68 research outputs found
Lattice QCD calculation of scattering length
We study s-wave pion-pion () scattering length in lattice QCD for
pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered
fermion formulation, we calculate the four-point functions for isospin
I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order
to extrapolate our simulation results. Extrapolating to the physical pion mass
gives the scattering lengths as and for isospin I=2 and 0 channels, respectively. Our lattice
simulation for scattering length in the I=0 channel is an exploratory
study, where we include the disconnected contribution, and our preliminary
result is near to its experimental value. These simulations are performed with
MILC 2+1 flavor gauge configurations at lattice spacing fm.Comment: Remove some typo
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Search for heavy neutral lepton production in K+ decays
A search for heavy neutral lepton production in K + decays using a data sample collected with a minimum
bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to 10−6 level
are established on the elements of the extended neutrino mixing matrix |Ue4|
2 and |Uμ4|
2 for heavy
neutral lepton mass in the ranges 170–448 MeV/c2 and 250–373 MeV/c2, respectively. This improves on
the previous limits from HNL production searches over the whole mass range considered for |Ue4|2 and
above 300 MeV/c2 for |Uμ4|2
Search for oscillations using inclusive lepton events
A search for Bs oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the prop er time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to Bs mixing is obtained by identifying subsamples of events having a Bs purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Dms>9.5 ps-1 at 95% CL. Combining with the ALEPH Ds based analyses yields Dms>9.6 ps-1 at 95% CL.A search for B0s oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991-1995. Compared to previous inclusive lepton analyses, the proper time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to B0s mixing is obtained by identifying subsamples of events having a B0s purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of Deltam_s>9.5ps^-1 at 95% CL. Combining with the ALEPH D-s based analyses yields Deltam_s>9.6ps^-1 at 95% CL
Measurement of the very rare decay
The decay K+→π+νν¯
, with a very precisely predicted branching ratio of less than 10−10
,
is among the best processes to reveal indirect effects of new physics.
The NA62 experiment at CERN SPS is designed to study the K+→π+νν¯
decay and to measure its branching ratio using a decay-in-flight technique.
NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model
for the K+→π+νν¯
decay by the analysis of the 2016 and 2017 data,
and providing the most precise measurement of the branching ratio to date
by the analysis of the 2018 data.
This measurement is also used to set limits on BR(K+→π+X
), where X
is a scalar
or pseudo-scalar particle.
The final result of the BR(K+→π+νν¯
) measurement and its interpretation in terms
of the K+→π+X
decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed
Recent results on kaon decays by the NA48/2 experiment at CERN
The NA48/2 experiment reports the first observation of the rare decay K → π π e e, based on about 2000 candidates from 2003 data. The preliminary branching ratio in the full kinematic region is . A sample of 4.687 × 10 events collected in 2003/4 is analyzed to search for the dark photon ( ) via the decay chain K → π π, , . No signal is observed, limits in the plane mixing parameter ε versus its mass are reported
Tests of Chiral Perturbation Theory with decays at CERN NA48/2 experiment
The NA48/2 collaboration has accumulated the largest sampl es to date of semi-leptonic charged kaon decays in the K + − e4 (K ± → π + π − e ± ν ) and K 00 e4 ( K ± → π 0 π 0 e ± ν ) modes. From 1.1 million K + − e4 decays, form factors in the S- and P-wave have been extensive ly studied. Branching ratio and form factors have been measured at unprecedented precis ion. From ∼ 66000 K 00 e4 decays, preliminary values of the Branching ratio and form factor ha ve been obtained at a percent level precision. The comparison of Branching ratio and form facto r values in both K e4 modes sheds new light on isospin symmetry breaking effects. Form factor measurements are major inputs to the study of low energy QCD and are powerful tests of Chiral Pe rturbation Theory prediction
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