Measurements of cross sections of inelastic and diffractive processes in proton–proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in ...inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass
M
X
<200 GeV/
c
2
)
, and
, respectively at centre-of-mass energies
; for double diffraction (for a pseudorapidity gap Δ
η
>3)
σ
DD
/
σ
INEL
=0.11±0.03,0.12±0.05, and
, respectively at
. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained:
mb at
and
at
. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton–antiproton and proton–proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present results of the performance of the second prototype of the CASTOR quartz–tungsten sampling calorimeter, to be installed in the very forward region of the CMS experiment at the LHC. The ...energy linearity and resolution, as well as the spatial resolution of the prototype to electromagnetic and hadronic showers are studied with E=20–200 GeV electrons, E=20–350 GeV pions, and E=50, 150 GeV muons from beam tests carried out at CERN/SPS in 2004. The responses of the calorimeter using two different types of photodetectors (avalanche photodiodes APDs, and photomultiplier tubes PMTs) are compared.
The CMS experiment at the CERN LHC Neukermans, L; Caudron, J; Makariev, M ...
Journal of instrumentation,
2008, Letnik:
3, Številka:
8
Journal Article
Recenzirano
Odprti dostop
The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a ...centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 1034 cm-2 s-1 (1027 cm-2 s-1). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4π solid angle. Forward sampling calorimeters extend the pseudorapidity coverage to high values (|η| ≤ 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.
The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, ...and results on the J/ψ polarization parameters λ(θ) and λ(φ) were obtained. The study was performed in the kinematic region 2.5<y<4, 2<p(t)<8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.
We present results of a search for two hypothetical strange dibaryon states, i.e. the H-dibaryon and the possible Λn‾ bound state. The search is performed with the ALICE detector in central (0–10%) ...Pb–Pb collisions at sNN=2.76 TeV, by invariant mass analysis in the decay modes Λn‾→d‾π+ and H-dibaryon →Λpπ−. No evidence for these bound states is observed. Upper limits are determined at 99% confidence level for a wide range of lifetimes and for the full range of branching ratios. The results are compared to thermal, coalescence and hybrid UrQMD model expectations, which describe correctly the production of other loosely bound states, like the deuteron and the hypertriton.
The inclusive production cross sections at forward rapidity of Formula: see text, Formula: see text, Formula: see text(1S) and Formula: see text(2S) are measured in Formula: see text collisions at ...Formula: see text with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pbFormula: see text. Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the Formula: see text invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum Formula: see text and rapidity Formula: see text, over the ranges Formula: see text GeV/c for Formula: see text, Formula: see text GeV/c for all other resonances and for Formula: see text. The measured cross sections integrated over Formula: see text and Formula: see text, and assuming unpolarized quarkonia, are: Formula: see text Formula: see textb, Formula: see text Formula: see textb, Formula: see text nb and Formula: see text nb, where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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