accelerator centers worldwide
SLAC: Stanford Linear Accelerator Center FNAL: Fermi National Accelerator Laboratory LEPP: Cornell Laboratory for Elementary Particle Physics BNL: Bookhaven National Laboratory DESY: Deutsches Elektronensynchotron CERN: Conseil europen pour la recherche nuclaire PSI: Paul-Scherrer-Institut LNF: Laboratori Nationali di Frascati LNGS: Laboratori Nationali del Gran Sasso BINP: Budker Instiute for Nuclear Physics BEPC: Beijing Electron Positron Collider KEK: Japanese accelerator center the worlds largest accelerators
accelerated particles Ebeam start luminosity [ 1030 cm-2 s-1] TEVATRON p p 2 x 900 GeV 1987 25 PEP II e+ e- 10.5 GeV 1999 5000 KEK B 13 000 HERA p e GeV 1992 15 LHC 2 x 7000 GeV 2009 >10 000 Recent major colliders and their experiments: TEVATRON collider (Fermilab, Chicago): proton/antiproton Experiments:CDF and D : top quark found.At present, looking for the Higgs particle and physics beyond the Standard Model. RHIC: Relativistic Heavy-Ion Collider, attempts to produce quark-gluon plasma (lumps of very hot matter in which quarks and gluons behave as free particles) BELLE experiment at KEK B (KEK, Japan) / BABAR experiment at PEPII (Stanford, California, USA): electron/positron: CP-violation in B-meson decays HERA (DESY, Hamburg, Germany): electron/proton:Strong interaction studies LHC collider (CERN, Geneva): proton/proton and lead/lead CMS and ATLAS experiments will be looking for the Higgs boson, Supersymmetry, and new physics (=beyong the Standard Model) ALICE: investigate quark-gluon plasma in heavy-ion (lead-lead) collisions LHCb: CP-violation in B-meson decays cross sections and rates
cross sections vary over many orders of magnitude inelastic: Hz W -> ln: Hz tt: Hz Higgs (100 GeV): Hz Higgs (600 GeV): Hz required selectivity 1 : trigger - projectiles SPS and Fermilab used proton-antiproton collisions
LHC uses proton-proton collisions why? proton-antiproton proton-proton
what do cross section and nb mean? how big is a proton? roughly 1 fm (10-15 m)
femtometer or fermi 1 barn is the area of a fm 10 fm square big unit derived from uranium nucleus physicists joked: that cross section is as big as a barn proton-proton cross section at LHC energies: 70 mbarn = 7 fm2 r ~ 1.5 fm Size of a real barn (saray) in barns: 100 m2 10^2 * 10^28 = 10^30 barns Size of Lake Baikal in barns:3 * 10^4 * 10^6 * 10^28 = 3 * 10^38 barns luminosity (instant) luminosity is rate per cross section
usual units: cm-2 s-1 e.g., 1030 cm-2 s-1 corresponds, for a reaction cross section of cm-2( = 1 barn), to a rate of 1 event per second for a collider, the luminosity can be calculated as follows: So, when building a collider, it is important to : accelerate a large number of particles make the beams in the interaction region very thin integrated luminosity
number of events collected divided by the cross section usual units: nb-1(inverse nanobarn), pb (inverse picobarn)etc. an integrated luminosity of1 fb-1means that for a process with a cross section of 1 fb,1 event (on average) should have been collected or 1000 events for a cross section of 1 nb, etc. so, 1 inverse femtobarn = 1000 inverse picobarns : 1 fb-1= 1000 pb-1 physicists are now looking for very rare events, so it is vital to reach not only high energies (so that heavy particles can be produced) but also high luminosities handling the resulting data rates is a challenge also for the detectors, trigger systems, and readout electronics When looking at performance parameters of an accelerator, be careful to check if people are talking about instantaneous luminosity, or integrated luminosity to be collected over a certain period of time. These two values are correlated by the duty cycle of the accelerator, i.e. the time it is actually operating (up-time). Instantaneous luminosity
Nearly all the parameters are variable (and not independent) Number of bunches per beamkb Number of particles per bunch Normalized emittancen Relativistic factor (E/m0) Beta function at the IP * Crossing angle factorF Full crossing anglec Bunch lengthz Transverse beam size at the IP* Total Intensity Beam Brightness Energy Interaction Region LHC proton-proton circumference: 27 km bunches: 3564 + 3564
protons / bunch: 1011 beam energy: 2 x 3.5 (7) TeV luminosity: cm-2s-1 bunch spacing: 25 ns collision rate: Hz dipole field: 8.4 T number of dipoles: ~ 1200 heavy ions (Pb-Pb) beam energy: 2.8 (5.5) TeV / nucleon pair luminosity: 1027 cm-2s-1 how to hit a proton p ~ 1 fm beam ~ 10 - 100 m = 1010 - 1011 fm
ratio of area: 1020 10-20 chance to hit one proton 1011 protons per beam typical distance between protons: m = 100000 fm rate: 1011 =102 nominal LHC:~ 20 interactions per bunch crossing (pileup) achieved now: ~ 8 , film: by Akira Kurosawa Siberia: (3000 km)^2 ~ 10^7 km2 = 10^13 m2 beam sizes around Atlas In a large accelerator center such as Cern, acceleration of various kinds of particles (protons, antiprotons, ions, electrons, positrons) is achieved in several stages in specialized machines. Some of these accelerators are able to switch between different kinds of particles (so, SPS used to alternate every few seconds between the acceleration of protons for fixed-target experiments and pre-acceleration of electrons and positrons for the LEP collider). layout of the LHC storage ring (built into the former LEP tunnel) Modern accelerators need a lot of space and are therefore usually built under ground, such as the large accelerators at Cern, Geneva, Switzerland. In the front one sees Geneva airoport, in the background the Jura mountains. The large circle shows the position of the underground LEP/LHC tunnel (circumference 27 km), the smaller circle shows the SPS (Super Proton Synchrotron) tunnel (circumference 5 km). Why did you think it was built underground? I dont want to fall into a black hooooolee... !!!
some (few) physicists believe that at LHC energies we could already produce mini black holes they would disappear very quickly but what if they dont ? could they engulf the Earth? eat up Cern, Geneva, Switzerland, Europa ... and then Siberia and Lake Baikal with the nice seals ?? are those scientists crazy ???? dont worry, be happy! there are convincing experimental arguments that we are safe I dont want to fall into a black hooooolee... !!!
physicist: those black holes will evaporate much too quickly we know that from calculations concerned citizen: and what if those calculations are wrong (as usual)?? physicist: the Earth has been bombarded by cosmic rays of much higher energy for the last 5 billion years and we are still here! concerned citizen: but maybe then they are so fast they just whiz through the Earth and have no chance to stop and grow? I dont want to fall into a black hooooolee... !!!
physicist: at least some of them would be charged and would be slowed down by the Earth concerned citizen: but maybe due to who knows why they are all neutral? Then they would fly through and we wouldnt notice physicist: through Earth, yes but there are neutron stars and they are so dense that there the black holes would stop! And my astronomer friends tell me there are lots of neutron stars out there, so they (and we) are in no danger! concerned citizen: you are right, Socrates! oops ... the last answer must have crept in from one of Platons dialogues