Quark Signal Research Articles

Lepton pairs below the Z 0: A detailed study

Lepton pairs with invariant masses M( l + l −) < M Z originate in p̄p collisions from two competitive sources: the Drell-Yan process and the associated production of heavy quarks followed by their semileptonic decay. We show that cuts required for lepton/hadron separation in the detectors suppress cc̄, bb̄ events, and that it is possible to obtain a clean Drell-Yan lepton-pair sample with a small tt̄ “background”. However the tt̄ signal can be easily isolated by specializing to e μ pairs or by requiring that the leptons are acollinear in the transverse plane. As the proposed heavy quark signature involves only charged leptons, it is at least as “clean” as the W → t b ̄ signature, although the predicted event rate (conservatively based on QCD fusion only) is somewhat less.

Glints: A signature of quark and lepton substructure

I explore experimental consequences of the idea that quarks and leptons may have a substructure, perhaps with some constituents in common. I argue that Glints: exceptional events with large multiplicities of hadrons and leptons, and enormous transverse momenta and acoplanarity, may offer the first glance into the new substructure. Glints could be observed in forth-coming p¯p and pp colliders, and may already have been seen in cosmic ray events.

A confining and asymptotically free solution for the renormalisation group invariant charge

The central role of the invariant charge in applications of the renormalisation group to quantum chromodynamics is discussed. The general structure of the invariant charge is examined, and it is shown to be a non-singular function of q2 for all finite non-zero q2. At q2=0 and q2=+or- infinity , there is always a solution for which the invariant charge vanishes. The zero at q2=0 is interpreted as a signal of quark and gluon confinement, and the zero at q2=+or- infinity shows that QCD is asymptotically free. Some applications of these general results are discussed.

A quark signature in the nuclear fireball model of heavy ion collisions

It seems possible that a definite quark matter signature may be observed in the near future in nuclear heavy ion collisions. For example, in experiments yielding a fireball temperature of at least 180 MeV, a lab energy of ∼ 11 GeV/nucleon must be reached for a 20Ne + U collision. These energies should be sufficient to produce quark matter in the fireball. The signature of this transition is observed by comparing particle spectra at higher energies. It is expected that once quark matter is reached the spectrum will remain constant at temperature greater than ∼ 180 MeV, rather than continue to change with energy.

Results of the torino search for quarks

After a brief review of previous experiments which have indicated the presence of « quark candidates » among the shower particles detected at 40 m w.e. underground, the results of a further search with two spark chamber telescopes are reported. Small pulses in the top scintillators of the triggering arrangement and delayed arrivals with respect to the shower front were used as initial « quark signature ». Interactions originated by the traversing particles in five layers of 5 cm Pb plus 1.8 cm Fe could serve as an additional criterion to establish the nature of the particles. The visualizing technique allowed rigorous elimination of all spurious effects resulting from soft accompaniment which could have contributed in the earlier measurements. Although also the final runs showed an unexplained excess of delayed small-pulse events corresponding to a « flux » of about 1 · 10−9 particles/cm2 s sr, the observations are not considered as convincing evidence for the existence of quarks. The interaction characteristics of the delayed particles are indistinguishable, within the statistical uncertainties, from those of the shower muons.