An Overview of CMS Experiment

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1 Gomel International School-Conference An Overview of CMS Experiment L. Benucci, University of Ghent, Belgium Disclaimer A tutorial-level insight into CMS Experiment and its Physics results CMS Detector
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1 Gomel International School-Conference An Overview of CMS Experiment L. Benucci, University of Ghent, Belgium Disclaimer A tutorial-level insight into CMS Experiment and its Physics results CMS Detector lecture (today): a general explanation for outsiders: motivations behind CMS structure, why a specific sub-detector, how the sub-detectors are implemented few examples of detector performance (from test beams and Run I) very first, preliminary results for Run II CMS Physics lecture (tomorrow): a recap of main motivations after the Higgs discovery a summary of Physics results after Run I very first, preliminary results for Run II Leonardo Benucci, The CMS Detector, Gomel International School-Conference 2 Disclaimer A tutorial-level insight into CMS Experiment and its Physics results CMS Detector lecture (today): a general explanation for outsiders: motivations behind CMS structure, why a specific sub-detector, how the sub-detectors are implemented few examples of detector performance (from test beams and Run I) very first, preliminary results for Run II CMS Physics lecture (tomorrow): a recap of main motivations after the Higgs discovery a summary of Physics results after Run I very first, preliminary results for Run II Leonardo Benucci, The CMS Detector, Gomel International School-Conference 3 CMS Experiment: The detector 4 Have a tour in LHC LHC CMS SPS LHCb ALICE ATLAS CERN Site (Meyrin) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 5 Have a tour in LHC Leonardo Benucci, The CMS Detector, Gomel International School-Conference 6 Have a tour in LHC CMS Compact Muon Solenoid (pp collisions) ALICE A Large Ion Collider Experiment (Ion-Ion collisions) LHCb (Study of CP violation in B-physics) ATLAS A Toroidal LHC ApparatuS (pp collisions) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 7 Have a tour in LHC B Two super-conducting magnet rings in the LEP tunnel Dipole field B=8.33 T Design parameters: Leonardo Benucci, The CMS Detector, Gomel International School-Conference 8 A needle in a straw pile Cross sections for various physics processes vary over many orders of magnitude Processes for New Physics are not the dominant ones 14 TeV: Higgs: 10 pb ( cm -2 s -1 ) t t production: 800 pb ( cm -2 s -1 ) W l n: 10 nb ( cm -2 s -1 ) Inelastic pp: 80 mb ( cm -2 s -1 ) Selection needed: 1: Thus LHC will deliver (under nominal conditions): ~25 minimum bias events every 25 ns an interesting event (maybe new particle) from time to time (maybe every s) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 9 A needle in a straw pile Cross sections for various physics processes vary over many orders of magnitude Processes for New Physics are not the dominant ones 14 TeV: Higgs: 10 pb ( cm -2 s -1 ) t t production: 800 pb ( cm -2 s -1 ) W l n: 10 nb ( cm -2 s -1 ) Inelastic pp: 80 mb ( cm -2 s -1 ) Selection needed: 1: Thus LHC will deliver (under nominal conditions): ~25 minimum bias events every 25 ns an interesting event (maybe new particle) from time to time (maybe every s) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 10 Many challenges for an experiment How do you get rid of minimum bias events? What about the radiation environment? Is it possible to record events every 25 ns? Need general-purpose experiment: covering as much of the solid angle as possible detectors must be able to detect as many particles and signatures as possible: e, m, t, g, n, jets, b-quarks LHC detectors must be: be highly granular (minimize probability that pile-up particles be in the same detector element as interesting object ) have fast response (integrate over 1-2 bunch crossings, pile-up of min-bias) be radiation