Jet properties ine+e− annihilation at center of mass energies of 14, 22, 35 and 43.7 GeV were studied with the data collected in the TASSO detector at PETRA, using the same evaluation procedures for all the energies. The total hadronic cross section ratio for the center of mass energy interval 39–47 GeV was determined to be ℛ=4.11±0.05 (stat)±0.18(syst.) at\(\langle \sqrt s \rangle= 43 - 7\) GeV. Corrected distributions of global shape variables are presented as well as the inclusive charged particle distributions for scaled momentum and transverse momentum. The center of mass energy evolution of the average sphericity, thrust, aplanarity and particle momentum is shown.
R values. First systematic error comes from selection cuts and Monte Carlo, the second from the luminosity measurement and missing terms in the radiative correction calculations.
Normalised scaled momentum distributions. Data have combined statistical and systematic errors. These data superceded previous TASSO data (ZP C22 (84) 307 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1279> RED = 1279 </a>)).
Normalised scaled momentum distributions. Data have combined statistical and systematic errors. The binning is as used in fits in the paper. These data superceded previous TASSO data (ZP C22 (84) 307 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1279> RED = 1279 </a>)).
We present the general properties of jets produced bye+e− annihilation. Their production and fragmentation characteristics have been studied with charged particles for c.m. energies between 12 and 43 GeV. In this energy rangee+e− annihilation into hadrons is dominated by pair production of the five quarksu, d, s, c andb. In addition, hard gluon bremsstrahlung effects which are invisible at low energies become prominent at the high energies. The observed multiplicity distributions deviate from a Poisson distribution. The multiplicity distributions for the overall event as well as for each event hemisphere satisfy KNO scaling to within ∼20%. The distributions ofxp=2p/W are presented; scale breaking is observed at the level of 25%. The quantityxpdδ/dxp is compared with multigluon emission calculations which predict a Gaussian distribution in terms of ln(1/x). The observed energy dependence of the maximum of the distributions is in qualitative agreement with the calculations. Particle production is analysed with respect to the jet axis and longitudinal and transverse momentum spectra are presented. The angular distribution of the jet axis strongly supports the idea of predominant spin 1/2 quark pair production. The particle distributions with respect to the event plane show clearly the growing importance of planar events with increasing c.m. energies. They also exclude the presence of heavy quark production,e+e−→Q\(\bar Q\) for quark masses up to 5<mQ<20.3 GeV (|eQ|=2/3) and 7<mQ<19 GeV (|eQ|=1/3). The comparison of 1/σtotdδ/dpT measured at 14, 22 and 34 GeV suggests that hard gluon bremsstrahlung contributes mainly to transverse momenta larger than 0.5 GeV/c. The rapidity distribution forW≧22 GeV shows an enhancement away fromy=0 which corresponds to an increase in yield of 10–15% compared to the centre region (y=0). The enhancement probably results from heavy quark production and gluon bremsstrahlung. The particle flux around the jet axis shows with increasing c.m. energy a rapidly growing number of particles collimated around the jet axis, while at large angles to the jet axis almost noW dependence is observed. For fixed longitudinal momentump‖ approximate “fan invariance” is seen: The shape of the angular distribution around the jet axis is almost independent ofW. The collimation depends strongly onp‖. For smallp‖,p‖<0.2 GeV/c, isotropy is observed. With increasingp‖ the particles tend to be emitted closer and closer to the jet axis.
R VALUES BELOW 32.5 GEV ARE IDENTICAL TO THOSE GIVEN IN BRANDELIK ET AL., PL 113B, 499 (1982).
No description provided.
CHARGED PARTICLE MULTIPLICITY DISTRIBUTIONS.
The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at sqrt(s) = 7 TeV. The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb-1, is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|eta|<1.37 and 1.52<|eta|<2.37) and with an angular separation Delta R>0.4, is 44.0 (+3.2) (-4.2) pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins--Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.
Experimental cross-section values per bin in PB*GEV**-1 for M(2GAMMA).
Experimental cross-section values per bin in PB*GEV**-1 for PT(2GAMMA).
Experimental cross-section values per bin in PB*RAD**-1 for DELTA(PHI(2GAMMA)).
The transverse momentum ($p_{\mathrm T}$) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC in the range $0.15<p_{\mathrm T}<50$ GeV/$c$. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for $p_{\mathrm T}$ larger than 2 GeV/$c$, with a weak indication of a Cronin-like enhancement for $p_{\rm T}$ around 4 GeV/$c$. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV.
Transverse momentum distributions of charged particles in minimum-bias (NSD) p-Pb collisions for different pseudorapidity ranges.
The histogram represents the reference spectrum (cross section scaled by the nuclear overlap function, T(pPb)) in inelastic pp collisions, determined in |eta(cms)| < 0.8.
The ratio of spectra in p-Pb at backward pseudorapidities to that at |eta(cms)| < 0.3.
Measurements of charged jet production as a function of centrality are presented for p-Pb collisions recorded at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon-nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-$k_{\rm T}$ algorithm for resolution parameters $R = 0.2$ and $R = 0.4$ in the transverse momentum range 20 to 120 GeV/$c$. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p-Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.
pp reference spectrum, obtained by scaling down the measured charged jets at 7 TeV to 5.02 TeV for R = 0.2 jets.
$p_{\rm T}$-differential production cross section of charged jets in p-Pb collisions at 5.02 TeV for R = 0.2 measured with the ALICE detector, centrality 0-20%.
