LHC State of the Art and News
Arno Straessner
TU Dresden
on behalf of the ATLAS Collaboration
Vulcano Workshop 2010
Frontier Objects in Astrophysics and Particle Physics
May 24-29, 2010
FSP 101
ATLAS
Outline
• Introduction
• Status of the Large Hadron Collider and
the LHC Experiments
• First LHC Measurements
• Physics Prospects until 2011
• Conclusion
• mainly ATLAS results are shown here
• results of other experiments very similar
LHC State of the Art and News - Arno Straessner 2
The Large Hadron Collider
LHC State of the Art and News - Arno Straessner
ATLAS
CMSALICE
LHCb
• LHC design values:
• pp collisions at 14 TeV centre-of-
mass energy
• 1232 super-conducting dipole
magnets with 8.3 T field
• instantaneous luminosity of
L = 1034 cm-2s-1
• 25 ns bunch spacing
• 2808 bunches per beam
• 1.15 x 1011 protons per bunch
• stored energy of 350 MJ/beam
3
The LHC Detectors
ATLAS CMS
LHCb ALICE
Standard Model, Higgs Bosons, SUSY, and more
CP physics Heavy Ion Collisions
LHC State of the Art and News - Arno Straessner 4
A Long Way Towards Regular LHC Running
• repair work after disastrous magnet incident in 2008
• new quench protection system for magnets
• sensitive to small resistance increases (nΩ)
• full repair will be carried out in LHC shutdown 2011/12
• LHC ready for pp collisions in Nov+Dec 2009:
• at 2 x 450 GeV injection energy
• integrated luminosity 20+18 μb−1 (ATLAS+CMS)
• recorded with stable beams: 12+15 μb−1 (±30% syst. uncertainty)
• 538,000 collision candidates in ATLAS during stable conditions
• collision candidates at 2.36 TeV: 34,000
• first LHC results on 0.9 TeV and 2.36 TeV collisions are now published
LHC State of the Art and News - Arno Straessner 5
World Record pp Collision Energy of 7 TeV
• LHC reached 7 TeV centre-of-mass energy with 1st collision events on March 30, 2010
LHC State of the Art and News - Arno Straessner
• very good luminosity lifetime
• longest physics fill: 30 hours
• peak luminosity continuously improved:
Lmax = 8x1028 cm-2s-1
• 2 and 3 colliding bunches
• collimator and beam dump tests
• very important:
machine studies for safe high intensity
operation → reached 1011 p per bunch
• goals for 2010/2011 run
• 7 TeV max. energy
• 768 colliding bunches
• total luminosity of 1 fb−1
• beyond 2013:
• go for 13-14 TeV ultimate energy
• 50-70 fb−1 until 2016
• 3000 fb−1 until 2030
β* squeezed to 2m
x10 improvement
6
higher beam
intensity
Integrated Luminosity
LHC State of the Art and News - Arno Straessner
• data taking efficiency ~ 95%
• very similar for CMS, LHCb, and ALICE (>80%)
7
7 TeV Collisions in ATLAS
LHC State of the Art and News - Arno Straessner
• largest physics cross-section at LHC: inelastic pp collisions (minimum bias)
8
7 TeV Collisions With Pile-Up
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CMS
• no. of pile-up events increases with intensity per bunch
• at nominal LHC luminosity and energy:
~25 pile-up events (in-time)
ATLAS Detector Performance
LHC State of the Art and News - Arno Straessner
|η|<2.5
|η|<4.9|η|<3.0
4 Tesla 2 Tesla
10
ATLAS Status Page on 1st Day of 7 TeV Run
LHC State of the Art and News - Arno Straessner 11
• high operational fraction of all
detector components:
• Pixel 97.5% of 80 M channels
• SCT 99.8% of 6 M channels
• TRT 98% of 370 k channels
• calorimeter channels
> 97.3 % (LAr, Tile)
• muon spectrometer
> 99% (MDT, CSC)
• muon trigger chambers
> 99% (RPC, TGC)
The ATLAS Trigger System
• primary trigger in trigger commissioning phase:
• minimum bias trigger scintillators
• MBTS hit on either of the detector sides
• >99.8 % efficient
• time difference between hits on both sides
is used to estimate beam background in
collision events
• other triggers run in parallel to compare their
performance to offline analysis
