Heavy Quark Production

The leading-order (LO) process for the production of a heavy quark Q with mass mq in hadronic collisions is flavor creation, i.e. quark-antiquark annihilation and gluon-gluon fusion 

1----p is the velocity of the heavy quark. The quark annihilation process vanishes 

In gluon splitting events the heavy quark occurs in QQ events in the initial- or final-state shower. The resulting heavy flavored final state can carry a large combined transverse momentum and thus be concentrated within a small cone of angular separation. The contribution of the different processes to the total Z -quark production cross section predicted by PYTHIA (see Sect. 3.6) is shown in Fig. 3.8 as a function of the center of mass energy. 

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The study of heavy quark production is an important research area at the LHC. Heavy quarks will be produced with a large cross section at a yet unreached center-of-mass energy, enabling precision measurements to improve our understanding of heavy flavor physics. In the context of this work the term heavy quark stands for charm and beauty quarks since the mass of the up, down and strange quark are significantly lower. The heavier top quark has a very short lifetime and does therefore not form bound states of heavy hadrons. 

Heavy quark production is interesting on its own as it presents a key process for the study of the theory of strong interactions. Quantum Chromodynamics (QCD). Furthermore, a well-established theory of heavy quark production is needed for many searches at the LHC. 

M. L. Mangano, Two lectures on heavy quark production in hadronic collisions. CERN-TH/97-328 (1997)... 

In the above we have kept all quark mass terms so that we can deal with the case of heavy quark production when is not much greater than ml- As previously we specify by... 

In this chapter the theoretical concepts relevant to describe the physics of heavy quarks at the LHC are introduced. The main ideas of Quantum Chromodynamics are reviewed, before their appUcation to high-energy hadron-hadron collisions is discussed. This includes the factorization ansatz, the evolution of the parton distribution functions, the partonic processes important for beauty quark production and the phenomenological treatment of heavy quark fragmentation. A further section is dedicated to the description of the decay of -hadrons via the weak interaction. The Monte Carlo event generators which are used in this analysis to generate full hadronic events within the QCD framework are presented in the last section. 

Soft processes resulting in the production of low momentum hadrons will be the most common events in proton-proton collision at the LHC. Although these processes are QCD related, they cannot be calculated by pQCD. Perturbative approaches only lead to reliable results if a hard scale is present in the interaction. In the case of heavy flavor physics, the hard scale is provided by the mass of the heavy quark, its transverse momentum or the virtuality of the process. 

Fig. 3.6 Reading order diagrams for heavy-quark pair production (a) quark-antiquark annihilation (b)-(d) gluon-gluon fusion gg -> QQ...

The presence of hadrons containing heavy quarks is deduced by the observation of their decay products. In a first approximation of fc-fiavored hadron decays, only the beauty quark participates in the transition while the other quark acts as a specta-... 

The subject of heavy flavours has e3q>anded tremendously in recent years stretching from the static properties (mainly spectroscopy, i.e. energy levels, lifetimes, branching ratios, decays, mixing etc.) of hadrons with one or more heavy quarks, e.g. bottom or charm, to more dynamical properties (like fragmentation, structure functions, jets etc.) and on to more exotic topics, e.g. production and decay of as yet undiscovered flavours like top, or speculations on a fourth generation or imphcations on Higgs or on non-standard effects and so on. 

Because NC interactions do not change the quark flavour, the only way to produce heavy quarks in the final state is for the vector boson to interact with the heavy quark itself. As mentioned earlier it is sensible to assume that there is no primitive cor b content to a nucleon so that the process relies on QQ production by gluons, as illustrated in Fig. 16.10. 

The experimental signatures of a phase transition include (a) suppression of production of the heavy vector mesons J/XV and E and the upsilon states, (b) the creation of a large number of ss quark-antiquark pairs, and (c) the momentum spectra, abundance, and direction of emission of di-lepton pairs. The first phase experiments in this held have been carried out. Energy densities of 2 GeV/fm3 were created. Strong J/XV suppression has been observed relative to p-A collisions along with an increase in strangeness production. 

Nuclei are constructed from protons and neutrons. The proton and the neutron are members of a class of elementary particles called baryons (the heavy ones) which are constructed from quarks. The quark orbital is the product... 

Diquarks are almost as old as quarks. The possibility that quarks might cluster pairwise in baryons, leading to a simple two-body structure, has been suggested by many authors since the early days of the quark model. There are currently many speculations on the use of diquarks to analyse baryon production in e e" experiments, in hadronization of jets, or in the decay of heavy particles [11]. We shall restrict ourselves here to the domain of baryon spectroscopy. 

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