We report on a CDF measurement of the total cross section and rapidity distribution, $d\sigma/dy$, for $q\bar{q}\to \gamma^{*}/Z\to e^{+}e^{-}$ events in the $Z$ boson mass region ($66
Total cross section integrated up to ABS(YRAP)=2.9.
Rapiditiy distribution of E+ E- pairs in the mass range from 66 to 116 GeV.
We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum pT > 0.5 GeV/c, pseudorapidity |\eta| < 1) produced in association with large transverse momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-pT jet production) in each event to define three regions of \eta-\phi space; toward, away, and transverse, where \phi is the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-pT jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.
Drell-Yan events. Charged particle density in the toward, transverse and away regions.
Drell-Yan events. Charged particle density in the transMAX, transMIN and transDIF regions.
Drell-Yan events. Charged particle PTsum density in the toward, transverse and away regions.
The upper limit of the total cross section for the pn --> pn eta' reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R_eta' = sigma(pn --> pn eta') / sigma(pp --> pp eta') with the corresponding ratio for eta-meson production does not favor the dominance of the N*(1535) resonance in the production process of the eta' meson and suggests nonidentical production mechanisms for eta and eta' mesons.
Upper limits of the total cross section.
The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |eta|<2.5 and pT>500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at eta = 0 is measured to be 1.333 +/- 0.003 (stat.) +/- 0.040 (syst.), which is 5-15% higher than the Monte Carlo models predict.
Average value of charged particle multiplicity per event and unit of pseudorapidity in the pseudorapidity range from -0.2 to 0.2.
Charged particle multiplicity as a function of pseudorapidity.
Charged particle multiplicity as a function of transverse momentum.
For the first time, differential inclusive-jet cross sections have been measured in neutral current deep inelastic ep scattering using the anti-kT and SIScone algorithms. The measurements were made for boson virtualities Q^2 > 125 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 82 pb^-1 and the jets were identified in the Breit frame. The performance and suitability of the jet algorithms for their use in hadron-like reactions were investigated by comparing the measurements to those performed with the kT algorithm. Next-to-leading-order QCD calculations give a good description of the measurements. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(alphas^3) terms. Values of alphas(Mz) were extracted from the data; the results are compatible with and have similar precision to the value extracted from the kT analysis.
Measured differential cross section DSIG/DE for inclusive jet production using the anti-KT jet algorithm.
Measured differential cross section DSIG/DE for inclusive jet production using the SIScone jet algorithm.
The measured differential cross section DSIG/DQ**2 for inclusive jet production using the anti-KT jet algorithm.
Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector for photon energies between 0.92 and 1.68~GeV at the electron accelerator ELSA. The beam asymmetry~$\Sigma$ has been extracted for $115^\circ < \theta_{\rm c.m.} < 155^\circ$ of the $\pi^0$~meson and for $\theta_{\rm c.m.} < 60^\circ$. The new beam asymmetry data improve the world database for photon energies above 1.5~GeV and, by covering the very forward region, extend previously published data for the same reaction by our collaboration. The angular dependence of $\Sigma$ shows overall good agreement with the SAID parameterization.
Photon beam asymmetry at incident photon energy 0.932 GeV.
Photon beam asymmetry at incident photon energy 0.965 GeV.
Photon beam asymmetry at incident photon energy 0.998 GeV.
Nuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons - composed of an antiproton, antineutron, and antilambda hyperon - produced by colliding gold nuclei at high energy. Our analysis yields 70 +- 17 antihypertritons and 157 +- 30 hypertritons. The measured yields of hypertriton (antihypertriton) and helium3 (antihelium3) are similar, suggesting an equilibrium in coordinate and momentum space populations of up, down, and strange quarks and antiquarks, unlike the pattern observed at lower collision energies. The production and properties of antinuclei, and nuclei containing strange quarks, have implications spanning nuclear/particle physics, astrophysics, and cosmology.
(A, B) show the invariant mass distribution of the daughter 3He + π. The open circles represent the signal candidate distributions, while the solid black lines are background distributions. The blue dashed lines are signal (Gaussian) plus background (double exponential) combined fit.
(A, B) show the invariant mass distribution of the daughter 3He + π. The open circles represent the signal candidate distributions, while the solid black lines are background distributions. The blue dashed lines are signal (Gaussian) plus background (double exponential) combined fit. A (B) shows the 3ΛH (3Λ¯H) candidate distributions.
The 3ΛH (solid squares) and Λ (open circles) yield distributions versus cτ. The solid lines represent the cτ fits. The inset depicts the $\chi^2$ distribution of the best 3ΛH cτ fit. The error bars represent the statistical uncertaintiesonly.
Differential measurements of the elliptic (v_2) and hexadecapole (v_4) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p_T) and collision centrality or the number of participant nucleons (N_part) for Au+Au collisions at sqrt(s_NN)=200 GeV. The v_{2,4} measurements at pseudorapidity |\eta|<=0.35 obtained with four separate reaction plane detectors positioned in the range 1.0<|\eta|<3.9 show good agreement, indicating the absence of significant \eta-dependent nonflow perturbations. Sizable values for v_4(p_T) are observed with a ratio v_4(p_T,N_part)/v_2^2(p_T,N_part)~0.8 for 50
Glauber quantities ($N_{part}$, $N_{coll}$, $b$) for Au+Au collisions at 200 GeV (PHENIX Run 2007)
Event-plane resolution factors vs. $N_{part}$ for $v_2$ and $v_4$ measurements for the indicated event planes.
Comparison of $v_2$ vs. $N_{part}$ and $v_4$ vs. $N_{part}$ for charged hadrons obtained with several reaction plane detectors for the $p_T$ selections indicated.
Measurements of the proton and deuteron $F_2$ structure functions are presented. The data, taken at Jefferson Lab Hall C, span the four-momentum transfer range $0.06 < Q^2 < 2.8$ GeV$^2$, and Bjorken $x$ values from 0.009 to 0.45, thus extending the knowledge of $F_2$ to low values of $Q^2$ at low $x$. Next-to-next-to-leading order calculations using recent parton distribution functions start to deviate from the data for $Q^2<2$ GeV$^2$ at the low and high $x$-values. Down to the lowest value of $Q^2$, the structure function is in good agreement with a parameterization of $F_2$ based on data that have been taken at much higher values of $Q^2$ or much lower values of $x$, and which is constrained by data at the photon point. The ratio of the deuteron and proton structure functions at low $x$ remains well described by a logarithmic dependence on $Q^2$ at low $Q^2$.
Proton and Deuteron F2 structure function for an x value of 0.040, determined via the Rosenbluth separation method. Error is shown without the contribution from radiative corrections.
Proton and Deuteron F2 structure function for an x value of 0.060, determined via the Rosenbluth separation method. Error is shown without the contribution from radiative corrections.
Proton and Deuteron F2 structure function for an x value of 0.080, determined via the Rosenbluth separation method. Error is shown without the contribution from radiative corrections.
A measurement of the $t\bar{t}$ production cross section in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II Detector. The result in a data sample corresponding to an integrated luminosity 2.8 $fb^{-1}$ is: $\sigma_{t\bar{t}}$ = 6.27 $\pm$ 0.73(stat) $\pm$ 0.63(syst) $\pm$ 0.39(lum) pb. for an assumed top mass of 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.
Forum