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:



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

  • Figure 1: Two-dimensional fit in the (m, d0)-space for pT(D+) in 1.5-2.5 GeV/c.

  • Figure 2: Two-dimensional fit in the (m, d0)-space for pT(D+) in 2.5-3.5 GeV/c.

  • Figure 3: Two-dimensional fit in the (m, d0)-space for pT(D+) in 3.5-4.5 GeV/c.

  • Figure 4: Two-dimensional fit in the (m, d0)-space for pT(D+) in 4.5-6.5 GeV/c.

  • Figure 5: Two-dimensional fit in the (m, d0)-space for pT(D+) in 6.5-14.5 GeV/c.

CROSS SECTION

  • Figure 6: D+ production cross section, averaged in pT-bins and integrated over |y|< 1, as a function of pT(D+) bins in both data and FONLL prediction. The measurement point is displayed at the pT point-value at which the theoretical cross section equals the observed value of the pT-averaged cross-section. The point values are 1.99, 2.97, 3.97, 5.37, and 9.14 GeV/c, as determined using the theoretical prediction.

  • Figure 7: D+ production cross section as a function of pT(D+) bins for both the current and 2003 CDF results. The current measurement is averaged in pT-bins and integrated over |y|< 1, while the 2003 result is a pT-point cross section and and integrated over |y|< 1. For the current result the measurement point is displayed at the mean pT point of the bin.

  • Figure 8: D+ production cross section as a function of pT(D+) bins for both the current and 2003 CDF results after the theory scaling. For the current result the measurement point is displayed at the pT point-value at which the cross section equals the observed value of the pT-averaged cross-section. The point values are 1.99, 2.97, 3.97, 5.37, and 9.14 GeV/c, as determined using the theoretical prediction.

ADDITIONAL MATERIAL

  • Figure 9: Invariant K-π+π+ mass before the optimization.

  • Figure 10: Signal and sideband defintion.

  • Figure 11: Impact-parameter distribution before (left) and after (right) the sidebands subtraction for pT(D+) in 1.5-2.5 GeV/c.

  • Figure 12: Conditional-silicon efficiency in both data and MC for the J/ψ sample (left) and the πsoft (right) sample.

  • Figure 13: Production cross section for even and odd subsamples.

  • Figure 14: Conditional-silicon efficiency as a function of cotθ for the J/ψ sample.

  • Figure 15: Conditional-silicon efficiency for π in D+-MC and in D*-data (left). (η,z0)-map for the πsoft dataset (right).

  • Figure 16: Fit to the pT-efficiency of the J/ψ and πsoft for the first (left) and second (right) time periods.

  • Figure 17: Fit to the pT-efficiency of the J/ψ and πsoft for the third (left) and fourth (right) time periods.

  • Figure 18: Fit to the pT-efficiency of the J/ψ and πsoft for the fifth time period.

  • Figure 19: Correlation study in both MC and data for the J/ψ sample: conditional silicon efficiency for the second muon when the first one is already detected by the COT.



List of public tables

  • Table I: Results of the 2D-fit for the five pT(D+)-bins.

  • Table II: Reconstruction efficiency as a function of pT(D+).

  • Table III: Scale factors for control samples.

  • Table IV: Correction factors for the five pT(D+)-bins.

  • Table V: Corrected reconstruction efficiency for the five pT(D+)-bins with the CF method.

  • Table VI: Summary of systematic uncertainties. When parenthes are present, the number in (out of) parenthesis refer to the contribution to the even (odd) sample.

  • Table VII: Differential cross-section results for D+ and D- separately.

  • Table VIII: Differential cross-section results for two separate data types, those resulting from the zero–bias (ZB) and minimum-bias (MB) online triggers.

  • Table IX: Present CDF differential cross-section measurement, averaged in pT-bins and integrated over |y|< 1, compared to the thoeretical prediction.

  • Table X: Previously published CDF differential cross-section measurement, pT-point and and integrated over |y|< 1, compared to the thoeretical prediction.

  • Table XI: Comparison between the previous and the present CDF measurement over the range 1.5 - 14.5 GeV/c for the current measurement and over the range 6.0 - 20.0 GeV/c for the 2003 result.