Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

ATLAS measures differential inclusive cross-sections for electrons and muons from heavy-flavour decays in 7 TeV pp collisions, subtracting W/Z/γ* contributions to isolate heavy-flavour production. The analysis uses data-driven lepton reconstruction and background subtraction with simulated samples (PYTHIA, POWHEG, HERWIG) and compares to FONLL predictions, as well as NLO and LO generators. The results show good agreement with FONLL within uncertainties and demonstrate sensitivity to NLL resummation terms at high pT; muon results extend to 4–100 GeV, while electrons are measured in 7–26 GeV. This validates heavy-flavour production modeling and informs fragmentation and decay parameters used in pQCD predictions.

Abstract

This letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 < pT < 100 GeV and within pseudorapidity |eta| < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < pT < 26 GeV and within |eta| <2.0, excluding 1.37<|eta|<1.52. Integrated luminosities of 1.3 pb-1 and 1.4 pb-1 are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-pT resummation, and to be sensitive to the effects of NLL resummation.

Figures (4)

• Figure 1: (a) Distribution of cluster transverse energy, $E_{\mathrm{T}}$, for the electron candidates. The simulation uses PYTHIA with the $W$ and $Z/\gamma^{\ast}$ components normalised to their NNLO total cross-sections and the heavy-flavour, conversion and hadronic components then normalised to the total expectation from the data. (b-d) PYTHIA simulations of the distributions of discriminating variables used to extract the electron heavy-flavour plus $W$/$Z$/$\gamma^{\ast}$ signal compared to data: (b) the ratio, $f_{\rm TR}$, between the number of high-threshold hits and all TRT hits on the electron track; (c) the number of hits, $n_{{\rm BL}}$, on the electron track in the pixel $B$-layer; (d) the ratio, $E/p$, between cluster energy and track momentum.
• Figure 2: The $\Delta p_{\mathrm{T}}$ distribution in the $p_{\mathrm{T}}$ bins 4-5 GeV (a), 10-11 GeV (b) and 18-20 GeV (c) for muon combined track candidates. The signal, early-$\pi/K$ and late-$\pi/K$ plus fakes components from simulation are shown. The early-$\pi/K$s are defined as those that decay close enough to the IP that the majority of hits on the ID track come from the decay muon.
• Figure 3: Muon differential cross-section as a function of the muon transverse momentum for $|\eta| <2.5$ compared to theoretical predictions. The Drell-Yan component corresponds to the $Z$/$\gamma^{\ast}$ for M$_{\mu^+ \mu^-} < 60$ GeV.
• Figure 4: (Left) Electron and muon differential cross-sections from heavy-flavour production as a function of the charged lepton transverse momentum for $|\eta| <2.0$ excluding the $1.37 < |\eta| <1.52$ region. (Right) Muon differential cross-section as a function of the muon transverse momentum for $|\eta| <2.5$. The data points include statistical and systematic uncertainties. The ratio of the measured cross-section and the other predicted cross-sections to the FONLL calculation is given in the bottom of each plot. The PYTHIA (L0) cross-sections are normalised to the data in order to compare the shape of the spectra.