Pheno 2011 Madison, WisconsinMay 09, 2011

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%

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

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)

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

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

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

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

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

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

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

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

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!

09 May 2011 Srivas Prasad, Harvard University 16

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h

09 May 2011 Srivas Prasad, Harvard University 19