resistant (cope with up to n/cm 2 and 10 7 Gy in 10 years of operation) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 11 A bit of history Aachen 1990: Concept of a compact detector based on high-b field superconducting solenoid Evian 1992: Conceptual Design Letter of Intent, October 1992 [CERN/LHCC 92-3] Technical Proposal, Dec 1994 [CERN/LHCC 94-38] Memorandum of Understanding (MoU) 1998 Technical Design Reports: Detectors Lvl-1 Trigger: 2000 DAQ/HLT: 2002 Computing & Physics TDR: : First data taking, LHC Incident Restart in Data taking [Run I]: 7 TeV (5fb 1 ) 8 TeV (20 fb 1 ) Heavy Ion: Pb-Pb and p-pb 2015 Data taking [Run II]: 13 TeV (~80 pb 1 ) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 12 From a paper towel Basic ideas for CMS general-purpose experiments covering as much of the solid angle as possible ( 4p ) a large B and large lever arm iron-core solenoid with an instrumented return yoke measurement of momentum p in the tracker and in the muon spectrometer (exploiting the 20 mm beam spot) leading to a design: superconducting solenoid powerful silicon tracker excellent electromagnetic calorimeter (high resolution on e,g) All calorimetry inside the coil redundant muon system as main trigger component Leonardo Benucci, The CMS Detector, Gomel International School-Conference 13 through a CMS slice Leonardo Benucci, The CMS Detector, Gomel International School-Conference 14 through reality Leonardo Benucci, The CMS Detector, Gomel International School-Conference 15 through reality Leonardo Benucci, The CMS Detector, Gomel International School-Conference 16 A general purpose experiment SUPERCONDUCTING COIL 3.8 T solenoidal field HCAL: hadrons energy and position Plastic scintillator + Cu sandwich HADRON YOKE (Fe) ECAL: e and g energy and position Scintillating PbWO 4 crystals TRACKER: p T and charge of tracks and secondary vertex Slicon microstrip + Pixel detector Neutrinos detected and measured through missing transverse energy in calorimeters. MUON DETECTOR: identify m and measure p T and charge (+Tracker) Drift Tube + RPC in the barrel CPC + RPC in the endcap Leonardo Benucci, The CMS Detector, Gomel International School-Conference 17 5 floors building 40 at CERN Leonardo Benucci, The CMS Detector, Gomel International School-Conference 18 The Solenoid Bending in the transverse plane: use 20mm beam spot excellent momentum resolution when combined with the tracker no PMT tubes in high magnetic field p T resolution: improved by Tracker at low momentum and by Muon detector at high momentum need very high Bdl for high momentum muons and good chamber hit resolution ( ~100 mm) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 19 The Solenoid Measure p T and charge of muons by bending in the transverse plane Dp/p ~ p / q B L 2 B = 4 T for 10% resolution A solenoid embedding calorimeters and tracker: L x Ø = 12.5 m x 6 m B = m 0 n I I = 20 ka n = 2168 turns / m The superconductor chosen is NbTi wrapped with Cu: needs to be cooled to ~4K magnetic radial pressure: 64 atm Superconducting cable structure to withstand the magnetic forces (B 2 / 2 m 0 ) V COIL =2.7 GJ are there! Al alloy mechanical stabilizer Ultra-pure Al magnetic stabilizer Superconducting cable Leonardo Benucci, The CMS Detector, Gomel International School-Conference 20 The Silicon Tracker: motivations A good tracking is mandatory for several reasons: measure Z ll with natural mass resolution reconstruct H 4m with the narrowest mass width match ECAL resolution for e calibrate ECAL identify secondary vertexes Leonardo Benucci, The CMS Detector, Gomel International School-Conference 21 The Silicon Tracker: motivations A good tracking is mandatory for several reasons: measure Z ll with natural mass resolution reconstruct H 4m with the narrowest mass width match ECAL resolution for e calibrate ECAL identify secondary vertexes The goals: Identify tracks with p T 2 GeV get rid of the huge multi-track environment and select only interesting events