Search

We study the cross sections for the inclusive production of $\psi(2S)$ 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.

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-flavour-number scheme. We compare our results with recent data from ALICE, LHCb and CMS at a centre-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.

We present the fully up-to-date calculation of the γZ-box correction which needs to be taken into account to determine the weak mixing angle at low energies from parity-violating electron proton scattering. We make use of neutrino and antineutrino inclusive scattering data to predict the parity-violating structure function F3γZ by isospin symmetry. Our new analysis confirms previous results for the axial contribution to the γZ-box graph and reduces the uncertainty by a factor of 2. In addition, we note that the presence of parity-violating photon-hadron interactions induces an additional contribution via F3γγ. Using experimental and theoretical constraints on the nucleon anapole moment we are able to estimate the uncertainty associated with this contribution. We point out that future measurements are expected to significantly reduce this latter uncertainty.

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., 28 pages

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., 22 pages. Replaced LHCb data: now match with revised version (v9) of arXiv:1612.05140

We calculate the next-to-leading-order cross section for the inclusive production of $\Lambda_b$ 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., Comment: 18 pages

A new QCD sum rule determination of the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, $a_{\mu}^{\rm hvp}$, 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, $\Pi_{\rm EM}^\prime(0)$. The idea is based on the observation that, in the relevant kinematic domain, the integration kernel $K(s)$, entering the formula relating $a_{\mu}^{\rm hvp}$ to $e^{+}e^{-}$ annihilation data, behaves like $1/s$ times a very smooth function of $s$, the squared energy. We find an expression for $a_{\mu}$ in terms of $\Pi_{\rm EM}^\prime(0)$, which can be calculated in lattice QCD. Using recent lattice results we find a good approximation for $a_{\mu}^{\rm hvp}$, but the precision is not yet sufficient to resolve the discrepancy between the $R(s)$ data-based results and the experimentally measured value., Comment: 14 pages, added some clarifying text and two references, removed typos, results unchanged. Version to be published in Phys.Rev.D

Physics letters / B 775, 233 - 238 (2017). doi:10.1016/j.physletb.2017.11.002, 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 $\overline{MS}$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., Published by Elsevier, Amsterdam

An exhaustive number of QCD finite energy sum rules for $\tau$-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 $\tau$-decay in the kinematic region above $s\simeq2.2$ GeV$^{2}$ for these kernels., Comment: Invited talk at the Workshop on Determination of the Fundamental Parameters in QCD. Mainz Institute of Theoretical Physics, Johannes Gutenberg University of Mainz

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., Comment: 19 pages

We consider pion production in parity-violating electron scattering (PVES) in the presence of nucleon strangeness in the framework of partial wave analysis with unitarity. Using the experimental bounds on the strange form factors obtained in elastic PVES, we study the sensitivity of the parity-violating asymmetry to strange nucleon form factors. For forward kinematics and electron energies above 1 GeV, we observe that this sensitivity may reach about 20\% in the threshold region. With parity-violating asymmetries being as large as tens p.p.m., this study suggests that threshold pion production in PVES can be used as a promising way to better constrain strangeness contributions. Using this model for the neutral current pion production, we update the estimate for the dispersive $\gamma Z$-box correction to the weak charge of the proton. In the kinematics of the Qweak experiment, our new prediction reads Re$\,\Box_{\gamma Z}^V(E=1.165\,{\rm GeV}) = (5.58\pm1.41)\times10^{-3}$, an improvement over the previous uncertainty estimate of $\pm2.0\times10^{-3}$. Our new prediction in the kinematics of the upcoming MESA/P2 experiment reads Re$\,\Box_{\gamma Z}^V(E=0.155\,{\rm GeV}) = (1.1\pm0.2) \times 10^{-3}$., Comment: 18 pages, 10 figures

The prospects of physics at high Q2 in deep inelastic scattering at HERA after the upgrade in 2000–1 are reviewed. With 1000 pb−1 and polarized lepton beams, precision tests of electroweak physics are becoming possible and the search for physics beyond the standard model is expected to provide much improved limits.

