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Mass-Producing B Mesons

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Mass-Producing B Mesons resolved definitively. MACHOs (MAssive Compact Halo quark) has emerged from the detec­ The relative deficit of muon to Objects) have seen nothing so far, tors ARGUS (at the DORIS ring, electron atmospheric neutrinos but only a small fraction of the data DESY, Hamburg) and CLEO (at the observed by the Kamiokande and has been analysed. A new genera­ Cornell CESR ring) as well as from 1MB collaborations is confirmed by tion of cryogenic detectors should CERN's LEP electron-positron recent data from Soudan II experi­ soon be able to probe the region collider and the proton-antiproton ment, albeit with large uncertainties. predicted for a supersymmetric dark colliders at CERN and Fermilab. While the Kamiokande results are matter candidate - the lightest But the mosj challenging goal of consistent with neutrino oscillations, neutralino. this physics is to explore the mystery 1MB collaboration does not make Gravitation sessions concentrated of CP violation, so far only seen in such a claim, due to much larger mainly on current tests of the equiva­ neutral kaon decays. This subtle systematic uncertainties (attributed lence principle, and the theoretical mechanism - a disregard for the mostly to simulations). significance of this effort. A special combined symmetry of particle- An experiment at a test beam at the section reviewed the development of antiparticle switching and left-right Japanese KEK Laboratory is being the STEP project for a satellite test of reflection - possibly moulded the set up in a joint IMB-Kamiokande the principle. Theoretical talks under­ evolution of the Universe after the effort using a 1-kiloton water lined the challenge of measuring the Big Bang, providing a world domi­ Cherenkov detector. This should extremely small effects of any such nated by matter, rather than one provide important information about violation. where matter and antimatter play electron-muon separation at low Covering such a wide range of comparable roles. energies, crucial for correct interpre­ different but interrelated areas of To fully explore CP violation in the tation of the Kamiokande and 1MB physics was a challenge. However in laboratory needs a dedicated ma­ data. the informal Moriond atmosphere chine - a particle 'factory' - to mass The Moscow-Heidelberg group participants could ask even 'elemen­ produce B mesons. Only when this searching for neutrinoless double tary' questions, increasing the scope, full picture of CP violation has been beta decay of germanium-76 using as well as the depth, of their physics revealed will physicists finally be able an enriched sample detector now knowledge. to solve its mysteries. has, as reported by Piepke, a lower The workshop was organized by As well as major proposals in the limit on the isotope lifetime of 1.6 x J. Tran Thanh Van and his col­ US and Japan, several ideas have 1024 yrs, implying an upper limit on a leagues with the financial support been launched in Europe. Over the Majorana mass of the electron from CNRS, CEA, NSF and the years, many working groups have neutrino of 1.2-1.4 eV (a Majorana Observatoire de Paris. accumulated an impressive amount particle is its own antiparticle - a of data and knowledge on the phys­ Dirac particle has a distinct antiparti­ Information from T.J. Bowles and ics as well as on the machine and cle). P.S. Joshi detectors. Although an excess of events below The spearheads of experimental B the endpoint is seen, the shape of physics are the ARGUS and CLEO the electron spectrum rules out Mass-producing B collaborations. Highlights include the Majoron emission for a Majoron- determination of the parameters of neutrino coupling greater than 1.8 x mesons the (Cabibbo-Kobayashi-Maskawa, 10~4. This makes it rather unlikely that CKM) quark mixing matrix, testing the excess of events in other experi­ Since the discovery of the upsilon the consistency of the Standard ments is due to Majorons. resonances in 1977 the physics of Model with six quarks and three Dark matter was covered by Larry the fifth quark - beauty - has played a leptons, and giving the first indirect Krauss and David Caldwell. The vital role in establishing and consoli­ hint that the as yet unseen sixth COBE and IRAS satellite data is best dating today's Standard Model of ('top') quark is very heavy, together fitted by a mix of hot and cold dark particle physics. with initial indications of how it should matter containing 30% of 7 eV (tau?) In recent years, a wealth of data on decay. neutrinos. Two groups searching for B particle (containing the beauty Valuable complementary informa- 16 CERN Courier, June 1993 A recent sighting at the Aleph experiment at CERN's LEP electron-positron collider was this beautiful fully reconstructed formation of a Bs meson and its subsequent decay into a psi prime (subsequently giving a muon pair) and a phi meson (giving a kaon pair). The Bs mass is 5.3746 GeV, in accord with theoretical