Today the CMS search for a dark photon at the GeV scale was made public. The search is performed using the 13 TeV pp collision data collected by the CMS detector during Run 2. On the same day, Professor David Sperka from Boston University presented this exciting result in the CERN LPCC EP-LHC Seminar.
The study was carried out by our group in close collaboration with our colleagues from Boston University across the Charles river including Professor David Sperka, Chris Cosby, and Elisa Fontanesi from Boston University and Professor Christoph Paus and Zhangqier Wang from the PPC.
The search utilizes the “data scouting” trigger system, a technique to store the events reconstructed in the trigger system, which allows CMS to collect the dimuon events at low momentum at a rate of almost 5 kHz. The scouting trigger was used in a previous CMS search to look for the potential dimuon resonance above 10 GeV. Now we extended this search well below, all the way to the GeV scale.
In this search, we ‘hunt for bumps’ on top of the dimuon mass ‘continuum’. The search was eventful as the continuum turned out to be full of surprises. During the hunt, we unexpectedly found the peaking structures from the D0 meson. The largest remaining bump we observe with boosted dimuons at 2.4 GeV has a local significance of 3.2 standard deviations. No significant excess is observed and we have pushed the sensitivity of the dimuon resonance to a new boundary, which proves the success of the data scouting technique.
The end of the Run 2 search for dimuon resonances opens up several interesting prospects for future projects. The first of course is the dimuon resonance search with Run 3 data, which has substantially more data, more physics objects in the scouting data, and some dedicated standard dimuon triggers at these low masses. These factors will significantly increase the sensitivity of the dimuon resonance search. The observation of the peaking structure of the D meson indicates that a rare decay of D0 to dimuons might also be worth exploring. For what concerns our little bump at 2.4 GeV we intend to keep an eye on it; who knows what will happen once we add more data?
— March 17, 2023 edit: the CMS collaboration has highlighted this result in a special physics briefing.