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, $\Delta a_\mu \equiv a^{EXP}_\mu - a^{SM}_\mu$, from $\Delta a_\mu = 28.7 (8.0) \times 10^{-10}$ to $\Delta a_\mu = 19.2 (8.0) \times 10^{-10}$, i.e. without changing the uncertainty., Comment: Revised version with additional paragraphs

We introduce a model independent method for the determination of the hadronic contribution to the QED running coupling, $\Delta\alpha_{\text{HAD}}(M_{Z}^{2})$, 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 $\Delta\alpha_{\text{HAD}}(M_{Z}^{2})$ 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 $\Delta\alpha_{\text{HAD}}(M_{Z}^{2})=275.7(0.8) \times 10^{-4}$, which currently is the most precise value of $\Delta\alpha_{\text{HAD}}(M_{Z}^{2})$.

In inclusive deep-inelastic lepton-nucleon scattering, the radiative 'tails' originating from processes at Q2 values from the interval Q2meas >= Q2 > 0 contribute to measurements at Q2 = Q2meas and a knowledge of the structure functions in this Q2 interval is necessary. We review and compare existing parametrizations of structure functions and their extrapolations into the as-yet unexplored very low-Q2 regions and discuss the resulting uncertainties for leptonic radiative corrections. The unfolding procedures to determine structure functions from observed cross sections by the experiments NMC, ZEUS and H1 are compared with each other.

The characteristic features of electroweak radiative corrections in deep-inelastic scattering at HERA are reviewed. Numerical results are presented and consequences for the applications of radiative corrections are discussed.

In deep-inelastic electron proton scattering, the emission of photons collinear with the incident electrons leads to a reduction of the effective beam energy. It is argued that this effect can be used to measure the longitudinal structure function at HERA. For an integrated luminosity of 200pb−1, the statistical accuracy onR is in the range of ΔR≌0.05–0.25 for 6·10−4≤x≤2·10−2 and 15GeV2≤Q 2≤120GeV2. Systematic effects from photon identification and from the background of elasticep scattering in the luminosity monitor, as well as corrections from bin size effects and from cutting out lowp T events are discussed.

Ringberg Workshop on New Trends in HERA Physics 2008, Ringberg Castle, Germany, 5 Oct 2008 - 10 Oct 2008; Nuclear physics / B / Proceedings supplements 191, 183 - 192 (2009). doi:10.1016/j.nuclphysbps.2009.03.125, I describe the theoretical framework of the general-mass variable-flavor-number scheme for one-particle inclusive heavy-meson production and present numerical results for the photoproduction of D^* mesons at HERA., Published by Elsevier, Amsterdam

Higher order electromagnetic radiative corrections to neutral current deep inelastic electron proton scattering are studied in collinear approximation. Second order corrections show qualitatively new features compared to the first order ones and are non-negligible for largey and smallx. We also show how kinematical cuts on the recoil quark jet, in particular the jet angle, will allow a strong reduction of the contribution from radiative events for smallx and largey.

A major contribution to the electroweak radiative corrections in deep inelastic electron proton scattering is due to hard photon bremsstrahlungep→eγX. The Monte Carlo event generator HERACLES is used to study this process. Predictions for event distributions are given and the observability of radiative events is discussed. As a result we find that cuts can be found that reduce the radiative corrections considerably.

The complete O(α) electromagnetic and weak radiative corrections for the differential cross section d2σ/dxdy of the charged-current deep inelastic lepton-proton scattering at HERA are calculated. A Monte Carlo integration technique for the evaluation of the single photon bremsstrahlung contribution is explained. We derive formulas that are relevant for the exponentiation of soft photonic corrections and show numerical results. Those differences in the predictions are discussed that arise when either MW or the μ decay constant Gμ is used as input. In particular the top quark mass dependence of the NC/CC cross section ratio is investigated.

The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.

We calculate the next-to-leading order cross section for the inclusive production of D^{*+-} mesons in p p-bar collisions as a function of the transverse momentum and the rapidity in two approaches using massive or massless charm quarks. For the inclusive cross section, we derive the massless limit from the massive theory. We find that this limit differs from the genuine massless version with MS-bar factorization by finite corrections. By adjusting subtraction terms, we establish a massive theory with MS-bar subtraction which approaches the massless theory with increasing transverse momentum. With these results and including the contributions due to the charm and anti-charm content of the proton and anti-proton, we calculate the inclusive D^{*+-} cross section in p p-bar collisions using realistic evolved non-perturbative fragmentation functions and compare with recent data from the CDF Collaboration at the Fermilab Tevatron at center-of-mass energy root(S) = 1.96 TeV. We find reasonable, though not perfect, agreement with the measured cross sections.

