Project leader: Kenneth Österberg   Personnel

The main focus of the CMS forward physics Project during 2023-25 will be the completion, full commissioning and operation of the time-of-flight (TOF) detector of the CMS Precision Proton Spectrometer (PPS) in LHC Run 3 (2022-25). The group will also take advantage of the Run 3 PPS data with a significantly improved PPS timing detector performance to search of physics beyond the Standard Model (BSM). In parallel with the PPS Run 3 and physics activities, the group will be involved in the planning and preparation of a new PPS for the high-luminosity LHC (HL-LHC) phase.

In addition, the project will have a leading role in the completion of the TOTEM physics program with the characterization of the Odderon and the study of glueball candidates using data already taken and data to be taken in 2023. Group members will have important responsibilities in the experiments including the CMS PPS TOF detector operation (F. Garcia) and the TOTEM physics coordination (K. Österberg).

CMS PPS TOF detector: The aim of the CMS PPS is to study high mass central exclusive processes (CEP) ppp + X + p, in standard LHC high luminosity runs. The final state protons are measured by PPS and the central system X by the CMS central part. CEP processes have unique sensitivity to BSM physics e.g. in the search for anomalous quartic gauge couplings and new particles. The main background to searches with PPS are coincidences between central systems from one proton-proton collision and protons from other simultaneous proton-proton collisions (“pilep”). This background can be significantly reduced by mass and rapidity matching between central and diproton systems or/and by correlating the longitudinal vertex between central and diproton systems exploiting the proton TOF measurements. With the increase of pileup in the LHC, the importance of the proton TOF measurements will grow.

The PPS ability for CEP processes has been proven using Run 2 data taken in 2016-18 however without usage of the TOF detector. The proof-of-concept of the diamond-based TOF detector has been shown on 2018 data. The TOF detector is currently being upgraded for Run 3 as joint project between HIP, INFN/University of Siena and CERN with the goal to achieve a 20-30 ps TOF resolution. For the 2022 data taking, two TOF modules were installed with two additional being prepared for the 2023-25 data taking. HIP is responsible for the purchase, metallization and quality control of the diamonds (Rantanen, Koponen, Österberg) as well as TOF module preparation for LHC tunnel installation (Garcia, Turpeinen). In 2023-25, the group will also be responsible for the TOF detector operation (Garcia) that will require additional resources and manpower.

For HL-LHC and Run 4, a completely refurbished PPS will be installed. At the expected pileup of HL-LHC, a TOF resolution of about 15 ps would be desirable. HIP will participate in the planning and testing of the different technology options for the PPS TOF detector for HL-LHC (Garcia, Rantanen). As one part of it, T. Naaranoja will return to HIP for a 6 month period to complete her PhD thesis on the radiation hardness of diamond sensors.

CMS PPS physics analysis: In addition to the increased integrated luminosity of Run 3, the improved PPS TOF measurement will open up the possibility to search for exclusive tau pair production and doubly-charged Higgs bosons (H++) decaying dominantly into tau leptons in left-right supersymmetric models (Milieva, Österberg). There is currently a significant interest to study high mass tau pair final states due to the recent excess observed by CMS in Run 2. Feasibility studies indicate improved sensitivity using PPS with respect to standard LHC searches in both of these scenarios, for the H++ especially when the H++ is from the right-handed triplet leading to an intact photon and a vanishing left-handed weak boson (W and Z) coupling. The analysis of these two channels using the Run 3 data will be made in close collaboration with the CMS experiment group (S. Lehti) with significant expertise in tau lepton tagging and triggering. In the case of the H++ search, there will also be collaboration with HIP phenomenologists (K. Huitu et al.).

TOTEM physics program completion: 

The special high β* optics run for the 13.6 TeV total cross section measurement was postponed to 2023. Hence, the nT2 finalisation and commissioning, where HIP has an essential role (Garcia), has been rescheduled to take place just before the total cross section run. HIP is also responsible for the nT2 offline software (Oljemark). Another special very high β* optics run for the 13.6 TeV ρ measurement will also most probably be scheduled to take place in 2023. This will be the last TOTEM standalone run, however the data analysis will still continue for a few years. The HIP group will, in addition to the coordination of the physics analyses and publications (Österberg), mainly will be involved in the completion of the TOTEM physics program through the nT2 and some analysis contributions to the 13.6 TeV total cross section measurement and study of glueball candidates.

The HIP group will as for the previous total cross section measurements determine the inelastic rate (Oljemark) that is one of the essential ingredients. The aim of the measurements at 13.6 TeV as well as the total cross section and ρ measurement at 900 GeV (using data taken in 2018) is to characterize the energy behaviour of the Odderon contribution. Also an update of the comparison of the elastic proton-proton and proton-antiproton differential cross section with D0 showing evidence for Odderon exchange will be presented in 2023 (Österberg). Finally, the study of scalar and tensor glueball candidates (Oljemark, Österberg) in the gluon rich CEP environment using the large common CMS-TOTEM high β* data set will also continue during the next years, efforts done in close collaboration with the CMS-TOTEM CERN and University of Kansas groups.

Composition of the research group: In 2023, the group will consist of Project Leader Prof. Kenneth Österberg, Prof. emer. Heimo Saarikko, Senior Scientist Dr. Francisco Garcia, post-doc Fredrik Oljemark and PhD students Anna Milieva, Tiina Naaranoja (1.3.-31.8.2023) and Milla-Maarit Rantanen. The Detector Laboratory will support the project for the diamond quality control (Pirkitta Koponen) and PPS TOF and nT2 detector commissioning/test beams (Raimo Turpeinen).