481 research outputs found
First observation of Bs -> D_{s2}^{*+} X mu nu decays
Using data collected with the LHCb detector in proton-proton collisions at a
centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and
Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass
spectrum at masses consistent with the known D^+_{s1}(2536) and
$D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the
total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)=
(3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm
1.2\pm 0.5)%, where the first uncertainty is statistical and the second is
systematic. This is the first observation of the D_{s2}^{*+} state in Bs
decays; we also measure its mass and width.Comment: 8 pages 2 figures. Published in Physics Letters
R & D for collider beauty physics at the LHC
We propose an R&D program for the development of a Beauty trigger and innovative elements of the associated spectrometer. A series of short test runs is proposed at the SPS p-pbar Collider with the minimal spectrometer which will allow a credible B signal to be obtained in an invariant mass spectrum of reconstructed B mesons. The program builds on the success of the recent collider run of the P238 Collaboration, in which clean signals from beam-beam interactions were observed in a large silicon strip microvertex detector running 1.5 mm from the circulating beams. A continuing successful R&D program of the type proposed could ultimately lead to a collider experiment at the LHC to study CP Violation and rare B decays
KLEVER: An experiment to measure BR() at the CERN SPS
Precise measurements of the branching ratios for the flavor-changing neutral
current decays can provide unique constraints on CKM
unitarity and, potentially, evidence for new physics. It is important to
measure both decay modes, and
, since different new physics models affect the rates
for each channel differently. The goal of the NA62 experiment at the CERN SPS
is to measure the BR for the charged channel to within 10%. For the neutral
channel, the BR has never been measured. We are designing the KLEVER experiment
to measure BR() to 20% using a high-energy
neutral beam at the CERN SPS starting in LHC Run 4. The boost from the
high-energy beam facilitates the rejection of background channels such as
by detection of the additional photons in the final state.
On the other hand, the layout poses particular challenges for the design of the
small-angle vetoes, which must reject photons from decays escaping
through the beam exit amidst an intense background from soft photons and
neutrons in the beam. Background from decays in the beam
must also be kept under control. We present findings from our design studies
for the beamline and experiment, with an emphasis on the challenges faced and
the potential sensitivity for the measurement of BR().Comment: 13 pages, 4 figures. Submitted as input to the 2020 update of the
European Strategy for Particle Physics. v2: Included authors unintentionally
omitted in v
Physics beyond the standard model with kaons at NA62
The NA62 experiment at CERN Super Proton Synchrotron was designed to measure BR(K+ \u2192 \u3c0+\u3bdv\u304) with an in-fight technique, never used before for this measurement. This decay is characterised by a very precise prediction in the Standard Model. Its branching ratio, which is expected to be less than 10-10, is one of the best candidates to indicate indirect effects of new physics beyond SM at the highest mass scales. NA62 result on K+ \u2192 \u3c0+\u3bdv\u304 from the full 2016 data set is described. Also a search for an invisible dark photon A\u2032 has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62. The signal stems from the chain K+ \u2192 \u3c0+\u3c00 followed by \u3c00 \u2192 A\u2032\u3b3. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60 - 110 MeV/c2
Search for Ïâ° decays to invisible particles
The NA62 experiment at the CERN SPS reports a study of a sample of 4 Ă 109 tagged Ï0 mesons from K+ â Ï+Ï0(Îł), searching for the decay of the Ï0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 Ă 10â9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+ â Ï+X, where X is a particle escaping detection with mass in the range 0.110â0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson
Measurement of the very rare K + â Ï+ÎœÎœÂŻ decay
The NA62 experiment reports the branching ratio measurement BR(K+âÏ+ÎœÎœÂŻ)=(10.6â3.4+4.0|stat±0.9syst)Ă10â11 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016â2018. This provides evidence for the very rare K+âÏ+ÎœÎœÂŻ decay, observed with a significance of 3.4Ï. The experiment achieves a single event sensitivity of (0.839 ± 0.054) Ă 10â11, corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4 ± 1.0) Ă 10â11. This measurement is also used to set limits on BR(K+â Ï+X), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample
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