Nome
Precision timining with forward protons at the HL-LHC

Código
PTDC/FIS-PAR/1214/2021

Entidade Beneficiária

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Sumário do Projecto

Since the first collisions in 2010, the CERN Large Hadron Collider (LHC) has been the focus of the global and Portuguese particle physics communities, discovering a Standard Model (SM)-like Higgs boson and performing a multitude of precise measurements and searches for new particles. While there are compelling reasons to believe new physics exists, none of the existing studies have discovered it to date. This implies that new physics either occurs at masses too high to be directly detected, at rates too small to have been observed to date, or in channels and topologies that have not yet been fully explored. By the end of operation, the LHC and upgrades will deliver at least 20 times more integrated luminosity than currently available, but without large increases in the collision energy. For this reason, studies of rare processes as a means to indirectly detect new physics, and searchestaking advantage of new detectors and analysis techniques, are becoming increasingly important.In recent years, the importance of detecting forward protons using tracking and time-of-flight detectors in proton-proton collisions has been recognized as a new method to probe electroweak and beyond-SM physics. The CMS experiment, at CERN, plans to install a new forward proton detector system for the High Luminosity LHC (HL-LHC) program, beginningin 2027. These detectors, while small, will open a window to explore photon-photon collisions at unprecedented energies and with unprecedented luminosities. They will also push the technological boundaries of what can be achieved in terms of timing precision and radiation hardness.By detecting and correctly reconstructing the forward protons in LHC collisions, a rare class of events involving photon-photon exchanges can be tagged and studied. This allows searches for New Physics, including the analysis of anomalous couplings of photons to other gauge bosons, top quarks, and tau leptons, in ways that are difficult to achieve with other methods. These processes may indirectly reveal physics beyond the Standard Model. By fully reconstructing the proton kinematics, direct searches for new physics will also be performed, via resonance and missing mass searches. Finally, the proposed forward proton detector system will allow measurements of Standard Model cross sections, including that of the Higgs boson, in central production.One of the major challenges of operating such detectors at the HL-LHC is the "pileup", or additional collisions occurring in the same proton bunch crossing as the collision of interest.By precisely measuring their time-of-flight, forward protons produced in these collisions can be correctly associated to the correct collision vertex, enabling rare photon-photon interactions to be reconstructed even at the maximum pileup foreseen for the HL-LHC. In order to fully resolve all collisions with forward protons, timing precisions of ~20ps or less will be of paramount importance, and enhance the sensitivity to these processes.During Run 2 of the LHC, proton fast timing detectors were already operated as a proof of principle, achieving resolutions of ~100ps with high efficiency. While these detectors were very resistant to radiation, they were limited, particularly by the TDC and related electronics, to timing resolutions of ~30-40ps per plane. For the HL-LHC, new technologies will be required to cope with the pileup, radiation, and event rates, both in terms of sensors and readout electronics. This project will help to address that challenge by exploring the latest developments in timing detectors and electronics, with the smallest possible segmentation and under extreme radiation conditions.One of the leading technology candidates is Low Gain Avalanche Detector (LGAD) silicon detectors. These detectors are already being implemented on a much larger scale for upgrades of the central CMS detectors. They have achieved excellent time resolution in testbeams, including the electronics readout chain. In particular, a dedicated ASIC design of a TDC has obtained resolutions of ~6ps. The sensors can potentially survive radiation levels up to ~5 * 10^15 neutron equivalents/cm^2, sufficient for the proposed forward proton detectors.In this project, we propose to lead the development of LGAD detectors and readout systems for the forward proton detector upgrade of the CMS experiment.This will consist of evaluating the candidate sensors and electronics in laboratory tests, their response to the realistic radiation conditions expected in the LHC, and their response to real hadron beams. The approaches used will include tests with laser signals, and in high irradiation facilities.The end result will be a full prototype of the detector and electronics to be used in the LHC, that will be tested in high-energy proton beams.

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