Reconstruct isolated e and isolated/in jets m Measure lepton charge up to p T ~2TeV Dp T /p T =0.1 p T [TeV] with h 2 Leonardo Benucci, The CMS Detector, Gomel International School-Conference 22 The Silicon Tracker: structure Outer radius: 110 cm Length: 270 cm pitch from 80 mm (inner layers) to 200 mm (outer layers) strip length from 10 cm (inner layers) to 20 cm (outer layers) Run at -10ºC for rad hardness ( 100 time better than at 25ºC) On average 12 hits per track Hit resolution: pitch/ 12 Leonardo Benucci, The CMS Detector, Gomel International School-Conference 23 The Silicon Tracker: structure Pixel detector: Very close to beam pipe (first point at 4cm) Different scenario for High luminosity Small pixel size (150mm) Occupancy: 10-4 Resolution: ~20mm. Leonardo Benucci, The CMS Detector, Gomel International School-Conference 24 The Silicon Tracker: performance Efficiency of reconstructing muon tracks in data and simulation as a function of η (left) and number of primary vertices (right) using the tag and probe method on Z to μμ events Tag muon is required to pass tight ID and isolation criteria. Both tag and probe muons are required to have p T 15 GeV Leonardo Benucci, The CMS Detector, Gomel International School-Conference 25 The Electromagnetic Calorimeter(ECAL) In both SM and MSSM, e and g may come from Higgs: H, h gg, H ZZ 4e The observed width will be determined by instrumental mass resolution. We need for e and g : good DE/E good angular resolution good two showers separation For S= N S / N B = 5, L=20 fb -1 and M H =110 GeV s(m)/m~1% H gg bad resolution H gg good resolution m gg background from pp gg s 1 s( E ) s( E ) s M 1 2 M 2 E E tg( /2) 1 2 s ( E) E a E b E c stochastic: a 5 10 % Gev 1/2 noise: b MeV calibration and non-unif: c % Leonardo Benucci, The CMS Detector, Gomel International School-Conference 26 The ECAL: structure ECAL Endcap 1 crystal shape Characteristics of PbWO 4 ECAL Barrel 17 xtal shapes Preshower based on Si sensors X 0 = 0.89cm = 8.28g/cm 3 R M (Molière radius) = 2.2cm Parameter Barrel Endcaps Coverage h h 3.0 Df x Dh x x to 0.05 x 0.05 Depth in X # of crystals 61,200 14,648 Leonardo Benucci, The CMS Detector, Gomel International School-Conference 27 The ECAL: structure CMS choice : Crystal calorimeter + new Photodetector to cope with the high B-Field): Avalanche Photo Detector ( APDs) 76,000 lead tungstate crystals (very compact) fast (95% light emitted in 25ns) highly granular (2.19 cm Moliere radius) Excellent energy resolution ECAL standalone performance thoroughly studied at test beams: Energy resolution for central impact on 3x3 arrays of barrel crystals: Constant term dominated by longitudinal nonuniformity of light collection Limited to less than 0.3% at construction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 28 The ECAL: performance Combined Precision: Barrel: 1% (~0.4% for h 1), Endcaps: ~2% (almost everywhere) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 29 The ECAL: performance Invariant mass spectrum of μμg passing the full selection Dielectron mass spectrum: electrons with pt 10 and η 2.5 Leonardo Benucci, The CMS Detector, Gomel International School-Conference 30 The Hadronic Calorimeter (HCAL) Physics requirements: Measure jets energy and directions to obtain a good resolution (narrow M(jj) peak) Low p T : W,Z jj High p T : Z jj Missing Energy: SUSY LSP Detector requirements: Fine lateral granularity for high p T (to cope with very collimated jets) Missing transverse energy resolution Hermeticity (minimize cracks and dead areas) and coverage to h 5 Absence of tails in energy distribution: more important that a low value in the stochastic term Good forward coverage required to tag processes from vector-boson fusion Leonardo Benucci, The CMS Detector, Gomel International School-Conference 31 HCAL: structure Three subdetectors: 1) HCAL Barrel (HB): Brass plates interleaved with plastic scintillator embedded with wavelength-shifting optical fibres 2) HCAL Endcap (HE): Brass