arXiv subjects

M. B. Voloshin

Publications and source records attributed to M. B. Voloshin.

At least 37 records · Page 2Linked to original sources

arXiv2016

Search for Hidden-Charm Pentaquark with CLAS12

LHCb recently announced the discovery of two exotic structures in the $J/ψ+ p$ decay channel, which have been referred to as charmonium-pentaquark states. Resolving between the models and clarifying the nature of the discovered hidden-charm pentaquark peaks, and possibly searching for similar peaks with other quantum numbers, requires further experimental studies. The states were observed in the decay mode $J/ψ+p$. Thus, it is natural to expect that these pentaquarks can be produced in the photoproduction process $γ+p\to P_c\to J/ψ+p$ where these states will appear as s-channel resonances at photon energy around 10 GeV. The energy and luminosity of the CLAS12 photon beam permit the detailed studies of the production and decay properties of the pentaquark resonances. By this reason the pentaquark search at Jefferson Laboratory looks extremely attractive.

hep-ph↗

arXiv2016

Constituent counting rule for exclusive production of heavy quarkoniumlike exotic resonance and a light hadron

The exclusive processes are considered, where a point-like source of heavy quark-antiquark pairs $Q \bar Q$, e.g. their electromagnetic current, produces a pair consisting of a heavy quarkoniumlike exotic meson (tetraquark) or baryon (pentaquark) and a light meson or an antibaryon. For a sufficiently large mass of the heavy quark $m_Q$ there is a range of the energy $E$ above the $Q \bar Q$ threshold, where $E \ll m_Q$ and still the energy is large compared to the strong interaction scale, $E \gg Λ_{QCD}$. It is shown that in this energy range, where the heavy quarks are nonrelelativistic, a specific `intermediate asymptotic' behavior sets in determined by the number $n$ of the pairs of constituent quarks, with the rate scaling as $E^{1-n}$.

hep-ph↗

arXiv2016

Two charmoniumlike charged axial resonances near 3885 MeV

It is argued that the charged $Z^+_c(3885)$ resonance, treated as a `molecular' state of charmed $D$ and $D^*$ mesons, is likely to consist of two peaks unequally coupled to the $D^{*+} \bar D^0$ and $D^+ \bar D^{*0}$ channels. The peaks should be split in mass by at least approximately 1.5 MeV. This behavior arises from an enhancement of the effect of isospin violation in the masses of the $D$ and $D^*$ mesons due to apparent suppression of forces between the mesons depending on the spins of the heavy as well as of the light quarks. The suggested double-peak structure can be studied either by direct shape measurement in the channels with heavy mesons, or by isospin-violating transitions from $Z_c^\pm(3885)$ to the states of charmonium plus a light meson.

hep-ph↗

arXiv2016

Sum rules for interaction of $Υ$ resonances with $Z_b π$

The strength of the amplitudes for the coupling between the bottomonium $Υ(nS)$ states, the bottomonium-like isovector resonances $Z_b$ and a pion, $Υ(nS) Z_b π$, is considered. These amplitudes describe the decays $Z_b \to Υ(nS) π$ for $n=1,\,2,\,3$, and the processes $Υ(nS) \to Z_b π$ for $n=5,\,6, \ldots$ with either $Z_b(10610)$ or $Z_b(10650)$. It is pointed out that analyticity and unitarity impose a sum rule for these couplings to each of the $Z_b$ resonances. With the currently available data it appears to be difficult or impossible to simultaneously satisfy the sum rules for the $Z_b(10610)$ and $Z_b(10650)$ resonances. This difficulty can be resolved if there is a considerable dissimilarity in the yield of the states $Z_b(10610) π$ and $Z_b(10650) π$ in the $e^+e^-$ annihilation at energies above the $Υ(5S)$ resonance.

hep-ph↗

arXiv2016

$Υ(6S)$ and triangle singularity in $e^+e^- \to B_1(5721) \bar B \to Z_b(10610) \, π$

