CERN–2014–0062 October 2014

ORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRE

CERN EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

RLIUP: Review of LHC and Injector Upgrade Plans

Centre de Convention, Archamps, France, 29–31 October 2013

Proceedings

Editors: B. GoddardF. Zimmermann

GENEVA2014

ISBN 978–92–9083–407–6ISSN 0007–8328Copyright c© CERN, 2014

Creative Commons Attribution 4.0Knowledge transfer is an integral part of CERN’s mission.This CERN Yellow Report is published in Open Access under the Creative Commons Attribution 4.0 license(http://creativecommons.org/licenses/by/4.0/) in order to permit its wide dissemination and use.The submission of a contribution to a CERN Yellow Report shall be deemed to constitute the contributor’sagreement to this copyright and license statement. Contributors are requested to obtain any clearances that maybe necessary for this purpose.

This report is indexed in: CERN Document Server (CDS), INSPIRE.

This report should be cited as:Proceedings of RLIUP: Review of LHC and Injector Upgrade Plans,Centre de Convention, Archamps, France, 29–31 October 2013, edited by B. Goddard and F. Zimmermann,CERN-2014-006 (CERN, Geneva, 2014), http://dx.doi.org/10.5170/CERN-2014-006

A contribution in this report should be cited as:[Author name(s)], in Proceedings of RLIUP: Review of LHC and Injector Upgrade Plans, Centre deConvention, Archamps, France, 29–31 October 2013, edited by B. Goddard and F. Zimmermann,CERN-2014-006 (CERN, Geneva, 2014), pp. [first page] – [lastpage],http://dx.doi.org/10.5170/CERN-2014-006.[first page]

Abstract

This report contains the Proceedings of the "Review of LHC and Injector Upgrade Plans" (RLIUP), held in theCentre de Convention, Archamps, France, 29–31 October 2013. The RLIUP examined the parameters of theLIU and HL-LHC projects following the experience and changes in the beam parameters experienced over theprevious two years. It discussed which level of integrated luminosity will necessitate a replacement of the innerdetectors and the insertions, the importance of reaching 3000 fb−1 or the minimum integrated luminosity whichwould be tolerated. The main outcome of RLIUP is a staged path from the LHC performance at the end of 2012to the required performance for the HL-LHC, along with a number of important recommendations on the workorganization of the coming years.

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Preface

The "Review of LHC and Injector Upgrade Plans" (RLIUP) was held in the Centre de Convention, Archamps,France, 29–31 October 2013 (see http://indico.cern.ch/event/260492/). RLIUP was attended by 111participants, coming mostly from the CERN Accelerators and Technology Sector. Also several representatives ofthe LHC experiments and all 9 members of the CERN Machine Advisory Committee (CMAC) had been invited(6 of the latter attended).

The workshop scope and programme had been drafted by an RLIUP Organizing Committee, comprisingGianluigi Arduini, Frederick Bordry (Co-Chair), Oliver Brüning, Paul Collier, Brennan Goddard (Deputy Sci-entific Secretary), Mike Lamont (Deputy Chair), Malika Meddahi, Steve Myers (Chair), Roland Garoby, LucioRossi, Roberto Saban, and Frank Zimmermann (Scientific Secretary).

The RLIUP examined the parameters of the LIU and HL-LHC projects following the experience and changesin the beam parameters experienced over the previous two years, according to which the LHC/HL-LHC luminos-ity performance will be determined by the event pile-up and pile-up density; by the bunch spacing, with electroncloud a possible issue for 25 ns, requiring scrubbing and a long-term solution; and by the machine availability,calling for a minimization of downtime and speeding up of the turnaround time. In addition, RLIUP discussedwhich level of integrated luminosity will necessitate a replacement of the inner detectors and the insertions, theimportance of delivering 3000 fb-1 or the minimum integrated luminosity which would be tolerated instead.

