Muonium annihilation into $ν_e\barν_μ$ and $ν_e\barν_μγ$

Progress Towards a Muonium Gravity Experiment

The gravitational acceleration of antimatter, $\bar g$, has yet to be directly measured but could change our understanding of gravity, the Universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and benefiting from a novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear to be feasible. With 100 nm grating pitch, measurements of $\bar g$ to 10%, 1%, or better can be envisioned. This could constitut…

On the possibility of observable signatures of leptonium from astrophysical sources

The formation of Ps in our Galaxy is well measured, and has led to important and unanswered questions on the origin of the positrons. In principle it should be possible to form analogous systems from mu and tau leptons, viz. true muonium and true tauonium. However the probability of formation for these systems is greatly reduced due to the intrinsically short lifetimes of the mu and tau leptons. Likewise, the decay of the atoms is hastened by the high probability of the constituent particles decaying. Nevertheless, if sufficient numbers of mu and tau pairs are produced in high energy astrophys…

μ⁺μ⁻谱的真空极化修正

Vacuum polarization corrections to $μ^+μ^-$ spectrum

本文基于正电子素高阶势计算真μ子素n=1、n=2能级，系统纳入电子真空极化、高阶微扰及多光子湮灭的α⁶阶修正，并给出基态超精细劈裂。

Instanton Effects in $N\bar N$ Annihilation

It is shown that specific spin-flavour properties of the nonperturbative interaction between quarks induced by instantons allow us to explain the peculiarities of the OZI rule violation in $N \bar N$ annihilation. New experiments to test the instanton mechanism of the OZI rule violation are proposed.

Channel coupling in e+ e- annihilation into heavy meson pairs at the D* {\bar D}* threshold

A threshold singularity in a heavier meson channel, e.g. $D^* {\bar D}^*$, generally reflects in the amplitudes of $e^+e^-$ annihilation into lighter meson pairs, such as $D^* {\bar D}$, $D {\bar D}$, and $D_s {\bar D}_s$, due to the channel coupling. The behavior of the cross section of the $e^+e^-$ annihilation into each channel in this situation is considered using general properties of the amplitudes near the new threshold. It is argued that the effects of the channel coupling can be quite significant in the observable cross section, in particular near the $D^* {\bar D}^*$ threshold.

Mixed QCD and Weak Corrections to $t\bar{t}$ Production by Quark-Antiquark Annihilation

We report on our computation of the mixed QCD and weak corrections to $q {\bar q} \to t\bar{t}$ including $t, \bar t$ spin effects, in particular on single top spin asymmetries.

Possible new resonance at the $D^* {\bar D^*}$ threshold in $e^+e^-$ annihilation

We argue that the recent CLEO-c data on $e^+e^-$ annihilation into pairs of charmed mesons at c.m. energy around 4.0 GeV are not well described by a single resonance $ψ(4040)$, but can be better understood if there is an additional narrow resonance with mass within few MeV from the $D^* {\bar D}^*$ threshold.

The OZI Rule Violation in $N \bar N$ Annihilation at Rest and the Skyrme Model

The question is raised if a large violation of the OZI rule, recently observed in many channels in $N \bar N$ annihilation at rest, can be explained in the framework of the Skyrme model.

${\bar p} p$ Annihilation: Manifestations of Instanton Induced Quark Pair Production ?

Production of strangeness in the low-energy ${\bar p} p$ annihilation is analyzed as a manifestation of the instanton induced multiquark vertex. Approach based on the {\it qualitative} properties of the 't Hooft mechanism provides a unified description of available experimental data on $K$- and $ϕ$-meson production. Crucial tests for the hypothesized mechanism are suggested.

