Preparation and decay of a single quantum of vibration at ambient conditions

A single quantum of excitation of a mechanical oscillator is a textbook example of the principles of quantum physics. Mechanical oscillators, despite their pervasive presence in nature and modern technology, do not generically exist in an excited Fock state. In the past few years, careful isolation of GHz-frequency nano-scale oscillators has allowed experimenters to prepare such states at milli-Kelvin temperatures. These developments illustrate the tension between the basic predictions of quantum mechanics that should apply to all mechanical oscillators existing even at ambient conditions, and the complex experiments in extreme conditions required to observe those predictions. We resolve the tension by creating a single Fock state of a vibration mode of a crystal at room temperature using a technique that can be applied to any Raman-active system. After exciting a bulk diamond with a femtosecond laser pulse and detecting a Stokes-shifted photon, the 40~THz Raman-active internal vibrational mode is prepared in the Fock state $|1>$ with $98.5\%$ probability. The vibrational state is read out by a subsequent pulse, which when subjected to a Hanbury-Brown-Twiss intensity correlation measurement reveals the sub-Poisson number statistics of the vibrational mode. By controlling the delay between the two pulses we are able to witness the decay of the vibrational Fock state over its $3.9$ ps lifetime at room temperature. Our technique is agnostic to specific selection rules, and should thus be applicable to any Raman-active medium, opening a new generic approach to the experimental study of quantum effects related to vibrational degrees of freedom in molecules and solid-state systems

Argilitas expansivas de un tunel del tren de alta velocidad (Barcelona-Lerida)

En la zona de Montblanc (Tarragona) se están construyendo unos túneles para el tren de alta velocidad que unirá Lérida con Barcelona. El túnel ha sido construido en los materiales de la depresión del Ebro situados entre la Sierra de Miramar y el límite nor-oriental de la Sierra de Prades

J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon

The J/$\psi$ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/$\psi$ mesons at SPS energies. Hence, the measurement of J/$\psi$ elliptic anisotropy, quantified by the Fourier coefficient v$_2$ of the J/$\psi$ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/$\psi$ suppression observed in Pb-Pb collisions. We present the measured J/$\psi$ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v$_{2}$ as a function of the collision centrality and of the J/$\psi$ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p$_{\rm T}$ sub-samples. The extracted v$_{2}$ values are significantly larger than zero for non-central collisions and are seen to increase with p$_{\rm T}$.Comment: proceedings of HP08 conference corrected a typo in one equatio

A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon

We present a new measurement of J/psi production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the (J/psi)/Drell-Yan cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.

Centrality Behaviour of J/ψ\psi Production in Na50

The J/$\psi$ production in 158 A GeV Pb-Pb interactions is studied, in the dimuon decay channel, as a function of centrality, as measured with the electromagnetic or with the very forward calorimeters. After a first sharp variation at mid centrality, both patterns continue to fall down and exhibit a curvature change at high centrality values. This trend excludes any conventional hadronic model and is in agreement with a deconfined quark-gluon phase scenario. We report also preliminary results on the measured charged multiplicity, as given by a dedicated detector.Comment: 5 pages, 7 figures (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

Charmonia production in 450 GeV/c proton-induced reactions

Absolute \jpsi\ and \psip\ production cross sections have been measured at the CERN SPS, with 450~GeV/$c$ protons incident on a set of C, Al, Cu and W targets. Complementing these values with the results obtained by experiment NA51, which used the same beam and detector with H and D targets, we establish a coherent picture of charmonia production in proton-induced reactions at SPS energies. In particular, we show that the scaling of the \jpsi\ cross section with the mass number of the target, A, is well described as A$^\alpha$ with $\alpha^\psi=0.919\pm0.015$. The ratio between the \jpsi\ and \psip\ yields, in our kinematical window, is found to be independent of A, with $\alpha^{\psi^\prime}-\alpha^{\psi}=0.014\pm0.0 11$

