Experimental foundations of subatomic physics A. Andronic. The Large Hadron Collider and the Higgs boson

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Gertrude Thornton
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1 Experimental foundations of subatomic physics The Large Hadron Collider and the Higgs boson

2 Prelude to the LHC The weak interaction governs decays...it was actually unified with the electromagnetic interaction, electro-weak theory ( 60ies) Nobel Prize 1979: Sheldon Glashow, Abdus Salam, Steven Weinberg It became clear that the weak interaction has to be mediated by heavy particles...charged and neutral particles needed by experimental observations Why those are so very different than photons and gluons, what gives them mass? The Higgs mechanism (symmetry breaking) was proposed by Higgs, Brout and Englert and others in 1964 Nobel Prize 2013: Peter Higgs and François Englert In the mid- 70ies, expectations grew of W ± and Z 0 particles of mass about 80 and 90 GeV, respectively They were discovered at CERN in 1983 p p collisions, Z 0 µ + µ Nobel prize 1984: Carlo Rubbia and Simon van der Meer

3 Motivations for the LHC find the Higgs boson discover supersymmetric particles discover other unknown things (micro black holes,?) study quark-gluon matter at extreme temperatures (in Pb-Pb collisions)

4 Higgs before the LHC The Higgs mechanism predicted a heavy particle (at least one:)...but could not tell its mass (could fortunately tell in what it decays)...nicely, the experiments could tell mass, here is the status in

5 Basics on colliders (...where charged particles are accelerated, guided and confined by electromagnetic fields) bending: dipole magnets; (de)focusing: quadrupoles; acceleration: RF cavities in a synchrotron (LHC) they are ramped synchronously to match the beam energy Energy: Bρ = p/q, B=bending field, ρ=radius, p=momentum, q=charge Luminosity: L σ X = N X /second, σ X =cross section for process X L = N 2 n b f rev 4πσ x σ y F, N=nr. of particles per bunch, n b =nr. of bunches, f rev =revolution frequency, σ x,y =colliding beam sizes, F =geometric factor F = 1/ 1 + ( θ c σ z 2σ ) 2, θc =crossing angle L 1/β beam size: σ x (s) = ɛβ x (s) + [D x (s)δ] 2 ɛ=transverse emittance; δ = ( p/p) rms =bunch energy spread β x (s)=beta function; D x (s)=dispersion... lattice properties Integral luminosity [cm 2 ]: L int = Ldt...[1 fb 1 =1000 pb 1 =10 6 nb 1 (1 b = cm 2 )] for L int = N fb 1 will get N events of X if σ X =1 fb

6 The CERN accelerator complex 43

7 The CERN accelerator complex p: LINAC2: 50 MeV; Booster (synchrotron): 1.4 GeV; Pb: LINAC3 + LEIR (with electron cooling) Proton Synchrotron: 26 GeV (generates the bunch pattern)

8 The Large Hadron Collider

9 The LHC in numbers (design values)... a behemoth (O. Brüning, P. Collier, Nature 448 (2007) 285)...probably humanity s most complex project 27 km long, 8 arcs ( 3 km), each 46 (1 quadrupole+3 dipole magnets) 8 straight sections: RF cavities (IP4) + beam cleaning (IP3,7), dump (IP6) 1232 superconducting dipoles (+3700 correctors); 392 quadrupoles (+2500 correctors); 8 RF cavities/beam (400 MHz); 108 collimators and absorbers cooled with 120 tons of (superfluid) He at 1.9 K; 8.33 T (1.5-2 ka/mm 2 ) 2808 bunches per ring, each protons (8 min filling time, 12 ribbons ) 592 bunches per ring, each Pb ions transverse beamsize: σ x,y =16 µm (β*=0.55 m); bunch length: σ z =7.6 cm beam kinetic energy: 362 MJ per beam (1 MJ melts 2 kg copper) total stored electromagnetic energy: 8.5 GJ (dipole magnets only)

10 The life of the beams circulation in the 27 km ring a lternating gradient lattice ( strong focusing, arrangement of focus-defocus)

11 The life of the beams acceleration in 16 (8 per beam) radio-frequency cavities (400 MHz) housed in 4 refrigerators (for superconductivity) 2 MV per cavity powerful electron beams modulate the field

12 The life of the beams squeeze and collide 25 vertically in CMS, LHCb horizontally in ATLAS, ALICE 3 V beam envelope [ mm ] TeV, squeezed 7 TeV, un-squeezed (injection optics) IP5: Vertical crossing: rad 0.5 mm separation in H IP5 Beam 1 Beam Longituinal coordinate [ km ]

