Design of the new ATLAS Inner Tracker for the High Luminosity LHC era Trevor Vickey on behalf of the ATLAS Collaboration University of Sheffield, United Kingdom July 3, 2017 19th iworid Krakow, Poland
The Large Hadron Collider (LHC) at CERN The world s highest-energy particle collider, just outside of Geneva, CH Proton-proton collider 27 km in circumference 14 TeV design CME Home to four major experiments: ATLAS, CMS, ALICE and LHCb 7 TeV CME running in 2011 8 TeV CME running in 2012 Run-1 2 year shut-down period 13 TeV CME running started in 2015, continuing through 2018 Run-2 on-going now 2 Running beyond 2035 is planned, and significant upgrades to the machine and experiments required
Current ATLAS Experiment at the LHC General purpose experiment, co-discovered the Higgs boson in 2012 Length ~44 m, Height ~22 m, Weight ~7k tons, Channels ~10 8 A collaboration of ~3000 physicists from 175 institutions and 38 countries Muon Spectrometer HAD calorimetry EM Calorimeter JINST 3 (2008) S08003 2-Level Trigger 3 Inner Detector ( η <2.5, B=2T): Si Pixels, Si strips,transition Radiation detector (straws); Precise tracking and vertexing, allows for e/π separation; Momentum resolution: σ/pt ~ 3.8x10-4 pt (GeV) 0.015 i.e. σ/pt <2% for pt < 35 GeV
CERN LHC Plans for Run-3, 4-5, Run-2 of the LHC began in mid-2015 and will continue through the end of 2018 The long-term plan is to have up to 4000 fb -1 of integrated luminosity LHC and ATLAS will need upgrades: 2024-26 the High Luminosity LHC (HL-LHC) The rest of this talk: ATLAS will get a new all-silicon charged particle tracking detector This Inner Tracking detector (ITk) will have inner part pixels, with the outer layers strips Today: Run-2 with LHC instantaneous luminosity L=0.5-1.5 x 10 34 cm -2 s -1 Phase-1 Upgrade for L=2-3 x 10 34 cm -2 s -1 In the advanced stages starting production 4 Phase-II Upgrade for L=5-7.5 x 10 35 cm -2 s -1 In the design and prototyping stage
Motivation for the ATLAS Phase-II Upgrade Precision measurements, searches for and studies of rare processes (e.g. a Standard Model Higgs boson decaying to μ+μ-; or Higgs self-coupling via di-higgs production) Searches for additional Higgs bosons (e.g. in the context of Supersymmetry) and other exotic particles predicted by theories that go Beyond the Standard Model Requirements for the new ATLAS Inner Tracking Detector: Instantaneous luminosity increase by a factor of 5-7 (particle density increases) Number of vertices increases from ~25 - ~200 (require higher granularity) Integrated luminosity increases by a factor of 10 (due to radiation, current detector damaged by ~2024; higher particle flow requires more radiation hardness 1x1016 neq/cm2) Results in this talk from the ATLAS ITk Strips TDR released earlier this year Current LHC: ~25 vertices High-Luminosity LHC: ~200 vertices Djouadi, A., Maiani, L., Polosa, A. et al. JHEP 06 (2015) 168 5
Phase-II: All-Silicon Tracking Detector for ATLAS Inner Tracking detector is critical for the identification of leptons, b-quark decays, and vertex identification for the rejection of background pile-up jets Radiation damage means that the current Inner Detector (ID) cannot survive 3000 fb -1 The straw tracker in the current ID cannot deal with the multiplicity of the LH-LHC Silicon pixel and strips for the new ATLAS Inner Tracker will have: Increased radiation hardness Higher granularity to keep occupancies low Larger readout bandwidth capabilities One quarter of the layout in r-z shown Reduced material in front of calorimeters Extended coverage at high η Phase-II Upgrade All Silicon (proposed) 6 Current Silicon and Straw tracker ATLAS Collaboration, JINST 3 (2008) S08003
Evolution of the ITk Layout To arrive at a decision regarding the layout (the arrangement of the silicon sensors), we worked with computer simulated HL-LHC proton-proton collisions as well as a computer rendering of the full detector layout, simulating the passive and active components and their interactions and performance Letter-of-Intent layout ~2012 Letter-of-Intent Very-Forward layout ~2013-2014 Letter-of-Intent Layout (rapidity coverage up to η =2.7) One quadrant of the layout in r-z shown Inclined versus Extended layout ~2015-2016 ITk strips Technical Design Report produced using the Inclined layout 2017 Currently working to converge on the ITk pixel layout and expect to release that late 2017 7
