Jon Butterworth UCL for the ATLAS collaboration First look with a new detector First look in a new kinematic regime Soft ish physics and tuning Hard physics and cross sections QCD plus ID: 504883
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Slide1
QCD Results from ATLAS
Jon Butterworth (UCL) for the ATLAS collaboration
First look with a new detectorFirst look in a new kinematic regimeSoft (-ish) physics and tuningHard physics and cross sectionsQCD plus…Slide2
Inner Detector (|
|<2.5, B=2T): Si Pixels, Si strips, Transition Radiation detector (straws) Precise tracking and vertexing,e/
separation
Momentum resolution: /pT ~ 3.8x10-4 pT (GeV) 0.015
Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons~108 electronic channels3000 km of cables
Muon Spectrometer
(||<2.7) : air-core toroids with gas-based muon chambersMuon trigger and measurement with momentum resolution < 10% up toE ~ 1 TeV
EM calorimeter: Pb-LAr Accordion
e/
trigger, identification and measurementE-resolution: /E ~ 10%/E
HAD calorimetry
(||<5): segmentation, hermeticityFe/scintillator Tiles (central), Cu/W-LAr (fwd)Trigger and measurement of jets and missing ETE-resolution:/E ~ 50%/E 0.03
3-level trigger
reducing the rate
from 40 MHz to
~200 HzSlide3
28/9/2010
JMB/ATLAS/Trento
3Slide4
ATLAS Operation
28/9/2010
JMB/ATLAS/Trento4Slide5
ATLAS Operation
28/9/2010JMB/ATLAS/Trento
5~95% data taking efficiencySlide6
Luminosity
Monitored by using rates in low-angle detectors & endcapsAbsolute calibration from van
der Meer scansUncertainty ~11% dominant error from knowledge of beam current28/9/2010JMB/ATLAS/Trento6Slide7
Trigger Performance Examples
28/9/2010JMB/ATLAS/Trento
7
Electron efficiency
Muon efficiency Jet efficiency Slide8
First collision results
Particle multiplicities in 900 GeV collisions Phys Lett B 688, 1 (2010) pp.21-4
Demonstrate excellent modeling of the detector 28/9/2010JMB/ATLAS/Trento8Slide9
First collision results
Particle multiplicities in 900 GeV collisions Phys Lett B 688, 1 (2010) pp.21-4
Demonstrate excellent modeling of the detector and reasonable modeling of the soft QCD physics (of which more later) 28/9/2010JMB/ATLAS/Trento9Slide10
Tracker alignment (Pixel)
28/9/2010
JMB/ATLAS/Trento10ATLAS-CONF-2010-067Slide11
Tracker alignment (SCT)
28/9/2010
JMB/ATLAS/Trento11ATLAS-CONF-2010-067Slide12
Tracker alignment (TRT)
28/9/2010JMB/ATLAS/Trento
12ATLAS-CONF-2010-067Slide13
First 7 TeV Results
28/9/2010
JMB/ATLAS/Trento13Slide14
…and also 2.36 TeV
28/9/2010
JMB/ATLAS/Trento14
NB Change of default (red) MC
ATLAS-CONF-2010-024, ATLAS-CONF-2010-047Slide15
Understanding the environment
Previous results in well-defined but limited phase space all events with > 0 stable charged particles with pT > 500
MeV, |h|<2.5.Extending this would be goodSensitive to unknown diffractive componentDisrupts tuning, and less relevant for underlying event 28/9/2010JMB/ATLAS/Trento
15Slide16
Extend to lower pT
28/9/2010
JMB/ATLAS/Trento16
ATLAS-CONF-2010-046Slide17
Diffraction and the underlying event
Diffraction contributes strongly to “minimum bias” (and so to pile up) but not much the “underlying event”Diffraction in pp is poorly understood even at lower energies.
However, lower multiplicity is general propertyMeasure “next-to-minimum” biasApply a higher multiplicity cut to reduce diffractionTune to this (AMBT1)28/9/2010JMB/ATLAS/Trento17Slide18
Diffraction and the underlying event
28/9/2010JMB/ATLAS/Trento
18ATLAS-CONF-2010-031Slide19
Diffraction and the underlying event
28/9/2010JMB/ATLAS/Trento
19ATLAS-CONF-2010-031Slide20
Diffraction and the underlying event
Not only is the new tune an improvement, but the older tunes seem to do better at the “reduced diffractive” sample.
