Meson System Research Articles

Low-energy scattering of the(DD¯*)±system and the resonance-like structureZc(3900)

In this exploratory lattice study, low-energy scattering of the $(D{\overline{D}}^{*}{)}^{\ifmmode\pm\else\textpm\fi{}}$ meson system is analyzed using lattice QCD with ${N}_{f}=2$ twisted mass fermion configurations with three pion mass values. The calculation is performed within single-channel L\"uscher's finite-size formalism. The threshold scattering parameters, namely the scattering length ${a}_{0}$ and the effective range ${r}_{0}$, for the $s$-wave scattering in ${J}^{P}={1}^{+}$ channel are extracted. For the cases in our study, the interaction between the two charmed mesons is weakly repulsive. Our lattice results therefore do not support the possibility of a shallow bound state for the two mesons for the pion mass values we studied. This calculation provides some useful information on the nature of the newly discovered resonance-like structure ${Z}_{c}(3900)$ by various experimental groups.

New physics in $$B_{d,s}$$ B d , s – $${\bar{B}}_{d,s}$$ B ¯ d , s mixings and $$B_{d,s}\rightarrow \mu ^+\mu ^-$$ B d , s → μ + μ - decays

A new way of probing new physics in the \(B\) meson system is provided. We define double ratios for the observables of \(B_{d,s}\)–\({\bar{B}}_{d,s}\) mixings and \(B_{d,s}\rightarrow \mu ^+\mu ^-\) decays, and find simple relations between the observables. By using the relations we predict the yet-to-be-measured branching ratio of \(B_d\rightarrow \mu ^+\mu ^-\) to be (0.809–1.03)\(\times 10^{-10}\), up to the new physics models.

Scattering lengths for two pseudoscalar meson systems

Scattering lengths for two pseudoscalar meson systems, $\ensuremath{\pi}\ensuremath{\pi}(I=2)$, $KK(I=1)$ and $\ensuremath{\pi}K(I=3/2,1/2)$, are calculated from lattice QCD by using the finite size formula. We perform the calculation with ${N}_{f}=2+1$ gauge configurations generated on $3{2}^{3}\ifmmode\times\else\texttimes\fi{}64$ lattice using the Iwasaki gauge action and a nonperturbatively $\mathcal{O}(a)$-improved Wilson action at ${a}^{\ensuremath{-}1}=2.19\text{ }\text{ }\mathrm{GeV}$. The quark masses correspond to ${m}_{\ensuremath{\pi}}=0.17--0.71\text{ }\text{ }\mathrm{GeV}$. For the $\ensuremath{\pi}K(I=1/2)$ system, we use the variational method with the two operators, $\overline{s}u$ and $\ensuremath{\pi}K$, to separate the contamination from the higher states. In order to obtain the scattering length at the physical quark mass, we fit our results at several quark masses with the formula of the $\mathcal{O}({p}^{4})$ chiral perturbation theory and that includes the effects of the discretization error from the Wilson fermion, Wilson chiral perturbation theory. We found that the mass dependence of our results near ${m}_{\ensuremath{\pi}}=0.17\text{ }\text{ }\mathrm{GeV}$ are described well by Wilson chiral perturbation theory but not by chiral perturbation theory. The scattering lengths at the physical point are given as ${a}_{0}^{(2)}{m}_{\ensuremath{\pi}}=\ensuremath{-}0.04263(22)(41)$, ${a}_{0}^{(1)}{m}_{K}=\ensuremath{-}0.310(17)(32)$, ${a}_{0}^{(3/2)}{\ensuremath{\mu}}_{\ensuremath{\pi}K}=\ensuremath{-}0.0469(24)(20)$, and ${a}_{0}^{(1/2)}{\ensuremath{\mu}}_{\ensuremath{\pi}K}=0.142(14)(27)$. Possible systematic errors are also discussed.

Study ofCP-violating charge asymmetries of single muons and like-sign dimuons inpp¯collisions

We measure the inclusive single muon charge asymmetry and the like-sign dimuon charge asymmetry in $p \bar{p}$ collisions using the full data set of 10.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron. The standard model predictions of the charge asymmetries induced by CP violation are small in magnitude compared to the current experimental precision, so non-zero measurements could indicate new sources of CP violation. The measurements differ from the standard model predictions of CP violation in these asymmetries with a significance of 3.6 standard deviations. These results are interpreted in a framework of $B$ meson mixing within the CKM formalism to measure the relative width difference $\dgg$ between the mass eigenstates of the $\Bd$ meson system, and the semileptonic charge asymmetries $\asld$ and $\asls$ of $\Bd$ and $\Bs$ mesons respectively.

