Calibration of Magnetic Distortions in the LHCb-RICH1 Photon - PowerPoint PPT Presentation

Imperial College London Calibration of Magnetic Distortions in the LHCb-RICH1 Photon Detectors Fatima Soomro

Imperial College London The LHCb Detector Calorimeters b bbar Cross section = 500 μb 10 12 b bbar pairs in one year Vertex Muon Chambers Locator Tracking Stations (VELO) A Single-arm spectrometer for precision measurements of CP violation in B-hadrons search for new physics in rare b decays March 6, 2008 Fatima Soomro 2

Imperial College London RICH1: upstream of the magnet. Ring Imaging Cherenkov Ring Imaging Cherenkov momentum range: ~2-60 GeV/c (RICH) Detectors for (RICH) Detectors radiators: Aerogel, n=1.03, L=5 cm Particle Identification (PID) C 4 F 10 ,n=1.0014, L= 95 cm in LHCb: Polar angles vs momenta RICH1 RICH2: downstream of the magnet RICH2 momentum range 60 to beyond 100 GeV/c radiator: CF 4 , n=1.0005, L=180 cm March 6, 2008 Fatima Soomro 3

Imperial College London Working Principle: Cherenkov Radiation A charged particle travelling in a medium, at a speed faster than the speed of light in that medium, emits Cherenkov Photons. cos θ θ c = 1/ nβ cos c = 1/ nβ Speed of the β charged particle β Opening angle of the cone θ c of Cherenkov Photons θ c Refractive index n of the medium n March 6, 2008 Fatima Soomro 4

Imperial College London The RICH1 Detector The RICH1 Detector The RICH1 design was motivated by the following considerations: Available space Minimize material within acceptance Access to beam pipe March 6, 2008 Fatima Soomro 5

Imperial College Photon Detectors for the RICH Detectors: London The Requirements The Choice High Quantum efficiency Pixel Hybrid photon High granularity 2.5 x 2.5 mm 2 Detectors (HPDs) High active to total area 64% after close packing Good signal to noise ratio Single photoelectron detection efficiency ~85% Readout compatible with 25 ns signal 5000 e bunch crossing of LHC noise 160 e Operable in magnetic field Threshold 1200 e (RMS spread 100e) B < 50 Gauss local shielding offline correction Withstand radiation dose of 3kRad/yr ability demonstrated March 6, 2008 Fatima Soomro 6

Imperial College London The HPD – Internal structure and Working Vacuum tube Quartz window S20 multi-alkali photocathode(-20 kV) Cross focusing electron optics Si pixel anode at ground (1024 elements) Pixel anode bump bonded to readout chip. March 6, 2008 Fatima Soomro 7

Imperial College London The HPD – Internal structure and Working Vacuum tube Quartz window S20 multi-alkali photocathode(-20 kV) Cross focusing electron optics Si pixel anode at ground (1024 elements) Pixel anode bump bonded to readout chip. March 6, 2008 Fatima Soomro 8

Imperial College London Test pattern measurements with locally shielded HPD The magnetic field at the HPD plane and Local Shielding Distortion patterns for 50 for the HPDs. Gauss transverse field Notice that the Magnetic (top) and 50 Gauss axial field is not uniform and field, overlapped with the varies from tube to tube. reference 0 Gauss image. March 6, 2008 Fatima Soomro 9

Imperial College London Characterizing the magnetic distortion ( My Future Work ) Scan a collimated light source over the entire HPD plane. Find a relationship between the position of light source on the HPD window and the signal on Si anode. Develop a map or look up table. March 6, 2008 Fatima Soomro 10

Imperial College London The magnetic distortion system March 6, 2008 Fatima Soomro 11

Imperial College London The magnetic distortion system The LED matrix A calculation assuming the LED to emit photons at a rate of 1Mhz shows that to scan the entire HPD plane with a resolution of 0.5 mm 2 will take 6 months!! It is very important to develop a strategy and pattern, which has an adequate resolution and is less time consuming. March 6, 2008 Fatima Soomro 12

