Search results for "Minimum bias"
showing 10 items of 10 documents
Pileup and underlying event mitigation with iterative constituent subtraction
2019
Abstract The hard-scatter processes in hadronic collisions are often largely contaminated with soft background coming from pileup in proton-proton collisions, or underlying event in heavy-ion collisions. This paper presents a new background subtraction method for jets and event observables (such as missing transverse energy) which is based on the previously published Constituent Subtraction algorithm. The new subtraction method, called Iterative Constituent Subtraction, applies event-wide implementation of Constituent Subtraction iteratively in order to fully equilibrate the background subtraction across the entire event. Besides documenting the new method, we provide guidelines for setting…
New results on kaon decays from NA48
2007
We report on recent results on rare and semileptonic kaon decays from NA48 and NA48/2. Using data from a minimum bias run in 1999 we present a new measurement of the CP violating decay K L → π + π − with over 40000 selected events. We measured the ratio Γ ( K L → π + π − ) / Γ ( K L → π ± e ∓ ν ) = ( 4.835 ± 0.038 ) × 10 −3 leading to the precise determination of the CP violation parameter | η + − | = ( 2.223 ± 0.013 ) × 10 −3 . From the same data we selected over 2 × 10 6 K L → π ± μ ∓ ν decays. Preliminary results from a dalitz plot fit yield the values for the form factors λ + = 0.0260 ± 0.0007 s t a t ± 0.0010 s y s t and λ 0 = 0.0120 ± 0.0008 s t a t ± 0.0015 s y s t . In one month of …
Charged jet cross sections and properties in proton-proton collisions at $\sqrt{s}=7$ TeV
2015
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at centre-of-mass energy $\sqrt{s}=7$ TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the mid-rapidity region using the sequential recombination $k_{\rm T}$ and anti-$k_{\rm T}$ as well as the SISCone jet finding algorithms with several resolution parameters in the range $R=0.2$ to $0.6$. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum ($p_{\rm T}$) interval $20<p_{\rm T}^{\rm jet,ch}<100$ GeV/$c$. They are also consistent w…
Impact of Energy and Luminosity upgrades at LHC on the Physics program of ATLAS
2002
The impact on the physics capabilities of the ATLAS detector of possible LHC upgrades is discussed. As a benchmark, an increase in the luminosity by a factor of ten is considered. For comparison, a doubling of the LHC energy is also explored. Both upgrades significantly enhance the physics capabilities of ATLAS. As measured in terms of the mass reach for new particles, the energy upgrade is more powerful. However, in cases where the effect of an upgrade is to increase the precision of measurements as a result of the larger data samples, the luminosity upgrade can be at least as powerful. The pile-up of minimum bias events at higher luminosity could limit the physics performance of ATLAS in …
Charged-particle multiplicities in pp interactions at s=900 GeV measured with the ATLAS detector at the LHC
2010
The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range vertical bar eta vertical bar 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charg…
Search for heavy neutral lepton production in K+ decays
2018
A search for heavy neutral lepton production in $K^+$ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the $10^{-7}$ to $10^{-6}$ level are established on the elements of the extended neutrino mixing matrix $|U_{\ell 4}|^2$ ($\ell=e,\mu$) for heavy neutral lepton mass in the range $170-448~{\rm MeV}/c^2$. This improves on the results from previous production searches in $K^+$ decays, setting more stringent limits and extending the mass range.
The ALICE Collaboration
2009
The production of mesons containing strange quarks (KS, φ) and both singly and doubly strange baryons ( , , and − + +) are measured at mid-rapidity in pp collisions at √ s = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields (〈dN/dy〉) of 0.184 ± 0.002(stat.) ± 0.006(syst.) for KS and 0.021 ± 0.004(stat.) ± 0.003(syst.) for φ. For baryons, we find 〈dN/dy〉 = 0.048 ± 0.001(stat.) ± 0.004(syst.) for , 0.047 ± 0.002(stat.) ± 0.005(syst.) for and 0.0101 ± 0.0…
Bremsstrahlung and the underlying event structure
1990
Abstract In this talk we address the problem of the structure of the underlying event and its dependence upon a specific trigger. Generally speaking, events selected without any special trigger, like the minimum bias events, need not have the same characteristics as those selected by the jet trigger or through the W and Z-boson selection criteria. We use perturbative QCD in order to unfold part of the structure. In particular we concentrate on the contribution to the underlying event structure which comes from initial state bremsstrahlung. In the present paper we discuss the relationship between transverse momentum and transverse energy for W and Z-boson production both in the low as well a…
Point-to-point readout for the ALICE EMCal detector
2014
Abstract It is anticipated that the LHC will deliver Pb+Pb collisions at a minimum bias interaction rate of about 50 kHz after the second long shutdown of the LHC in 2018. This will be roughly two orders of magnitude greater than the current data recording rate capability of the ALICE experiment. Therefore a major upgrade of the ALICE detector is planned for the next shutdown to enable ALICE to record data at the full Pb+Pb minimum bias interaction rate delivered by the LHC. A new point-to-point readout system for the electromagnetic calorimeter (EMCal) of ALICE has been developed, to replace the legacy readout bus, that essentially accomplishes this goal, and is being installed during the …
Constraining nPDFs with inclusive pions and direct photons at forward rapidities in p+Pb collisions at the LHC
2014
Abstract In this talk, we present NLO pQCD predictions for inclusive pion and direct photon nuclear modifications in p + Pb collisions at mid- and forward rapidities at the LHC. In addition to the minimum bias predictions, we also address the centrality dependence with spatially dependent nuclear PDFs. To understand which regions of the nuclear momentum fraction x 2 these observables predominantly probe, we present also the underlying x 2 distributions at different rapidities. We are led to conclude that the isolated photons at forward rapidities are more sensitive to the small- x 2 dynamics than the inclusive pions.