Colour connections of four quark $Q\bar{Q}Q'\bar{Q}'$ system and doubly heavy baryon production in $e^{+}e^{-}$ annihilation

The hadronization effects induced by various colour connections of the four quark system in $e^{+}e^{-}$ annihilation are briefly reviewed. A special colour connection of four heavy quark system without colour-separation favours the production of doubly heavy baryons. For the related three-jet case, the corresponding hadronization has not been considered. We argue that it can be effectively described as two string fragmentation besides the leading heavy diquark fragmentation. The production rate and the properties of final state hadron systems are discussed. Emphasis is on the string effect as…

Excitation of physical vacuum through $\bar p p$ annihilation in selected channels

In this work we discuss the interest of measuring the ratio of of $p\bar p$ annihilation into kaon and pion pairs near the threshold region, where $S$ state dominates. It is shown that a good agreement with existing data on the ratio of the yields of charged kaon to pion pairs is obtained taking into account not only quark rearrangement in the incident hadrons, but also vacuum excitations.

Re-analysis of some bubble chamber data on $N \bar{N}$ annihilation

A re-analysis of some $\bar{p}p$ and $\bar{p}n$ data, at rest and in flight, obtained in bubble chamber experiments, is presented. The ($π^{+}π^{-}$) and ($K_{S}K_{S}$) final states for the channels (2$π^{-}π^{+}$) and ($K_{S}K_{S}π$) are investigated. Evidence for a narrow meson resonance structure, cautiously suggested as $f_{0} (1500)$, is given. In the ($π^{+}π^{-}$) invariant mass distribution from $\bar{p}n$ annihilations in flight, using the method of difference spectra, a very clear evidence for $ρ^{0}, f_{2}(1270)$ and $f_{0} (1500)$ is first time obtained from these data. This re-ana…

The Effect of Supersymmetric CP Phases on qq-bar Annihilations

We compute the rates for $q \bar{q}$ annihilation into charginos and neutralinos by taking into account the effects of supersymmetric soft phases. In particular, the phase of the $μ$ parameter gains direct accessibility via the production of dissimilar charginos and neutralinos. The phases of the trilinear soft masses do not have a significant effect on the cross sections. Our results can be important for sparticle searches at the LHC.

Role of the hadron molecule Lambda_c(2940) in the p bar(p) -> p D0 bar(Lambda)_c(2286) annihilation reaction

The annihilation process p bar(p) -> p D0 bar(Lambda)_c(2286) is studied taking into account t-channel D0, D*0 meson exchange and the resonance contribution of Lambda_c(2286) and Lambda_c(2940) baryons. We assume that the Lambda_c(2940) baryon is a pD*0 molecular state with spin-parity (1/2)+ and (1/2)-. Our results show that near the threshold of p bar(p) -> Lambda_c(2286) bar(Lambda)_c(2286) the contribution from the intermediate state Lambda_c(2940) is also sizeable and can be observed at the PANDA experiment. Another conclusion is that the spin-parity assignment (1/2)- for Lambda_c(2940) g…

Four-Quark States and Nucleon-Antinucleon Annihilation within the Quark Model with Instanton Induced Interaction

The spectrum of $q^2\bar q^2, J^p=0^+,2^+$ mesons is discussed. We have shown that due to instanton - induced forces the physical states are strong mixtures of the $SU_f(3)$ group basis states. The cross-sections for annihilation of the $N\bar N$ system into $(q^2\bar q^2)(q\bar q)$ mesons are obtained. The $a_0(980)$ meson is considered as $q^2\bar q^2$ meson consisting of $9_f$ and $36_f$ plets. The branchings are also predicted for the cross-sections for production of the $a_0(980)$ and tensor $q^2\bar q^2$ mesons in $N\bar N$ annihilation.

