Charmed-meson production by 350 GeV/c π − particles incident on copper and tungsten targets has been studied in the WA92 experiment, performed at the CERN Ω′ spectrometer. Results obtained are reported and discussed. Reconstruction of decays from the set D 0 → K − π + D 0 → K − π − π + π + , D s + → φπ + and charge conjugates has yielded a sample of 7280 ± 108 charmed mesons, produced with χ F > 0, ( χ F ) = 0.18 and〈 p T 2 〉 = 1.86 ( GeV / c ) 2 . Assuming a relationship σ = σ 0 A α between the cross section, σ, per nucleus of mass A and the nucleonic cross section, σ 0 the α value found for the detected charmed particles is 0.95 ± 0.06 ± 0.03. Taking α = 1, the measured cross sections per nucleon for χ F > 0 production are 7.78 ± 0.14 ± 0.52 μ b for D 0 / D 0 , 3.28 ± 0.08 ± 0.29 μ b for D + /D − and 1.29 ± 0.16 ± 0.33 μ b for D s + /D s − . Differential cross sections with respect to χ F and p T 2 have been determined for the various types of charmed meson, and particle-antiparticle asymmetries have been analysed.
Nuclear dependence is fitted by SIG=CONST*A**POWER for CU and WT nuclei.
The cross section production per nucleon evaluated for POWER = 1.
Differential cross section w.r.t. XL assuming POWER=1.
We report measurements of D ∗± production in interactions between 350 GeV/ c π − particles and nuclei. Reconstruction of the decay D ∗+ → D 0 π + and charge conugate, with D 0 identified via its decays to K − π + and K − π − π + π + , has allowed isolation of a sample of 611 ± 28 D ∗± mesons, produced at positive x F . Assuming a linear A-dependence, the cross-section per nucleon in the region x F > 0 is measured to be 1.41 ± 0.10 ± 0.11 μ b for D ∗+ and 1.84 ± 0.12 ± 0.15 μ b for D ∗− . We present measurements of differential cross-sections with respect to x F and P t 2 , and compare data for D ∗± (vector-meson) production with data for production of charmed pseudoscalar mesons.
No description provided.
Data on D0, DBAR0, D+, and D- meson production are taken from previous publication of this collaboration (see NP B495, 3).
No description provided.
The production of charmed particles by Sigma- of 340 Gev/c momentum was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the Omega-spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of 1600 microb^-1 on copper and carbon targets was recorded. From the reconstruction of 930 +- 90 charm particle decays in 10 decay channels production cross sections for D, antiD, Ds and Lambdac were determined in the region xF>0. Assuming an A^1 dependence of the cross section on the nucleon number, we calculate a total ccbar production cross section of sigma(x_F > 0) = 5.3+- 0.4(stat)+-1.0(syst)+1.0(Xi_c) microb per nucleon. The last term is an upper limit on the unknown contribution from charmed-strange baryon production.
Fits to the DSIG/DXL and DSIG/DPT**2 distributions in the range XL > 0. Theerrors shown are statistical only.. The fits are of the following form:. DSIG/DXL : Const*(1-X)**N. DSIG/DPT**2 : Const*EXP(-B*PT**2).
The production cross sections for anti-charmed and charmed hadrons in the range XL > 0. The Errors are statistical only.
The total CQUARK+CQUARKBAR cross section in the range XL > obtained as the weighted average of the sum of all the measured contributions to the charmed andanti-charmed hadron production in the previous table. second systematic (DSYS) error is due to the uncertainty in the contribution of XI/C production to the cross section.
We report on a measurement of the differential and total cross sections of inclusive production of Xi resonances in Sigma - nucleus collisions at 345 GeV/c.
Feynman X distribution (times BR) per nucleon for XI(1820) and XI(1950) production. The quoted errors are statistical.
PT**2 distribution (times BR) per nucleon for XI(1530) and XI(1890) production. The quoted errors are statistical.
Total cross section per nucleus and per nucleon. The quoted errors are statistical.
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken x range 0.003<x<0.7. The new measurements have small statistical and systematic uncertainties of a few percent and confirm with considerably better accuracy the previous COMPASS measurement. The Sivers asymmetry is found to be compatible with zero for negative hadrons and positive for positive hadrons, a clear indication of a spin-orbit coupling of quarks in a transversely polarised proton. As compared to measurements at lower energy, a smaller Sivers asymmetry for positive hadrons is found in the region x > 0.03. The asymmetry is different from zero and positive also in the low x region, where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong dependence on the four-momentum transfer to the nucleon, in agreement with the most recent calculations.
The Sivers asymmetry, from the 2010 data set, for positive hadrons as a function of X for full range. Also shown are the mean values of other variables plus the correlation with the Collins data measurments.
The Sivers asymmetry, from the 2010 data set, for negative hadrons as a function of X for full range. Also shown are the mean values of other variables plus the correlation with the Collins data measurments.
The Sivers asymmetry, from the 2010 data set, for positive hadrons as a function of PT for full range. Also shown are the mean values of other variables plus the correlation with the Collins data measurments.
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Collins asymmetry of the proton was extracted in the Bjorken x range 0.003<x<0.7. These new measurements confirm with higher accuracy previous measurements from the COMPASS and HERMES collaborations, which exhibit a definite effect in the valence quark region. The asymmetries for negative and positive hadrons are similar in magnitude and opposite in sign. They are compatible with model calculations in which the u-quark transversity is opposite in sign and somewhat larger than the d-quark transversity distribution function. The asymmetry is extracted as a function of Bjorken $x$, the relative hadron energy $z$ and the hadron transverse momentum p_T^h. The high statistics and quality of the data also allow for more detailed investigations of the dependence on the kinematic variables. These studies confirm the leading-twist nature of the Collins asymmetry.
