We report on double-differential inclusive cross-sections of the production of secondary protons and charged pions, in the interactions with a 5% interaction length thick stationary beryllium target, of proton and pion beams with momentum from +/-3 GeV/c to +/-15 GeV/c. Results are given for secondary particles with production angles between 20 and 125 degrees.
Double differential inclusive cross section for the reaction P BE --> P X with a 3 GeV beam and production angles 20 to 30 degrees.
Double differential inclusive cross section for the reaction P BE --> P X with a 3 GeV beam and production angles 30 to 40 degrees.
Double differential inclusive cross section for the reaction P BE --> P X with a 3 GeV beam and production angles 40 to 50 degrees.
Differential cross sections for the reaction $\gamma p \to n \pi^+$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes.
Differential cross sections for incident photon energies 0.725, 0.775, 0.825and 0.875 GeV.
Differential cross sections for incident photon energies 0.925, 0.975, 1.025and 1.075 GeV.
Differential cross sections for incident photon energies 1.125, 1.175, 1.225and 1.275 GeV.
Using a data sample with a total integrated luminosity of 10.0 pb$^{-1}$ collected at center-of-mass energies of 2.6, 3.07 and 3.65 GeV with BESII, cross sections for $e^+e^-$ annihilation into hadronic final states ($R$ values) are measured with statistical errors that are smaller than 1%, and systematic errors that are about 3.5%. The running strong interaction coupling constants $\alpha_s^{(3)}(s)$ and $\alpha_s^{(5)}(M_Z^2)$ are determined from the $R$ values.
R values.
A sample of 7253 $K^\pm\to\pi^\pm e^+e^-(\gamma)$ decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be ${\rm BR}=(3.11\pm0.12)\times 10^{-7}$, where the uncertainty includes also the model dependence. The shape of the form factor $W(z)$, where $z=(M_{ee}/M_K)^2$, was parameterized according to several models, and, in particular, the slope $\delta$ of the linear form factor $W(z)=W_0(1+\delta z)$ was determined to be $\delta=2.32\pm0.18$. A possible CP violating asymmetry of $K^+$ and $K^-$ decay widths was investigated, and a conservative upper limit of $2.1\times 10^{-2}$ at 90% CL was established.
The $d\Gamma_{\pi ee}/dz$ spectrum (background subtracted, corrected for trigger efficiency). Systematic errors, notably the external one due to the branching ratios of the normalization decay mode according to PDG 2008, are not included.
This paper reports a measurement of the cross section for the pair production of top quarks in ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron. The data was collected from the CDF II detector in a set of runs with a total integrated luminosity of 1.1 fb^{-1}. The cross section is measured in the dilepton channel, the subset of ttbar events in which both top quarks decay through t -> Wb -> l nu b where l = e, mu, or tau. The lepton pair is reconstructed as one identified electron or muon and one isolated track. The use of an isolated track to identify the second lepton increases the ttbar acceptance, particularly for the case in which one W decays as W -> tau nu. The purity of the sample may be further improved at the cost of a reduction in the number of signal events, by requiring an identified b-jet. We present the results of measurements performed with and without the request of an identified b-jet. The former is the first published CDF result for which a b-jet requirement is added to the dilepton selection. In the CDF data there are 129 pretag lepton + track candidate events, of which 69 are tagged. With the tagging information, the sample is divided into tagged and untagged sub-samples, and a combined cross section is calculated by maximizing a likelihood. The result is sigma_{ttbar} = 9.6 +/- 1.2 (stat.) -0.5 +0.6 (sys.) +/- 0.6 (lum.) pb, assuming a branching ratio of BR(W -> ell nu) = 10.8% and a top mass of m_t = 175 GeV/c^2.
Measured cross section assuming a top quark mass of 175 GeV. The second systematic error is the uncertainty on the luminosity.
We present a measurement of the $\ttbar$ differential cross section with respect to the $\ttbar$ invariant mass, dSigma/dMttbar, in $\ppbar$ collisions at $\sqrt{s}=1.96$ TeV using an integrated luminosity of $2.7\invfb$ collected by the CDF II experiment. The $\ttbar$ invariant mass spectrum is sensitive to a variety of exotic particles decaying into $\ttbar$ pairs. The result is consistent with the standard model expectation, as modeled by \texttt{PYTHIA} with \texttt{CTEQ5L} parton distribution functions.
The measured differential cross section. The first error is the statistical plus jet energy scale uncertainty and the DSYS is the systematic error excluding the uncertainty in the luminosity.
The integrated cross section with statistical plus jet energy scale errors.
