Di-jet production in γγ collisions at LEP2 Adam, W.; Amapane, N.; Anjos, N. ...
The European physical journal. C, Particles and fields,
2008/12, Letnik:
58, Številka:
4
Journal Article
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Odprti dostop
The production of two high-
p
T
jets in the interactions of quasi-real photons in
e
+
e
−
collisions at
from 189 GeV to 209 GeV is studied with data corresponding to an integrated
e
+
e
−
luminosity ...of 550 pb
−1
. The jets reconstructed by the
k
⊥
-cluster algorithm are defined within the pseudo-rapidity range −1<
η
<1 and with jet transverse momentum,
p
T
, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum
of the jets and is compared to perturbative QCD calculations.
The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the Delphi detector at the Z resonance between 1992 and ...1995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy \({\rm e}^+{\rm e}^-\) annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio \(C_A/C_F\) is measured to be:
Multilayer optical filters, appropriately designed to reject the optical noise emitted in the range between the main UV spectral lines of the atmospheric N2 fluorescence, induced by the Ultra High ...Energy Cosmic Rays (UHECR) via the effect of Extensive Air Showers (EAS), are presented in this work. For the design we used the method of simulated annealing, assuming 40 dielectric layers. A simplified model of the main optical noise components has been used for calculating the evolution of the trigger probability and the resulting duty cycle of a pixel detector. The method has been applied for the fluorescence telescope of the AUGER Observatory, assuming the use of various optical filters.
An updated analysis using about 1.5 million events recorded at s=MZ\sqrt{s} = M_Zs=MZ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are ...measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in O(αs2){\cal O} (\alpha_s^2)O(αs2) including the event orientation. A combined fit of αs\alpha_sαs and of the renormalization scale xμx_{\mu}xμ in O(αs2\cal O(\alpha_s^2O(αs2) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is αs(MZ2)=0.1174±0.0026\alpha_s(M_Z^2) = 0.1174 \pm 0.0026αs(MZ2)=0.1174±0.0026. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is αs(MZ2)=0.1180±0.0006(exp.)±0.0013(hadr.)±0.0008(scale)±0.0007(mass)\alpha_s(M_Z^2) = 0.1180 \pm 0.0006 (exp.) \pm 0.0013 (hadr.) \pm 0.0008 (scale) \pm 0.0007 (mass)αs(MZ2)=0.1180±0.0006(exp.)±0.0013(hadr.)±0.0008(scale)±0.0007(mass). Further studies include an αs\alpha_sαs determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and O(αs2\cal O(\alpha_s^2O(αs2) predictions as well as theoretically motivated optimized scale setting methods. The influence of higher order contributions was also investigated by using the method of Pad\'{e} approximants. Average αs\alpha_sαs values derived from the different approaches are in good agreement. (arXiv)
DELPHI results are presented on the inclusive production of two (KKπ)0 states in the mass region 1.2–1.6 GeV/c2 in hadronic Z decays at LEP I. The measured masses (widths) are 1274±6 MeV/c2 ...(29±12 MeV/c2) and 1426±6 MeV/c2 (51±14 MeV/c2), respectively. A partial-wave analysis of the (KKπ)0 system shows that the first peak is consistent with the IG(JPC)=0+(1++)/(0−+)a0(980)π and the second with the IG(JPC)=0+(1++)K∗(892)K+c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165±0.051) and (0.056±0.012), respectively. These measurements are consistent with the two states being the f1(1285) and f1(1420) mesons.
The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995 and 1996, have been used to determine the hadronic and leptonic ...cross-sections and leptonic forward–backward asymmetries. In addition, the cross-section ratios and forward–backward asymmetries for flavour-tagged samples of light (uds), c and b quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted by performing S-matrix fits to these data and to the data collected previously at the energies near the \({\rm Z}^0\) resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions, R-parity violating SUSY particle exchange and of possible Z\(^{'}\) bosons.
An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies greater than 10
19
eV, based on observations of the depth of shower maximum performed with the ...hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample support the conclusion that a photon origin of the observed events is not favored.
The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in collisions at LEP. As in deep inelastic scattering, ...these data are important for tests of QCD. The transverse and longitudinal components of the total hadronic cross section are evaluated from the measured fragmentation functions. They are found to be and respectively. The strong coupling constant is calculated from in next-to-leading order of perturbative QCD, giving Including non-perturbative power corrections leads to The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, The fragmentation functions and multiplicities in and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated.
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