13 The life of the beams dumped after some hours

14 The beam dump...the place where the beam ends its life (graciously:)...and here is the dumped beam...10 bunches (1.6 mm rms xy) 7 m graphite 1 m Al 2 m Fe 1000 tons of concrete shielding

15 The LHC dipole magnet...admittedly, the most innovative component of LHC... 2-in-1 design Length: 15 m Diameter: 1 m Weight: 30 tons Rings aperture: cm transverse beam size: below 1.3 mm

16 The superconducting cables 7000 km of braids...idea must have come from african hair superconductivity means large currents without Joule effect (heating), realized at very low temperature discovered in 1911 by H. Kamerlingh Onnes, who produced liquid He Nobel Prize 1913 explained by Bardeen, Cooper and Schriffer, 1957; Nobel Prize 1972 liquid He in the LHC is superfluid; Nobel Prize 2003 Abrikosov, Ginzburg, Leggett

17 LHC earthly facts project approved in produced collisions in 2009 (70-40 m underground) the distance between bunches is 15 m, or 50 ns travel time...there are also empty buckets (bunch slots) mean colliding rate: 31.6 MHz the beams circles the 27 km ring times per second it takes 15 minutes to accelerate to full energy power consumption: 120 MW (experiments: 22 MW; cryogenics: 27 MW) total cost: 3 billion euros (LHC) + 1 billion euros (experiments) the superconducting cables (NbTi) are made of 6300 filaments, each 6 µm thick (total length: 70 light-minutes, or five times to Sun and back) the kinetic energy of 1 beam is like the ICE train (200 tons) at 200 km/h tons are cooled down to C in 2 weeks (8 circuits)...using tons of liquid nitrogen down to -193 C 6500 m 3 are pumped down to atm (ultra-high vacuum)

18 The LHC in 2010 Beam energy: p: 3.5 TeV; Pb: =287 TeV Bunch intensity: p: ; Pb: (nominal) Maximum bunches: p: 368 (348 colliding in ATLAS & CMS; 16 in ALICE); Pb: 121 (114 colliding in ALICE)...as of Beam sizes: p: σ x,y =40 µm, σ z 7 cm; Pb: similar bunch spacing: p: 150 ns (50 ns tried); Pb: 500 ns Peak luminosity: pp: cm 2 s 1 ; PbPb: Delivered luminosity: pp: L int =50 pb 1 (β*=3.5 m); PbPb: ongoing... Stored energy: pp: 28 MJ (25.2 MJ in stable beams)...and in 2011: 3.5 TeV; 1380 bunches; 50 ns separation; β*=2.5 m total number of protons per beam: Peak luminosity pp: L = cm 2 s 1 ; PbPb:

19 The LHC: summary of delivered luminosity number of pp collisions: L int σ inel (more than 1 mil. billion collisions!) σ inel = 70 mb is the pp inelastic interaction cross section

20 Discovery of the Higgs boson discovery announced on 4th July 2012 by the ATLAS and CMS collab. pp collisions, s = 7, 8 TeV other decay channels also observed S/(S+B) Weighted Events / 1.5 GeV CMS -1 s = 7 TeV, L = 5.1 fb Data S+B Fit B Fit Component ±1σ ±2 σ Events / 1.5 GeV s = 8 TeV, L = 5.3 fb Unweighted (GeV) m γγ m γγ (GeV)

21 The Higgs boson now S/(S+B) weighted events / GeV CMS H γγ µ = m H = ± 0.34 GeV fb (8 TeV) fb (7 TeV) S/(S+B) weighted sum Data S+B fits (weighted sum) B component ±1σ ±2σ B component subtracted m γγ (GeV)

22 Was there anything else discovered?...not yet... - no sign of supersymmetric particles (ATLAS, CMS) - no sign of black holes or other exotic things (ATLAS, CMS)...but some very nice measurements - signs of particles with more than 3 quarks (LHCb) - the quark-gluon matter is hotter than ever (ALICE) everything will be scrutinized again in half a year, when LHC will run at its full energy (after a break of 2 years for preparations)

HIGH-ENERGY COLLIDER PARAMETERS: e + e Colliders (I)

28. High-energy collider parameters 1 HIGH-ENERGY COLLIDER PARAMETERS: e + e Colliders (I) Updated in early 2012 with numbers received from representatives of the colliders (contact J. Beringer, LBNL).