LHC@ATLAS Status and Recent Results. Ljiljana Simic Institute of Physics, Belgrade Gravity: New ideas for unsolved problems Divcibare, 2011 In honour of 67 th birthday of Milutin Blagojevic. 1. LHC. From the civil engineering, to the manufacturing of the various magnet
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Institute of Physics, Belgrade
Gravity: New ideas for unsolved problems Divcibare, 2011
In honour of 67th birthday of Milutin Blagojevic
From the civil engineering, to the manufacturing of the various magnet
types, each building block of this extraordinary machine required ambitious
leaps in innovation…
…There were many challenges - scientific, technological, managerial
that had to be met during the various phases of R&D, industrialization,
construction, installation and commissioning.
L. Evans (LHC Project Leader, 1994-2008).
“Thanks to the superb performance of the LHC, we have recorded a huge amount of new data
over the last month.This has allowed us to make great strides in our understanding of the
Standard Model and in the search for the Higgs bosonand new physics.”
ATLAS spokesperson Fabiola Gianotti, Geneva, 26 August 2011
“It’s great that the LHC’s fantastic performance this year has brought us this close to a region
of possible discovery. Whatever the final verdict on Higgs, we’re now living in very exciting times for all
involved in the quest for new physics.”
CMS spokesperson Guido Tonelli, Geneva, 26 August 2011
First 7 TeV collisions on March 30th
N = bunch population
nb = number of bunches
frev = revolution frequency
σx,y = colliding beam sizes
F = geometric factor
B = bending field
ρ = bending radius
p = momentum
e = charge
Determined by the maximum field of bending dipoles, B
Depends on machine parameters: charge per bunch (N), num. of bunches (nb) and transverse beam sizes (σ)
Event with 11 vertices and 1 Z
ATLAS: running smoothly with>95%data taking efficiency,
2.55 fb-1 of 2011 data recorded by 8 September!
Relative fraction of good quality data delivered by the various ATLAS
Subsystemsbetween 90 and 100%.
Subdetector#ChannelsApprox. Operational Fraction
Pixels 80 M 96.9%
SCT Silicon Strips 6.3 M 99.1%
TRT Transition Radiation Tracker 350 k 97.5%
LAr EM Calorimeter 170 k 99.5%
Tile calorimeter 9800 97.9%
Hadronic endcap LAr calorimeter 5600 99.6%
Forward LAr calorimeter 3500 99.8%
LVL1 Calo trigger 7160 99.9%
LVL1 Muon RPC trigger 370 k 99.5%
LVL1 Muon TGC trigger 320 k 100%
MDT Muon Drift Tubes 350 k 99.8%
CSC Cathode Strip Chambers 31 k 98.5%
RPC Barrel Muon Chambers 370 k 97.0%
TGC Endcap Muon Chambers 320 k 98.4%
submitted/published 63 papers
on collision data (15 in August)
Minimumbias, Jets, W,Z,
Prompt Photons, Dibosons,
Top quark, B physics, Higgs
arXiv: 1003.3124 ; arXiv:1012.5104
Phys. Lett. B 688,1,21; New J. Phys. 13,053033 (2011)
Fully inclusive-inelastic distributions in data with no model dependent corrections are
compared to different MC models, and significant differences were observed.
We have to use the soft QCD distributions to test the
phenomenological models and “tune” the Monte-Carlo
event generators to give the best description of the data
Pre-LHC models seen not to agree with most of the “soft”-QCD distributions
Full Inelastic Cross-Section
Acc. by Nature Comm.
Hot topic at hadron colliders since the 1960’s
An inelastic cross-section of 60.3 ±2.1 mbis measured for ξ> 5 x 10-6.
Compares to 64.7 mb from Pythia (1.2σ) and 73.5 mb from Phojet (2.5σ).
All the pre-LHC MC tunes considered show
lower activity than the data in the transverse region
Coming soon: interesting UE results with leading jet, in Z-boson events
Inclusive jet cross section
Dijet cross section
Multijet cross section
All measurements agree with SM expectation (so far)
Probing cross sections of ~10 pb
ATLAS (up to 0.7 fb -1)
The top quark is the heaviest known elementary particle,
and could play a special role in the Standard Model.
Its coupling to the Higgs boson is large, and it could also
play a role in electroweak symmetry breaking and
the generation of particle masses in alternatives to
the Higgs mechanism.
Dependence of σtt on √s from theoretical predictions based on a top mass of 172.5 GeV together with the dilepton, single lepton, and combined measurements from ATLAS
Measurements agree with QCD predictions
(although a little higher)
The combined upper limit on the Standard Model Higgs boson production cross section divided by the SM expectation as a function of Higgs mass (solid line), ATLAS-CONF-2011-135, 22/08/2011.
A wide range of Higgs search channels cover Higgs masses from 110 to 600 GeV
The Higgs boson mass ranges from
146 to 232 GeV
256 to 282 GeV
296 to 466 GeV
are excluded at 95% CL.
An excess of events is observed in the low mass range.
Its significance is at most approximately 2 above expected SM background.
Invariant mass distribution of jet pairs produced in association with a leptonically decaying W boson using 1.02 fb-1 of 2011 data.No excess over SM data.
Search for W’ with 1.04 fb -1 of 2011 data
exclude m(W’)<2.15 TeV for SM couplings
combining eν and μν decay modes
Dijet resonance search with 0.81 fb-1 of 2011 data excludes excited quarks with M(q*)<2.91 TeV and axigluons with M(A)<3.21 TeV and color octetscalar resonances with m(s8)<1.91 TeV. ATLAS-CONF-2011-095
Search for SUSY in final states with
one isolated e, µ, jets and ETmiss
with 165 pb-1
No sign of disagreement with SM expectation
The LHC and ATLAS are working very well
An abundance of important measurements now available at 7TeV
Now pushing deep into unexplored regions of phase space
with both simple and complex search topologies
Major increase in sensitivity with 1 - 2.3 fb-1 of 2011 data
As yet no conclusive evidence of Higgs production
ATLAS excludes at 95% CL production of Standard Model Higgs boson over 146-252 GeV, 256-282 GeV and 296-466 GeV