The four LEP Collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb−1 of e+e− collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for ...the Standard Model Higgs boson. The search results of the four Collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson.
Measurements of b-hadron masses are performed with the exclusive decay modes B+→J/ψK+, B0→J/ψK⁎0, B0→J/ψKS0, Bs0→J/ψϕ and Λb0→J/ψΛ using an integrated luminosity of 35 pb−1 collected in pp collisions ...at a centre-of-mass energy of 7 TeV by the LHCb experiment. The momentum scale is calibrated with J/ψ→μ+μ− decays and verified to be known to a relative precision of 2 ×10−4 using other two-body decays. The results are more precise than previous measurements, particularly in the case of the Bs0 and Λb0 masses.
The full LEP-1 data set collected with the ALEPH detector at the
Z pole during 1991–1995 is analysed in order to measure the
τ
decay branching fractions. The analysis follows the global method used ...in the published study based on 1991–1993 data, but several improvements are introduced, especially concerning the treatment of photons and
π
0
's. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to over 300
000 measured and identified
τ
decays. Branching fractions are obtained for the two leptonic channels and 11 hadronic channels defined by their respective numbers of charged particles and
π
0
's. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied to the hadronic channels to derive branching ratios for exclusive final states without kaons. Thus the analyses of the full LEP-1 ALEPH data are combined to yield a complete description of
τ
decays, encompassing 22 non-strange and 11 strange hadronic modes. Some physics implications of the results are given, in particular related to universality in the leptonic charged weak current, isospin invariance in
a
1
decays, and the separation of vector and axial-vector components of the total hadronic rate. Finally, spectral functions are determined for the dominant hadronic modes and updates are given for several analyses. These include: tests of isospin invariance between the weak charged and electromagnetic hadronic currents, fits of the
ρ
resonance lineshape, and a QCD analysis of the non-strange hadronic decays using spectral moments, yielding the value
α
s
(
m
τ
2
)
=
0.340
±
0
.
005
exp
±
0
.
014
th
. The evolution to the
Z mass scale yields
α
s
(
M
Z
2
)
=
0.1209
±
0.0018
. This value agrees well with the direct determination from the
Z width and provides the most accurate test to date of asymptotic freedom in the QCD gauge theory.
First observation of the decay B+ → π+μ+μ Adametz, A.; Adrover, C.; Ajaltouni, Z. ...
The journal of high energy physics,
12/2012, Letnik:
2012, Številka:
12
Journal Article
Recenzirano
Odprti dostop
A
bstract
A discovery of the rare decay
B
+
→
π
+
μ
+
μ
−
is presented. This decay is observed for the first time, with 5.2
σ
significance. The observation is made using
pp
collision data, ...corresponding to an integrated luminosity of 1.0 fb
−1
, collected with the LHCb detector. The measured branching fraction is (2.3 ± 0.6 (stat.) ± 0.1 (syst.))×10
−8
, and the ratio of the
B
+
→
π
+
μ
+
μ
−
and
B
+
→
K
+
μ
+
μ
−
branching fractions is measured to be 0.053 ± 0.014 (stat.) ± 0.001 (syst.).
The hadronic final states observed with the ALEPH detector at LEP in e+e- annihilation are analysed using 730 pb-1 of data collected between 91 and 209 GeV in the framework of QCD. In particular ...event-shape variables and inclusive charged particle spectra are measured. The energy evolution of quantities derived from these measurements is compared to analytic QCD predictions. The mean charged particle multiplicity, the charged particle momentum spectrum and its peak position are compared to predictions of the modified-leading-logarithmic approximation. The strong coupling constant alpha_s is determined from a fit of the QCD prediction to distributions of six event-shape variables at eight centre-of-mass energies. A study of non-perturbative power law corrections is presented
The B0, B0s, B+ and Λ0b hadron production asymmetries are measured using a data sample corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment in proton-proton ...collisions at centre-of-mass energies of 7 and 8 TeV. The measurements are performed as a function of transverse momentum and rapidity of the b hadrons within the LHCb detector acceptance. The overall production asymmetries, integrated over transverse momentum and rapidity, are also determined.
The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s√=13TeV, corresponding to an integrated ...luminosity of 279±11pb−1. The measurement is performed for J/ψ mesons with a transverse momentum of less than 10GeV/c in the rapidity range 2.0<y<4.5. The production cross-section is measured to be 13.5±0.9±0.8nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.
The suppressed decay Λ0b→pπ−μ+μ−, excluding the J/ψ and ψ(2S)→μ+μ− resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with ...proton-proton collision data corresponding to an integrated luminosity of 3fb−1 collected with the LHCb experiment. The Λ0b→pπ−μ+μ− branching fraction is measured relative to the Λ0b→J/ψ(→μ+μ−)pπ− branching fraction givingB(Λ0b→pπ−μ+μ−)B(Λ0b→J/ψ(→μ+μ−)pπ−)=0.044±0.012±0.007,where the first uncertainty is statistical and the second is systematic. This is the first observation of a b→d transition in a baryonic decay.
Search for the B0s→η′φ decay Aaij, R.; Beaucourt, L.; Chefdeville, M. ...
The journal of high energy physics,
05/2017, Letnik:
5
Journal Article
Recenzirano
A search for the charmless B0s→η′ϕ decay is performed using pp collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of ...3 fb−1. No signal is observed and upper limits on the B0s→η′ϕ branching fraction are set to 0.82×10−6 at 90% and 1.01×10−6 at 95% confidence level.
PDF