Response to Comment on "Dark Matter Annihilation Can Produce a Detectable Antihelium Flux through $\barΛ_b$ Decays"

In a recent paper we showed that the decay of intermediate $\barΛ_b$ baryons can dramatically enhance the antihelium flux from dark matter annihilation. Our antihelium predictions were derived using several implementations of the Pythia and Herwig event generators which were calibrated to existing data on antideuteron and antihelium formation. Kachelriess et al. have argued for a smaller antihelium flux compared to our most optimistic Monte Carlo model. However, we show that the arguments by Kachelriess et al. are either incorrect or irrelevant for antihelium formation. Thus, the results of ou…

Some comments on $\bar n p$-annihilation branching ratios into $ππ$-, $\bar K K$- and $πη$-channels

We give some remarks on the $\bar n p$-partial branching ratios in flight at low momenta of antineutron, measured by OBELIX collaboration. The comparison is made to the known branching ratios from the $p \bar p$-atomic states. The branching ratio for the reaction $\bar n p \to π^+π^0$ is found to be suppressed in comparison to what follows from the $ p \bar p$-data. It is also shown, that there is no so called dynamic I=0-amplitude suppression for the process $N\bar N \to K\bar K$.

Comment on "Dark Matter Annihilation Can Produce a Detectable Antihelium Flux through $\barΛ_b$ Decays"

In a recent Letter, it was suggested that a previously neglected Standard Model process, namely, the production of antihelium-3 nuclei through decays of $\barΛ_b$ baryons can lead to a flux of antihelium-3 from dark matter annihilations detectable by AMS-02. We show that an essential condition for its detectability -- the introduction of the "$\barΛ_b$ tune" of Pythia -- is excluded by a wealth of measurements of (anti-) baryon and (anti-) meson production at accelerators. Moreover, we argue that Monte Carlo generators like Pythia should not be used to predict branching ratios like $BR(\barΛ_b…

The annihilation decays $B^-_c \to η^{'}(η,π^0) l^- \barν$

We investigate the simileptonic OZI-forbidden annihilation decays $B^-_c \to η^{'}(η,π^0) l^- \barν$ for $l=μ,e$ in the perturbative QCD, and carry out a precise calculation without any approximation for the one-loop contributions, which involves integrals of 4- and 5-point loop functions. Our results show that the branching ratios of decays $B^-_c \to η^{'} l^- \barν$, $B^-_c \to ηl^- \barν$ and $B^-_c \to π^0 l^- \barν$, turn out to be of orders $10^{-4}$, $10^{-5}$ and $10^{-6}$, respectively, which could be observable in the future experiments at the LHC.

Heavy QQ(bar) "Fireball" Annihilation to Multiple Vector Bosons

Drawing analogy of replacing the nucleon by heavy chiral quark $Q$, the pion by Goldstone boson $G$, and $πNN$ coupling by $GQQ$ coupling, we construct a statistical model for $Q\bar Q \to nG$ annihilation, i.e. into $n$ longitudinal weak bosons. This analogy is becoming prescient since the LHC direct bound $m_Q > 611$ GeV implies strong Yukawa coupling. Taking $m_Q \in (1, 2)$ TeV, the mean number $<n_G>$ ranges from 6 to over 10, with negligible two or three boson production. With individual $t'$ or $b'$ decays suppressed either by phase space or quark mixing, and given the strong Yukawa cou…

Annihilation Contributions and CP Asymmetries in $B^+ \to π^+ K^0, K^+ K^0$ and $B^0\to K^0 \bar K^0$

Recently the branching ratios for $B^+\to K^+\bar K^0$ and $B^0 \to K^0 \bar K^0$ have been measured. Data indicate that the annihilation amplitudes in these decays are not zero. A non-zero annihilation amplitude plays an important role in CP violation for $B^+\to π^+ K^0, K^+ \bar K^0$. Using the measured branching ratios for these decays, we show that there is an absolute bound of 5% for the size of CP asymmetry in $B^+\to π^+ K^0$ from a relation between the amplitudes of these decays. The size of CP asymmetry in $B^+ \to K^+\bar K^0$ can, however, be as large as 90%. Future experimental da…

电子正电子湮灭中产生的具有不同自旋组合的两个重子的极化分析

Polarization analysis of two baryons with various spin combinations produced in electron-positron annihilation

