Photoproduction of the cascade resonances has been investigated in the reactions $\gamma p \to K^+ K^+ (X)$ and $\gamma p \to K^+ K^+ \pi^- (X)$. The mass split of the $\Xi$ doublet is measured to be $5.4\pm 1.8$ MeV/c$^2$, consistent with existing measurements. The differential (total) cross sections for the $\Xi^{-}$ have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a possible production mechanism of $Y^*\to K^+\Xi^-$ through a $t$-channel process. The reaction $\gamma p \to K^+ K^+ \pi^-[\Xi^0]$ has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the $\Xi^-(1530)$ is observed. The cross section results of the $\Xi^-(1530)$ have also been obtained for photon beam energies from 3.35 to 4.75 GeV.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.79 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.89 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.99 Gev.
We report the first observation of the associated production of a W boson and a Z boson. This result is based on 1.1 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We observe 16 WZ candidates passing our event selection with an expected background of 2.7 +/- 0.4 events. A fit to the missing transverse energy distribution indicates an excess of events compared to the background expectation corresponding to a significance equivalent to six standard deviations. The measured cross section is sigma(ppbar -> WZ) = 5.0^{+1.8}_{-1.6} pb, consistent with the standard model expectation.
Measured cross section.
The reaction $^2$H$(e,e^\prime p)n$ has been studied with full kinematic coverage for photon virtuality $1.75<Q^2<5.5$ GeV$^2$. Comparisons of experimental data with theory indicate that for very low values of neutron recoil momentum ($p_n<100$ MeV/c) the neutron is primarily a spectator and the reaction can be described by the plane-wave impulse approximation. For $100<p_n<750$ MeV/c proton-neutron rescattering dominates the cross section, while $\Delta$ production followed by the $N\Delta \to NN$ transition is the primary contribution at higher momenta.
Recoil neutron momentum distributions.
Recoil neutron angular distributions for neutron momenta in the range 400 to 600 MeV.
Recoil neutron angular distributions for neutron momenta in the range 200 to 300 MeV.
We report on measurements of the inclusive jet production cross section as a function of the jet transverse momentum in pp-bar collisions at sqrt{s} = 1.96 TeV}, using the k_T algorithm and a data sample corresponding to 1.0 fb^-1 collected with the Collider Detector at Fermilab in Run II. The measurements are carried out in five different jet rapidity regions with |yjet| < 2.1 and transverse momentum in the range 54 < \ptjet < 700 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
Measured inclusive jet differential cross section as a function of PT for the rapidity range -0.1 to 0.1 with the jet resolution parameter D = 0.7.
Measured inclusive jet differential cross section as a function of PT for the absoloute rapidity range 0.1 to 0.7 with the jet resolution parameter D = 0.7.
Measured inclusive jet differential cross section as a function of PT for the absolute rapidity range 0.7 to 1.1 with the jet resolution parameter D = 0.7.
The upgraded Collider Detector at Fermilab (CDF II) has a high bandwidth available for track based triggers. This capability in conjunction with the unprecedented integrated luminosity in excess of 1 fb −1 enables detailed studies of charm hadron production. CDF is now releasing first measurements of the prompt charm meson pair cross sections, which give access to QCD mechanisms by which charm quarks are produced in proton anti-proton collisions. Recent results on the spin alignment of J/ψ and ψ(2S) as well as on the relative production of the χc1(P1) and χc2(1P) challenge our understanding of the fragmentation of charm quarks into charmonium states.
The D0 D*- pair cross section as a function of DELTA(PHI) in bins of trigger side D0 pT.
The D+ D*- pair cross section as a function of DELTA(PHI) in bins of trigger side D+ pT.
The D0 D*- pair cross section as a function of DELTA(PHI).
