Deutsches Elektronen-Synchrotron DESY
Notkestraße 85
22607 Hamburg

Universität Hamburg
Luruper Chaussee 149
22761 Hamburg

The Standard Model of particle physics is a very successful theory describing the fundamental particles of matter, the fermions, and their interactions through the exchange of force-carrying bosons. However, there are many cosmological observations that the Standard Model cannot explain, for example why there is more matter than antimatter in the universe or the existence of dark matter. The Higgs boson, discovered at the Large Hadron Collider (LHC) in 2012, can be used as a probe to investigate some of these unsolved comological puzzles. The focus of the proposed Young Investigators Group (YIG) will be to search for dark matter candidates and other new physics at the ATLAS experiment in two complementary ways: directly by looking for Higgs boson decays to invisible particles, which do not leave a trace in the detector, and could be the dark matter candidates, and indirectly by comparing Higgs boson properties to Standard Model predictions. The YIG will be part of the DESY ATLAS group. Strong ties to the University of Hamburg are foreseen, through students, teaching and exchange with theorists.
The YIG will use Higgs boson decays to invisible particles to directly search for physics beyond the Standard Model, in particular dark matter candidates coupling to the Higgs boson. Since the transverse momentum of all produced particles should add up to zero in a proton- proton collison, these particles can be detected by looking for missing transverse momentum. To reject background processes, two distinctive Higgs production channels will be used, one in which the Higgs boson is produced together with two hadronic jets, the other in which the Higgs boson is produced in association with a Z boson. In 2015, the LHC increased the center-of-mass energy of the proton-proton collisions from 8 to 13 TeV, and is planning to collect ~125 fb-1 in the next 4 years, almost 5 times as much as recorded until now. This, as well as improvements to the analysis strategy will allow to increase the sensitivity of the search significantly with respect to previous analyses.
The properties of the Higgs boson will be studied in the H → ZZ* → 4l decay channel, often termed the ''golden channel'' because the four leptons in the final state cause the background contamination to be very low. The YIG will play a leading role in measuring the cross sections of Higgs boson production differentially, as a function of Higgs boson kinematics, like the transverse momentum of the Higgs boson, and as a function of the properties of hadronic jets produced in association with the Higgs boson. These distributions can be used to test the calculations of Standard Model Higgs boson production. Furthermore, deviations from Standard Model predictions could indicate the presence of new physics. For example, the transverse momentum of the Higgs boson could be affected if it is produced in association with dark matter. The 2012 analysis was limited by large statistical uncertainties, which will be decreased with the larger dataset. In addition, the group plans a number of improvements to the analysis strategy.
A combination with differential cross section measurements in the H→γγ channel, to which another DESY group contributes, will allow for valuable cross checks and further reduction of the statistical uncertainties. The YIG will improve electron identification and efficiency measurements at low energies, a key ingredient especially in the H → ZZ* → 4l analysis. The higher collision rates of the LHC and the resulting overlapping events in the detector will require continuous development in the coming years. In 2024, the LHC will be upgraded to run at even higher luminosities. The goal is to produce 3000 fb-1 of proton-proton collisions for precision tests of the Standard Model and the direct search for very rare new physics. The current Inner Detector will be replaced by an all-silicon detector to cope with the high collision rates. This replacement is already in preparation in parallel with the operation of the current detector and consists of an inner pixel and an outer microstrip detector. Together with international partners, the proposed YIG will develop and implement the data readout infrastructure for testing and operating one of the endcaps of the new silicon microstrip detector, which is foreseen to be built at DESY.

Leader of the Helmholtz Young Investigators Group:

Dr. Sarah Heim
DESY
Notkestr. 85
22607 Hamburg
Office:
Phone: +49 40 8998-0
Email: sarah.heim@desy.de

Partner universitiy

Prof. Dr. rer. nat. Peter Schleper
Institut für Experimentalphysik Universität Hamburg
Luruper Chaussee 49
22761 Hamburg
Deutschland
email peter.schleper@desy.de

Weiterführende Links

Sachbericht 2016 (98KB)

 

Sachbericht 2017 (103KB)

 

Sachbericht 2018 (107KB)

 

Sachbericht 2019 (1.5 MB)