本研究提出了电子正电子湮灭中不同自旋组合双重重子极化关联的分析方法，建立了任意自旋的自旋密度矩阵，给出多自旋组合的分析方案及激发重子自旋宇称的测定方法，为重子谱和跃迁形状因子研究提供支撑。

Spin-dependent structure functions $\hat g_1$ and $\hat g_2$ for inclusive spin-half baryon production in electron-positron annihilation

Two spin-dependent structure functions $\hat g_1$ and $\hat g_2$ for the inclusive spin-half baryon production in electron-positron annihilation are studied in the context of QCD factorization as well as in the naive quark parton model. As a result, it is found that the sum of $\hat g_1$ and $\hat g_2$ is related to $\hat h_1$ and $\hat g_T$, two quark fragmentation functions defined by Jaffe and Ji. In connection with the measurement of quark fragmentation functions, the possible phenomenological consequences are discussed.

Electron-Positron Radiative Annihilation : Timelike Virtual Compton Scattering

We report on a recent work proposing measurements of the deeply virtual Compton amplitude (DVCS) $γ^* \to h \bar h γ$ in the timelike kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process $e^+ e^- \to h \bar h γ$.

Study of Pure Annihilation Decays B_{d,s} \to D^{0} \bar D^{0}

With heavy quark limit and hierarchy approximation $λ_{QCD}\ll m_D\ll m_B$, we analyze the $B\to D^0\bar D^0$ and $B_s\to D^0\bar D^0$ decays, which occur purely via annihilation type diagrams. As a roughly estimation, we calculate their branching ratios and CP asymmetries in Perturbative QCD approach. The branching ratio of $B\to D^0\bar D^0$ is about $3.8\times10^{-5}$ that is just below the latest experimental upper limit. The branching ratio of $B_s\to D^0\bar D^0$ is about $6.8\times10^{-4}$, which could be measured in LHC-b. From the calculation, it could be found that this branching rat…

Proton-Antiproton Annihilation in Baryonium

A possible interpretation of the near-threshold enhancement in the $(p\bar{p})$-mass spectrum in $J/ψ{\to}γp{\bar p}$ is the of existence of a narrow baryonium resonance X(1860). Mesonic decays of the $(p\bar{p})$-bound state X(1860) due to the nucleon-antinucleon annihilation are investigated in this paper. Mesonic coherent states with fixed $G$-parity and $P$-parity have been constructed . The Amado-Cannata-Dedoder-Locher-Shao formulation(Phys Rev Lett. {\bf 72}, 970 (1994)) is extended to the decays of the X(1860). By this method, the branch-fraction ratios of $Br(X\to η4π)$, $Br(X\to η2π)$…

Large Strong Phases and CP Violation in the Annihilation Processes $\bar{B}^0\to K^+K^-$, $K^{*\pm}K^\mp$, $K^{*+}K^{*-}$

The strong phases and CP violation in the rare $\bar{B}^0\to K^+K^-$, $K^{*\pm}K^\mp$, $K^{*+}K^{*-}$ decays are investigated. As these decays proceed only via annihilation type diagrams in the standard model (SM), a dynamical gluon mass is introduced to avoid the infrared divergence in the soft endpoint regions. The Cutkosky rule is adopted to deal with a physical-region singularity of the on mass-shell quark propagators, which leads to a big imaginary part and hence a large strong phase. As a consequence, large CP asymmetries are predicted in those decay modes due to a big interference betwe…