We present a calculation of the next-to-leading order cross section for the inclusive hadroproduction of D and B mesons as a function of the transverse momentum and the rapidity in a massive variable flavor number scheme. We compare our numerical results with recent data from the CDF Collaboration at the Fermilab Tevatron for the production of D^0, D^{*+}, D^+, and D_s^+ mesons at center-of-mass energy $\sqrt{S} = 1.96$ TeV and find reasonably good agreement with the measured cross sections., Comment: 4 pages, 2 figures. To appear in proceedings of XIII International Workshop on Deep Inelastic Scattering, April,27 - May,1, 2005, Madison, Wisconsin, USA

In supersymmetric theories with R-parity breaking, trilinear couplings of two leptons to scalar sleptons are possible. In electron-positron collisions such interactions would manifest themselves through contact terms in Bhabha scattering and in annihilation to mu or tau pair Interpreting the high x, high Q2 DIS HERA events as charm squark production with squark masses of order 200 GeV, the formation of tau sneutrinos with a mass in the range close to the LEP2 energy or even in reach, is an exciting speculation which can be investigated in the coming LEP2 runs with energies close to 200 GeV., 13 pages, LaTex file with 3 figures, uses axodraw.sty (included). References updated / limits from rare B decays on Yukawa couplings updated, favoring tau-sneutrinos over mu-sneutrinos/ numerical results unchanged

The cross sections for the formation of scalar resonances, leptoquarks or squarks, in electron/positron-proton collisions at HERA are presented including next-to-leading order QCD corrections. Depending mildly on the mass of the resonances, the K-factors increase the production cross sections by up to 30% if the target quarks are valence quarks. The QCD corrections to the partial decay widths of leptoquarks/squarks to leptons and quarks are small. The electron spectrum in the decays is softened nevertheless by perturbative gluon radiation at a level of 3.4 GeV for a leptoquark/squark mass of 200 GeV., 10 pages, LaTex file with 3 figures, uses axodraw.sty (included)

In supersymmetric theories with R-parity breaking, sleptons can be produced in quark-antiquark annihilation at the Tevatron through interactions in which two quark fields are coupled to a slepton field. If at the same time trilinear slepton-lepton-lepton couplings are present, the sleptons can be searched for as resonances in $p\bar{p}\to \tilde{\nu} \to l^+l^-$ and $\tilde{\tau}\to l\nu $ final states. Existing Tevatron data can be exploited to derive bounds on the Yukawa couplings of sleptons to quark and lepton pairs. Similar bounds can also be obtained from $e^+e^-$ annihilation to hadrons at LEP2., Comment: LaTeX file, 12 pages, 4 figures, uses epsfig, axodraw

We present a new calculation of the $O(\alpha_s^2)$ coefficient of the energy-energy correlation function (EEC) using two different schemes to cancel infrared and collinear poles. The numerical evaluation uses the phase space slicing and the hybrid subtraction method. Both schemes converge with decreasing slicing cut. The results are independent of the scheme for small cuts. For the pure phase space slicing method, the cut must be below $10^{-6}$ to achieve good results. All four approaches agree with each other and confirm the results of Kunszt and Nason and Glover and Sutton, for the latter also with respect to contributions of different colour factors., Comment: 22 pages, uuencoded latex with postscript figures included

I discuss radiative corrections due to the emission of photons from quarks which contribute to deep inelastic lepton--nucleon scattering as well as to $pp$ collisions at high energies. These corrections are dominated by quark-mass singularities which have to be absorbed into the parton distribution functions. Observable effects appear as a modification of the $Q^2$ dependence of the distribution functions. Numerical results indicate, however, that these QED corrections are negligible except at extremely large $Q^2$ and large $x$. Therefore it is safe to neglect the single and multiple photon effects in $pp$ scattering at LHC energies., 13 pages, uuencoded latex with postscript, 3 figures included

