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Research at CERN

Growing Hints of Lepton Universality Violation

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Portrait von Prof. Johannes Albrecht © Nikolas Golsch​/​ TU Dort­mund
Johannes Albrecht is Professor for particle physics at TU Dort­mund Uni­ver­sity.

The Standard Model of particle physics describes the behavior of all forces and particles in the universe. However, there are increasing signs that not all measurements can be explained in the context of the Standard Model. The LHCb collaboration, which involves TU-physicist Johannes Albrecht, has unveiled some intriguing new results.

On March 23, 2021, an in­ter­na­tio­nal team of particle physicists from the Large Hadron Collider beauty collaboration reported two im­por­tant measurements made at the LHCb detector at CERN, Switzerland. RWTH Aachen Uni­ver­sity, TU Dort­mund Uni­ver­sity and the Uni­ver­sity of Heidelberg are significantly involved in the LHCb experiment.

According to the Standard Model, all three types of charged lepton particles – electrons, muons and taus – interact in the same way with other particles, as long as differences in their mass are taken in into account. As a result, the different lepton types should be created equally often in particle transformations, or “decays.” This symmetry is called lepton universality. In the measurements now reported, B mesons seemed to decay to electrons more often than to muons, which would violate the lepton universality. The statistical significance of the result is 3.1 standard deviations – however, particle physicists tend not to claim a new dis­cov­ery until a result reaches a significance 5.0.

Intriguing new results

"There are cracks in the theory of the symmetry between electrons and muons! If we are able to confirm the measurements with further data, this would strongly hint at a new physics beyond the standard model," says Dr. Eluned Smith from the RWTH Physics In­sti­tute IB. She coordinated the analysis in collaboration with Professor Johannes Albrecht of TU Dort­mund Uni­ver­sity and Dr. Martino Borsato of the Uni­ver­sity of Heidelberg.

"This result fits into a series of measurements that, taken together, provide a consistent picture. At present, the data clearly require explanation and models that go beyond the Standard Model, such as models that account for the existence of so-called leptoquarks," Albrecht adds.

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Location & approach

The campus of TU Dort­mund Uni­ver­sity is located close to interstate junction Dort­mund West, where the Sauerlandlinie A 45 (Frankfurt-Dort­mund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is “Dort­mund-Eichlinghofen” (closer to South Campus), and from B 1 / A 40 “Dort­mund-Dorstfeld” (closer to North Campus). Signs for the uni­ver­si­ty are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dort­mund.

To get from North Campus to South Campus by car, there is the connection via Vo­gel­pothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.

TU Dort­mund Uni­ver­sity has its own train station (“Dort­mund Uni­ver­si­tät”). From there, suburban trains (S-Bahn) leave for Dort­mund main station (“Dort­mund Hauptbahnhof”) and Düsseldorf main station via the “Düsseldorf Airport Train Station” (take S-Bahn number 1, which leaves every 20 or 30 minutes). The uni­ver­si­ty is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.

You can also take the bus or subway train from Dort­mund city to the uni­ver­si­ty: From Dort­mund main station, you can take any train bound for the Station “Stadtgarten”, usually lines U41, U45, U 47 and U49. At “Stadtgarten” you switch trains and get on line U42 towards “Hombruch”. Look out for the Station “An der Palmweide”. From the bus stop just across the road, busses bound for TU Dort­mund Uni­ver­sity leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dort­mund main station to the stop “Dort­mund Kampstraße”. From there, take U43 or U44 to the stop “Dort­mund Wittener Straße”. Switch to bus line 447 and get off at “Dort­mund Uni­ver­si­tät S”.

The AirportExpress is a fast and convenient means of transport from Dort­mund Airport (DTM) to Dort­mund Central Station, taking you there in little more than 20 minutes. From Dort­mund Central Station, you can continue to the uni­ver­si­ty campus by interurban railway (S-Bahn). A larger range of in­ter­na­tio­nal flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the uni­ver­si­ty station.

The H-Bahn is one of the hallmarks of TU Dort­mund Uni­ver­sity. There are two stations on North Campus. One (“Dort­mund Uni­ver­si­tät S”) is directly located at the suburban train stop, which connects the uni­ver­si­ty directly with the city of Dort­mund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.

The facilities of TU Dort­mund Uni­ver­sity are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the uni­ver­si­ty are located in the adjacent “Technologiepark”.

Site Map of TU Dort­mund Uni­ver­sity (Second Page in English).