Study of meson systems with isospin I = 3/2 at the VES setup

Preliminary results obtained by studying K−π−, K−π−π0, and K−π−η systems in the VES experiment are presented. No statistically significant signals from possible resonances were observed in two- and three-particle mass spectra of doubly charged (sub)systems.

Decoherence freeBdandBsmeson systems

We study the impact of decoherence on $B$ meson systems with specific emphasis on ${B}_{s}$. For consistency we also study the ${B}_{d}$ mesons based on the most recent data. Even though the study of decoherence made here depends upon the basis chosen and the final decay products, our analysis suggests that the coherence property of $B$ meson systems is robust and could be a good candidate for making a study of foundational aspects of quantum mechanics.

Solution of the Relativistic Bound State Problem for Hadrons

A second order extension of a generalised QED Lagrangian (including boson-boson coupling) has been used to describe qhadrons. Assuming massless elementary fermions (quantons) this results in a finite theory without open parameters, which may be regarded as a fundamental description of the strong interaction. Two potentials are deduced, a boson-exchange potential and one, which can be identified with the known confinement potential in hadrons. This formalism has been applied the mesonic systems !(782), Φ(1020), J= (3097) and Y(9460) with a good description of their masses. The most important results are: 1. The confinement of hadrons is not due to colour, but is a general property of relativistic bound states. 2. Massive quarks in the Standard Model (QCD) are understood as effective fermions with a mass given by the binding energy in the boson-exchange potential.

CONSTRAINING NEW PHYSICS IN $B_{s}^0$ MESON MIXING

Neutral mesons exhibit a phenomenon called flavour mixing. As a consequence of a second order weak process the flavour eigenstates corresponding to the meson and its anti-meson are superpositions of two mass eigenstates. A meson produced in a flavour state changes into an anti-meson and back again as a function of time. Such flavour oscillations are considered sensitive probes of physics beyond the Standard Model. In this brief review I summarize the status of experimental constraints on mixing parameters in the [Formula: see text] meson system.

Direct observation of time.reversal violation in B mesons at BABAR

Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavour states (B0 or B̄0), and J/ψK0L or cc̄K0s final states (referred to as B+ or B−), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, B̄0 → B− and B− → B̄0, as a function of the time difference between the two B decays. Using 468 million BB̄ pairs produced in Υ(4S) decays collected by the BABAR detector at SLAC, T-violating parameters in the time evolution of neutral B mesons have been measured, yielding ΔS+T = −1.37 ± 0.14 (stat.) ± 0.06 (syst.) and ΔS−T = 1.17 ± 0.18 (stat.) ± 0.11 (syst.) [1]. These non-zero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.

The Belle II pixel detector: High precision with low material

An upgrade of the existing Japanese flavor factory (KEKB in Tsukuba, Japan) is under construction, and foreseen for commissioning by the end of 2014. This new e+e− machine (“SuperKEKB”) will deliver an instantaneous luminosity of 8×1035cm-2 s−1, which is 40 times higher than the world record set by KEKB.In order to be able to fully exploit the increased number of events and provide high precision measurements of the decay vertex of the B meson systems in such a harsh environment, the Belle detector will be upgraded (“Belle II”) and a new silicon vertex detector, based on the DEPFET technology, will be designed and constructed. The new pixel detector, close to the interaction point, will consist on two layers of DEPFET active pixel sensors. This technology combines the detection together with the in-pixel amplification by the integration, on every pixel, of a field effect transistor into a fully depleted silicon bulk. In Belle II, DEPFET sensors thinned down to 75μm with low power consumption and low intrinsic noise will be used.