Imperial College London Conclusion and current status Conclusion and current status The HPDs are extremely elegant The distortion system is in photon detectors providing advance stages of good quantum efficiency manufacture and will be good signal to noise delivered to CERN around excellent resolution Easter. Their operating conditions in The DAQ and analysis LHCb: not optimal software is yet to be Performance can be restored with written. local shielding calibration offline correction March 6, 2008 Fatima Soomro 13

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Imperial College London Particle Identification (PID) Polar angles vs momenta in LHCb: RICH1 Ring Imaging Cherenkov (RICH) Ring Imaging Cherenkov (RICH) Detectors Detectors RICH2 π/K Separation by different PID methods March 6, 2008 Fatima Soomro 16

Imperial College London (b) (a) (a) Response curve shows excellent signal to noise separation (b) QE of a single HPD (c)The average QE(%) at 270 nm versus the HPD batch number (c) March 6, 2008 Fatima Soomro 17

B ┴ ⊗ B ║ March 6, 2008 Fatima Soomro 18

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OPTICAL COLLIMATION PA / ADC / PC PMT Moving (3″) Screen x D L d C D E F R. Mountain, Syracuse University LHCb RICH1 Mag Cal Meeting, 05 Sep 2007 5 March 6, 2008 Fatima Soomro 22

VI.1: LHC 25 February 2008 V.Gibson SUSSP57 St Andrews 104 March 6, 2008 Fatima Soomro 23

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The angle of emission is given by: Θ = cos 1 β ∗ λ n ( ) and the number of photons by: 2 Θ dN sin = ⋅ ⋅ N l 0 λ λ 2 d [ ] λ = ⋅ ⋅ − ⋅ ⋅ Θ 6 2 N 4 . 6 10 l ( cm ) sin 1 1 2 λ λ ( A ) ( A ) λ 2 1 1 March 6, 2008 Fatima Soomro 26

The Cherenkov radiation condition: The same, but let us consider how a charged particle interacts with the medium ε real q and m 0 ≤ cos( Θ ) ≤ 1 β ω k Conservation of If:   energy and momentum ω = β ⋅ k ω < < γ = m E < < β γ = k m p The behavior of a photon in a medium is described by then: 2 k the dispersion relation ω − = 2 1 0 Θ = cos ε β ε March 6, 2008 Fatima Soomro 27

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RICH1 Design Photon detector Upper Magnetic plane 14 by 7 Hybrid Shielding Protecting Photon Detectors 4m HPDs, mounted on (HPDs) cavern wall, supports upper HPDs Quartz Windows UV transparent Spherical Mirrors Lightweight carbon Flat Mirrors fibre mirrors 1.5% Glass mirror radiation length planes VELO Exit Beampipe Window 2mm made from aluminium beryllium Gas Enclosure RICH1 Exit supports mirrors Window and aerogel, Carbon fibre contains C 4 F 10 Lower Photon Lower Magnetic detector plane Shielding mounted Mounted on lower on cavern floor, shield supports lower HPDs and Gas Enclosure Radiation length(total) of RICH1 is 8 X 0 March 6, 2008 Fatima Soomro 29

Momentum Resolution p distribution for B tracks March 6, 2008 Fatima Soomro 30

Impact Parameter Resolution 1/p t distribution for B tracks March 6, 2008 Fatima Soomro 31

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40 Project Costs (kCHF) Why silicon Item RICH1 RICH2 Mechanics, Optics 527 1204  Low ionization energy ( good signal ) Photodetectors 1473 2290  Long mean free path ( good charge Electronics 537 814 Gas system, monitoring 365 365 collection efficiency ) Aerogel 102 -  High mobility ( fast charge collection ) Total: 3004 4673  Low multiple scattering  Little cooling required Total Cost (incl. spares) 7677 kCHF March 6, 2008 Fatima Soomro 33

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