Atomic mass dependence ofD±andD0,D¯

G. A. Alves¹,

S. Amato²,

J. C. Anjos³

et al.

Abstract

We measure the relative cross sections for D mesons produced in interactions of TC~ and 7r + beams with targets of Be, Cu, Al, and W. The measurement is based on 1400 fully reconstructed decays of the types D° -> K~TT + , D + -• K~7r + 7r~*~, and charge conjugates. We find that the cross section for the production of both neutral and charged £>'s by either TT~ or 7r + is well fitted by the form A a where A is the atomic mass and a = 1.00 ± 0.05 ± 0.02, where the errors are statistical and systematic, respectively. There is no significant dependence of a on the transverse or longitudinal momentum of the D meson or on the charge of either the incident pion or the produced D meson.PACS numbers: 13.85. Ni, 12.38.Qk, 25.80.Ls Measurement of the nuclear target dependence of the hadroproduction of charm mesons allows one to probe the distance scale important in the production and hadronization of charmed quarks. Also, since in the standard model the dominant subprocess contributing to charm quark production is gluon-gluon fusion, this measurement provides a means for studying the distribution of gluons in nuclear matter. If the distance scale is small compared to the size of a nucleon, and if the gluon distribution is the same in different nuclei, then the cross section per nucleon should not depend on the target type. If the dependence of the cross section per nucleus on atomic mass, A, is parametrized by the form A a , then the behavior described above is characterized by a = 1. In contrast, for the total inelastic cross section in pion-nucleon collisions, a -0.75 [1], which can be compared to the value of 2/3 expected from scattering by a totally absorbing sphere. The target dependence of the charm cross section is also important in comparing results from experiments with different target materials and in choosing the target material for future heavy quark experiments.The measurements presented here are from Fermilab experiment E769. This experiment utilized a charged, secondary beam of momentum 250 GeV. Data were taken with both negative and positive charged beams. These beams consisted of a mixture of pions, kaons, and protons. The beam content was measured with a differential Cherenkov counter (DISC) [2]. The negative beam consisted of 93% 7r~, 5% K~, and 1.5% p, and the positive polarity beam consisted of 61% 7r + , 4.4% K + , and 34% p. During normal data taking, the DISC detected kaons, with an efficiency of about 40% and negligible contamination from pions. After removing DISC-tagged kaons, the negative beam sample used in this analysis consisted of 95% 7r~ with a contamination of 3% K~ and 2% p. The pions were tagged in the positive data with a transition radiation detector (TRD) [3] with a typical efficiency of 87%. After tagging, the positive beam sample consisted of 98% 7r + and contamination of 2% p. The beam particle measurement was also aided by 8 multiwire proportional chambers (MWPC's) and 2 silicon microstrip detectors (SMD's).The A dependence measurement was made by simul- 722

Quarkonium production through hard comover scattering

“…Data shows that α = 1.02 ± .03 ± .02 for D/D production at x F = 0.031 [37], whereas α = 0.92±0.01 for J/ψ and ψ ′ [29]. The deviation of α from unity for charmonium appears to be independent of E CM , and increases with the charmonium momentum fraction x F .…”

Total forward and differential cross sections of neutral D mesons produced in 500 GeV/c π−–nucleon interactions

“…We obtain the total forward cross section by summing the x F differential cross section for x F >0 and assuming the cross section for 0.8<x F <1.0 is half that of the cross section for 0.6<x F <0.8 but with the same error. Assuming a linear dependence on the atomic number [22], we obtain the neutral D total forward a turnover point greater than zero (x c = 0.0131±0.0038) in the Feynman-x distribution, providing evidence for a harder gluon distribution in the pion than in the nucleon.…”

The dynamics of quarkonium production

“…The J/ψ and ψ ′ cross sections both scale as σ A ≃ σ N A α , with α = 0.92 ± 0.01 [10]. On the other hand, for open charm (D) production α = 1.02 ± 0.03 ± 0.02 [12]. This difference in A-dependence is quite remarkable.…”