The cross sections for different channels in heavy ion nuclear reactions

Estimates have been made for the critical value lc of the orbital angular momentum above which a complete fusion nucleus cannot be formed. The results have been obtained by measurements of cross sections for noncompound inelastic processes (inelastic scattering, transfer. reactions, α particle emission) when Ag targets were bombarded by 86 MeV 12C ions and by 78 and 113 MeV 14N ions. The average value of lc was found between 38 and 45 ħ. A short discussion is given on the range of angular momenta at which transfer reactions occur. It is shown that quasi elastic single and multi-nucleon transfer reactions are possible only for large values of l called lT. When the bombarding energy is high enough, theses values lT are larger than lc and there is a region of l between l c and lT where a very inelastic mechanism takes place. A model called « fusion prompt scission » process is proposed. It is suggested that a deformed shape for the two fissioning nuclei is temporarly formed and breaks off very shortly after.La valeur critique lc du moment angulaire au-delà duquel un noyau composé de fusion ne peut plus être formé, a été estimée. Les résultats ont été obtenus selon une nouvelle méthode qui consiste à mesurer la section efficace de tous les processus ne faisant pas intervenir le noyau composé (diffusion inélastique, réactions de transfert, émission de particules alpha vers l'avant). L'étude a été effectuée au moyen d'ions 12C de 86 MeV et d'ions 14N de 78 et 113 MeV bombardant des cibles d'argent. On a trouvé lc compris entre 38 et 45 ħ quelque soit l'ion incident et l'énergie. On discute ensuite brièvement pour quelle région de moments angulaires les réactions de transfert ont lieu. On montre que les cas de transferts quasi élastiques sont possibles seulement pour des l élevés, de valeur moyenne lT dépendant de l'énergie incidente. lT devient très supérieur à lc lorsque l'énergie croit et un mécanisme d'échange de nucléons très inélastique intervient dans la région comprise entre lc et l T. Un modèle est proposé qui consiste en une fusion de durée très brève des deux noyaux sous la forme d'une configuration très déformée

NA50 final results on charmonia suppression

NA50The last results from the NA50 experiment on charmonia production in Pb-Pb interactions at 158 GeV/c per nucleon are presented. A strong J/$\psi$ suppression is observed, which increases with the centrality of the collisions. The J/$\psi$ production is seen to be anomalously suppressed starting at mid-centralities, when compared to a reference taken from proton-induced collisions. The most recent developments on the determination of this normal absorption curve are explained. It is also shown that for sulphur-induced reactions there is full agreement with the extrapolated normal p-A behaviour. The suppression of $\psi'$ production in heavy ion collisions (Pb-Pb and S-U) is also presented. It is seen to increase with the centrality of the collisions, and to be significantly stronger than the one measured in proton-induced reactions

Low mass dimuon production in proton and ion induced interactions at SPS

The low mass dimuon spectra collected in p-U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The `excess' events have a harder \pt\ distribution than the muon pairs from $\eta$ and $\omega$ Dalitz decays, expected to dominate the mass window 0.4--0.65~GeV/$c^2$. We conjecture that the excess events might be due to \qqbar\ annihilations, negligible at low \pt\ but made visible by the \mt\ cut applied in the NA38 data. Taking this assumption to parametrise the p-U spectra, we proceed with the analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, where we find that the measured mass spectra does not seem to exceed the expected low mass `cocktail' by more than 20\,\%

Anomalous J/ψJ/\psi suppression in Pb-Pb interactions at 158 GeV per nucleon

The Drell-Yan and J/psi cross-sections measured in Pb-Pb collisions are compared with the values extrapolated from the results obtained in proton and light ion induced reactions. While the Drell-Yan production exhibits the normal expected behaviour, the yield of J/psi in Pb-Pb interactions is abnormally low, as it lies 9 standard deviations below the expected value. Moreover, the departure from the expected behaviour increases significantly from peripheral to central collisions. (C) 1997 Elsevier Science B.V