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Journal ArticleDOI

A study of kinematical correlations between charmed particles produced in π-Cu interactions at √s = 26 GeV

TL;DR: In this article, a sample of 475 events, in which two charmed-particle decays are observed, is analyzed to determine distributions of twoparticle kinematic variables.
About: This article is published in Physics Letters B.The article was published on 1996-09-26 and is currently open access. It has received 9 citations till now. The article focuses on the topics: Quantum chromodynamics.

Summary (2 min read)

1 Introduction

  • Hadroproduction of heavy quarks is an important testing ground for Quantum Chro- modynamics (QCD).
  • The observed experimental correlations between charmed particles provide a test of the NLO QCD calculations.
  • These variables are useful in subsequent comparisons with the predictions of charm production models.
  • The DkD has analogue readout so that secondary interactions in the detector material may be identi ed by their large energy deposits.
  • More details of the description and performance of the experimental apparatus can be found in Refs. [3, 4].

2 Event selection

  • Events are selected in which one charmed particle is fully reconstructed, while recon- struction of the decay vertex is all that is required for the second.
  • At this stage no cut is applied on the charmed candidate's invariant mass, except that 2-prong vertices compatible with K0 or 0 decays are rejected.
  • From the events which satisfy the previous requirements, 690 (2251) in the 1992 (1993) data, the authors extract two samples: the signal sample if the mass of the fully reconstructed vertex in the hypothesis D !.
  • The range and width of the side-bands has been chosen to allow the subtraction of a linear background distribution and at the same time to minimize the statistical error of this subtraction.
  • They were found to be compatible, so only the combined results are presented.

3 Momentum estimator

  • As previously noted, the momenta of the charmed particles is not needed for the measurement of ; however, it is required for the determination of the other correlation variables.
  • Thus it is necessary to have an estimator for the momentum of the partially reconstructed vertex which takes into account the unseen decay products.
  • The charm momentum can be deduced imposing the charm mass: pD = D DMD: A comparison between these two methods and the simulation indicates that both methods give useful and independent information; however the rst method systematically underestimates the momentum while the second method systematically overestimates it.
  • The optimal weights are acceptance dependent; for their experimental setup equal weights give a good result.
  • The resulting fractional errors on the correlation variables are well below 10% over most of the range of their measurements.

4 Background subtraction and acceptances

  • The invariant mass distribution for the fully reconstructed vertex is shown in Fig. 2a.
  • Fitting the data mass distributions with a Gaussian peak above a linear background, the authors nd that the background in the signal region is 15% for both the 1992 and 1993 data sets.
  • Comparison of the data and Monte Carlo distributions shows that the charm events with reconstruction errors account for all the background in this mass interval.
  • 3 and 4, therefore acceptance corrections were evaluated by dividing each distribution of reconstructed events by the corresponding distribution of generated events.

5 Results

  • 3 and 4 show the distributions of the charm correlation variables after back- ground subtraction and acceptance correction.
  • Table 1 reports the mean values found by the present analysis for all measured correlation variables.
  • The asymmetry in these distributions is thought to result from asymmetry in quark contents of the beam and target particle.
  • The and p2T distributions are plotted in Fig. 3 along with the results of a model based on a NLO QCD calculation [22] which includes non-perturbative e ects such as hadronization and initial transverse momentum of the incident partons [23].
  • Within the context of this model, no meaningful prediction is available for comparison with the data.

6 Conclusions

  • This paper presents correlations observed in the WA92 experiment between two charmed particles produced in {Cu interactions at p s = 26GeV, where one of the charmed particles, which is fully reconstructed, has positive xF .
  • The distributions observed are similar in shape and statistics to the previous highest statistics experiment.
  • A comparison has been made between the and p2T distributions observed and a model based on NLO QCD.

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