This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb$^{-1}$. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: $|\eta^\gamma|<1.37$ and $1.56<|\eta^\gamma|<2.37$. The measurement covers photon transverse energies $25 < E_\textrm{T}^\gamma<400$ GeV and $25 < E_\textrm{T}^\gamma<350$ GeV respectively for the two $|\eta^\gamma|$ regions. For each jet flavour, the ratio of the cross sections in the two $|\eta^\gamma|$ regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central $\gamma+b$ measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.
Measured fiducial integrated $\gamma+b$ and $\gamma+c$ cross sections for $|\eta^\gamma|<1.37$ and $1.56<|\eta^\gamma|<2.37$.
Measured $\gamma+b$ fiducial differential cross section as a function of $E_\text{T}^\gamma$ for $|\eta^\gamma|<1.37$.
Measured $\gamma+b$ fiducial differential cross section as a function of $E_\text{T}^\gamma$ for $1.56<|\eta^\gamma|<2.37$.
A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton-proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to 36.1 $\mathrm{fb}^{-1}$ of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays $H^{\pm\pm}\rightarrow e^{\pm}e^{\pm}$, $H^{\pm\pm}\rightarrow e^{\pm}\mu^{\pm}$ and $H^{\pm\pm}\rightarrow \mu^{\pm}\mu^{\pm}$, fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section are derived at 95% confidence level. The observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons ($e$,$\mu$) varies from 770 GeV to 870 GeV (850 GeV expected) for $B(H^{\pm\pm}\rightarrow \ell^{\pm}\ell^{\pm})$ = 100% and both the expected and observed mass limits are above 450 GeV for $B(H^{\pm\pm}\rightarrow \ell^{\pm}\ell^{\pm})$ = 10% and any combination of partial branching ratios.
Observed and expected upper limit on the cross-section for $pp \to H^{++}H^{--}$ for a combination of partial branching ratios of $B(ee) = 100\%$, $B(e \mu ) = 0\%$, and $B( \mu \mu ) = 0\%$.
Observed and expected upper limit on the cross-section for $pp \to H^{++}H^{--}$ for a combination of partial branching ratios of $B(ee) = 0\%$, $B(e \mu ) = 0\%$, and $B( \mu \mu ) = 100\%$.
Observed and expected upper limit on the cross-section for $pp \to H^{++}H^{--}$ for a combination of partial branching ratios of $B(ee) = 0\%$, $B(e \mu ) = 100\%$, and $B( \mu \mu ) = 0\%$.
We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|\eta|<0.35$), in 0%--5% central $p$$+$Au and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. When taken together with previously published measurements in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries. We observe a clear mass-dependent splitting of $v_2(p_{T})$ in $d$$+$Au and $^3$He$+$Au collisions, just as in large nucleus-nucleus ($A$$+$$A$) collisions, and a smaller splitting in $p$$+$Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low $p_T$ ($< 1.5$ GeV/$c$), but fail to describe various features at higher $p_T$. In all systems, the $v_2$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($KE_T/n_q$), which was also seen previously in $A$$+$$A$ collisions.
Values of $v_2$($p_T$) for kaons in central 0-5% $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Values of $v_2$($p_T$) for kaons in central 0-5% $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Transverse momentum dependence of $v_2$ for identified pions and protons within $|\eta|$ < 0.35 in 0-5% central $p$+Au collisions.
A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb$^{-1}$ of $\sqrt{s}=$ 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, $\tilde{t}$, which decays promptly into two quarks through $R$-parity-violating couplings. Top squarks with masses in the range 100 GeV < $m_{\tilde{t}}$ < 410 GeV are excluded at 95% confidence level. If the decay is into a $b$-quark and a light quark, a dedicated selection requiring two $b$-tags is used to exclude masses in the ranges 100 GeV < $m_{\tilde{t}}$ < 470 GeV and 480 GeV < $m_{\tilde{t}}$ < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.