We discuss the possibility that production of final states with bottomonium and light mesons at the peak $Υ(6S)$ in the $e^+e^-$ annihilation at approximately 11.00 GeV is in fact due to a triangular singularity at the threshold of the heavy meson pair production $B_1(5721) \bar B + c.c.$ through the process $e^+e^- \to B_1(5721) \bar B \to Z_b(10610) \, π$. The presence of the hidden-bottom resonance $Z_b(10610)$ then explains the observed enhanced production of the final channels with both ortho- and para- bottomonium states, $Υ(nS) ππ$ and $h_b(kP) ππ$. The discussed mechanism also predicts a distinct pattern for production of hidden-bottom states at the $Υ(6S)$ energy that can be tested by experiment.

hep-ph↗

arXiv2016

Light Quark Spin Symmetry in $Z_b$ Resonances?

It is argued that the recent Belle data, consistent with no activity in the spectrum of the $B^* \bar B + B \bar B^*$ pairs at the mass of the $Z_b(10650)$ resonance, imply that the part of the interaction between heavy mesons that depends on the total spin of the light quark and antiquark is strongly suppressed. In particular this part appears to be significantly weaker than can be inferred from pion exchange. If confirmed by future more detailed data, the symmetry with respect to the light quark spins, in combination with the heavy quark spin symmetry, would imply existence of four additional $I^G=1^-$ resonances at the thresholds for heavy meson-antimeson pairs.

hep-ph↗

arXiv2015

Remarks on measurement of the decay $Ξ_b^- \to Λ_b π^-$

The interpretation of the recent observation by LHCb of a heavy-flavor-conserving and strangeness-changing decay $Ξ_b^- \to Λ_b π^-$ in terms of the branching fraction for the decay suffers from the uncertainty in the yield of the $Ξ_b^-$ hyperons relative to that of the $Λ_b$. It is pointed out here that this relative yield can be determined with a significantly reduced uncertainty by measuring within the same experimental conditions the decays related by the flavor $SU(3)$ symmetry and/or the heavy quark symmetry, such as $Ξ_b \to J/ψ\, Ξ$, $Λ_b \to J/ψ\, Λ$, or $Ξ_b^- \to Ξ_c^0 \ell ν$, $Λ_b \to Λ_c \ell ν$.

hep-ph↗

arXiv2015

Formation of hidden-charm pentaquarks in photon-nucleon collisions

The cross section for formation in $γ+ p$ collisions of the recently found hidden-charm pentaquark states $P_c(4380)$ and $P_c(4450)$ is discussed and estimated. The studies of these resonances in photon beam experiments can be complementary to those in the LHCb experiment setting, and may be more advantageous for measurement of their additional decay channels. It is pointed out that both the relative importance of such decays and the yield of the resonances in the $γ+ p$ collisions are sensitive to the internal dynamics of the pentaquarks and can resolve between theoretical models. Specific numerical estimates are discussed within a simple `baryocharmonium' model, where the the observed $P_c$ resonances are composites of $J/ψ$ and excited nucleon states with the quantum numbers of $N(1440)$ and $N(1520)$.

hep-ph↗

arXiv2015

Modification by pion exchange of near threshold resonance line shape in open heavy flavor channel

The effect of the pion exchange on the line shape of near threshold bottomoniumlike resonances decaying into an $S$ wave pair of $B^{(*)}$ mesons is considered. It is pointed out that this effect, parametrically enhanced by the heavy meson mass, can be of a practical significance in determining the parameters of the bottomoniumlike resonances such as the known $Z_b(10610)$ and $Z_b(10650)$ states.

hep-ph↗

arXiv2015

Condensed state of heavy vectorlike neutrinos

Some extensions of the Standard Model suggest existence of vectorlike fermions whose mass $M$ can be by up to several orders of magnitude larger than the electroweak scale $v$, and with the Higgs mechanism providing only a small part $m$ of this mass that is a fraction of $v$. It is shown that in a certain range of the parameters $m$ and $M$ there exist stable globules of degenerate fermionic matter made from the lighter of the neutral vectorlike leptons (superheavy neutrinos) with a number density much larger than $m_h \, v^2$, with $m_h$ being the Higgs boson mass. The stability is due to the deformation of the Higgs field inside the globule to values greatly exceeding $v$. The globules are absolutely stable if the lighter of the vectorlike neutrinos is stable and can be (a part of) the dark matter.

