arXiv subjects

Xian-Wei Kang

Publications and source records attributed to Xian-Wei Kang.

51 records · Page 3Linked to original sources

arXiv2017

Testing B-violating signatures from Exotic Instantons in future colliders

We discuss possible implications of Exotic Stringy instantons for Baryon-violating signatures in future colliders. In particular, we discuss high-energy quarks collisions and $Λ-\barΛ$ transitions. In principle, $Λ-\barΛ$ process can be probed by high-luminosity electron-positron colliders. However, we find that an extremely high luminosity is needed in order to provide a (somewhat) stringent bound compared to the current data on $NN\rightarrow ππ,KK$. On the other hand, (exotic) instanton-induced six quark interactions can be tested in near future high-energy colliders beyond LHC, at energies around $20-100\, \rm TeV$. Super proton-proton collider (SppC) is capable of such measurement given the proposed energy level of 50-90 TeV. Comparison with other channels is made. In particular, we show the compatibility of our model with neutron-antineutron and $NN\rightarrow ππ,KK$ bounds.

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arXiv2017

Different pole structures in line shapes of the $X(3872)$

We introduce a near-threshold parameterization that is more general than the effective-range expansion up to and including the effective-range because it can also handle with a near-threshold zero in the $D^0\bar{D}^{*0}$ $S$-wave. In terms of it we analyze the CDF data on inclusive $p\bar{p}$ scattering to $J/ψπ^+π^-$, and the Belle and BaBar data on $B$ decays to $K\, J/ψπ^+π^-$ and $K D\bar{D}^{*0}$ around the $D^0\bar{D}^{*0}$ threshold. It is shown that data can be reproduced with similar quality for the $X(3872)$ being a bound {\it and/or} a virtual state. We also find that the $X(3872)$ might be a higher-order virtual-state pole (double or triplet pole), in the limit in which the small $D^{*0}$ width vanishes. Once the latter is restored the corrections to the pole position are non-analytic and much bigger than the $D^{*0}$ width itself. The $X(3872)$ compositeness coefficient in $D^0\bar{D}^{*0}$ ranges from nearly 0 up to 1 in the different scenarios.

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arXiv2016

$P$-wave coupled-channel scattering of $B_sπ,\,B_s^π,\,B\overline K,\,B^{}\overline K$ and the puzzling $X(5568)$

The D0 Collaboration has recently reported a narrow peak structure in the $B_s^0π^\pm$ invariant-mass spectrum, that is called $X(5568)$. Its proposed quantum numbers $J^P=0^+/1^+$ are not determined unambiguously, and we show that one can fit the data assuming $J^P=1^-$ with the same mass and width for the resonance signal. The corresponding isovector $P$-wave coupled-channel scattering involving the states $B_sπ$, $B_s^*π$, $B \overline{K}$ and $B^*\overline K$ is studied employing leading-order Heavy Meson Chiral Perturbation Theory, which is then unitarized making use of standard techniques from Unitary Chiral Perturbation Theory. The subtraction constants that appear in the unitarization process are determined by a $u$-channel crossing symmetry constraint or by naturalness arguments, being the numerical values obtained in both cases quite closed, and no further freedom is left in the model. A crucial point is that if the $X(5568)$ is $1^-$ and decaying into $B_s^0π^\pm$ then it should appear as a pole in the $T$-matrix elements. It finally turns out that no $X(5568)$ pole is found that can be qualified as dynamically generated from the isovector $P$-wave coupled-channel dynamics. This result disfavors the interpretation of the $X(5568)$ within a "molecular" picture.

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arXiv2016

General considerations on the nature of $Z_b(10610)$ and $Z_b(10650)$ from their pole positions

The nature of the bottomonium-like states $Z_b(10610)$ and $Z_b(10650)$ is studied by calculating the $B^{(*)}\overline B^{*}$ compositeness ($X$) in those resonances. We first consider uncoupled isovector $S$-wave scattering of $B^{(*)}\overline B^{*}$ within the framework of effective-range expansion (ERE). Expressions for the scattering length ($a$) and effective range ($r$) are derived exclusively in terms of the masses and widths of the two $Z_b$ states. We then develop compositeness within ERE for the resonance case and deduce the expression $X=1/\sqrt{2r/a-1}$, which is then applied to the systems of interest. Finally, the actual compositeness parameters are calculated in terms of resonance pole positions and their experimental branching ratios into $B^{(*)}\overline{B}^*$ by using the method of Ref.[1]. We find the values $X=0.66\pm 0.11$ and $0.51\pm 0.10$ for the $Z_b(10610)$ and $Z_b(10650)$, respectively. We also compare the ERE with Breit-Wigner and Flatté parameterizations to discuss the applicability of the last two ones for near-threshold resonances with explicit examples.

