arXiv subjects

H. Spiesberger

Publications and source records attributed to H. Spiesberger.

At least 19 recordsLinked to original sources

arXiv2024

Estimating the strong coupling from $τ$ decay using accelerating series convergence

We apply the Euler transformation to accelerate the convergence of the QCD perturbative series with the aim to determine the strong coupling $α_s$ in terms of the total $τ$-decay rate $r_τ$. The variation of the result with the order of the QCD perturbation theory is small and comparable with the uncertainties of $r_τ$. We also present an estimate of a range of the yet unknown 5th and 6th order coefficients $k_5$ and $k_6$ of the Adler function.

hep-ph↗

arXiv2022

EpIC: novel Monte Carlo generator for exclusive processes

We present the EpIC Monte Carlo event generator for exclusive processes sensitive to generalised parton distributions. EpIC utilises the PARTONS framework, which provides a flexible software architecture and a variety of modelling options for the partonic description of the nucleon. The generator offers a comprehensive set of features, including multi-channel capabilities and radiative corrections. It may be used both in analyses of experimental data, as well as in impact studies, especially for future electron-ion colliders.

hep-ph↗

arXiv2022

Reply to Comment on "New physics constraints from atomic parity violation in $^{133}$Cs"

In Phys. Rev. D 103, L111303 (2021), we had reported an improved calculation of the nuclear spin-independent parity violating electric dipole transition amplitude ($E1_{PV}$) for the $6s ~ ^2S_{1/2} - 7s ~ ^2S_{1/2}$ transition in $^{133}$Cs by employing a relativistic coupled-cluster (RCC) theory. In a recent Comment, B. M. Roberts and J. S. M. Ginges have raised questions about our calculation of the so-called Core contribution to $E1_{PV}$. Our result for this contribution does not agree with theirs, but is in agreement with results from previous calculations where this contribution is given explicitly. In our reply, we explain in detail the validity of the evaluation of our core contribution. We emphasize that the Main, Core and Tail contributions have been treated on an equal footing in our work unlike the sum-over-states calculations. We also address their concerns about our approximate treatment of the contributions from the QED corrections, which was not the aim of our work, but was carried out for completeness. Nonetheless, conclusion of our above mentioned paper is not going to affect if we replace our estimated QED contribution to $E1_{PV}$ by earlier estimation.

hep-ph↗

arXiv2021

Perturbative heavy quark contributions to the anomalous magnetic moment of the muon

We discuss a method for calculating the heavy quark vacuum polarisation contribution to the muon anomalous magnetic moment, $a_μ$, using perturbative QCD. This approach is independent of $e^+e^-$ cross-section data allowing a fully theoretical evaluation of these contributions. We confirm an existing result at lower orders in $α_s$ and state a new explicit analytic formula which includes terms up to $\mathcal{O}\left(α_s^3\right)$. Numerically the charm quark contribution to $a_μ$ is found to be $a_μ^c = (14.5 \pm 0.2)\times 10^{-10}$ and the bottom contributes $a_μ^b = (0.302 \pm 0.002) \times 10^{-10} $. Our uncertainty estimates include both parametric uncertainties from $\hat{m}_q(\hat{m}_q)$ and $α_s(\hat{m}_q)$, and theoretical uncertainties in the perturbative expansion. Comparison is made between these results and alternative approaches such as lattice QCD or those based on a dispersion relation and cross-section data.

hep-ph↗

arXiv2021

Cross sections of inclusive $ψ(2S)$ and $X(3872)$ production from $b$-hadron decays in $pp$ collisions and comparison with ATLAS and CMS data

We study the cross sections for the inclusive production of $ψ(2S)$ and $X(3872)$ hadrons in $pp$ collisions at the LHC at two different center-of-mass energies and compare with experimental data obtained by the ATLAS, CMS, and LHCb collaborations.

hep-ph↗

arXiv2021

New Physics Constraints from Atomic Parity Violation in $^{133}$Cs

Our improved calculation of the nuclear spin-independent parity violating electric dipole transition amplitude ($E1_{PV}$) for $6s ~ ^2S_{1/2} - 7s ~ ^2S_{1/2}$ in $^{133}$Cs in combination with the most accurate (0.3\%) measurement of this quantity yields a new value for the nuclear weak charge $Q_W=-73.71(26)_{ex} (23)_{th}$ against the Standard Model (SM) prediction $Q_W^{\text{SM}}=-73.23(1)$. The advances in our calculation of $E1_{PV}$ have been achieved by using a variant of the perturbed relativistic coupled-cluster theory which treats the contributions of the core, valence and excited states to $E1_{PV}$ on the same footing unlike the previous high precision calculations. Furthermore, this approach resolves the controversy regarding the sign of the core correlation effects. We discuss the implications of the deviation of our result for $Q_W$ from the SM value by considering different scenarios of new physics.

