This paper presents measurements from the ATLAS experiment of the forward-backward asymmetry in the reaction $pp\rightarrow Z/\gamma^{*}\rightarrow l^{+}l^{-}$, with $l$ being electrons or muons, and the extraction of the effective weak mixing angle. The results are based on the full set of data collected in 2011 in $pp$ collisions at the LHC at $\sqrt{s}$ = 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$. The measured asymmetry values are found to be in agreement with the corresponding Standard Model predictions. The combination of the muon and electron channels yields a value of the effective weak mixing angle of $0.2308 \pm 0.0005 \mathrm{(stat.)} \pm 0.0006 \mathrm{(syst.)} \pm 0.0009\mathrm{(PDF)}$, where the first uncertainty corresponds to data statistics,the second to systematic effects and the third to knowledge of the parton density functions. This result agrees with the current world average from the Particle Data Group fit.
Summary of central values and total systematical uncertainties for the $A_{FB}$ values unfolded for mass bin migration and dilution effects in the CC electron channel, CF electron channel and muon channel.
Summary of central values and total systematical uncertainties for the unfolded $A_{FB}$ values which takes into account mass bin migration only in CC electron channel for Born and Dressed leptons. Dressed leptons are constructed by adding 4-vectors of the bare lepton and all real photons coming from the boson/lepton decay within a $\Delta R<$0.1.
Summary of central values and total systematical uncertainties for the unfolded $A_{FB}$ values which takes into account mass bin migration only in CF electron channel for Born and Dressed leptons. Dressed leptons are constructed by adding 4-vectors of the bare lepton and all real photons coming from the boson/lepton decay within a $\Delta R<$0.1.
This letter reports a measurement of the muon charge asymmetry from W Boson produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W Boson to muon decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb-1. The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.
The muon charge asymmetry from $W$-boson decays in bins of absolute pseudorapidity. Note that these numbers are taken from the journal version which differ slightly from those in the archive version 1.
The forward-backward charge asymmetry for the process $q\bar{q} \rightarrow Z/\gamma^{\ast} \rightarrow \mu^{+}\mu^{-}$ is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton proton collision data collected with the LHCb detector at $\sqrt{s} = 7$ and 8\tev, corresponding to integrated luminosities of $1$fb$^{-1}$ and $2$fb$^{-1}$ respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be $$sin^{2}\theta_{W}^{eff} = 0.23142 \pm 0.00073 \pm 0.00052 \pm 0.00056 $$ where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.
Values for $A_{\rm{FB}}$ with the statistical and positive and negative systematic uncertainties for $\sqrt{s}$ = 7 TeV data. The theoretical uncertainties presented in this table, corresponding to the PDF, scale and FSR uncertainties described in Sec. 5, affect only the predictions of $A_{\rm{FB}}$ and the sin$^2\theta^{\rm{eff}}_{\rm W}$ determination, and do not apply to the uncertainties on the measured $A_{\rm{FB}}$.
Values for $A_{\rm{FB}}$ with the statistical and positive and negative systematic uncertainties for $\sqrt{s}$ = 8 TeV data. The theoretical uncertainties presented in this table, corresponding to the PDF, scale and FSR uncertainties described in Sec. 5, affect only the predictions of $A_{\rm{FB}}$ and the sin$^2\theta^{\rm{eff}}_{\rm W}$ determination, and do not apply to the uncertainties on the measured $A_{\rm{FB}}$.
We present measurements of Collins asymmetries in the inclusive process $e^+e^- \rightarrow h_1 h_2 X$, $h_1h_2=KK,\, K\pi,\, \pi\pi$, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb$^{-1}$ collected by the BaBar experiment at the PEP-II $B$ factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike- to like-sign, and unlike- to all charged $h_1 h_2$ pairs, which increase with hadron energies. The $K\pi$ asymmetries are similar to those measured for the $\pi\pi$ pairs, whereas those measured for high-energy $KK$ pairs are, in general, larger.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for kaon pairs. In the first column, the $z$ bins and their respective mean values for the kaon in one hemisphere are reported; in the following column, the same variables for the second kaon are shown; in the third column the mean value of $\sin^2\theta_{th}/(1+\cos^2\theta_{th})$ is summarized, calculated in the RF12 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $KK$ pair and dividing by the number of $KK$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for kaon pairs. In the first column, the $z$ bins and their respective mean values for the kaon in one hemisphere are reported; in the following column, the same variables for the second kaon are shown; in the third column the mean value of $\sin^2\theta_{2}/(1+\cos^2\theta_{2})$ is summarized, calculated in the RF0 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $KK$ pair and dividing by the number of $KK$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for $K\pi$ hadron pairs. In the first column, the $z$ bins and their respective mean values for the hadron ($K$ or $\pi$) in one hemisphere are reported; in the following column, the same variables for the second hadron ($K$ or $\pi$) are shown; in the third column the mean value of $\sin^2\theta_{th}/(1+\cos^2\theta_{th})$ is summarized, calculated in the RF12 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $K\pi$ pair and dividing by the number of $K\pi$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
Using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally-segmented electromagnetic and hadronic calorimeters. The underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.
