The ALICE collaboration at the CERN Large Hadron Collider reports the first measurement of the inclusive differential jet cross section at mid-rapidity in pp collisions at sqrt(s) = 2.76 TeV, with ...integrated luminosity of 13.6 nb^-1. Jets are measured over the transverse momentum range 20 to 125 GeV/c and are corrected to the particle level. Calculations based on Next-to-Leading Order perturbative QCD are in good agreement with the measurements. The ratio of inclusive jet cross sections for jet radii R = 0.2 and R = 0.4 is reported, and is also well reproduced by a Next-to-Leading Order perturbative QCD calculation when hadronization effects are included.
The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for anti-p/p, anti-\Lambda/\Lambda, anti-\Xi+/\Xi- and anti-\Omega+/\Omega- in pp collisions ...at sqrt(s) = 0.9, 2.76 and 7TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of anti-p/p, anti-\Lambda/\Lambda, anti-\Xi+/\Xi- and anti-\Omega+/\Omega-, reaching values compatible with unity for sqrt(s) = 7TeV, complement the earlier anti-p/p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of \alpha_j ~ 0.5, which are suppressed with increasing rapidity interval \Delta y. Any significant contribution of an exchange not suppressed at large \Delta y (reached at LHC energies) is disfavoured.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The objective of this paper is to deliver the most accurate ozone (O3) and carbon monoxide (CO) climatology for the pure troposphere only, i.e. exclusively from the ground to the dynamical tropopause ...on an individual profile basis. The results (profiles and columns) are derived solely from the Measurements of OZone and water vapour by in-service AIrbus airCraft programme (MOZAIC) over fifteen years (1994-2009). The study, focused on the northern mid-latitudes 24° N-50° N and 120° W-140° E, includes more than 40 000 profiles over 11 sites to give a quasi-global zonal picture. Considering all the sites, the pure tropospheric column peak-to-peak seasonal cycle ranges are 23.7-43.2 DU for O3 and 1.7-6.9 × 1018 mol cm−2 for CO. The maxima of the seasonal cycles are not in phase, occurring in February-April for CO and May-July for O3. The phase shift is related to the photochemistry and OH removal efficiencies. The purely tropospheric seasonal profiles are characterized by a typical autumn-winter/spring-summer O3 dichotomy, (except in Los Angeles, Eastmed - a cluster of Cairo and Tel Aviv - and the regions impacted by the summer monsoon) and a summer-autumn/winter-spring CO dichotomy. We revisit the boundary-layer, mid-tropospheric (MT) and upper-tropospheric (UT) partial columns, using a new monthly-varying MT ceiling. Interestingly, the seasonal cycle maximum of the UT partial columns is shifted from summer to spring for O3 and to very early spring for CO. Conversely, the MT maximum is shifted from spring to summer and is associated with a summer (winter) MT thickening (thinning). Lastly, the pure tropospheric seasonal cycles derived from our analysis are consistent with the cycles derived from spaceborne measurements, the correlation coefficients being r = 0.6-0.9 for O3, and r > 0.9 for CO. The cycles observed from space are nevertheless greater than MOZAIC for O3 (by 9-18 DU) and smaller for CO (up to 1 × 1018 mol cm−2). The larger winter O3 difference between the two data sets suggests probable stratospheric contamination in satellite data due to the tropopause position. The study underlines the importance of rigorously discriminating between the stratospheric and tropospheric reservoirs and avoiding use of a monthly-averaged tropopause position without this strict discrimination, in order to assess the pure O3 and CO tropospheric trends.
The ALICE collaboration reports the measurement of the inclusive J/psi yield as a function of charged particle pseudorapidity density dN_{ch}/deta in pp collisions at sqrt{s} = 7 TeV at the LHC. ...J/psi particles are detected for p_t > 0, in the rapidity interval |y| < 0.9 via decay into e+e-, and in the interval 2.5 < y < 4.0 via decay into mu+mu- pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN_{J/psi}/dy)/ with (dN_{ch}/deta)/ is observed in both rapidity ranges, where dN_{ch}/deta is measured within |eta| < 1 and p_t > 0. In the highest multiplicity interval with = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y < 4 (8 at |y| < 0.9) is observed.
