Jet and Underlying Event Properties as a Function of Charged-particle Multiplicity in Proton-proton Collisions at Sqrt(s)

Jet and Underlying Event Properties as a Function of Charged-particle Multiplicity in Proton-proton Collisions at Sqrt(s)
Author:
Publisher:
Total Pages: 41
Release: 2013
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ISBN:

Characteristics of multi-particle production in proton-proton collisions at sqrt(s) = 7 TeV are studied as a function of the charged-particle multiplicity, N[ch]. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity abs(eta) 2.4 and transverse momentum pt 0.25 GeV. Jets are reconstructed from charged-particles only and required to have pt> 5 GeV. The distributions of jet pt, average pt of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of N[ch] and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the N[ch]-dependence observed in the data. For increasing N[ch], PYTHIA systematically predicts higher jet rates and harder pt spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data-model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.

A Measurement of the Underlying Event Distributions in Proton-Proton Collisions at Sqrt(s)

A Measurement of the Underlying Event Distributions in Proton-Proton Collisions at Sqrt(s)
Author: Joseph Salvatore Virzi
Publisher:
Total Pages: 184
Release: 2012
Genre:
ISBN:

Underlying Event distributions are studied in events containing at least one charged particle jet produced in proton-proton collisions at sqrt(s) = 7 TeV. Jets are reconstructed from charged particles using the anti-Kt algorithm with radius parameter R = 0.6. The jet with the largest transverse momentum (pT) and.

Measurement of Neutral Strange Particle Production in the Underlying Event in Proton-proton Collisions at Sqrt(s)

Measurement of Neutral Strange Particle Production in the Underlying Event in Proton-proton Collisions at Sqrt(s)
Author:
Publisher:
Total Pages: 35
Release: 2013
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Measurements are presented of the production of primary K(S)0 and Lambda particles in proton-proton collisions at sqrt(s) = 7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of K(S)0 and Lambda particles measured at pseudorapidities abs(eta)

Study of Double Parton Scattering Using Four-Jet Scenarios

Study of Double Parton Scattering Using Four-Jet Scenarios
Author: Paolo Gunnellini
Publisher: Springer
Total Pages: 290
Release: 2015-08-24
Genre: Science
ISBN: 3319222139

This thesis addresses in a very new and elegant way several measurements and the extraction of so-called double parton scattering. The new and elegant way lies in the combination of measurements and a very smart extraction of double parton scattering results, which is easy to apply and overcomes many of the technical difficulties of older methods. Many new phenomena in particle physics can be observed when particles are collided at the highest energies; one of the highlights in recent years was the discovery of the Higgs boson at the Large Hadron Collider at CERN. Understanding the production mechanism of the Higgs boson at the LHC requires detailed knowledge of the physics of proton-proton collisions. When the density of partons in the protons becomes large, there is a non-negligible probability that more than one parton participates in the interaction and the so-called double parton scattering becomes important. In some cases very particular final state signatures can be observed, which can be regarded as an indication of such double partonic scattering and where the different interactions can be separated. Such multiple partonic interactions play an important role when precise predictions from known processes are required.

Properties of Jets Measured with Charged Particles with the ATLAS Detector at the Large Hadron Collider

Properties of Jets Measured with Charged Particles with the ATLAS Detector at the Large Hadron Collider
Author: Seth Conrad Zenz
Publisher:
Total Pages: 248
Release: 2011
Genre:
ISBN:

Jets are identified and their properties studied, in proton-proton collisions at the Large Hadron Collider at center-of-mass energy √s = 7 TeV, using charged particles measured by the ATLAS Inner Detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and the tran- sition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-kt algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown, for four ranges in rapidity extending to 1.9, and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.

Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at $ \sqrt{s_{\mathrm{NN}}}

Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at $ \sqrt{s_{\mathrm{NN}}}
Author:
Publisher:
Total Pages: 39
Release: 2016
Genre:
ISBN:

In this study, the quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity ([Delta][eta]) and relative azimuthal angle ([Delta][Phi]) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pT) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pT, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pT. A centrality-dependent excess of low-pT particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pT particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of [Delta][eta] ≈ 1 and [Delta][Phi] ≈ 1.

Measurement of the Charged-particle Multiplicity Inside Jets from $$\sqrt{s}

Measurement of the Charged-particle Multiplicity Inside Jets from $$\sqrt{s}
Author:
Publisher:
Total Pages: 23
Release: 2016
Genre:
ISBN:

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with pT > 500 MeV inside high-momentum jets in dijet events using 20.3 fb-1 of data recorded with the ATLAS detector in pp collisions at √s=8 TeV collisions at the LHC. The jets considered have transverse momenta from 50 GeV up to and beyond 1.5 TeV . The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Lastly, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately.