Global polarization of $\Xi$ and $\Omega$ hyperons has been measured for the first time in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The measurements of the $\Xi^-$ and $\bar{\Xi}^+$ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay $\Xi\rightarrow\Lambda+\pi$, as well as by measuring the polarization of the daughter $\Lambda$-hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $\Xi^-$ and $\bar{\Xi}^+$, is measured to be $\langle P_\Xi \rangle = 0.47\pm0.10~({\rm stat.})\pm0.23~({\rm syst.})\,\%$ for the collision centrality 20%-80%. The $\langle P_\Xi \rangle$ is found to be slightly larger than the inclusive $\Lambda$ polarization and in reasonable agreement with a multi-phase transport model (AMPT). The $\langle P_\Xi \rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of $\Omega$, $\langle P_\Omega \rangle = 1.11\pm0.87~({\rm stat.})\pm1.97~({\rm syst.})\,\%$ was obtained by measuring the polarization of daughter $\Lambda$ in the decay $\Omega \rightarrow \Lambda + K$, assuming the polarization transfer factor $C_{\Omega\Lambda}=1$.
$\Xi$ and $\Omega$ global polarization in Au+Au collisions at 200 GeV. Decay parameter from PDG2020, $\alpha_{\Xi}$=-$\alpha_{\bar{\Xi}}$=-0.401, is used.
The energy dependence of $\Lambda$ and $\bar{\Lambda}$ global polarization. Note that the results from previous measurements are rescaled using updated decay parameters (PDG2020), $\alpha_{\Lambda}$=0.732 and $\alpha_{\bar{\Lambda}}$=-0.758. The original data can be found in <a href="https://www.hepdata.net/record/ins1510474">this page</a>.
Centrality dependence of $\Xi$ global poalrization in Au+Au collisions at 200 GeV. Decay parameter from PDG2020, $\alpha_{\Xi}$=-$\alpha_{\bar{\Xi}}$=-0.401, is used.
We present an angular analysis of the $B^{+}\rightarrow K^{\ast+}(\rightarrow K_{S}^{0}\pi^{+})\mu^{+}\mu^{-}$ decay using 9$\,\mbox{fb}^{-1}$ of $pp$ collision data collected with the LHCb experiment. For the first time, the full set of CP-averaged angular observables is measured in intervals of the dimuon invariant mass squared. Local deviations from Standard Model predictions are observed, similar to those in previous LHCb analyses of the isospin-partner $B^{0}\rightarrow K^{\ast0}\mu^{+}\mu^{-}$ decay. The global tension is dependent on which effective couplings are considered and on the choice of theory nuisance parameters.
Results for the CP-averaged observables Fl, Afb and S3–S9. The first uncertainties are statistical and the second systematic.
Results for the optimised observables FL and P1–P'8. The first uncertainties are statistical and the second systematic.
The CP-averaged observable Fl versus q2. The first (second) error bars represent the statistical (total) uncertainties.
The STAR Collaboration reports measurements of the transverse single-spin asymmetry (TSSA) of inclusive $\pi^0$ at center-of-mass energies ($\sqrt s$) of 200 GeV and 500 GeV in transversely polarized proton-proton collisions in the pseudo-rapidity region 2.7 to 4.0. The results at the two different energies show a continuous increase of the TSSA with Feynman-$x$, and, when compared to previous measurements, no dependence on $\sqrt s$ from 19.4 GeV to 500 GeV is found. To investigate the underlying physics leading to this large TSSA, different topologies have been studied. $\pi^0$ with no nearby particles tend to have a higher TSSA than inclusive $\pi^0$. The TSSA for inclusive electromagnetic jets, sensitive to the Sivers effect in the initial state, is substantially smaller, but shows the same behavior as the inclusive $\pi^0$ asymmetry as a function of Feynman-$x$. To investigate final-state effects, the Collins asymmetry of $\pi^0$ inside electromagnetic jets has been measured. The Collins asymmetry is analyzed for its dependence on the $\pi^0$ momentum transverse to the jet thrust axis and its dependence on the fraction of jet energy carried by the $\pi^0$. The asymmetry was found to be small in each case for both center-of-mass energies. All the measurements are compared to QCD-based theoretical calculations for transverse-momentum-dependent parton distribution functions and fragmentation functions. Some discrepancies are found, which indicates new mechanisms might be involved.
Transverse single-spin asymmetry as a function of Feynman-x for \pi^0 production in transversely polarized proton-proton collisions at 200 GeV.
Transverse single-spin asymmetry as a function of Feynman-x for \pi^0 production in transversely polarized proton-proton collisions at 500 GeV.
average transverse momentum of the \pi^0 for each xF bin in transversely polarized proton-proton collisions at 200 GeV.
