Post on 18-Jan-2018
description
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