Many of you have contacted me recently concerning the LHC detector upgrades, with some questions about the planning of future work. It is true that the one year stop after the LHC incident in September 2008, the need of a further shutdown to consolidate the interconnecting splices between magnets before reaching the design energy and finally the analysis of the limitations and potentials of the injectors chain performed last year and presented at the Chamonix Workshop in January 2010 have strongly modified our perception of the next two decades. Recent discussions at all levels (directorate, experiments, accelerators and LHC Committee)have nevertheless allowed us to define a broad-brush scenario, which I would like to present below. Please be aware that it may change again, depending on the LHC, injectors and experiments performance, progress of the various projects and/or on potential physics discoveries.

Before defining the possible scenario, it is  a good idea to introduce  a few keywords that are  used to define the
various steps for the LHC.

• The nominal LHC corresponds  to the  design energy (~ 14  TeV) and peak luminosity of 1034  cm^-2  s^-1.  It should allow the experiments to record an integrated luminosity of about 50 fb^-1 per year.
• The ultimate LHC corresponds to a peak luminosity of ~ 2 10³⁴ cm^-2s^-1and should yield about 100 fb^-1 per year.
• The High-Luminosity LHC (HL-LHC) would offer a leveled luminosity of ~ 5 10³⁴ cm^-2s^-1  yielding about 300 fb^-1 per yea

•    Accelerators

To reach the nominal performance, the LHC requires:

Consolidating  the  interconnect  between  magnets  to  reach  the  design  energy,  an  operation  which  is scheduled during a long shutdown in 2012

Completing the collimator project which may be started in 2012  (to be  confirmed) and completed in a “mid-decade shutdown”, around 2016.

The ultimate LHC is more  demanding and requires some  modifications  of the injectors. The initial idea was  to replace the current PS-Booster and the PS by new accelerators (SPL and PS2). At Chamonix, a cheaper and faster
proposal was made, with an increase of the PS-Booster energy from 1.4 to 2 GeV.  This could be done in the mid- decade shutdown.  In both cases, a further limitation is due to the SPS which will require some improvements as well (RF, vacuum chamber), that are under study.

A new LINAC (LINAC-4), which is under construction, is going to be ready and commissioned by 2014 and therefore connected to the PS during the same mid-decade shutdown. This new LINAC is particularly important if one remembers that the current linac-2 was setup 32 years ago and that any failure would stop the whole proton physics research at CERN !

The HL-LHC requires modifications to the LHC proper to improve the focusing towards the experiments (new inner triplets), obtain luminosity leveling etc… This is envisaged at the earliest by the start of the next decade.

As one can see, the main steps articulate around three long shutdowns (2012, mid-decade most probably around 2016, start of next decade). There are many other consolidation and improvement tasks that are not described here and that should be done in the shadow of the main ones.

•    Detectors

Detectors also require consolidation and modifications to make the most of the LHC. It is clear that the work has to be organized in synchronization with accelerators improvements during the same shutdowns mentioned above.

Consolidation will be the main task of the 2012 shutdown. It concerns primarily th detectors infrastructure such as cooling, ventilation, electrical network, fixing the known defects and removing single points of failure. ATLAS intends to replace its forward beam pipe by a thinner one. CMS may also use this opportunity to start replacing the HCAL photodetectors by a new type (not available at the time of construction) which are more robust and less sensitive to magnetic field orientation. The same shutdown offers the possibility to introduce part of the subdetectors which were staged, for example the 4^th forward muon station of CMS (YE4). This work (together with the HCAL photodetectors) could be completed in the mid-decade shutdown. ALICE will complete the TRD and EMCAL detectors.

ATLAS and CMS detectors were designed to sustain about 10 years of nominal LHC (500 fb^-1) and therefore radiation hardness of the components may not be the main issue, even if the LHC reaches its ultimate performance in 2018 or 2019. However the instantaneous luminosity of 2 10³⁴ cm^-2 s^-1 is beyond the initial design parameters and requires detectors modifications. The first area concerns the pixel detectors, whose readout efficiency will strongly decrease particularly in the first layers at this luminosity. For this reason, ATLAS and CMS would like to improve their pixel systems. ATLAS is proposing to add a small radius layer (the IBL) with a new readout. CMS proposes to change the whole pixel detector with a 4 layers pixel system (compared to 3 in the present setup) including a faster readout. This new pixel detector would also have a smaller material budget. In both cases, it is proposed to install a smaller beam pipe, so that the impact parameter for secondary vertices would improve, increasing the efficiency for B mesons tagging. Another area of concern for ultimate LHC is the ability to trigger at this high luminosity. Both ATLAS and CMS study important modifications of their trigger systems with the Muons detectors and Calorimeters, which in turn may imply changes in the detectors electronics. Data acquisition will also need improvements. All this has to be ready to be installed and commissioned in the mid-decade shutdown, an intense work for the coming years!

LHCb is studying the possibility to increase drastically the speed of its readout up to 40 MHz, compared to few MHz today. This would allow the experiment accept a factor of 10 higher luminosity and therefore to reach higher precision or rarer processes. This requires changing all subdetectors Front-End electronics. ALICE is also studying a replacement of part of its silicon tracking system, with again a smaller beam pipe which would improve the flavor tagging and give access to charmed baryons. Both collaborations are again targeting the mid-decade shutdown for these important changes.

As in the case of the accelerators, this list may not be exhaustive and may evolve in the light of the present operation.

Optimizing the CMS and ATLAS detectors for the HL-LHC is another, more complex endeavor. It will most probably require changing part or even all the central Trackers. The forward area, where the radiation doses are very high, will certainly need important upgrades a well. The trigger systems may have to be replaced. Our experience with the LHC detectors construction shows that 10 years is not such a long time for major projects of this kind. And to start with, a vigorous R&D is needed. In the PH department, common “generic” R&D has already started in 2008, thanks to the White Paper funding. It is expected that this will soon evolve into dedicated R&D for the various experiments.

In summary, the expected evolution of the LHC and its injectors chain has to be accompanied by a large amount of upgrades for the detectors, implying many technical developments in parallel with the operation. Of course all these projects have to be first scrutinized by the scientific committees. The experiments intend to submit Technical Design Reports in the next months for the mid-decade upgrades and perhaps Letters of Intents for the longer term. Last but not least, the Funding Agencies and CERN have to agree on the funding of these projects!

But one can expect that the landscape is going to become more and more acute, keeping always in mind that the reality (and good surprises) may always change the detailed schedule.