Glueballs, Hybrids, Multiquarks. Experimental facts versus QCD inspired concepts

Single crystals for radiation detectors

http://cds.cern.ch/record/190460/files/198809149.pdf

J/Ψ decays

Hadron spectroscopy has received revitalised interest due to the discovery of states with unexpected properties. Discussed are the recent findings at BABAR, CLEO, BELLE and BES. A detailed report is given on the many experiments reporting evidence (or counter--evidence) for the $\Theta^+(1540)$ and other pentaquarks. In conventional meson and in baryon spectroscopy, evidence is emerging that one--gluon--exchange does not provide the appropiate means to understand low--energy QCD; instanton--induced interactions yield much more insight. In particular the rich spectrum of baryon resonances is very well suited to test dynamical quark models using constituent quarks, a confinement potential plus some residual interactions. A still controversial issue is the question if glueballs and hybrids exist. There is the possibility that two $q\bar q$ scalar states and a glueball form three observed resonances by mixing. However, there is also rather conclusive evidence against this interpretation. Mesons with exotic quantum numbers have been reported but there is no reason why they should be hybrids: a four--quark interpretation is enforced for the $\pi_1(1400)$ and not ruled out in the other cases.

Glueballs, Hybrids, Pentaquarks : Introduction to Hadron Spectroscopy and Review of Selected Topics

The authors review the techniques used to measure the energy of elementary particles. The methods discussed span more than 20 orders of magnitude in energy, ranging from a small fraction of an electronvolt, where relic remainders of the Big Bang are being looked for, to the 1020 eV domain, where the highest-energy cosmic rays can be found. The emphasis is, however, on techniques employed in particle physics for studying collision processes at accelerators in the GeV-TeV range.

/pdf/energy-measurement-of-elementary-particles-1pz0ir41ph.pdf

Energy measurement of elementary particles

A prototye NaI(Tl) detector (the Cluster of 54) of spherical geometry subtending a solid angle of 7.5% of 4? at its center, has recently been assembled and tested. This detector consisted of 54 close-packed but optically isolated NaI(Tl) modules and the associated electronic circuitry. The Cluster of 54 is the predecessor of an almost complete spherical detector, the Crystal Ball, which will cover 94% of 4?. The latter detector is now under construction and is especially designed for the study of ?-rays produced in electron-positron collisions at colliding beam facilities. This article will outline the mechanical, optical, and electronic assembly of the prototype system. Cluster of 54 test data will be presented.

Design and Performance of a Modularized NaI(Tl) Detector (The Crystal Ball Prototype)

Results from a detailed study using the Crystal Ball detector at SPEAR of the inclusive photon spectra from 1.8. lo6 $J’ and 2.2. lo6 J/lc, decays are presented. Radiative transitions from the 9’ to the x2,1,0 states are observed with photon energies of (126.0 f 0.2 f 4) MeV, (169.6 f 0.3 f 4) MeV and (258.4 f 0.4 f 4) MeV and branching ratios B($’ -+ 7 x,,,,,) = (8.0 f 0.5 f 0.7)%, (9.0 f 0.5 f 0.7)%, and (9.9 It 0.5 f 0.8)‘?’ 0, respectively. Values for the natural line widths of the x states are obtained: I’(x,,,,,) = (0.8 4.9) MeV, (< 3.8) MeV and (1321) MeV, respectively (90% C.L.). I m roved values are found for the branching p ratios B(~!J’ + 7r],) = (0.28 f 0.06)?’ o and B(J/$ + 7~~) = (1.27 kO.36)%, and forthe natural width I’(r],) = (11.5 f 4.5) MeV. 1. SPECTROSCOPY OF THE 4 FAMILY Since the discovery of the resonances of the ci~ charmonium family more than a decade ago, the T/J’ and J/+ h ave continued to stimulate considerable theoretical and experimental interest to explore the spectrum of states accessible via radiative photon decays. Potential models’ and dispersion relation models2 have predicted the spectrum of states, radiative transition rates, and natural line widths, in lowest order quantum chromodynamics (&CD). Calculations of relativistic and higher order QCD corrections3 have also been made. Two early experiments measured the inclusive photon spectra in J/$J and $’ decays. Ten years ago the Mark I magnetic detector, sensitive to converted photons above 200 MeV, discovered the $’ + 7x,, transition4 at the SPEAR e+ecolliding ring. In a short run at SPEAR the SP-27 experiment5 used a moderately segmented NaI(T1) detector to obtain a highly structured photon spectrum in $’ decays. The $’ radiative decay branching ratios to each of the triplet 1 3P2,1,~ (XJ) states6 were measured and found to be significantly below the naive potential model predictions. In a more recent work7 at the CERN-ISR and using a very different technique, the x2,1 states have also been measured. Furthermore a candidate for the 1 lS’0 ground state, the r],(2980) was observed in the inclusive photon spectra from G’ and J/$ decays by the Crystal Ball experiment.8 This state was confirmed in exclusive decays of the $J’ by the Mark II experiment9 and has recently been well measured by the Mark III experiment” which also determined the spin and parity to be O+. The Crystal Ball also reported existence of a 2 lS0 candidate,ll the vL(3590) seen in the $J’ inclusive photon spectrum. A candidate for the lP1 state has not been observed so far.12 In this paper we present final results of a detailed study of the radiative tran-

Charmonium spectroscopy from inclusive $’ and j/$ radiative decays*

The data acquisition system for the Crystal Ball project at SLAC is described. A PDP-11/t55 using RSX-11M connected to the SLAC Triplex is the basis of the system. A "physics pipeline" allows physicists to write their own equipment-monitoring or physics tasks which require event sampling. As well, an interactive analysis package (MULTI) is in the pipeline. Histogram collection and display on the PDP are implemented using the Triplex histogramming package. Various interactive event displays are also implemented.

/pdf/the-crystal-ball-data-acquisition-system-1ze8gqblol.pdf

D. G. Coyne

Papers

Design and Performance of a Modularized NaI(Tl) Detector (The Crystal Ball Prototype)

Charmonium spectroscopy from inclusive $’ and j/$ radiative decays*

The Crystal Ball Data Acquisition System