RLIUP concluded that shutdowns have to be planned well in advance, including a global resources-loadedschedule; that the weaknesses in some expertise areas need to be rectified; and that any new designs should bebased on the ALARA principle using the correct materials. As a primary outcome, RLIUP produced a stagedpath from the LHC performance at the end of 2012 to the required performance for the HL-LHC. RLIUP alsosuggested investigating an increase of the maximum beam energy, noting the planned installation of some 11-Tmagnets as part of the HL-LHC project.

Further information on the review can be accessed from its indico web site http://indico.cern.ch/event/260492/.The RLIUP was organized in 6 (or 7) plenary sessions, covering (1) experiments, (2) post-LS1 scenarios withand without Linac 4, (3a) PICs and upgrade scenario 1: adding performance improving consolidation, (3b) PICsand upgrade scenario 1: upgrade scenario 1, (4) upgrade scenario 2, (5) ions, and (6) close out. The proceedingsare structured according to these plenary sessions:

• Session 1: experiments (conveners A. Ball and M. Lamont)

• Session 2: post-LS1 scenarios with and without Linac4 (conveners G. Arduni and S. Hancock)

• Session 3a: PICs and upgrade scenario 1: adding performance improving consolidation, (conveners M.Meddahi and L. Rossi)

• Session 3b: PICs and upgrade scenario 1: upgrade scenario 1 (conveners M. Meddahi and L. Rossi)

• Session 4: upgrade scenario 2 (conveners B. Goddard and R. Garoby)

• Session 5: ions (conveners O. Brüning and M. Ferro-Luzzi)

• Session 6: close out (conveners S. Myers and F. Zimmermann)

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These proceedings have been published in paper and electronic form. The paper copy is in black and white;the electronic version contains colour pictures. Electronic copies can be retrieved through the CERN CDS pages.

The compilation of these proceedings would not have been possible without the help of the conveners and theexcellent contributions from the speakers. The organizational support by the workshop secretary Shauna Dillon,technical support by Pierre Charrue, and indispensable editorial assistance in the preparation of the proceedingsby Valeria Brancolini, Evelyne Delucinge, and Lucie Mainoli are also most gratefully acknowledged.

Finally, we would like to thank all the participants for the stimulating and lively discussions.

Geneva, 18 July 2014B. Goddard and F. Zimmermann

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Contents

PrefaceB. Goddard and F. Zimmermann . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Session 1: experiments (conveners A. Ball and M. Lamont)Performance parameters – experiments perspectiveD. Contardo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Plans and physics outlook for non-high luminosity experiments until and after LS3R. Jacobsson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Post LS1 scheduleM. Lamont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Highlights from ECFA, A. Ball1

Physics landscape, F. Gianotti1

Detector Limits, B. Di Girolamo1

Session 2: post LS1 scenarios with and without Linac4 (conveners G. Arduni and S. Hancock)Expected performance in the injectors at 25 ns without and with Linac4G. Rumolo, H. Bartosik, H. Damerau. A. Findlay, S. Hancock, B. Mikulec, A. Oeftiger . . . . . . . . . . . . . . . . . . . 17

Integrated performance of the LHC at 25 ns without and with Linac4J. Wenninger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

What are the required maintenance and consolidation activities to run at design performance levels (injectorsand LHC) until 2035?S. Baird, K. Foraz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

What could stop us and whenL. Bottura, P. Fessia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Session 3a: PICs and upgrade scenario 1: adding performance improving consolidation,(conveners M. Meddahi and L. Rossi)PICs in the injector complex – what are we talking about?K. Hanke, B. Goddard, B. Mikulec, S. Gilardoni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

LHC PICs: what are we talking about?P. Fessia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

PICs: what do we gain in beam performanceG. Arduini, D. Banfi, J. Barranco, R. Bruce, O. Brüning, R. De Maria, O. Dominguez, P. Fessia, M. Fitterer,S. Gilardoni, M. Giovannozzi, B. Gorini, G. Iadarola, V. Kain, M. Kuhn, E. Métral, N. Mounet, T. Pieloni,S. Redaelli, L. Rossi, G. Rumolo, R. Tomás, J. Wenninger, A. Valishev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Session 3b: PICs and upgrade scenario 1: upgrade scenario 1 (conveners M. Meddahi andL. Rossi)US1: what do we gain in beam performanceG. Arduini, H. Bartosik, R. Bruce, O. Brüning, H. Damerau, R. De Maria, S. Fartoukh, M. Fitterer, S. Gilardoni,M. Giovannozzi, B. Gorini, M. Lamont, E. Métral, N. Mounet, S. Redaelli, L. Rossi, G. Rumolo, R. Tomás . . 57

