A double scattering experiment, performed at the Paul-Scherrer-Institut (PSI), has measured a large variety of spin observables for free np elastic scattering from 260 to 535 MeV in the c.m. angle ran
Relative uncertainties on the carbon polarimeter analysing power (AC).
Relative uncertainty in the beam polarisation (PB).
Measurements of DNN with statistical errors only.
We report the branching ratios of the χc2(13P2) and χc0(13P0) charmonium resonances to two photons using event samples collected by Fermilab experiment E835 in the reactions p¯p→χc2(13P2)[χc0(13P0)]. Our result for the χc2 is B(χc2→γγ)=(1.35±0.25±0.12)×10−4. We set a 95% upper limit for the χc0 branching ratio B(χc0→γγ) at 2.09×10−4.
No description provided.
A first measurement of the cross section of the process e+e- -> Z gamma gamma is reported using a total integrated luminosity of 231 pb^-1 collected with the L3 detector at centre-of-mass energies of 182.7 GeV and 188.7 GeV. By selecting hadronic events with two isolated photons the e+e- -> Z gamma gamma cross section is measured to be 0.49 +0.20 -0.17 +/- 0.04 pb at 182.7 GeV and 0.47 +/- 0.10 +/- 0.04 pb at 188.7 GeV. The measurements are consistent with Standard Model expectations. Limits on Quartic Gauge Boson Couplings a_0/Lambda^2 and a_c/Lambda^2 of -0.009 GeV^-2 < a_0/Lambda^2 < 0.008 GeV^-2 and -0.007 GeV^-2 < a_c/Lambda^2 < 0.013 GeV^-2 are derived at 95% confidence level.
The measured cross section for the hadronic decay of the Z0.
The cross sections scaled for the hadronic Z0 branching ratio.
A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV and 189 GeV is reported. Final states containing only leptons, (l+l-l+l- and l+l-nu nubar), quark and lepton pairs, (q qbar l+l-, q qbar nu nubar) and the all-hadronic final state (q qbar q qbar) are considered. In all states with at least one Z boson decaying hadronically, q qbar and b bbar final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At sqrt(s) = 189 GeV the Z-pair cross section was measured to be 0.80 (+0.14-0.13, stat.) (+0.06-0.05, syst.) pb, consistent with the Standard Model prediction. At sqrt(s) = 183 GeV the 95% C.L. upper limit is 0.55 pb. Limits on anomalous ZZgamma and ZZZ couplings are derived.
Measured cross sections for Z0 pair production.
The DELPHI detector at LEP has collected 54 pb^{-1} of data at a centre-of-mass energy around 183 GeV during 1997, 158 pb^{-1} around 189 GeV during 1998, and 187 pb^{-1} between 192 and 200 GeV during 1999. These data were used to measure the average charged particle multiplicity in e+e- -> b bbar events, <n>_{bb}, and the difference delta_{bl} between <n>_{bb} and the multiplicity, <n>_{ll}, in generic light quark (u,d,s) events: delta_{bl}(183 GeV) = 4.55 +/- 1.31 (stat) +/- 0.73 (syst) delta_{bl}(189 GeV) = 4.43 +/- 0.85 (stat) +/- 0.61 (syst) delta_{bl}(200 GeV) = 3.39 +/- 0.89 (stat) +/- 1.01 (syst). This result is consistent with QCD predictions, while it is inconsistent with calculations assuming that the multiplicity accompanying the decay of a heavy quark is independent of the mass of the quark itself.
Only statistical errors.
No description provided.
Production of Sigma- and Lambda(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The Sigma- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its Sigma -> n pi decay leading to a kink between the Sigma- and pi-track. The reconstruction of the Lambda(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to be <N_{Sigma-}/N_{Z}^{had}> = 0.081 +/- 0.002 +/- 0.010, <N_{Lambda(1520)}/N_{Z}^{had}> = 0.029 +/- 0.005 +/- 0.005. The production rate of the Lambda(1520) suggests that a large fraction of the stable baryons descend from orbitally excited baryonic states. It is shown that the baryon production rates in Z decays follow a universal phenomenological law related to isospin, strangeness and mass of the particles.
The measured differential cross section for SIGMA- production.
The total production rate of SIGMA-. The second systematic (DSYS) error is due to the extrapolation to the fullx-range.
The measured differential cross section for LAMBDA(1520) production. The first error is the fit error.
Bhabha scattering data recorded at \sqrt{s}=189 GeV by the L3 detector at LEP are used to measure the running of the effective fine-structure constant for spacelike momentum transfers. The results are alpha^-1(-2.1 GeV^2) - alpha^-1(-6.25 GeV^2) = 0.78 +/- 0.26 alpha^-1(-12.25 GeV^2) - alpha^-1(-3434 GeV^2) = 3.80 +/- 1.29, in agreement with theoretical predictions.
No description provided.
Results extracted from the small angle Bhabha scattering sample at Z peak. Results contained total experimental uncertainty.
Results extracted from the large angle Bhabha scattering sample at sqrt(s) = 189 GeV. Results contained total experimental and theoretical uncertainty.
A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of pi+, K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, xi^*, of the xi-distributions for kaons in gluon and quark jets are observed to be different.
Jet flavor tagging is used. (C=DUSCB), (C=DUSC), (C=UDS) mean quark-jet flavors. CONST(C=GLUON/JET) is the ratio gluon/jet for all charged particles. 'Y' events, mirror symmetric events, the angle between the most energetic jet and other two jets is 150 +- 15 deg.
Jet flavor tagging is used. (C=DUSCB), (C=DUSC), (C=UDS) mean quark-jet flavors. CONST(C=GLUON/JET) is the ratio gluon/jet for all charged particles. 'Y' events, mirror symmetric events, the angle between the most energetic jet and other two jets is 150 +- 15 deg.
Jet flavor tagging is used. (C=DUSCB), (C=DUSC), (C=UDS) mean quark-jet flavors. CONST(C=GLUON/JET) is the ratio gluon/jet for all charged particles. 'Y' events, mirror symmetric events, the angle between the most energetic jet and other two jets is 150 +- 15 deg.
An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ 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 ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is $\alpha_s(M_Z^2) = 0.1180 \pm 0.0006 (exp.) \pm 0.0013 (hadr.) \pm 0.0008 (scale) \pm 0.0007 (mass)$. Further studies include an $\alpha_s$ determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and $\cal O(\alpha_s^2$) 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 $\alpha_s$ values derived from the different approaches are in good agreement.
The weighted value of ALPHA-S from all the measured observables using experimentally optimized renormalization scale values and corrected for the b-mass toleading order.
The value of ALPHA-S derived from the JCEF and corrected for heavy quark mass effects. The quoted errors are respectively due to experimental error, hadronization, renormalization scale and heavy quark mass correction uncertainties.
Energy Energy Correlation EEC.
Excitation functions AN(pp,Θc.m.) of the analyzing power in pp→ elastic scattering have been measured with a polarized atomic hydrogen target for projectile momenta pp between 1000 and 3300 MeV/ c. The experiment was performed for scattering angles 30°≤Θc.m.≤90° using the recirculating beam of the proton storage ring COSY during acceleration. The resulting excitation functions and angular distributions of high internal consistency have significant impact on the recent phase shift solution SAID SP99, in particular, on the spin triplet phase shifts between 1000 and 1800 MeV, and demonstrate the limited predictive power of single-energy phase shift solutions at these energies.
No description provided.
No description provided.
No description provided.
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