- - - - - - - - - - - - - - - - - - - - <p><b>Cutflows:</b><br> <a href="79059?version=1&table=CutflowTable1">Stop 100GeV</a><br> <a href="79059?version=1&table=CutflowTable2">Stop 500GeV</a><br> <a href="79059?version=1&table=CutflowTable3">Coloron 1500GeV</a><br> </p> <p><b>Event Yields:</b><br> <a href="79059?version=1&table=SRdistribution1">Inclusive stop SR</a><br> <a href="79059?version=1&table=SRdistribution2">Inclusive coloron SR </a><br> <a href="79059?version=1&table=SRdistribution3">b-tagged stop SR</a><br> </p> <p><b>Acceptances and Efficiencies:</b><br> <a href="79059?version=1&table=Acceptance1">Inclusive stop SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance2">Inclusive stop SR, after mass window</a><br> <a href="79059?version=1&table=Acceptance3">Inclusive coloron SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance4">Inclusive coloron SR, after mass window</a><br> <a href="79059?version=1&table=Acceptance5">b-tagged stop SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance6">b-tagged stop SR, after mass window</a><br> </p> <p><b>Cross section upper limits:</b><br> <a href="79059?version=1&table=Limitoncrosssection1">Inclusive stop SR</a><br> <a href="79059?version=1&table=Limitoncrosssection2">Inclusive coloron SR</a><br> <a href="79059?version=1&table=Limitoncrosssection3">b-tagged stop SR</a><br> </p> <p><b>Truth Code</b> and <b>SLHA Files</b> for the cutflows are available under "Resources" (purple button on the left) </p>
Cutflow table for a pair produced top squark of 100 GeV decaying into a b- and an s-quark.
Cutflow table for a pair produced top squark of 500 GeV decaying into a b- and an s-quark.
A search is conducted for new resonances decaying into a $WW$ or $WZ$ boson pair, where one $W$ boson decays leptonically and the other $W$ or $Z$ boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector-boson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton.
Limit
Limit
A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The dataset corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.
Expected exclusion limit contour in the (BRe,BRtau) plane for a 600 GeV stop. All limits are computed at 95% CL.
Observed exclusion limit contour in the (BRe,BRtau) plane for a 600 GeV stop. All limits are computed at 95% CL.
Expected exclusion limit contour in the (BRe,BRtau) plane for a 700 GeV stop. All limits are computed at 95% CL.
This paper presents a measurement of the triple-differential cross section for the Drell--Yan process $Z/\gamma^*\rightarrow \ell^+\ell^-$ where $\ell$ is an electron or a muon. The measurement is performed for invariant masses of the lepton pairs, $m_{\ell\ell}$, between $46$ and $200$ GeV using a sample of $20.2$ fb$^{-1}$ of $pp$ collisions data at a centre-of-mass energy of $\sqrt{s}=8$ TeV collected by the ATLAS detector at the LHC in 2012. The data are presented in bins of invariant mass, absolute dilepton rapidity, $|y_{\ell\ell}|$, and the angular variable $\cos\theta^{*}$ between the outgoing lepton and the incoming quark in the Collins--Soper frame. The measurements are performed in the range $|y_{\ell\ell}|<2.4$ in the muon channel, and extended to $|y_{\ell\ell}|<3.6$ in the electron channel. The cross sections are used to determine the $Z$ boson forward-backward asymmetry as a function of $|y_{\ell\ell}|$ and $m_{\ell\ell}$. The measurements achieve high-precision, below the percent level in the pole region, excluding the uncertainty in the integrated luminosity, and are in agreement with predictions. These precision data are sensitive to the parton distribution functions and the effective weak mixing angle.
Detailed breakdown of systematic uncertainties for the measurement in the central rapidity muon channel. Common systematic uncertainty on the luminosity measurment of 1.8% is not included. Correlated systematic uncertainties with the suffix :A should be treated as additive and with the suffix :M should be treated as multiplicative. The source 'sys,uncor' represents bin-to-bin uncorrelated systematic uncertainty. The cross sections are given at the Born QED level. 'C Dressed' represents the multiplicative correction factor to translate the cross sections to the dressed level with the cone radius of 0.1: SigmaDressed = C Dressed * SigmaBorn.
Detailed breakdown of systematic uncertainties for the measurement in the central rapidity electron channel. Common systematic uncertainty on the luminosity measurment of 1.8% is not included. Correlated systematic uncertainties with the suffix :A should be treated as additive and with the suffix :M should be treated as multiplicative. The source 'sys,uncor' represents bin-to-bin uncorrelated systematic uncertainty. The cross sections are given at the Born QED level. 'C Dressed' represents the multiplicative correction factor to translate the cross sections to the dressed level with the cone radius of 0.1: SigmaDressed = C Dressed * SigmaBorn.