Upgrade scenario one: work effortE. Todesco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

1A paper was not submitted to the proceedings. However, the slides presented are available in electronic form at https://indico.cern.ch/event/260492/.

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LIU: which beams in the injectors fulfil HL-LHC upgrade scenario 1S. Gilardoni, G. Arduini, W. Bartmann, H. Bartosik, O. Brüning, H. Damerau, R. Garoby, B. Goddard,S. Hancock, K. Hanke, G. Iadarola, M. Meddahi, B. Mikulec, G. Rumolo, E. Shaposhnikova, G. Sterbini,R. Wasef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Work effort in the LHC injector complex for the upgrade scenariosB. Mikulec, J-B. Lallement, E. Chapochnikova, H. Damerau, S. Gilardoni, B. Goddard, K. Hanke, D. Hay,S. Mataguez, D. Mcfarlane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Session 4: upgrade scenario 2 (conveners B. Goddard and R. Garoby)How to maximize the HL-LHC performanceG. Arduini, D. Banfi, J. Barranco, H. Bartosik, R. Bruce, O. Brüning, R. Calaga, F. Cerutti, H. Damerau, R. DeMaria, L. Esposito, S. Fartoukh, M. Fitterer, R. Garoby, S. Gilardoni, M. Giovannozzi, B. Goddard, B. Gorini,M. Lamont, E. Métral, N. Mounet, T. Pieloni, S. Redaelli, L. Rossi, G. Rumolo, E. Todesco, R. Tomás,F. Zimmermann, A. Valishev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Can we ever reach the HL-LHC requirements with the injectors?H. Bartosik, T. Argyropoulos, B. Goddard, G. Iadarola, Y. Papaphilippou, G. Rumolo, E. Shaposhnikova . . . 95

How to implement all HL-LHC upgradesL. Rossi, G. Arduini, A. Ballarino, O. Brüning, E. Jensen, S. Redaelli, L. Tavian, E. Todesco . . . . . . . . . . . . . 105

HL-LHC alternativesR. Tomás, O. Dominguez, S. White . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

LIU: exploring alternative ideasH. Damerau, H. Bartosik, R. Garoby, S. Gilardoni, S. Hancock, B. Mikulec, Y. Papaphilippou, G. Rumolo,E. Shaposhnikova, R. Tomás . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

How to reach the required availability in the HL-LHC eraM. Lamont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

How to reach the required availability in the HL-LHC eraV. Kain, G. Arduini, H. Bartosik, B. Goddard, W. Höfle, G. Iadarola, M. Meddahi, T. Pieloni, G. Rumolo,B. Salvant, J. Wenninger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Session 5: ions (conveners O. Brüning and M. Ferro-Luzzi)Heavy ion plans: experiments perspectivesE. Meschi, B. Gorini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Performance of the injectors with ions after LS1D. Manglunki for the LIU-Ions team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

How to run ions in the future?D. Küchler, D. Manglunki, R. Scrivens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Heavy ion operation from run 2 to HL-LHCJ.M. Jowett, M. Schaumann, R. Versteegen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Session 6: close out (conveners S. Myers and F. Zimmermann)Experiments: session 1 SummaryM. Lamont, A. Ball . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Session 2: post LS1 scenarios without and with Linac4G. Arduini, S. Hancock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

Session 3: PICs and upgrade scenario 1M. Meddahi, L. Rossi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

Summary of session 4 – upgrade scenario 2R. Garoby, B. Goddard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

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Summary of session 5 on ion operation during HL-LHCO. Brüning, M. Ferro-Luzzi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

