Christian Grefe

@cgrefe.bsky.social

670 Followers 331 Following

Particle physicist at University of Bonn, working on the ATLAS experiment at CERN. https://orcid.org/0000-0001-7050-5301

Sunset over the Atlantic ocean behind a pool and some palm trees.
Cover of "the incredible Hulk" Comic
Picture of the new ATLAS experiment colouring book.
7 days weather forecast for Geneva. Daily maxima between 33° and 38°C
A group of policemen in front of a Tiffany & Co with barricaded windows.
A picture of Fry from Futurama squinting, overlaid with text: "Not sure if sarcasm or serious"
Announcement by an online bank that one can now have savings up to 5000000€ on their accounts
Mitglieder des Deutschen Bundestages besuchen den ATLAS Kontrollraum.
Number of reconstructed primary vertices as a function of the number of simulated pp interactions per bunch crossing in simulated tt events.
Relative q/pT resolution for track seeds, track candidates, and selected tracks as a function of the η of the generator-level particles to which they are matched. The resolutions represent the average over the full pT spectrum of the sample. The observed asymmetries in the distributions for seeds are due to the inactive modules included in the simulation, to reflect data taking conditions during Run 2.
A visualization of an event recorded by the ATLAS experiment (run 508073, event 22881991) on October 8, 2025, when the Large Hadron Collider accelerator was providing proton-proton collisions at 13.6 TeV with a "high-mu" setup. In a "high-mu" setup, the proton beams in the accelerator are focused and directed to produce a high number of collisions per bunch crossing. The event visualized here was recorded in a collision with an average of 150 proton-proton interactions, and 92 primary vertices were reconstructed. The image shows three views of the same event. The top left view shows a transversal view of the event, where, from the center, the tracks of the charged particles as reconstructed in the inner detectors are displayed (multicolor lines) as well as the energy deposits (yellow bars) in the electromagnetic and hadronic calorimeters. A blue line shows the reconstructed track of a muon. The bottom view shows the same event in a longitudinal projection, where the reconstructed 92 primary vertices are also shown, visualized as white spheres. The right view shows the energy deposits in the calorimeters represented on a projected surface of the ATLAS detector; this kind of plot (called a "Lego plot") shows the overall activity of an event.
Illustration of the stages of inside-out track pattern recognition in a simplified representation of the Inner Detector transverse plane. The silicon space points are shown in yellow, and TRT drift circles in orange. The seeds reconstructed from combinations of space points are indicated in blue. The dashed blue seed illustrates a case where two seeds correspond to the trajectory of the same charged particle. The green seed is rejected by the requirement that the seed be consistent with a particle from the nominal interaction point. The track candidates are shown with lines. The green dashed track candidate is rejected because it is inconsistent with the nominal interaction point. The black track candidate is reconstructed up to the CKF stage. The red track candidates are fully reconstructed silicon tracks fit with the global χ2 where an extension into the TRT is possible.
Entwicklung der Lebenserwartung in Ost- und Westdeutschland seit der Wiedervereinigung. Quelle: https://www.destatis.de/DE/Themen/Gesellschaft-Umwelt/Bevoelkerung/Sterbefaelle-Lebenserwartung/sterbetafel.html
Historische Ansicht des Gendarmenmarktes um 1900. Blick auf das Konzerthaus und den Französischen Dom. Im Vordergrund sind Gärten zu sehen. Quelle: https://www.gendarmenmarkt.de/geschichte-des-gendarmenmarktes-berlin-mitte.htm
Letter of recommendation for John Nash: "Mr. Nash is nineteen years old and graduating from Carnegie Tech in June. He is a mathematical genius."
Screenshot of the CERN job advertisement page
„Ganze Studiengänge stehen vor dem Aus“, heißt es in einer Erklärung der „AG Ausfinanzierung“, die Studierende, wissenschaftliche Mitarbeitende und Lehrende gegründet haben, um das Ruder noch herumzureißen. Sie fordern, dass die Stadt Hamburg das Loch von etwa 30 Millionen Euro im Budget seiner größten Uni ausgleicht. Rechnen würde sich das, sagen sie, flössen doch von jedem in Hochschulen investierten Euro rund 1,90 Euro in die Stadt zurück.
DPG logo in front of a tree
Pizza im Hörsaal
10. Jahrestreffen der yHEP Association
Blossom of a yellow Phalaenopsis.
Silhouette von Bäumen im Licht der Dämmerung
LHC Page1 reporting first PbPb stable beam collisions in 2025
Publicity e-mail from Elsevier promoting their "AI-supported peer review".
Oktoberfestzelt in Genf.
IC Netzkarte in der Schweiz.
Karte des Shinkansen-Netzes in Japan.
Sonnenuntergang über den Dächern einer Kleinstadt im Atlasgebirge.
Bust of Nobel laureate in physics Heinrich Hertz, former professor at the University of Bonn.
"Verordnung des Reichspräsidenten zum Schutz von Volk und Staat vom 28. Februar 1933. Auf Grund des Artikels 48 Absatz 2 der Reichsverfassung wird zur Abwehr kommunistischer staatsgefährdender Gewaltakte folgendes verordnet: § 1 Die Artikel 114, 115, 117, 118, 123, 124 und 153 der Verfassung des Deutsches Reiches werden bis auf weiteres ausser Kraft gesetzt. Es sind daher Beschränkungen der persönlichen Freiheit, des Rechts der freien Meinungsäusserung, einschliesslich der Pressefreiheit, des Vereins- und Versammlungsrechts, Eingriffe in das Brief-, Post-, Telegraphen- und Fernsprechgeheimnis, Anordnungen von Haussuchungen und von Beschlagnahmen, sowie Beschränkungen des Eigentums auch ausserhalb der sonst hierfür bestimmten gesetzlichen Grenzen zulässig."
Directions in a building at the university of Bonn. The directions to the physics institute have been fixed by a piece of paper and scotch.
Sunrise over Lac Leman and the Rhône seen from Bel Air in Geneva. In the foreground people are waiting at a tram stop.
Sunset over the Arve river in Geneva
Protest by Extinction Rebellion at Piazza San Marco in Venice
Cover of Pink Floyd's dark side of the moon