Strange baryon signals of deconfinement in Pb−Pb collisions at 158 GeV/c per nucleon

The main results of the CERN WA97 heavy ion experiment are summarized. The evidence for the formation of a deconfined state of matter in Pb?Pb collisions at CERN SPS energies, provided by these results, is discussed. The ongoing experimental efforts, by the CERN NA57 experiment, to investigate the onset of deconfinement are briefly reviewed.     

Azimuthal anisotropy of photon and charged parti cle emissionin 208Pb + 208Pb collisions at 158 $\ cdot A$ GeV/ c

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in ²⁰⁸Pb + ²⁰⁸Pb collisions at 158 GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.Received: 22 May 2004, Revised: 14 April 2005, Published online: 4 May 2005PACS: 25.75.Dw     

Observation of meson central production in baryon exchange processes

The central production of ⁰,f ₂ and ₃ ⁰ mesons is observed for the first time in processes which are originated by ⁺ p reactions proceeding via baryon exchange mechanism. The data come from the CERN WA56 experiment designed to separate the baryon exchange reactions in ⁺ p-collisions at 20 GeV/c. We report on the measured integral and differential cross sections and also give the density matrix elements of the meson resonances observed.     

The contribution of bremsstrahlung γ to the highp T γ production cross-section in π− p collisions at 280 GeV/c

The production of charged hadrons accompanying the highp _T photons in the reactions ^– pX at 280 GeV/c has been studied using data from the WA70 experiment at the CERN SPS. The energy distribution of these hadrons cannot be explained by direct photon processes and their hadrons background alone. The rate of bremsstrahlung processes has been estimated on the assumption that the hadronic excess results from such processes alone.     

Evidence for non-q \bar q mesons

The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. In addition,q q states are also predicted. This paper describes a search for these non-q q mesons performed by experiment WA 76 using the CERN Omega Spectrometer and discusses three candidates which have been observed.Invited talk at HEXAM 89, Bechyn Castle, Czechoslovakia, June 25–30, 1989.     

Hadron program at COMPASS

The fixed target COMPASS experiment at CERN offers the opportunity to search for exotic mesons and glueball candidates in the light quark sector with unprecedented statistics.Preliminary results from the2008 data taken with an incoming negative hadron beam(190 GeV/c,mainly pions)on a liquid hydrogen target are presented.New detectors dedicated to hadron beam measurements have been added.These give access to rare neutral and kaonic channels.An amplitude analysis which will allow to fit simultaneously diffractively and/or centrally produced resonances will be described and compared with those used in the CERN WA102and BNL E852 experiments.     

Knock-on electrons in WA98 silicon drift detector

Silicon Drift Detector is used to estimate production of knock-on electrons created by passage of 158 GeV/u fully stripped Pb ion through thick lead target. Analysed data were collected in 1995 during Pb+Pb run in WA98 heavy ion experiment at CERN SPS. Information from WA98 Cherenkov beam counter makes it possible to classify events according to number of additional Pb ions which have during detector's read-out time passed through the target without nuclear interaction. Events with one and none pile-up ion are used for statistical separation of knock-on electrons from all detected charged particles. Resulting inclusive spectra of knock-on electrons are compared with GEANT simulations and good agreement is found.     

Transverse momentum distributions for meson resonances at central rapidity andP T≧2 GeV/c

The transverse momentum distributions for and (1020) have been studied in thep _t region between 2 and 4 GeV/c and central rapidity. The data analysed come from the WA77 experiment at CERN with a 300 GeV/c ^– beam incident on a Be target. These distributions are well described by the functionp _t ^–n withn8. A sample of simulated events from the Lund Monte Carlo in the same experimental conditions reproduces well the data.     

Observation of direct photons in central 158A GeV (208)P(208)b+Pb collisions

A measurement of direct photon production in 208Pb+208Pb collisions at 158A GeV has been carried out in the CERN WA98 experiment. The invariant yield of direct photons in central collisions is extracted as a function of transverse momentum in the interval 0.51.5 GeV/c. The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions. It could be significant for diagnosis of quark-gluon-plasma formation.     

Three-pion interferometry results from central Pb+Pb collisions at 158A GeV/c

Three-particle correlations have been measured for identified pi(-) from central 158A GeV Pb+Pb collisions by the WA98 experiment at CERN. A substantial contribution of the genuine three-body correlation has been found as expected for a mainly chaotic and symmetric source.     

Recent results from fixed target charm and beauty experiments

In the last year there have been new observations of beauty by two fixed target experiments (E672/706 and E653). A few new results on charm have recently been presented by the photoproduction experiment E687 and by E789 and E769. An intriguing result on the purely muonic decay of charm comes from the CERN experiment WA75. These results are summarized and we conclude with a hint of the promise of E791, the very high statistics charm experiment, which is beginning to produce physics results     

Antibaryon\left( {\bar p,\bar \Lambda } \right) production in relativistic nuclear collisions

The relativistic meson field theory is used to study the effects of the in-medium interaction on the predicted antibaryon abundancy in hot hadronic matter. It is demonstrated that subtreshold production of antiprotons in high energy heavy ion collisions at E_lab =1–2 GeV/nucleon is enhanced by 2–3 orders of magnitude as compared to a standard fireball model estimate. Furthermore, we show that after the inclusion of interactions the anti-hyperon yields, e.g. \(\bar \Lambda \) /π ^? are enhanced by about a factor ten. Predicted yields are in excess of the data measured by the NA35 and WA85 collaborations at CERN. The annihilation of antibaryons in surrounding matter at the final stage of the reaction may essentially reduce their abundancy.     

