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 double-differential inclusive jet cross section is measured as a function of jet transverse momentum pT and absolute rapidity y, using proton-proton collision data collected with the CMS experiment at the LHC, at a center-of-mass energy of sqrt(s) = 2.76 TeV and corresponding to an integrated luminosity of 5.43 inverse picoboarns. Jets are reconstructed within the pT range of 74 to 592 GeV and the rapidity range |y| < 3.0. The reconstructed jet spectrum is corrected for detector resolution. The measurements are compared to the theoretical prediction at next-to-leading-order QCD using different sets of parton distribution functions. This inclusive cross section measurement explores a new kinematic region and is consistent with QCD predictions.
No description provided.
No description provided.
No description provided.
The production of Z bosons in pPb collisions at sqrt(s[NN]) = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.
Differential cross section of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Forward-backward asymmetry (AFB) distribution of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Differential cross section of the Z bosons in pPb collisions as a function of transverse momentum in the fiducial region for the combined leptonic decay channel.
We present an analysis of the decay $D^{+} \to K^{-} \pi^+ e^+ \nu_e$ based on data collected by the BESIII experiment at the $\psi(3770)$ resonance. Using a nearly background-free sample of 18262 events, we measure the branching fraction $\mathcal{B}(D^{+} \to K^{-} \pi^+ e^+ \nu_e) = (3.71 \pm 0.03 \pm 0.08)\%$. For $0.8
The $S$-wave phase $\delta_{S}$ measured in the 12 $m_{K\pi}$ bins with statistical and systematic uncertainties. The systematic uncertainties include: (I) background fraction, (II) background shape, (III) the $\bar K_{0}^{*}(1430)^{0}$ mass and width, (IV) additional resonances, (V) tracking efficiency correction, (VI) PID efficiency correction.
Average form-factor products in the $K^{*}$-dominated region.
The quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at sqrt(s[NN]) = 2.76 TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity (Delta eta) and relative azimuthal angle (Delta phi) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pt) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pt, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pt. A centrality-dependent excess of low-pt particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pt particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of Delta eta approximately 1 and Delta phi approximately 1.
Symmetrized dEta distributions (projected over |dPhi|<1) of background-subtracted particle yields correlated to PbPb and pp inclusive jets with pT > 120 GeV for tracks with 1 < pT < GeV in 50-100% central events.
Symmetrized dEta distributions (projected over |dPhi|<1) of background-subtracted particle yields correlated to PbPb and pp inclusive jets with pT > 120 GeV for tracks with 1 < pT < GeV in 30-50% central events.
Symmetrized dEta distributions (projected over |dPhi|<1) of background-subtracted particle yields correlated to PbPb and pp inclusive jets with pT > 120 GeV for tracks with 1 < pT < GeV in 10-30% central events.
Measurements of the top quark-antiquark (t t-bar) spin correlations and the top quark polarization are presented for t t-bar pairs produced in pp collisions at sqrt(s) = 8 TeV. The data correspond to an integrated luminosity of 19.5 inverse femtobarns collected with the CMS detector at the LHC. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The spin correlations and polarization are measured from the angular distributions of the two selected leptons, both inclusively and differentially, with respect to the invariant mass, rapidity, and transverse momentum of the t t-bar system. The measurements are unfolded to the parton level and found to be in agreement with predictions of the standard model. A search for new physics in the form of anomalous top quark chromo moments is performed. No evidence of new physics is observed, and exclusion limits on the real part of the chromo-magnetic dipole moment and the imaginary part of the chromo-electric dipole moment are evaluated.
Inclusive values of the asymmetry variables.
Values of the 12 bins of the normalized differential cross section as a function of $\left|\Delta \phi_{\ell^+\ell^-}\right|$.
Statistical covariance matrix for the 12 bins of the normalized differential cross section as a function of $\left|\Delta \phi_{\ell^+\ell^-}\right|$.