We present the first measurement of photoproduction of J/psi and of two-photon production of high-mass e+e- pairs in electromagnetic (or ultra-peripheral) nucleus-nucleus interactions, using Au+Au data at sqrt(s_NN) = 200 GeV. The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Au^{star} nuclei. The event sample consists of 28 events with m_{e+e-} > 2 GeV/c^2 with zero like-sign background. The measured cross sections at midrapidity of d\sigma / dy (J/psi + Xn, y=0) = 76 +/- 33 (stat) +/- 11 (syst) micro b and d^2\sigma/dm dy (e^+e^- + Xn, y=0) = 86 +/- 23 (stat) +/- 16 (syst) micro b/(GeV/c^2) for m_{e+e-} \in [2.0,2.8] GeV/c^2 are consistent with various theoretical predictions.
J/PSI N for ultra peripheral Au+Au reactions. The values has been obtained from the fit of the number of counts as a function of the mass of the e+e- pairs detected. The J/PSI pick has been fixed at the known mass ofJ/PSI : 3.097 GeV/c2.
e+e- pairs N in ultra peripherals Au + Au reactions. The values has been obtained from the fit of the number of counts as a function of the mass of the e+e- pairs.The results are given for 3 intervals of masses of the electron pair : 2.0 to 2.3, 2.3 to 2.8 and 2.0 to 2.8 Gev/c2.
J/PSI production cross section at mid rapidity for ultra peripheral Au+Au reactions.
The momentum distribution of electrons from semi-leptonic decays of charm and bottom for mid-rapidity |y|<0.35 in p+p collisions at sqrt(s)=200 GeV is measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) over the transverse momentum range 2 < p_T < 7 GeV/c. The ratio of the yield of electrons from bottom to that from charm is presented. The ratio is determined using partial D/D^bar --> e^{+/-} K^{-/+} X (K unidentified) reconstruction. It is found that the yield of electrons from bottom becomes significant above 4 GeV/c in p_T. A fixed-order-plus-next-to-leading-log (FONLL) perturbative quantum chromodynamics (pQCD) calculation agrees with the data within the theoretical and experimental uncertainties. The extracted total bottom production cross section at this energy is \sigma_{b\b^bar}= 3.2 ^{+1.2}_{-1.1}(stat) ^{+1.4}_{-1.3}(syst) micro b.
Bottom contribution to the electrons from heavy flavor decay as a function of PT. These values has been obtained using g3data software which to extract the data from the plot and should therefore be used with caution. The g3data program indicates an extra uncertainty of 0.01 on these values.
Differential bottom production cross section at mid rapidity (y=0) To obtain this value, the differential "bottom-decay" electrons cross-section has been extrapolated to PT=0 using the spectrum shape predicted by pQCD. The b->e branching ratio used was 10 +-1%.
Invariant cross section of electrons from heavy flavor decay versus PT These values has been obtained using g3data software which to extract the data from the plot and should therefore be used with caution. The values in the last column indicate the level of uncertainty intoduced by g3data.
We report the observation at the Relativistic Heavy Ion Collider (RHIC) of suppression of back-to-back correlations in the direct photon+jet channel in Au+Au relative to p+p collisions. Two-particle correlations of direct photon triggers with associated hadrons are obtained by statistical subtraction of the decay photon-hadron background. The initial momentum of the away-side parton is tightly constrained, because the parton-photon pair exactly balance in momentum at leading order in perturbative quantum chromodynamics (pQCD), making such correlations a powerful probe of the in-medium parton energy loss. The away-side nuclear suppression factor, I_AA, in central Au+Au collisions, is 0.32 +/- 0.12(stat) +/- 0.09(syst) for hadrons of 3 < p_T < 5 in coincidence with photons of 5 < p_T < 15 GeV/c. The suppression is comparable to that observed for high-p_T single hadrons and dihadrons. The direct photon associated yields in p+p collisions scale approximately with the momentum balance, z_T = p_T^hadron/p_T^photon, as expected for a measure of the away-side parton fragmentation function. We compare to Au+Au collisions for which the momentum balance dependence of the nuclear modification should be sensitive to the path-length dependence of parton energy loss.
direct $\gamma$-hadron yields per trigger p+p and Au+Au at 5<$p_{T}^{\gamma}$<7 GeV/c.
direct $\gamma$-hadron yields per trigger p+p and Au+Au at 7<$p_{T}^{\gamma}$<9 GeV/c.
direct $\gamma$-hadron yields per trigger p+p and Au+Au at 9<$p_{T}^{\gamma}$<12 GeV/c.
Measurements of the azimuthal anisotropy of high-\pT neutral pion neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX experiment are presented. The data included in this paper were collected during the 2004 RHIC running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of pi^0s detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v_2) of the angular distributions are presented as a function of pi^0 transverse momentum p_T for different bins in collision centrality. Measured reaction plane dependent pi^0 yields are used to determine the azimuthal dependence of the pi^0 suppression as a function of p_T, R_AA (Delta phi,p_T). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the pi^0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region, and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.
$\pi^0 v_2$ as function of centrality. All errors are absolute.
$\pi^0 v_2$ as function of centrality. All errors are absolute.
Rebinned $R_{AA}$ for $\Delta \phi$, $p_T$, and path length dependence,
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