Flavor Decays Research Articles

On the role of leptonic CPV phases in cLFV observables

In extensions of the standard model by Majorana fermions, the presence of additional CP violating phases has been shown to play a crucial role in lepton number violating processes. In this work we show that (Dirac and Majorana) CP violating phases can also lead to important effects in charged lepton flavour violating (cLFV) transitions and decays, in some cases with a significant impact for the predicted rates of cLFV observables. We conduct a thorough exploration of these effects in several cLFV observables, and discuss the implications for future observation. We emphasise how the presence of leptonic CP violating phases might lead to modified cLFV rates, and to a possible loss of correlation between cLFV observables.

Status of the Electromagnetic Calorimeter Trigger system at the Belle II experiment

The Belle II experiment at the SuperKEKB collider in Japan has been under the construction toward a physics run in 2018 with an ultimate target of 40 times higher instantaneous luminosity than the KEKB collider. The main physics motivation is to search for the New Physics from heavy quark/lepton flavor decays. In order to select an event of interest efficiently under much higher luminosity and beam background environment than the KEKB, we have upgraded the Electromagnetic Calorimeter (ECL) hardware trigger system. It would be realized by the improvement of ECL trigger logic based on two main triggers, the total energy and the number of clusters, with an FPGA-based flexible architecture and a high speed serial link for the data transfer. We report the current status of hardware, firmware, and software that has been achieved so far. The overall scheme of the system will be presented as well.

Probing radiative neutrino mass generation through monotop production

We present a generalization of a model where the right-handed up-type quarks serve as messengers for neutrino mass generation and as a portal for dark matter. Within this framework the Standard Model is extended with a single Majorana neutrino, a coloured electroweak-singlet scalar and a coloured electroweak-triplet scalar. We calculate the relic abundance of dark matter and show that we can match the latest experimental results. Furthermore, the implications from the scattering between nuclei and the dark matter candidate are studied and we implement the latest experimental constraints arising from flavour changing interactions, Higgs production and decay and LHC collider searches for a single jet and jets plus missing energy. In addition, we implement constraints arising from scalar top quark pair-production. We also study the production of a single top in association with missing energy and calculate the sensitivity of the LHC to the top quark semileptonic decay mode with the current $20$ fb$^{-1}$ data set at a centre of mass energy of $\sqrt{s}=8$ TeV. Furthermore, we carry out the analysis to centre of mass energies of $\sqrt{s}=14$ TeV with $30$ and $300$ fb$^{-1}$ of data.

Search for [formula omitted] oscillations at SLD

We present preliminary results on the time dependence of B s 0− B s 0 and B d 0− B d 0 mixing using a sample of 400, 000 hadronic Z 0 decay collected by the SLD experiment at the SLC. The analyses take advantage of the excellent decay length resolution of the CCD vertex detector. The B or B production flavor is determined by exploiting the large forward-backward asymmetry of polarized Z 0 → b b decays. This flavor tag is enhanced by incorporating additional information from the hemisphere opposite that of the reconstructed B decay. The B d 0- B d 0 mixing analysis uses the charge of high momentum kaons to identify the B or B decay flavor. The result is Δm d = 0.503 ± 0.028(stat) ± 0.020(syst) ps −1. The results of three separate B s 0- B s 0 mixing analyses are presented. These analyses determine the B decay flavor using the lepton charge in B semileptonic decays, the charge of fully reconstructed D s decays, and the charge difference between topologically reconstructed B and D decays. The three analyses are combined to set a lower limit on the B s 0 − B s 0 oscillation frequency of 12.0 ps −1 at 95% CL.

Search for time-dependentBs0−Bs0¯oscillations using a vertex charge dipole technique

We report a search for B{sub s}{sup 0} - {bar B}{sub s}{sup 0} oscillations using a sample of 400,000 hadronic Z{sup 0} decays collected by the SLD experiment. The analysis takes advantage of the electron beam polarization as well as information from the hemisphere opposite that of the reconstructed B decay to tag the B production flavor. The excellent resolution provided by the pixel CCD vertex detector is exploited to cleanly reconstruct both B and cascade D decay vertices, and tag the B decay flavor from the charge difference between them. We exclude the following values of the B{sub s}{sup 0} - {bar B}{sub s}{sup 0} oscillation frequency: {Delta}m{sub s} < 4.9 ps{sup -1} and 7.8 < {Delta}m{sub s} < 10.3 ps{sup -1} at the 95% confidence level.

Search for time-dependentBs0−Bs0¯oscillations using exclusively reconstructedDs±mesons

A search for Bs0-Bs0bar oscillations is performed using a sample of 400,000 hadronic Z0 decays collected by the SLD experiment. The Bs0 candidates are reconstructed in the Bs0 to Ds-,X channel with Ds- to phi,pi- or K*0K-. The Bs0 production flavor is determined using the large forward-backward asymmetry of polarized Z0 to b,bbar decays and charge information in the hemisphere opposite that of the Bs0 candidate. The decay flavor is tagged by the charge of the Ds+/-. From a sample of 361 candidates with an average Bs0 purity of 40%, we exclude the following values of the oscillation frequency: Delta m_s < 1.4 ps^{-1} and 2.4 < Delta m_s < 5.3 ps^{-1} at the 95% confidence level.

A study of B meson oscillations using hadronic $\mathrm Z^0$ decays containing leptons

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z(0) decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B-d(0) mass eigenstates upper-delta-m(d)=0.444plusminus0.029(-0.017)(+0.020)ps(-1).For the B-s(0) system, we find upper-delta-m(s)>3.1ps(-1) at the 95% confidence level. This limit varies only a little if alternative limit setting approaches are adopted. Regions at higher upper-delta-m(s) values are also excluded with some methods for setting the limit.By studying the charge symmetry of the B-d(0) mixing structure, we are able to constrain possible CP and CPT violating effects. We measure the CP violation parameter Re-epsilon(B)=-0.006plusminus0.010plusminus0.006 and the indirect CPT violating parameter Im-delta(B)=-0.020plusminus0.016plusminus0.006. If we invoke CPT symmetry, then we obtain Re-epsilon(B)=0.002plusminus0.007plusminus0.003.