585 research outputs found
The mass gap and its applications
No full textQuantum Chromodynamics (QCD) is the most up-to-date theory of the strong interaction. Its predictions have been verified experimentally, and it is a cornerstone of the Standard Model of particle physics. However, standard perturbative procedures fail if applied to low-energy QCD. Even the discovery of the Higgs Boson will not solve the problem of masses originating from the non-perturbative behavior of QCD.This book presents a new method, the introduction of the 'mass gap', first suggested by Arthur Jaffe and Edward Witten at the turn of the millennium. It attempts to show that, to explain th
KNO-like scaling within a jet in proton--proton collisions at LHC energies
No full textWe study the multiplicity distributions of events with hard jets in proton-proton collisions at LHC energies using PYTHIA 8 Monte-Carlo simulations. We demonstrate that the charged-hadron multiplicity distributions scale with jet momentum. This suggests that the Koba--Nielsen--Olesen (KNO) scaling holds within a jet. The in-jet scaling is fulfilled without multiple-parton interactions (MPI), but breaks down in case MPI is present without color reconnection. Our findings imply that KNO scaling is violated by parton shower or multiple-parton interactions in higher-energy collisions.6 pages, 4 figure
Differences in high meson production between CERN SPS and RHIC heavy ion collisions
No full textIn this talk we present a perturbative QCD improved parton model calculation for light meson production in high energy heavy ion collisions. In order to describe the experimental data properly, one needs to augment the standard pQCD model by the transverse momentum distribution of partons ("intrinsic k/sub T/"). Proton-nucleus data indicate the presence of nuclear shadowing and multi-scattering effects. Further corrections are needed in nucleus-nucleus collisions to explain the observed reduction of the cross section. We introduce the idea of proton dissociation and compare our calculations with the SPS and RHIC experimental data. (18 refs).In this talk we present a perturbative QCD improved parton model calculation for light meson production in high energy heavy ion collisions. In order to describe the experimental data properly, one needs to augment the standard pQCD model by the transverse momentum distribution of partons (intrinsic k_T). Proton-nucleus data indicate the presence of nuclear shadowing and multiscattering effects. Further corrections are needed in nucleus-nucleus collisions to explain the observed reduction of the cross section. We introduce the idea of proton dissociation and compare our calculations with the SPS and RHIC experimental data
ML-based muon identification using a FNAL-NICADD scintillator chamber for the MID subsystem of ALICE 3
No full textThe ALICE Collaboration is planning to construct a newdetector (ALICE 3) aiming at exploiting the potential of thehigh-luminosity Large Hadron Collider (LHC). The new detector willallow ALICE to participate in LHC Run 5 scheduled from 2036 to2041. The muon-identifier subsystem (MID) is part of the ALICE 3reference detector layout. The MID will consist of a standardmagnetic iron absorber (≈4 nuclear interaction lengths)followed by muon chambers. The baseline option for the MID chambersconsiders plastic scintillation bars equipped with wave-lengthshifting fibers and readout with silicon photomultipliers. Thispaper reports on the performance of a MID chamber prototype using3 GeV/c pion- and muon-enriched beams delivered by the CERNProton Synchrotron (PS). The prototype was built using extrudedplastic scintillator produced by FNAL-NICADD (Fermi NationalAccelerator Laboratory - Northern Illinois Center for Acceleratorand Detector Development). The prototype was experimentallyevaluated using varying absorber thicknesses (60, 70, 80, 90, and100 cm) to assess its performance. The analysis was performed usingMachine Learning techniques and the performance was validated withGEANT 4 simulations. Potential improvements in both hardware anddata analysis are discussed.The ALICE Collaboration is planning to construct a new detector (ALICE 3) aiming at exploiting the potential of the high-luminosity Large Hadron Collider (LHC). The new detector will allow ALICE to participate in LHC Run 5 scheduled from 2036 to 2041. The muon-identifier subsystem (MID) is part of the ALICE 3 reference detector layout. The MID will consist of a standard magnetic iron absorber ( nuclear interaction lengths) followed by muon chambers. The baseline option for the MID chambers considers plastic scintillation bars equipped with wave-length shifting fibers and readout with silicon photomultipliers. This paper reports on the performance of a MID chamber prototype using 3 GeV/ pion- and muon-enriched beams delivered by the CERN Proton Synchrotron (PS). The prototype was built using extruded plastic scintillator produced by FNAL-NICADD (Fermi National Accelerator Laboratory - Northern Illinois Center for Accelerator and Detector Development). The prototype was experimentally evaluated using varying absorber thicknesses (60, 70, 80, 90, and 100 cm) to assess its performance. The analysis was performed using Machine Learning techniques and the performance was validated with GEANT 4 simulations. Potential improvements in both hardware and data analysis are discussed
Measurement of prompt J/ψ and beauty hadron production cross sections at mid-rapidity in pp collisions at √s =7 TeV
No full textThe ALICE experiment at the LHC has studied J/ψ production at mid-rapidity in pp collisions at s √ =7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L int = 5.6 nb−1. The fraction of J/ψ from the decay of long-lived beauty hadrons was determined for J/ψ candidates with transverse momentum p t > 1.3 GeV/c and rapidity |y| 1.3 GeV/c, |y| 1.3 GeV/c and |y| 1.3 GeV/c, |y| <0.9) = 1.46 ± 0.38 (stat.) +0.26 −0.32 (syst.) μb. The results are compared to QCD model predictions. The shape of the p t and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section t
Underlying Event measurements in pp collisions at = 0.9 and 7 TeV with the ALICE experiment at the LHC
No full textWe present measurements of Underlying Event observables in pp collisions at = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum pT,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different pT thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track pT threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed pT in the Transverse region by about 10-30%.We present measurements of Underlying Event observables in pp collisions at = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different thresholds: 0.15, 0.5 and 1.0 GeV/. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed in the Transverse region by about 10-30%
Predictions for Collisions at
No full textAlbacete JL, Armesto N, Baier R, et al. Predictions for Collisions at . International Journal of Modern Physics E. 2013;22(04): 1330007.Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p + Pb collisions at root s(NN) = 5 TeV are compiled and compared. When test run data are available, they are compared to the model predictions
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at √sNN = 2.76 TeV
No full textD meson elliptic flow in non-central PbPb collisions at sqrt(s_NN)=2.76 TeV
No full textAzimuthally anisotropic distributions of D0, D+, and D*+ mesons were studied in the central rapidity region (|y|<0.8) in Pb-Pb collisions at a center-of-mass energy sNN ̅ ̅ ̅ ̅√=2.76 TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient v2 (commonly denoted elliptic flow) was measured in the centrality class 30%–50% as a function of the D meson transverse momentum pT, in the range 2–16 GeV/c. The measured v2 of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2<pT<6 GeV/c with 5.7σ significance, based on the combination of statistical and systematic uncertainties
Pion, Kaon, and Proton Production in Central Pb-Pb Collisions at √sNN=2.76 TeV
No full textIn this Letter we report the first results on π±, K±, p, and p̅ production at midrapidity (|y|<0.5) in central Pb-Pb collisions at √sNN=2.76 TeV, measured by the ALICE experiment at the LHC. The pT distributions and yields are compared to previous results at √sNN=200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with √sNN, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/π ratio is in line with predictions from the thermal model, the p/π ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood
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