# Measurement of low pT D+ meson production cross section at CDF

Primary authors: Jeffrey A. Appel1, Luigi Marchese1, 2, Manuel Mussini3, Luciano Ristori1, 4, Diego Tonelli5

1. Fermilab
2. University of Oxford
3. INFN and Università degli studi di Bologna
4. INFN - sede di Pisa
5. Cern

We report on a measurement of cross section for D+ mesons whose pT extends down to 1.5 GeV/c, a range still unexplored in proton-antiproton collisions.The measurement is conducted as a function of meson transverse momentum using D+→ K-π+π+ decays reconstructed in the full CDF Run II data set. Events are collected through minimal, if any, requirements on the event features, thus reducing biases to the physics properties of the collected charm decays. The sample is divided into subsamples according to the D+-candidate pT (pT bins). In each, we apply a data-driven optimization of the offine selection and perform a two-dimensional simultaneous fit of the resulting distributions of K-π+π+ mass and D+ impact-parameter, the minimum transverse distance between the D+ trajectory and the beam. The fit determines, for each pT bin, the signal yield of D+ candidates genuinely produced in the proton-antiproton interaction or originated from excited charm resonances (primary D+) by statistically subtracting D+ candidates originated from b-hadron decays (secondary D+). Each primary yield is combined with corresponding reconstruction and selection effciencies derived using simulation to determine the differential cross section. Charge-conjugate decays are implied throughout. The cross section σi, averaged in each pT bin i and integrated in the range |y|<1 (where y = 0.5 ln[(E + pz)/(E-pz)] and E and pz are charm meson energy and longitudinal momentum, respectively) is determined using the following equation:

$\frac{d\sigma_{i}}{dp_{T}}=\frac{N_{i}/2}{\int&space;Ldt&space;\cdot&space;\epsilon_{i}&space;\cdot&space;B}$

where Ni is the observed number of primary D+ and D mesons in each pT bin. The factor 1/2 is included because both D+ and D- mesons contribute to Ni and we report results solely for D+, assuming flavor-symmetric hadroproduction of charm quarks in the strong interaction. The integrated luminosity ∫ Ldt is normalized to an inelastic proton-antiproton cross section of σ = 60.7 ± 2.4 mb and εi is the global detection, reconstruction, and selection efficiency. The branching fraction B is taken from the PDG .
The differential cross section is averaged in each pT bin and integrated over the D+ rapidity interval |y| < 1.
The total cross section is σ(D+; pT > 1.5 GeV/c; |y| < 1) = 71.9± 6.8 ± 9.3 μb where the first contribution to the uncertainty is statistical and the second systematic. The results agree with earlier determinations at higher transverse momenta. While the measurements agree with theoretical predictions within the uncertainties, there is a systematic variation suggesting that theoretical cross section as a function of transverse momentum is in need of further refinement taking into account these results.
The complete analysis is described in CDF public note 11199.

# List of public plots

INVARIANT-MASS AND IMPACT-PARAMETER

CROSS SECTION