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Title: The coming era of discoveries at the Large Hadron Collider


1
The coming era of discoveries at the Large Hadron
Collider
  • Yuri Gershtein

2
Colliders have been essential tools to understand
the worlds structure
3
They started small
Discovery of Atomic Nucleus
no acceleration yet!
4
They started small
The first cyclotron
5
Then got a bit bigger
Lawrence next to the Berkeley cyclotron
discovery of pions (simultaneously with cosmic
rays)
6
and then even bigger
Most were just lets build it and see whats
there. Most discoveries in the field were indeed
surprises! SppS was built to see W/Z for masses
of which there were precise predictions LHC is
built to explore electroweak energy scale which
it completely covers
7
and bigger yet
Lac Leman
Jura Mountains
The Alps
Geneve
8
Hadron Colliders
  • Easiest way to achieve high center-of-mass energy
    is colliding beams of protons or anti-protons
  • heavy, so no synchrotron radiation
  • stable, so can take time accelerating
  • But messy!
  • quark/gluon colliders

constituents of proton that carry small
fraction of its energy
constituents of proton that carry large
fraction of its energy
9
LHC
  • 27km proton-proton ring at CERN
  • Reuse the tunnel previously home for the LEP
    collider
  • Dig new collision areas for new experiments
  • ATLAS CMS
  • hermetic, large, general purpose
  • LHCb Alice
  • Smaller in size and physics scope

10
So colliders had gotten very big and relatively
expensiveWhat do we learn from them?
11
Problems of Particle Physics
  • Problem 1 while discovering building blocks of
    matter we have found more pieces that we need

Problem 2 even with the extra pieces, we can
explain only 5 of what we see in the Universe
12
The Standard Model
Why so many flavors? Why three
generations? For our world to function today
we just need the first generation! May be
three generations were needed to form the
Universe?
13
Cosmological Connection
WMAP, astro-ph/0302207
  • From studying microwave background
  • W WM W? 1.020.02
  • WM 0.29 0.07
  • WB 0.047 0.006
  • 70 of the universe is energy (some unknown
    repulsive force?)
  • 5 is baryonic matter
  • 25 is some non-baryonic cold dark matter
  • Similar conclusions from galactic rotation
    curves, type IA supernovae and gravitational
    lensing

14
Dont Be Fooled by Bright Lights
The Dark Side Rules The Universe
Dark Matter Binds It Together
Dark Energy Controls Its Destiny
stolen from M. Turner
15
The Standard Model
Still, we have achieved a dramatic reduction
of complexity from gt100 atoms to just a few
quarks and leptons And achieved some
success in unification of forces
16
Unification of Forces
Heavy Light
17
The Standard Model
  • Amazing Precision! But
  • Gravity? What happens at energies Mplanck?
  • Can forces be unified?
  • Dark Matter candidate?
  • What is origin of flavor? Why three
    generations?
  • Why Mass?

18
Mass
  • Higgs Mechanism
  • Separate piece of SM
  • introduced by hand
  • Mass ? Rest energy
  • If we make particle interact with vacuum it will
    acquire additional energy ? MASS
  • In the Standard Model the vacuum is skewed by
    the Higgs field, and particles get mass from
    interaction with the Higgs field
  • If one just puts the masses into Lagrangian the
    theory breaks looses gauge invariance and
    becomes unrenormalizable
  • no viable theoretical alternatives

19
Where Is the Higgs?
  • Artificial add-on to the Standard Model (is it
    even there?)
  • There is a mounting tension between direct and
    indirect limits
  • SM fits prefer light Higgs, leading to vacuum
    instability at high renormalization scales

160 GeV
115 GeV
20
Higgs A Weak Link
  • We want theory that can be unified with gravity
    (energies MP)
  • Quantum correction to fundamental scalar mass
    are order of MP 1019 GeV, and are obviously very
    unlikely to cancel to give mh 102 GeV

All predict new particles, that can be looked for
directly or in loop effects
21
Higgs Boson
  • Electroweak symmetry breaking in the SM
  • 1 complex Higgs scalar doublet (4 d.o.f.)
  • W, W- and Z get mass (three Higgs d.o.f. become
    longitudinal W/Z components)
  • photon remains massless - symmetry between
    electromagnetism and weak force is broken!
  • Fermions get masses
  • One remaining observable Higgs
    boson
  • hasnt been observed yet
  • can not hide much longer!

