The LHC Part 1 Corsi di Dottorato Corso di Fisica delle Alte Energie Maggio 2014 Per Grafstrom CERN and University of Bologna
Organizzazione Part 1 Part 2 Part 3 Introduction Energy challenge Luminosity challenge Life time and beam vacuum Injection Filling and cycle Instrumentation Collimation Dump 2
pp physics at the LHC corresponds to conditions around here HI physics at the LHC corresponds to conditions around here Experimental Methods in Particle Physics 3
Understanding the Universe Unification? Electroweak Transition Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics 4
A most basic question is why particles (and matter) have masses (and so different masses) The mass mystery could be solved with the Higgs mechanism which predicts the existence of a new elementary particle, the Higgs particle (theory 1964, P. Higgs, R. Brout and F. Englert) History by now Peter Higgs The Higgs (H) particle has been searched for since decades at accelerators, but not yet found The LHC has sufficient energy to produce it for sure, if it exists Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics Francois Englert 5
https://twiki.cern.ch/twiki/pub/atlaspublic/higgspublicresults//hgg-fixedscale-short2.gif 6
Supersymmetry (SUSY) (Julius Wess and Bruno Zumino, 1974) Establishes a symmetry between fermions (matter) and bosons (forces): ~ - Each particle p with spin s has a SUSY partner p with spin s -1/2 ~ - Examples q (s=1/2) q ~(s=0) squark Our known world Maybe a new world? Motivation: Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics - Unification (fermions-bosons, matter-forces) - Solves some deep problems of the Standard Model 7
LHC- Requirements/ Challenges/the Energy Required Energy: At the TeV scale WHY? Standard Model: Missing piece in the puzzle WAS the HIGGS LEP result: The Higgs mass in the 100 GeV to 200 GeV range TeV scale accelerator needed Quantum corrections to the Higgs mass are infinite so how is a mass of a couple of 100 GeV possible? There must be fine tuning or cancellations. One possibility is Super Symmetry that cancels the infinities and predict new particles at the TeV scale New energy scale suprises.the unknown 1994 decision to build a 7 TeV + 7 TeV machine in the LEP tunnel very challenging as we will see 8
Are the LHC energies the highest ever? No s = 14 TeV corresponds to E ~ 100 PeV fixed target proton beam The LHC will be the first machine able to explore the high-e part of the cosmic ray spectrum 9 Experimental Methods in Particle Physics
LHC- Requirements/Challenges/ Luminosity Required Luminosity: 10 34 /cm 2 /sec WHY Higgs cross section in fb to pb range. The event rate i.e number of events /sec (N) N = L x σ σ 1 pb = 10-24 x 10-12 cm 2 = 10-36 cm 2 L =10 34 /cm 2 /sec 1 Higgs /100 sec 10 34 /cm 2 /sec is challenging as we will se. Nota bene: also challenging for the experiments: σ total 100 mb 10 9 interactions /sec 10
LEP: e+e- 104 GeV/c (1989-2000) CMS Circumference 26.8 km LHC proton-proton Collider 7 TeV/c in the LEP tunnel ALICE LHCb LHC will also collide heavy ions ATLAS
LHC: From first ideas to realisation 1982 : First studies for the LHC project 1983 : Z0 detected at SPS proton antiproton collider 1985 : Nobel Price for S. van der Meer and C. Rubbia 1989 : Start of LEP operation at 45 GeV (Z-factory) 1994 : Approval of the LHC by the CERN Council 1996 : Final decision to start the LHC construction 1996 : LEP operation at 100 GeV (W-factory) 2000 : End of LEP operation 2002 : LEP equipment removed (second life for sc cavities?) 2003 : Start of the LHC installation 2005 : Start of hardware commissioning 2007/8 : Commissioning with beam
How the LHC came to be (see a nice article by Chris Llewellyn Smith in Nature 448, p281) Some early key dates 1977 The community talked about the LEP project, and it was already mentioned that a new tunnel could also house a hadron collider in the far future 1981 LEP was approved with a large and long (27 km) tunnel 1983 The early 1980s were crucial: The real belief that a dirty hadron collider can actually do great discovery physics came from UA1 and UA2 with their W and Z boson discoveries at CERN Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics A very early Z ee online display from UA2
1984 For the community it all started in a way with the 1 st CERN ECFA Workshop Lausanne on the feasibility of a hadron collider in the future LEP tunnel 1987 La Thuile LHC Workshop Many LHC colleagues were already involved in this, a clear evolution started for detectors away from a 4µ iron-ball experiment (C Rubbia) towards multi-purpose detectors ) 1989 ECFA Study Week in Barcelona for LHC instrumentation At this conference a few decided to start setting up a structure for an LHC 14 proto-collaboration.
