Single top production via the flavour changing neutral current reactions e+e−→t̄c,t̄u is searched for within the 214 pb−1 of data collected by ALEPH at centre-of-mass energies between 204 and ...209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t→Zc)+BR(t→Zu)<14%, for BR(t→γc)+BR(t→γu)=0 and mt=174 GeV/c2.
A search for charged Higgs bosons produced in pairs is performed with data collected at centre-of-mass energies ranging from 189 to 209 GeV by ALEPH at LEP, corresponding to a total luminosity of ...629 pb
−1. The three final states
τ
+ν
ττ
−
ν
̄
τ
,
c
s
̄
τ
−
ν
̄
τ
and
c
s
̄
s
c
̄
are considered. No evidence for a signal is found and lower limits are set on the mass
m
H
±
as a function of the branching fraction
B(
H
+→τ
+ν
τ
)
. In the framework of a two-Higgs-doublet model, and assuming
B(
H
+→τ
+ν
τ
)+
B(
H
+→c
s
̄
)=1
, charged Higgs bosons with masses below 79.3 GeV/
c
2 are excluded at 95% confidence level independently of the branching ratios.
I will review new studies of b-quark fragmentation performed at the Z peak by ALEPH and SLD. An improved sensitivity to distinguish between fragmentation model and more accurate measurements of the ...mean b-hadron scaled energy have been obtained.
This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, ...(II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.
Searches for scalar top, scalar bottom and mass-degenerate scalar quarks are performed in the data collected by the ALEPH detector at LEP, at centre-of-mass energies up to 209 GeV, corresponding to ...an integrated luminosity of 675 pb
−1. No evidence for the production of such particles is found in the decay channels
t
̃
→
c/
uχ
,
t
̃
→
bℓ
ν
̃
,
b
̃
→
bχ
,
q
̃
→
qχ
or in the stop four-body decay channel
t
̃
→
bχ
f
f
̄
′
studied for the first time at LEP. The results of these searches yield improved mass lower limits. In particular, an absolute lower limit of 63 GeV/
c
2 is obtained for the stop mass, at 95% confidence level, irrespective of the stop lifetime and decay branching ratios.
This Report summarizes the proceedings of the 2015 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, ...(II) the new PDF4LHC parton distributions, (III) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (IV) a host of phenomenological studies essential for comparing LHC data from Run I with theoretical predictions and projections for future measurements in Run II, and (V) new developments in Monte Carlo event generators.
The single top production via flavour changing neutral currents in the reactions ee -> t c/u is searched for in approximately 411 pb-1 of data collected by ALEPH at centre-of-mass energies in the ...range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. A 95\%~CL upper limit of 0.72 pb on the single top production cross section at 202 GeV is derived assuming a top mass of 174 GeV/c^2 and a 100% branching ratio of the top decay into bW. A model dependent limit on the flavour-changing couplings kZ and kg is obtained by combining all centre-of-mass energies.
Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 pb^-1 of data collected at Ecm = 188.6~GeV with the ALEPH detector.These ...topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states.No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/c^2 on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter Lambda are derived, independently of the NLSP lifetime.
The production rates and the inclusive cross sections of the isovector meson $\pi^0$, the isoscalar mesons $\eta$ and $\eta^\prime(958)$, the strange meson $\mathrm{K^0_S}$ and the $\Lambda$ baryon ...have been measured as functions of scaled energy in hadronic events two-jet events and each jet of three-jet events from hadronic Z decays and compared to Monte Carlo models. The analysis is based on 3.7~million hadronic events collected with the ALEPH detector at LEP at a centre-of-mass energy of $\sqrt{s}=91.2$~GeV. The JETSET modelling of the gluon fragmentation into isoscalar mesons is found to be in agreement with the experimental results. HERWIG fails to describe the $\mathrm{K^0_S}$ spectra in gluon-enriched jets and the $\Lambda$ spectra in quark jets.
Searches for charginos and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies near 183 GeV. In these searches, it is assumed that R-parity is ...conserved and that the lightest neutralino is the LSP. No evidence of a signal is observed in the 57 pb\(^{-1}\) accumulated, which excludes chargino and associated neutralino production up to the kinematic limit over large regions of the MSSM parameter space. Under the assumptions of common gaugino and common sfermion masses at the unification scale, the interplay between the chargino, neutralino and slepton exclusion limits allows a lower bound of 27 GeV/\(c^2\) to be set on the mass of the lightest neutralino. Tighter constraints on the MSSM parameter space are obtained using in addition exclusions in the Higgs sector. Finally, the results are interpreted within the framework of minimal supergravity.
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