We present STAR measurements of the azimuthal anisotropy parameter $v_2$ for pions, kaons, protons, $\Lambda$, $\bar{\Lambda}$, $\Xi+\bar{\Xi}$, and $\Omega + \bar{\Omega}$, along with $v_4$ for pions, kaons, protons, and $\Lambda + \bar{\Lambda}$ at mid-rapidity for Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV. The $v_2(p_T)$ values for all hadron species at 62.4 GeV are similar to those observed in 130 and 200 GeV collisions. For observed kinematic ranges, $v_2$ values at 62.4, 130, and 200 GeV are as little as 10%--15% larger than those in Pb+Pb collisions at $\sqrt{s_{_{NN}}}=17.3$ GeV. At intermediate transverse momentum ($p_T$ from 1.5--5 GeV/c), the 62.4 GeV $v_2(p_T)$ and $v_4(p_T)$ values are consistent with the quark-number scaling first observed at 200 GeV. A four-particle cumulant analysis is used to assess the non-flow contributions to pions and protons and some indications are found for a smaller non-flow contribution to protons than pions. Baryon $v_2$ is larger than anti-baryon $v_2$ at 62.4 and 200 GeV perhaps indicating either that the initial spatial net-baryon distribution is anisotropic, that the mechanism leading to transport of baryon number from beam- to mid-rapidity enhances $v_2$, or that anti-baryon and baryon annihilation is larger in the in-plane direction.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
We present a new measurement of the $B^+$ meson differential cross section $d\sigma/d p_T$ at $\sqrt{s}=1960$ GeV. The data correspond to an integrated luminosity of 739pb$^{-1}$ collected with the upgraded CDF detector (CDF II) at the Fermilab Tevatron collider. $B^+$ candidates are reconstructed through the decay $B^+ \to J/\psi K^+$, with $J/\psi \to \mu^+ \mu^-$. The integrated cross section for producing $B^+$ mesons with $p_T \geq 6$ GeV/c and $|y| \leq 1$ is measured to be $2.78 \pm 0.24 \mu$b
The differential cross section (nb/GeV/c) for B+ mesons as a function of pT.
The The B+ production cross section.
Spin transfer from circularly polarized real photons to recoiling hyperons has been measured for the reactions $\vec\gamma + p \to K^+ + \vec\Lambda$ and $\vec\gamma + p \to K^+ + \vec\Sigma^0$. The data were obtained using the CLAS detector at Jefferson Lab for center-of-mass energies $W$ between 1.6 and 2.53 GeV, and for $-0.85<\cos\theta_{K^+}^{c.m.}< +0.95$. For the $\Lambda$, the polarization transfer coefficient along the photon momentum axis, $C_z$, was found to be near unity for a wide range of energy and kaon production angles. The associated transverse polarization coefficient, $C_x$, is smaller than $C_z$ by a roughly constant difference of unity. Most significantly, the {\it total} $\Lambda$ polarization vector, including the induced polarization $P$, has magnitude consistent with unity at all measured energies and production angles when the beam is fully polarized. For the $\Sigma^0$ this simple phenomenology does not hold. All existing hadrodynamic models are in poor agreement with these results.
Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.032 GeV and W = 1.679 GeV.
Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.132 GeV and W = 1.734 GeV.
Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.232 GeV and W = 1.787 GeV.
We report measurements of the exclusive electroproduction of $K^+\Lambda$ and $K^+\Sigma^0$ final states from a proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions $\sigma_T$, $\sigma_L$, $\sigma_{TT}$, and $\sigma_{LT}$ were extracted from the $\Phi$- and $\epsilon$-dependent differential cross sections taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis represents the first $\sigma_L/\sigma_T$ separation with the CLAS detector, and the first measurement of the kaon electroproduction structure functions away from parallel kinematics. The data span a broad range of momentum transfers from $0.5\leq Q^2\leq 2.8$ GeV$^2$ and invariant energy from $1.6\leq W\leq 2.4$ GeV, while spanning nearly the full center-of-mass angular range of the kaon. The separated structure functions reveal clear differences between the production dynamics for the $\Lambda$ and $\Sigma^0$ hyperons. These results provide an unprecedented data sample with which to constrain current and future models for the associated production of strangeness, which will allow for a better understanding of the underlying resonant and non-resonant contributions to hyperon production.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.6 to 1.7 GeV.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.70 to 1.75 GeV.
Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.75 to 1.80 GeV.
We present the first observation of exclusive $e^+e^-$ production in hadron-hadron collisions, using $p\bar{p}$ collision data at \mbox{$\sqrt{s}=1.96$ TeV} taken by the Run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of \mbox{532 pb$^{-1}$}. We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy {$E_T>5$ GeV} and pseudorapidity {$|\eta|<2$}. With these criteria, 16 events are observed compared to a background expectation of {$1.9\pm0.3$} events. These events are consistent in cross section and properties with the QED process \mbox{$p\bar{p} \to p + e^+e^- + \bar{p}$} through two-photon exchange. The measured cross section is \mbox{$1.6^{+0.5}_{-0.3}\mathrm{(stat)}\pm0.3\mathrm{(syst)}$ pb}. This agrees with the theoretical prediction of {$1.71 \pm 0.01$ pb}.
Exclusive cross section.
Forum