1991 December CERN Council: LHC is the right machine for advance of the subject and the future of CERN (thanks to the great push by DG C Rubbia) 1993 December proposal of LHC with commissioning in 2002 1994 June Council: Staged construction was proposed, but some countries could not yet agree, so the Council session vote was suspended until 16 December 1994 Council: (Two-stage) construction of LHC Phs 15 was approved
The LHC is the largest machine that has ever been built, and probably the most complex one To make the LHC a reality: Accelerators physics and... Electromagnetism und Relativity Thermodynamics Mechanics Physics of nonlinear systems Solid state physics und surface physics Quantum mechanics Particle physics and radiation physics Vacuum physics
LHC Layout eight sectors eight arcs eight long straight sections (insertions) about 700 m long IR4: RF + Beam instrumentation IR5:CM S IR6: Beam dumping system Beam dump blocks IR3: Momentum Beam Cleaning (warm) IR7: Betatron Beam Cleaning (warm) Main dipole magnets: making the circle IR2:ALICE IR8: LHC-B IR1: ATLAS Injection Injection
Organizzazione Part 1 Part 2 Part 3 Introduction Energy challenge Luminosity challenge Life time and beam vacuum Injection Filling and cycle Instrumentation Collimation Dump 18
What field is needed? The energy challenge 7 TeV in a tunnel of 27 km ( radius =4.30 km) Use : B ρ = 3.33 p (Units:Tm if p in GeV B= 3.33 x 7000/4300 Tesla = 5.42 Tesla BUT the whole tunnel is not filled with magnets. The arcs makes up totally 22.2 km of the 27 km and only 80 % can be filled with bending magnets Thus the filed needed is : 5.42 x 27/22/0.8 Tesla = 8.3 Tesla How to achieve 8.3 Tesla? 100 000 x earth field 5 times the field of the magnets in SPS 4.5 Tesla in the tevatron 5.2 Tesla in HERA 19
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Descent of the last dipole magnet, 26 April 2007 Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) 30 000 km underground transports at a speed of 2 km/h! 41
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Not only dipoles. Inner triplet quads assembly hall 181 Dipoles 1232 Quadrupoles 400 Sextupoles 2464 Octupoles/decapoles 1568 Orbit correctors 642 Others 376 Assembly of Short Straight Sections Total ~ 6700 Particle Physics and Philosophy Maria in der Aue, March 2011, P. Jenni (CERN) Experimental Methods in Particle Physics 46
A cell in the LHC arcs Vertical / Horizontal plane (QF / QD) Quadrupole magnets controlling the beam size to keep protons together (similar to optical lenses) LHC Cell - Length about 110 m (schematic layout) SSS quadrupole orbit MQF corrector sextupole corrector (MCS) quadrupole MQD orbit corrector quadrupole MQF orbit corrector main dipole MB main dipole MB main dipole MB main dipole MB main dipole MB main dipole MB special corrector (MQS) lattice sextupole (MS) decapole octupole corrector (MCDO) special corrector (MO) lattice sextupole (MS) special corrector (MO) lattice sextupole (MS)
Organizzazione Part 1 Part 2 Part 3 Introduction Energy challenge Luminosity challenge Life time and beam vacuum Injection Filling and cycle Instrumentation Collimation Dump 48
The luminosity challenge High bunch current beam-beam effects Many bunches long range beam effects Small beam size inner triplet aperture, space 49
High bunch current
Limitation: beam-beam interaction Y Force Y Quadrupole Lense Force Beam - Beam Lense
Bunch intensity limitation due to this of order N= 1011
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Many bunches Solution Crossing angle 55
Many bunches IP Crossing angle to avoid beam beam interaction (only long range beam beam interaction present) However reduction of luminosity
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Small beam size- inner triplet QF QD QF QD QF QD Interaction point Experiment distance about 100 m Focusing quadrupole for beam 1, defocusing for beam 2 High gradient quadrupole magnet triplet with large aperture (US-JAPAN) Total crossing angle of 300 µrad Beam size at interaction point 16 µm, in arcs about 0.3 mm
Layout of insertion for ATLAS and CMS quadrupole Q5 quadrupole Q4 recombination dipole separation dipole (warm) inner quadrupole triplet inner quadrupole separation triplet dipole recombination dipole quadrupole Q4 quadrupole Q5 beam distance 194 mm beam II ATLAS or CMS beam I collision point 200 m 24 m Example for an LHC insertion with ATLAS or CMS
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Luminosity -Summary N 10 11 2800 bunches i.e each 25 ns Spotsizes 16 µm L= 10 34 /cm 2 /sec 61