Strange particles


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Strange particles

Bound states of quarks, in which at least one of these constituents is of the strange (s) type. Strange quarks are heavier than the up (u) and down (d) quarks, which form the neutrons and protons in the atomic nucleus. Neutrons (udd) and protons (uud) are the lightest examples of a family of particles composed of three quarks, known as baryons. These and other composite particles which interact dominantly through the strong (nuclear) force are known as hadrons. The first strange hadron discovered (in cosmic rays in 1947) was named the lambda baryon, &Lgr;; it is made of the three-quark combination uds. A baryon containing a strange quark is also called a hyperon. Although strange particles interact through the strong (nuclear) force, the strange quark itself can decay only by conversion to a quark of different type (such as u or d) through the weak interaction. For this reason, strange particles have very long lifetimes, of the order of 10-10 s, compared to the lifetimes of the order of 10-23 s for particles which decay directly through the strong interaction. This long lifetime was the origin of the term strange particles. See Baryon, Hadron, Neutron, Proton, Strong nuclear interactions

In addition to strange baryons, strange mesons occur. The lightest of these are the kaons (K+ = u and K 0 = d) and the antikaons (= s and - = s). Kaons and their antiparticles have been very important in the study of the weak interaction and in the detection of the very weak CP violation, which causes a slow transition between neutral kaons and neutral antikaons. See Elementary particle, Meson, Quarks

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Naumova et al., "A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment," Nuclear Physics B, vol.
Study of Strange Particle Production in [v.sub.[mu]] CC Interactions
Baldisseri et al., "A study of strange particle production in [v.sub.[mu]] charged current interactions in the NOMAD experiment," Nuclear Physics B, vol.
Aderholz et al., "Neutral strange particle production in antineutrino-neon charged current interactions," Zeitschriftfur Physik C, vol.
Kennedy et al., "Neutral strange particle production in neutrino and antineutrino charged current interactions on protons," Zeitschrift fur Physik C, vol.
Another experiment, by 12 institutions ranging from the Punjab to Pittsburgh and from Athens to Bergen (Norway), will look for strange particles with a time-projection chamber.
This indicates that the chemical composition still alters slightly during the hadron gas through strange particle annihilation, decay, and baryon annihilation [21, 22].
The crucial role here is played by the non-negligible strange quark mass, which modifies the emission temperature for such quarks: in the Hawking-Unruh approach the temperature associated with strange particle production is different from that one of nonstrange particles.
Although a complete statistical hadronization model calculation has been necessary for a detailed comparison with experimental results [28], a rather simple, coarse grain argument can illustrate why a reduction of the H-U temperature for strange particle production reproduces the [[gamma].sub.s] effect.