hep-ph↗

arXiv2020

$Λ_c^{\pm}$ production in pp collisions with a new fragmentation function

We study inclusive $Λ_c^{\pm}$-baryon production in $pp$ collisions in the general-mass variable-flavor number scheme and compare with data from the LHCb, ALICE and CMS collaborations. We perform a new fit of the $c \to Λ_c^+$ fragmentation function combining $e^+e^-$ data from OPAL and Belle. The agreement with LHC data is slightly worse compared with a calculation using an older fragmentation function, and the tension between different determinations of $Λ_c^{\pm}$ production cross sections from the LHC experimental collaborations is not resolved. The ratio of data for $Λ_c^+$-baryon and $D^0$-meson production seems to violate the universality of $c$-charm quark to $c$-hadron fragmentation.

hep-ph↗

arXiv2019

B-meson production in the general-mass variable-flavour-number scheme and LHC data

We study inclusive $B$-meson production in $pp$ collisions at the LHC and compare experimental data with predictions of the general-mass variable-flavour-number scheme at next-to-leading order of perturbative QCD. We find almost perfect agreement provided that the factorization scale parameters and the parton distribution functions are chosen appropriately.

hep-ph↗

arXiv2018

Second-Order Leptonic Radiative Corrections for Lepton-Proton Scattering

The interpretation of high-precision lepton-nucleon scattering experiments requires the knowledge of higher-order radiative corrections. We present a calculation of the cross section for unpolarized lepton-proton scattering including leptonic radiative corrections up to second order, including one- and two-loop corrections, radiation of one and two photons and one-loop corrections for one-photon radiation. Numerical results are given for the planned P2 experiment at the MESA facility in Mainz, and some results are also discussed for Qweak and the suggested MUSE experiment.

hep-ph↗

arXiv2018

Determination of electroweak parameters in polarised deep-inelastic scattering at HERA

The parameters of the electroweak theory are determined in a combined electroweak and QCD analysis using all deep-inelastic $e^+p$ and $e^-p$ neutral current and charged current scattering cross sections published by the H1 Collaboration, including data with longitudinally polarised lepton beams. Various fits to Standard Model parameters in the on-shell scheme are performed. The mass of the $W$ boson is determined as $m(W)=80.520\pm 0.115$ GeV. The axial-vector and vector couplings of the light quarks to the $Z$ boson are also determined. Both results improve the precision of previous H1 determinations based on HERA-I data by about a factor of two. Possible scale dependence of the weak coupling parameters in both neutral and charged current interactions beyond the Standard Model is also studied. All results are found to be consistent with the Standard Model expectations.

hep-ex↗

arXiv2018

b-Hadron production in the general-mass variable-flavour-number scheme and LHC data

We study inclusive b-hadron production in pp collisions at the LHC at different center-of-mass energies and compare with experimental data from the LHCb and CMS collaborations. Our predictions for cross sections differential in the transverse momentum and (pseudo-)rapidity agree with data within uncertainties due to renormalization scale variations. A small tension is found if data and theory predictions are compared for cross section ratios at different center-of-mass energies.

hep-ph↗

arXiv2018

$Λ_b^0$-baryon production in pp collisions in the general-mass variable-flavour-number scheme and comparison with CMS and LHCb data

We calculate the next-to-leading-order cross section for the inclusive production of $Λ_b$ baryons in pp collisions in the general-mass variable-flavor-number scheme. We use realistic evolved non-perturbative fragmentation functions obtained from fits to B-meson production in $e^+ e^-$ annihilation and compare our results for transverse-momentum and rapidity distributions with recent experimental data from the CMS and the LHCb collaborations at the CERN LHC. We find satisfactory agreement in general, with some indication for the need to modify the available fragmentation functions at larger values of the scale variable.

hep-ph↗

arXiv2017

Study of heavy meson production in p-Pb collisions at $\sqrt{S}$=5.02 TeV in the general-mass variable-flavour-number scheme

We study inclusive charm and bottom production, for both D and B mesons, in p-Pb collisions at the LHC. Numerical results for p_T-differential production cross sections are obtained at next-to-leading-order in the general-mass variable-flavor-number scheme. We compare our results with recent data from ALICE, LHCb and CMS at a center-of-mass energy of 5 TeV and find good agreement. A comparison with p-p cross sections does not reveal the presence of nuclear initial-state interaction effects that could be expected to become visible as deviations of the ratio of p-Pb and p-p cross sections from one.

