pheno 2011madison, wisconsin may 09, 2011
DESCRIPTION
W/Z and Di-Boson Results from ATLAS Srivas Prasad Harvard University On behalf of the ATLAS Collaboration. Pheno 2011Madison, Wisconsin May 09, 2011. Outline. W, Z Measurements with Electrons and Muons W and Z Inclusive Cross-section Forward Z Cross-section W Charge Asymmetry - PowerPoint PPT PresentationTRANSCRIPT
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Pheno 2011 Madison, WisconsinMay 09, 2011
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W, Z Measurements with Electrons and Muons W and Z Inclusive Cross-section Forward Z Cross-section W Charge Asymmetry
W, Z Observation with Taus
W and Z + jets
Diboson Results W and Z WW Cross-section
09 May 2011 Srivas Prasad, Harvard University 2/13
Most results for full 2010 dataset
LINT 31-37 pb-1 depending on analysis Uncertainty brought down to
3.4%
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Compare to theory at NNLO in QCDVital for detector performance
High pT leptons: reconstruction / trigger / identification efficiencies, resolution, scale…
ETmiss resolution and scale
Update 320 nb-1 result with x100 data
Improved analysis e.g. tag-and-probe, binning
Systematics reduced by factor of three ET
miss scale/resolution largest experimental uncertainty (2%)
09 May 2011 Srivas Prasad, Harvard University 3/13
ATLAS-CONF-2011-041
EXCELLENT AGREEMENT BETWEEN ELECTRON AND MUON RESULTS
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Z→
Z→ee: central-forward
Define fiducial cross-sections using analysis kinematic requirements All detector corrections included
Most precise experimental measurements for theory comparison
Extend Z cross-section measurement using forward electrons (2.5<||<4.9) Expands range of sensitivity to parton-x Reduces extrapolation uncertainty FID = 0.179 ± 0.004 (sta) ± 0.017 (sys) ±
0.006 (lum)09 May 2011 Srivas Prasad, Harvard University 4/13
ATLAS-CONF-2011-041
FIDUCIAL CROSS-SECTION [nb]
W→
4.959 ± 0.015 (sta) ± 0.120 (sys) ± 0.181 (lum)
W→e
4.877 ± 0.015 (sta) ± 0.138 (sys) ± 0.166 (lum)
Z→ 0.456 ± 0.004 (sta) ± 0.005 (sys) ± 0.015 (lum)
Z→ee0.433 ± 0.004 (sta) ± 0.016 (sys) ±
0.015 (lum)
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09 May 2011 Srivas Prasad, Harvard University 5/13
ATLAS-CONF-2011-041
Uncertainty from extrapolation to full phase space, using Pythia / MRST LO*
RESULTS AGREE (∼5% UNCERTAINTY) WITH NNLO PREDICTIONS
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More valence u in proton: W+ favored Rapidity dependence probes u and
d quark parton distribution functions Measurement versus muon rapidity Luminosity and systematics cancel
09 May 2011 Srivas Prasad, Harvard University 6/13
arxiv:1103.2929Submitted to Phys. Lett. B
valence
sea
valence
sea
Dominant systematic from statistics on tag-and-probe studiesALREADY CONSTRAINS LIGHT QUARK PDFS FOR MEDIUM AND LOW-X
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Impressive control over reconstruction
W→hadronic observation with 546 nb-1
Z observed with e, ehadronic and hadronic modes
Important stepping stone toward H→ Yields compatible with SM expectations
09 May 2011 Srivas Prasad, Harvard University 7/13
ATLAS-CONF-2011-010ATLAS-CONF-2011-045
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09 May 2011 Srivas Prasad, Harvard University 8/13
ATLAS-CONF-2011-042ATLAS-CONF-2011-060
Jets from pileup or near leptons (R≤0.5) removed Background:
Mainly top at higher multiplicities QCD especially in electron channel (estimated from data)
Bin-by-bin unfolding for detector and acceptance Systematics: jet scale (dominant, 10-20%), pileup
removal
Test of QCD and Monte Carlo predictions NLO predictions Matrix element and parton shower,
matching Dependence on QCD scale
Background to top, di-bosons, new physics
Jet defined with anti-kT algorithm (R=0.4) |yjet|<2.8 pT>20 GeV for W+jet, 30 GeV for Z+jet
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09 May 2011 Srivas Prasad, Harvard University 9/13
ATLAS-CONF-2011-042ATLAS-CONF-2011-060
Z+jet, ee
W+jet,
Similar results in electron and muon channelsGood agreement with MCFM, Alpgen and Sherpa
Pythia not expected to describe distributions for more than one jet
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09 May 2011 Srivas Prasad, Harvard University 10/13
ATLAS-CONF-2011-042ATLAS-CONF-2011-060
Z+jet,
W+jet, e
pT spectra, multiplicities useful in background estimation
Ratios constrain s, PDFs
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Highest di-boson processes Study triple gauge couplings (TGC) Probe ZZ and Z (forbidden at
tree level in Standard Model)
Signature: add isolated to W/Z signature (isolation energy, distance from lepton)
192 (48) W (Z) candidates Signal extracted from 2D sideband
using photon isolation: 80% purity
09 May 2011 Srivas Prasad, Harvard University 11/13
ATLAS-CONF-2011-013
Z
EXCELLENT AGREEMENT WITH SM PREDICTIO
NS
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Probe electroweak theory at high energy
Study triple gauge couplings BSM expectations of anomalous
values Important background to H→WW WW
NLO = [44±3] pb
Signature has opposite sign leptons, large ET
miss, reduced jet activity Backgrounds: 1.7±0.6 events
Veto on Z mass, high pT jet W+jets from loose lepton control
Eight candidate events seen (5 in e) 3 signal signal significance09 May 2011 Srivas Prasad, Harvard University 12/13
arXiv:1104.5225Submitted to PRL
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Reviewed W/Z results from ATLAS with 2010 dataset Powerful tests of pQCD theoretical predictions; constraining
PDFs Excellent understanding of detector performance demonstrated W/Z Observations with made; demonstrate reconstruction More differential measurements upcoming
First Diboson results for WW, W and Z In agreement with Standard Model expectations Currently limited statistically
2011 data will dramatically sharpen results Allow WZ and ZZ measurements TGC will become interesting! Differential W/Z measurements will further constrain PDFs
09 May 2011 Srivas Prasad, Harvard University 13/13
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Maximum instantaneous luminosity of 8.8 × 1032 cm-2 s-
1!
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h
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