LHC State of the Art and News - Arno Straessner
Minimum Bias
Trigger Scintillator
40 MHz Collision Rate
75 kHz L1 Trigger
200 Hz EF Trigger
3 kHz L2 Trigger
~1.5
MB/evstorage
Hardware
ACTIVE
SoftwareMONITORING
MODE
12
The ATLAS Trigger System
• primary trigger in trigger commissioning phase:
• minimum bias trigger scintillators
• MBTS hit on either of the detector sides
• >99.8 % efficient
• time difference between hits on both sides
is used to estimate beam background in
collision events
• other triggers run in parallel to compare their
performance to offline analysis
LHC State of the Art and News - Arno Straessner
Minimum Bias
Trigger Scintillator
40 MHz Collision Rate
75 kHz L1 Trigger
200 Hz EF Trigger
3 kHz L2 Trigger
~1.5
MB/evstorage
Hardware
ACTIVE
SoftwareMONITORING
MODE
13
after offline
vertex
identification
The ATLAS Trigger System
LHC State of the Art and News - Arno Straessner 14
• example: turn-on curves of trigger efficiencies measured at 900 GeV
L1 jet trigger L1 e/γ trigger
• these triggers are ready to be used
• ATLAS is prepared for higher luminosities
• same holds for CMS, LHCb, and ALICE
Performance of the Inner Detector
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RMS dominated by
vertex resolution of 75 μmintrinsic accuracy:
pixel 10 μm (rφ) 115 μm (z)
SCT 17 μm (rφ) 580 μm (z)
TRT 130 μm
TRTSCT
Pixel
hits on reconstructed particle tracks:
overlay of many
events from one run
Reconstruction of Kaons and Lambdas
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• reconstructed mass peaks in good
agreement with PDG values
• well described by MC simulation
• very good understanding of detector
PDG: mK0=497.6 MeV
PDG: mΛ=1115.7 MeV
Tagging of b-Jets• important for top physics measurements, since BR(t → Wb)=100%
• essential for particle searches, e.g. b-associated production of SUSY-Higgs-Bosons
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secondary vertex
with 4 tracks
Calorimeter Performance
• e.m. shower profiles well described
• example: energy of photon candidates
in 2nd LAr calorimeter layer
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π0 →γγ
• reconstruction of π0 →γγ mass peak
• very good understanding of calorimetry
Missing Transverse Energy and Jet pT
• missing transverse energy agrees well with
MC predictions over 6 orders of magnitude
• missing ET resolution as expected from MC
• important ingredient for searches for SUSY
→ look for LSP signatures
• highest jet pT of 350 GeV observed in 7 TeV
collisions
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ATLAS Muon Spectrometer
• muon system with
large η coverage
• for momentum
measurement and
trigger
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• J/ψ → μμ signal observed
• muon tracks reconstructed in muon
spectrometer and inner detector
• gaussian-mean mass: 3.06±0.02 GeV
• resolution: 0.08±0.02 GeV
• Nsignal = 49±12
• Nbackground = 28±4
(computed in a mass range 3σ around the peak)
√s=7 TeV
∫Ldt=320 μb-1
Ready For Some Physics – An Overview
• inelastic pp scattering dominates
→ minimum bias
• QCD processes have large cross-
sections → 2-jet events, 3-jet
events, ...
• with and w/o b-jets
• many events with W and Z bosons
• LHC is a top quark factory
• new particles searches for:
Higgs (SM and supersymmetric),
SUSY, ..
• 13 orders of magnitude
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Measurement of Hadron Production
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• model independent measurement of
primary charged particle multiplicity
distributions from inelastic events
• kinematic range |η|<2.5 and pT> 500 MeV,
Nch≥ 1 in this phase space
• use MBTS single-arm scintillator trigger
for high efficiency in phase space
• no removal of Single Diffractive (SD)
component.