Measurements of the total and differential fiducial cross sections for the Z boson decaying into two neutrinos are presented at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were collected by the CMS detector in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. In these measurements, events are selected containing an imbalance in transverse momentum and one or more energetic jets. The fiducial differential cross section is measured as a function of the Z boson transverse momentum. The results are combined with a previous measurement of charged-lepton decays of the Z boson.
The measured and predicted inclusive fiducial cross sections in fb. The experimental measurement includes both statistical and systematics uncertainties. The theoretical prediction includes both the QCD scale and PDF uncertainties.
The measured and predicted inclusive fiducial cross sections in fb. The experimental measurement includes both statistical and systematics uncertainties. The theoretical prediction includes both the QCD scale and PDF uncertainties.
Experimental uncertainties affecting transfer factors in the analysis that is used to estimate the W background in the signal region (SR). The number of W boson events are denoted as $W_{SR}$ for the SR and in analogy as $W_{\mu\nu}$ ($W_{e\nu}$) for the single-muon (single-electron) control region (CR).
The STAR Collaboration reports a measurement of the transverse single-spin asymmetries, $A_{N}$, for neutral pions produced in polarized proton collisions with protons ($pp$), with aluminum nuclei ($p\rm{Al}$) and with gold nuclei ($p\rm{Au}$) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudo-rapidity region $2.7<\eta<3.8$. Results are presented for $\pi^0$s observed in the STAR FMS electromagnetic calorimeter in narrow Feynman x ($x_F$) and transverse momentum ($p_T$) bins, spanning the range $0.17<x_F<0.81$ and $1.7<p_{T}<6.0$ GeV/$c$. For fixed $x_F<0.47$, the asymmetries are found to rise with increasing transverse momentum. For larger $x_F$, the asymmetry flattens or falls as ${p_T}$ increases. Parametrizing the ratio $r(A) \equiv A_N(pA)/A_N(pp)=A^P$ over the kinematic range, the ratio $r(A)$ is found to depend only weakly on $A$, with ${\langle}P{\rangle} = -0.027 \pm 0.005$. No significant difference in $P$ is observed between the low-$p_T$ region, $p_T<2.5$ GeV/$c$, where gluon saturation effects may play a role, and the high-$p_T$ region, $p_T>2.5$ GeV/$c$. It is further observed that the value of $A_N$ is significantly larger for events with a large-$p_T$ isolated $\pi^0$ than for events with a non-isolated $\pi^0$ accompanied by additional jet-like fragments. The nuclear dependence $r(A)$ is similar for isolated and non-isolated $\pi^0$ events.
A_N pAl 0.17<x_F<0.19
A_N pp 0.17<x_F<0.19
A_N pAu 0.17<x_F<0.19
A search for leptoquarks produced singly and in pairs in proton-proton collisions is presented. We consider the leptoquark (LQ) to be a scalar particle of charge -1/3$e$ coupling to a top quark plus a tau lepton ($\mathrm{t}\tau$) or a bottom quark plus a neutrino ($\mathrm{b}\nu$), or a vector particle of charge +2/3$e$, coupling to $\mathrm{t}\nu$ or $\mathrm{b}\tau$. These choices are motivated by models that can explain a series of anomalies observed in the measurement of B meson decays. In this analysis the signatures $\mathrm{t}\tau\nu\mathrm{b}$ and $\mathrm{t}\tau\nu$ are probed, using data recorded by the CMS experiment at the CERN LHC at $\sqrt{s} =$ 13 TeV and that correspond to an integrated luminosity of 137 fb$^{-1}$. These signatures have not been previously explored in a dedicated search. The data are found to be in agreement with the standard model prediction. Lower limits at 95% confidence level are set on the LQ mass in the range 0.98-1.73 TeV, depending on the LQ spin and its coupling $\lambda$ to a lepton and a quark, and assuming equal branching fractions for the two LQ decay modes considered. These are the most stringent constraints to date on the existence of leptoquarks in this scenario.
Pair leptoquark (LQ) total selection efficiency, accounting for both the decay branching fraction and the event selection, for events that pass the signal region requirements and any of the top quark or b jet categories defined in the search.
Single scalar leptoquark (LQs) total selection efficiency, accounting for both the decay branching fraction and the event selection, for events that pass the signal region requirements and any of the top quark or b jet categories defined in the search.
Single vector leptoquark (LQv) k = 0 total selection efficiency, accounting for both the decay branching fraction and the event selection, for events that pass the signal region requirements and any of the top quark or b jet categories defined in the search.
