Hadroduction of heavy flavors
[report]
I.D. Leedom
1986
unpublished
Fermi lab The subject of this review, as one can gather from the title, is the current state of knowledge (or ignorance) of heavy quark production, particularly charm, by hadron beams. The only report of B mesons in a hadron experiment is that of the WA75 collaboration. (l) We shal I come back to that experiment because of its interesting implications for B lifetimes, but the rest of the paper wi I I deal exclusively with charm production. Charm hadroproduction, I ike al I Gaul, can be divided
more »
... nto three parts: total cross section, pT and xF dependence. The only other question that arises is the species which have been observed. Of the mesons, the charged and neutral D and o* have certainly been seen. C 2 , 3 , 4 ) The F has probably been found(S) but the evidence is sketchy and somewhat contradictory. secure (S,?,S) ' Cross Sections The Ac and the A+ baryons appear while the TO is on much shakier ground. (Q) 2 Quoted charm cross sections are large, but there exist great uncertainties as to how large. The reason for this is due primarily to: uncertainties in nuclear cross sections and the extrapolation to hydrogen; large and difficult acceptance and efficiency calulations; and poorly known exclusive branching ratios. As D production is the best known, we begin with it. The published values are shown in Table 1. Most hadron-nucleon charm cross sections have been derived from results on heavy nuclei. Such cross sections are normally calculated by assuming that (1) with a a constant. If heavy quarks are formed in hard scattering processes, then one expects that the exponent should be equal to unity. This would be in agreement with J/~ production. The E613 collaboration has measured prompt v fluxes, which presumably come from charm decays, on three different target materials: beryl I ium, copper and tungsten. (lO) The best fit gives a=0.75. The inferred cross section of 28.6 µb./nucleon is twice as large as that found by the NA27 collaboration using the hydrogen bubble chamber LEBC. (ll) In fact the beam dump values shown in Table 1 have been calculated using a=l so that they agree with the LEBC data. The smaller value of a found by E613 3 would give a consequent increase in these cross sections by factors of 1.7, 2.7 and 3.7 for beryllium, iron and tungsten respectively. The question of the relation of p-p top-nucleus cross sections was investigated by Barton et al. (l 2 ) for the production of strange and non-strange species. Figure 1 shows their findings for a as a function of xF. They showed that cross sections on nuclei extrapolate to larger proton cross sections than are measured in hydrogen and that a is a function of x independent of beam or product type. A recent CERN experiment, (l 3 ) however, seems to indicate that a may depend on the produced species. What is certain 1s that the simple assumption embodied in Eq. 1 is naive and that charm production on nuclei is a much more complicated process than was anticipated. One is led to conclude that the only reliable cross sections are those found using proton targets. This only leaves the !SR and LEBC results. The latter are smal I statistics experiments (NA16 and NA27), but with very clean, reliable data samples and cross sections which are inferred from topological rather than exclusive decay channels. The !SR experiments typically have correction factors~ 10 6 and depend critically on exclusive branching ratios into the observed final states. These cross sections have been calculated using values of the D branching ratios 4 which have changed by factors of 2-4, depending on the mode, over the past 8 years. (l 4 ) The ISR results cannot, therefore, be considered to give reliable cross sections. The only known cross sections for D production are the LEBC measurements for pions at vs=26 GeV and protons at vs=27 GeV.
doi:10.2172/5764735
fatcat:7c6bremrrfb4zlcpkb7jgof6oe