Charm Fragmentation Function Research Articles

Measurement of [formula omitted] at HERA

Recent results on the extraction of the charm contribution, F 2 c c ¯ , to the inclusive proton structure function F 2 in deep inelastic ep scattering at HERA are presented. Different methods of charm tagging and measurements of the charm fragmentation function are shown. The issues related to the extrapolation of the visible cross sections to the full phase space are discussed.

Measurement of the charm fragmentation function inD* photoproduction at HERA

The charm fragmentation function has been measured in D* photoproduction with the ZEUS detector at HERA using an integrated luminosity of 120 pb(-1). The fragmentation function is measured versus z = (E + p(parallel to))(D)* / 2E(jet), where E is the energy of the D* meson and p(parallel to) is the longitudinal momentum of the D* meson relative to the axis of the associated jet of energy E-jet. Jets were reconstructed using the k(T) clustering algorithm and required to have transverse energy larger than 9GeV. The D* meson associated with the jet was required to have a transverse momentum larger than 2GeV. The measured function is compared to different fragmentation models incorporated in leading-logarithm Monte Carlo simulations and in a next-to-leading-order QCD calculation. The free parameters in each fragmentation model are fitted to the data. The extracted parameters and the function itself are compared to measurements from e(+)e(-) experiments.

Crossing heavy-flavour thresholds in fragmentation functions

In analogy with parton distribution functions, also parton fragmentation functions obey matching conditions when crossing heavy-flavour thresholds. We compute these matching conditions at next-to-leading order in the strong coupling constant αs in the scheme. Our results can be used for the dynamical generation of the heavy-flavour component in next-to-leading order fits to light-hadrons fragmentation functions. Furthermore, when computing perturbatively the charm fragmentation function from first principles and evolving it to higher scales, our matching conditions should be used for consistency when crossing the bottom threshold.

Open charm production at HERA

Inclusive charm meson production cross sections in the deep inelastic scattering and photoproduction regimes are compared with QCD leading and next-to-leading (NLO) calculations. The NLO predictions are significantly below the data in some parts of the measured kinematic range. Angular distributions of dijet events with charm show clear evidence for the existence of charm originating from the incoming photon. The charm fragmentation function is measured for the first time at HERA. Various fragmentation ratios and the fragmentation fractions of the low-lying charm hadrons are determined and compared to previous e+e- results.

Charm production and fragmentation in charged current DIS

In charged current deep inelastic scattering charm is dominantly produced in scattering events on strange quarks, thereby allowing for an experimental determination of the nucleon's strange sea density. A measurement of the energy spectrum of final state charm fragments (D-mesons) determines the charm fragmentation function at spacelike scales considerably below typical e + e − c.m.s. energies. NLO corrections to the naive s → c parton model production picture are important and well understood.

Heavy quark fragmentation in deep inelastic scattering

We perform an analysis of semi-inclusive production of charm (D-mesons) in neutral current (NC) and charged current (CC) deep inelastic scattering (DIS) at full O(alpha_s^1). Our calculation is based on the heavy quark scheme developed by Aivazis, Collins, Olness and Tung (ACOT) where we include an O(alpha_s^1) calculation of quark scattering contributions for general masses and couplings. We review the relevant massive formulae and subtraction terms and discuss their massless limits. We show how the charm fragmentation function can be measured in CC DIS and we investigate whether the charm production dynamics may be tested in NC DIS. We also discuss finite initial state quark mass effects in CC and NC DIS.