The Rare Radiative Annihilation Decays $\bar{B}^0_{s,d} \to J/ψγ$

We investigate the physics potential of the annihilation decays $\bar{B}^0_{s,d} \to J/ψ$ $γ$ in the Standard Model and beyond. In naive factorization approach, the branching ratios are estimated to be $\mathcal{B}(\bar{B}^0_s \to J/ψγ)=1.40\times 10^{-6}$ and $\mathcal{B}(\bar{B}^0_d \to J/ψγ)=5.29\times 10^{-8}$. In the framework of QCD factorization, we compute the non-factorizable corrections and get $\mathcal{B}(\bar{B}^0_s \to J/ψγ) = 2.11\times10^{-7}$, $\mathcal{B}(\bar{B}^0_d \to J/ψγ) =7.65\times10^{-9}$. Future measurements of these decays would be useful for testing the factorizati…

Production of $J/ψ+c\bar{c}$ through two photons in $e^+e^-$ annihilation

We study the production of $J/ψ+c\bar{c}$ in $e^+e^-$ annihilation through two virtual photons. The cross section is estimated to be 23 fb at $\sqrt{s}=10.6$ GeV, which is smaller by a factor of six than the calculated cross section for the same process but through one virtual photon. As a result, while the annihilation into two photons may be important for certain exclusive production processes, the big gap between the inclusive production cross section $σ(e^+e^- \to J/ψ+ c\bar{c})\simeq$ 0.9pb observed by Belle and the current nonrelativistic QCD prediction of $\simeq$0.15pb still remains ve…

Nucleon-Antinucleon Annihilation at the Open Charm Threshold

We discuss the $p\bar{p}$ annihilation into a pair of charmed $D$ mesons not far from the threshold of the reaction. An interesting interference pattern in the differential cross section is predicted to arise from the existence of both $t$-channel charmed-baryon exchange and $s$-channel $Ψ^{''}$ charmonium resonance amplitudes. We argue that the experimental study of this process would provide new and valuable information about the unknown $p\bar{p}Ψ^{''}$ and $Λ_c N D$ couplings. These are important to know to solve the long-standing puzzle of the heavy flavour contents of baryons and to test…

Two-Photon Annihilation into Baryon-Antibaryon Pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard gamma gamma -> q qbar subprocess and form factors describing the soft q qbar -> B Bbar transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called B Bbar distribution amplitudes. A characteristic feature of the handbag mechani…

Discovery potential for the neutral charmoniumlike $Z^{0}(4200)$ by $\bar{p}p$ annihilation

Inspired by the observation of charmoniumlike $Z(4200)$, we explore the discovery potential of the neutral $Z^{0}(4200)$ production by antiproton-proton annihilation with an effective Lagrangian approach. By investigating the $\bar{p}p\rightarrow J/ψπ^{0}$ process including the $Z^{0}(4200)$ signal and background contributions, it is found that the center of mass energy $E_{c.m.}\simeq 4.0-4.5$ GeV is the best energy window for searching the neutral $Z^{0}(4200)$, where the signal can be clearly distinguished from background. The relevant calculations is not only helpful to search for the neut…

Non-singlets in Semi-inclusive DIS and inclusive e+e- annihilation

We show that non-singlets in semi-inclusive DIS with pi^\pm determine without assumptions Delta u_V, Delta d_V and D_u^{π+ - pi-}. Non-singlets in SIDIS and inclusive e+e- -annihilation with K^\pm determine (s-bar s) and (Delta s-Delta bar s), but an assumption is necessary -- we choose as most natural D_d^{K+ - K-}=0. Measurements with charged K^\pm and neutral K0+bar K0 in semi-inclusive DIS and e+e--annihilation determine D_{u,d,s}^{K+ + K-} without any assumptions and allow tests of LO approximation in QCD.

