1,445 research outputs found
Machine learning as an instrument for data unfolding
A method for correcting for detector smearing effects using machine learning
techniques is presented. Compared to the standard approaches the method can use
more than one reconstructed variable to infere the value of the unsmeared
quantity on event by event basis. The method is implemented using a sequential
neural network with a categorical cross entropy as the loss function. It is
tested on a toy example and is shown to satisfy basic closure tests. Possible
application of the method for analysis of the data from high energy physics
experiments is discussed.Comment: 9 pages, 6 figure
Probing the photonic content of the proton using photon-induced dilepton production in collisions at the LHC
We propose a new experimental method to probe the photon parton distribution
function inside the proton (photon PDF) at LHC energies. The method is based on
the measurement of dilepton production from the reaction in proton--lead collisions. These
experimental conditions guarantee a clean environment, both in terms of
reconstruction of the final state and in terms of possible background. We
firstly calculate the cross sections for this process with collinear photon
PDFs, where we identify optimal choice of the scale, in analogy to deep
inelastic scattering kinematics. We then perform calculations including the
transverse-momentum dependence of the probed photon. Finally we estimate rates
of the process for the existing LHC data samples
Heavy-flavor parton distributions without heavy-flavor matching prescriptions
We show that the well-known obstacle for working with the zero-mass variable
flavor number scheme, namely, the omission of O(1) mass power corrections close
to the conventional heavy flavor matching point (HFMP) mu_b=m, can be easily
overcome. For this it is sufficient to take advantage of the freedom in
choosing the position of the HFMP. We demonstrate that by choosing a
sufficiently large HFMP, which could be as large as 10 times the mass of the
heavy quark, one can achieve the following improvements: 1) above the HFMP the
size of missing power corrections O(m) is restricted by the value of mu_b and,
therefore, the error associated with their omission can be made negligible; 2)
additional prescriptions for the definition of cross-sections are not required;
3) the resummation accuracy is maintained and 4) contrary to the common lore we
find that the discontinuity of alpha_s and pdfs across thresholds leads to
improved continuity in predictions for observables. We have considered a large
set of proton-proton and electron-proton collider processes, many through NNLO
QCD, that demonstrate the broad applicability of our proposal
Spontaneous radiation of a finite-size dipole emitter in hyperbolic media
We study the radiative decay rate and Purcell effect for a finite-size dipole
emitter placed in a homogeneous uniaxial medium. We demonstrate that the
radiative rate is strongly enhanced when the signs of the longitudinal and
transverse dielectric constants of the medium are opposite, and the
isofrequency contour has a hyperbolic shape. We reveal that the Purcell
enhancement factor remains finite even in the absence of losses, and it depends
on the emitter size.Comment: 6 pages, 3 figure
Cavity-control of interlayer excitons in van der Waals heterostructures
Monolayer transition metal dichalcogenides integrated in optical microcavities host exciton-polaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe2-WSe2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavity - van der Waals heterostructure systems
Cavity-control of interlayer excitons in van der Waals heterostructures
Monolayer transition metal dichalcogenides integrated in optical microcavities host exciton-polaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe2-WSe2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavity – van der Waals heterostructure systems
The PDF4LHC report on PDFs and LHC data: Results from Run I and preparation for Run II
The accurate determination of the Parton Distribution Functions (PDFs) of the
proton is an essential ingredient of the Large Hadron Collider (LHC) program.
PDF uncertainties impact a wide range of processes, from Higgs boson
characterisation and precision Standard Model measurements to New Physics
searches. A major recent development in modern PDF analyses has been to exploit
the wealth of new information contained in precision measurements from the LHC
Run I, as well as progress in tools and methods to include these data in PDF
fits. In this report we summarise the information that PDF-sensitive
measurements at the LHC have provided so far, and review the prospects for
further constraining PDFs with data from the recently started Run II. This
document aims to provide useful input to the LHC collaborations to prioritise
their PDF-sensitive measurements at Run II, as well as a comprehensive
reference for the PDF-fitting collaborations.Comment: 55 pages, 13 figure
Parton Distribution Functions of the Charged Pion Within The xFitter Framework
We present the first open-source analysis of parton distribution functions
(PDFs) of charged pions using xFitter, an open-source QCD fit framework to
facilitate PDF extraction and analyses. Our calculations are implemented at
next-to-leading order (NLO) using APPLgrids generated by MCFM generator. Using
currently available Drell-Yan and photon production data, we find the valence
distribution is well constrained; however, the considered data are not
sensitive enough to unambiguously determine sea and gluon distributions.
Fractions of momentum carried by the valence, sea and gluon components are
discussed, and we compare with the results of JAM collaboration and the GRV
group.Comment: 9 pages, 6 figure
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