118506962
Chiral perturbation theory and the $\bar B \bar B$ strong interaction
We have calculated the potentials of the heavy (charmed or bottomed) pseudoscalar mesons up to $O(\epsilon^2)$ with the heavy meson chiral perturbation theory. We take into account the contributions from the football, triangle, box, and crossed diagrams with the 2$\phi$ exchange and one-loop corrections to the contact terms. We notice that the total 2$\phi$-exchange potential alone is attractive in the small momentum region in the channel ${\bar B \bar B}^{I=1}$, ${\bar B_s \bar B_s}^{I=0}$, or ${\bar B \bar B_s}^{I=1/2}$, while repulsive in the channel ${\bar B \bar B}^{I=0}$. Hopefully the analytical chiral structures of the potentials may be useful in the extrapolation of the heavy meson interaction from lattice QCD simulation.
118416217
Pseudoscalar Goldstone bosons scattering off charmed baryons with chiral perturbation theory
Abstract We have systematically calculated the pseudoscalar Goldstone boson and charmed baryon scattering lengths to the third order with heavy baryon chiral perturbation theory. The scattering lengths can reveal the interaction of K Λ c , K Σ c , π Ω c , etc. For each channel, we take into account of the interaction between the external particle and every possible charmed baryon in the triplet, sextet, and excited sextet. We use dimensional regularization and modified minimal subtraction to get rid of the divergences in the loop-diagram corrections. We notice that the convergence of chiral expansion for most of the channels becomes better after we let the low energy constants absorb the analytic contributions of the loop-diagram corrections and keep the non-analytic terms only.
67819117
Pseudoscalar Mesons Scattering off D*-mesons with Chiral Perturbation Theory
We have systematically calculated the s-wave pseudoscalar mesons and D*- mesons scattering lengths to the third order with chiral perturbation theory, which will be helpful to reveal their strong interaction. We present the scattering lengths (1) in the framework of the heavy meson chiral perturbation theory and (2) in the framework of the infrared regularization.
119307246
Pseudoscalar meson and heavy vector meson scattering lengths
We have systematically studied the S-wave pseudoscalar meson and heavy vector meson scattering lengths to the third order with the chiral perturbation theory, which will be helpful to reveal their strong interaction. For comparison, we have presented the numerical results of the scattering lengths (1) in the framework of the heavy meson chiral perturbation theory and (2) in the framework of the infrared regularization. The chiral expansion converges well in some channels.
121627789
Pseudoscalar Meson and Charmed Baryon Scattering Lengths
We have calculated the scattering lengths between the pseudoscalar meson and charmed triplet, sextet, and excited sextet baryon to the third order with the heavy baryon chiral perturbation theory. The chiral expansion of the pion channels converges well.
118457565
Pseudoscalar Meson and Decuplet Baryon Scattering Lengths
The excited states of the nucleon and their strong interactions with various hadrons play an important role in our understanding of non-perturbative QCD. Generally speaking, their coupling with the pseudoscalar pion, kaon and eta is governed by chiral dynamics. The first excited state of the nucleon, J = 3/2 ∆(1232), belongs to the lightest decuplet. It is degenerate with the nucleon in the large Nc limit [1, 2]. From the strong decay widths, one can extract the coupling constants of the pseudoscalar meson decuplet baryon interaction. Although it may be quite difficult to measure their scattering lengths experimentally, unlike in the pion-nucleon and kaon-nucleon cases [3–5], it is still interesting to study the scattering processes theoretically. As two well-known non-perturbative approaches of QCD at low energy, chiral perturbation theory and lattice QCD have been widely used in studying meson-baryon interactions [6–14]. With the explicitly consistent power counting scheme, the heavy baryon chiral perturbation theory (HBχPT) is a practical and useful tool in the study of the meson baryon scattering. The expansion is organized with p/Λχ, where p represents the momentum (mass) of the meson or the small residue momentum of the baryon in the non-relativistic limit, and Λχ = 4πfπ is the scale of chiral symmetry breaking. Numerically it is around the baryon mass in the chiral limit. Because of the large mass of the strange quark, the chiral corrections from the kaon and eta meson loops are significantly larger than that from the pion loop, which leads to the worse convergence of the chiral expansion in the SU(3) case. In HBχPT, the effects of excited baryons are encoded in the unknown low energy constants (LECs) in the Lagrangians. In the large Nc limit, one expects that the inclusion of the decuplet baryon contribution may partially cancel the octet contribution and be helpful to the chiral expansion. In order to investigate the contributions of the ∆, HBχPT with explicit spin-3/2 baryons and the small-scale expansion scheme have been developed in Refs. [15, 16]. Now the expansion is organized with ǫ, where ǫ means p in HBχPT or the mass difference δ between ∆ and the nucleon in the chiral limit, which is widely used in the exploration of the decuplet related processes [17–21]. There exists another power counting scheme “δ expansion” in the two-flavor case, where mπ scales as δ 2 [22–25]. In our previous work [21], we studied the decuplet contributions to the pseudoscalar meson octet baryon scattering lengths, which is an important observable reflecting their strong interaction near the threshold. The inclusion of the decuplet baryons does not improve the convergence significantly. In this paper, we will study the scattering lengths of the pseudoscalar mesons and the light decuplet baryons in the framework of the SU(3) heavy baryon chiral perturbation theory with explicit decuplet baryons. We will explore whether the small scale expansion works well in this case.
