Saeid Paktinat School of Particles and accelerators IPM, Tehran

Transcription

1 LHC/CMS Saeid Paktinat School of Particles and accelerators IPM, Tehran Third National Workshop on Detectors and Calculation Methods in Particle Physics Azar 26-28, 1387

2 Introduction CERN What and Where is it? Who works there? What do we do there? Particle Physics Questions, answers and the theory of everything... The Large Hadron Collider The Compact Muon Solenoid

3 What is CERN?

4 What is CERN? Founded in 1954 (12 countries) Now: 20 European member states +United States, Russian Federation, India, Japan

5 Who works at CERN? 3000 people employed by CERN Physicists, engineers, computer scientists, mathematicians, firemen, cooks, builders, technicians, secretaries, security, etc >7500 physicists associated with CERN Including yours truly

6 Who works at CERN? CERN

7 Who visits CERN CERN is an open laboratory Anyone is welcome to visit, ask questions, take photographs, etc Every year, 25,000 people visit CERN Schools are welcome

8 What do we do at CERN?

9 Basic vs applied research Two types of science research Basic research (how do things work) Applied research (how do I make...) CERN only does basic research But usually we need to build things that do not exist yet... Applied research needs basic research

10 CERN - where the web was born Tim Berners-Lee

11 But also... PET scans Radiation therapy Loads of computing/internet development GRID

12 Basic Questions What is everything around us made of? How does matter stick together? What, really, is mass? Are there really only 3 spatial dimensions? Are the smallest particles we know fundamental? Where did the anti-matter go? Where s the rest of the matter anyway??

13 What is everything around us made of? Chemistry answer:

14 What are we made of? mainly water (H 2 O) Lots of oxigen (oxides) 96% out there unknown! C H O unknown waterstof en helium

15 What is everything around us made of? Physics answer:

16 The particle drawings are simple artistic representations the periodic table of modern physics Leptons Strong Electromagnetic Tau Electric Charge -1 0 Tau Neutrino Gluons (8) Photon Muon -1 0 Muon Neutrino Quarks Electron -1 0 Electron Neutrino Mesons Baryons Nuclei Atoms Light Chemistry Electronics Bottom Quarks Electric Charge -1/3 2/3 Top Gravitational Graviton? Bosons (W,Z) Weak Strange -1/3 2/3 Charm Down -1/3 2/3 Up each quark: R, B, G 3 colours Solar system Galaxies Black holes Neutron decay Beta radioactivity Neutrino interactions Burning of the sun

17 Anti-matter Anti-matter: discovered in 1923 Predicted by theory Almost same as matter... But oppositely charged Problem: at big bang there was just as much matter as anti-matter... Where did it go?

18 The four fundamental forces Electro-magnetic force Strong force?gravity Weak force

19 The Big Bang 1 second second years ago

20 The Big Bang seconds! Particle physics

21 The first particle detectors Liquid hydrogen bubble chamber The hydrogen acts as a target (for incoming particles) and a detector Aircraft leaving contrails in the sky

22 The first particle detectors Particle colliding with with a proton in in liquid hydrogen --A Bubble Chamber

23 How do we know all this? Cosmic rays Accelerator experiments Radioactivity experiments And about 100 years of hard work by many people...

24 Example collisions oranges!

25 But other things can happen too! Example collisions

26 The Large Hadron Collider Starts collisions in 2008!

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29 Experiment at particle accelerator: schematic

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31 ATLAS is twice as big! five-storey building ATLAS CMS

32 Dig experimental caverns

33 LHC magnet installation

34 Possible LHC Schedule 2007 Completion of machine and detectors 2008 first physics year at 7 TeV proton energy try to reach /cm 2 /s integrated luminosity O(1 fb -1 ) three years at /cm 2 /s 30 fb -1 in total important for precision physics and discoveries 2011 high luminosity running at /cm 2 /s 100 fb -1 per year 2015 Upgrade to Super LHC /cm 2 /s under discussion requires major machine and detector upgrades

35 Cross Section of Various SM Processes Low luminosity phase /cm 2 /s = 1/nb/s approximately 10 8 pp interactions 10 6 bb events 200 W-bosons 50 Z-bosons 1 tt-pair will be produced per second and 1 light Higgs per minute! The LHC is a b, W, Z, top, Higgs, factory! The problem is to detect the events!

36 Detector Design Aspects good measurement of leptons (high p T ) muons: large and precise muon chambers electrons: precise electromagnetic calorimeter and tracking good measurement of photons good measurement of missing transverse energy (E T miss ) requires in particular good hadronic energy measurements down to small angles, i.e. large pseudo-rapidities (η 5, i.e. θ 1 ) in addition identification of b-quarks and τ-leptons precise vertex detectors (Si-pixel detectors) Very important: radiation hardness e.g. flux of neutrons in forward calorimeters n/cm 2 in 10 years of LHC operation

37 Online Trigger Trigger of interesting events at the LHC is much more complicated than at e + e - machine interaction rate: 10 9 events/s max. record rate: 100 events/s event size 1 MByte 1000 TByte/year of dat trigger rejection 10 7 collision rate is 25 ns (corresponds to 7.5 m cable delay) trigger decision takes a few µs store massive amount of data in front-end pipelines while special trigger processors perform calculations

38 A basic Tracker Multiple thin layers of, for example, silicon sensors

39 Components of CMS: the TRACKER

40 Numbers: TRACKER Largest silicon-sensor system ever made More than 220m 2 of sensors More than 60 million electronics channels (pixels and microstrips) 6m long, ~2.2m diameter, operates at -15 o C

