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Shi-Lin Zhu

Publications and source records attributed to Shi-Lin Zhu.

At least 289 records · Page 16Linked to original sources
arXiv2004

Nuclear Parity-Violation in Effective Field Theory

We reformulate the analysis of nuclear parity-violation (PV) within the framework of effective field theory (EFT). To order Q, the PV nucleon-nucleon (NN) interaction depends on five a priori unknown constants that parameterize the leading-order, short-range four-nucleon operators. When pions are included as explicit degrees of freedom, the potential contains additional medium- and long-range components parameterized by PV piNN couplings. We derive the form of the corresponding one- and two-pion-exchange potentials. We apply these considerations to a set of existing and prospective PV few-body measurements that may be used to determine the five independent low-energy constants relevant to the pionless EFT and the additional constants associated with dynamical pions. We also discuss the relationship between the conventional meson-exchange framework and the EFT formulation, and argue that the latter provides a more general and systematic basis for analyzing nuclear PV.

nucl-th↗
arXiv2004

Theoretical Development on Pentaquarks

I first give a brief overview of the status of exotic hadron search so far. Then I review the recent theoretical development on pentaquarks. Finally I emphasize that none of theoretical formalisms predicts the existence of $Θ$ pentaquark very reliably. None of them explains its narrow width in a natural way.

hep-ph↗
arXiv2004

Possible Interpretations of $D_{sJ}^+(2632)$ If It Really Exists

We analyze various possible interpretations of the narrow state $D_{sJ}^+(2632)$ observed by SELEX Collaboration recently, which lies above threshold and has abnormal decay pattern. These interpretations include: (1) several versions of tetraquarks; (2) conventional $c\bar s$ meson such as the first radial excitation of $D_s(2112)$ with abnormally large SU(3) symmetry breaking; (3) conventional $c\bar s$ meson with abnormally large $η_1$ coupling; (4) heavy hybrid meson. We discuss the physical implications of each interpretation. For example, if the existence of $D_{sJ}^+(2632)$ is confirmed as the first radial excitation of $D_s(2112)$ by other experiments, it will be helpful to look for (1) its SU(3) flavor partners $D_{J}^{0,+}(2530)$; (2) its B-meson analogues $B_{J}^{0,+}(5840), B_{sJ}^+(5940)$; (3) S-wave two pion decay modes.

hep-ph↗
arXiv2004

$D_{sJ}^+(2632)$: An Excellent Candidate of Tetraquarks

We analyze various possible interpretations of the narrow state $D_{sJ}(2632)$ which lies 100 MeV above threshold. This interesting state decays mainly into $D_s η$ instead of $D^0 K^+$. If this relative branching ratio is further confirmed by other experimental groups, we point out that the identification of $D_{sJ}(2632)$ either as a $c\bar s$ state or more generally as a ${\bf {\bar 3}}$ state in the $SU(3)_F$ representation is probably problematic. Instead, such an anomalous decay pattern strongly indicates $D_{sJ}(2632)$ is a four quark state in the $SU(3)_F$ ${\bf 15}$ representation with the quark content ${1\over 2\sqrt{2}} (ds\bar{d}+sd\bar{d}+su\bar{u}+us\bar{u}-2ss\bar{s})\bar{c}$. We discuss its partners in the same multiplet, and the similar four-quark states composed of a bottom quark $B_{sJ}^0(5832)$. Experimental searches of other members especially those exotic ones are strongly called for.

hep-ph↗
arXiv2004

Pentaquarks

Since LEPS collaboration reported the first evidence of $Θ^+$ pentaquark in early 2003, eleven other experimental groups have confirmed this exotic state while many other groups didn't see any signal. If this state is further established by future high statistical experiments, its discovery shall be one of the most important events in hadron physics for the past three decades. This exotic baryon with such a low mass and so narrow a width imposes a big challenge to hadron theorists. Up to now, there have appeared more than two hundred theoretical papers trying to interpret this charming state. I will review some important theoretical developments on pentaquarks based on my biased personal views.

