-quark sector this is obtained from the well known heavy quark expansion in perturbative QCD, leading to values of $a_μ^{HAD}$ in the charm- and bottom-quark region which were fully confirmed by later lattice QCD (LQCD) results. In the light-quark sector, using recent preliminary LQCD results for the first derivative of the vector current correlator at zero-momentum leads to the value $a_μ^{HAD} = (729 - 871)\, \times\,10^{-10}$, which is significantly larger than values obtained from using $e^+ e^-$ data. A separate approach based on the operator product expansion (OPE), and designed to quench the contribution of these data, reduces the discrepancy by at least 40\%. In addition, it exposes a tension between the OPE and $e^+ e^-$ data, thus suggesting the blame for the discrepancy on the latter.

hep-ph↗

arXiv2016

Summary of workshop on Future Physics with HERA Data

Recent highlights from the HERA experiments, Hermes, H1 and ZEUS, are reviewed and ideas for future analyses to fully exploit this unique data set are proposed. This document is a summary of a workshop on future physics with HERA data held at DESY, Hamburg at the end of 2014. All areas of HERA physics are covered and contributions from both experimentalists and theorists are included. The document outlines areas where HERA physics can still make a significant contribution, principally in a deeper understanding of QCD, and its relevance to other facilities. Within the framework of the Data Preservation in High Energy Physics, the HERA data have been preserved for analyses to take place over a timescale of 10 years and more. Therefore, although an extensive list of possibilities is presented here, safe storage of the data ensures that it can also be used in the far future should new ideas and analyses be proposed.

hep-ex↗

arXiv2015

Inclusive photoproduction of bottom quarks for low and medium pT in the general-mass variable-flavour-number scheme

We present predictions for b-quark production in photoprodcution and compare with experimental data from HERA. Our theoretical predictions are obtained at next-to-leading-order in the general-mass variable-flavor-number scheme, an approach which takes into account the finite mass of the b quarks. We use realistic evolved nonperturbative fragmentation functions obtained from fits to e+e- data. We find in general good agreement of data with both the GM-VFNS and the FFNS calculations, while the more precise ZEUS data seem to prefer the GM-VFNS predictions.

hep-ph↗

arXiv2015

HERAFitter, Open Source QCD Fit Project

HERAFitter is an open-source package that provides a framework for the determination of the parton distribution functions (PDFs) of the proton and for many different kinds of analyses in Quantum Chromodynamics (QCD). It encodes results from a wide range of experimental measurements in lepton-proton deep inelastic scattering and proton-proton (proton-antiproton) collisions at hadron colliders. These are complemented with a variety of theoretical options for calculating PDF-dependent cross section predictions corresponding to the measurements. The framework covers a large number of the existing methods and schemes used for PDF determination. The data and theoretical predictions are brought together through numerous methodological options for carrying out PDF fits and plotting tools to help visualise the results. While primarily based on the approach of collinear factorisation, HERAFitter also provides facilities for fits of dipole models and transverse-momentum dependent PDFs. The package can be used to study the impact of new precise measurements from hadron colliders. This paper describes the general structure of HERAFitter and its wide choice of options.

hep-ph↗

arXiv2015

A review of the intrinsic heavy quark content of the nucleon

We present a review of the state-of-the-art of our understanding of the intrinsic charm and bottom content of the nucleon. We discuss theoretical calculations, constraints from global analyses, and collider observables sensitive to the intrinsic heavy quark distributions. A particular emphasis is put on the potential of a high-energy and high-luminosity fixed target experiment using the LHC beams (AFTER@LHC) to search for intrinsic charm.

hep-ph↗

arXiv2015

Chiral sum rules and vacuum condensates from tau-lepton decay data

QCD finite energy sum rules, together with the latest updated ALEPH data on hadronic decays of the tau-lepton are used in order to determine the vacuum condensates of dimension $d=2$ and $d=4$. These data are also used to check the validity of the Weinberg sum rules, and to determine the chiral condensates of dimension $d=6$ and $d=8$, as well as the chiral correlator at zero momentum, proportional to the counter term of the ${\cal{O}}(p^4)$ Lagrangian of chiral perturbation theory, $\bar{L}_{10}$. Suitable (pinched) integration kernels are introduced in the sum rules in order to suppress potential quark-hadron duality violations. We find no compelling indications of duality violations in the kinematic region above $s \simeq 2.2$ GeV$^2$ after using pinched integration kernels.

hep-ph↗

arXiv2015

Inclusive B-meson production at small p_T in the general-mass variable-flavor-number scheme

We calculate the cross section for the inclusive production of B mesons in pp and ppbar collisions at next-to-leading order in the general-mass variable-flavor-number scheme and show that a suitable choice of factorization scales leads to a smooth transition to the fixed-flavor-number scheme. Our numerical results are in good agreement with data from the Tevatron and LHC experiments at small and at large transverse momenta.

hep-ph↗

arXiv2013

Hadronic Contribution to the muon $g-2$ factor

The lowest order hadronic contribution to the $g-2$ factor of the muon is analyzed in the framework of the operator product expansion at short distances, and a QCD finite energy sum rule designed to quench the role of the $e^+ e^-$ data. This procedure reduces the discrepancy between experiment and theory, $Δa_μ\equiv a^{EXP}_μ- a^{SM}_μ$, from $Δa_μ= 28.7 (8.0) \times 10^{-10}$ to $Δa_μ= 19.2 (8.0) \times 10^{-10}$, i.e. without changing the uncertainty.

