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SM measurements at ATLAS
Elena Oliver
(IFIC Valencia)

on behalf of the ATLAS collaboration

Saint Petersburg, Russia

QFTHEP '13 23 ­ 30 June 2013


Standard Model at ATLAS


We perform SM measurements:


to validate the SM in a new energy regime. to understand the background for other studies. to improve the precision of SM parameters. to constrain new physics contributions (like anomalous couplings)
69 SM studies have been published since LHC started!!



Categories:


Soft and Non-perturbative QCD (tunes,PDFs) Jet Physics (pQCD) Electroweak: W and Z, Dibosons, .... Direct Photons
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Soft QCD
Hard double-parton interactions in W( l)+2 jet events
J. Phys. 15 (2013) 033038 L= 36 pb-1 s = 7 TeV

Two hard parton interactions in the same hadron-hadron collision.
(D) DP

Fraction of W+2jets from hard double parton interaction at detector level: (D)DP

=0.08±0.01(stat.)±0.02(syst.)

Effective area parameter: eff = 15±3(stat.)
+5 -3

(syst.) mb

Consistent with previous measurements at lower s. DPI as background for many other Hard scales processes like W cross-section
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Jet Physics
Inclusive jet cross section comparison
Ref: arXiv:1304.4739

Ratio at s=2.76 TeV(L = 0.20 pb-1) and s =7 TeV agrees with fixed order NLO pQCD. pQCD can describe jet production at High pT. Ratio starts to show preference for certain PDF sets.

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Jet Physics
kt splitting scales in W l events
Eur. Phys. J. C, 73 5 (2013) 2432 L= 36 pb-1 s = 7 TeV

Four hardest splitting scales in Kt clustering.
Multi-leg+PS (ALPGEN-HERWIG, SHERPA) agrees well with data, NLO+PS (MC@NLO/POWHEG+PYTHIA) products significantly less hard activity than observed.
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Jet Physics
Jet Substructure
JHEP 1205 (2012) 128 L = 35 pb-1 s = 7 TeV

First particle-level measurement of these variables at the LHC Parton shower provides adequate description of the data. Jet mass exhibits the largest disagreements with Monte Carlo simulations.
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Properties: Jet mass, Splitting scales, N-subjettines
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W/Z Physics High-mass Drell-Yan differential cross-section
arXiv:1305.4192 L=4.9 fb-1 s =7 TeV

FEWZ NNLO QCD productions compatible with data for 5 PDF sets Potential to constrain large antiquark PDFs at large x MC predictions consistent with shape of measured mee distribution.

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W/Z Physics
Production of a W boson in association with a charm hadron
ATLAS-CONF-2013-045 L=4.6 fb-1 s=7 TeV

Predicted cross section depend on the choice of PDF Data agree with predictions for the epWZ and NNPDF2.3coll Larger discrepancies with MSTW2008, HERAPDF15 and NNPDF2.3

(W±D*)+(W±D)=84.3±2.4(stat)±7.2(syst)pb
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Direct Photons Isolated-photon pair production in pp collisions
arXiv:1211.1913 L= 4.9 fb-1 s = 7 TeV

Motivation: test of QCD background for H = 44.0 pb+3.2-4.2 LO 36 pb (20%) 2NNLO 44+6-5 pb (excellent agreement)

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Electroweak
Total ZZ and WZ production cross sections
ATLAS-CONF-2013-020 (ZZ) L=20 fb-1 s =8 TeV

ATLAS-CONF-2013-021(ZW) L=13 fb-1 s =8 TeV

Consistent with the SM expectations totZZ=7.1+0.5-0.4(stat.)±0.3(syst)±0.2(lumi.)pb totwz=20.3+0.8-0.7(stat.)+1.2-1.1(syst.)+0.7-0.6(lumi.) pb

ZZ

WZ

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Electroweak
Forward-backward asymmetry of Z/* bosons
ATLAS-CONF-2013-043 L=4.8 fb-1 s = 7 TeV

Use asymmetry to determine the effective weak mixing angle: sin2Weff=0.2297±0.0004(stat)±0.0009(syst) Consistent with previous measurements. Precision comparable with Tevatron.
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Conclusions


SM measurements are important to explore new regimes, to test theoretical predictions and PDFs and to improve precision of the SM parameters. New measurements for soft QCD, Jet production, Electroweak studies and Direct Photons. All ATLAS SM measurements can be found here:
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/StandardModelPublicResults
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Thanks for your attention

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Backup

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Moriond Summary SM Results

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W/Z Physics
Production cross section of jets in association with a Z boson
arXiv:1304.7098 L = 4.6 fb-1 s = 7 TeV

Large jet multiplicities, larger p

T

MC@NLO+PS clearly insufficient Multi-leg+PS generally consistent with data. Fixed order NLO QCD struggles to predict distribution of HT, ST, PTll

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W/Z Physics
Cross-section for W boson production in association with b-jets
arXiv:1302.2929 L = 4.6 fb-1 s = 7 TeV

Better with low pT of b-jet =7.1±0.5(stat.)±1.4(syst.)pb Consistent within 1.5 with MCFM = 4.70±0.09(stat)+0.60
-0.49(sca

l)±0.06(PDF)±0.16(non-pert)+0.52

-0.38(DPI

)pb

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