35 research outputs found
Measurement of B(b)over-bar Correlations At the Cern P(p)over-bar Collider
No full textWe report on measurements of correlated bbBAR production in ppBAR collisions at square-root s = 630 GeV, using dimuon data to tag both the b and bBAR quarks. Starting from an inclusive dimuon sample we obtain improved cross-sections for single inclusive beauty production and confirm our earlier results on B0-B0BAR mixing. From a study of bbBAR correlations we derive explicit cross-sections for semi-differential bbBAR production. We compare the measured cross-sections and correlations to O(alpha(s)3) QCD predictions and find good quantitative agreement. From the measured angular distributions we establish a sizeable contribution from higher order QCD processes with a significance of about seven standard deviations. A large nonperturbative contribution to these higher order corrections is excluded
Measurement of alpha-s from b anti-b production at the CERN p anti-p collider
No full textThe UA1 Collaboration has recently improved its measurement of the beauty production cross-section by including explicit measurements of correlations. Using these data we have determined the strong coupling constant alpha(s). The comparison of the measured cross-section for 2-body final states with O(alpha(s)(3)) QCD predictions yields a measurement of alpha(S)(20 GeV) = 0.145(-0.010exp-0.016 th)(+0.012+0.013), corresponding to alpha(S)(M(Z)) = 0.113(-0.006 exp-0.009 th)(+0.007+0.008). This is the first theoretically well-defined measurement of alpha(S) from a purely hadronic production process. Evaluating alpha(S) from cross-sections at different Q(2)-values we find that the running of alpha(S) is needed for internal consistency of the UA1 data
Limits on t quark decay into charged Higgs from a direct search at the CERN p anti-p collider
No full textA search for t-quark decay into charged Higgs, t --> H+b, with the charged Higgs decaying via the H+ --> tau+nu-tau mode, has been done in proton-antiproton collisions at square root s = 0.63 TeV with the UA1 experiment. No evidence for this decay has been observed. Mass limits at 95% and 90% CL for the t-quark and the charged Higgs are presented. The results have also been interpreted in terms of the tan beta-parameter of a two-doublet Higgs sector
J/PSI AND PSI' PRODUCTION AT THE CERN P-BARP COLLIDER
No full textWe have measured the production cross-section times branching ratio for J/PSI --> mu+ mu- in ppBAR interactions at square-root s = 630 GeV in the kinematic range /y/ 5 GeV/c, BR (J/PSI --> mu+ mu-)sigma(ppBAR --> J/PSI) = 6.18 +/- 0.24 +/- 0.81 nb. The data sample collected in 1988 and 1989 for an integrated luminosity of 4.7 pb-1 represents a fivefold improvement over the statistics in our earlier study of the J/PSI production process, and the P(T) distribution which is measured extends to 28 GeV/c. Using event topology we show that the rate for the direct production of J/PSI, via radiative decays of chi-states, is larger than that for production via B-hadrons. Production of PSI' is also studied using the decay modes PSI' --> mu+ mu- and PSI' --> J/PSI-pi+pi-
CONSTRUCTION AND PERFORMANCE OF A POSITION DETECTOR FOR THE UA1 URANIUM - TMP CALORIMETER
No full textSEARCH FOR NEW HEAVY QUARKS IN PROTON - ANTI-PROTON COLLISIONS AT s**(1/2) = 0.63-TeV
No full textWe report on a search for new heavy quarks using data collected by the UA1 experiment during 1983, 1984 and 1985 at the CERN proton-antiproton collider, corresponding to an integrated luminosity of approximately 700 nb-1. Studying events with a muon or an isolated electron, accompanied by one or more jets, we find good agreement between our data and Monte Carlo predictions for the production of charm and beauty, without the need for a new quark. A top quark model, involving the decay W→t {Mathematical expression} and direct t {Mathematical expression} production via the strong interaction, is used to determine our detection efficiency for top. This allows us to place an upper limit on the cross section for producing top quarks as a function of the top quark mass. Our analysis is not sensitive to the W→t {Mathematical expression} process alone. By comparing our limit with a calculation of the t {Mathematical expression} cross section, added to the W→t {Mathematical expression} cross section derived from our own measurements of W →lv, we are able to place a lower limit on the mass of the top quark. From the lowest order (αs 2) calculation, using the choice of structure functions and Q2 scale that give the lowest cross section, we find: {Mathematical expression} Including an estimate of the next higher order (αs 2) and calculating the cross section with the EUROJET QCD Monte Carlo program using a less extreme choice for the structure functions and Q2 scale gives: {Mathematical expression} A search has also been made for a fourth generation, charge 1/3 quark (b'). Assuming that the b' mass is smaller than that of the top quark and that it can-not be produced in W decays, the mass limits, using the above procedures, are respectively mb'>32 GeV/c2 and mb'>44 GeV/c2, both at 95% confidence level. © 1988 Springer-Verlag
J / psi and psi-prime production at the CERN p anti-p collider
No full textWe have measured the production cross-section times branching ratio for J/PSI --> mu+ mu- in ppBAR interactions at square-root s = 630 GeV in the kinematic range /y/ 5 GeV/c, BR (J/PSI --> mu+ mu-)sigma(ppBAR --> J/PSI) = 6.18 +/- 0.24 +/- 0.81 nb. The data sample collected in 1988 and 1989 for an integrated luminosity of 4.7 pb-1 represents a fivefold improvement over the statistics in our earlier study of the J/PSI production process, and the P(T) distribution which is measured extends to 28 GeV/c. Using event topology we show that the rate for the direct production of J/PSI, via radiative decays of chi-states, is larger than that for production via B-hadrons. Production of PSI' is also studied using the decay modes PSI' --> mu+ mu- and PSI' --> J/PSI-pi+pi-
A search for rare B meson decays at the CERN S p anti-p S collider
No full textWe report on a search for the decays B0 --> mu+mu-, B --> mu+mu-X and B(d)0 --> mu+mu-K0*, which are expected to be rare if mediated by flavor changing neutral currents. Using data collected during the 1984-1989 CERN ppBAR Collider runs, the UA1 search was carried out using mu+mu- events with 3.9 mu+mu- of 8.3 x 10(-6), for B --> mu+mu-X of 5.0 x 10(-5), and for B(d)0 --> mu+mu-K0* of 2.3 x 10(-5). Implications for upper limits on the t-quark mass are discussed
Measurement of the ratio R = sigma(w) Br (W) ---> mu neutrino) / sigma(Z) Br (Z ---> mu mu) and gamma(W) total at the CERN proton - anti-proton collider
No full textAn analysis of W and Z boson production at UA1, using 4.66 pb-1 of data from the 1988 and 1989 CERN ppBAR Collider runs at square root of s = 0.63 TeV, yields R = sigma(w)Br(W --> mu-v)/sigma(z)Br(z --> mu-mu) = 10.4(-1.5)(+1.8)(stat.) +/- 0.8(syst). We find R = 9.5(-1.0)(+1.1)(stat. + syst.) when combining all available UA1 data, in both the electron and muon channel, taken in the period 1983-1989. In the framework of the standard model, the value of R is used to infer the total width of the W boson, I(w) (tot) = 2.18(-0.24)(+0.26) (exp.) +/- 0.04 (theory) GeV/c2
