proton density is more than 1014 per (May 19.91, page 6). More complex sq cm. superlattices have been investigated T. Niinikoski looked at polarized by a KEK/Nagoya/NEC group. Light cone approach solid target developments, where the Turning to the future, A.D. Krisch high deuteron polarization in organic looked at what is in store at UNK, One of the most challenging prob­ materials through r.f modulation is Fermilab and the US Superconduct­ lems in theoretical high energy impressive. High polarizations in ing Supercollider. RHIC at physics is to compute the bound- lithium compounds have been Brookhaven will also offer interesting state structure of the proton and achieved at Saclay, LAMP F and PSI polarized proton possibilities. KEK's other hadronslrom quantum (Switzerland), and the possibility of 12 GeV proton machine will cover a chromodynamics (QCD), the field proton polarization at room tempera­ complementary kinematic range. theory of quarks and gluons. ture proposed by the Kyoto/KEK P. Taxil showed how polarized The goal is not only to calculate the group is intriguing. S.Y. Lee ex­ beam physics at future large proton spectrum of hadron masses from first plained polarized beam acceleration colliders will probe beyond the principles, but also to derive the with 'snakes', indicating the possibili­ Standard Model, while D. Burke momentum and spin distributions of ties for major ongoing projects. looked at what electron-positron the quarks and gluons which control Highlights of the parallel workshop colliders will offer. Spin physics will high energy hadron interactions. on polarized electron sources and continue to be a fruitful field. One approach to these difficult electron spin polarimeters were calculations is to simulate QCD on an summarized by T. Nakanishi. From Akira Masaike artificial lattice. Recently, several new Remarkable progress in methods based on "light-cone" photoemission from semiconductors quantization have been proposed as has been seen in recent years. alternatives to lattice theory for Nagoya has obtained 86% polariza­ solving non-perturbative problems in tion with strained gallium arsenide, Tau production and decay in experiments at QCD and other field theories. CERN's LEP electron-positron collider while SLAC/Wisconsin has achieved provides valuable precision information on The basic idea is a generalization of 71% with indium gallium arsenide Standard Model parameters. Heisenberg's pioneer matrix formula­ tion of quantum mechanics: if one could numerically diagonalize the matrix of the Hamiltonian represent­ ing the underlying QCD interaction, then the resulting eigenvalues would give the hadron spectrum, while the corresponding eigenstates would describe each hadron in terms of its quark and gluon degrees of freedom. The new ingredient which appears to make this method tractable is quantization on the light-cone - as if the observer were travelling at the speed of light. For example if a laser is shone along the z-axis of an atom, the scattered photons determine the coordinates of each electron at a fixed value of t-z/c, where c is the speed of light. The equations of quantum electrodynamics then predict the electron coordinates at later values of t-z/c.

14 CERN Courier, March 1993 More valves. answers. Because their engineers know valves. Better design. And how to solve vacuum problems. First-class tech support. Plus, they've got a lot more than valves . . Whether you need butterfly or gate valves. Pneumatic or Its all in the free catalog. manual. Bakeable or elastomer- Everything. From positioners to sealed. Right-angle, in-line or straight-through - connectors to full custom chambers. To get Huntington is the place . . . the catalog, just call: Huntington Laboratories, Broader selection and better designs. Like their unique 1040 L'Avenida, Mountain View, CA 94043. conical seats, for tighter seals. Or their patented butterfly (800) 227-8059 or (415) 964-3323. floating shaft, for perfect flapper centering. Or their solid construction, with less welding for better integrity . . . Huntington And when you call Huntington, you get intelligent Better-Built Vacuum Components This allows a finite basis of non- provides .a precise definition of model For QCD(1+1), complete numerical interacting quark and gluon states structure in terms of quarks and solutions for the spectrum and light- without violating the essential relativ­ gluons, and a general calculus for cone wavefunctions can be obtained ists invariance of the theory. computing relativistic scattering, form as a function of the coupling strength, The foundations of light-cone quan­ factors, electroweak transitions, and the quark masses, and the number of tization date back to Dirac, who in other hadronic phenomena. flavours and colour. 1949 showed that there are remark­ The problem of computing the Light-cone quantization of QCD in able advantages in quantizing relativ­ hadronic spectrum and the corre­ physical space-time is a highly- ists field theories at fixed "light-cone sponding light-cone wavefunctions of challenging numerical computational time", t-z/c, rather than ordinary time. QCD can thus be reduced to the problem. In the DLCQ method, the In the traditional formulation, han­ diagonalization of a finite matrix size of the quark and gluon basis and dling a moving bound state is as representation of the light-cone the discretization of the transverse complicated as diagonalizing the Hamiltonian. This method, called momenta quickly leads to very large Hamiltonian itself. On the other hand, "discretized light-cone quantization" matrices. In addition, the quantization on the light-cone can be (DLCQ), has now been successfully Hamiltonian must be supplemented formulated without having to choose applied to a number of quantum field by renormalization terms. a specific frame of reference. Thus a theories in one-space and one-time Approximate methods have also light-cone QCD Hamiltonian de­ dimension, including QCD, quantum been developed which use effective scribes bound states of confined electrodynamics, Yukawa models, light-cone Hamiltonians and a trunca­ relativistic quarks and gluons of and the two-dimensional matrix tion of the quark and gluon states arbitrary four-momentum. It also models of superstring theory. t (the "Light-Front Tamm Dancoff method"), or a combination of light- cone quantization with traditional lattice gauge theory in the transverse dimensions. In the case of quantum electrodynamics in 3+1 dimensions, the positronium spectrum has been obtained at large coupling strength (a=0.3) by solving an integral equa­ tion derived from the truncated QED light-cone Hamiltonian. The most subtle problem now confronting light-cone quantization methods is how to understand the spontaneous symmetry breaking normally associated with the struc­ ture of the vacuum. In light-cone quantization the momentum-inde­ pendent "zero modes" of the quan­ tum fields are determined from

