CERN Collider Research Articles

Isolation of hard scattering effects in minimum bias data

Abstract A moment analysis is used to separate the “hard” and “soft” components of the multiplicity distributions observed at the CERN collider. The multiplicity distribution for the hard component is compared with that obtained from a QCD Monte Carlo calculation for the production and fragmentation of jets. The tail of the multiplicity distribution is shown to provide a useful comparison of the hard component with QCD. Reasonable agreement is obtained provided initial state bremsstrahlung is included in the QCD calculation.

New physics from the CERN collider

Experimental results from the CERN collider, having features that may not be explicable within the standard model of the strong, electromagnetic, and weak interactions, are described. They include events with dimuons and events with jets accompanied by missing energy. The evidence for the top quark is also presented.

Dynamics of elastic scattering

If the energy scale of the long-range interaction is determined by the string tension and not by the nucleon mass, our previous dynamical model for high-energy pp and pp scattering is in excellent agreement with the data, both from the CERN ISR and the CERN Collider. Thus the interpretation of these data does not require any novel dynamical mechanism.

A Micro Vertex Detector for Experiment UA1 at the CERN SppS Collider

This paper describes the design and operation of a pressurized drift chamber. The chamber provides 16 coordinates between 3 and 8 cm from the beam axis of the CERN collider.

High energy multi-jets at the CERN [formula omitted] collider and the SSC

Multi-jet topologies at large transverse energy in p p collisions at W = 540 GeV are studied using a QCD parton-shower Monte Carlo model. The model includes gluon radiation off partons in both the initial and final state and hadrons are labeled according to whether they result from beam and target fragmentation of from outgoing parton fragmentation. Results of the QCD model are compared with CERN collider data from UA1 and UA2 and with predictions of the naive 4-jet parton model. The data show qualitative agreement with the QCD Monte Carlo and deviate greatly with the predictions of the naive parton model. Estimates of multi-jet production in p p collisions at the SSC energy of W = 40 TeV are presented and discussed.

Colored lepton mass bounds from p [formula omitted] collider data

If leptons are composite particles containing colored preons one expects the existence of color octet fermions with quantum numbers similar to those of ordinary leptons. Such “colored leptons” are expected to decay predominantly into a lepton and a gluon. Comparing the present CERN collider data with the calculated cross section for colored lepton pair production via strong interactions we derive a lower limit on the mass of neutral colored leptons of 55–80 GeV. The colored partner μ 8 of the muon must be heavier than about 110 GeV.

Monojets from Z decay in the massive majoron model

We show that in a very simple extension of the standard SU(2) × U(1) electroweak model with complex triplet Higgs particles (the massive majoron model) the monojet events seen at the CERN collider can be explained as Z decays into Higgs scalars.

A two-component model for hadron production in high-energy pp collisions

A two-component model for low-PT hadron production in high-energy nondiffractive proton-proton collisions is proposed. The model combines together the ideas of Van Hove and Pokorski with the empirical findings of Basileet al. It consists of a nonscaling component, corresponding to a neutral-central fireball, which hadronizes according to the scheme of the hydrodynamic model, and a scaling component corresponding to two leading clusters which carry the quantum numbers of the proton and yield the leading particles. The charged-particle multiplicity predicted by the model is in good agreement with experimental data all the way up to the CERN collider energy. A comparison of the predictions for inclusive proton distributions with data in the energy range of the ISR and of the pp collider suggests energy dependence of the Van Hove parameters characterizing the recombination of the valence quarks into the observed proton.

Pp vs p-barp: From intersecting storage rings to superconducting supercollider.

The difference between the $\mathrm{pp}$ and $p\overline{p}$ elastic $\frac{d\ensuremath{\sigma}}{\mathrm{dt}}'\mathrm{s}$ found at the CERN intersecting storage rings and the behavior of the $\overline{p}p$ $\frac{d\ensuremath{\sigma}}{\mathrm{dt}}$ at the CERN collider have profound implications for the high-energy behavior of hadron scattering amplitudes. The consequences are shown to be striking in the tetraelectronvolt region.

KNO scaling violation and the “bremsstrahlung analogy”

We show the KNO scaling violation observed at the CERN Collider can be explained as a finite energy correction due to energy conservation effects, as calculated in the “bremsstrahlung analogy”.

Squark pair production mechanisms in [formula omitted] collisions

Through a phenomenological analysis in the transverse plane of a p p collision, we study different production mechanisms of squark pairs, decaying into a quark and a photino (missing energy): excitation of squarks inside the proton, fusion of light partons into squark pairs, and decay of heavier gluinos into squarks. The rates for missing transverse momentum are calculated and confronted with the monojet events observed at the CERN collider. In the framework of “minimal” supergravity models the excitation and fusion of squark pairs are disfavoured, whereas the dominant processes involve heavier gluinos and squarks cascading into photinos through intermediate squarks. The agreement with experimental data is better if heavier squarks and gluinos decay through an intermediate b-squark. We remark that energy dissipating effects during the cascade towards the final state tend to improve the comparison between theory and experiment.

