Differential cross sections for the reaction $\gamma p \to p \pi^0$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.675 to 2.875 GeV. The results reported here possess greater accuracy in the absolute normalization than previous measurements. They disagree with recent CB-ELSA measurements for the process at forward scattering angles. Agreement with the SAID and MAID fits is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been extended to 3 GeV. Resonance couplings have been extracted and compared to previous determinations.
Differential cross section for indicent photon energy 675 MeV.
Differential cross section for indicent photon energy 725 MeV.
Differential cross section for indicent photon energy 775 MeV.
We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-$\Lambda$ and $\Lambda$-$\Lambda$, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at $\sqrt{s}$ = 7 TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-$\Lambda$ and $\Lambda$-$\Lambda$ correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems 'Correlation Analysis Tool using the Schr\"odinger Equation' (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to $r_{0} = 1.144\pm0.019$ (stat) $^{+0.069}_{-0.012}$ (syst) fm. The sensitivity of the measured p-$\Lambda$ correlation is tested against different scattering parameters which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the $\Lambda$-$\Lambda$ correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models.
The p$-$p $\oplus$ $\overline{\mathrm{p}}-\overline{\mathrm{p}}$ correlation function.
The p$-\Lambda$ $\oplus$ $\overline{\mathrm{p}}-\overline{\Lambda}$ correlation function.
The $\Lambda-\Lambda$ $\oplus$ $\overline{\Lambda}-\overline{\Lambda}$ correlation function.
Differential cross sections for the reaction gamma p -> eta-prime p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data indicate for the first time the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710) resonances, known to couple strongly to the eta N channel in photoproduction on the proton, and the importance of j=3/2 resonances in the process.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.527, 1.577 and 1.627 GeV. The errors shown are combined statistical and systematic.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.677, 1.728 and 1.779 GeV. The errors shown are combined statistical and systematic.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.829, 1.879 and 1.930 GeV. The errors shown are combined statistical and systematic.
None
No description provided.
Measurements of the proton structure function $F_2$ for $0.6 < Q^2 < 17 {GeV}^2$ and $1.2 \times 10^{-5} < x <1.9 \times 10^{-3}$ from ZEUS 1995 shifted vertex data are presented. From ZEUS $F_2$ data the slopes $dF_2/d\ln Q^2$ at fixed $x$ and $d\ln F_2/d\ln(1/x)$ for $x < 0.01$ at fixed $Q^2$ are derived. For the latter E665 data are also used. The transition region in $Q^2$ is explored using the simplest non-perturbative models and NLO QCD. The data at very low $Q^2$ $\leq 0.65 {GeV}^2$ are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range $3\times 10^{-5} < x < 0.7$. Data from NMC and BCDMS constrain the fit at large $x$. Assuming the NLO QCD description to be valid down to $Q^2\sim 1 {GeV}^2$, it is found that the $q\bar{q}$ sea distribution is still rising at small $x$ and the lowest $Q^2$ values whereas the gluon distribution is strongly suppressed.
F2.
F2.
F2.
Differential cross-sections for proton-proton elastic scattering have been measured covering the angular range from 50° to 90° c.m. at twelve incident momenta from 1.3 to 3.0 GeV/c. The angular distributions are quite smooth, but there is evidence of structure in the energy dependence of fixed-angle cross-sections at |t| ∼ 1 (GeV)2.
No description provided.
No description provided.
No description provided.
A measurement of the W$^+$W$^-$ boson pair production cross section in proton-proton collisions at $\sqrt{s} =$ 13 TeV is presented. The data used in this study are collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The W$^+$W$^-$ candidate events are selected by requiring two oppositely charged leptons (electrons or muons). Two methods for reducing background contributions are employed. In the first one, a sequence of requirements on kinematic quantities is applied allowing a measurement of the total production cross section: 117.6 $\pm$ 6.8 pb, which agrees well with the theoretical prediction. Fiducial cross sections are also reported for events with zero or one jet, and the change in the zero-jet fiducial cross section with the jet transverse momentum threshold is measured. Normalized differential cross sections are reported within the fiducial region. A second method for suppressing background contributions employs two random forest classifiers. The analysis based on this method includes a measurement of the total production cross section and also a measurement of the normalized jet multiplicity distribution in W$^+$W$^-$ events. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory, and constraints on the presence of dimension-6 operators are derived.
Summary of cross sections obtained in the sequential cut analysis. The uncertainty listed is the total uncertainty obtained from the fit to the yields. Same flavor, SF, and different flavor, DF, cross sections are given.
Summary of cross sections obtained in the sequential cut analysis. The uncertainty listed is the total uncertainty obtained from the fit to the yields. Same flavor, SF, and different flavor, DF, cross sections are given.
Measured fraction of events after unfolding for $N_J = 0, 1, \geq 2$ jets. The first uncertainty is statistical and the second combines systematic uncertainties from the response matrix and from the background subtraction.
A search for the leptonic decays of W bosons produced in the reaction e^+ p\to e^+ W^\pm X at a centre-of-mass energy of 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb^-1 . Three events consistent with W\to e\nu decay are found, giving a cross section of 0.9 +1.0 -0.7 \pm 0.2 pb, in good agreement with the Standard Model prediction. The corresponding 95% C.L. upper limit on the cross section is 3.3 pb. A search for the decay W\to \mu\nu has a smaller selection efficiency and yields no candidate events. Limits on the cross section for W production with large hadronic transverse momentum have been obtained. A search for high-transverse-momentum isolated tracks in events with large missing transverse momentum yields results in good agreement with Standard Model expectations, in contrast to a recent report by the H1 collaboration of the observation of an excess of such events.
Measured cross section from three events.
95 PCT CONFIDENCE UPPER LIMIT TO THE PROCESS.
The W+jet angular distribution is measured using W→eν events recorded with the Collider Detector at Fermilab (CDF) during the 1988-89 and 1992-93 Tevatron runs. The data agree well with both a leading order and a next-to-leading order theoretical prediction. The shape of the angular distribution is similar to that observed in photon + jet data and significantly different from that observed in dijet data.
Data normalized to 1 in the cos(theta) range -0.6 to 0.6.
Data normalized to 1 in the abs(cos(theta)) range <0.3.
The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward ($-4.46 < y_{\rm cms} < -2.96$) and forward ($2.03 < y_{\rm cms} < 3.53$) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of $60<m_{\mu\mu}<120$ GeV/$c^2$ and muon transverse momentum ($p_{\rm T}^\mu$) larger than 20 GeV/$c$, is measured. The production cross section and charge asymmetry of muons from W-boson decays with $p_{\rm T}^\mu>10$ GeV/$c$ are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.
Z-boson production cross section in the dimuon decay channel at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
Cross section of $\mu^{+}$ from W$^{+}$ boson decay at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
Cross section of $\mu^{-}$ from W$^{-}$ boson decay at backward and forward rapidities measured in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The first uncertainty is statistical, the second is systematic.
Forum