Comparison of features of high-energy proton and alpha-particle interactions with C, Fe, and Pb nuclei in various models

The results that the FLUKA, GHEISHA, and QGSM codes produce for the features of hadron interactions are compared with one another and with experimental data. Distinctions between hadronic cascades computed in lead and iron on the basis of the different codes are analyzed. The possibility of using model concepts underlying the codes in question at energies above 1 TeV is considered.     

Determination of energies of cosmic-ray nuclei in the region above 1 TeV

A method is proposed for measuring energies of particles in the region above 1 TeV. The method is based on detecting the greatest specific energy deposition in hadronic cascades propagating in dense matter. This makes it possible to improve accuracy in measuring energy by thin calorimeters in studying the energy spectra of high-energy cosmic rays at high altitudes. Attainable accuracies in measuring energy are considered for protons and He nuclei. The results of a relevant simulation are compared with the results of a satellite-borne experiment with Kosmos-1713.     

Total Hadronic Cross-Section Data and the Froissart–Martin Bound

The energy dependence of the total hadronic cross section at high energies is investigated with focus on the recent experimental result by the Total Elastic and Diffractive Cross-section Measurement Collaboration at 7?TeV and the Froissart?CMartin bound. On the basis of a class of analytical parametrization with the exponent ?? in the leading logarithm contribution as a free parameter, different variants of fits to pp and $\bar{\textrm{p}}$ p total cross-section data above 5?GeV are developed. Two ensembles are considered, the first comprising data up to 1.8?TeV and the second also including the data collected at 7?TeV. We show that in all fit variants applied to the first ensemble, the exponent is statistically consistent with ???=?2. Applied to the second ensemble, however, the same variants yield ?? values above 2, a result already obtained in two other analysis, by Amaldi et al. and by the UA4/2 Collaboration. As recently discussed by Azimov, this faster-than-squared-logarithm rise does not necessarily violate unitarity. Our results suggest that the energy dependence of the hadronic total cross section at high energies still constitutes an open problem.     

Backward yields of pions,protons, and deuterons in relativistic 28Si+Pb collisions at 14.6 A GeVc

The production of pions, protons and deuterons is studied at a laboratory angle of 144° in ²⁸Si+Pb collisions at 14.6 GeV/c per nucleon. The centrality dependence of the pion yields is studied over the full impact parameter range using a zero degree calorimeter. The results are compared with the hadronic cascade model RQMD. These calculations are generally in agreement with the experimental results. According to these calculations, the pion yield in our acceptance is completely dominated by Δ-decay at freeze-out. Our measurements thus support the importance of baryon resonance production as one of the central features of relativistic heavy ion collisions at AGS energies. Although the strength of the pion spectrum is adequately described for kinetic energies above 50 MeV, an additional very soft component is observed in the pion spectra which is not predicted by RQMD. This very soft component accounts for a significant fraction of the total pion yield in this rapidity range but remains unexplained.     

High-energy spectra of atmospheric neutrinos

A calculation of the atmospheric high-energy muon neutrino spectra and zenith-angle distributions is performed for two primary spectrum parameterizations (by Gaisser and Honda and by Zatsepin and Sokolskaya) with the use of QGSJET-II-03 and SIBYLL 2.1 hadronic models. A comparison of the zenith angle-averaged muon neutrino spectrum with the data of Frejus, AMANDA-II, and IceCube40 experiments makes it clear that, even at energies above 100 TeV, the prompt neutrino contribution is not apparent because of the considerable uncertainties of the experimental data in the high-energy region.     

Isolated photon cross section in p&pmacr; collisions at radicals = 1. 8 TeV

We report a new measurement of the cross section for the production of isolated photons with transverse energies ( E(gamma)(T)) above 10 GeV and pseudorapidities |eta|<2.5 in p&pmacr; collisions at sqrt[s] = 1.8 TeV. The results are based on a data sample of 107.6 pb(-1) recorded during 1992-1995 with the D0 detector at the Fermilab Tevatron collider. The background, predominantly from jets which fragment to neutral mesons, was estimated using the longitudinal shower shape of photon candidates in the calorimeter. The measured cross section is in good agreement with the next-to-leading order QCD calculation for E(gamma)(T) greater, similar36 GeV.     