The Collins asymmetry, from the 2010 data set, for positive hadrons as a function of X for full range. Also shown are the mean values of other variables plus the correlation with the Sivers data measurments.
The Collins asymmetry, from the 2010 data set, for negative hadrons as a function of X for full range. Also shown are the mean values of other variables plus the correlation with the Sivers data measurments.
The Collins asymmetry, from the 2010 data set, for positive hadrons as a function of PT for full range. Also shown are the mean values of other variables plus the correlation with the Sivers data measurments.
This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a $Z \gamma$ pair in association with two jets. The analysis uses 140 fb$^{-1}$ of LHC proton-proton collision data taken at $\sqrt{s}$=13 TeV recorded by the ATLAS detector during the years 2015-2018. Events with a $Z$ boson candidate decaying into either an $e^+e^-$ or $\mu^+ \mu^-$ pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and a large rapidity gap between the two jets and is measured with an observed and expected significance well above five standard deviations. The fiducial $pp \rightarrow Z \gamma jj$ cross-section for the electroweak production is measured to be 3.6 $\pm$ 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be $16.8^{+2.0}_{-1.8}$ fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions.
Post-fit mjj distributions in the mjj>500 GeV SR. The uncertainty band around the expectation includes all systematic uncertainties (including MC statistical uncertainty) and takes into account their correlations as obtained from the fit. The error bar around the data points represents the data statistical uncertainty. Events beyond the upper limit of the histogram are included in the last bin.
Post-fit mjj distributions in the mjj>500 GeV CR. The uncertainty band around the expectation includes all systematic uncertainties (including MC statistical uncertainty) and takes into account their correlations as obtained from the fit. The error bar around the data points represents the data statistical uncertainty. Events beyond the upper limit of the histogram are included in the last bin.
Post-fit mjj distributions in the mjj>150 GeV Extended SR. The uncertainty band around the expectation includes all systematic uncertainties (including MC statistical uncertainty) and takes into account their correlations as obtained from the fit. The error bar around the data points represents the data statistical uncertainty. Events beyond the upper limit of the histogram are included in the last bin.
A search for invisible decays of the Higgs boson as well as searches for dark matter candidates, produced together with a leptonically decaying $Z$ boson, are presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of 13 TeV, delivered by the LHC, corresponding to an integrated luminosity of 139 fb$^{-1}$ and recorded by the ATLAS experiment. Assuming Standard Model cross-sections for $ZH$ production, the observed (expected) upper limit on the branching ratio of the Higgs boson to invisible particles is found to be 19% (19%) at the 95% confidence level. Exclusion limits are also set for simplified dark matter models and two-Higgs-doublet models with an additional pseudoscalar mediator.
The expected exclusion contours as a function of (m(med), m($\chi$)), with Axial-vector mediator)
The observed exclusion contours as a function of (m(med), m($\chi$)), with Axial-vector mediator)
The expected exclusion contours as a function of (m(med), m($\chi$)), with Vector mediator)
This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for $e^+ \mu^-$ and $e^- \mu^+$ pairs to constrain physics processes beyond the Standard Model. It uses $139 \text{fb}^{-1}$ of proton$-$proton collision data recorded at $\sqrt{s} = 13$ TeV at the LHC. Targeting sources of new physics which prefer final states containing $e^{+}\mu^{-}$ to $e^{-}\mu^{+}$, the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the $R$-parity-violating coupling $\lambda'_{231}$ is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=1$, at 95% confidence level. The limit on the coupling reduces to $g_{\text{1R}}^{eu}=g_{\text{1R}}^{\mu c}=0.46$ for a mass of 1420 GeV.
Observed yields, and (post-fit) expected yields for the data-driven SM estimates. Yields are shown for the benchmark RPV-supersymmetry signal points in SR-RPV and the leptoquark signal points in SR-LQ after a fit excluding the $e^{+}\mu^{-}$ signal region and setting $\mu_{\text{sig}}=1$. Small weights correcting for muon charge biases affect all rows except that containing the fake-lepton estimate. These weights, $w_i$, cause non-integer yields. The uncertainties, $\sqrt{\sum_i w_i^2}$, are given for data to support the choice made to model the yields with a Poisson distribution.
The observed exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.0$.
The expected exclusion contour at 95% CL as a function of the smuon and neutralino masses, for $\lambda_{231}^{'}=1.0$.
Searches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb$^{-1}$ of $\sqrt{s} = $ 13 TeV $pp$ collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass.
The expected and observed upper limits at 95\% CL on the fiducial cross-section times branching ratio to two photons of a narrow-width (Γ_X = 4 MeV) spin-0 resonance as a function of its mass m_X. For masses greater than 1000 GeV, pseudo-experiments are used to verify the expected and observed limits, and used in place of the asymptotic limit when differences are observed.
The expected and observed upper limits at 95\% CL on the fiducial cross-section times branching ratio to two photons of a narrow-width (Γ_X = 4 MeV) spin-0 resonance as a function of its mass m_X. For masses greater than 1000 GeV, pseudo-experiments are used to verify the expected and observed limits, and used in place of the asymptotic limit when differences are observed.
The expected and observed upper limits at 95\% CL on the production cross-section times branching ratio to two photons of the lightest KK graviton as a function of its mass for k/Mpl=0.10. For masses greater than 1000 GeV, pseudo-experiments are used to verify the expected and observed limits, and used in place of the asymptotic limit when differences are observed.
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