Measurements of inclusive vector boson production from ATLAS

Abstract. The measurements of single W, Z boson production in association with jets probes QCD in a multi-scale environment. In this paper, we summarize the latest measurements of W+jet and Z+jet production and their ratio, extending to high jet multiplicities over a large set of kinematic distributions for proton-proton collisions at a center of mass energy of 7 TeV data at the LHC. The results are compared to the latest theoretical predictions of modern Monte Carlo generators. In addition, the measurement of production of vector bosons in association with heavy flavours allows to study c and b-quark parton distribution functions (PDFs) and gluon splitting effects. Also the corresponding measurements of W + c and Z + b(b) are reported and compared to predictions based on various PDFs in four and five-flavour schemes.

The mass spectrum is sensitive to the parton distribution functions (PDFs) for a wide kinematic range. The differential cross-section dσ/dm ll is described by perturbative QCD (pQCD) calculations at next-to-next-to-leading order (NNLO).
Studies of invariant mass shape at higher masses is interesting for searching of new resonances.

Not reviewed, for internal circulation only
Low Mass DY at 7 TeV m ll shape was measured down to 25 GeV in e channel and 12 GeV in µ channels.
Dominant uncertainty is due to imperfect knowledge of background (vary from 3.9% to 1.6% from lowest to highest mass bin in electron channel) Combined data are in agreement with measurements performed with 2010 and 2011 data sets and with NNLO theory predictions.
[ The measurement is performed in electron channel and covers the mass region 166-1500 GeV Dominant systematic uncertainties is due to electron identification for the lower mass bins and background subtraction in the higher mass bins Statistical uncertainties is larger than systematic for mee > 400 GeV The measurement was compared to the predictions of the PYTHIA, MC@NLO and SHERPA MC generators.
The deviations between predictions based on different PDFs are within the total uncertainty band assigned to the MSTW2008 prediction. The predictions show a good compatibility with data points.

Measurement forward-backward asymmetry A FB
The leptons produced in the annihilation process are asymmetric with respect to the quark direction in the rest frame of the di-lepton system.
The forward-backward asymmetry A FB was measured using angles in the Collins-Soper frame in electron (both central-central and central-forward) and muon channels.
Electron central-forward (|ηe 1 | < 2.5, |ηe 2 | > 2.5) measurement is most sensitive to forward-backward asymmetry. Measurements of the leptonic effective weak mixing angle, sin 2 θ eff W , have been made using the raw A FB spectra. The dominant uncertainty is due to the limited knowledge of the proton parton density function. Presented measurement is in agreement with with SM and most precise measurements. Probe of p Z T spectrum can be studied by the reconstructed p ll T and alternatively by the φ * = tan((π − ∆φ)/2) sin(θ * ), where cos(θ * ) = tanh((η − − η + )/2) is a complementary to p Z T measurement but have smaller uncertainties. The ResBos-GNW prediction agrees with the data within 5-7%, NLO+NNLL calculation matches the data within 10-12%. The prediction uncertainties are almost sufficient to cover the difference with the data.
Born-level combined result was compared to theoretical predictions from Fewz, Dynnlo, ResBos (all with CT10 PDFs) and NLO+NNLL (with CTEQ6m PDFs) calculation. Not reviewed, for internal circulation only MC tuning using Z pT and φ * data.
Comparison of the Pythia8 generator with the 4C and AZ tunes to the muon-channel Z pT data and electron-channel φ * data are presented The tuned predictions agree with the measurement to better than 2% in the range used for the tuning, below Z pT = 50 GeV At higher transverse momentum, discrepancies of around 15% for Pythia8 remain, indicating the limited accuracy of the NLO signal matrix element and suggesting the need for contributions from higher parton multiplicity.
[GeV] inclusive 4l production cross-section were measured at 4e 4µ and 2e2µ final states for each 7 TeV and 8 TeV datasets.

Summary
Several properties of Z /γ * production at ATLAS were measured at higher accuracy using high statistics data (millions of Z events).
Inclusive and differential Z → ll cross-section measurements are sensitive to PDFs and provide new constraints for future PDF-sets Cross-section measurements in bins of boson transverse momentum provide precision tests of QCD dynamics from soft re-summation effects to hard multiple jet emission.
Analysis of the 2011 data is almost finalized.
Several 8 TeV analyses are in progress