LHC Start-up

1
LHC Start-up

• Dark Matter at the Crossroads
• DESY Theory Workshop 2008

Klaus DeschUniversität Bonn02/10/2008
2
First collisions - CMS
3
First collisions - ATLAS
4
Contents

1. LHC status
2. Commissioning of ATLAS and CMS
3. Towards first physics results
4. First searches
5. Summary and Outlook

5
LHC parameters
Beam energy 7 TeV Design Luminosity 1034
cm-2s-1 Bunch spacing 25 ns Particles/Bunch 1011
x 2808 bunches SC Dipoles 1232, 15 m,
8.33T Stored Energy 350 MJ/Beam
LHCb
ATLAS
CMS
ALICE
6
Cooldown
7
First beams September 10, 2008
8
First beams in ATLAS
9
First beams and CMS
10
First beams and everywhere else
11
After Sept 10
Successful continuationof commissioning with
beam (low intensity, 109 protons) Sept
11 Switched on RF for beam 2circulating beam
for 10 min Many tests (orbit, dump,) Sept
12 Measure horizontal beamprofile with wire
scanner Evening transformer failure
pt8replacement recovery Continue with machine
checkout(without beam)
12
Problem in Sector 34

• Friday, Sept 19
• Commissioning without beam of final sector for 5
  TeV operation
• Faulty electrical connection between two magnets
• Leading to large helium leak into the tunnel
• Sector has to be warmed up (started, takes
  several weeks) before diagnosis and repair
  can start, then cool down again (several weeks)
  ? runs into winter shutdown
• Restart of accelerators spring 2009 LHC beams
  to follow

please be patient
BTW greetings from the DG-elect nothing worse
than creating false rumours ?
13
Original Schedule There is no new schedule yet
Health warning Luminosity estimates havehigh
uncertainties
we were here
we wont getthis (but morecosmics ?)
if repair goeswell, we willget this! (?
immediateimpact hugebut overallimpact isstill
limited)
14
Commissioning the experiments
15
Status of the Experiments
In short ATLAS CMS ALICE LHCb
are ready to take data
will only cover ATLAS and CMS
16
ATLAS
A historical momentClosure of the LHC beam pipe
ringon 16th June (the last piece was the one
shown here in ATLAS side A)
17
CMS
18
Commissioning with cosmics
19
Example ATLAS tracking
Cosmic track in Muon system Si-Tracker
Cosmic Shower in Transition Radiation Tracker
20
Example Tracking Alignment
Relative position of various sub-detectors is
vital to achievedesired good momentum
resolution Relative alignment of pixel
detectorand silicon strip tracker with
cosmics(only few 100 tracks!) Nominal layer
positions as measured Alignment
1/2/3 after correction
of these positions But still o(mm) goal
20 ?m 36000 alignment constants
(positions,angles) to be determined!
21
Example CMS Electromagnetic Calorimeter
Barrel ECAL clusters matching muon tracks
A Dee of endcap ECAL
clearm.i.p. signal
sometimes huge energydepositionfrom
cosmicmuon in ECAL
22
ExampleTrigger
Few days of (intermittent) beams helped
enormously to adjust timing of different triggers
1 Bunch Crossing Number 25 ns
23
Towards first physics results
24
The first 10 pb-1
1 pb-1 is 3 days of data at 1031 cm-2s-1, with
30 efficiency
Process Events (10 pb-1)
minimum bias ?
W?e? 105
Z?ee 104
tt 103
Higgs (130 GeV) 10
Gluinos (1 TeV) 1

• Focus
• Establish SM signals
• Use them for detector calibration(tag and
  probe)
• Tune MC
• Perform basic cross sectionmeasurements

Examples ?
25
Minimum bias
Energy dependence of dN/d? ? Vital for tuning
Underlying Event model Important for all
analyses Only requires a few thousand events.

• PYTHIA models favour ln2(s)
• PHOJET suggests a ln(s) dependence.

