We present a measurement of the pion form factor based on e+e- annihilation data from the CMD-2 detector in the energy range 0.6<sqrt(s)<1.0 GeV with a systematic uncertainty of 0.8%. A data sample is five times larger than that used in our previous measurement.
Measured values of the pion form factor. The errors are statistical only.
Measured value of the bare PI+ PI- cross section including corrections for radiative effects but excluding corrections for vacuum polarization effects. The errors are statistical only.
We present a measurement of the cross section of the process $e^+e^-\to\pi^+pi^-\psi(2S)$ from threshold up to 8 GeV center-of-mass energy using events containing initial-state radiation, produced at the PEP-II $e^+e^-$ storage rings. The study is based on 298 fb$^{-1}$ of data recorded with the BaBar detector. A structure is observed in the cross-section not far above threshold, near 4.32 GeV. We also investigate the compatibility of this structure with the Y(4260) previously reported by this experiment.
The measured c.m. energy dependence of the cross section with statistical errors only.. Bins with no recorded data are shown as a 'dash'.
The dependence of transverse momentum spectra of neutral pions and eta mesons with p_T <16 GeV/c and p_T < 12 GeV/c, respectively, on the centrality of the collision has been measured at mid-rapidity by the PHENIX experiment at RHIC in d+Au collisions at sqrt(s_(NN)) = 200 GeV. The measured yields are compared to those in p + p collisions at the same sqrt(s_(NN)) scaled by the number of underlying nucleon-nucleon collisions in d+Au. At all centralities the yield ratios show no suppression, in contrast to the strong suppression seen for central Au+Au collisions at RHIC. Only a weak p_T and centrality dependence can be observed.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
We present measurements of the total production rates and momentum distributions of the charmed baryon $\Lambda_c^+$ in $e^+e^- \to$ hadrons at a center-of-mass energy of 10.54 GeV and in $\Upsilon(4S)$ decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in $e^+e^- \to c\bar{c}$ events, allowing direct studies of $c$-quark fragmentation. We measure a momentum distribution for $\Lambda_c^+$ baryons that differs significantly from those measured previously for charmed mesons. Comparing with a number of models, we find none that can describe the distribution completely. We measure an average scaled momentum of $\left< x_p \right> = 0.574\pm$0.009 and a total rate of $N_{\Lambda c}^{q\bar{q}} = 0.057\pm$0.002(exp.)$\pm$0.015(BF) $\Lambda_c^+$ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, $pK^-\pi^+$. In $\Upsilon (4S)$ decays we measure a total rate of $N_{\Lambda c}^{\Upsilon} = 0.091\pm$0.006(exp.)$\pm$0.024(BF) per $\Upsilon(4S)$ decay, and find a much softer momentum distribution than expected from B decays into a $\Lambda_c^+$ plus an antinucleon and one to three pions.
LAMBDA/C+ differential production rate per hadronic event for the continuum at cm energy 10.54 GeV.
The integrated number of LAMBDA/C+'s per hadronic event for the continuum at cm energy 10.54 GeV.
LAMBDA/C+ differential production rate per UPSILON(4S) decay at cm energy 10.58 GeV.
Muon production at forward rapidity (1.5 < |\eta| < 1.8) has been measured by the PHENIX experiment over the transverse momentum range 1 < p_T \le 3 GeV/c in sqrt(s) = 200 GeV p+p collisions at the Relativistic Heavy Ion Collider. After statistically subtracting contributions from light hadron decays an excess remains which is attributed to the semileptonic decays of hadrons carrying heavy flavor, i.e. charm quarks or, at high p_T, bottom quarks. The resulting muon spectrum from heavy flavor decays is compared to PYTHIA and a next-to-leading order perturbative QCD calculation. PYTHIA is used to determine the charm quark spectrum that would produce the observed muon excess. The corresponding differential cross section for charm quark production at forward rapidity is determined to be d\sigmac c^bar)/dy|_(y=1.6)=0.243 +/- 0.013 (stat.) +/- 0.105 (data syst.) ^(+0.049(-0.087) (PYTHIA syst.) mb.
Differential charm cross section at forward rapidity of 1.6 An additional +0.049 -0.087 systematic uncertainty associated with the PYTHIA normalization is not included in the values given.
