Search results for "DECAYS"
showing 10 items of 244 documents
A Precise Measurement of the Tau Lepton Lifetime
1996
The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result of \tau_\tau = 291.8 \pm 3.3 \mbox{ (stat.)} \pm 2.0 \mbox{(sys.) fs} while the decay length distribution of three-prong decays gives the result \tau_{\tau} = 286.7 \pm 4.9 \mbox{ (stat.)} \pm 3.3 \mbox{ (sys.) fs}. Combining the results presented here with previous DELPHI measurements, we get \tau_{\tau} = 291.4 \pm 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 \pm 0.009, compatible with lepton universality.
Measurement of the B-0 -> K*(0) e(+) e(-) branching fraction at low dilepton mass
2013
The branching fraction of the rare decay B-0 -> K*(0) e(+) e(-) in the dilepton mass region from 30 to 1000 MeV/c(2) has been measured by the LHCb experiment, using pp collision data, corresponding to an integrated luminosity of 1.0 fb(-1), at a centre-of-mass energy of 7 TeV. The decay mode B-0 -> J/psi (e(+) e(-)) K*(0) is utilized as a normalization channel. The branching fraction B(B-0 -> K*(0) e(+) e(-)) is measured to be B(B-0 -> K*(0) e(+) e(-))(30-1000 MeV/c2) = (3.1(-0.8)(-0.3)(+0.9)(+0.2) +/- 0.2) x 10(-7) where the fi rst error is statistical, the second is systematic, and the third comes from the uncertainties on the B-0 -> J/K*(0) and J/psi -> e(+) e(-) branching fractions.
Measurement of CP asymmetries in the decays B0 → K*0 μ+μ- and B+ → K+ μ+μ-
2014
The direct CP asymmetries of the decays B 0 → K *0 μ + μ − and B + → K + μ + μ − are measured using pp collision data corresponding to an integrated luminosity of 3.0 fb−1 collected with the LHCb detector. The respective control modes B 0 → J/ψK *0 and B + → J/ψK + are used to account for detection and production asymmetries. The measurements are made in several intervals of μ + μ − invariant mass squared, with the ϕ(1020) and charmonium resonance regions excluded. Under the hypothesis of zero CP asymmetry in the control modes, the average values of the asymmetries are ACP(B0→K∗0μ+μ−)=−0.035±0.024±0.003,ACP(B+→K+μ+μ−)=0.012±0.017±0.001, where the first uncertainties are statistical and the …
Measurement of branching fractions and rate asymmetries in the rare decays B -> K((*))l(+)l(-)
2012
In a sample of 471 million BB events collected with the BABAR detector at the PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is either e+e- or mu+mu-. We report results on partial branching fractions and isospin asymmetries in seven bins of di-lepton mass-squared. We further present CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi resonance. We find no evidence for CP or lepton-flavor violation. The partial branching fractions and isospin asymmetries are consistent with the Standard Model predictions and with results from other experiments.
Charged kaon femtoscopic correlations inppcollisions ats=7 TeV
2013
Correlations of two charged identical kaons (KchKch) are measured in pp collisions at root s = 7 TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional (KKch)-K-ch correlation functions are constructed in three multiplicity and four transverse momentum ranges. The (KKch)-K-ch femtoscopic source parameters R and lambda are extracted. The (KKch)-K-ch correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with increasing transverse momentum. These trends are similar to the ones observed for pi pi and K-s(0) K-s(0) correlations in pp and heavy-ion collisions. However at high multiplicities, there is an indica…
A search for invisible Higgs bosons produced in e+e- interactions at LEP 2 energies
1999
Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field. (C) 1999 Elsevier Science B.V. All rights reserved.
A strategy to study the role of the charm quark in explaining the Delta{I}=1/2 rule
2004
We present a strategy designed to separate several possible origins of the well-known enhancement of the Delta{I}=1/2 amplitude in non-leptonic kaon decays. In particular, we seek to disentangle the contribution of physics at the typical QCD scale (soft-gluon exchange) from the effects at the scale of the charm quark mass. This is achieved by considering QCD with an unphysically light charm quark, so that the theory possesses an approximate SU(4)_L x SU(4)_R chiral symmetry. By computing the relevant operator matrix elements and monitoring their values as the charm quark mass departs from the SU(4)-symmetric situation, the role of the charm quark can be assessed. We study the influence of t…
Measurement of the Z$^0$ branching fraction to b quark pairs using the boosted sphericity product
1992
Abstract From a sample of about 120 000 hadronic Z 0 decays, using a technique based on a separation of the different event categories in the boosted sphericity product, the fraction of b b decays has been measured to be 0.219 ± 0.014 (stat)± 0.019 (syst). Using the DELPHI determination of the hadronic Z 0 width, this corresponds to a partial width τ b b = 378 ± 42 MeV (in good agreement with the standard model prediction of ∼-380 MeV). Combining this measurement with the determinations based on events with high p t leptons gives an estimate for the branching ratio of b into leptons at LEP of (11.2 ± 1.2)%, consistent with previous determinations.
A Measurement of Sin2-theta-w From the Charge Asymmetry of Hadronic Events At the Z0 Peak
1992
Abstract View references (24)The weak mixing angle has been measured from the charge asymmetry of hadronic events with two different approaches using the DELPHI detector at LEP. Both methods are based on a momentum-weighted charge sum to determine the jet charge in both event hemispheres. In a data sample of 247 300 multihadronic Z0 decays a charge asymmetry of 〈QF〉 - 〈QB〉 = -0.0076±0.0012(stat.)±0.0005(exp. syst.)±0.0014(frag.) and a raw forward-backward asymmetry of Araw FB = -0.0109±0.0020(stat.)±0.0010(exp. syst.)±0.0017(frag.) have been measured. This result corresponds to a value of sinθeff=0.2345±0.0030(exp.)±0.0027(frag.) ,sin2θMS=0.2341±0.0030(exp.)±0. 0027(frag.) and to sin2θW=1-m…
W pair production cross-section and W branching fractions in $e^{+}e^{-}$ interactions at 189 GeV
2000
The cross-section for the process e+e- -> W+W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 189 GeV and corresponding to an integrated luminosity of 155 pb^{-1}. Based on the 2392 events selected as WW candidates, the cross-section for the doubly resonant process e+e- -> W+W- has been measured to be 15.83 +- 0.38 (stat) +- 0.20 (syst) pb. The branching fractions of the W decay were also measured and found to be in good agreement with the Standard Model expectation. From these a value of the CKM mixing matrix element |V_{cs}| = 1.001 +- 0.040 (stat) +- 0.020 (syst) was derived.