X(3872) is not a true molecule

A solvable coordinate-space model is employed to study the \(c\bar{c}\) component of the X(3872) wave function, by coupling a confined 3 P 1 \(c\bar {c}\) state to the almost unbound S-wave \(D^{0}\overline{D}^{*0}\) channel via the 3 P 0 mechanism. The two-component wave function is calculated for different values of the binding energy and the transition radius a, always resulting in a significant \(c\bar{c}\) component. However, the long tail of the \(D^{0}\overline{D}^{*0}\) wave function, in the case of small binding, strongly limits the \(c\bar{c}\) probability, which roughly lies in the range 7–11 %, for the average experimental binding energy of 0.16 MeV and a between 2 and 3 GeV−1. Furthermore, a reasonable value of 7.8 fm is obtained for the X(3872) r.m.s. radius at the latter binding energy, as well as an S-wave \(D^{0}\overline{D}^{*0}\) scattering length of 11.6 fm. Finally, the \(\mathcal{S}\)-matrix pole trajectories as a function of coupling constant show that X(3872) can be generated either as a dynamical pole or as one connected to the bare \(c\bar{c}\) confinement spectrum, depending on details of the model. From these results we conclude that X(3872) is not a genuine meson–meson molecule, nor actually any other mesonic system with non-exotic quantum numbers, due to inevitable mixing with the corresponding quark–antiquark states.

The anatomy of Z ′ and Z with flavour changing neutral currents in the flavour precision era

The simplest extension of the SM that generally introduces new sources of flavour and CP violation as well as right-handed currents is the addition of a U(1) gauge symmetry to the SM gauge group. If the corresponding heavy gauge boson Z' mediates FCNC processes in the quark sector at tree-level, these new physics contributions imply a pattern of deviations from SM expectations for FCNC processes depending only on Z' couplings to fermions and on its mass. This implies stringent correlations between Delta F=2 and Delta F=1 observables which govern the landscape of the allowed parameter space for Z'-models. Anticipating the Flavour Precision Era (FPE) ahead of us we illustrate this by searching for allowed oases in this landscape assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze Delta F=2 observables in K^0-bar K^0 and B^0_{s,d}-bar B^0_{s,d} systems and rare K and B decays including both left-handed and right-handed Z'-couplings to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different Z' scenarios. The important role of b->s l^+ l^- and b->s nu bar nu transitions in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in B_{s,d} and K meson systems emerges provided M_Z'<3 TeV. While for M_Z'>5 TeV Z' effects in rare B_{s,d} decays are found typically below 10% and hard to measure even in the FPE, K->pi nu bar nu and K_L-> pi^0 l^+ l^- decays provide an important portal to scales beyond those explored by the LHC. We apply our formalism to NP scenarios with induced flavour changing neutral Z-couplings to quarks. We find that in the case of B_d and K decays, but not B_s decays, such Z-couplings still allow for sizable departures from the SM.

On the correlations between flavour observables in minimal U(2)3 models

The stringent correlations between flavour observables in models with CMFV are consistent with the present data except for the correlation Delta M_{s,d}-epsilon_K. Motivated by the recent work of Barbieri et al, we compare the CMFV correlations with the ones present in a special class of models with an approximate global U(2)^3 flavour symmetry, constrained by a minimal set of spurions governing the breakdown of this symmetry and the assumption that only SM operators are relevant in flavour physics. This analog of CMFV to be called MU(2)^3 allows to avoid the Delta M_{s,d}-epsilon_K tension in question because of reduced flavour symmetry and implied non-MFV contributions to Delta M_{s,d}. While the patterns of flavour violation in K meson system is the same as in CMFV models, the CP-violation in B_{s,d} meson systems can deviate from the one in the SM and CMFV models. We point out a stringent triple S_{psi K_S}-S_{psi phi}-|V_ub| correlation in this class of models that could in the future provide a transparent distinction between different MU(2)^3 models and in the context of these models determine |V_ub| by means of precise measurements of S_{psi K_S} and S_{psi phi} with only small hadronic uncertainties. For fixed S_{psi K_S} the correlation between B(B^+ -> tau^+nu_tau) and S_{psi phi} follows. We also find that MU(2)^3 models could in principle accommodate a negative value of S_{psi phi}, provided |V_ub| is found to be in the ballpark of exclusive determinations and the particular MU(2)^3 model provides a 25% enhancement of epsilon_K. A supersymmetric U(2)^3 model worked out in the Barbieri-School appears to satisfy these requirements. However if B(B^+ -> tau^+nu_tau)>1.0 10^{-4} will be confirmed by future experiments only positive S_{psi phi} is allowed in this framework. We summarize briefly the pattern of flavour violation in rare K and B_{s,d} decays in MU(2)^3 models.

Comment on testing the time-reversal symmetry in neutral meson systems

Following a stimulating question raised by R. Winston during the CP violation session of the BEACH 2012 Conference, we briefly comment about testing the time reversal symmetry in neutral meson systems, reviewing the criticism of a previous test in the neutral K meson system performed using the Kabir asymmetry, and discussing how this difficulty can be overcome exploiting the entanglement in K and B meson pairs produced at ϕ- and B-factories.

