Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 $\text{TeV}$ proton-proton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum ($p_{\text{T}}$) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the $t\bar{t} \rightarrow W W b \bar{b}$ branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have $p_{\text{T}} > 500$ GeV and $p_{\text{T}} > 350$ GeV, respectively, is $331 \pm 3 \text{(stat.)} \pm 39 \text{(syst.)}$ fb. This is approximately 20$\%$ lower than the prediction of $398^{+48}_{-49}$ fb by Powheg+Pythia 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is $1.94 \pm 0.02 \text{(stat.)} \pm 0.25 \text{(syst.)}$ pb. This agrees with the NNLO prediction of $1.96^{+0.02}_{-0.17}$ pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.
Fiducial phase-space cross-section at particle level.
$p_{T}^{t}$ absolute differential cross-section at particle level.
$|y^{t}|$ absolute differential cross-section at particle level.
Central collisions of 800-GeV protons with the heavy components of nuclear emulsion, Ag107 and Br80, have been investigated to determine the characteristics of small-impact-parameter collisions and, by comparison with the analysis of inclusive proton-emulsion inelastic interactions and inelastic proton-nucleon collisions, to study the dependence of the interaction process on the mean number of intranuclear collisions 〈ν〉. The data are also compared with the results obtained in proton-emulsion collisions, both central and inclusive, at 200 GeV. The variations in the secondary-particle multiplicities and the normalized pseudorapidity density correlate with 〈ν〉 and demonstrate that proton-nucleus interactions, both central and inclusive, can be described adequately by the incoherent superposition of proton-nucleon collisions.
NUCLEUS IS AVERAGE NUCLEUS OF EMULSION.
NUCLEUS IS AVERAGE NUCLEUS OF EMULSION.
NUCLEUS IS AVERAGE NUCLEUS OF EMULSION.
The interaction of 800-GeV protons in nuclear emulsion has been investigated. The multiplicities and angular distributions of charged particles emitted by both the projectile and the target nucleus have been measured for 1718 inelastic events and are compared with the data obtained in proton-emulsion collisions at 67, 200, and 400 GeV. The target excitation is found to be independent of energy while the production of secondary particles continues to increase with incident proton energy.
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Correlations among the produced particles in interactions of 800-GeV protons with nuclei in photographic emulsion provide evidence for nonindependent production of the secondary particles. Assuming particle production in clusters, the analysis implies an average multiplicity of about 3 charged particles per cluster.
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IN THIS TABLE ETARAP(P=3)=ETARAP(P=4).
We report on the production characteristics and total cross section for 9 beauty hadron pairs produced by a 600 GeV/ c π − beam, the first such information in this energy region. The events were detected in the hybrid emulsion spectrometer of Fermilab Experiment E653. The measured pair cross section for all χ F , assuming linear A dependence, is 33±11 (stat.)±6(syst.) nb/nucleon. Fits of the inclusive single-hadron production distribution to the forms d σ d χ F ∝ (1−|χ F −χ 0 |) n and d σ d p T 2 ∝ exp (−bp t 2 ) give n=5.0 −2.1−1.7 +2.7+1.7 , χ 0 =0.06 −0.07−0.03 +0.06+0.02 , and b=0.13 −0.04−0.02 +0.05+0.02 ( GeV /c −2 . .The pairs tend to be produced back-to-back.
Cross section over all x assuming A**1 nuclear dependence.
Fit to data of form dsig/dx ^ (1-ABS(X-X0))**N yields X0 = 0.06 +0.06,-0.07(DSYS=+0.02,-0.03) and N = 5.0 +2.7,-2.1(DSYS=+-1.7).
Fit to data of form dsig/dPT**2 ^ exp(-B*PT**2) yields B = 0.13 +0.05,-0.04(DSYS=+-0.02).
A search for charm production in the coherent diffractive dissociation reaction pSi→XSi was carried out for the modes D 0 → K − π + , D 0 → K − π + π + π − , and D + → K − π + π + . No charm signals were observed, and the 90% confidence level upper limit for coherent charm pair production was determined to be 26 μ b per silicon nucleus. The results are interpreted as an upper limit of 0.2% on the amount of intrinsic charm in the proton.
90 pct CL upper limits.
We present total and differential cross sections for charm mesons produced in 600 GeV/ c π - emulsion interactions. Fits to d 2 σ / dx F dp T 2 ∞ (1−| x F |) n exp (- bp T 2 ) for 676 electronically reconstructed D mesons with x F >0 give n =4.25±0.24 ( stat .)±0.23 ( syst .) and b =0.76±0.03±0.03 ( GeV / c ) -2 . The total inclusive D + and D 0 cross sections are σ ( π - N → D ± ; x F >0) = 8.66±0.46±1.96 μb nucleon and σ(π - N→D 0 D 0 ; x F >0)=22.05±1.37±4.82μb nucleonk, where a linear dependence on the mean atomic weight of the target is assumed. These results are compared to next-to-leading order QCD predictions.
Linear A-dependence. Different modes of the charm mesons detection were used (see text for detail). The differential cross section is fitted by the equation : D2(SIG)/D(XL)/D(PT**2) = CONST*(1-XL)**POWER*EXP(-SLOPE*PT**2).
Linear A-dependence.
Inclusive dijet production at large pseudorapidity intervals (delta_eta) between the two jets has been suggested as a regime for observing BFKL dynamics. We have measured the dijet cross section for large delta_eta in ppbar collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic cross section increases strongly with the size of delta_eta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of a_{BFKL}(20GeV)=1.65+/-0.07.
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
We present asymmetries between the production of D+ and D- mesons in Fermilab experiment E791 as a function of xF and pt**2. The data used here consist of 74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C and Pt foils. The measurements are compared to results of models which predict differences between the production of heavy-quark mesons that have a light quark in common with the beam (leading particles) and those that do not (non-leading particles). While the default models do not agree with our data, we can reach agreement with one of them, PYTHIA, by making a limited number of changes to parameters used.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of Feynman variable X. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
Using a prompt neutrino beam in which a nu_tau component was identified for the first time, the nu_tau magnetic moment was measured based on a search for an anomalous increase in the number of neutrino-electron interactions. One such event was observed when 2.3 were expected from background processes, giving an upper 90% confidence limit of 3.9x10^-7 Bohr magnetons.
CONST(NAME=BOHR MAGNETON) is Bohr magneton.