This NASA funded project is proceeding to develop a Monte Carlo-based computer simulation of the radiation environment in space. With actual funding only initially in place at the end of May 2000, ...the study is still in the early stage of development. The general tasks have been identified and personnel have been selected. The code to be assembled will be based upon two major existing software packages. The radiation transport simulation will be accomplished by updating the FLUKA Monte Carlo program, and the user interface will employ the ROOT software being developed at CERN. The end-product will be a Monte Carlo-based code which will complement the existing analytic codes such as BRYNTRN/HZETRN presently used by NASA to evaluate the effects of radiation shielding in space. The planned code will possess the ability to evaluate the radiation environment for spacecraft and habitats in Earth orbit, in interplanetary space, on the lunar surface, or on a planetary surface such as Mars. Furthermore, it will be useful in the design and analysis of experiments such as ACCESS (Advanced Cosmic-ray Composition Experiment for Space Station), which is an Office of Space Science payload currently under evaluation for deployment on the International Space Station (ISS). FLUKA will be significantly improved and tailored for use in simulating space radiation in four ways. First, the additional physics not presently within the code that is necessary to simulate the problems of interest, namely the heavy ion inelastic processes, will be incorporated. Second, the internal geometry package will be replaced with one that will substantially increase the calculation speed as well as simplify the data input task. Third, default incident flux packages that include all of the different space radiation sources of interest will be included. Finally, the user interface and internal data structure will be melded together with ROOT, the object-oriented data analysis infrastructure system. Beyond the benefits of 'objectivity', ROOT's incorporation will also provide a graphical user interface with powerful tools for input prior to the calculation, as well as for data analysis and visualization of the results.
The first measurements of the invariant differential cross sections of inclusive $\pi^0$ and $\eta$ meson production at mid-rapidity in proton-proton collisions at $\sqrt{s}=0.9$ TeV and $\sqrt{s}=7$ ...TeV are reported. The $\pi^0$ measurement covers the ranges $0.4
Angular correlations between unidentified charged trigger ($t$) and associated ($a$) particles are measured by the ALICE experiment in \PbPb\ collisions at $\snn=2.76$ TeV for transverse momenta ...$0.25 < p_{T}^{t,\, a} < 15$ GeV/$c$, where $p_{T}^t > p_{T}^a$. The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval $|\eta| < 1.0$. Distributions in relative azimuth $\Delta\phi \equiv \phi^t - \phi^a$ are analyzed for $|\Delta\eta| \equiv |\eta^t - \eta^a| > 0.8$, and are referred to as "long-range correlations". Fourier components $V_{n\Delta} \equiv <\cos(n\Delta\phi)>$ are extracted from the long-range azimuthal correlation functions. If the particle pair correlation arises dominantly from production mechanisms that distribute according to a common plane of symmetry, then the pair $\vnd$ coefficients are expected to factorize as the product of single-particle anisotropies $v_n (\pt)$, i.e. $V_{n\Delta}(p_{T}^t, p_{T}^a) = v_n(p_{T}^t) \, v_n(p_{T}^a)$. This expectation is tested for $1 \leq n \leq 5$ by applying a global fit of all $\vnd (p_{T}^t, p_{T}^a)$ to obtain the best values $\vngf (\pt)$. It is found that for $2 \leq n \leq 5$, the factorization holds for associated particle momenta up to $\pta \sim 3$-4 GeV/$c$, with a trend of increasing deviation between the data and the factorization hypothesis as $p_{T}^t$ and $p_{T}^a$ are increased or as collisions become more peripheral. $V_{1\Delta}$ does not factorize precisely at any $\pt$ or centrality, as indicated by the lack of a good global fit over the full $\ptt, \pta$ range. The $\vngf$ values for $2 \leq n \leq 5$ from the global fit are in close agreement with previous measurements.
Dark propagation modes in optical lattices Schiavoni, M.; Sanchez-Palencia, L.; Carminati, F.-R. ...
Physical review. A, Atomic, molecular, and optical physics,
11/2002, Letnik:
66, Številka:
5
Journal Article
Odprti dostop
We examine the stimulated light scattering onto the propagation modes of a dissipative optical lattice. We show that two different pump-probe configurations may lead to the excitation, via different ...mechanisms, of the same mode. We found that in one configuration the scattering on the propagation mode results in a resonance in the probe transmission spectrum while in the other configuration no modification of the scattering spectrum occurs, i.e., the mode is dark. A theoretical explanation of this behavior is provided.
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