Precision measurements of SM parameters give
indirect limit Mh lt 144 GeV _at_95CL
Direct search (LEP) Mh gt 114.9 GeV
22
Guaranteed Success
  • Whatever the ultimate theory of everything is,
    the electro-weak symmetry breaking
    mechanism will be revealed at the
    LHC
  • W boson scattering amplitude grows at large
    masses
  • violates Unitarity at around 1000 GeV
  • something has to appear and cancel the growth. In
    the SM it is the Higgs but it does not have to
    be

23
SuperconductingSuper-Collider
24
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25
Cryogenics
  • Dipoles sit in a 1.9 K bath of superfluid helium
    at atmospheric pressure
  • Bath cooled by low pressure liquid helium flowing
    in heat exchanger tubes threaded along the string
    of magnets
  • Each of 8 sectors is by itself the largest
    operating cryogenic system

26
LHC Progress
27 km of dipoles in liquid He!
Installation in progress
27
Detectors
  • Basic principles since Rutherford and Chadwick
  • detect charge particles traversing the material
  • use magnetic field to measure momentum

Calorimeter as dense as possible, particle
breaks up into many low energy particles, and
their combined ionization is proportional to the
initial particle energy
Type of particle is inferred from how far
it penetrated into material
Tracker as low as possible density, focus
on precise measurement of the path of the
particles
28
Discovery of Z boson
C. Rubbia 1984 Nobel Prize
29
A Typical Detector
  • although charged pions and muons are unstable,
    they live long enough to travel through the
    detector
  • different types of particles interact with
    detector material differently and are detected
    through their (and their daughter particles)
    ionization
  • curvature of particle tracks in magnetic field
    determines momentum
  • for electrons, photons and hadrons measure
    energy in the calorimeters

30
Solenoid
4 Tesla
2.7 GJ stored
31
Silicon Tracker
32
PbWO4 Crystals for Calorimeter
33
ECAL Crystal Matrix Production
Single Crystal
Sub - Module mounting
Assembled Sub - Modules
Free mounting bench
34
CMS is coming together
35
HCAL in the Solenoid in the Muon System
36
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37
Heavy Lowering
1300 tons
38
Tracker is Inserted
39
Final Closure Sept.08
40
First Events from CMS high energy cosmic rays!
41
Cosmic Muons Spectra
42
CMS Collaboration
1976 Physicists and Engineers 36 Countries
153 Institutions
43
LHC Start-up
Carlo Rubbia, Nobel Laureate and LHC proponent
Lyn Evans, LHC Project Leader
44
First Beam at CMS
45
Meanwhile, at FNALs ROC
46
No RF, debunching in 2510 turns, i.e.
roughly 25 mS
Courtesy E. Ciapala
47
First attempt at capture, at exactly the wrong
injection phase
Courtesy E. Ciapala
48
Capture with corrected injection phasing
Courtesy E. Ciapala
49
Capture with optimum injection phasing, correct
reference
Courtesy E. Ciapala
50
Black Friday(s)
  • Friday night, 12-Sep.
  • 1120pm Lose main 30ton 12 MVA transformer at
    Point 8 (LHCb)
  • There are no spares, and it would take 6-9 months
    to procure another.
  • Borrow from surplus capacity at CMS
  • 13-18 Sep, Hardware commissioning consolidation
  • Power, cryogenic, and vacuum problems lead to 6
    days of downtime
  • Advance commissioning of magnet control system to
    5 TeV beam operation for 2008 (avoid 10 day
    shutdown)
  • CMS investigates issues with magnet
  • Thu, 18-Sep
  • Return to beam 1 operation
  • CMS takes data overnight
  • Friday noon, 19-Sep
  • Massive helium loss in one arc of the tunnel
    (1-2 tons), cryogenics lost
  • Broke insulation vacuum in sector
  • Suspected failure of interconnection between
    quadrupole and dipole magnet during 5 TeV
    commissioning of last sector of LHC

