We propose that the inclusive $Xi_{bc} to Xi_{cc}^{++}+X$ decay can be a potential discovery channel for beauty-charmed baryons $Xi_{bc}$ at the LHC. The unique feature of this process is that it produces a displaced $Xi_{cc}^{++}$, which makes it al
most background free. Within the heavy diquark effective theory, the $Xi_{bc} to Xi_{cc}^{++}+X$ branching ratio is calculated to be about 3%. Further considering the production rate of $Xi_{bc}$ and the detection efficiency of $Xi_{cc}^{++}$, it is expected that hundreds of signal events will be collected by the LHCb Run3.
In this study, we investigate the discovery potential of double-charm tetraquarks $T^{{cc}}_{[bar{q}bar{q}]}$. We find that their production cross sections at the LHCb with $sqrt{s} = 13$ TeV reach $mathcal{O}(10^4)$ pb, which indicates that the LHCb
has collected $mathcal{O}(10^8)$ such particles. Through the decay channels of $T^{{cc}}_{[bar{u}bar{d}]}to D^{+}K^{-}pi^{+}$ or $D^0D^+gamma$ (if stable) or $T^{{cc}}_{[bar{u}bar{d}]}to D^0D^{*+}to D^0D^0pi^+$ (if unstable), it is highly expected that they get discovered at the LHCb in the near future. We also discuss the productions and decays of the double-charm tetraquarks at future Tera-$Z$ factories.
The well-known counterintuitive phenomenon, where the combination of unfavorable situations can establish favorable ones, is called Parrondos paradox. Here, we study one-dimensional discrete-time quantum walks, manipulating two different coins (two-s
tate) operators representing two losing games A and B, respectively, to create the Parrondo effect in the quantum domain. We exhibit that games A and B are losing games when played individually but could produce a winning expectation when played alternatively for a particular sequence of the different periods. Moreover, we also analyze the relationships between Parrondos games and quantum entanglement in our scheme. Along with the applications of different kinds of quantum walks, our outcomes potentially encourage the development of new quantum algorithms.
We analyze the capacity of future $Z$-factories to search for heavy neutrinos with their mass from 10 to 85 GeV. The heavy neutrinos $N$ are considered to be produced via the process $e^+e^-to Zto u N$ and to decay into an electron or muon and two j
ets. By means of Monte Carlo simulation of such signal events and the Standard Model background events, we obtain the upper bounds on the cross sections $sigma(e^+e^-to u Nto uell jj)$ given by the $Z$-factories with integrated luminosities of 0.1, 1 and 10 ab$^{-1}$ if no signal events are observed. Under the assumption of a minimal extension of the Standard Model in the neutrino sector, we also present the corresponding constraints on the mixing parameters of the heavy neutrinos with the Standard Model leptons, and find they are improved by at least one order compared to current experimental constraints.
We study two rare decays, $Z to pi^+pi^-$ and $K^+K^-$, in the perturbative QCD approach up to the next-to-leading order of the strong coupling and the leading power of $1/m_Z$, $m_Z$ being the $Z$ boson mass. The branching ratios $mathcal{B}(Zto pi^
+pi^-) = (0.83 pm 0.02 pm 0.02 pm 0.04)times 10^{-12}$ and $mathcal{B}(Zto K^+K^-) = (1.74^{+0.03}_{-0.05} pm 0.04 pm 0.02)times 10^{-12}$ are obtained and can be measured at a tera-$Z$ factory. Because the subleading-power contributions to the branching ratios are negligible, and the leading one does not depend on any free parameter, the two channels can serve as a touchstone for the applicability of the perturbative QCD approach.
We calculate tree-level contributions to the inclusive rare $bar B to X_{s(d)} , ell^+ell^-$ decays. At the partonic level they stem from the five-particle process $b to s(d) , q bar q , ell^+ell^-$, with $q in {u,d,s}$. While for $b to d$ transition
s such five-body final states contribute at the same order in the Wolfenstein expansion compared to the three-body partonic decay, they are CKM suppressed in $b to s$ decays. In the perturbative expansion, we include all leading-order contributions, as well as partial next-to-leading order QCD and QED effects. In the case of the differential branching ratio, we present all results completely analytically in terms of polylogarithmic functions of at most weight three. We also consider the differential forward-backward asymmetry, where all except one interference could be obtained analytically. From a phenomenological point of view the newly calculated contributions are at the percent level or below.
Studying superpartner production together with a hard initial state radiation (ISR) jet has been a useful strategy for searches of supersymmetry with a compressed spectrum at the Large Hadron Collider (LHC). In the case of the top squark (stop), the
ratio of the missing transverse momentum from the lightest neutralinos and the ISR momentum, defined as $bar{R}_M$, turns out to be an effective variable to distinguish the signal from the backgrounds. It has helped to exclude the stop mass below 590 GeV along the top corridor where $m_{tilde{t}} - m_{tilde{chi}_1^0} approx m_t$. On the other hand, the current experimental limit is still rather weak in the $W$ corridor where $m_{tilde{t}} - m_{tilde{chi}_1^0} approx m_W +m_b$. In this work we extend this strategy to the parameter region around the $W$ corridor by considering the one lepton final state. In this case the kinematic constraints are insufficient to completely determine the neutrino momentum which is required to calculate $bar{R}_M$. However, the minimum value of $bar{R}_M$ consistent with the kinematic constraints still provides a useful discriminating variable, allowing the exclusion reach of the stop mass to be extended to $sim 550$ GeV based on the current 36 fb$^{-1}$ LHC data. The same method can also be applied to the chargino search with $m_{tilde{chi}_1^pm} -m_{tilde{chi}_1^0} approx m_W$ because the analysis does not rely on $b$ jets. If no excess is present in the current data, a chargino mass of 300 GeV along the $W$ corridor can be excluded, beyond the limit obtained from the multilepton search.
The top squarks (stops) may be the most wanted particles after the Higgs boson discovery. The searches for the lightest stop have put strong constraints on its mass. However, there is still a search gap in the low mass region if the spectrum of the s
top and the lightest neutralino is compressed. In that case, it may be easier to look for the second stop since naturalness requires both stops to be close to the weak scale. The current experimental searches for the second stop are based on the simplified model approach with the decay modes $tilde{t}_2 to tilde{t}_1 Z$ and $tilde{t}_2 to tilde{t}_1 h$. However, in a realistic supersymmetric spectrum there is always a sbottom lighter than the second stop, hence the decay patterns are usually more complicated than the simplified model assumptions. In particular, there are often large branching ratios of the decays $tilde{t}_2 to tilde{b}_1 W$ and $tilde{b}_1 to tilde{t}_1 W$ as long as they are open. The decay chains can be even more complex if there are intermediate states of additional charginos and neutralinos in the decays. By studying several MSSM benchmark models at the 14 TeV LHC, we point out the importance of the multi-$W$ final states in the second stop and the sbottom searches, such as the same-sign dilepton and multilepton signals, aside from the traditional search modes. The observed same-sign dilepton excesses at LHC Run 1 and Run 2 may be explained by some of our benchmark models. We also suggest that the vector boson tagging and a new kinematic variable may help to suppress the backgrounds and increase the signal significance for some search channels. Due to the complex decay patterns and lack of the dominant decay channels, the best reaches likely require a combination of various search channels at the LHC for the second stop and the lightest sbottom.