Asymmetry in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.
Asymmetry in 7 TeV P-P collisions.
This paper reports inclusive and differential measurements of the $t\bar{t}$ charge asymmetry $A_{\textrm{C}}$ in 20.3 fb$^{-1}$ of $\sqrt{s} = 8$ TeV $pp$ collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the $t\bar{t}$ system. The $t\bar{t}$ pairs are selected in the single-lepton channels ($e$ or $\mu$) with at least four jets, and a likelihood fit is used to reconstruct the $t\bar{t}$ event kinematics. A Bayesian unfolding procedure is performed to infer the asymmetry at parton level from the observed data distribution. The inclusive $t\bar{t}$ charge asymmetry is measured to be $A_{\textrm{C}} = 0.009 \pm 0.005$ (stat.$+$syst.). The inclusive and differential measurements are compatible with the values predicted by the Standard Model.
The inclusive $t\bar{t}$ production charge asymmetry, $A_C$, with statistical and systematic uncertainties combined.
Measured charge asymmetry, $A_C$, values for the electron and muon channels combined after unfolding as a function of the $t\bar{t}$ invariant mass, $m_{t\bar{t}}$. The quoted uncertainties include statistical and systematic components after the marginalisation.
Measured charge asymmetry, $A_C$, values for the electron and muon channels combined after unfolding as a function of the $t\bar{t}$ velocity along the z-axis, $\beta_{z,t\bar{t}}$. The quoted uncertainties include statistical and systematic components after the marginalisation.
In the $pp \rightarrow t\bar{t}$ process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} =$ 8 TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair ($m_{t\bar{t}} > $ 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within $-$2 $ < |y_t| - |y_{\bar{t}}| <$ 2 is measured to be 4.2 $\pm$ 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three $t\bar{t}$ mass bins is also presented.
The measured charge asymmetry after the unfolding to parton level in four intervals of the invariant mass of the $t\bar{t}$ system. The phase space is limited to $|(\Delta |y|)|<$ 2. The uncertainties correspond to the sum in quadrature of statistical and systematic uncertainties (for the data) or to the theory uncertainty (for the SM prediction).
The t t-bar charge asymmetry is measured in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data, collected with the CMS experiment at the LHC, correspond to an integrated luminosity of 19.7 inverse femtobarns. Selected events contain an electron or a muon and four or more jets, where at least one jet is identified as originating from b-quark hadronization. The inclusive charge asymmetry is found to be 0.0010 +/- 0.0068 (stat) +/- 0.0037 (syst). In addition, differential charge asymmetries as a function of rapidity, transverse momentum, and invariant mass of the t t-bar system are studied. For the first time at the LHC, the measurements are also performed in a reduced fiducial phase space of top quark pair production, with an integrated result of -0.0035 +/- 0.0072 (stat) +/- 0.0031 (syst). All measurements are consistent within two standard deviations with zero asymmetry as well as with the predictions of the standard model.
Corrected asymmetry as a function of $|y_\mathrm{t\bar{t}}|$ in the fiducial phase space. The value 9999 is used as a placeholder for infinity. The correlation matrix for these values can be found in a separate table.
Correlation matrix for the asymmetries as a function of $|y_\mathrm{t\bar{t}}|$ in the fiducial phase space. Both statistical and systematic effects are considered.
Corrected asymmetry as a function of $p_\text{T}^\mathrm{t\bar{t}}$ in the fiducial phase space. The value 9999 is used as a placeholder for infinity. The correlation matrix for these values can be found in a separate table.
The t t-bar charge asymmetry in proton-proton collisions at sqrt(s) = 7 TeV is measured using the dilepton decay channel (ee, e mu, or mu mu). The data correspond to a total integrated luminosity of 5.0 inverse femtobarns, collected by the CMS experiment at the LHC. The t t-bar and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be Ac = -0.010 +/- 0.017 (stat.) +/- 0.008 (syst.) and Ac[lep] = 0.009 +/- 0.010 (stat.) +/- 0.006 (syst). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the t t-bar system. All measurements are consistent with the expectations of the standard model.
The unfolded ASYMC and ASYMC(LEPTON) measurements.
Measurements of the unfolded ASYMC(LEPTON) values in bins of M(TOP TOPBAR).
Measurements of the unfolded ASYMC(LEPTON) values in bins of ABS(YRAP(TOP TOPBAR)).
A measurement of the forward-backward asymmetry (A[FB]) of Drell-Yan lepton pairs in pp collisions at sqrt(s) = 7 TeV is presented. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 5 inverse femtobarns. The asymmetry is measured as a function of dilepton mass and rapidity in the dielectron and dimuon channels. Combined results from the two channels are also presented. The A[FB] measurement in the dimuon channel and the combination of the two channels are the first such results obtained at a hadron collider. The measured asymmetries are consistent with the standard model predictions.
The unfolded mu+mu- measurement of AFB at the Born level in four rapidity bins. The errors on data are statistical only.
The unfolded e+e- measurement of AFB at the Born level in four rapidity bins. The errors on data are statistical only.
Unfolded combined measurements of AFB in each M-|y| bin (mu+mu- and e+e- combined).
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