宇宙线高能族事例中簇射粒子的横向分布

对甘巴拉山铅乳胶室实验所获取的总观测能为100TeV至400TeV的高能族事例中簇射粒子的横向分布进行了分析,并与相应的Monte Carlo模拟计算进行了比较.模拟计算采用的是CORSIKA程序,其中的强相互作用采用QGSJET模型.结果表明:采用CORSIKA(QGSJET)程序进行模拟所给出的族事例中簇射粒子的横向分布以及族事例能量集中率分布的整体趋势均与相应的实验数据基本相符.     

Underground horizontal ionization-neutron calorimeter-pairmeter

The necessity, prospects, and possibility of development of an underground multipurpose device for detecting high-energy penetrating particles (muons) are described. The use of lead as an absorber and plastic scintillators with gadolinium allow the simultaneous use of the device as an ionization-neutron calorimeter and a pairmeter for detecting nuclear and electromagnetic cascades from penetrating particles and separating ones from the others. The presented results of calculations of the pairmeter characteristics using the GEANT program show the possibility of estimating the muon energy from 100 GeV to 200 TeV with an accuracy of 40% for a version with 150 layers (2 cm lead + 1 cm plastic each).     

Total photoproduction cross section at very high energy

In this paper we apply to the photoproduction total cross section a model we have proposed for purely hadronic processes and which is based on QCD mini-jets and soft gluon re-summation. We compare the predictions of our model with the HERA data as well as with other models. For cosmic rays, our model predicts substantially higher cross sections at TeV energies than models based on factorization, but lower than models based on mini-jets alone, without soft gluons. We discuss the origin of this difference.     

Cross section and transverse momentum of hadron interactions with air nuclei at primary cosmic ray energies of 0.3–5 PeV

The Tien Shan experimental data on hadrons with energies exceeding 0.5 TeV in extensive air showers (EAS) from primary cosmic rays with energies from 0.3 to 5 PeV are compared with the results of CORSIKA + QGSJET model simulations. Some conclusions are drawn on the increase of the cross section and transverse momentum in the hadron interactions with air atom nuclei from 0.1 TeV (accelerator with a fixed target) to 5 PeV (EAS) energies.     

Search for quark compositeness with the dijet centrality ratio in pp collisions at √s=7 TeV

A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at √s=7 TeV, is described. The data sample of the study corresponds to an integrated luminosity of 2.9 pb(-1) collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the standard model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.     

Fluxes of high- and ultrahigh-energy cosmic-ray muons

The positive excess of cosmic-ray muons at energies higher than 1 TeV is estimated taking into account the data obtained from accelerator experiments on the production of particle and antiparticles in proton-proton interactions at energies of ～20 TeV. The fluxes of cosmic-ray muons at energies up to ～10¹¹ GeV and the production functions of muon bremsstrahlung photons at different depths in the atmosphere are calculated with due regard for the contribution from the decay of J/ψ mesons. The analysis performed is based on the accelerator data and their extrapolation to higher energies.     

Charged-particle multiplicity density at midrapidity in central Pb-Pb collisions at sqrt[S(NN)] = 2.76 TeV

The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair √ S NN = 2.76 TeV is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is 1584 ± 4(stat) ± 76(syst), which corresponds to 8.3 ± 0.4(syst) per participating nucleon pair. This represents an increase of about a factor 1.9 relative to pp collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at √ S NN = 2.76 TeV. This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies.     

Possible observations of new physics in ultrahigh-energy cosmic rays

The muon lateral structure functions in giant air showers induced by primary photons have been simulated with the help of original codes. Particularly, the densities of muons with energies above 0.5 and 1 GeV at a distance of 1000 m from the shower core have been estimated for gamma-induced showers of various energies. A comparison with the results of calculations for hadronic showers shows a considerable deficit of muons in the gamma-induced showers. The density of muons at a distance of 1000 m from the shower core happened to be ≳ 10 times larger for the hadronic showers. Some possible constraints of the source models with superheavy-dark-matter particles and topological defects are discussed. The text was submitted by the authors in English.     