hep-ph↗

arXiv2013

Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment

The mini-proceedings of the Workshop on "Constraining the hadronic contributions to the muon anomalous magnetic moment" which included the "13th meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements at BES-III" held in Trento from April 10th to 12th, 2013, are presented. This collaboration meeting aims to bring together the experimental e+e- collider communities from BaBar, Belle, BESIII, CMD2, KLOE, and SND, with theorists working in the fields of meson transitions form factors, hadronic contributions to (g-2)_μand effective fine structure constant, and development of Monte Carlo generator and Radiative Corrections for precision e+e- and tau physics.

hep-ph↗

arXiv2012

Hadronic contribution to the QED running coupling $α(M_{Z}^2)$

We introduce a model independent method for the determination of the hadronic contribution to the QED running coupling, $Δα_{\text{HAD}}(M_{Z}^{2})$, requiring no $e^+e^-$ annihilation data as input. This is achieved by calculating the heavy-quark contributions entirely in perturbative QCD, whilst the light-quark resonance piece is determined using available lattice QCD results. Future reduction in the current uncertainties in the latter shall turn this method into a valuable alternative to the standard approach. Subsequently, we find that the precision of current determinations of $Δα_{\text{HAD}}(M_{Z}^{2})$ can be improved by some 20% by computing the heavy-quark pieces in PQCD, whilst using $e^+e^-$ data only for the low-energy light-quark sector. We obtain in this case $Δα_{\text{HAD}}(M_{Z}^{2})=275.7(0.8) \times 10^{-4}$, which currently is the most precise value of $Δα_{\text{HAD}}(M_{Z}^{2})$.

hep-ph↗

arXiv2012

Inclusive D-Meson Production at the LHC

I present predictions for the inclusive production of D mesons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Numerical results are compared to data where available, and uncertainties due to scale variations, parton distribution functions and charm mass are discussed. I point out that measurements at large rapidity have the potential to pin down models of intrinsic charm.

hep-ph↗

arXiv2012

Inclusive Charmed-Meson Production at the CERN LHC

We present predictions for the inclusive production of charmed hadrons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Detailed numerical results are compared to data where available, or presented in a way to ease future comparisons with experimental results. We also point out that measurements at large rapidity have the potential to pin down models of intrinsic charm.

hep-ph↗

arXiv2012

How to pin down the CP quantum numbers of a Higgs boson in its tau decays at the LHC

We investigate how the CP quantum numbers of a neutral Higgs boson or spin-zero resonance, produced at the CERN Large Hadron Collider, can be determined in its tau-pair decay mode. We use a method developed in an earlier paper based on the distributions of two angles and apply it to the major 1-prong tau decays. We show for the resulting dilepton, lepton-pion, and two-pion final states that appropriate selection cuts significantly enhance the discriminating power of these observables. From our analysis we conclude that, provided a Higgs boson will be found at the LHC, it appears feasible to collect the event numbers needed to discriminate between a CP-even and -odd Higgs boson and/or between Higgs boson(s) with CP-conserving and CP-violating couplings after several years of high-luminosity runs.

hep-ph↗

arXiv2011

Confronting electron-positron annihilation into hadrons with QCD: an operator product expansion analysis

Experimental data on the total cross section of $e^+ e^-$ annihilation into hadrons are confronted with QCD and the operator product expansion using finite energy sum rules. Specifically, the power corrections in the operator product expansion, i.e. the vacuum condensates, of dimension $d = 2$, 4 and 6 are determined using recent isospin $I=0+1$ data sets. Reasonably stable results are obtained which are compatible within errors with values from $τ$-decay. However, the rather large data uncertainties, together with the current value of the strong coupling constant, lead to very large errors in the condensates. It also appears that the separation into isovector and isoscalar pieces introduces additional uncertainties and errors. In contrast, the high precision $τ$-decay data of the ALEPH collaboration in the vector channel allows for a more precise determination of the condensates. This is in spite of QCD asymptotics not quite been reached at the end of the $τ$ spectrum. We point out that isospin violation is negligible in the integrated cross sections, unlike the case of individual channels.

hep-ph↗

arXiv2011

Inclusive B-Meson Production at the LHC in the GM-VFN Scheme

We calculate the next-to-leading-order cross section for the inclusive production of B mesons in pp collisions in the general-mass variable-flavor-number scheme, an approach which takes into account the finite mass of the b quarks. We use realistic evolved non-perturbative fragmentation functions obtained from fits to e+e- data and compare results for the transverse-momentum and rapidity distributions at a center-of-mass energy of 7 TeV with recent data from the CMS Collaboration. We find good agreement, in particular at large values of pT.

hep-ph↗

arXiv2009

Photon 2009: Summary of Theory Talks

The conference 'Photon 2009' on the structure and the interactions of the photon included sessions on photon-photon collisions and a future high-energy photon linear collider. This summary of theoretical contributions to the conference therefore has two parts. I will discuss the physics potential of photon colliders with an emphasis on the study of electroweak physics and the search for physics beyond the standard model. Secondly, I will describe a few highlights in recent progress in the understanding of the properties and the interaction of the photon, comprising the production of prompt photons, the photon structure and exclusive hadron production, small-x and total cross sections of deep inelastic scattering. Finally, I will review the status of the comparison of measurement and theory for the muon anomalous magnetic moment g-2.

hep-ph↗