Large contributions to dark matter annihilation from three-body final states

The annihilation rate of dark matter particles plays a crucial role in dark matter studies, for it determines their relic density and their indirect detection signal. In this paper, we show that this annihilation rate can receive large additional contributions from three-body final states consisting of a real and a virtual massive particle, such as WW* (Wf \bar f') and t \bar t* (tW\bar b). We consider two specific examples, from the singlet model and the MSSM, and find that, due to the new three-body final state contributions, the prediction for the relic density may decrease by more than a f…

Effects of Flavor-dependent $q\bar{q}$ Annihilation on the Mixing Angle of the Isoscalar Octet-Singlet and Schwinger's Nonet Mass Formula

By incorporating the flavor-dependent quark-antiquark annihilation amplitude into the mass-squared matrix describing the mixing of the isoscalar states of a meson nonet, the new version of Schwinger's nonet mass formula which holds with a high accuracy for the $0^{-+}$, $1^{--}$, $2^{++}$, $2^{-+}$ and $3^{--}$ nonets is derived and the mixing angle of isoscalar octet-singlet for these nonets is obtained. In particular, the mixing angle of isoscalar octet-singlet for pseudoscalar nonet is determined to take the value of $-12.92^\circ$, which is in agreement with the value of $-13^\circ\sim-17^…

重子-反重子对的自旋密度矩阵在电子-正电子湮灭中包含P和CP违反现象及电子质量

Spin density matrix of baryon-antibaryon pairs in electron-positron annihilation with $P$ and $CP$ violation including electron mass

研究在极化电子-正电子湮灭中，基于单光子交换近似确定重子-反重子对的自旋密度矩阵，考虑P和CP违反及电子质量影响，为后续物理量计算提供基础。

On Connection between Coefficient Functions for Deep-Inelastic and Annihilation Processes

It has been shown that the one-loop behavior of the axial anomaly, occurring when the axial current is appropriately normalized, leads to the cancellation of the corrections of type $C_F^N{\bar α}_s^N,~~ (N\geq 1) $ in the Crewther relation for the coefficient functions of deep-inelastic and annihilation processes. The arguments in favour of the overall factorization of the factor $β({\bar α}_s)/ {\bar α}_s$ in all orders of perturbation theory in this relation are presented.

First results of proton antiproton annihilation into a pion pair at large scattering angles within the handbag approach

We propose to describe the process $ p ~ \bar{p} \rightarrow π^+ ~ π^-$ in a perturbative, QCD motivated framework in which a hard $ud \, \bar{u} \bar{d} \rightarrow d \, \bar{d} $ annihilation factorizes from soft transition distribution amplitudes. We advocate that the scale allowing for this factorization is the large transverse momentum transfer. In our simplified model, in which the proton is considered as a (scalar)diqark-quark system, a transition distribution amplitude describes the non-perturbative transition of the proton to the meson by emission of a scalar, isoscalar $ ud $-diquark…

Revisiting the annihilation decay $\bar{B}_{s}\toπ^{+}π^{-}$

It is very important to know the strength of annihilation contribution in B charmless nonleptonic decays. $\bar{B}_{s}\to π^{+}π^{-}$ process could serve a good probe of the strength. We have studied the process in QCD factorization framework. Using a gluon mass scale indicted by the studies of infrared behavior of gluon propagators to avoid enhancements in the soft end point regions, we find that the CP averaged branching ratio is about $1.24\times 10^{-7}$, the direct CP asymmetry $C_{ππ}$ is about -0.05, while the mixing-induced CP asymmetry quite large with the value $S_{ππ}$=0.18. The pro…

CP violation in the annihilation $e^{+}~e^{-} \to t~\bar{t}$ within the Model-III of the two-Higgs-doublet extension

The CP-violating effects are studied in the electron-positron annihilation to produce $t\bar{t}$ pair within the Model-III of the two-Higgs-doublet extensions, which allows flavor changing neutral currents via Higgs exchanges. Complete analytical expressions for the form factors of the top quark electric and weak dipole moment induced in the framework of the model are presented. Several observables sensitive to the CP violation are calculated. The dependences of the CP-violating effects on Higgs boson masses and the possible phase angles are discussed. We find that the CP-violating observables…

Probes of Heavy Meson Substructure in $e^+ e^-$ annihilation

We apply Heavy Quark Effective Theory to the production of $0^-$ and $1^-$ $Q\bar{q}$ states in $e^+ e^-$ annihilation. We show that HQET implies that the electric quadrupole amplitudes vanish and we propose tests for this theory. We also show how HQET can be applied to distinguish the $^3D_1$ and $^3S_1$ $Q\bar{Q}$ states.