Charmonium-state production in heavy-ion collisions

An overview of existing experimental data on the production of charmonium states (J/ψ and ψ′) at the superproton synchrotron (SPS, CERN) and the relativistic heavy ion collider (RHIC, Brookhaven National Laboratory, United States) is given. The production of J/ψ mesons shows an anomalous suppression discovered by the NA50 Collaboration (CERN) in collisions of lead nuclei at an energy of 158 GeV per nucleon and confirmed in the NA60 experiment (CERN) in collisions of indium nuclei at the same energy. The suppression of J/ψ production depends on interaction centrality and becomes anomalous at about 122 participant nucleons in PbPb collisions and at about 86 participant nucleons in InIn collisions. The experimental data in question are compared with the predictions of existing theoretical models. None of the models is able to simultaneously describe data on PbPb and InIn collisions. Data obtained in the PHENIX experiment at RHIC from measurements of J/ψ production in AuAu and CuCu collisions at an energy of 200 GeV (in the nucleon-nucleon c.m. frame) indicate that the suppression of J/ψ production at such energies approximately corresponds to the suppression of J/ψ production in PbPb collisions at SPS. Theoretical models that describe SPS data on PbPb collisions predict a stronger suppression of J/ψ production. Models that take into account J/ψ-meson regeneration better describe experimental data obtained at RHIC. Measurement of cross sections for charmonium and bottomonium production at the Large Hadron Collider (LHC, CERN) would make it possible to study the properties of matter and to explore the mechanism of quarkonium production at ultrahigh energy densities and temperature and high transverse momenta, as well as to investigate the effect of the regeneration and suppression of quarkonium production as the energy increases.     

Particle manipulation techniques in AEgIS

The AEgIS experiment (http://aegis.web.cern.ch) will measure the gravitational acceleration g of antihydrogen. Once performed this could be the first direct test of the gravitational interaction between matter and antimatter. In the AEgIS experiment a beam of antihydrogen will travel horizontally along a path of about 1 m trough a moir?? deflectometer followed by a position sensitive detector. The g value will be obtained measuring the vertical displacement of the annihilation patterns. Before producing the beam, several tasks have to be performed mainly involving positron and electron plasma manipulation and particles cooling in Malmberg-Penning traps. The AEgIS experiment is currently under construction at CERN, meanwhile several tests involving particle manipulation and particle cooling are in progress. In this report some experimental results involving diocotron manipulation of plasma will be presented.     

The NA62 experiment at CERN

The goal of the NA62 experiment at CERN is to collect O(100) events of the ultrarare K\(^{+}\rightarrow \pi ^{+}\nu \bar {\nu }\) decay in two years. After a long R&D phase and a successful pilot run in 2014, the first data-taking phase took place in 2015. In this paper the importance of the experiment’s physics goal, as well as the experimental solutions adopted in order to attain it, will be reviewed.     

Antihydrogen synthesis in a double-CUSP trap towards test of the CPT-symmetry

The aim of the ASACUSA-CUSP experiment at CERN is to produce a cold, polarised antihydrogen beam and perform a high precision measurement of the ground-state hyperfine transition frequency of the antihydrogen atom and compare it with that of the hydrogen atom using the same spectroscopic beam line. Towards this goal a significant step was successfully accomplished: synthesised antihydrogen atoms have been produced in a CUSP magnetic configuration and detected at the end of our spectrometer beam line in 2012 [1]. During a long shut down at CERN the ASACUSA-CUSP experiment had been renewed by introducing a new double-CUSP magnetic configuration and a new semi-cylindrical tracking detector (AMT) [2], and by improving the transport feature of low energy antiproton beams. The new tracking detector monitors the antihydrogen synthesis during the mixing cycle of antiprotons and positrons. In this work the latest results and improvements of the antihydrogen synthesis will be presented including highlights from the last beam time.     

Study of theA-dependence of inclusivep,\bar p,Λ and\bar \Lambda production in π±-Nucleus interactions at 30 GeV/c

We present the first results on the production of fast (p>10 GeV/c)p, \(\bar p\) , Λ and \(\bar \Lambda \) from π^± hydrogen and nucleus interactions at 30 GeV/c using the CERN Ω′ spectrometer. We have used five nuclear targets (C, Al, Cu, Sn, Pb) to study theA-dependence of the inclusive particle distributions in the region 0.3<x _F <0.6. The high statistical level of our experiment allows us to demonstrate the differentA-behaviour of baryon and antibaryon inclusive reactions. We relate this difference to the final state interaction inside a nucleus using the formation-zone model.     

Photofission for the production of radioactive beams: Experimental data from an on-line measurement

A PARRNe 1 experiment (Production d'Atomes Radioactifs Riches en Neutrons) aimed at the production of neutron-rich radioactive noble gases produced by photofission has been performed at CERN. The LEP Pre-Injector (LPI) has been used to deliver a 50 MeV electron beam. The results obtained show clearly that the use of an electron beam to produce neutron-rich fission fragments for futur RNB facilities is an option that should not be neglected. Received: 20 July 2001 / Accepted: 5 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: ibrahim@ipno.in2p3.fr Communicated by D. Guerreau     

Gravitation and electromagnetism

Through an examination of the Bohm-Aharonov experiment, we shall propose a new theory of gravitation and electromagnetism. The fundamental assumption of our theory is that the motion of a particle in a combination of gravitational and electromagnetic fields is determined from a variational principle of the form f _A ^B d = 0. The form of the physical time is determined from an examination of the Maxwell-Einstein action function. The field and motion equations are formally identical to those of Maxwell-Einstein theory. The theory predicts that even in a field-free region of space, electromagnetic potentials can alter the phase of a wave function and the lifetime of a charged particle. The phase alteration has been observed in the Bohm-Aharonov experiment. There is an indication that the lifetime alteration has shown up in a recent CERN storage ring experiment. Experimental tests are proposed.