Evolution of the ITk Layout: LoI-VF Performing physics studies with simulated collision events and various simulated detector layouts showed a genuine benefit to having more pixel detectors in the very forward region Letter-of-Intent Very-Forward Layout (rapidity coverage up to η =4.0) 8
Evolution of the ITk Layout: Pixel Layers Studies showed a real benefit to moving from 4 pixel + 5 strip layers in the barrel, to 5 pixel + 4 strip barrel layers Example: A tau lepton that decays hadronically via a 3-prong mode (relatively light particle at high pt means decay products are heavily boosted); performance at higher pt noticeably improved when there is more information available due to additional pixel layers The additional pixel layers help to separate fake and genuine decay signatures with μ~200 Performance of tracking in dense environments is improved 9
Evolution of the ITk Layout: Pixel Layouts Extended Pixel Layout Two layouts considered for the Pixels: Each of these have the support structures and end-of-barrel material moved out far along the z-axis Extended Layout: uses a long barrel for the two inner-most layers Inclined Pixel Layout Inclined Layout: uses rings to incline the forward-most modules in the barrels 10
Evolution of the ITk Layout: Pixel Layouts Current ATLAS Inner Detector Figures show the number of radiation lengths, X0, as a function of η (based on material estimates) Due to the geometry of the Inclined layout tracks traverse the detector more perpendicular than for Extended there is less material (less silicon needed to cover the high η range) ITk with Inclined Pixel Layout Additional drawbacks for the Extended: long clusters produced in the sensors by particles, whereas with the Inclined layout sensors provide two or more hits in the first layer 11
ITk Layout for the Strips TDR In the preparation of the ITk Strips TDR, ultimately decided on the Inclined layout This layout has 5 pixel + 4 strips barrel layers The small stub strip barrel layer has been removed The forward-most barrel modules for the pixels are inclined This was the layout used in all of the performance studies carried out with simulated events 12
ITk Layout for the Strips TDR Blah 13
ITk Strip Modules Basic unit of the ITk Strip detector is a module (17.9k modules; 60 M channels; 165 m2) Consists of one sensor, PCB ( hybrid ), and multiple readout ASICs (CMOS 130 nm) Endcap modules are arranged into petals; Barrel modules are assembled onto staves 14 See ITk Strips poster by Laurelle Maria Veloce
ITk Pixel Modules Basic electrical unit of the ITk Pixel detector is also a module Using a future chip based on RD53 developments is the baseline, to be used with different kinds of sensors (planar, 3D, passive/active); CMOS also being considered Pixel detector layout to be finalized at the end of 2017, when ITk Pixels TDR to be released Prototype of the quadmodule with four FE-I4 chips Typical CMOS sensor pixel cell Composite halfcylindrical shells supporting half rings carrying pixel modules for the Endcaps 15 See ITk Pixel talks by Francisca Munoz Sanchez and Andrea Gaudiello
Examples of Performance with the ITk Particle identification performance comparable to or better than in Run-2, even with μ~200, for ITk Inclined layout Shows that our reconstruction algorithms are performing well in this challenging environment, and correct choices have been made in terms of optimal layout geometry Many physics and performance results shown in the ITk Strips TDR; this is a very small sample Muon Identification (ITk and Run-2) Tau Lepton Identification (ITk) Tau Lepton Identification (Run-2) 16
Summary Many exciting opportunities for precision measurements and new discoveries with the HL-LHC Extremely challenging environment poses many challenges Many years of work have now resulted in the design of an all-silicon tracking detector for ATLAS that is able to tackle these challenges, and the strip detector layout has been finalized (ITk Strips TDR released early this year) Currently working on the finalization of the pixel detector layout (ITk Pixels TDR to be released at the end of 2017) A lot of R&D is still on-going, and some components moving into pre-production Sensors and Front-End chips Readout Powering and protection Layout and mechanics An enormous amount of work to do before installation in a bit less than 10 years time! 17 CERN LHC-2017-005