Relative yield of heavy hadrons as a function of the transverse momentum in LHC experiments
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EMENTARY PARTICLES AND FIELDS Theory
Relative Yield of Heavy Hadrons as a Function of the Transverse Momentum in LHC Experiments A. V. Berezhnoy1)* and A. K. Likhoded2), 3)** Received March 25, 2014; in final form, October 14, 2014
Abstract—The relative yield of hadrons involving a b quark (Bc , Bs , B, Λb , etc.) is studied as a function of the transverse momentum. It is shown that the yields in question exhibit a nontrivial transversemomentum dependence because of the difference in nonperturbative fragmentation functions and because of the contribution of power-law corrections at low transverse momenta. DOI: 10.1134/S1063778815020106
1. INTRODUCTION As a rule, the cross section for heavy-hadron production is calculated on the basis of the socalled factorization theorem. Within this approach, the production process is broken down into the hard subprocess of heavy-quark production and the soft subprocess of heavy-quark hadronization. The hard part can be calculated by various methods: the FONLL method [1, 2], the method combining perturbative QCD in the leading order with kT factorization (pQCD LO +kT factorization) [3], and the GM–VFNS method [4]. Within this approach, hadronization is totally determined by the so-called fragmentation function (FF), which can be extracted from data on heavy-hadron production in e+ e− annihilation. It is noteworthy that, in the hadronic production of Bc mesons, this approach is inapplicable at low and intermediate transverse momenta. According to the results obtained in earlier studies of our group [5–7], the fragmentation mechanism describes satisfactorily Bc -meson production only at transverse momenta higher than 40 GeV (see also [8–11] and more recent studies reported in [12–15]). In the case of Bc meson production in e+ e− annihilation, the fragmen-
tation approximation is on the contrary applicable over nearly the whole phase space.4) The reason behind this difference is that, in hadroproduction, b quarks interact with a hadron remnant. The contribution of this interaction to the cross section for Bc -meson production features a pT dependence in the 1/p5T form, whereas the fragmentation contribution changes in proportion to 1/p3T . Obviously, the contribution of nonfragmentation mechanisms is negligible at very high transverse momenta. Nevertheless, the nonfragmentation mechanism is dominant in Bc -meson production at experimentally observed transverse momenta, and a similar mechanism should in principle make a significant contribution to the yield of other B mesons. The fragmentation-mechanism contribution depends on the mass of the spectator quark in the B meson. This is one of the reasons why the relative yield of B mesons involving different spectator quarks depends on the transverse momentum. The importance of the ratio in question can be seen, for example, from the observation of the rare decay Bs → μ+ μ− (LCHb [16, 17] and CMS [18]), which is sensitive to manifestations of physics beyond the Standard Model. At the present time, the branching ratio for this decay is deter
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