We derive exact expressions for luminosities of massive vector-boson pairs which can be used to describe the cross sections for processes in hadron collisions or $e^+e^-$ annihilation which proceed via two-vector-boson scattering. Our approach correctly takes into account the mutual influence of the emission of one vector boson on the emission of a second one. We show that only approximately the exact luminosities can be factorized into convolutions of single-vector-boson distributions. Numerical results are given and compared to simplified approaches., Latex 2.09, 33 pages with figures, figures in separate uuencoded Postscript file

We have calculated the leading and next-to-leading logarithm coefficients of $O(\alpha_s^2)$ $e^+e^-$ annihilation jet cross sections, thrust distribution and energy-energy correlation in the two-jet limit when the jet resolution and the event shape variables vanish. We have compared our results with expectations based on leading logarithm approximations used to resum the pertubative cross sections where this is possible. There is good agreement for the leading and next-to-leading coefficients of jet cross sections in the Durham scheme. Also for the thrust distribution and energy-energy correlation we find results which are consistent with the leading logarithm predictions., Comment: 22 pages, uuencoded postscript, no figures

We discuss some theoretical uncertainties in the calculation of the cross section for charm production in charged current deep inelastic neutrino scattering related to ambiguities in the treatment of terms which are singular in the limit of a vanishing charm mass. In particular we compare the so-called variable flavour scheme where these terms are absorbed in the parton distribution functions containing the charm as an active flavour, with the so-called fixed flavour scheme with no charm mass subtraction where the charm appears only in the final state of fixed-order scattering matrix elements. Using available parametrizations of parton distribution functions we find that the two schemes lead to largely differing results for separate structure functions whereas the differences cancel to a large extent in the total cross section in that kinematical region which has been measured so far., Comment: 20pages, uuencoded postscript, figures included

The uncertainties in interpreting photon bremsstrahlung in the process\(e^ + e^ - \to Z^0 \to q\bar q\) with matrix element calculations ofO(ααs) are discussed. We address the stability of the calculations with respect to the emission of collinear photons and to higher-order QCD corrections and discuss the bias due to experimental photon isolation cuts. We analyze the resulting uncertainties for various procedures to define an event with a final state photon. Of particular interest are (i) a two-step procedure where first jets are reconstructed from hadrons alone and in a second step the photon is required to be isolated from these jets, and (ii) a ‘democratic’ procedure where the photon is inculded in the jet reconstruction but a certain maximum hadronic energy is allowed in the photon jet. In both cases we estimate that the uncertainties of the theoretical predictions, hadronization effects and the experimental photon isolation are of the order of 4%. To obtain this level of accuracy, however, the democratic procedure requires very hard cuts that reduce the event samples significantly.

We discuss different prescriptions for the exponentiation of multiple photonic corrections and their application to the cross section for e+e- annihilation near the Z resonance. Our results are based on a modified soft photon approximation that respects the resonant character of the matrix element. Also the influence of a cutoff for the total radiated energy is investigated.

In reference to the recently observed high Q^2, large x events in deep-inelastic positron-proton scattering at HERA, various leptoquark and supersymmetric scenarios are discussed. We study the impact of virtual leptoquark or R-parity breaking squark exchange as well as generic contact interaction on the production of quark-antiquark pairs in $e^+e^-$ annihilation, in particular at LEP2.

We calculate for the standard electroweak model the 1-loop radiative corrections to purely leptonic reactions like μ decay,\(\mathop v\limits^{( - )} _\mu e\) scattering and μ pair production ine+e− annihilation. A renormalization scheme with the particle massesM W ,M Z ,M H ,m f as parameters and the minimal number of wave function renormalization constants leading to finite Green functions is used. We perform a test of the standard model by comparing these low energy data with the results of thePP collider experiments for theW andZ boson masses.

We present analytic formulas and numerical results for the complete electroweak radiative corrections of O ( α 3 ) to charged current deep inelastic electron-proton scattering at HERA energies. The calculations are performed in the framework of the quark parton model and the electroweak standard theory. Hard bremsstrrahlung contributions integrated over the full available phase space are included.

We calculate the complete electromagnetic and weak radiative corrections of O (α3) to neutral current deep inelastic lepton proton scattering at HERA energies in the framework of the quark parton model. QCD scaling violations in the leading logarithmic approximation are also included. We give predictions for the unpolarized cross section and the polarization and charge asymmetries and discuss the theoretical uncertainties due to the dependence of the radiative corrections on electroweak parameters, quark masses and parton distribution functions.