1,211 research outputs found
Two-particle azimuthal correlations in collisions at 91--209 GeV with archived ALEPH data at LEP-2
We present the first measurement of two-particle angular correlations of
charged particles produced in annihilation up to 209 GeV.
This analysis utilized the archived hadronic data at center-of-mass
energy between 91 and 209 GeV collected with the ALEPH detector at LEP between
1992 and 2000. The angular correlation functions are measured over a broad
range of pseudorapidity and full azimuth as a function of charged particle
multiplicity for the first time with LEP-2 data. At 91 GeV, no significant
long-range correlation is observed in either the beam coordinate analysis or
the thrust coordinate analysis, where the latter is sensitive to a medium
expanding transverse to the color string between the outgoing pair
from the Z boson decays. Results with data at higher collision energy
than 91 GeV, providing higher event multiplicity reach up to around 50, are
presented for the first time. The thrust axis analysis shows a long-range
near-side excess in the two-particle correlation function. We performed Fourier
series decomposition of the two-particle correlation functions. In high
multiplicity events with more than 50 particles, the extracted Fourier
coefficients and magnitudes in data are larger than the MC
reference.Comment: ICHEP2022 Proceeding
Measurements of two-particle correlations in collisions at 91 GeV with ALEPH archived data
Measurements of two-particle angular correlations of charged particles
emitted in hadronic decays are presented. The archived
annihilation data at a center-of-mass energy of 91 GeV were collected with the
ALEPH detector at LEP between 1992 and 1995. The correlation functions are
measured over a broad range of pseudorapidity and full azimuth as a function of
charged particle multiplicity. No significant long-range correlation is
observed in either the lab coordinate analysis or the thrust coordinate
analysis, where the latter is sensitive to a medium expanding transverse to the
color string between the outgoing pair from boson decays. The
associated yield distributions in both analyses are in better agreement with
the prediction from the PYTHIA v6.1 event generator than from HERWIG v7.1.5.
They provide new insights to showering and hadronization modeling. These
results serve as an important reference to the observed long-range correlation
in proton-proton, proton-nucleus, and nucleus-nucleus collisions.Comment: Replaced with the published version. Added the journal reference and
the DO
First measurement of anti-k jet spectra and jet substructure using the archived ALEPH data at 91.2 GeV
We present the first anti-k jet spectrum and substructure measurements
using the archived ALEPH data taken in 1994 at a center of mass energy
of GeV. Jets are reconstructed with the anti-k
algorithm with a resolution parameter of 0.4. It is the cleanest test of jets
and QCD without the complication of hadronic initial states. The fixed
center-of-mass energy also allows the first direct test of pQCD calculation. We
present both the inclusive jet energy spectrum and the leading dijet energy
spectra, together with a number of substructure observables. They are compared
to predictions from PYTHIA6, PYTHIA8, Sherpa, HERWIG, VINCIA, and PYQUEN. None
of the models fully reproduce the data. The data are also compared to two
perturbative QCD calculations at NLO and with NLL'+R resummation. The results
can also serve as reference measurements to compare to results from hadronic
colliders. Future directions, including testing jet clustering algorithms
designed for future electron-ion collider experiments, will also be discussed
Measurement of differential cross sections for top quark pair production using the lepton plus jets final state in proton-proton collisions at 13 TeV
National Science Foundation (U.S.
Energy Resolution Performance of the CMS Electromagnetic Calorimeter
The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals
Particle-flow reconstruction and global event description with the CMS detector
The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic tau decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions
Pseudorapidity and transverse momentum dependence of flow harmonics in pPb and PbPb collisions
info:eu-repo/semantics/publishe
Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV
Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, are presented. Heavy-flavour jet identification algorithms have been improved compared to those used previously at centre-of-mass energies of 7 and 8 TeV. For jets with transverse momenta in the range expected in simulated events, these new developments result in an efficiency of 68% for the correct identification of a b jet for a probability of 1% of misidentifying a light-flavour jet. The improvement in relative efficiency at this misidentification probability is about 15%, compared to previous CMS algorithms. In addition, for the first time algorithms have been developed to identify jets containing two b hadrons in Lorentz-boosted event topologies, as well as to tag c jets. The large data sample recorded in 2016 at a centre-of-mass energy of 13 TeV has also allowed the development of new methods to measure the efficiency and misidentification probability of heavy-flavour jet identification algorithms. The heavy-flavour jet identification efficiency is measured with a precision of a few per cent at moderate jet transverse momenta (between 30 and 300 GeV) and about 5% at the highest jet transverse momenta (between 500 and 1000 GeV)
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