Production of charmed mesons inZ decays

The production of charmed mesons $$\mathop {D^0 }\limits^{( - )} $$ ,D ± , andD *± is studied in a sample of 478,000 hadronicZ decays. The production rates are measured to be $$\begin{gathered} \frac{{\Gamma ({\rm Z} \to D^{* \pm } X)}}{{\Gamma _{had} }} = 0.187 \pm 0.015(\exp .) \pm 0.013(BR), \hfill \frac{{\Gamma ({\rm Z} \to D^ \pm X)}}{{\Gamma _{had} }} = 0.251 \pm 0.026(\exp .) \pm 0.025(BR), \hfill \frac{{\Gamma ({\rm Z} \to \mathop {D^0 }\limits^{( - )} X)}}{{\Gamma _{had} }} = 0.518 \pm 0.052(\exp .) \pm 0.035(BR), \hfill \end{gathered} $$ where the errors from this analysis are separated from those coming from theD branching ratios (BR). TheD *± momentum distribution is extracted separately for $$Z \to c\bar c$$ and $$Z \to b\bar b$$ events with the help of event shape variables. It is consistent with the prediction of the JETSET Monte Carlo program after adjustment of the charm fragmentation function. Constraining the shape of the $$Z \to b\bar b$$ contribution, the average fraction of the beam energy taken by aD * meson produced in the fragmentation of a charm quark is extracted by a parametric fit to be <X E > c =0.495±0.011±0.007. Evidence forD **0 (D 1(2420)0 and/orD 2 * (2460)0) production is found in the $$D^{* \pm } \pi ^ \mp $$ channel, accounting for a fraction (18±5±2)% of allD *± production. The relative production of vector and pseudoscalar mesons is dicussed, together with the possible effects ofD ** production. Thec-quark forward-backwardZ-pole asymmetry is detrmined from that of high momentumD *± to beA =(7.7±4.4)%.

D [formula omitted] correlations in photoproduction

Kinematic correlations between the charmed D and D mesons produced by a photon beam of mean energy 100 GeV c have been measured by the NA 14 2 experiment at CERN using a sample of almost background-free fully reconstructed D D events. The observed D and D D distributions are compared to the predictions of production models using different parameters for the charm fragmentation function and for the intrinsic transverse momentum of the partons.

Experimental studies on the heavy quark fragmentation functions

The influence of perturbative QCD gluon radiation and initial state photon radiation on the experimental determination of the heavy quark fragmentation functions is studied in order to extract <z c>, the mean of the charm fragmentation function, from the recent measurements of inclusiveD * production ine + e − annihilation processes. The result is <z c>=0.71±0.014±0.03, which is scale invariant in the c.m. energy range of 10GeV to 34GeV. This result is interpreted in terms of kinematical calculations on heavy quark fragmentation functions and also compared with results fromv-N-reactions and from investigations of inclusive lepton production ine + e − annihilation. Results of a QCD shower model are in good agreement with the data and offer an alternative description of phenomenological fragmentation functions.

Charged D production in e+e- annihilation at 29 GeV and a limit on D0-D-bar 0 mixing.

We have studied inclusive D*± production using the DELCO detector at PEP. Our technique involved kaon identification in the momentum range above 3.2 GeV/c using a threshold gas Čerenkov counter. This leads to a model-independent upper limit on D0−D¯0 mixing of 8.1% (90% confidence level). We also have measured the charm fragmentation function, which peaks at x≡PD*(Ebeam2−MD*2)12 of 0.56±0.06(stat.), and the total cross section for D* production, σ(D*±)=0.140±0.021(stat.)±0.032(syst.) nb (x>0.3, with radiative correction).Received 5 November 1984DOI:https://doi.org/10.1103/PhysRevLett.54.522©1985 American Physical Society

An unfolding procedure for determining the charm fragmentation function from neutrino dimuon data

We present an unfolding procedure to retrieve the charm fragmentation function D( z D) from vN→ μ − μ +X data, under the usual assumption that the extra muon originates from the decay of a charmed meson. The method is based on results of the mathematical theory of ill-posed linear problems, which allow a sort of Wiener filtering of the “noise” associated with statistical errors, and makes use of a Monte Carlo simulation program incorporating also the experimental effects of the apparatus. The discussion of simple numerical examples leads to the conclusion that the basis shape of D( z D) is satisfactorily reproduced with experimental statistics of a few thousand events.