The positronium mass spectrum (for a=0.3) computed from a truncated quantum electrody­ namics light-cone Hamiltonian (from M. Krautgârtner, H. C. Pauli, and F. Wôlz) showing the convergence of the bound and continuum spectrum of positronium, including the hyperfine splitting, as one increases the number of integration points. This light cone approach promises new insights into complex field theory calculations.

16 CERN Courier, March 1993 MAKE YOUR BUDGET GO FURTHER.

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CERN Courier, March 1993 17 constraint equations derived from the development of showers in the equations of motion of the theory. atmosphere has been estimated from Although the vacuum is simple in Proton-proton reaction simulations assuming no significant light-cone quantization, these rates at extreme break in kinematical scaling up to the vacuum zero modes thus determine highest energies and that the number the phase and physics of the theory. energies of secondary particles increases as There are other fundamental the square of the logarithm of the renormalization and gauge invari­ Results on proton-antiproton reaction collision energy. ance issues that still have to be rates (total cross-section) at collision The proportion of showers pro­ completely understood, such as how energies of 1.8 TeV from experi­ duced by primary protons among the symmetries lost in the truncation can ments at Fermilab have suggested a observed showers is unknown at be restored, how to deal consistently lower rate of increase with energy such ultra-high energies. Air showers with massless particles, and how to compared to the extrapolation based initiated by heavier primaries gener­ control singularities. All of these on results previously obtained at ally start their cascades in the higher problems make the field quite excit­ CERN's proton-antiproton collider atmosphere. In order to optimize ing and challenging. (CERN Courier, October 1991). selection of showers which have a In addition to its potential for solving Now an independent estimate of the larger probability of being produced QCD problems, light-cone values for the proton-proton total by primary protons, only 10% of the quantization has already led to many cross-section for collision energies total showers in each energy range, new insights into the quantization of from 5 to 30 TeV has been provided those which have developed deep in gauge theories. Light-cone quantiza­ by the analysis of cosmic ray shower the atmosphere, have been used to tion not only provides a consistent data collected over ten years at the determine the proton attenuation language for representing hadrons as Akeno Observatory operated by the length. QCD bound-states of relativistic Institute for Cosmic Ray Research of The upper bound on the proton-air quarks and gluons, but it also pro­ University of Tokyo. inelastic cross-section increases with vides a novel method for simulating These results are based on the energy as 290E0052mb in the energy quantum field theory on a computer inelastic cross-section for collisions range101618eV, where E is the and understanding features of QCD. of cosmic ray protons with air nuclei incident proton energy in TeV (see The appealing features of light-cone at energies in the range101618eV. figure). The total cross-section for quantization for quantum field theory A new extensive air shower experi­ proton-proton collisions has been have brought together a new commu­ ment was started at Akeno, 150 km derived from the proton-air inelastic nity of theorists interested in solving west of Tokyo, in 1979 with a large cross-section using conventional both the practical and formal prob­ array of detectors, both on the (Glauber) theory of multiple scatter­ lems. A series of conferences were ground and under a 1-metre concrete ing inside the nucleus and a nucléon held in 1991 and 1992 at Heidelberg, absorber. This measured the total profile function derived from a QCD Aspen, Telluride, and Dallas. Two numbers of electrons and muons of parton model using a diffraction light-cone meetings in this series are energies above 1GeV for individual scattering formulation. being planned for this summer. showers with much better accuracy The total cross-section is found to Daniel Wyler of Zurich University than before. Data collection was vary as 38.5+1.37ln2(collision energy/ ([email protected]) is almost continuous for ten years 10GeV)mb. These fit fairly well with organizing a conference from 14-18 without any change in the triggering results from CERN's proton- June at the Paul Scherrer Institute criteria for showers above1016eV. antiproton collider at 540GeV and near Zurich, and Antonio Bassetto The mean free path for proton-air 900GeV and from Fermilab's (bassetto@ipdinfn) under the support nuclei collisions has been determined Tevatron collider at 1.8TeV, although of the Istituto Nazionale di Fisica from the zenith angle of the observed the Tevatron value is a little smaller Nucleare (INFN) is organizing a frequency of air showers which have than what is expected from the best workshop at the Gran Sasso Labora­ the same effective path length for fit to the Akeno results. tory from 17-27 August. development in the atmosphere and The observed frequency atten­ the same primary energy. The effect uation length depends on the By Stan Brodsky of fluctuations in the longitudinal fluctuation of air shower development

18 CERN Courier, March 1993