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arXiv2015

Antiproton-proton interaction and related hadron physics

Antinucleon-nucleon interaction has been established in chiral effective field theory. The strong threshold enhancement observed in the reactions $J/ψ\toγ\overline pp$ and $e^+e^-\to\overline pp$ are interpreted by the strong $\overline pp$ interaction. Concerning the channel $J/ψ\toγ\overline pp$, the topic on the $\overline pp$ bound state is also discussed.

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arXiv2015

Origin of the structures observed in $e^+e^-$ annihilation into multipion states around the $\bar pp$ threshold

We analyze the origin of the structures observed in the reactions $e^+e^-\to 3(π^+π^-)$, $2(π^+π^-π^0)$, $ωπ^+π^-π^0$, and $e^+e^-\to 2(π^+π^-)π^0$ around the antiproton-proton ($\bar pp$) threshold. We calculate the contribution of the two-step process $e^+e^-\to \bar NN \to$ multipions to the total reaction amplitude. The amplitude for $e^+e^-\to \bar NN$ is constrained from near-threshold data on the $e^+e^-\to \bar pp$ cross section and the one for $\bar NN \to$ multipions can be likewise fixed from available experimental information, for all those $5 π$ and $6π$ states. The resulting amplitude for $e^+e^-\to$ multipions turns out to be large enough to play a role for the considered $e^+e^-$ annihilation channels and, in three of the four reactions, even allows us to reproduce the data quantitatively near the $\bar NN$ threshold. The structures seen in the experiments emerges then as a threshold effect due to the opening of the $\bar NN$ channel.

nucl-th↗

arXiv2015

On the near-threshold $\bar pp$ invariant mass spectrum measured in $J/ψ$ and $ψ'$ decays

A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/ψ\to x \bar pp$ and $ψ(3686) \to x \bar pp$ $(x = γ,\, ω,\, ρ,\, π,\, η)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered and, in addition, an older phenomenological model constructed by the Jülich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar pp$ FSI. It turns out that the interaction in the isospin-1 $^1S_0$ channel required for the description of the $J/ψ\to γ\bar pp$ decay predicts a $\bar NN$ bound state.

nucl-th↗

arXiv2014

B_l4 decays and the extraction of |V_ub|

The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| is not well determined yet. It can be extracted from both inclusive or exclusive decays, like B --> pi (rho) l nu-bar_l. However, the exclusive determination from B --> rho l nu-bar_l, in particular, suffers from a large model dependence. In this paper, we propose to extract |V_ub| from the four-body semileptonic decay B --> pi pi l nu-bar_l, where the form factors for the pion-pion system are treated in dispersion theory. This is a model-independent approach that takes into account the pi-pi rescattering effects, as well as the effect of the rho meson. We demonstrate that both finite-width effects of the rho meson as well as scalar pi-pi contributions can be considered completely in this way.

hep-ph↗

arXiv2013

Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.

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arXiv2011

Study of CP violation in $Λ_c^+$ decay

In this paper, we study CP violation in $Λ_c^+\to BP$ and $Λ_c^+\to BV$ decays, where $B,P$ and $V$ denote a light spin-1/2 baryon, pseudoscalar and a vector meson respectively. In these processes the $T$ odd CP violating triple-product (TP) correlations are examined. The genuine CP violating observables which are composed of the helicity amplitudes occurring in the angular distribution are constructed. Experimentally, by performing a full angular analysis it is shown how one may extract the helicity amplitudes and then obtain the TP asymmetries. We estimate the TP asymmetries in $\lam$ decays to be negligible in the standard model making these processes an excellent place to look for new physics. Taking a two Higgs doublet model, as an example of new physics, we show that large TP asymmetries are possible in these decays. Finally, we discuss how BES-III and Super $τ$-Charm experiments will be sensitive to these CP violating signals in $Λ_c^+$ decays.