hep-ph↗

arXiv2017

Anomalous magnetic moment of the muon, a hybrid approach

A new QCD sum rule determination of the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, $a_μ^{\rm hvp}$, is proposed. This approach combines data on $e^{+}e^{-}$ annihilation into hadrons, perturbative QCD and lattice QCD results for the first derivative of the electromagnetic current correlator at zero momentum transfer, $Π_{\rm EM}^\prime(0)$. The idea is based on the observation that, in the relevant kinematic domain, the integration kernel $K(s)$, entering the formula relating $a_μ^{\rm hvp}$ to $e^{+}e^{-}$ annihilation data, behaves like $1/s$ times a very smooth function of $s$, the squared energy. We find an expression for $a_μ$ in terms of $Π_{\rm EM}^\prime(0)$, which can be calculated in lattice QCD. Using recent lattice results we find a good approximation for $a_μ^{\rm hvp}$, but the precision is not yet sufficient to resolve the discrepancy between the $R(s)$ data-based results and the experimentally measured value.

hep-ph↗

arXiv2017

Running of the Charm-Quark Mass from HERA Deep-Inelastic Scattering Data

Combined HERA data on charm production in deep-inelastic scattering have previously been used to determine the charm-quark running mass $m_c(m_c)$ in the MSbar renormalisation scheme. Here, the same data are used as a function of the photon virtuality $Q^2$ to evaluate the charm-quark running mass at different scales to one-loop order, in the context of a next-to-leading order QCD analysis. The scale dependence of the mass is found to be consistent with QCD expectations.

hep-ph↗

arXiv2017

QCD determination of the leading order hadronic contribution to the muon g-2

The leading order hadronic contribution to the muon magnetic moment anomaly, $a^{HAD}_μ$, is determined entirely in the framework of QCD. The result in the light-quark sector, in units of $10^{-10}$, is $a^{HAD}_μ|_{uds} =686 \pm 26$, and in the heavy-quark sector $a^{HAD}_μ|_{c} =14.4 \pm 0.1$, and $a^{HAD}_μ|_{b} =0.29 \pm 0.01$, resulting in $a^{HAD}_μ= 701 \pm 26$. The main uncertainty is due to the current lattice QCD value of the first and second derivative of the electromagnetic current correlator at the origin. Expected improvement in the precision of these derivatives may render this approach the most accurate and trustworthy determination of the leading order $a^{HAD}_μ$.

hep-ph↗

arXiv2016

Tests of quark-hadron duality in tau-decays

An exhaustive number of QCD finite energy sum rules for $τ$-decay together with the latest updated ALEPH data is used to test the assumption of global duality. Typical checks are the absence of the dimension $d=2$ condensate, the equality of the gluon condensate extracted from vector or axial vector spectral functions, the Weinberg sum rules, the chiral condensates of dimensions $d=6$ and $d=8$, as well as the extraction of some low-energy parameters of chiral perturbation theory. Suitable pinched linear integration kernels are introduced in the sum rules in order to suppress potential quark-hadron duality violations and experimental errors. We find no compelling indications of duality violations in hadronic $τ$-decay in the kinematic region above $s\simeq2.2$ GeV$^{2}$ for these kernels.

hep-ph↗

arXiv2016

Tau-decay hadronic spectral functions: probing quark-hadron duality

The vector and axial-vector ALEPH hadronic spectral functions from $τ$-decay are used to probe potential quark-hadron duality violations (DV). This is done in the framework of finite energy QCD sum rules (FESR). A pinched integration kernel is introduced in the FESR in order to (a) quench potential duality violations on the real axis in the complex squared energy $s$-plane, and (b) effectively extend the analysis well beyond the kinematical $τ$-decay end-point where there is no longer data, i.e.\ in the range $s = 3 - 10 \,{\mbox{GeV}}^2$. In the vector channel this procedure is supplemented with actual data from $e^+ e^-$-annihilation into hadrons, above the tau-decay kinematical end-point, with results fully supporting this extension. Very good agreement is obtained between data and two specific pinched FESR. Results from this analysis are confronted with those from a specific model of DV. As the sum rules are well satisfied in both cases within experimental errors, we conclude that possible DV must be buried under the experimental uncertainties. In other words, there seems to be no need for explicit models of DV in this case. Pinched kernels work as well, but with far less free parameters.

hep-ph↗