17580246
Baryon masses with dynamical twisted mass fermions
We present results on the mass of the nucleon and the $\Delta$ using two dynamical degenerate twisted mass quarks. The evaluation is performed at four quark masses corresponding to a pion mass in the range of 690-300 MeV on lattices of size 2.1 fm and 2.7 fm. We check for cutoff effects by evaluating these baryon masses on lattices of spatial size 2.1 fm with lattice spacings $a(\beta=3.9)=0.0855(6)$ fm and $a(\beta=4.05)=0.0666(6)$ fm, determined from the pion sector and find them to be within our statistical errors. Lattice results are extrapolated to the physical limit using continuum chiral perturbation theory. 
The nucleon mass at the physical point provides a determination of the lattice spacing. Using heavy baryon chiral perturbation theory at ${\cal O}(p^3)$ we find $a(\beta=3.9)=0.0879(12)$ fm, with a systematic error due to the chiral extrapolation estimated to be about the same as the statistical error. This value of the lattice spacing is in good agreement with the value determined from the pion sector. We check for isospin breaking in the $\Delta$-system. We find that $\Delta^{++,-}$ and $\Delta^{+,0}$ are almost degenerate pointing to small flavor violating effects.
116009345
Measurements of $\psi^\prime \to \bar{p} K^+ \Sigma^0$ and $\chi_{cj} \to \bar{p} K^+ \Lambda$
Using a sample of 1.06 x 10(8) psi' mesons collectedwith the BESIII detector at the BEPCII e(+)e(-) collider and chi(cJ) mesons produced via radiative transitions from the psi', we report the first observation for psi' -> (p) over barK(+)Sigma(0) + c.c. (charge conjugate), as well as improved measurements for the chi(cJ) hyperon decays chi(cJ) -> (p) over barK(+) Lambda + c.c. The branching fractions are measured to be B(psi' -> (p) over barK(+) Sigma(0) + c.c) = (1.67 +/- 0.13 +/- 0.12) x 10(-5), B(chi(c0) -> (p) over barK(+) Lambda + c.c) = (13.2 +/- 0.3 +/- 1.0) x 10(-4), B(chi(c1) -> (p) over barK(+) Lambda + c.c) = (4.5 +/- 0.2 +/- 0.4) x 10(-4), and B(chi(c2) -> (p) over barK(+) Lambda + c.c) = (8.4 +/- 0.3 +/- 0.6) x 10(-4), where the first error is statistical, and the second is systematic. In the decay of chi(c0) -> (p) over barK(+) Lambda + c.c:, an anomalous enhancement near threshold is observed in the invariant mass distribution of (p) over bar Lambda + c.c:, which cannot be explained by phase space. DOI: 10.1103/PhysRevD.87.012007
55532447
Nonperturbative renormalization of overlap quark bilinears on 2+1-flavor domain wall fermion configurations
Department of Physics, Zhejiang University, Hangzhou 311027, China(Received 9 January 2014; published 19 August 2014)We present renormalization constants of overlap quark bilinear operators on 2þ 1-flavor domain wallfermion configurations. This setup is being used by the χQCD Collaboration in calculations of physicalquantities such as strangeness in the nucleon and the strange and charm quark masses. The scale-independent renormalization constant for the axial-vector current is computed using the Ward identity.The renormalization constants for scalar, pseudoscalar, and vector currents are calculated in the RI-MOMscheme. Results in the MS scheme are also given. The step scaling function of quark masses in theRI-MOM scheme is computed as well. The analysis uses, in total, six different ensembles of three seaquarks, each on two lattices with sizes 24
56336430
Meson mass decomposition from lattice QCD
Hadron masses can be decomposed as a sum of quark and glue components which are defined through hadronic matrix elements of QCD operators. The components consist of the quark mass term, the quark energy term, the glue energy term, and the trace anomaly term. We calculate these components for mesons with lattice QCD for the first time. The calculation is carried out with overlap fermion on $2+1$ flavor domain-wall fermion gauge configurations. We confirm that $\sim 50\%$ of the light pion mass comes from the quark mass term and $\sim 10\%$ comes from the quark energy; whereas, while for the $\rho$ meson, the quark energy contributes roughly half of its mass but the quark mass term contributes little. The combined glue components contribute $\sim 40 - 50\%$ for both mesons. It is interesting to observe that the quark mass contribution to the mass of the vector meson is almost linear in quark mass over a large quark mass region below the charm quark mass. For heavy mesons, the quark mass term dominates the masses, while the contribution from the glue components is about $200$ MeV (a bare value around 2GeV) for the heavy pseudoscalar and vector mesons. The charmonium hyperfine splitting is found to be dominated by the quark energy term which is consistent with the picture of the quark potential model.
18308235
Search for new particles in hadronic events with isolated photons
Abstract A search for the neutral Higgs boson in the processes e + e − → Z → H 0 γ → q q γ and e + e − → Z → Z ∗ H 0 → q q γγ has been performed using 2.8 million hadronic Z decays collected with the L3 detector at LEP from 1991 through 1994. No evidence for these processes has been observed. Upper limits at 95% confidence level for the corresponding cross sections have been set and the results have been compared with theoretical predictions beyond the Standard Model.