CP violation measurements with the ATLAS detector

The ATLAS experiment at the Large Hadron Collider measures CP violation in the neutral Bs0 meson system through the exclusive decay Bs0→J/ψ(μ+μ−)ϕ(K+K−) by analysing time dependent angular correlations of the final state. With 4.9fb−1 of integrated luminosity recorded in 2011 in pp collisions at the LHC at a centre of mass energy of s=7 TeV, first ATLAS results on the values of the CP-violating phase ϕs, the decay width difference ΔΓs as well as other physics parameters of the Bs0 meson decay have been obtained and will be presented here.

Observation of Time-Reversal Violation in theB0Meson System

Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time reversal violation. The decays of entangled neutral B mesons into definite flavor states ($B^0$ or $\bar{B}^0$), and $J/\psi K_S^0$ or $c\bar{c} K_S^0$ final states (referred to as $B_+$ or $B_-$), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, $\bar{B}^0 \rightarrow B_-$ and $B_- \rightarrow \bar{B}^0$, as a function of the time difference between the two B decays. Using 468 million $B\bar{B}$ pairs produced in $\Upsilon(4S)$ decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding $\Delta S_T^+ = -1.37 \pm 0.14 (stat.) \pm 0.06 (syst.)$ and $\Delta S_T^- = 1.17 \pm 0.18 (stat.) \pm 0.11 (syst.)$. These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.

夸克-强子二重性综述

It is an important method to study the quark-hadron duality through the mesons produced by electron scattering, and the exclusive electron-nuclei scattering, under deep inelastic scattering at energy region around √ S =2 GeV, is optimal for verifying the duality of the resonance state. This paper describes the resonance states of exclusive reaction through fixed target experiments, which is based on quark-hadron duality. The analyzing method using data from the resonance states is introduced. The characteristics of the mesons system have been calculated, including the four-momentum and scattering angle, and the experimental method is also discussed. In conclusion, it is demonstrated, theoretically and experimentally, that the fixed target electron scattering equipment on Beijing test-beam line is an important database to study the quark-hadron duality.

Measurement of the effective [formula omitted] lifetime

A precise determination of the effective Bs0→K+K− lifetime can be used to constrain contributions from physics beyond the Standard Model in the Bs0 meson system. Conventional approaches select B meson decay products that are significantly displaced from the B meson production vertex. As a consequence, B mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0 fb−1 of data recorded by the LHCb experiment, the effective Bs0→K+K− lifetime is measured as 1.455±0.046(stat.)±0.006(syst.)ps.

Branching ratio measurements ofBsdecays

We have just entered an era of precision measurements for $B_s$-decay observables. A characteristic feature of the $B_s$-meson system is $B^0_s$--$\bar B^0_s$ mixing, which exhibits a sizable decay width difference. The latter feature leads to a subtle complication for the extraction of branching ratios of $B_s$ decays from untagged data samples, leading to systematic biases as large as O(10%) that depend on the dynamics of the considered decay. We point out that this effect can only be corrected for using information from a time-dependent analysis and suggest the use of the effective $B_s$ decay lifetime, which can already be extracted from the untagged data sample, for this purpose. We also address several experimental issues that can play a role in the extraction of effective lifetimes at a hadron collider, and advocate the use of the $B_s$ branching ratios, as presented in this note, for consistent comparisons of theoretical calculations and experimental measurements in particle listings.

Description of Heavy Quark $\overline{MS}$ Mass by Lippmann-Schwinger Equation

Quark masses are of great prominence in high-energy physics. In this paper, we have studied the heavy meson systems via solving the Lippmann-Schwinger equation by using the Martin potential for heavy quark masses. We have also attempted to use Martin potential to find an acceptable mass spectrum for heavy quarkonia. We obtained this spectrum via minimal phenomenological model (M. Melles, Phys. Rev. D \textbf{62}: 074019 2000). The mass spectra for $b\bar{b}$ and $c\bar{c}$ are calculated without taking into account the relativistic corrections and spin-dependent effects. The obtained mass spectra turn out to fit the experimental findings. By using the conventional spectrum, we extract the pole mass of heavy quarks and use it along with the relation between $\overline{MS}$ mass (modified minimal subtraction scheme) and the on-shell quark mass to find $\overline{MS}$ mass for these quarks. The obtained results for $\overline{MS}$ mass are in good agreement with corresponding values reported in the literature.