Introduction Motivation Requirements Engineering Commissioning ATLAS Pixel Detector Upgrade The Insertable B-Layer David Bertsche November 8th, 2012 ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Introduction ◮ Experimental High Energy Physics (HEP) is done using particle accelerators and detectors. ◮ The OU HEP group is part of the ATLAS detector collaboration. ◮ The innermost section suffers heavy radiation damage - thus the upgrade. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Top Physics Higgs Studies Motivation: b Physics Figure: http://CPEPweb.org ◮ Free quarks hadronize into a collimated spray of particles called a jet. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Top Physics Higgs Studies Top Physics Figure: t → Wb and subsequent decays ◮ Free top quarks have a lifetime of ∼ 10 − 25 s, not enough time to hadronize ( ∼ 10 − 23 s). ◮ The SM t → Wb branching fraction is ∼ 100%. ◮ b tagging efficiency will remove a large amount of background for top physics (such as W + n jets and QCD). ◮ Observing a different branching fraction could lead to physics beyond the SM. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Top Physics Higgs Studies Higgs Studies Figure: Theoretial Standard Model Higgs Boson branching Figure: Experimental Higgs Boson branching ratios, including theoretical uncertainties. ratios. ◮ If the SM Higgs mass is indeed ∼ 125 GeV, H → b ¯ b is the dominant decay mode ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design LHC Accelerator p - p Design Parameters: ◮ Max Energy = 14TeV ◮ 1.15 × 10 11 particles per bunch ◮ 25 ns between bunch crossings ◮ 19 collisions per crossing (avg) ◮ Luminosity = 10 34 cm − 2 s − 1 These parameters are unprecedented, requiring faster radiation-hard electronics. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design The ATLAS Detector ◮ ATLAS > Inner Detector > Pixel Detector ◮ 4 π solid angle coverage ◮ z points along beam, x to LHC ring center and y vertically ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design The ATLAS Inner Detector ◮ Functions are tracking and vertexing ◮ The Insertable B-Layer (IBL) will be the innermost layer of the detector. ◮ The IBL specializes in identifying interaction vertices. ◮ 2 T solenoidal magnetic field curves charged particle trajectory. ◮ Pixel Detector ◮ Silicon Microstrip Tracker (SCT) ◮ Transition Radiation Tracker (TRT) Figure: Cut-away view of the Inner Detector. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design Radiation Passage Through Matter ◮ Particles are detected by the energy they deposit in the detector. ◮ Multiple scattering and energy loss should be minimized in the Inner Detector. ◮ Charged heavy particles primarily experience elastic collisions with electrons as described by the Bethe-Bloch formula: � 2 m e γ 2 v 2 W max e m e c 2 ρ Zz 2 dE � � − 2 β 2 − δ − 2 C � ∝ 1 dx = 2 π N o r 2 β 2 ln (const · β 2 γ 2 ) ln A β 2 I 2 Z Figure: A charged pion traveling through silicon. (The dotted line shows density and shell correction terms.) ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design Tracking ◮ The momentum and charge of a particle are determined from the track curvature. Figure: Multiple scattering worsens the momentum resolution. Figure: First stable beam collision in with the ID fully powered. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design Vertexing and Impact Parameter Measurement Figure: The Impact Parameter (IP) is determined from the distance of closest approach to the primary vertex. Figure: Vertices and Jets ◮ IBL improves primary vertex reconstruction resolution from 15 µ m to 11 µ m (in x - y ) and from 34 µ m to 24 µ m (in z ). ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design b Tagging Figure: The Impact Parameter sign is determined from the relative geometry of the Figure: Relative transverse momentum can be primary and secondary vertices. used to differentiate between b and c jets. ◮ Up, down and strange quarks create light jets which cannot usually be distinguished from each other. ◮ Jets from charm quarks are sometimes grouped with light jets and sometimes uniquely identified. ◮ b hadrons (lifetime ∼ 10 − 12 s) can travel a few mm. b jets have a secondary vertex with a large positive IP. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design b Tagging Figure: Jet tagging weight distribution. Figure: Tagging efficiency must be balanced against light jet rejection. ◮ Computer algorithms are used to b tag, their parameters are adjusted with the goal of maximizing efficiency while minimizing the number of jets erroneously b tagged. ◮ Typical efficiencies are 60%-70% with a mistag rate of ∼ 1%. ◮ Algorithms are tested and optimized using Monte Carlo simulations of detector events. Efficiency = # of jets that were b tagged actual # of b jets ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design IBL Design Requirements Primary motivation : Alleviate radiation damage and to provide improved measurement accuracy. Long term motivation : Prepare for the High Luminosity LHC (HL-LHC), planned in 2020. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design IBL Design Requirements Primary motivation : Alleviate radiation damage and to provide improved measurement accuracy. Long term motivation : Prepare for the High Luminosity LHC (HL-LHC), planned in 2020. Luminosity Requirements : With increased luminosity comes increased pileup and occupancy ◮ Both are decreased by faster readout speed, smaller pixel size, and improved vertexing and track reconstruction. ◮ IBL Increases B -layer lifetime integrated luminosity from 300 fb − 1 to 550 fb − 1 . ◮ IBL Increases ID peak design luminosity from 1 × 10 34 cm − 2 s − 1 to 3 × 10 34 cm − 2 s − 1 . ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning LHC Inner Detector Tracking b Tagging Design IBL Design Requirements Primary motivation : Alleviate radiation damage and to provide improved measurement accuracy. Long term motivation : Prepare for the High Luminosity LHC (HL-LHC), planned in 2020. Luminosity Requirements : With increased luminosity comes increased pileup and occupancy ◮ Both are decreased by faster readout speed, smaller pixel size, and improved vertexing and track reconstruction. ◮ IBL Increases B -layer lifetime integrated luminosity from 300 fb − 1 to 550 fb − 1 . ◮ IBL Increases ID peak design luminosity from 1 × 10 34 cm − 2 s − 1 to 3 × 10 34 cm − 2 s − 1 . Novel engineering solutions developed : ◮ Tight tolerances and clearances - no module overlap in z and sensors with thin edges. ◮ Minimizing materials - thin sensor design, low density carbon foam staves, CO 2 evaporative cooling and aluminum electrical conduits. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Detector Layout Support Manufacturing Installation Solid State Detectors ◮ The p-n junction diode is the building block of solid state detectors. ◮ The depleted junction region is useful. ◮ It is expanded by applying a reverse bias voltage. ◮ Ionizing radiation excites electrons from the valence band into the conduction band, leaving a hole behind. ◮ Collected electrons are processed into a signal. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
Introduction Motivation Requirements Engineering Commissioning Detector Layout Support Manufacturing Installation Pixel Detector Module Figure: Sensor bump bonded to readout electronics. Figure: One cell. ◮ The sensor bulk is divided into many pixels. ◮ Electrons transferred to the electronics chip through a conducting bump bond. ◮ Proximity of sensor and FE chip allows for high readout speeds. ATLAS Pixel Detector Upgrade: The Insertable B-Layer (IBL)
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