hep-ph↗
arXiv2004

Diquarks, Pentaquarks and Dibaryons

We explore the connection between pentaquarks and dibaryons composed of three diquarks in the framework of the diquark model. With the available experimental data on H dibaryon, we estimate the Pauli blocking and annihilation effects and constrain the $P=-$ pentaquark $SU(3)_F$ singlet mass. Using the $Θ^+$ pentaquark mass, we estimate $P=-$ dibaryon mass.

hep-ph↗
arXiv2004

Heavy and Light Pentaquark Chiral Lagrangian

Using the SU(3) flavor symmetry, we construct the chiral Lagrangians for the light and heavy pentaquarks. The correction from the nonzero quark is taken into account perturbatively. We derive the Gell-Mann$-$Okubo type relations for various pentaquark multiplet masses and Coleman-Glashow relations for anti-sextet heavy pentaquark magnetic moments. We study possible decays of pentaquarks into conventional hadrons. We also study the interactions between and within various pentaquark multiplets and derive their coupling constants in the symmetry limit. Possible kinematically allowed pionic decay modes are pointed out.

hep-ph↗
arXiv2004

Heavy Pentaquarks

We construct the spin-flavor wave functions of the possible heavy pentaquarks containing an anti-charm or anti-bottom quark using various clustered quark models. Then we estimate the masses and magnetic moments of the $J^P={1\over 2}^+$ or ${3\over 2}^+$ heavy pentaquarks. We emphasize the difference in the predictions of these models. Future experimental searches at BESIII, CLEOc, BELLE, and LEP may find these interesting states.

hep-ph↗
arXiv2004

$J^P={1/2}^-$ Pentaquarks in Jaffe and Wilczek's Diquark Model

If Jaffe and Wilczek's diquark picture for $Θ_5$ pentaquark is correct, there should also exist a $SU_F$(3) pentaquark octet and singlet with no orbital excitation between the diquark pair, hence $J^P={1/2}^-$. These states are lighter than the $Θ_5$ anti-decuplet and lie close to the orbitally excited (L=1) three-quark states in the conventional quark model. We calculate their masses and magnetic moments and discuss their possible strong decays using the chiral Lagrangian formalism. Among them two pentaquarks with nucleon quantum numbers may be narrow. Selection rules of strong decays are derived. We propose the experimental search of these nine additional $J^P={1/2}^-$ baryon states. Especially there are two additional $J^P={1/2}^-$ $Λ$ baryons around $Λ(1405)$. We also discuss the interesting possibility of interpreting $Λ(1405)$ as a pentaquark. The presence of these additional states will provide strong support of the diquark picture for the pentaquarks. If future experimental searches fail, one has to re-evaluate the relevance of this picture for the pentaquarks.

hep-ph↗
arXiv2004

The Narrow $Θ_5$ Pentaquark As The First Non-planar Hadron With the Diamond Structure And Negative Parity

Using the picture of the flux tube model, we propose that the $Θ_5$ pentaquark as the first candidate of the three-dimensional non-planar hadron with the extremely stable diamond structure. The up and down quarks lie at the corners of the diamond while the anti-strange quark sits in the center. Various un-excited color flux tubes between the five quarks bind them into a stable and narrow color-singlet. Such a configuration allows the lowest state having the negative parity naturally. The decay of the $Θ_5$ pentaquark into the nucleon and kaon requires the breakup of the non-planar diamond configuration into two conventional planar hadrons, which involves some kind of structural phase transition as in the condensed matter physics. Hence the width of the $Θ^+$ pentaquark should be narrow despite that it lies above the kaon nucleon threshold. We suggest that future lattice QCD calculation adopt non-planar interpolating currents to explore the underlying structure of the $Θ_5$ pentaquark.

