Scenarios for the LHC Upgrade

Abstract

Listen

Translate article

The projected lifetime of the LHC low-beta quadrupoles, the evolution of the statistical error halving time, and the physics potential all call for an LHC luminosity upgrade by the middle of the coming decade. In the framework of the CARE-HHH network three principal scenarios have been developed for increasing the LHC peak luminosity by more than a factor of 10, to values above 10 cm−2s−1. All scenarios imply a rebuilding of the high-luminosity interaction regions (IRs) in combination with a consistent change of beam parameters. However, their respective features, bunch structures, IR layouts, merits and challenges, and luminosity variation with β∗ differ substantially. In all scenarios luminosity leveling during a store would be advantageous for the physics experiments. An injector upgrade must complement the upgrade measures in the LHC proper in order to provide the beam intensity and brightness needed as well as to reduce the LHC turnaround time for higher integrated luminosity. 1 MOTIVATION AND TIME FRAME The Large Hadron Collider (LHC) will collide two proton beams with a centre-of-mass energy of 14 TeV at design and “ultimate” luminosities of 10 cm−2s−1 and 2.3 × 10 cm−2s−1. The LHC proton beams will cross each other at the four detectors of the two high-luminosity experiments ATLAS and CMS, the B physics experiment LHCb, and the ion experiment ALICE. The LHC is set to explore an extremely rich physics landscape, spanning from the Higgs particle, over supersymmetry, extra dimensions, black holes, precision measurements of the top quark, the unitarity triangle, to the quark-gluon plasma [1]. Simple models for the LHC luminosity evolution over the first few years of operation [2] indicate that the IR quadrupoles may not survive for more than 8 years due to high radiation doses, and that already after 4–5 years of operation the halving time of the statistical error may exceed 5 years. Either consideration points out the need for an LHC luminosity upgrade around 2016. Actually there exists even a third reason for an LHC upgrade, which is extending the physics potential of the LHC: A ten-fold increase in the luminosity will increase the discovery range for new particles by about 25% in mass [1]. Detailed physics examples can be found in Ref. [3]. The particle-physicists’ goal for the upgrade is to collect 3000 fb−1 per experiment in 3–4 years of data taking. Simlar upgrades were performed at previous hadron colliders, where, for example, the Tevatron upgrade has resulted in an integrated Run-II luminosity about 50 times larger than that of Run I. The LHC upgrade could consist of a series of improvements, e.g. two stages – the first one consolidating the nominal performance and providing a luminosity of up to 3× 10 cm−2s−1 and the second one increasing the luminosity by more than an order of magnitude from nominal, to values above 10 cm−2s−1. Possible LHC upgrade paths were first examined around 2001 [4]. They have been further developed by the CARE [5] HHH network [6], in collaboration with the US LARP [7].