We determine rapidity asymmetry in the production of charged pions, protons and anti-protons for large transverse momentum (pT) for d+Au collisions at \sqrt s_NN = 200 GeV. The identified hadrons are measured in the rapidity regions |y| < 0.5 and 0.5 < |y| < 1.0 for the pT range 2.5 < pT < 10 GeV/c. We observe significant rapidity asymmetry for charged pion and proton+anti-proton production in both rapidity regions. The asymmetry is larger for 0.5 < |y| < 1.0 than for |y|< 0.5 and is almost independent of particle type. The measurements are compared to various model predictions employing multiple scattering, energy loss, nuclear shadowing, saturation effects, and recombination, and also to a phenomenological parton model. We find that asymmetries are sensitive to model parameters and show model-preference. The rapidity dependence of \pi^{-}/\pi^{+} and \bar{p}/p ratios in peripheral d+Au and forward neutron-tagged events are used to study the contributions of valence quarks and gluons to particle production at high pT. The results are compared to calculations based on NLO pQCD and other measurements of quark fragmentation functions.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
Cross sections for mid-rapidity production of direct photons in p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are reported for 3 < p_T < 16 GeV/c. Next-to-leading order (NLO) perturbative QCD (pQCD) describes the data well for p_T > 5 GeV/c, where the uncertainties of the measurement and theory are comparable. We also report on the effect of requiring the photons to be isolated from parton jet energy. The observed fraction of isolated photons is well described by pQCD for p_T > 7 GeV/c.
Direct photon spectra with NLO pQCD calculations for three theory scales, $\mu$ and a comparison to the NLO pQCD calculations for $\mu$ = $p_T$.
Ratio of isolated direct photons to all direct photons from the $\pi^0$-tagging method.
Ratio of isolated direct photons to all direct photons from the $\pi^0$-tagging method.
We present a study of events with Z bosons and jets produced at the Fermilab Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV. The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding to the integrated luminosity of 0.4 fb-1 collected using the D0 detector. Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross section have been measured for n = 1 to 4 jet events. Our measurements are found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization.
Ratio of the cross sections.
Number of observed events per 5 GeV bin for the >=`1Jet sample. Data read from plots.
Number of observed events per 5 GeV bin for the >=2Jet sample. Data read from plots.
We present the first statistically meaningful results from two-K0s interferometry in heavy-ion collisions. A model that takes the effect of the strong interaction into account has been used to fit the measured correlation function. The effects of single and coupled channel were explored. At the mean transverse mass m_T = 1.07 GeV, we obtain the values R = 4.09 +/- 0.46 (stat.) +/- 0.31 (sys) fm and lambda = 0.92 +/- 0.23 (stat) +/- 0.13 (sys), where R and lambda are the invariant radius and chaoticity parameters respectively. The results are qualitatively consistent with m_T systematics established with pions in a scenario characterized by a strong collective flow.
K0s invariant mass distribution
Signal to (Signal + Background) ratio for K0s decay length > 6 cm.
Mean KT distribution of K0s pairs
We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.
(a) Inclusive differential cross section for p+p -> jet +X at sqrt(s) = 200 GeV versus jet pT for a jet cone radius of 0.4. The symbols show MB (open squares) and HT (filled circles) data from the years 2003 and 2004 combined. The horizontal bars indicate the ranges of the pT intervals. The curve shows a NLO calculation. (b) Comparison of theory and data. The band indicates the experimental systematic uncertainty. The upper (lower) dashed line indicates the relative change of the NLO calculation when it is evaluated at &mu = pT/2 (&mu = 2pT).
(a) Inclusive differential cross section for p+p -> jet +X at sqrt(s) = 200 GeV versus jet pT for a jet cone radius of 0.4. The symbols show MB (open squares) and HT (filled circles) data from the years 2003 and 2004 combined. The horizontal bars indicate the ranges of the pT intervals. The curve shows a NLO calculation. (b) Comparison of theory and data. The band indicates the experimental systematic uncertainty. The upper (lower) dashed line indicates the relative change of the NLO calculation when it is evaluated at &mu = pT/2 (&mu = 2pT).
The longitudinal double-spin asymmetry ALL in p+p-> jet +X at sqrt(s) = 200 GeV versus jet pT. The uncertainties on the data points are statistical. The gray band indicates the systematic uncertainty from the beam polarization measurement, and the hatched band the total systematic uncertainty. The curves show predictions based on deep-inelastic scattering parametrizations of gluon polarization.
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