plates interleaved with plastic scintillator 3) HCAL Forward (HF): Steel wedges stuffed with quartz fibres Tower size: Dfx Dh=0.087 x This is the basic trigger unit Leonardo Benucci, The CMS Detector, Gomel International School-Conference 32 Beam tests: absolute scale calibration with single hadrons for a few barrel and endcap wedges study of linearity and energy resolution s(e)/e Energy Response: HCAL: performance Corrections necessary to take into account the energy deposited in upstream material, particularly for low E T particles/jets The Particle Flow technique gives a substantial improvement in Jet energy resolution Leonardo Benucci, The CMS Detector, Gomel International School-Conference 33 The Muon System: motivations Muons are likely to come from the decay of a heavy particle they are excellent signatures of interesting physics All particles but muon are virtually absorbed by the large amount of material between the interaction point and the m chambers they are easy do detect Muon chambers contribute strongly to the CMS Trigger system very high rate from Real muons (semileptonic decays of b,c ). Need to keep p T cut as low as possible ( ~5 GeV) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 34 The Muon System M E 4/ 2 f superlayer of 4 DT layers h superlayer of 4 DT layers f superlayer of 4 DT layers Position measurement: Drift Tubes (DT) in barrel (MB) (100µm) Cathode Strip Chambers (CSC) in endcaps (ME) (80 450µm) Trigger: Resistive Plate Chambers (RPCs) in barrel (RB) and endcaps (RE) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 35 The Muon System Tag and Probe method on Z 0 mm (tag m is selected with tight cuts, then probe m fairly unbiased) HLT_IsoMu24 efficiency vs muon η data (2012 D) η = : dips due to cracks b/w DT wheels 0 and ±1 η 1.2: asymmetry due to CSC non-operational chambers Selection Efficiency: Data, MC and scale factors vs h Tag and Probe method used on Zs Probe: general tracks Leonardo Benucci, The CMS Detector, Gomel International School-Conference 36 Events / GeV The Muon System Selection Efficiency (Data and MC) and scale factors vs h Tag and Probe method used on Zs Probes general tracks CMS Preliminary w f J/y y' B s U pb (13 TeV) Trigger paths f J/y y' B s U low mass double muon + track double muon inclusive Z We re-discover the Standard Model in 1.5 month! m + m 10 invariant mass [GeV] 2 Leonardo Benucci, The CMS Detector, Gomel International School-Conference 37 Beam Instrumentation (BRIL) CMS needs to continuously monitor the background of the beam This is to guarantee safe operation of the detectors especially the pixel and the silicon strip detectors which are close to the beam A beam abort is triggered if the background reaches dangerous levels The Silicon Tracker high-voltage in CMS is only switched on, if background values are below a certain threshold Beam gas and beam halo interactions reflect the quality of the beam LHC needs these values in real-time for feedback on the beam conditions We have to measure luminosities: real time, integrated delivered and recorded These values are needed for physics and by the LHC as feedback CMS measures luminosity with standard sub-detectors like HF (the main luminosity detector) or Pixel and with a set of dedicated detectors built and operated under the BRIL project (BCM1F, PLT) The calculation of the luminosity of ALL these detectors is done under the BRIL project Leonardo Benucci, The CMS Detector, Gomel International School-Conference 38 BRIL Project Leonardo Benucci, The CMS Detector, Gomel International School-Conference 39 Needed from LHC: luminosity Istantaneous Luminosity L is defined by: dr/dt = L s where dr/dt is the rate of production of a process which has cross section s The luminosity L quantifies the performance of the collider in this respect (units cm -2 s -1 ) In practice if s x and s y are the transverse areas of the beam interaction region we use the equivalent formula to measure the Luminosity. The areas of the