A search for pair-produced scalar or vector leptoquarks decaying into a $b$-quark and a $\tau$-lepton is presented using the full LHC Run 2 (2015-2018) data sample of 139 fb$^{-1}$ collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =13$ TeV. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio $B$ into a $\tau$-lepton and $b$-quark. For scalar leptoquarks, masses below 1460 GeV are excluded assuming $B=100$%, while for vector leptoquarks the corresponding limit is 1650 GeV (1910 GeV) in the minimal-coupling (Yang-Mills) scenario.
Acceptance $\times$ efficiency for the $\tau_\text{lep}\tau_\text{had}$ signal region assuming $\beta$ = 0.5 as a function of m$_\text{LQ}$.
Acceptance $\times$ efficiency for the $\tau_\text{had}\tau_\text{had}$ signal region assuming $\beta$ = 0.5 as a function of m$_\text{LQ}$.
The observed and expected 95% CL upper limits on the scalar LQ pair production cross-sections assuming B = 1 as a function of m$_\text{LQ}$.
We present the measurement of non-photonic electron production at high transverse momentum ($p_T > $ 2.5 GeV/$c$) in $p$ + $p$ collisions at $\sqrt{s}$ = 200 GeV using data recorded during 2005 and 2008 by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The measured cross-sections from the two runs are consistent with each other despite a large difference in photonic background levels due to different detector configurations. We compare the measured non-photonic electron cross-sections with previously published RHIC data and pQCD calculations. Using the relative contributions of B and D mesons to non-photonic electrons, we determine the integrated cross sections of electrons ($\frac{e^++e^-}{2}$) at 3 GeV/$c < p_T <~$10 GeV/$c$ from bottom and charm meson decays to be ${d\sigma_{(B\to e)+(B\to D \to e)} \over dy_e}|_{y_e=0}$ = 4.0$\pm0.5$({\rm stat.})$\pm1.1$({\rm syst.}) nb and ${d\sigma_{D\to e} \over dy_e}|_{y_e=0}$ = 6.2$\pm0.7$({\rm stat.})$\pm1.5$({\rm syst.}) nb, respectively.
The electron pair invariant mass distributions for electrons at $2.5 < p_{T} < 3.0$ GeV/c
The electron pair invariant mass distributions for electrons at $8 < p_{T} < 10$ GeV/c
The simulated electron pair invariant mass distributions for electrons at $2.5 < p_{T} < 3$ GeV/c
PHENIX has measured the e^+e^- pair continuum in sqrt(s_NN)=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e^+e^- yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c^bar-c production, though other mechanisms are not ruled out. In the low mass region (below the phi) the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7+/-0.4(stat)+/-1.5(syst)+/-0.9(model) At low mass (m_ee<0.3 GeV/c^2) and high p_T (1<p_T<5 GeV/c) an enhanced e^+e^- pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p_T, with inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T_init ~=300--600 MeV at times of 0.6--0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p_T<1 GeV/c the low mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T ~=100 MeV. Theoretical models under predict the low mass, low p_T enhancement.
(Color online) Inclusive mass spectrum of $e^+e^-$ pairs in the PHENIX acceptance in $p$+$p$ collisions compared to the expectations from the decays of light hadrons and correlated decays of charm, bottom, and Drell-Yan. The contribution from hadron decays is independently normalized based on meson measurements in PHENIX. The bottom panel shows the ratio of data to the cocktail of known sources. The systematic uncertainties of the data are shown as boxes, while the uncertainty on the cocktail is shown as band around 1.
(Color online) Inclusive mass spectrum of $e^+e^-$ pairs in the PHENIX acceptance in minimum-bias Au+Au compared to expectations from the decays of light hadrons and correlated decays of charm, bottom, and Drell-Yan. The charm contribution expected if the dynamic correlation of $c$ and $\bar{c}$ is removed is shown separately. Statistical (bars) and systematic (boxes) uncertainties are shown separately. The contribution from hadron decays is independently normalized based on meson measurements in PHENIX. The bottom panel shows the ratio of data to the cocktail of known sources. The systematic uncertainties of the data are shown as boxes, while the uncertainty on the cocktail is shown as band around 1.
(Color online) Inclusive mass spectrum of $e^+e^-$ pairs in the PHENIX acceptance in minimum-bias Au+Au compared to expectations from the decays of light hadrons and correlated decays of charm, bottom, and Drell-Yan. The charm contribution expected if the dynamic correlation of $c$ and $\bar{c}$ is removed is shown separately. Statistical (bars) and systematic (boxes) uncertainties are shown separately. The contribution from hadron decays is independently normalized based on meson measurements in PHENIX. The bottom panel shows the ratio of data to the cocktail of known sources. The systematic uncertainties of the data are shown as boxes, while the uncertainty on the cocktail is shown as band around 1.