正负电子湮灭过程中$Ω^{-} \arΩ^{+}$极化的精细分析

Refined analysis of $Ω^{-} \barΩ^{+}$ polarization in electron-positron annihilation process

本文在螺旋度振幅框架下提出新的基矩阵选择与振幅参数化，分析正负电子湮灭中双标记$Ω^-\arΩ^+$的极化关联，并给出衰变表达式以缓解$ϕ_Ω$等参数的测量分歧。

Glueballs: Charmonium Decay and $\bar p p$ Annihilation

The vector glueball $O$, made of 3 valence gluons, is expected to be ``clean": it mixes less with quarkonia, but mediates OZI violations. The recent $0^{++} $ glueball candidate and the persistence of the $J/ψ, ψ' \to ρπ$ puzzle suggest $m_O\simeq m_{J/ψ}$, with mixing angle $\sim 2^\circ - 4^\circ$, hence $Γ(O\to ρπ$, $K^+K^-$, $e^+e^-) \sim$ MeV, few keV, few eV. Lower and upper bounds on $Γ_O$ can be argued from $e^+e^- \to ρπ$ energy scan data and the condition $B(O\to ρπ) > B(J/ψ\to ρπ)$. $O$ dominance may explain the ``large" OZI violation in $^1S_0(\bar pp)\to ϕγ$ vs. $ωγ$.

Production of axial-vector D_sJ in e+e- annihilation

If one of the recently discovered charmed-strange mesons (D_sJ(2317)) is the 0+ state of cs-bar, the other (D_sJ(2460)) is most likely the 1+ state with j=1/2. They could be produced in e+e- annihilation by fragmentation from cc-bar jets or as decay products of B mesons. If one analyzes the cc-bar jet events and the B decay events separately, one will have a direct test as to whether D_sJ(2460) is the j=1/2 state or not, how much D_sJ(2460) is mixed with the j=3/2 state, and whether the four-quark interpretation is viable.

Study of resonant processes for multi-pion production in $\bar p +p\to\ell ^++\ell^- +n_ππ$ annihilation

In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study multi-pion production in antiproton nucleon collisions. The main interest of this reaction is related to the possibility to study the properties of the presumable $\bar N N$ atom and of its resonances. For the case of formation of a scalar or pseudoscalar resonant state, with $I^G(J^{P})=1^-(0^{\pm}),~0^+(0^-)$ numerical results are obtained. The differential cross section in an experimental set-up where the pions invariant mass is measured, is given with explicit dependence on the lepton pair and pions …

Charm-meson Triangle Singularity in ${e^+e^-}$ Annihilation into ${ D^{*0} \bar{D}^0 + γ}$

We calculate the cross section for $e^+ e^-$ annihilation into $D^{*0} \bar D^0 +γ$ at center-of-mass energies near the $D^{*0} \bar D^{*0}$ threshold under the assumption that $X(3872)$ is a weakly bound charm meson molecule. The Dalitz plot has a $\bar D^{*0}$ resonance band in the squared invariant mass $t$ of $\bar D^0 γ$. In the limit as the decay width of the $D^{*0}$ goes to 0, the Dalitz plot also has a narrow band in the squared invariant mass $u$ of $D^{*0} \bar D^0$ from a charm-meson triangle singularity. At the physical value of the $D^{*0}$ width, the narrow band reduces to a sho…

Elektroweak one-loop corrections for e^+e^- annihilation into t\bar{t} including hard bremsstrahlung