Collider monojets as a signature of new dynamics

The production of W, Z or γ gauge bosons, accompanied by a single energetic jet, is calculated in terms of the the tail of new interaction which satisfies SU(3)×SU(2)×U(1) invariance at presently available energies. We investigate whether this can account for the rare energetic monojets and the massive e v + jet events observed at the CERN collider. For comparison we present the p T distribution arising from the decays of a massive excited quark state.

Asymmetry effects of supersymmetric QCD in dilepton production

A Callan-Gross-type relation between the structure functions determining dilepton production, which is satisfied by the basic O(1) and O(..cap alpha../sub s/) subprocesses of conventional QCD, is investigated in supersymmetric QCD (SQCD). It is found that SQCD subprocesses, mainly due to the presence of scalar quarks, strongly violate this relation, thus leading to sizable asymmetry effects in the angular distribution of dileptons. As an illustration, calculations are carried for p-barp..-->..l/sup +/l/sup -/+X at CERN collider and Fermilab Tevatron energies (..sqrt..s = 540 and 1600 GeV, respectively) and for pp..-->..l/sup +/l/sup -/+X at Tevatron energy; with scalar quarks of mass 20 GeV and light gluinos, asymmetries in the range of 20%--5% are found. The significance of the effects as a test of the short-distance structure of SQCD (valence part of the scalar-quark distribution) is discussed.

Composite Quarks and Nonstandard Bosons inp¯pCollisions

Quarks and antiquarks within colliding protons and antiprotons are assumed to be composites which can factorize into spin-\textonehalf{} and spin-0 constituents. If the spin-0 constituents can form by their recombination the standard ${W}^{\ifmmode\pm\else\textpm\fi{}}$ or ${Z}^{0}$, the possibility arises that the spin-\textonehalf{} constituents can recombine into new, nonstandard bosons. Along the lines of Abbott and Farhi a simple model is constructed predicting processes which may be releveant for CERN collider experiments in progress.

Implications of supersymmetric origins for monojets

Events with large missing momentum, seen at the CERN collider, could be produced by various supersymmetric processes. The broad implications for supersymmetric models are considered. For the case of squark pair production, it is found that N = 1 supergravity models become very highly constrained. Further experimental consequences of each mechanism are pointed out.

The SSC: A Machine for the Nineties

In July of 1983, the High Energy Physics Advisory Panel of the Department of Energy recommended that the highest priority be given to construction of a very large accelerator, the Superconducting Super Collider. The recommended energy per beam of this accelerator is 20 TeV, or 20 000 GeV—this is a macroscopic energy of about 32 ergs for each proton in the beam. Head-on collisions of protons against protons will thus make 40 TeV available in the center of mass, more than 60 times the energy available at the present CERN collider and 20 times that to become available at the Fermi National Accelerator Laboratory in the near future. The committee urged, moreover, that this facility be completed and available for physics research within about a decade. The solemnity of the advice was underscored by the simultaneous recommendations that all other proposals for high-energy accelerators not be approved. This included both the Colliding Beam Accelerator, in which the Brookhaven National Laboratory had invested considerable effort, and the Dedicated Collider, a proposed expansion of the Fermilab complex.

Comparison of top-quark and scalar-quark production at the CERN collider.

Antiproton-proton total cross sections at \ensuremath{\surd}s =540 GeV for production of a top quark, decaying into bottom quark plus e plus neutrino, and of a scalar quark, decaying into quark plus e plus scalar neutrino, are compared in detail. In each case branching ratios are taken into account. In general, scalar-quark production is found to exceed top-quark production.

Improved perturbative QCD estimates for the hadroproduction of heavy flavors.

Conservative estimates of heavy-flavor production are made within a parton perturbative QCD model, and lead to sizable cross sections. In particular, the integrated cross sections sigma/sub t/(p/sub T/>2 GeV) for M/sub t/ = 20 GeV top-quark production change from 2 ..mu..b at ..sqrt..s = 540 GeV to 14 ..mu..b at ..sqrt..s = 8000 GeV. The masses of the heavy quarks are taken into account in the kinematics and the evolution equations. The cross section sigma(p/sub T/>2 GeV) for heavy-quark production is in good approximation equal to (1/M/sup 2/)f(ln(s/Mp/sub T/))Vertical Bar p/sub T/ = 2 GeV, where f(x) is a quadratic polynomial of x for sufficiently high energy and masses (4 GeV/sup 2/<15 GeV) electrons from such decays are calculated for the CERN collider.

A model for diffractive top-quark production

A model for the diffractive production of particles containing heavy quarks, based on the scattering of intrinsic heavy quarks which then recombine to produce heavy hadrons, is confronted with the data on strangeness and charm production and is used to predict the rates for top-quark production at the CERN Collider.

Unitarity bounds on the production of (pseudo)scalar particles in p [formula omitted] collisions

We consider the production via gluon fusion and the subsequent decay of color singlet (pseudo)-scalar particles ø at the CERN collider. Stringent upper bounds on the allowed production cross section are obtained from unitarity which make the interpretation of the missing energy events as being due to φ decay highly unprobable.