Review of LHC and injector upgrade plans - SummaryS. Myers, F. Zimmermann . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

List of Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

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PERFORMANCE PARAMETERS – EXPERIMENTS PERSPECTIVE

D. Contardo, Universite Claude Bernard Lyon 1, CNRS-IN2P3

Abstract In its physics program for the next two decades, the

LHC foresees a series of upgrades to steadily increase the

instantaneous luminosity of the accelerator. This paper

describes the experimental challenges for the ATLAS and

CMS detectors to operate and perform at increasing rates

and occupancies. It focuses on the upgrades that will be

implemented to maintain the physics acceptance in the

trigger selection and the high efficiency and resolution in

the reconstruction of the many interactions that will occur

at each beam crossing.

INTRODUCTION

The upgrades of the ATLAS and CMS experiments

will be accomplished in three stages during the long

shutdowns foreseen for the upgrades of the LHC. In LS1,

the CM energy will be increased to 13 TeV (or slightly

higher), and it is expected that the bunch spacing will be

reduced to 25 ns for future RUNs. It is anticipated that the

peak luminosity can exceed the nominal value of 1x1034

Hz/cm2

before LS2 and reach more than 2x1034

Hz/cm2

after LS2. The experiment upgrades during LS1 will

complete the original detector designs, consolidate

operation and start to prepare for luminosities beyond the

nominal value. In the period through LS2 (Phase 1) the

upgrades will be completed for operation at a mean pile-

up (PU) of ∼50 proton-proton collisions per bunch

crossing, with margin up to ∼70. In LS3 the LHC itself

will be upgraded to optimize the bunch overlap at the

interaction region. It is foreseen that the peak luminosity,

exceeding 1035

Hz/cm2

at the beginning of the fills, will

be leveled at ∼5 x 1034

Hz/cm2 to control the PU. The

goal for the High Luminosity LHC (Phase 2) is to deliver

a further 2500 fb-1

in the decade after LS3. ATLAS and

CMS will need major upgrades during this shutdown to

solve detector and system aging, high occupancy and

radiation hardness issues, mitigate pile-up effects and

enhance performance where statistics/systematics limited.

PHASE 1 UPGRADES

The phase 1 upgrades [1,2] are mainly driven by

technical constraints of integration in the current

detectors, in addition to the external constraints of

schedule and funding. They essentially consist in:

completing the original detector; increasing the readout

granularity when possible without changing the detector

themselves; and using new high power and large

bandwidth FPGA and xTCA telecommunication

standards for the data processing. These allow sufficient

improvements of the trigger selection to maintain the

performance of the present detectors.

The hardware trigger in ATLAS and CMS is limited to

100 kHZ and it is based on muon systems and

calorimeters information. Events are selected when they

contain individual or multiple particles with a momentum

or energy above a threshold defining the rate allocate to

each type of event. A simplified example of such a trigger

menu and of the thresholds applied in CMS is presented

in Fig. 1. For efficient selection of the interesting physics

signals, the threshold must be maintained at low values.

When luminosity and therefore rates increase, this can be

achieved by improving the measurement precision and

implementing more sophisticated selection algorithms,

either at the level of individual detectors or in their

combination.

Figure 1: Example of a simplified CMS menu at 50 PU.

The thresholds are adjusted to maintain the bandwidth of

each trigger at similar levels for the upgraded and non-

upgraded systems.

During Phase 1, the completion of the muon systems in

the forward regions both in ATLAS and CMS, will allow

improving the sharpness of the muon selection. Some

upgrades of the calorimeter front-end and back-end

electronics will allow finer granularity of the information

available for the trigger. These improvements of the input

data together with the additional processing power in the

back-end electronics will result in better turn-on selection

at the thresholds, more efficient subtraction of PU energy,

better isolation of particles and identification of narrow τ-

jets. New topological selection will also be introduced,

based on particle masses or angular correlations. An

example of the physics acceptance benefit provided by

the CMS trigger upgrade is presented in Fig. 2.

