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H. Spiesberger

Publications and source records attributed to H. Spiesberger.

At least 55 records · Page 3Linked to original sources
arXiv2009

Inclusive D*-meson production in ep scattering at low Q2 in the GM-VFN scheme at NLO

We have calculated the next-to-leading order cross sections for the inclusive production of D*-mesons in ep collisions at HERA for finite, although very small Q2. In this Q2-range, the same approximations as for photoproduction can be used. Our calculation is performed in the general-mass variable-flavour-number scheme. In this approach, large logarithms of the charm transverse momentum are resummed and finite terms depending on m^2/p_T^2 are kept in the hard scattering cross sections. The theoretical results are compared with recent data from the ZEUS collaboration at HERA. On average, we find good agreement.

hep-ph↗
arXiv2009

Open charm hadroproduction and the charm content of the proton

We advocate charmed-hadron inclusive hadroproduction as a laboratory to probe intrinsic charm (IC) inside the colliding hadrons. Working at next-to-leading order in the general-mass variable-flavor-number scheme endowed with non-perturbative fragmentation functions recently extracted from a global fit to e^+e^- annihilation data from KEKB, CESR, and LEP1, we first assess the sensitivity of Tevatron data of D^0, D^+, and D^{*+} inclusive production to the IC parameterizations provided by Pumplin et al. We then argue that similar data from pp collisions at RHIC would have the potential to discriminate between different IC models provided they reach out to sufficiently large values of transverse momentum.

hep-ph↗
arXiv2009

Inclusive photoproduction of D*+- mesons at next-to-leading order in the General-Mass Variable-Flavor-Number Scheme

We discuss the inclusive production of D*+- mesons in gamma-proton collisions at DESY HERA, based on a calculation at next-to-leading order in the general-mass variable-flavor-number scheme. In this approach, MSbar subtraction is applied in such a way that large logarithmic corrections are resummed in universal parton distribution and fragmentation functions and finite mass terms are taken into account. We present detailed numerical results for a comparison with data obtained at HERA and discuss various sources of theoretical uncertainties.

hep-ph↗
arXiv2008

Determination of QCD condensates from tau-decay data

We have used the latest data from the ALEPH Collaboration to extract values for QCD condensates up to dimension d=12 in the V-A channel and up to dimension d=8 in the V, A and V+A channels. Performing 2- and 3-parameter fits, we obtain new results for the correlations of condensates. The results are consistent among themselves and agree with most of the previous results found in the literature.

hep-ph↗
arXiv2007

Finite-Mass Effects on Inclusive B-Meson Hadroproduction

We calculate the transverse-momentum (p_T) distribution for the inclusive hadroproduction of B mesons at intermediate values of p_T at next-to-leading order (NLO) in a dedicated finite-mass scheme using realistic non-perturbative fragmentation functions that are obtained through a global fit to e^+e^- data from CERN LEP1 and SLAC SLC exploiting their universality and scaling violations. We find that finite-mass effects moderately enhance the cross section, by about 20% at p_T = 2 m_b, and rapidly fade out with increasing value of p_T, so that the zero-mass prediction is reached. We also perform comparisons with recent ppbar data taken by the CDF Collaboration in run II at the Fermilab Tevatron and comment on the usefulness of the fixed-flavor-number scheme.

hep-ph↗
arXiv2007

Speculations on Isolated Lepton Events at HERA

Speculations on mechanisms which might be responsible for events with an isolated high p_T lepton, a hadron jet and missing energy, as observed in the H1 experiment at HERA, are discussed.

hep-ph↗
arXiv2007

Heavy Quarks: Summary Report

The present status of the heavy-quark production theory is critically reviewed in the first contribution. The second contribution summarises the present heavy flavour data from HERA and gives an outlook of what can be expected from HERA-II. The potential of the LHC experiments for charm and beauty physics is reviewed in the 3rd contribution. Then the relevance of saturation and small-x effects to heavy quark production at HERA and at the LHC are discussed. The non-perturbative aspects of heavy-quark fragmentation and their relevance to HERA and LHC are discussed in the next contribution. Finally, a comparison of different theoretical predictions for HERA and LHC based on different approaches is presented.

hep-ph↗
arXiv2007

Isolated Lepton Events at HERA: SUSY R-Parity Violation?

