High Luminosity Large Hadron Collider
The High Luminosity Large Hadron Collider (HL-LHC; formerly referred to as HiLumi LHC, Super LHC, and SLHC) is an upgrade to the Large Hadron Collider, operated by the European Organization for Nuclear Research (CERN), located at the French-Swiss border near Geneva.
[1][2][3] The upgrade started as a design study in 2010, for which a European Framework Program 7 grant was allocated in 2011,[4][5] with goal of boosting the accelerator's potential for new discoveries in physics.
[6][7] The upgrade work is currently in progress and physics experiments are expected to start taking data at the earliest in 2028.
[8][9] The HL-LHC project will deliver proton-proton collisions at 14 TeV with an integrated luminosity of 3 ab−1 for both ATLAS and CMS experiments, 50 fb−1 for LHCb, and 5 fb−1 for ALICE.
The increase in the integrated luminosity for the aforementioned major LHC experiments will provide a better chance to see rare processes and improving statistically marginal measurements.
A collection of different designs of the high luminosity interaction regions is being maintained by the European Organization for Nuclear Research (CERN).
The resultant higher event rate posed challenges for the particle detectors located in the collision areas.
[9] The HL-LHC upgrade being applicable to almost all major LHC experiments has a wide range of physics goals.
The boost in the integrated luminosity, or evidently the larger collision event datasets that would be accumulated through HL-LHC in case of all the LHC experiments, is the most significant aspect towards achieving the goals described below.
Major goals of HL-LHC thus belong to the following five categories; improved Standard Model measurements, searches for beyond the Standard Model (BSM) physics, flavor physics of heavy quarks and leptons, studies of the properties of the Higgs boson, and the studies of QCD matter at high density and temperature.
[17][10] Measurements of the Higgs boson and understanding its connection to the electroweak symmetry breaking remains the primary goal.
HL-LHC will also add to the knowledge of parton distribution functions (PDFs) by measuring several Standard Model processes with the jets, top quarks, photons and electroweak gauge bosons in their final state.
The jet and photon production in the heavy ion collisions forms the basis of QCD perturbation theory probes, and HL-LHC will measure this at very high energy scales.
[17][10][18][19] The upgrades to the heavy-ion injectors are also in progress and would bring up even more opportunities to observe very rare phenomena and to search for BSM physics.
2025-2027: New magnets, crab-cavities, cryo-plants, collimators, superconducting links, ancillary equipment, and absorbers are planned to be installed.
A ten-year-long joint project between CERN, Brookhaven National Laboratory, Fermilab, and Lawrence Berkeley National Laboratory known as United States Department of Energy LHC Accelerator Research Program (US–LARP) successfully built and tested such quadrupole magnets.
ATLAS and CMS together will have 16 crab cavities; which will give transverse momentum to the beams to increase the collision probability.
[35] To handle the increased luminosity, number of simultaneous particle interactions, massive amount of data, and radiation of the HL-LHC environment, the detectors will be upgraded.
The main readout electronics of the calorimeter will be completely replaced to let the detector identify rare particle interactions.
The upgrade plan for SND at HL-LHC is to continue developing the detector with the aim of improving the statistics of collision events, and expand its pseudorapidity range for studies of heavy-quark production and neutrino interactions.