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arXiv2011

Final state interactions in $D\to Kπlν$ decay

The semileptonic $D_{l4}$ decay including $D\to Kπlν$ and $D\to ππlν$ have been extensively studied. In these references, the form factors and differential decay rate are explicitly stated. However, we would like to stress that in these papers the final state interactions are often overlooked, i.e. rescattering effect of the pseudoscalars produced by $D_{l4}$ decay may be very important, at least on the side of phase of form factors due to Watson's theorem. In this short paper, we will display this rescattering effect in the framework of heavy hadron chiral perturbation theory, it thus must be a very useful and indispensable supplement of the previous papers on $D_{l4}$ study.

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arXiv2010

Extracting strong phase and $CP$ violation in $D$ decays by using quantum correlations in $ψ(3770)\to D^0 \overline{D}^0 \to (V_1V_2)(K π)$ and $ψ(3770)\to D^0\overline{D}^0\to (V_1V_2)(V_3V_4)

We exploit the angular and quantum correlations in the $D\bar{D}$ pairs produced through the decay of the $ψ(3770)$ resonance in a charm factory to investigate CP-violation in two different ways. We consider the case of $ψ(3770)\rightarrow D\bar{D}\rightarrow (V_1V_2)(Kπ)$ decays, which provide a new way to measure the strong phase difference $δ$ between Cabibbo-favored and doubly-Cabibbo suppressed $D$ decays required in the determination of the CKM angle $γ$. We also build CP-violating observables in $ψ(3770)\rightarrow D\bar{D}\rightarrow (V_1V_2)(V_3 V_4)$ to isolate specific new physics effects in the charm sector. Neglecting the systematics, we give a first rough estimate of the sensitivities of these measurements at BES-III with an integrated luminosity of 20 fb$^{-1}$ at $ψ(3770)$ peak and at a future super $τ$-charm factory with a luminosity of $10^{35}$ cm$^{-2}$s$^{-1}$

hep-ph↗

arXiv2010

Partial wave analysis of $ψ'\toγχ_{c0}\to γp K^- \barΛ$ used for searching for baryon resonance

The abundant $ψ'$ events have been collected at the Beijing Electron Positron Collider-II (BEPCII) that could undoubtedly provide us with a great opportunity to study the more attractive charmonium decays. As has been noticed before, in the process of $J/ψ$ decaying to the baryonic final states, $p K^- \barΛ$, the evident $Λ^*$ and $N^*$ bands have been observed. Similarly, by using the product of $χ_{cJ}$ from $ψ'$ radiative decay, we may confirm it or find some extra new resonances. $χ_{c0}$'s data samples will be more than $χ_{c1,2}$ taking into account the larger branching ratio of $ψ'\toγχ_{c0}$. Here, we provide explicit partial wave analysis formulae for the very interesting channel $ψ'\toγχ_{c0}\to γp K^- \barΛ$.

hep-ph↗

arXiv2010

Study of $Λ- \Lambdabar$ Oscillation in quantum coherent $Λ\Lambdabar$ state by using J/ψ\to Λ\barΛ$ decay

We discuss the possibility of searching for the $\Lam - \Lamb$ oscillations for coherent $\Lam\Lamb$ production in the J/$ψ\to \Lam \Lamb$ decay process. The sensitivity of measurement of $\Lam -\Lamb$ oscillation in the external field at BES-III experiment is considered. These considerations indicate an alternative way to probe the $ΔB =2$ amplitude in addition to neutron oscillation experiments. Both coherent and time-dependent information can be used to extract the $\Lam-\Lamb$ oscillation parameter. With one year's luminosity at BES-III, we can set an upper limit of $δm_{\Lam \Lamb} < 10^{-15}$ MeV at 90% confidence level, corresponding to about $10^{-6}$ s of $\Lam-\Lamb$ oscillation time.

hep-ph↗

arXiv2010

Study of CP violation in D->VV decay at BESIII

In this paper, we intend to study the problem of CP violation in $D$ meson by $D\to VV$ decay mode in which the T violating triple-product correlation is examined. That would undoubtedly be another excellent probe of New Physics beyond Standard Model. For the neutral $D$, we focus on direct CP violation without considering $D^0-\bar D^0$ oscillation. Experimentally, by a full angular analysis one may obtain such CP violating signals, and particularly it is worth mentioning that the upcoming large $D$ data samples at BES-III in Beijing will provide a great opportunity to perform it.

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