arXiv subjects

Jan Kretzschmar

Publications and source records attributed to Jan Kretzschmar.

8 recordsLinked to original sources

arXiv2024

From trees to rain: Enhancement of cloud glaciation and precipitation by pollen

The ability of pollen to enable the glaciation of supercooled liquid water has been demonstrated in laboratory studies; however, the potential large-scale effect of trees and pollen on clouds, precipitation and climate is pressing knowledge to better understand and project clouds in the current and future climate. Combining ground-based measurements of pollen concentrations and satellite observations of cloud properties within the United States, we show that enhanced pollen concentrations during springtime lead to a higher cloud ice fraction. We further establish the link from the pollen-induced increase in cloud ice to a higher precipitation frequency. In light of anthropogenic climate change, the extended and strengthened pollen season and future alterations in biodiversity can introduce a localized climate forcing and a modification of the precipitation frequency and intensity.

physics.ao-ph↗

arXiv2023

Compatibility and combination of world W-boson mass measurements

The compatibility of W-boson mass measurements performed by the ATLAS, LHCb, CDF, and D0 experiments is studied using a coherent framework with theory uncertainty correlations. The measurements are combined using a number of recent sets of parton distribution functions (PDF), and are further combined with the average value of measurements from the Large Electron-Positron collider. The considered PDF sets generally have a low compatibility with a suite of global rapidity-sensitive Drell-Yan measurements. The most compatible set is CT18 due to its larger uncertainties. A combination of all mW measurements yields a value of mW = 80394.6 +- 11.5 MeV with the CT18 set, but has a probability of compatibility of 0.5% and is therefore disfavoured. Combinations are performed removing each measurement individually, and a 91% probability of compatibility is obtained when the CDF measurement is removed. The corresponding value of the W boson mass is 80369.2 +- 13.3 MeV, which differs by 3.6 sigma from the CDF value determined using the same PDF set.

hep-ex↗

arXiv2022

A standard convention for particle-level Monte Carlo event-variation weights

Streams of event weights in particle-level Monte Carlo event generators are a convenient and immensely CPU-efficient approach to express systematic uncertainties in phenomenology calculations, providing systematic variations on the nominal prediction within a single event sample. But the lack of a common standard for labelling these variation streams across different tools has proven to be a major limitation for event-processing tools and analysers alike. Here we propose a well-defined, extensible community standard for the naming, ordering, and interpretation of weight streams that will serve as the basis for semantically correct parsing and combination of such variations in both theoretical and experimental studies.

hep-ph↗

arXiv2018

Standard Model physics at the LHC

In this contribution to the volume "From My Vast Repertoire -- The Legacy of Guido Altarelli" I discuss selected topics of Standard Model (SM) physics at the LHC and their connection to the work of Guido Altarelli. An overarching connection is given by Guido's fundamental contributions to our understanding of the strong force, parton distribution functions and their evolution, and techniques to calculate theoretical predictions through perturbative Quantum Chromodynamics. The increasingly precise LHC measurements of diverse processes can be confronted with SM predictions relying on these foundations to test the SM and contribute to the knowledge of the proton structure. The LHC experiments have also started to perform precise measurements of SM parameters, such as the mass of the W boson, and have measured a variety of processes sensitive to interactions of multiple electroweak bosons. The discovery of the Higgs boson in 2012 and the measurements of its properties are crucial to establish the nature of the mechanism of electroweak symmetry breaking and the status of these studies is summarised.

hep-ex↗

arXiv2018

WG1: Structure Functions and Parton Densities

This paper gives a summary of selected highlights discussed in the working group on "Structure Functions and Parton Densities" (WG1) at the DIS 2017 conference. From the many talks presented we extract some general themes discussed with respect to global PDF fits, new PDF-sensitive measurements from the LHC experiments and elsewhere, exploitation of new ideas, tools to perform PDF fits, PDFs of heavy nuclei, and finally progress in basic theory calculations.

hep-ph↗

arXiv2012

Electroweak Measurements with the ATLAS and CMS Experiments

Highlights of ATLAS and CMS measurements involving the production of heavy electroweak gauge bosons, W and Z, at the LHC are presented. Cross sections of single W and Z bosons are studied with very high precision and differential in various kinematic variables. The rapidity differential measurements are shown to have a so far unique impact on our knowledge of proton structure with regards to the strange quark density. The production in association with one or more light or heavy flavour jets is studied. Furthermore measurements of τ final states, W polarisation and the weak mixing angle sin2θW are presented. Various di-boson measurements are presented and measurements are in general found to be well described by the Standard Model predictions. These measurements test the non-Abelian gauge structure and limits on anomalous triple gauge couplings are derived, which are of impact comparable to the corresponding LEP and Tevatron results.

hep-ex↗

arXiv2009

Measurement of F2 at Medium Q2 and the PDF Determination using H1 HERA I Data

A new measurement of the inclusive DIS ep cross section using H1 data from the year 2000 is performed and combined with published results using 1996/97 data. The new data covers the region of Q2 from 12 to 150 GeV2 at HERA with unprecedented accuracy. The structure Function F2 is extracted and studied. A QCD analysis, H1PDF 2009, is performed including the new and published H1 inclusive measurements.

hep-ex↗

arXiv2009

Proton Structure Measurements and the HERAPDF fit

New and previously published measurements on the deep inelastic $ep$ scattering cross section by the H1 and ZEUS collaborations are presented. The uncertainties can be significantly reduced by a model independent combination procedure, which treats the systematic error correlations in a coherent way. The combined H1 and ZEUS measurements of the inclusive neutral and charged current cross sections are used to perform a common NLO QCD fit, called HERAPDF 0.1. The resulting set of parton density functions (PDFs) have a much improved experimental uncertainty compared to previous extractions using the uncombined H1 or ZEUS data.

hep-ex↗