28/9/2010JMB/ATLAS/Trento20Slide21
…and also 2.36 TeV
28/9/2010JMB/ATLAS/Trento
21ATLAS-CONF-2010-024, ATLAS-CONF-2010-047Slide22
Underlying event
Comparison to underlying event measurement
28/9/2010JMB/ATLAS/Trento22
ATLAS-CONF-2010-081Slide23
Focus on diffraction
Compare sample with exactly one side hit in the MBTS against those with any/both hitEnhances single diffractive in the one-side sample
28/9/2010JMB/ATLAS/Trento23ATLAS-CONF-2010-048
Proportional of single-sided events in data = Slide24
Particle correlations
Plot the f distribution of all tracks relative to the highest
pT track. 28/9/2010JMB/ATLAS/Trento24
ATLAS-CONF-2010-082Slide25
Particle correlations
Plot the f
distribution of tracks relative to the highest pT track separately with same sign and opposite sign h, and substract. 28/9/2010JMB/ATLAS/Trento
25
ATLAS-CONF-2010-082
ATLAS-CONF-2010-082Slide26
Hard QCD : Jet Shapes
28/9/2010JMB/ATLAS/Trento
26ATLAS-CONF-2010-049
4
GeV
< Track jet pT < 6 GeV 15 GeV < Track jet p
T < 24 GeV Slide27
Hard QCD : Jet Shapes
28/9/2010JMB/ATLAS/Trento
27
CERN
-PH-EP-2010-
034To be submitted to EPJCSlide28
Jet Energy Scale
Current strategyElectromagnetic scale from test beam measurements (electrons & muons)
Correction for Difference in hadronic/electromagnetic responseLosses in material in front of CalorimeterLeakage from back of the calorimeterMagnetic field Cluster and jet algorithmic inefficiencyare all dealt with by simulation28/9/2010
JMB/ATLAS/Trento
28
CERN-PH-EP-2010-034To be submitted to EPJCSlide29
Jet Energy Scale Uncertainty
Dominant systematic in ~all measurements involving jets or missing energy.Uncertainties from Translating test beam EM scale to in situ (3-4%)
Material knowledge/simulation ~2%Noise <3%Beamspot position <1%“closure test” <2%Hadronic (GEANT) shower model ~4%Hadronic (generator) show model <4%Pile up: variable. (<1% for cross section measurement)Intercalibration in y (from in situ dijet balance) <3%
For
dijet
measurements, decorrelated error ~3% 28/9/2010JMB/ATLAS/Trento29Slide30
Jet Energy Scale Uncertainty
< 9% everywhere. ~6% for high pT
~40% error on jet cross sectionChecked with extensive single-particle studies in collision data and soon by photon-jet balance20/9/2010JMB/ATLAS/Coseners30
CERN
-PH-EP-2010-
034To be submitted to EPJCSlide31
Hard QCD : Jet Cross Sections
28/9/2010JMB/ATLAS/Trento
31
CERN
-PH-EP-2010-
034To be submitted to EPJCSlide32
Inclusive Jet cross sections
28/9/2010JMB/ATLAS/Trento
32
CERN
-PH-EP-2010-
034To be submitted to EPJCSlide33
Dijet cross sections
28/9/2010JMB/ATLAS/Trento
33
c
= (1+cos
q*)/(1-cos q*)CERN-PH-EP-2010-034To be submitted to EPJCSlide34
Jet cross sections vs MC
28/9/2010JMB/ATLAS/Trento
34
CERN
-PH-EP-2010-
034To be submitted to EPJCSlide35
Multijets
28/9/2010
JMB/ATLAS/Trento35ATLAS-CONF-2010-084
p
T
> 30 GeV |y| < 2.8 Ratio of Njet to (N-1)jet cross section vs NSlide36
Multijets
28/9/2010JMB/ATLAS/Trento
36ATLAS-CONF-2010-084pT
> 30
GeV |y| < 2.8 HT is the sum of the transverse energy in the jetsSlide37
Azimuthal Jet Decorrelations
28/9/2010
JMB/ATLAS/Trento37ATLAS-CONF-2010-084Slide38
Azimuthal Jet Decorrelations
28/9/2010
JMB/ATLAS/Trento38ATLAS-CONF-2010-084Slide39
Minijet Veto
Select dijet events; jet p
T > 30 GeV, average jet pT > 60 GeV. Two selections:A:boundary jets are the highest pT jetsB:boundary jets are the most forward/backward satisfying the aboveVeto on any extra jets between the boundary jets with pT>30
GeV
28/9/2010JMB/ATLAS/Trento39
ATLAS-CONF-2010-085Slide40
QCD plus: Vector bosons
28/9/2010JMB/ATLAS/Trento
40
Cross sections and charged lepton asymmetry (W)
ATLAS-CONF-2010-051Slide41
QCD plus: Vector bosons
28/9/2010JMB/ATLAS/Trento
41Cross sections (Z)
ATLAS-CONF-2010-076Slide42
QCD plus: Vector bosons
28/9/2010
JMB/ATLAS/Trento42Slide43
QCD plus: Vector bosons
28/9/2010JMB/ATLAS/Trento
43Slide44
QCD plus: Top
28/9/2010
JMB/ATLAS/Trento44
Jet
pT > 20 GeV
(anti-kt)
At least one b-tagged jet
ATLAS-CONF-2010-087Slide45
QCD plus: Searches
Seach for resonances in dijet mass distribution.
q* mass limit ~ 1.26 TeV28/9/2010JMB/ATLAS/Trento45
arXiv:1008.2461
(accepted by PRL)Slide46
Summary
ATLAS and the LHC are performing very well Detailed studies of the soft QCD environment, and MC tuning, well underwayJet cross sections measured, agree with NLO QCD
W & Z cross sections and asymmetries measuredStudies of jet+W,Z well advanced, t+jets underwayNew physics searches exploiting the understanding of QCD and of the detectors.28/9/2010JMB/ATLAS/Trento
46Slide47
Minijet Veto
Select dijet events; jet p
T > 30 GeV, average jet pT > 60 GeV. Two selections:A:boundary jets are the highest pT jetsB:boundary jets are the most forward/backward satisfying the aboveVeto on any extra jets between the boundary jets with pT>30
GeV
28/9/2010JMB/ATLAS/Trento47