hep-ph↗
arXiv2004

D_s(2317) and D_s(2457) from HQET Sum Rules

Within the framework of the heavy quark effective theory, QCD sum rules are used to calculate the masses of p-wave (c-bar s) states. The results for 0^+ and 1^+ states with the angular momentum of the light component j_l=1/2 are consistent with the experimental values for D_s(2317) and D_s(2457), respectively.

hep-ph↗
arXiv2004

Magnetic Moments of $J^P={3/2}^+$ Pentaquarks

If the $J^P$ of $Θ_5^+$ and $Ξ_5^{--}$ pentaquarks is really found to be ${1\over 2}^+$ by future experiments, they will be accompanied by $J^P={3\over 2}^+$ partners in some models. It is reasonable to expect that these $J^P={3\over 2}^+$ states will also be discovered in the near future with the current intensive experimental and theoretical efforts. We estimate $J^P={3/2}^+$ pentaquark magnetic moments using different models.

hep-ph↗
arXiv2004

Magnetic Moment of The $Θ^+$ Pentaquark State

We have calculated the magnetic moment of the recently observed $Θ^+$ pentaquark in the framework of the light cone QCD sum rules using the photon distribution amplitudes. We find that $μ_{Θ^+}=(0.12\pm 0.06) μ_N$, which is quite small. We also compare our result with predictions of other groups.

hep-ph↗
arXiv2003

Understanding Pentaquark States in QCD

We estimate the mass of the pentaquark state with QCD sum rules and find that pentaquark states with isospin $I=0, 1, 2$ lie close to each other around $(1.55\pm 0.15)$ GeV. The experimentally observed baryon resonance $Θ^+ (1540)$ with $S=+1$ can be consistently identified as a pentaquark state if its $J^P={1\over 2}^-$. Such a state is expected in QCD. If its parity is positive, this pentaquark state is really exotic. Now the outstanding issue is to determine its quantum numbers experimentally.

hep-ph↗
arXiv2003

Understanding the $D^+_{sJ}(2317)$ and $D^+_{sJ}(2460)$ with Sum Rules in HQET

In the framework of heavy quark effective theory we use QCD sum rules to calculate the masses of the $\bar c s$ $(0^+, 1^+)$ and $(1^+, 2^+)$ excited states. The results are consistent with that the states $D_{sJ}(2317)$ and $D_{sJ}(2460)$ observed by BABAR and CLEO are the $0^+$ and $1^+$ states in the $j_l={1\over 2}^+$ doublet.

hep-ph↗
arXiv2003

Understanding the Possible Proton Antiproton Bound State Observed by BES Collaboration

We comment on the quantum numbers and decay channels of the possible proton antiproton bound state observed by BES Collaboration. Based on the general symmetry consideration and available experimental information, we conclude that the quantum number of this state is very likely to be $J^{PC}=0^{-+}, I^G=0^+$, which can not decay into final states $π^+π^-, 2π^0, K{\bar K}, 3π$. Besides its dissociation into $p\bar p$, the other important mesonic decay modes could be $ηππ$, $η'ππ$, $ηηη$, $4π$, $K{\bar K}π$, $ηK{\bar K}$, $K\bar K ππ$, 6$π$. Experimental search of this signal in these meson final states is strongly called for.

hep-ph↗
arXiv2002

The Off-diagonal Goldberger-Treiman Relation and Its Discrepancy

We study the off-diagonal Goldberger-Treiman relation (ODGTR) and its discrepancy (ODGTD) in the N, Delta, pi sector through O(p^2) using heavy baryon chiral perturbation theory. To this order, the ODGTD and axial vector N to Delta transition radius are determined solely by low energy constants. Loop corrections appear at O(p^4). For low-energy constants of natural size, the ODGTD would represent a ~ 2% correction to the ODGTR. We discuss the implications of the ODGTR and ODGTD for lattice and quark model calculations of the transition form factors and for parity-violating electroexcitation of the Delta.

hep-ph↗