• correct reconstructed-track distributions
back to hadron level
• trigger and vertex corrections are
measured in data
• main systematics is from track
reconstruction efficiency (4% on dNch/dη) 1st ATLAS pp physics paper
Phys Lett B 688 (2010) 21
More Hadronic Activity Then Predicted
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• rate higher than modeled by PYTHIA and
PHOJET tunes, both at 0.9 TeV and 7 TeV
• similar observation by CMS
Parton Luminosities And Event Rates
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Process Evts (7 TeV)
in 100 pb-1
Ratio
7 TeV/14 TeV
QCD, pT>100 GeV 32 M 0.2
Z inclusive (NLO) 3 M (3% Z→ℓℓ) 0.4
W inclusive (NLO) 10 M (11% W→ℓv) 0.5
top pairs (NLO+NNLL) 16000 0.2
H (mH=150 GeV, NNLO) 1000 0.3
• examples of dominating partonic
processes at the LHC:
• several W→μv, W→ev and
Z→ee candidates observed at
7 TeV using ~8 nb-1 of data
W/Zq(')
q
(no selection cuts)
Hg
g
t
t
t
g
g
t
t
g
g
tt
t
Expectations For The 2010/2011 Run
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• the goal is to collect 1 fb-1 of data per experiment at √s=7 TeV (ATLAS, CMS)
• we expect 2.5 M selected events in the channels W→ev and W→μv each
• 5 times more than Tevatron today
• measurement of W boson mass possible, but systematics are challenging:
• lepton energy scale, missing pT calibration, PDF's, W pT, backgrounds, pile-up, ...
• top physics will be very interesting:
we will overtake
Tevatron with ~150 pb-1
Top Pair Yields
• cross-section measurements of top pairs at
7 TeV centre-of-mass energy
• top quark mass measurement
• aim for mtop by ATLAS and CMS
by the end of 2010
• systematics: jet energy scale, background,
pile-up, ...
Standard Model Higgs Searches
• LEP and Tevatron today: mH <114.4 GeV and 162 GeV<mH <166 GeV excluded (95% C.L.)
• gg→H→WW is the most sensitive channels in the relevant mass range
LHC State of the Art and News - Arno Straessner 28
7 TeV
• with two experiments and 1 fb-1 at √s=7 TeV:
• if no signal found: 95% CL exclusion between 140 GeV and 200 GeV possible
• evidence/discovery with 3-5 sigma for mH =160-170 GeV
SUSY Searches – mSUGRA
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• no mass degeneracy of particles and sparticles → breaking of super-symmetry
• gravity mediated SUSY breaking → mSUGRA model
• R-parity is conserved in mSUGRA:
→ SUSY production in pairs
→ lightest stable SUSY particle (LSP)
is the neutralino
• typical SUSY signatures:
• multi-jets, multi-leptons, missing ET ....
• understanding the SM background
is essential
LSP escapes detection missing ET
p p
g
Lq 0
2R
0
1
X q
SUSY Discovery Reach
• CMS expectation in
all-hadronic channels:
30
200 pb-1
LHC State of the Art and News - Arno Straessner
• ATLAS estimate for
lepton + jets + missing-ET channel:
• quickly beyond Tevatron reach with 100 pb-1
• squarks and gluinos with masses above
500 GeV can be discovered with 1fb-1
at 7 TeV
• higher energies in 2013 will push the search
window wide open
Conclusion
• LHC had a very good start in 2010 at 7 TeV record centre-of-mass energy
→ continuous machine development in parallel to data taking
• ATLAS, CMS, LHCb, and ALICE detectors are in good shape
• work ongoing to further improve performance
• first measurements of charged particle production at 0.9 TeV – 7 TeV
• Standard Model physics is about to take off
• new physics signatures are in close reach
• stay tuned:
www.atlas.ch
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