Charm quark decay

Estimates can be made, however, if we use the free quark-parton model and assume that partons convert into hadrons with unit probability. A very rough estimate for the inclusive semi-leptonic D decay can be obtained along the lines given previously [eqn (13.2.2)] if we forget all complications coming from non-spectator diagrams and assume that the light quark behaves purely like a spectator while the charm quark decay proceeds as if it were a free particle. In this case one has... 

In this zoo of particles, only the electron, which was discovered even before the atomic theory was proven and the atomic structure was known, is really unseeable, stable, and isolatable. The proton also is stable and isolatable, but it is made up of two quarks up (with charge -1-2/3) and one quark down (with charge —1/3). As for the quarks, while expected to be stable, they have not been isolated. The other particle constitutive of the atomic nucleus, the neutron, is also made up of three quarks, one up and two down, but it is not stable when isolated, decaying into a proton, an electron, and an antineutrino (with a 15-min lifetime). The fermions in each of the higher two classes of the electron family (muon and tau) and of the two quark families (strange charmed and bottom/top) are unstable (and not isolatable for the quarks). Only the elusive neutrinos in the three classes, which were postulated to ensure conservation laws in weak interaction processes, are also considered as being unseeable, stable, and isolatable. 

A harder distribution is observed in the re-weighted data with respect to simulation. In order to validate the weighting procedure, it was applied to the simulated track spectrum. The results from simulation agree within the statistical error. For comparison, the measured distribution calculated from muons which were most likely generated in light quark or charm decays is also shown in Fig. 5.8. 

Prom the CERN SppS colliders we have a limit on a possible second generation of gauge vector bosons (CHARM, 1989) Mz > 280 GeV. No squark or gaugino (i.e. the supersymmetric partners of quarks and gauge vectors) below 100 GeV have been found nor have any heavy stable charged particles been seen at the 1.8 Tevatron by CDF (CDF, 1989). No fourth quark generation (i.e. no 6 ) is found by DELPHI at LEP 1 below 44 GeV in the decay of the Z (DELPHI, 1990). A summary of the situation can be found in Dydak (1991). 

Next, we discuss in detail the properties of the members of the J/ family (bound states of a charm-anticharm pair), their quantum numbers, decay patterns and the dynamical and kinematical reasons for their narrow widths. We then tturn to the most recently discovered family (T) whose members are remarkably heavy 10 GeV/c ) and which are supposed to be bound states of the heaviest quark-antiquark pair so far identified ( bottom or beauty ). 

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. 

In terms of quark diagrams (Fig. 13.1), a charm particle will decay into ordinary hadrons, according to the standard model, via the dominant quark transitions (see Section 9.2)... 

Several techniques have been devised to identify charm and bottom hadrons, such as (a) invariant mass peaks, (b) direct analysis of the decay vertex, (c) detection of leptons from semi-leptonic decays of heavy quarks. The key ingredients in these analyses are (i) the relatively long lifetime and (m) the lepton signature of heavy hadron decays,... 

All Cabibbo allowed decays of non-strange charm particles involve a single strange particle which therefore provides a prominent signal for charm. As already mentioned, the same signal is expected for bottom particles given that i> —> c + W is the main decay mode of b quarks. 

An antibaryon with charm C = -3 would not annihilate on ordinary matter, and instead would scatter elastically until it decays weakly. In a flavour-independent potential, indeed, the heavy quarks preferentially remain together, to experience more binding. TTiis effect is also responsible for the stability of the tetraquark QQqq [83,47]. 

Many subatomic particles have been identified. Leptons and quarks are the elementary particles of matter. The electron is a lepton. Protons and neutrons are made of quarks. There are six types of quarks that differ in mass and charge. They are named up, down, strange, charm, bottom, and top. Protons consist of two up quarks and one down quark, and neutrons consist of two down quarks and one up quark. Although individual quarks have not been isolated, their existence explains the patterns of nuclear binding and decay. 

We expect PEP-II to produce high statistics samples of meson decays, thus presenting a wealth of new physics opportunities, beyond the principal objective of probing ti e origin of CP violation. These opj>ortunities in other aspects of 6-quark weak and electromagnetic decay, in charm decay, in r decay, and in two-photon physics have been discussed in detail in [1]. This section l)iiefly summarize and updates tliat discussion. 

Further topics of interest that can be studied at PEP-II include semileptonic decays of D s and the spectroscopy of D mesons. There are interesting predictions concerning the spins and decay patterns of excited D meson states [26] that result from the simplicity of a heavy quark - light quark bound state. In addition, charmed baryons will be copiously produced and their spectroscopy and decay patterns can be studied. The sample will be more than an order of magnitude larger than that currently available. 

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