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[email protected] 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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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









30 march 2010 first 7 tev collisions
30 March, 2010, First 7 TeV collisions

First 7 TeV collisions on March 30th

What do experiments want
What do experiments want?

High energy

High luminosity

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)

Lhc design parameters
LHC design parameters

  • Excellent LHC performance:

  • maximum #bunches - 1331, peak stable luminosity delivered: 2.37x1033cm-2s-1

  • maximum luminosity delivered:

  • in one day - 97.4pb-1, in7 days - 499.45 pb-1(02- 08/08/11)

  • - longest time of stable beam – 26 h

  • - maximum peak events number per bunch crossing:14.01

Pile-up challenge in 2011

Event with 11 vertices and 1 Z

  • Detailed ATLAS performance studies in

  • presence of high pile-up

  • - Understanding impact with data & simulation

ATLAS: running smoothly with>95%data taking efficiency,

2.55 fb-1 of 2011 data recorded by 8 September!


Atlas operation status
ATLAS Operation Status

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%

Performance for physics
Performance for physics

mee (GeV)

PTjet (GeV)

mµµ (GeV)



submitted/published 63 papers

on collision data (15 in August)

Minimumbias, Jets, W,Z,

Prompt Photons, Dibosons,

Top quark, B physics, Higgs

Supersymmetry, Exotics,

Heavy Ions

Soft qcd in a new high energy and high multiplicity frontier
Soft-QCDin a new high energy and high multiplicity frontier

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

Soft qcd

Underlying Event

Full Inelastic Cross-Section



arXiv: 1104.0326

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

Jets impresiv agreement between data and theory
Jets: Impresiv agreement between data and theory

Inclusive jet cross section

Dijet cross section

Multijet cross section

  • Jet production is the dominant high-pT process in p-p collisions.

  • Provides a stringent test of QCD at the TeV scale.

  • Inclusive and dijet cross sections are presented covering a phasespace among the widest currently accessed in collider physics.

  • Measurements in which specific dijet and multijet configurations are selected to enhance sensitivity to higher order effects, allowing the study of QCD radiation at large rapidity intervals.

  • Measurements of heavy flavours in jets, the internal structure of jets,

  • and of single-jet mass which carry information about soft physics and the QCD cascade..


Atlas w z and top cross sections summary
ATLAS W, Z and Top Cross Sections Summary








All measurements agree with SM expectation (so far)

Probing cross sections of ~10 pb


Top quark pair cross section summary
Top Quark Pair Cross Section Summary

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)


Higgs search at atlas
Higgs search at ATLAS

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.

Channels included:


WH lbb

ZH llbb








Searches for physics beyond sm
Searches for Physics Beyond SM

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

arXiv: 1108.1316

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