Events with an isolated high $p_T$ lepton, a hadron jet and missing energy as observed in the H1 experiment at HERA, are potentially associated with R-parity violation in supersymmetric theories. However, stringent kinematic constraints must be fulfilled if the production of supersymmetric particles in R-parity violating scenarios were the correct path for explaining these puzzling events. A reference point \RF is specified for which these constraints are illustrated and implications of the supersymmetric interpretation for new classes of multi-lepton events are indicated.

hep-ph↗
arXiv2006

QCD condensates of dimension D=6 and D=8 from hadronic tau-decays

The high-precision data from hadronic tau decays allows one to extract information on QCD condensates. Using the finalized ALEPH data, we obtain a more rigorous determination of the dimension 6 and 8 condensates for the V-A correlator. In particular, we find that the recent data fix a certain linear combination of these QCD condensates to a precision at the level of O(2%). Our approach relies on more general assumptions than alternative approaches based on finite energy sum rules.

hep-ph↗
arXiv2005

Reconciling open charm production at the Fermilab Tevatron with QCD

We study the inclusive hadrodroduction of D^0, D^+, D^{*+}, and D_s^+ mesons at next-to-leading order in the parton model of quantum chromodynamics endowed with universal non-perturbative fragmentation functions (FFs) fitted to e^+e^- annihilation data from CERN LEP1. Working in the general-mass variable-flavor-number scheme, we resum the large logarithms through the evolution of the FFs and, at the same time, retain the full dependence on the charm-quark mass without additional theoretical assumptions. In this way, the cross section distributions in transverse momentum recently measured by the CDF Collaboration in run II at the Fermilab Tevatron are described within errors.

hep-ph↗
arXiv2005

Hadroproduction of D and B mesons in a massive VFNS

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.

hep-ph↗
arXiv2005

The role of polarized positrons and electrons in revealing fundamental interactions at the Linear Collider

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.

hep-ph↗
arXiv2005

Collinear Subtractions in Hadroproduction of Heavy Quarks

We present a detailed discussion of the collinear subtraction terms needed to establish a massive variable-flavour-number scheme for the one-particle inclusive production of heavy quarks in hadronic collisions. The subtraction terms are computed by convoluting appropriate partonic cross sections with perturbative parton distribution and fragmentation functions relying on the method of mass factorization. We find (with one minor exception) complete agreement with the subtraction terms obtained in a previous publication by comparing the zero-mass limit of a fixed-order calculation with the genuine massles results in the MSbar scheme. This presentation will be useful for extending the massive variable-flavour-number scheme to other processes.

hep-ph↗
arXiv2004

Inclusive D^{*+-} Production in p p-bar Collisions with Massive Charm Quarks

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.

hep-ph↗
arXiv2004

Inclusive Photoproduction of D* Mesons with Massive Charm Quarks

We have calculated the next-to-leading order cross sections for the inclusive production of D* mesons in gamma-p collisions at HERA in two approaches using massive or massless charm quarks. The usual massive theory for the direct cross section with charm quarks only in the final state was transformed into a massive theory with MS-bar subtraction by subtracting the mass divergent and additional finite terms calculated earlier in connection with the process gamma+gamma -> D*+X. This theory approaches the massless theory with increasing transverse momentum. The difference between the massive and the massless approach with MS-bar subtraction is studied in detail in those kinematic regions relevant for comparison with experimental data. With these results and including the resolved cross section which is dominated by the part originating from the charm in the photon, we compute the fully inclusive D* cross section and compare it with preliminary data from the ZEUS collaboration at HERA. We find on average good agreement.

hep-ph↗
arXiv2004

QCD condensates from tau-decay data: A functional approach

We study a functional method to extract the V-A condensate of dimension 6 from a comparison of tau-decay data with the asymptotic space-like QCD prediction. Our result is in agreement within errors with that from conventional analyses based on finite energy sum rules.

hep-ph↗
arXiv2003

Inclusive D* production in gamma-gamma collisions: including the single-resolved contribution with massive quarks

We have calculated the next-to-leading order cross section for the inclusive production of charm quarks as a function of the transverse momentum p_T and the rapidity in two approaches using massive or massless charm quarks. For the single-resolved cross section we have derived 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 very fast with increasing transverse momentum. With these results and including the equivalent results for the direct cross section obtained previously as well as double-resolved contributions, we calculate the inclusive D*+- cross section in gamma-gamma collisions using realistic evolved non-perturbative fragmentation functions and compare with recent data from the LEP collaborations ALEPH, L3 and OPAL. We find good agreement.

hep-ph↗