Search results for "hadron"
showing 10 items of 3505 documents
Tau lepton physics: theory overview
1996
20 páginas, 5 figuras, 11 tablas.-- Comunicación presentada en la 4ª International Workshop on Tau Lepton Physics (TAU96), Colorado, September 1996.-- arXiv:hep-ph/9612308v1
Measurement of the strong coupling constant alfa_s from global event-shape variables of hadronic Z decays
1991
Abstract An analysis of global event-shape variables has been carried out for the reaction e+e−→Z0→hadrons to measure the strong coupling constant αs. This study is based on 52 720 hadronic events obtained in 1989/90 with the ALEPH detector at the LEP collider at energies near the peak of the Z-resonance. In order to determine αs, second order QCD predictions modified by effects of perturbative higher orders and hadronization were fitted to the experimental distributions of event-shape variables. From a detailed analysis of the theoretical uncertainties we find that this approach is best justified for the differential two-jet rate, from which we obtain αs(MZ2) = 0.121 ± 0.002(stat.)±0.003(s…
Violation of quark-hadron duality and spectral chiral moments in QCD
2010
We analyze the spectral moments of the V - A two-point correlation function. Using all known short-distance constraints and the most recent experimental data from tau decays, we determine the lowest spectral moments, trying to assess the uncertainties associated with the so-called violations of quark-hadron duality. We have generated a large number of acceptable spectral functions, satisfying all conditions, and have used them to extract the wanted hadronic parameters through a careful statistical analysis. We obtain accurate values for the chi PT couplings L-10 and C-87, and a realistic determination of the dimension six and eight contributions in the operator product expansion, O-6 = (-5.…
Hadron structure at small momentum transfer
2008
Giving three examples, the form factors of the nucleon, the polarisability of the charged pion and the interference of the $S_{11}(1535)$ with the $D_{13}(1520)$ excitation of the nucleon in the $\eta p$-decay channel, it is argued that the hadron structure at low momentum transfer is highly significant for studying QCD.
Isovector and isoscalar meson cloud contributions to the nucleon electromagnetic form factors
1998
We have calculated the nucleon form factors ${G}_{E,M}^{(p,n)}{(q}^{2})$ in the linear \ensuremath{\sigma} model to one-meson-loop order plus (two-loop) $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly. The previously derived $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly generally reduces the nucleon radii and produces a shift of the magnetic moments of order 0.1 ${\ensuremath{\mu}}_{N}$ or less. We present analytical results for ${G}_{E,M}^{p,n}(0)$ which display explicitly their dependence on hadron masses and coupling constants. Analytical results for the radii are also given and the chiral singularities they contain $(\mathrm{…
Study of jet shapes in inclusive jet production inppcollisions ats=7 TeVusing the ATLAS detector
2011
Jet shapes have been measured in inclusive jet production in proton-proton collisions at root s = 7 TeV using 3 pb(-1) of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-k(t) algorithm with transverse momentum 30 GeV < p(T) < 600 GeV and rapidity in the region vertical bar y vertical bar < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the je…
Higher-order QCD predictions for dark matter production in mono- Z searches at the LHC
2015
We present theoretical predictions for mono-$Z$ production in the search for dark matter in Run-II at the LHC, including next-to-leading order QCD corrections and parton-shower effects. We consider generic simplified models with vector and scalar $s$-channel mediators. The calculation is performed by implementing the simplified models in the FeynRules/MadGraph5_aMC@NLO framework, which allows us to include higher-order QCD corrections and parton-shower effects in an automated way. We find that these corrections are sizeable and help to reduce the theoretical uncertainties. We also investigate the discovery potential in several benchmark scenarios in the 13 TeV run at the LHC.
J/psi Production at the LHC
1997
We firstly examine hadroproduction of prompt J/psi's at the Fermilab Tevatron in a Monte Carlo Framework by means of the event generator PYTHIA 5.7 in which those colour-octet matrix elements processes relevant for charmonium production have been implemented accordingly. We find that colour-octet matrix elements presented in literature from p-pbar collider data are systematically overestimated due to overlooking of the effective primordial transverse momentum of partons (i.e. including higher-order QCD effects). We estimate the size of these effects using different parton distribution functions. Finally, after normalization to Tevatron data, we extrapolate up to LHC energies making a predic…
Initial conditions of heavy ion collisions and small x
2009
The Color Glass Condensate (CGC), describing the physics of the nonlinear gluonic interactions of QCD at high energy, provides a consistent first-principles framework to understand the initial conditions of heavy ion collisions. This talk reviews some aspects of the initial conditions at RHIC and discusses implications for LHC heavy ion phenomenology. The CGC provides a way compute bulk particle production and understand recent experimental observations of long range rapidity correlations in terms of the classical glasma field in the early stages of the collision.
Simultaneous measurements of thett¯,W+W−, andZ/γ*→ττproduction cross-sections inppcollisions ats=7 TeVwith the ATLAS detector
2015
Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected ...