Multimuon events have been recorded with the ALEPH-detector, located 140 m underground, in parallel with e + e , data taking. Benefitting from the high spatial and momentum resolution of the ALEPH tracking chambers narrowly spaced muons in high multiplicity bundles could be analysed. The bulk of the data can be successfully described by standard production phenomena. The multiplicity distribution favors, though not with very high significance, a chemical composition which changes from light to heavier elements with increasing energy around the "knee". The five highest multiplicity events, with up to 150 muons within an area of 8 m 2 , occur with a frequency which is almost an order of magnitude above the simulation. To establish a possible effect, more of these events should be recorded with a larger area detector. (Submitted to Astroparticle Physics)a Retired from CERN b visitor from ARCADA Polytechnic, Helsinki, Finland c now at Mainz University IntroductionThe distributions of muons accompanying extensive air showers, initiated by primary cosmic rays interacting in the upper atmosphere, have been studied with large-area arrays close to the surface of the ground [1][2][3] and deep underground [4][5][6][7]. A primary goal of these experiments has been to better understand the mass composition and energy spectrum of primary cosmic ray nuclei, particularly in the energy range of 1 to 100 PeV. The data presented here are for muons observed at an intermediate depth, corresponding to a vertical muon threshold energy of 70 GeV. The primary composition is known from direct measurements with satellite and balloon-borne experiments up to about 10 14 eV due to the rapidly falling flux vs. energy; higher energies require larger detector areas and longer exposure times than have been possible with instrumentation flown at the top of the atmosphere. Better knowledge of composition vs. energy may aid in interpreting the origin and acceleration mechanism of cosmic rays in this energy range.The cosmic ray community has been studying air showers for decades, seeking to learn the primary composition at energies above those accessible to direct observation. The problem is that the determination of the primary composition is inextricably linked to the dynamics of the first interactions, as far as air shower observables are concerned. The Monte Carlo models which simulate the primary interaction are based upon experimental observations at energies many decades below those discussed here and additionally have to use elementary-particle models to describe the interactions at the energies of interest. There are several Monte Carlo models which have been used to simulate this interaction -VENUS, QGSJET, SIBYLL, etc [8]. Different experiments using the above Monte Carlo simulations have reported very different mass compositions in the "knee" region [9]. For example, the deduced composition appears significantly different for ground hadron measurements and for electron-muon measurements [10].Ultimately, one must 'tune' the Monte ...
We report results on inclusive direct photon (); 0 , and production in both pp and pp interactions at p s = 2 4 : 3 GeV in the transverse momentum range 4:1 p T 7:7 GeV/c and rapidity range 0:1 y 0:9. The data were collected between 1988 and 1990 by the UA6 experiment at CERN, which employed an internal H 2 gas jet target in the S ppS collider. The inclusive direct photon cross sections and the cross section dierence (pp) (pp) expressed as functions of p T () are compared with next-to-leading order QCD predictions.
The FELIX collaboration had proposed the construction of a full-acceptance detector for the LHC. The primary mission of FELIX was the study of QCD: to provide comprehensive and definitive observations of a very broad range of strong-interaction processes. This document contains an extensive discussion of this physics menu. In a further paper the FELIX detector will be reviewed. Contents HISTORYWith the advent of the large hadron collider (LHC), we are on the threshold of a new era in high-energy physics. With instrumentation in the form of dedicated experiments of unprecedented precision and complexity, the LHC will move significantly beyond the current high-energy frontier, and dramatically improve our understanding of particle physics at the highest energies and shortest distances accessible to man.As currently planned, however, the LHC experimental programme is incomplete. Moreover, these deficiencies continue and extend what has been a gap in the experimental programme of all hadron colliders. The problem lies in the design of the detectors instrumenting hadron colliders: they are all optimized for rare, high-pt events. These 'general purpose' detectors are anything but that. Rather, they are designed to explore extreme shortdistance phenomena. Without intending to demean the efforts of the collaborations which have built or are building these detectors, it is nevertheless these events in which the theorists are most confident that they understand the physics, and are in many ways experimentally most accessible.While there is no doubt that such physics and such detectors should be the centrepiece of any programme of hadron collider physics, it seems much less clear that they should be the only item on the agenda. Indeed, it can be argued that a full-acceptance detector, capable of detecting and measuring each particle in an event well, may have the greatest discovery potential. Alas, the absence of any experimental effort in this direction in the collider era has meant that both theoretical investigations and experimental design of such detectors has languished, to the point that many in the community have come to think of high-pt physics as the last frontier in particle physics.The FELIX collaboration sought to rectify this situation. With support from the CERN administration, some 160 physicists collaborated in preparing the FELIX LoI. Many of these could not officially join the collaboration, and so their help could only be acknowledged. While the FELIX proposal was never officially killed, it was nevertheless effectively killed without the collaboration making a formal presentation to the LHC committee.All of this, of course, is history, and not very pleasant history at that. The motivation for a full-acceptance detector remains, however, and interest on the part of the broader community, despite the implications of this history, remains high. Because of this, the FELIX collaboration, together with those who helped but were not members, believes that it is important to document the physics of a ...
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