We present the complete electroweak one-loop corrections to top-pair production at a linear e^+e^- collider in the continuum region. Besides weak and photonic virtual corrections, real hard bremsstrahlung with simple realistic kinematical cuts is included. For the bremsstrahlung we advocate a semi-analytical approach with a high numerical accuracy. The virtual corrections are parametrized through six independent form factors, suitable for Monte-Carlo implementation. Alternatively, our numerical package topfit, a stand-alone code, can be utilized for the calculation of both differential and int…

$P$-wave coupled channel effects in electron-positron annihilation

$P$-wave coupled channel effects arising from the $D\bar{D}$, $D\bar{D}^*+c.c.$, and $D^*\bar{D}^*$ thresholds in $e^+e^-$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the $e^+e^-$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum n…

Cancellation of Infrared Divergences in Hadronic Annihilation Decays of Heavy Quarkonia

In the framework of a newly developed factorization formalism which is based on NRQCD, explicit cancellations are shown for the infrared divergences that appeared in the previously calculated hadronic annihilation decay rates of P-wave and D-wave heavy quarkonia. We extend them to a more general case that to leading order in $v^2$ and next-to-leading order in $α_s$, the infrared divergences in the annihilation amplitudes of color-singlet $Q\bar{Q}(^{2S+1}L_J)$ pair can be removed by including the contributions of color-octet operators $Q\bar{Q}(^{2S+1}(L-1)_{J'})$, $Q\bar{Q}(^{2S+1}(L-3)_{J''}…

Discovery potential for the LHCb fully-charm tetraquark $X(6900)$ state via $\bar{p}p$ annihilation reaction

Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\bar{p}p\rightarrow J/ψJ/ψ$ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, rel…

Using an Effective Charges Method to extract Lambda-MS-bar from event shape moments in e+e- annihilation

We use an Effective Charges (ECH) method to extract Lambda-MS-bar, and hence alpha_s(M_z), from event shape moments in e+e- annihilation. We compare these results with ones obtained using standard MS-bar perturbation theory. The ECH method at NLO is found to perform better than standard MS-bar perturbation theory when applied to means of event shape observables. For example, when we apply the NLO ECH method to <1-T> we get alpha_s(M_z)=0.1193\pm0.0003. However ECH at NNLO is found to work less well than ECH at NLO, and the ECH method also fails to describe data for higher moments of event shap…

Timelike Virtual Compton Scattering from Electron-Positron Radiative Annihilation

We propose measurements of the deeply virtual Compton amplitude (DVCS), gamma* to H H-bar gamma, in the timelike t = (p_{H} + p_{H-bar})^2 > 0 kinematic domain which is accessible at electron-positron colliders via the radiative annihilation process e+ e- to H H-bar gamma. These processes allow the measurement of timelike deeply virtual Compton scattering for a variety of H H-bar hadron pairs such as pi+ pi-, K+ K-, and D D-bar as well as p p-bar. As in the conventional spacelike DVCS, there are interfering coherent amplitudes contributing to the timelike processes involving C= - form factors.…

Precision Measurements in Electron-Positron Annihilation: Theory and Experiment

Theory results on precision measurements in electron-positron annihilation at low and high energies are collected. These cover pure QCD calculations as well as mixed electroweak and QCD results, involving light and heavy quarks. The impact of QCD corrections on the $W$-boson mass is discussed and, last not least, the status and the perspectives for the Higgs boson decay rate into $b\bar b$, $c\bar c$ and into two gluons.

Hadronic Rare $B$ Decays via Exchange or Annihilation Diagrams

The two-body mesonic $B$ decays induced only via a single $W$-exchange or annihilation quark diagram, such as $B^-_u\rightarrow D^{(*)-}_sK^{(*)0}$ and $\bar{B}^0_d\rightarrow D^{(*)+}_sK^{(*)-}$, are analyzed in the factorization approximation. We estimate the branching ratios for those transitions into two pseudoscalar mesons, and find them to be negligibly small. The significant effect of final-state rescattering is illustrated by taking $B^-_u\rightarrow D^-\bar{K}^0$ for example.