51
First Beam _at_ CMS
52
First Beam _at_ CMS
53
First Beam _at_ CMS
Muons associated with beam (but outside beam
pipe) arising from the decays of pions created
when off-axis protons scrape collimators or other
elements along beamline
54
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55
QCD Confinement
  • Quarks and gluons can not exist by themselves -
    they only comes in pairs (mesons) or triplets
    (baryons)
  • If an energetic quark or gluon is produced it
    fragments

56
  • Very large background from gluon scattering
  • jets are everywhere
  • jets are least precise measured object,
    especially bad at low energies
  • Many interesting things decay into jets too
  • i.e. h?bb but signal to background ratio is
    10-7
  • 1. require multiple leptons or photons in the
    final state then interesting events are very
    rare, but very few spectacular events may
    constitute a discovery
  • 2. look at high energy / high mass distributions
  • 3. accumulate a lot of events and look for
    deviations in distributions of energy, mass, etc

57
Data Rates
  • Event size 1Mbyte
  • Event rate 40MHz collisions
  • Total amount of data produced
    40 Terabytes/sec
  • Equivalent to 100M simultaneous cell phone
    conversations
  • How we handle this much data is a science in
    itself!

58
Trigger
  • Store data in circular buffer
  • Better decide by the end of the buffer length if
    the data should be kept this is the trigger
    decision
  • Implement trigger using custom built hardware
    pipeline processor
  • Has to take less time than the smallest circular
    buffer. For CMS this is 128 clocks
  • Output is either 1 (keep) or 0 (throw away)
  • Accept rate is 1 in 400 crossings
  • At the High Level trigger further reduces rate
    to 100 Hz
  • O(1000) CPUs run simplified version of the
    reconstruction program
  • Data Rate to tape
  • 100 Hz x 1 MByte 1 Gbit/s
  • Year of data taking 106 GB, 1PB
  • And that is just RAW data
  • it need to be calibrated, reconstructed,
    distributed, skimmed
  • and we need to have even larger simulated sample!
  • 1000 PB of data in the first decade of operations

59
Tiered System for Data Mgmt
  • T0 at CERN
  • Record raw data and DST
  • Distribute raw data and DST to T1s

FNAL Chicago
RAL Oxford
T1
T1
  • T1 centers
  • Pull data from T0 to T1 and store
  • Make data available to T2

FZK Karlsruhe
T1
T0
T1
T1
CNAF Bologna
T1
IN2P3 Lyon
  • T2 centers
  • DST analysis.
  • Local data distribution

PIC Barcelona
60
LHC Grid
CMS Experiment
Online System
CERN Computer Center
200 - 1500 MB/s
Tier 0
10-40 Gb/s
Tier 1
gt10 Gb/s
OSG
Tier 2
2.5-10 Gb/s
Tier 3
Tier 4
Physics caches
PCs
61
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62
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63
10 11th Floors of the Wilson Hall
  • Meeting Rooms/Video Conferencing/Internet
  • terminals/printers/office supplies
  • secretarial and computer support
  • Coffee machines/Water cooler

Room for 200 visitors
64
LHC Physics Center _at_ FNAL
65
FNAL LPC
66
Summary And Outlook
  • The LHC is finally happening
  • We might find out our world is even stranger then
    we thought
  • This very well may be a dawn of a new era in
    physics STAY TUNED!
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