 Award ID(s):
 1915093
 Publication Date:
 NSFPAR ID:
 10165379
 Journal Name:
 EPJ Web of Conferences
 Volume:
 235
 Page Range or eLocationID:
 05002
 ISSN:
 2100014X
 Sponsoring Org:
 National Science Foundation
More Like this

A bstract A measurement of inclusive fourjet production in protonproton collisions at a centerofmass energy of 13 TeV is presented. The transverse momenta of jets within η < 4 . 7 are required to exceed 35, 30, 25, and 20 GeV for the first, second, third, and fourthleading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower modeling, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and doubleparton scattering contributions is shown to be important. The doubleparton scattering contribution is extracted by means of a template fit to the data, using distributions for singleparton scattering obtained from Monte Carlo event generators and a doubleparton scattering distribution constructed from inclusive singlejet events in data. The effective doubleparton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single parton scattering background.

A bstract One of the key tasks of any particle collider is measurement. In practice, this is often done by fitting data to a simulation, which depends on many parameters. Sometimes, when the effects of varying different parameters are highly correlated, a large ensemble of data may be needed to resolve parameterspace degeneracies. An important example is measuring the topquark mass, where other physical and unphysical parameters in the simulation must be profiled when fitting the topquark mass parameter. We compare four different methodologies for topquark mass measurement: a classical histogram fit similar to one commonly used in experiment augmented by softdrop jet grooming; a 2D profile likelihood fit with a nuisance parameter; a machinelearning method called DCTR; and a linear regression approach, either using a leastsquares fit or with a dense linearlyactivated neural network. Despite the fact that individual events are totally uncorrelated, we find that the linear regression methods work most effectively when we input an ensemble of events sorted by mass, rather than training them on individual events. Although all methods provide robust extraction of the topquark mass parameter, the linear network does marginally best and is remarkably simple. For the top study, we conclude that themore »

Abstract The Lyα forest provides one of the best means of mapping largescale structure at high redshift, including our tightest constraint on the distanceredshift relation before cosmic noon. We describe how the largescale correlations in the Lyα forest can be understood as an expansion in cumulants of the optical depth field, which itself can be related to the density field by a bias expansion. This provides a direct connection between the observable and the statistics of the matter fluctuations which can be computed in a systematic manner. We discuss the way in which complex, smallscale physics enters the predictions, the origin of the muchdiscussed velocity bias and the `renormalization' of the largescale bias coefficients. Our calculations are within the context of perturbation theory, but we also make contact with earlier work using the peakbackground split. Using the structure of the equations of motion we demonstrate, to all orders in perturbation theory, that the largescale flux power spectrum becomes the linear spectrum times the square of a quadratic in the cosine of the angle to the line of sight. Unlike the case of galaxies, both the isotropic and anisotropic pieces receive contributions from smallscale physics.

A bstract The ALICE Collaboration reports the first fullycorrected measurements of the N subjettiness observable for trackbased jets in heavyion collisions. This study is performed using data recorded in pp and PbPb collisions at centreofmass energies of $$ \sqrt{s} $$ s = 7 TeV and $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 2 . 76 TeV, respectively. In particular the ratio of 2subjettiness to 1subjettiness, τ 2 /τ 1 , which is sensitive to the rate of twopronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavyion collisions is expected to change the rate of twopronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0 . 4 and charged jet transverse momentum of 40 ≤ p T , jet ≤ 60 GeV/ c , which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavyion collisions. This has been achieved by utilising a semiinclusive hadronjet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ 2 /τ 1 observable for trackbased jets in PbPb collisions is observed relative to vacuum PYTHIA6more »

ABSTRACT The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast Xray variability and perform a full spectraltiming analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. We model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous timescale between the hot flow and variable disc. Our model naturally gives the doublehumped shape of the power spectra, and the increasing highfrequency variability with energy in the second hump. Including reflection and reprocessing from a disc truncated at a few tens of gravitational radii quantitatively reproduces the switch in the lagfrequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hardmore »