In 2015, the PHENIX collaboration has measured very forward ($\eta>6.8$) single-spin asymmetries of inclusive neutrons in transversely polarized proton-proton and proton-nucleus collisions at a center of mass energy of 200 GeV. A previous publication from this data set concentrated on the nuclear dependence of such asymmetries. In this measurement the explicit transverse-momentum dependence of inclusive neutron single spin asymmetries for proton-proton collisions is extracted using a bootstrapping-unfolding technique on the transverse momenta. This explicit transverse-momentum dependence will help improve the understanding of the mechanisms that create these asymmetries.
Measured and unfolded forward neutron single spin asymmetries using 3rd order polynomial parameterization in unfolding
Measured and unfolded forward neutron single spin asymmetries using a Power law parameterization in unfolding
Measured and unfolded forward neutron single spin asymmetries using an exponential parameterization in unfolding
We present a measurement of the transverse single-spin asymmetry for $\pi^0$ and $\eta$ mesons in $p^\uparrow$ $+$ $p$ collisions in the pseudorapidity range $|\eta|<0.35$ and at a center-of-mass energy of 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. In comparison with previous measurements in this kinematic region, these results have a factor of 3 smaller uncertainties. As hadrons, $\pi^0$ and $\eta$ mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Comparisons of the differences in their transverse single-spin asymmetries have the potential to disentangle the possible effects of strangeness, isospin, or mass. These results can constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function.
Data from Figs. 2, 4, and 5 of the transverse single-spin asymmetry of neutral pions measured at $|\eta|<0.35$ in $p^\uparrow$$+$$p$ collisions at $\sqrt{s} = 200$ GeV. An additional scale uncertainty of 3.4\% due to the polarization uncertainty is not shown. The total $\sigma_{\rm syst}$ in the lowest $p_T$ bin includes an additional systematic uncertainty of $1.06\times10^{-4}$ from bunch shuffling.
Data from Figs. 3 and 4 of the transverse single-spin asymmetry of eta mesons measured at $|\eta|<0.35$ in $p^\uparrow$$+$$p$ collisions at $\sqrt{s} = 200$ GeV. An additional scale uncertainty of 3.4\% due to the polarization uncertainty is not shown. The total $\sigma_{\rm syst}$ in the lowest $p_T$ bin includes an additional systematic uncertainty of $6.20\times10^{-4}$ from bunch shuffling.
Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, $\mathrm{PbPb}(\gamma\gamma) \rightarrow \mu^+\mu^- (\mathrm{Pb}^{(\star)}\mathrm{Pb}^{(\star)} )$, is studied using $\mathcal{L}_{\mathrm{int}} = 0.48$ nb$^{-1}$ of $\sqrt{s_\mathrm{NN}}=5.02$ TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region $p_{\mathrm{T}\mu} > 4$ GeV, $|\eta_{\mu}| < 2.4$, invariant mass $m_{\mu\mu} > 10$ GeV, and $p_{\mathrm{T,\mu\mu}} < 2$ GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of $m_{\mu\mu}$, absolute pair rapidity ($|y_{\mu\mu}|$), scattering angle in the dimuon rest frame ($|\cos \vartheta^{\star}_{\mu\mu}|$) and the colliding photon energies. The total cross section of the UPC $\gamma \gamma \rightarrow \mu^{+}\mu^{-}$ process in the fiducial volume is measured to be $\sigma_{\mathrm{fid}}^{\mu\mu} = 34.1 \! \pm \! 0.3 \mathrm{(stat.)} \! \pm \! 0.7 \mathrm{(syst.)}$ $\mu\mathrm{b}$. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger $|y_{\mu\mu}|$ are found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations.
Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $10 < |m_{\mu\mu}| < 20$ GeV.
Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $20 < |m_{\mu\mu}| < 40$ GeV.
Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $40 < |m_{\mu\mu}| < 80$ GeV.
A search for the $K^{+}\rightarrow\pi^{+}X$ decay, where $X$ is a long-lived feebly interacting particle, is performed through an interpretation of the $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of $X$ masses, $0$-$110\,\text{MeV}/c^{2}$ and $154$-$260\,\text{MeV}/c^{2}$, and lifetimes above $100\,\text{ps}$ are considered. The limits set on the branching ratio, $\text{BR}(K^{+}\rightarrow\pi^{+}X)$, are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.
Observed and expected upper limits on branching ratio \(K^{+}\rightarrow\pi^{+}X\) at 90% CL.
Observed upper limits on branching ratio \(K^{+}\rightarrow\pi^{+}X\) at 90% CL as functions of X mass and lifetime.
Exclusion region limits on coupling strength \(sin^{2}\theta\) at 90% CL as a function of X mass, for visible X decays.
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