beam are obtained by scanning the two beams and measuring the rate of collisions while the number of protons in the bunches is measured by dedicated devices of the accelerator L = f N 1 N 2 /(4πσ x σ y ) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 40 Needed from LHC: luminosity Design ( s= 14 Tev): L = cm -2 s -1 f= Hz N~ p/bunch e n = 3.75 µm β* =0.55 m Transverse Emittance (e) can be defined as the smallest opening you can squeeze the beam through, and can also be considered as a measurement of the parallelism of a beam. The amplitude function, β, is determined by the accelerator magnet configuration (basically, the quadrupole magnet arrangement) and powering. When expressed in terms of σ (cross-sectional size of the bunch) and the transverse emittance, the amplitude function β becomes β = π σ 2 / ε β* is referred as the distance from the focus point that the beam width is twice as wide as the focus point Run I ( s= 7-8 TeV): L = cm -2 s -1 f= Hz N~ p/bunch e n = 1.75 µm β* =0.60 m Run I ( s= 13 TeV): L = cm -2 s -1 f= Hz N~ p/bunch e n = 1.75 µm β* =0.60 m Leonardo Benucci, The CMS Detector, Gomel International School-Conference 41 How to filter on data LV1 Input: 1 GHz HLT Input: 100 khz Mass Storage: ~500 Hz Collision rate at LHC: MHz Event size:1-2 Mbyte Band width limit ~ 200 GB/s Mass storage rate ~ Hz First step in analysis is trigger Leonardo Benucci, The CMS Detector, Gomel International School-Conference 42 Triggering in CMS CMS Trigger system has two stages: Level-1 trigger: Implemented in hardware Uses coarse-grain information from calorimeters and muon chambers to make a quick decision in 4msec (high pt electrons, muons, jets, missing ET) e.g.: are there 2 muons with momenta above certain thresholds? Is there an electromagnetic energy deposit 40 GeV? Reduces rate from 40 MHz to a maximum of ~100 khz High level triggers: 100 khz data passed through a high bandwidth switching network to a farm of ~1000 commercial PCs running data selection algorithms effectively on-line data analysis Use fine-grain information from all sub-detectors, e.g. Is an ECAL energy deposit matched to hits in the pixel detector? (if so, this signifies the presence of an electron) Reduces rate from ~100 khz to ~100 Hz, for storage on tape Leonardo Benucci, The CMS Detector, Gomel International School-Conference 43 Triggering in CMS Data network bandwidth (EVB): ~ Tb/s Computing power (HLT): ~ 10 Tflop Computing cores: Local storage: ~ 300 TB ~same as whole world s telecom network! Minimize custom design Exploit data communication and computing technologies DAQ staging by modular design (scaling) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 44 Triggering in CMS ON-line LEVEL-1 Trigger Hardwired processors (ASIC, FPGA) Pipelined massive parallel OFF-line HIGH LEVEL Triggers Farms of processors Reconstruction&ANALYSIS TIER0/1/2 Centers 25ns 3µs ms sec hour year Giga Tera Petabit Leonardo Benucci, The CMS Detector, Gomel International School-Conference 45 Triggering in CMS Leonardo Benucci, The CMS Detector, Gomel International School-Conference 46 Particle reconstruction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 47 Particle reconstruction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 48 Particle reconstruction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 49 Particle reconstruction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 50 CMS is looking at its future Nominal performance: 5x10 34 levelling Leonardo Benucci, The CMS Detector, Gomel International School-Conference 51 CMS is looking at its future Ultimate performance: same beam, 7.5x10 34 levelling (average PU~200) Leonardo Benucci, The CMS Detector, Gomel International School-Conference 52 CMS is looking at its future CMS Phase 2 Upgrades: construction Leonardo Benucci, The CMS Detector, Gomel International School-Conference 53 CMS is looking at its future Technical Proposal: Submitted fo
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