Published by CERN in the Proceedings of RLIUP: Review of LHC and Injector Upgrade Plans, Centre de Convention, Archamps,France, 29–31 October 2013, edited by B. Goddard and F. Zimmermann, CERN–2014–006 (CERN, Geneva, 2014)

978-92-9083-407-6, 0007-8328 – c© CERN, 2014. Published under the Creative Common Attribution CC BY 4.0 Licence.http://dx.doi.org/10.5170/CERN-2014-006.1

1

Figure 2: Trigger acceptance for few key physics

channels with the upgraded and non-upgraded systems

and for the menu presented in Fig. 1.

In addition to the trigger upgrades, ATLAS and CMS

will upgrade their pixel detectors to measure one more

space point at a lower radius of ∼3 cm. In ATLAS this

will be achieved by inserting a new long inner barrel

layer, while CMS will replace the full pixel detector.

These upgrades will allow improving the position

precision on the origin of the charged tracks, with

substantial gain in the efficiency to associate them to a

primary vertex or to identify secondary vertices

associated to the decay of light or heavy quarks. This is

illustrated in Fig. 3, showing that an increase of 65% of

the ZH µµbb signal statistics can be reached with the

CMS new pixel detector.

Figure 3: The ratio Phase-1 / current of events left after

each selection cut at 50 PU. The cuts where the upgrade

detector is expected to excel are highlighted.

PHASE 2 UPGRADES

The physics program at the HL-LHC aims at precise

measurement of the Higgs couplings, as well as

measurement of very low cross section processes and

search and/or study of other new particles [3]. This

imposes severe constraints on the detector acceptance in a

challenging PU environment, especially in the forward

region of the detectors that will become extremely

important. The goal for the ATLAS and CMS upgrades

[4, 5] is to maintain the present performance at least up to

∼140 PU with a capability to take data up to ∼200 PU.

While the required replacement of some systems will

allow performance enhancement to cope with the highest

PU, assessing the best operation point of the full

experiment will need thorough investigation and major

work to tune the event selection, the data reconstruction

and the physics analyses.

For both ATLAS and CMS, a major upgrade will be the

replacement of the tracker motivated by longevity issues

and the need for a higher granularity device, also

implemented in the hardware trigger event selection. To

cope with the increased readout bandwidth, significant

amount of the other detector front-end electronics will

need replacement, also accommodating the new

specifications for the trigger system. This concerns all

systems in ATLAS and the DT muon chambers and the

electromagnetic calorimeter in the CMS barrel. In

addition, CMS will have to replace the endcap

calorimeters due to longevity issues, while only the most

forward part of the detector could be affected by

irradiation in ATLAS.

The main features for the new silicon trackers will be a

strip length divided by about a factor 4 in the outer layers,

and pixels with smaller size of about 25x100 µm2.

Thinner sensors will be used to accommodate the large

radiation doses. The assembly will be lighter than in the

present detectors, significantly reducing the γ conversions

and the multiple scattering of charged particles. This will

ensure high reconstruction efficiency and excellent

association of tracks to the proper vertices. As an

example, the expected b-quark tagging performance in the

future ATLAS tracker is presented in Fig. 4.

Figure 4: Performance of b-tagging with the ATLAS

Phase1 (IBL) and Phase 2 (ITK) trackers.

A new feature of the future trackers could be an extension

of the pixel systems in the region of pseudo-rapidity

between 2.4 and 4 to cover the full range of the

calorimeters. The association of charged tracks to their

energy deposits will provide PU mitigation. This has been

shown to be extremely powerful to reject fakes in the

D. CONTARDO

2

identification of jets from the Vector Boson Fusion or

Scattering processes that will be of major importance in

the HL-LHC physics program.