Detailed breakdown of systematic uncertainties for the measurement in the forward rapidity electron channel. Common systematic uncertainty on the luminosity measurment of 1.8% is not included. Correlated systematic uncertainties with the suffix :A should be treated as additive and with the suffix :M should be treated as multiplicative. The source 'sys,uncor' represents bin-to-bin uncorrelated systematic uncertainty. The cross sections are given at the Born QED level. 'C Dressed' represents the multiplicative correction factor to translate the cross sections to the dressed level with the cone radius of 0.1: SigmaDressed = C Dressed * SigmaBorn.
A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one high-mass displaced vertex with five or more tracks, and uses 32.8 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95\% CL exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of $\mathcal{O}(10^{-2})$-$\mathcal{O}(10)$ ns in a simplified model inspired by Split Supersymmetry.
Vertex reconstruction efficiency as a function of radial position $R$ with and without the special LRT processing for one $R$-hadron signal sample with $m_{\tilde{g}} = 1.2$ TeV, $m_{\tilde{\chi}_{1}^{0}} = 100$ GeV and $\tau_{\tilde{g}} = 1$ ns. The efficiency is defined as the probability for a true LLP decay to be matched with a reconstructed DV fulfilling the vertex preselection criteria in events with a reconstructed primary vertex.
Vertex reconstruction efficiency as a function of radial position $R$ for two $R$-hadron signal samples with $m_{\tilde{g}} = 1.2$ TeV, $\tau_{\tilde{g}} = 1$ ns and different neutralino masses. The efficiency is defined as the probability for a true LLP decay to be matched with a reconstructed DV fulfilling the vertex preselection criteria in events with a reconstructed primary vertex.
Fractions of selected events for several signal MC samples with a gluino lifetime $\tau = 1$ ns, illustrating how $\mathcal{A}\times\varepsilon$ varies with the model parameters.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of $\phi$(1020) meson production at forward rapidity in $p$$+$$p$ collisions at $\sqrt{s}=$510 GeV via the dimuon decay channel. The integrated cross section in the rapidity and $p_T$ ranges $1.2<|y|<2.2$ and $2
The $\phi$-meson-production cross section d$\sigma_{\phi}$/dy in $p$ + $p$ collisions at $\sqrt{s}$ = 510 GeV integrated in the transverse-momentum range 2 < $p_T$ < 7 GeV/$c$.
The $\phi$-meson-production cross section d$\sigma_{\phi}$/dy in $p$ + $p$ collisions at $\sqrt{s}$ = 510 GeV integrated in the transverse-momentum range 2 < $p_T$ < 7 GeV/$c$.
The $\phi$-meson-differential-production cross section d${}^{2}$$\sigma_{\phi}/dp_T dy$ for 1.2 < |y| < 2.2 in $p$ + $p$ collisions at $\sqrt{s}$ = 510 GeV.
A search for neutral heavy resonances is performed in the $WW\to e\nu\mu\nu$ decay channel using $pp$ collision data corresponding to an integrated luminosity of 36.1 fb$^{-1}$, collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. No evidence of such heavy resonances is found. In the search for production via the quark--antiquark annihilation or gluon--gluon fusion process, upper limits on $\sigma_X \times B(X \to WW)$ as a function of the resonance mass are obtained in the mass range between 200 GeV and up to 5 TeV for various benchmark models: a Higgs-like scalar in different width scenarios, a two-Higgs-doublet model, a heavy vector triplet model, and a warped extra dimensions model. In the vector-boson fusion process, constraints are also obtained on these resonances, as well as on a Higgs boson in the Georgi--Machacek model and a heavy tensor particle coupling only to gauge bosons.
Figure 1, left, subfigure a, Acceptance times efficiency as a function of signal mass for the ggF or qqA production. The "0" efficiency mass point means there's no such signal sample for the corresponding model.
Figure 1, right, subfigure b, Acceptance times efficiency as a function of signal mass for the VBF production. The "0" efficiency mass point means there's no such signal sample for the corresponding model.
Figure 2, left, subfigure a, Transverse mass distribution in the ggF top-quark control regions. For NWA signals, the "0" value means lack of statistics.