26
J/?
High cross-section Very useful for tracking /
muon tuning and data quality O(10k) J/? ? ?? per
pb-1 Measurements also feasible with very little
data...
With 1 pb-1 could already measure R
?(bb-gtJ/?)/?(pp-gtJ/?)? with lt5 statistical
precision provided muon trigger
working tracking understood well enough
27
W/Z
25 k Z?ee for 50 pb-1 Quickly dominated by
systematics Initial precision of W/Z cross
sections 4-5
28
Top

• Top (tt) NLO cross-section at 14 TeV 830
  pb(Tevatron 7 pb)
• Invaluable channel for data-driven calibration
• can select without b-tags
• commission b tagging
• general performance
• calibrate the light jet energy scale with W?jj

29
Calibration of ETmiss

• ETmiss is one of the hardestquantities to
  measure
• Understanding of all detector components
  required
• Strategy calibrate ETmiss with known SM
  processes from data
• Example DY-Production of Z??? 1. Tune
  Z??? MC with data 2. Remove muons and compare
  with Z??? 3. Tune ETmiss from observed
  differences

30
The first searches for phenomena beyond SM
31
The first searches

• will start once initial detector calibration has
  been achieved and verified with known SM
  processes
• need conservative estimates of systematics
• data driven methods for background determination
• concentrate on searches which can yield
  signifcant results with first 10 pb-1 to few
  fb-1

32
Contact interactions
Cross section for QCD jet production is
huge! With 10 pb-1 at 14 TeV 10 events at gt 1.8
TeV Uncertainties PDFs, Jet Energy Scale
Resolution New energy regime beyond Tevatron
limits to be probed quickly
33
Leptonic Resonances
Example Z' ? ??

• Z' mass peak on top of small Drell-Yan
  background
• with 100 pb-1 large enough signal for discovery
  up to m 1.5 TeV
• ultimate calorimeter performance not needed
• ultimate reach (300 fb-1) 5 TeV

34
SUSY

• Supersymmetry (after all those years) most
  attractive model(s) for physics beyond the
  Standard model
• Huge variety of complex experimental
  signatures
• MSSM with R-parity conservation canonical
  model for experimental searches (NB other
  signatures are studied as well)
• key signature missing transverse energy
  from undetected LSPs (augmented by high-pt
  leptons and jets)
• most generic search strategy
• Inclusive search for ETmiss excess

35
SUSY inclusive search
Simple selection 4 jets with ET gt 50 GeV, 1 jet
with ET gt 100 GeV Various methods for data-driven
estimatation of tt,W,Z backgrounds
36
SUSY leptonic signatures
Although more rare, leptons (e,?) in addition to
large ETmiss may provide a more robust
signature(and thus faster result) Almost
background free Appearance of a kinematicedge
most strinkingsignature of SUSY No SM processes
with this feature (but SUSY does not always
guarantee such a feature)

37
SUSY reach
Defined representative benchmark points for
full simulationExtrapolate to other regions of
mSugra parameter space (m0, m1/2, tan?)?
Reach for squark and gluino masses using
4-jets0-lepton channel at 14 TeV 0.1 fb-1 ?
M 750 GeV 1 fb-1 ? M 1350
GeV 10 fb-1 ? M 1800 GeV Deviations
from the Standard Model due to SUSY at the ltTeV
scale can be detected fairly quickly
(2009/10)? ATLAS and CMS quite similar
38
SUSY parameters
If hints for SUSY are seen, parameter estimations
can start General MSSM has too many parameters
start with (highly) constrained model
assumptions (e.g. mSugra) Produce Likelihood
maps of parameter planes
39
SM Higgs probably nothing fast
SM Higgs discovery is guaranteed over the whole
theoretically possible mass range. Multitude of
production mechanisms and decay
modes
main sensitivity from lepton/photon modes H?bb
only in association with tt,W,Z Discovery
channels ??, qq?? for light Higgs ZZ?4l, WW,
qqWW for heavier Higgs
40
The easier case H?4 leptons
H-gtZZ-gt4l for mH gt 140 GeV Robust signal Small
and well controllablebackground
41
The tough case light (lt 130 GeV Higgs)
This is, where everybody expects it to be.
42
SM Higgs Reach ATLAS CMS combined
43
Summary Outlook

• LHC is complete after 14 years of construction
• Very successful first beams in the machine
  early September
• Sector34 problem under investigation ? hope
  for restart after regular winter shutdown
• ATLAS and CMS in very good shape
  commissioning with cosmics (and some beam)
  progressing well
• 1st phase in 2009 commisioning with collisions
  rediscover SM
• 2nd phase in 2009 various opportunities to
  enter into unexplored territory
• Discovery of DM-candidates likely not before
  2010
• Discovery of Higgs very likely not before
  2010-2011
• Many other scenarios/models studied surprises
  not studied ?

44
10 vs 14 TeV?

• At 10 TeV, lower cross-section for high mass
  objects due to lower parton luminosities...
• Below about 200 GeV, the suppression is lt50
  (process dependent)?
• e.g. tt factor 2 lower cross-section (still 50x
  Tevatron)?
• Above 2-3 TeV the effect is more marked

James Stirling