The configuration of the ATLAS and CMS trackers

will essentially differ in their implementation for trigger

purpose. While the ATLAS detector will be read-out in

regions of interest at 500 kHz, based on a calorimeter and

muon first-level trigger; the CMS tracker will implement

an on-detector selective read-out to provide track-trigger

stubs at 40 MHz. This will be achieved measuring the

bending of the tracks in the high magnetic field, over the

few mm separating two sensors connected to a same read-

out chip. A cut on the distance between the strip hits will

allow sending only the information for tracks of

transverse momentum ≥ 2 GeV. Both in ATLAS and

CMS, the hardware reconstruction of tracks in the back-

end electronics could then be performed from the

comparison of the hit map with a bank of patterns stored

in Associative Memories. CMS is also investigating a

propagation method using FPGAs. The track matching

with the calorimeter and muon system objects, will

provide high momentum resolution for leptons and

photons, improved isolation, proper association of

particles to a same vertex to reduce combinatorial

background from the PU, especially in Jets, and improved

total and missing transverse energy resolution.

Preliminary studies indicate that the lepton trigger rates

could be reduced by factors up to 10, for a given

threshold (Fig. 5).

Figure 5: Single muon trigger rates in CMS with and without track matching as a function of transverse momentum

threshold (left), single isolated e/γ rates in ATLAS with (red) and without (black) track information as a function of

transverse energy (center), and τ signal efficiency versus rate and thresholds with and without track selection (right).

The new front-end electronics design, will also allow

increasing the trigger read-out rate from the present

100 kHz up to ≥250 kHz in ATLAS and up to 0.5/1 MHz

in CMS, depending in this latter case on the bandwidth

sustainable in the pixel detector. The subsequent rise in

the required computing power at the high-level trigger

appears manageable within the expected progress of

technologies in the timescale of the project.

As mentioned above, the potential to fully exploit the

HL-LHC luminosity will be driven by the experiments

performance. It has recently been shown that a new

scheme of the beam crossings using a specific crab cavity

configuration, could allow to lengthen the beam luminous

region and to reduce the PU density. This could be a

powerful mean to improve the charged tracks association

to vertices to mitigate pile-up effects. However,

demonstrating if it would be sufficient to allow operation

at higher PU will need careful simulations and tuning of

the reconstruction algorithms. Especially, the tracker

doesn’t allow mitigating the effect of neutral particles PU

in the calorimeters. Experiments are in the process of

evaluating these effects, as well as the possibility to

mitigate the PU of neutrals through a precise time of

flight measurement.

CONCLUSION After the crucial discovery of a Higgs boson in 2012,

the LHC has an extremely exciting and unique program to

expand the physics reach through the next two decades.

This requires major upgrades of the accelerator and of the

ATLAS and CMS experiments. The first stage of these

upgrades is already at construction level and studies and

R&D for the High Luminosity LHC are ramping-up.

Many exciting ideas are being discussed to meet the

challenges of operation in the highest pile-up

environment.

ACKNOWLEDGMENT

I wish to thank Pr. Philip Patrick Allport from the

ATLAS collaboration for his help in preparing material

for this paper.

REFERENCES

[1] ATLAS Phase 1 upgrades Technical Design Reports;

CERN-LHCC-2013-018; ATLAS-TDR-023, CERN-

LHCC-2013-017; ATLAS-TDR-022, CERN-LHCC-2013-

007; ATLAS-TDR-021, CERN-LHCC-2013-006; ATLAS-

TDR-020

PERFORMANCE PARAMETERS – EXPERIMENTS PERSPECTIVE

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[2] CMS Phase 1 upgrades Technical Design Reports: CERN-

LHCC-2013-011; CMS-TDR-12, CERN-LHCC-2012-016;

CMS-TDR-11, CERN-LHCC-2012-015; CMS-TDR-10

[3] ECFA HL-LHC Experiments Workshop agenda and

summary report:

https://cmsdocdb.cern.ch/cgibin/PublicDocDB//ShowDocu

ment?docid=12141

https://indico.cern.ch/conferenceDisplay.py?confId=25204

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[4] Letter of intent for the Phase II Upgrade of the ATLAS

detector: CERN-LHCC-2012-022 ; LHCC-I-023

[5] CMS Phase 2 Upgrade: Preliminary Plan and Cost

Estimate: https://cds.cern.ch/record/1605208/files/CERN-

RRB-2013-124.pdf

D. CONTARDO

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