predictions. tion has come from proton-antiproton violation in kaon decays to constrain on charmed particles, and in the collider data and particularly from the the Standard Model. However, there limiting case of an infinitely heavy LEP experiments at the Z resonance. are still large uncertainties, especially quark system, both of which have Experiments at LEP have measured the top quark mass, which to the best been studied by lattice techniques. average and individual lifetimes of of our knowledge is somewhere These methods are well on their way the various B hadron species as well between 91 and 180 GeV. to providing fully quantitative predic­ as the weak neutral current proper­ Top quark particles will hopefully tions for many aspects of B decays. ties of the b quark, while both elec­ soon be found at Fermilab's Tevatron Awaiting experimental determina­ tron-positron and proton-antiproton collider. However determination of tion of several important quark studies have been able to establish a the various quark couplings and form couplings, recent measurements of significant signal for neutral B mixing. factors needs a reliable theoretical the Ds meson (strange antiquark and The Bs-meson (containing a strange framework. Here lattice gauge theory charmed quark) by the WA75 col­ antiquark and a b quark) and calculations are promising. Although laboration at CERN provide a useful lambda-b baryon have been seen by the present lattice-volumes are not check on a number of theoretical experiments at CERN. sufficient to simulate B physics models and strengthen confidence in B physics information can be directly, reliable methods have been lattice results. combined with results from CP developed in extrapolating the results To match the precision and reach of CERN Courier, June 1993 17 experiments at a B factory needs mesorrs to transform into each other further development of theoretical provide another possibility, while the Physics and tools. A particular goal is to perfect interference of this effect with direct the lattice techniques needed to B decay gives a third. In the Stand­ astrophysics of quark- compute B decays with a precision of ard Model, this latter class might gluon plasma 10% or better. exhibit large CP violating effects, In the same vein, the discovery of much larger than those seen in kaon heavy quark symmetry by Isgur and decays. The quark gluon plasma - matter Wise in 1989 and its subsequent While the bulk of analysis so far too hot or dense for quarks to crystal­ consolidation has opened up reliable uses a Standard Model context, B lize into particles - played a vital role predictions for B decays. This ap­ decays also provide a scenario for in the formation of the Universe. proach exploits the big difference physics beyond the Standard Model. Efforts to recreate and understand between quark masses, revealing With high production rates for tau this type of matter are forefront powerful symmetries in heavy quark leptons, a B factory will allow physics and astrophysics, and systems which facilitate computa­ searches for many decays at levels progress was highlighted in the tions. The approach has already paid at least two orders of magnitude Second International Conference on handsome dividends, but data from B more sensitive than present limits. Physics and Astrophysics of Quark factory experiments would increase The wide diversity of B decay Gluon Plasma (ICPA-QGP 93), held its usefulness. channels needs to be exploited to in Calcutta from 19-23 January. (The Flavour changing neutral current improve our understanding of weak first conference in the series was transitions in B decays creep in as decays. Present measurements and held in Bombay in February 1988). higher order (rare) processes and are theoretical analyses support the Although primarily motivated to­ dominated by virtual top quark Standard Model, but consistency is wards enlightening the Indian physics contributions. Measurements would not yet complete. Experiments at a B community in this new and rapidly provide valuable constraints on the meson factory will pin this down. evolving area, in which India now top quark mass and its inter-quark In particular, the possibility of plays an important role, the confer­ couplings. The recent observation by observing CP violation in B decays is ence also catered for an international the CLEO collaboration at Cornell's an outstanding opportunity to finally audience. Particular emphasis was CESR electron-positron collider of get to grips with a fundamental placed on the role of quark gluon the decay of a B meson into a K* and physical phenomenon vital to our plasma in astrophysics and cosmol­ a photon provides a good check of understanding of the evolution of ogy. the strength of so-called 'penguin' universe. While Charles Alcock of Lawrence processes (see page 1 ) and opens a Last but not least, there is the Livermore looked at a less conven­ new chapter in the study of weak general dissatisfaction with the tional picture giving inhomogeneous decays.
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