The long term schedule for the LHC was established during the fall of 2013, following two important workshops of the experiments and LHC machine.

The ECFA High Luminosity LHC workshop in Aix-les-Bains at the beginning of October discussed the long term plans of the LHC experiments including many details on physics motivations, detector technologies and shutdown needs.

The RLIUP (Review of LHC Injector Upgrade Projects) workshop at the end of October discussed the strategy for the LHC machine that should lead to an integrated pp luminosity of  3000fb^-1 and Heavy Ion luminosity of 10nb^-1 by the end of the HL-LHC programme.

Based on this input, the long term LHC schedule was established in December of 2013. It foresees the next Long Shutdown (LS2) to start in July of 2018, lasting for 18 months and foresees LS3, that will see the implementation of the HL-LHC, to start in 2023 and lasting for 30 months. In addition, the ‘year end technical stop’ of 2016/2017 is extended from 13 to 19 weeks.

Following the accepted terminology, the LHC experiments will install the Phase1 upgrade during LS2 and Phase2 upgrade during LS3. The Phase2 upgrades of  ATLAS and CMS will involve major changes to their apparatus to prepare for a leveled HL-LHC luminosity of 5 x 10³⁵ cm^-2s^-1  In constrast, ALICE and LHCb will implement their main detector upgrade already during LS2.

The upgrade plans for all detector subsystems are formulated in technical design reports that are reviewed by the LHCC and the UCG (Upgrade Cost Group) and upon positive recommendation approved by the Research Board. ATLAS and CMS have all their Phase1 upgrade TDRs approved and the TDRs for ALICE and LHCb are at present in the approval process.

ATLAS and CMS presented their Phase1 upgrade plans for the Long Shutdown 2 that will start in July 2018. (Image: Installation works ATLAS Experiment, Marcelloni De Oliveira, Claudia). 

The Phase1 upgrades of ATLAS and CMS are targeting detector improvements that will allow them in addition to cope with about twice the LHC design luminosity i.e. 2 x 10³⁴ cm² s^-1.

ATLAS has formulated this program in 4 TDRs. The New Small Wheel refers to a new forward muon station that increases the trigger and tracking capabilities of the muon system. The so called ‘Fast Tracker’ is a hardware based track finder that runs after L1 and provides input to the L2 trigger. The Liquid Argon calorimeter trigger will use more segmented information to avoid performance degradation at high pileup. Major Trigger and DAQ improvements are also being implemented. The precise scope of the Atlas Forward Physics (AFP) is presently under discussion.

CMS has described their phase1 upgrade plans in 3 TDRs. A new 4 layer pixel detector will be installed in the 2016/2017 year end technical stop. The photon detectors of the Hadron Calorimeter will be changed to the novel silicon photomultiplier technology and the readout electronics will be upgraded. The L1 trigger will also undergo a major upgrade.

In order to cope with the new LHC design luminosities and energy upgrades, all LHC experiments are planning to upgrade their detector subsystems. (Image: Pojer Mirko)

The TOTEM experiment is in the process of preparing two technical design reports that outline the upgrade of the experiment between now and LS2

As mentioned above, ALICE and LHCb will implement major detector upgrades already during LS2. Both are targeted at increased collision rates and performance improvement. Although very different in physics scope, these two experiments follow similar readout strategies for this upgrade, namely to eliminate hardware based triggers and read the full event rate into the online systems. This results in a data rate of 1TByte/s for ALICE and 4TByte/s for LHCb between detector and online farm. LHCb will then perform event selection in the online farm while ALICE will reduce the data of each event and write all events to permanent storage. For both experiments this requires the replacement of some key detectors and replacement of the entire readout electronics of the remaining detector systems.

The LHCb detector upgrade targets a pp luminosity of 2 x 10³³ cm² s^-1 which will increase the event statistics by a factor 5-10 compared to the number expected in Run2. This will bring the measurement errors close to the theoretical uncertainties of the respective processes.

The upgrade of the ALICE experiment will focus on physics channels that do not exhibit a signature that can be easily triggered in the very high multiplicity environment of Heavy Ion collisions and all events will therefore be written to permanent storage. With an increase of luminosity from the present 1 x 10²⁷  cm² s^-1  to >6 x 10²⁷ cm² s^-1   and considering the present event storage rate of 0.5kHz, the statistics for these physics channels will therefore increase by a factor of 100 following the upgrade.

The details of the LHCb and ALICE upgrades are presented in the following articles.