We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au+Au collisions for energies ranging from $\sqrt{s_{NN}}=7.7$ GeV to 200 GeV. The third harmonic $v_3^2\{2\}=\langle \cos3(\phi_1-\phi_2)\rangle$, where $\phi_1-\phi_2$ is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs $\Delta\eta = \eta_1-\eta_2$. Non-zero {\vthree} is directly related to the previously observed large-$\Delta\eta$ narrow-$\Delta\phi$ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity Quark Gluon Plasma (QGP) phase. For sufficiently central collisions, $v_3^2\{2\}$ persist down to an energy of 7.7 GeV suggesting that QGP may be created even in these low energy collisions. In peripheral collisions at these low energies however, $v_3^2\{2\}$ is consistent with zero. When scaled by pseudorapidity density of charged particle multiplicity per participating nucleon pair, $v_3^2\{2\}$ for central collisions shows a minimum near {\snn}$=20$ GeV.
Representative results on $v_3^2\{2\}$ from Au+Au collisions as a function of $\Delta\eta$ for charged hadrons with pT > 0.2 GeV/c and |$\eta$| < 1.
Representative results on $v_3^2\{2\}$ from Au+Au collisions as a function of $\Delta\eta$ for charged hadrons with pT > 0.2 GeV/c and |$\eta$| < 1.
Representative results on $v_3^2\{2\}$ from Au+Au collisions as a function of $\Delta\eta$ for charged hadrons with pT > 0.2 GeV/c and |$\eta$| < 1.
A measurement of the forward-backward asymmetry A[FB] of oppositely charged lepton pairs (mu mu and e e) produced via Z/gamma* boson exchange in pp collisions at sqrt(s) = 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.7 inverse femtobarns collected with the CMS detector at the LHC. The measurement of A[FB] is performed for dilepton masses between 40 GeV and 2 TeV and for dilepton rapidity up to 5. The A[FB] measurements as a function of dilepton mass and rapidity are compared with the standard model predictions.
Unfolded combined measurements of AFB in each M-|y| bin (mu+mu- and e+e- combined).
Unfolded measurement of AFB for the forward rapidity region (e+e-).
Unfolded measurements of AFB in each M-|y| bin (mu+mu-).
We present measurements of 2$^{nd}$ order azimuthal anisotropy ($v_{2}$) at mid-rapidity $(|y|<1.0)$ for light nuclei d, t, $^{3}$He (for $\sqrt{s_{NN}}$ = 200, 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV) and anti-nuclei $\bar{\rm d}$ ($\sqrt{s_{NN}}$ = 200, 62.4, 39, 27, and 19.6 GeV) and $^{3}\bar{\rm He}$ ($\sqrt{s_{NN}}$ = 200 GeV) in the STAR (Solenoidal Tracker at RHIC) experiment. The $v_{2}$ for these light nuclei produced in heavy-ion collisions is compared with those for p and $\bar{\rm p}$. We observe mass ordering in nuclei $v_{2}(p_{T})$ at low transverse momenta ($p_{T}<2.0$ GeV/$c$). We also find a centrality dependence of $v_{2}$ for d and $\bar{\rm d}$. The magnitude of $v_{2}$ for t and $^{3}$He agree within statistical errors. Light-nuclei $v_{2}$ are compared with predictions from a blast wave model. Atomic mass number ($A$) scaling of light-nuclei $v_{2}(p_{T})$ seems to hold for $p_{T}/A < 1.5$ GeV/$c$. Results on light-nuclei $v_{2}$ from a transport-plus-coalescence model are consistent with the experimental measurements.
Mid-rapidity v2(pT) for d,anti-d,t,He,anti-He from minimum bias (0-80%) Au+Au collisions 200 GeV (d data points are also shown in Fig 5).
Mid-rapidity v2(pT) for d,anti-d,t,He from minimum bias (0-80%) Au+Au collisions 62.4 GeV.
Mid-rapidity v2(pT) for d,anti-d,t,He from minimum bias (0-80%) Au+Au collisions 39 GeV.
The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with $p_\text{T}>500$ MeV inside high-momentum jets in dijet events using 20.3 fb$^{-1}$ of data recorded with the ATLAS detector in $pp$ collisions at $\sqrt{s}=8$ TeV collisions at the LHC. The jets considered have transverse momenta from 50 GeV up to and beyond 1.5 TeV. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Furthermore, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately.
The average charged particle multiplicity for the more forward jet and a charged particle threshold of 0.5 GeV as a function of the jet transverse momentum.
The average charged particle multiplicity for the more forward jet and a charged particle threshold of 2 GeV as a function of the jet transverse momentum.
The average charged particle multiplicity for the more forward jet and a charged particle threshold of 5 GeV as a function of the jet transverse momentum.
Forum