41 Track reconstruction

42 Calorimetry Calorimeters to measure the energies of different types of particle Electromagnetic sensitive to photons, electrons, positrons Hadronic sensitive to hadrons (particles containing quarks) such as protons, neutrons, pions etc. The calorimeters stop the incoming particles so must go outside of the tracker

43 A basic calorimeter Total # of particles is proportional to energy of incoming particle Light materials (blue) produce a signal proportional to the number of charged particles traversing

44 Components of CMS: the ECAL

45 Numbers: ECAL Homogeneous calorimeter Lead tungstate (PbWO 4 ) crystals create electromagnetic showers and produce scintillation light Barrel: ~64000 crystals constructed in 36 supermodules (1700 crystals each); light detected by avalanche photodiodes Endcaps: ~16000 crystals constructed as supercrystals 5x5 arrays; light detected by vacuum phototriodes

46 Components of CMS: HCAL

47 Numbers: HCAL Three parts to the puzzle Barrel HCAL made of 36 brass wedges, each of which is ~35 tonnes Endcap HCAL made from brass recuperated from Russian military Forward HCAL (known as HF) made from steel embedded with quartz fibres

48 Muon system Need to identify the different types of particle Combination of signals in the tracker and calorimeters can identify many particles Also have dedicated sensors for muons These are the only particles that travel all the way through the calorimeters without stopping

49 Components of CMS: the MUON system

50 MUON system Position measurement Drift Tubes (DT) in barrel Cathode Strip Chambers (CSC) in endcaps Trigger Resistive Plate Chambers (RPCs) in barrel and endcaps

51 Some final thoughts on the technology The LHC detectors are the most complex scientific instruments ever made A typical LHC detector has about 100 million individual sensors (c.f. a typical digital camera with ~6 Mpixels) But it takes a digital photo 40 million times every second! The detectors have to operate for at least ten years with little or no intervention Technology sensors and electronics are cutting-edge

52 What is a Solenoid? A solenoid is essentially a cylinder of wire. Passing an electric current down the wire creates a magnetic field The CMS solenoid is designed to provide an axial magnetic field of 4 teslas about times that of the earth The current required is ~20 k amperes need to use a superconducting wire (zero resistance) The superconductor chosen is Niobium Titanium (NbTi) wrapped with copper needs to be cooled to ~4K The CMS solenoid is 13m long with an inner diameter of 5.9m The solenoid is sufficiently large that the tracking and all central calorimeters can fit inside Charged particles only bend in one projection (looking along the beam line see next page) Makes life easier for the physicist! (oh, and it costs about 80 million CHF!)

53 Components of CMS: the SOLENOID

54 Construction of the Solenoid 7 main parts: Outer vacuum tank: made in 3 pieces, assembled at CERN Inner vacuum tank: single piece transported to CERN from ~120km away in the Jura Solenoid itself: 5 coils, welded to each other Also a huge return yoke ~10500 tonnes of solid steel pieces surround the solenoid to control the magnetic field Also act as the skeleton of CMS Yoke is divided into 5 barrel rings and 6 endcap disks (3 on each side)

55 Transporting and constructing the solenoid

56 Swivelling the coil Coil is constructed vertically but needs to be horizontal!

57 Inserting the coil

58 Numbers: Solenoid (2) Outer barrel rings x 4 2 per side Endcap disks x 6 (3 per endcap) Central barrel ring Central Ring Outer Rings Barrel ring 1250 tonnes 1174 tonnes Vacuum vessel 264 tonnes - Superconducting coil 234 tonnes - Support feet 72 tonnes 66 tonnes Cabling on vacuum vessel 150 tonnes - Support for racks and cables 10 tonnes 10 tonnes Total 1980 tonnes 1250 tonnes Total weight tonnes Diameter 15m Length 21.6m Magnetic field 4 Tesla Endcap disk 1 (YE1) ~730 (disk) + 90 (cart) tonnes Endcap disk 2 (YE2) ~730 (disk) + 90 (cart) tonnes Endcap disk 3 (YE3) ~300 (disk) + 90 (cart) tonnes

59 Lowering parts of CMS the central ring

60 You go down here The underground caverns CMS is in here! Electronics/PCs are in here!

61 The physics goals of CMS

62 Examples Low M H < 140 GeV/c 2 Medium 130<M H <500 GeV/c 2 High M H > ~500 GeV/c 2

63 LHC Reach for a Higgs Discovery Different channels Total sensitivity 30 fb years LHC can cover the whole region of interest with 10 fb -1

64 What might a real Higgs event look like? 2 muons 2 electrons

65 Higgs Roadmap Discover the Higgs (in the range GeV < M H < 1 TeV) Determine its properties/profile The mass Spin and parity quantum numbers How does it decay? Measure Yukawa like patterns Measure relations between fermion and gauge boson couplings Observe rare decay modes Observe unexpected decay modes? (new particles?) Measure total width Reconstruction of the Higgs potential by determination of the Higgs self coupling Its nature: is it standard, supersymmetric, composite. BOTH LHC and LC will be crucial in establishing Higgs Dynamics

66 More open questions Are the quarks and leptons elementary particles? Are there other particles we have not seen yet? Why are the masses different? Matter/Antimatter asymmetry in universe? What about gravity? Or superstrings? Or extra dimensions? Properties of the neutrino? Answering any one of these questions will get you a Nobel Prize!

67 The future of CERN is you In the coming 20 years, the scientists at CERN intend to answer at least some of these questions Working at CERN is an exciting job Groundbreaking science International collaboration Fun We are always looking for more smart people!

68 Want to know more? Surf to the oldest web page in the world!