Study of fermion pair production in \mathrm{e^+ e^-} collisions at 130–183 GeV

The cross sections and forward-backward asymmetries of hadronic and leptonic events produced in collisions at centre-of-mass energies from 130 to 183 GeV are presented. Results for , , , , and production show no significant deviation from the Standard Model predictions. This enables constraints to be set upon physics beyond the Standard Model such as four-fermion contact interactions, leptoquarks, bosons and R-parity violating squarks and sneutrinos. Limits on the energy scale of contact interactions are typically in the range from 2 to 10 TeV. Limits on R-parity violating sneutrinos reach masses of a few hundred GeV/ for large values of their Yukawa couplings. Received: 8 March 1999 / Published online: 8 December 1999     

TeV gamma rays from photodisintegration and daughter deexcitation of cosmic-ray nuclei

It is commonly assumed that high-energy gamma rays are made via either purely electromagnetic processes or the hadronic process of pion production, followed by decay. We investigate astrophysical contexts where a third process (A*) would dominate: namely, the photodisintegration of highly boosted nuclei followed by daughter deexcitation. Starburst regions such as Cygnus OB2 appear to be promising sites for TeV gamma-ray emission via this mechanism. A unique feature of the A* process is a sharp flattening of the energy spectrum below approximately 10 TeV/(T/eV) for gamma-ray emission from a thermal region of temperature T. The A* mechanism described herein offers an important contribution to gamma-ray astronomy in the era of intense observational activity.     

Quark-gluon state of matter and positive excess of cosmic-ray muons at high energies

The problem of the relationship between the numbers of positively and negatively charged particles in the flux of cosmic-ray muons arriving at sea level with energies in excess of 0.1 TeV (up to 100 TeV) is discussed. It is shown that the formation of quark—gluon matter as the result of high-energy nuclear interactions leads to a reduction of the positive excess in cosmic-ray muons at the above energies. At the present time, the quark-gluon state of matter is studied in accelerator experiments at colliding-particle energies of up to √s = 200 GeV per nucleon. Estimates presented in this article for the positive excess of muons having energies of up to 3 or 4 TeV are based on available data from accelerator experiments; at higher muon energies, the respective estimates are based on extrapolating these data.     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130–172 GeV at LEP

Production of events with hadronic and leptonic final states has been measured in collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z events, and compared to Standard Model expectations. The ratio of the cross-section for production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of -Z interference. The energy dependence of has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for -channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair. Received: 30 July 1997 / Published online: 10 March 1998     

Observations of high-energy hadron-gamma families with extremely large lateral spreads

Summary Two very high-energy hadron-gamma families, named ?Halina? and ?C141G4836?, with unusually large lateral spread were detected by the carbon chamber of the Pamir emulsion chamber experiment. The total observed energies of the events are 3540 TeV and 2290 TeV, respectively (E ^(γ)≥2 TeV). The events have extraordinarily wide lateral spread both in electromagnetic component and hadronic component and they are rich in hadrons. One of the lateral characteristics of the events is described in the form of ER-flow density, Δ≡d(ΣER)/d(InR). Both of the experimental events have a very largeER-flow density of gamma-rays, Δ∼17 GeV·km forE _γ≥4 TeV and a high value ofER-flow density is arising from both high particle density and largeER of individual particles. It is shown that the longitudinal and lateral characteristics of the experimental data cannot be fully explained by model calculations even when we consider the contributions of heavy nuclei in primary particles if we assume no fundamental change in elementary process. To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.     

Searches for new particles using cone and cluster jet algorithms: a comparative study

We discuss the reconstruction of the hadronic decays of heavy particles using jet algorithms. The ability to reconstruct the mass of the decaying particles is compared between a traditional cone-type algorithm and a recently proposed cluster-type algorithm. The specific examples considered are the semileptonic decays of a heavy Higgs boson at TeV, and of top quark-antiquark pairs at TeV. We find that the cluster algorithm offers considerable advantages in the former case, and a slight advantage in the latter. We briefly discuss the effects of calorimeter energy resolution, and show that a typical resolution dilutes these advantages, but does not remove them entirely.