$p_{\rm T}$-differential production cross section of charged jets in p-Pb collisions at 5.02 TeV for R = 0.2 measured with the ALICE detector, centrality 20-40%.
The ALICE Collaboration has measured the inclusive production of muons from heavy flavour decays at forward rapidity, 2.5 < y < 4, in pp and Pb-Pb collisions at $\sqrt {s_{NN}}$ = 2.76 TeV. The $p_{\rm T}$-differential inclusive cross section of muons from heavy flavour decays in pp collisions is compared to perturbative QCD calculations. The nuclear modification factor is studied as a function of pt and collision centrality. A weak suppression is measured in peripheral collisions. In the most central collisions, a suppression of a factor of about 3-4 is observed in 6 < $p_{\rm T}$ < 10 GeV/$c$. The suppression shows no significant $p_{\rm T}$ dependence.
Transverse momentum differential inclusive cross section of muons from heavy-flavour decays in the rapidity range 2.5-4.
RAA of muons from heavy-flavour decays in the rapidity range 2.5-4 as a function of PT in the 0-10% and 40-80% centrality classes. The second (sys) error is the separate normalization error for each class.
RAA of muons from heavy-flavour decays as a function of the mean number of participating nucleons, NPART, in the rapidity range 2.5-4.0 and PT 6-10 GeV. The first (sys) error is the correlated systematic error and the second is the uncorrelated systematic error.
The beauty production cross section for deep inelastic scattering events with at least one hard jet in the Breit frame together with a muon has been measured, for photon virtualities Q^2 > 2 GeV^2, with the ZEUS detector at HERA using integrated luminosity of 72 pb^-1. The total visible cross section is sigma_b-bbar (ep -> e jet mu X) = 40.9 +- 5.7 (stat.) +6.0 -4.4 (syst.) pb. The next-to-leading order QCD prediction lies about 2.5 standard deviations below the data. The differential cross sections are in general consistent with the NLO QCD predictions: however at low values of Q^2, Bjorken x, and muon transverse momentum, and high values of jet transverse energy and muon pseudorapidity, the prediction is about two standard deviations below the data.
Total visible cross section in the specified kinematic region.
Differential cross section w.r.t. Q**2.
Differential cross section w.r.t. log10(x).
The $p_{\rm T}$-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at mid-rapidity in proton-proton collisions at $\sqrt{s} = 2.76$ TeV in the transverse momentum range 0.5 < $p_{\rm T}$ < 12 GeV/$c$ with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties.
Double-differential cross section for the production of electrons, i.e. (electron + positron)/2, from heavy-flavour hadron decays as a function of transverse momentum at mid-rapidity. The systematic uncertainties do not include an additional normalization uncertainty of 1.9%.
Inclusive production of $D^*(2010)$ mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.9 pb$^{-1}$. The decay channel $D^{* +}\to D^0 \pi^+ $ with $D^0\to K^-\pi^+$ and corresponding antiparticle decay were used to identify $D^*$ mesons. Differential $D^*$ cross sections with $1.5<Q^2<1000$ GeV$^2$ and $0.02<y<0.7$ in the kinematic region $1.5<p_T(D^*)<15$ GeV and $|\eta(D^*)|<1.5$ are compared to different QCD calculations incorporating different parameterisations of the parton densities in the proton. The data show sensitivity to the gluon distribution in the proton and are reasonably well described by next-to-leading-order QCD with the ZEUS NLO QCD fit used as the input parton density in the proton. The observed cross section is extrapolated to the full kinematic region in $p_T(D^*)$ and $\eta(D^*)$ in order to determine the open-charm contribution, $F_2^{\rm charm}(x,Q^2)$, to the proton structure function, $F_2$. Since, at low $Q^2$, the uncertainties of the data are comparable to those from the QCD fit, the measured differential cross sections in $y$ and $Q^2$ should be used in future fits to constrain the gluon density.
Overall total cross section. The second DSYS error is due to the uncertainty in the BR for D* and D0 decay.
Measured differential cross section as a function of Q**2.
Measured differential cross section as a function of X.
We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a centre-of-mass energy $\sqrt{s}=$ 7 TeV. Jets with pseudo-rapidity $\left| \eta \right| < {\rm 0.5}$ are reconstructed from charged particles using the anti-$k_{\rm T}$ jet finding algorithm with a resolution parameter $R$ = 0.4. The jet cross section is measured in the transverse momentum interval 5 $\leq p_{\rm T}^{\rm ch \; jet} <$ 100 GeV/$c$. Jet fragmentation is studied measuring the scaled transverse momentum spectra of the charged constituents of jets in four intervals of jet transverse momentum between 5 GeV/$c$ and 30 GeV/$c$. The measurements are compared to calculations from the PYTHIA model as well as next-to-leading order perturbative QCD calculations with POWHEG + PYTHIA8. The charged jet cross section is described by POWHEG for the entire measured range of $p_{\rm T}^{\rm ch \; jet}$. For $p_{\rm T}^{\rm ch \; jet}$ $>$ 40 GeV/$c$, the PYTHIA calculations also agree with the measured charged jet cross section. PYTHIA6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for PYTHIA8.
Measured charged jet differential cross sections for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV.
Measured charged jet differential cross section ratios for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV for $5<p_{T}^{ch jet}<10$ GeV/$c$.
Measured charged jet differential cross section ratios for INEL proton-proton collisions at $\sqrt{s}$ = 7 TeV for $10<p_{T}^{ch jet}<15$ GeV/$c$.
Forum