:.;:.NA.:.:.TURE=.....:v.:::ot:::.;.306=...:1~7.;,;;NO::..:VEMBER==-.:.:.1983~------NEWSANDVIEWS ------=213 binding together the quark and anti-quark. Particle physics In principle, from a knowledge of this binding force together with a face value for the effective masses of the various flavours The F meson found at Cornell of quark, it should be possible to calculate from J. M. Yelton the masses of all mesons. This is made more difficult by the fact that in the charmed PARTICLE physicists using the CLEO the signal in another channel (for example, mesons the quark masses are small 1 detector at Cornell have recently shown F+ -+ +n+n-n+ would be very welcome, compared with the kinetic energy of the the most compelling evidence yet of the there seems little doubt that the resonance quarks inside the mesons, so relativistic existence of the F+ meson, the com­ observed by CLEO is, indeed, an F+ effects are important bination of a charm quark with a strange meson. The CLEO experiment will not be able to anti-quark2 • They measure the invariant Previous experiments have shown some measure the lifetime of the F+ produced, mass of the F+ to be 1970 MeV/c2 , evidence for the existence ofF+, produced but several experiments using optical filling an important gap in physicists techniques (bubble chambers and nuclear 4 knowledge of charmed mesons. emulsions) have already tried • Their main The discovery of the J/tp in 1974 started problem is unambiguously separating the a new era of particle physics and its identi­ F+ from other charmed partcles. The F+ fication as a bound state of a charm quark lifetime is expected to be similar to that of with a charm anti-quark was seen as a vali­ the oo (around 4 x 10 ·13 s), but there is still dation of the quark model of hadronic ?:! some controversy as to the exact decay matter. The model then predicted a whole mechanism of charmed mesons and a spectrum of mesons containing charm precise measurement of the F + lifetimes quarks. Combination of charm quarks should help clarify the situation. with up and down anti-quarks, the D0 and At a time when there are big projects o+, were found in 1975, and their excited 30 being undertaken to create e + e· collisions states, the o•o and o·+ followed soon of energies around 100 Ge V, the CLEO after. However, the F+ meson, the combi­ result highlights the amount of physics still 0~~~~~~~~~~_.~~ nation of a charm quark with a strange 1.6 1.8 2.0 2.2 2.4 2.6 2.8 to be explored at lower mass scales. D anti-quark, has proved difficult to detect. .p.,:t Mass (GeV) The properties of F + mesons may be J.M. Yelton is at the Stanford Linear predicted by analogy with D mesons. The F by a variety of mechanisms and decaying Accelerator Centre, Stanford University, P.O. mass is expected to be somewhat greater into an '1 and pions3.4, and also into a+ and Box 4349, Stanford, Co 94305. than that of the D+ {1,868 MeV /c2), and its a Q + (ref. 5). Although the mass measure­ I. A. Chen eta/. Phys. Rev. Lell. 51,(1983). The CLEO group decay products to be typically an '1 or a + ment from each individual experiment was is a collaboration from the Universities of Cornell, meson together with a number of pions. weak they tended to indicate an F + mass of Harvard~ Ohio, Rochester. Rutgers, Syracuse and The CLEO collaboration has sought for, around 2,030 MeV I c2 , so the CLEO result Vanderbilt, and Ithaca College. 2. Reference to a state will always imply the sum of that state and found, a resonance that decays into has come as something of a surprise. and its charge conjugate state. +n+ and which they identify with the Theoretically, the exact value of the F+ 3. R. Ammar eta/. Phys. Lett. 948, 118 (1979). 4. R. 8randelik eta/. Phys. Lett. 1108,412 (1979). D. Aston et F+meson. mass is interesting as it helps constrain a/. Phys. Lei/. 1008,91 (1981). The CESR e+e- collider at Cornell models of the shape of the potential force S. D. Aston et at. Nucl. Phys. 8189 205. (1981). produces collision energies of around 10 Ge V, just sufficient to create mesons including bottom quarks, but also fairly Human genetics well matched for studies of charmed mesons. The CLEO detector is a general Human gene mapping rolls purpose detector operating at CESR, and incorporates good charged particle along momentum measurement. The first stage in their analysis is to make the invariant from Ellen Solomon and Peter Goodfellow mass combination of oppositely charged THE enormous task of mapping the human 300 genes to be assigned to particular tracks under the hypothesis that they are genome was begun in 1936 using the autosomes- compared with only 20 in the kaons (tracks clearly identified as pions are classical Mendelian techniques of family previous 50 years. excluded). A clear signal corresponding to and population linkage studies. This Now the new decade has contributed a the+ meson (mass = 1,020 MeV/c2) is approach eventually ran into difficulties new revolution: gene cloning. Paradoxi­ seen. Those combinations with mass within because there were not enough cally this revolution has completed the 5 MeV /c2 of the +mass were taken as + polymorphic markers available, and in circle; the application of DNA probes and candidates. Combinations were then made 1970, it gave way to new methods using associated restriction enzyme site poly­ of the + candidates with each remaining somatic cell genetics. The random loss of morphisms (also known as RFLP for pion in the event. The invariant mass human chromosomes from human/rodent restriction fragment length polymor­ spectrum for +n+ combinations with somatic cell hybrids made it possible to phisms) can provide an unlimited number momentum greater than 2.5 GeV /c2 is map genes by correlating the presence of of genetic markers for studying human shown in the figure. A clear peak is seen, human genes, or gene products, with families. Mendelian genetics is once again with a width consistent with that due to particular human chromosomes. In the major tool for mapping the human experimental resolution alone and an addition, the large genetic differences genome. Future historians of science will invariant mass measured to be 1970 ±5 ±5 between humans and rodents meant that have no difficulty in discerning these trends MeV /c2 , where the errors are statistical many more genes could be studied. By 1980 as they are illustrated by biannual meetings and systematic respectively. The proba­ the technique had allowed approximately devoted to human gene mapping. The bility that the peak is due to a statistical latest• was held in California and was the fluctuation alone is around 1 in 20,000, and 'Human Gene Mapping 7, to b< published by the March of first fully to reflect the resurgence of the Dimes and Cytogenetics and Cell Genetics. Organised by R. its decay characteristics are consistent with Sparkes, M.A. Spence and T. Mohandas hi Auaust, 1983, and old genetics. it being an F +. Although confumation of held at U.C.l.A. The short-term goal of human gene

0028~36/83 /~23.a2S01.00 C 1983 Macmillan Journals ltd