accelerator centers worldwide
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
1
the world’s largest accelerators
accelerator
accelerated
particles
Ebeam
start
luminosity
[ 1030 cm-2 s-1]
TEVATRON
pp
2 x 900 GeV
1987
25
PEP II
e+ e-
10.5 GeV
1999
5000
KEK B
e+ e-
10.5 GeV
1999
13 000
HERA
p e±
26 + 820
GeV
1992
15
pp
2 x 7000
GeV
2009
>10 000
LHC
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
2
cross sections and rates
cross sections vary over
many orders of magnitude
• inelastic:
• W -> ln:
• tt:
- • Higgs (100 GeV):
• Higgs (600 GeV):
109 Hz
100 Hz
10 Hz
0.1 Hz
0.01 Hz
required selectivity
1 : 10 10 - 11
trigger
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
3
projectiles

SPS and Fermilab used proton-antiproton collisions

LHC uses proton-proton collisions

why?
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
4
proton-antiproton
proton-proton
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
5
how big is a proton?

roughly 1 fm (10-15 m)
– “femtometer” or “fermi”

1 barn is the area of a
10 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
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
6
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 10-30
cm-2 ( = 1 μbarn), to a rate of 1 event per second

Manfred Jeitler
for a collider, the luminosity can be calculated as follows:
The Physics of LHC
Baikal Physics School 2011
7
integrated luminosity


number of events collected divided by the cross section
usual units: nb-1 (“inverse nanobarn”),
pb-1 (“inverse picobarn”) etc.
 an integrated luminosity of 1 fb-1 means 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
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
8
Instantaneous luminosity
N
kf
N
kf

L

F

F
*
4

 4


x y
n
2
b
•
Nearly all the parameters are variable (and not independent)
–
–
–
–
–
–
Number of bunches per beam
Number of particles per bunch
Normalized emittance
Relativistic factor (E/m0)
Beta function at the IP
Crossing angle factor
• Full crossing angle
• Bunch length
• Transverse beam size at the IP
Manfred Jeitler
2
b
The Physics of LHC
kb
Total Intensity

n

*
F
c
*
Beam Brightness
Energy
Interaction Region


c z
F
1
/ 1

 *

2
2
z
Baikal Physics School 2011
9
LHC
proton-proton
circumference: 27 km
bunches: 3564 + 3564
protons / bunch: 1011
beam energy: 2 x 3.5 (7) TeV
luminosity: 1033-1034 cm-2s-1
bunch spacing: 25 ns
collision rate: 108 - 109 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
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
10
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
11
how to hit a proton



p ~ 1 fm
beam ~ 10 - 100 μm = 1010 - 1011 fm
ratio of area: 1020
– 10-20 chance to hit one proton

1011 protons per beam
– typical distance between protons: 10-10 m = 100’000 fm

rate: 1011 × 1011 × 10-20 = 102
– nominal LHC: ~ 20 interactions per bunch crossing (“pileup”)
– achieved now: ~ 8
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
12
beam sizes around Atlas
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
13
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
14
layout of the LHC storage ring
(built into the former LEP tunnel)
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
15
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
16
16
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
17
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
18
I don’t 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 don’t ?
– 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 ????


don’t worry, be happy!
there are convincing experimental arguments that we are
safe
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
19
I don’t 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?
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
20
I don’t 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
wouldn’t 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 Platon’s dialogues
Manfred Jeitler
The Physics of LHC
Baikal Physics School 2011
21