hep-ph↗

arXiv2015

The process $e^+e^- \to ππX(3823)$ in the soft pion limit

The production of the resonance $X(3823)$, identified as the charmonium $^3D_2$ state, in the process $e^+e^- \to ππX(3823)$ has been recently reported by BESIII. It is pointed out that this process is fully described, up to one overall coupling constant, in the soft pion limit. An interpretation of the available and possible future data within the discussed theoretical framework may reveal new features of the charmoniumlike states. In particular, the observed relative yield for this process at different energies strongly suggests a very significant enhancement of the amplitude at the charmoniumlike peak near 4.36\,GeV.

hep-ph↗

arXiv2015

$X(3915)$ as a $D_s \bar D_s$ bound state

We suggest that the observed properties of the charmoniumlike resonance $X(3915)$ can possibly be explained if it is an $S-$wave molecular bound state of $D_s \bar D_s$ meson pair with binding energy about 18\,MeV. In particular, the decays of $X(3915)$ to pairs of non-strange $D$ mesons are suppressed and proceed at a rate comparable to that of the decay $X(3915) \to ωJ/ψ$, whose branching fraction can be as large as about 0.3. Other major types of decay of $X(3915)$ with a comparable (or slightly smaller) rate are the transition $X(3915) \to ηη_c$ and the decays into light hadrons due to the annihilation of the $c \bar c$ quark pair. The existence of a bound state should lead to an enhancement in the spectrum of the invariant mass for the $D_s \bar D_s$ near threshold in $B$ decays, e.g. in $B \to K D_s \bar D_s$ which enhancement can be tested experimentally.

hep-ph↗

arXiv2014

$χ_{c0} \, ω$ production in $e^+e^-$ annihilation through $ψ(4160)$

We argue that the recent BESIII data on the cross section for the process $e^+e^- \to χ_{c0} \, ω$ in the center of mass energy range 4.21 - 4.42 GeV can be described by the contribution of the known charmonium-like resonance $ψ(4160)$ with the mass of about 4190\,MeV. The value of the coupling in the transition $ψ(4160) \to χ_{c0} \, ω$ needed for this mechanism is comparable to that in another known similar transition $χ_{c0}(2P) \to J/ψ\, ω$. The suggested mechanism also naturally explains the reported relative small value of the cross section for the final states $χ_{c1} \, ω$ and $χ_{c2} \, ω$ above their respective thresholds.

hep-ph↗

arXiv2014

Metastable vacuum decay in center-stabilized Yang-Mills theory at large N

We calculate the rate of the decay of a metastable vacuum state in $SU(N)$ gauge theory on ${\mathbb R}^3 \times {\mathbb S}^1$ space with a double trace deformation suggested by Ünsal and Yaffe. The derived analytical expression for the exponential factor in the decay rate, including the dependence on the parameter $θ$, gives the exact behavior in the leading power of $N$ in the limit of large $N$ and provides a better approximation than a recently found in the literature numerical result.

hep-th↗

arXiv2014

The decays $Ξ_b \to Λ_b \, π$ and diquark correlations in hyperons

The decays $Ξ_b \to Λ_b π$ are strangeness changing weak transitions involving only the light diquark in the baryon. Thus these decays can test the properties of such diquarks, in particular the suggestions existing in the literature of enhanced correlations in $J^P=0^+$ light diquarks. We revisit the estimates of the rates of these decays and point out that with the enhanced correlation their branching fraction can reach a few percent and may become visible in the measurements of differences of the lifetimes of $b$ baryons.

hep-ph↗

arXiv2014

Contribution of $Z_b$ resonances to $Υ(5S) \to πππχ_b$

We discuss the recently presented Belle results on the decays $Υ(5S) \to πππχ_{bJ}(1P)$. The data indicate that in addition to the $ω$ emission, $Υ(5S) \to ωχ_{bJ}$, there is a significant non resonant background in the three pion spectrum. We suggest that a sizable fraction of this background may be associated with the cascade process $Υ(5S) \to πZ_b \to πρχ_b$ involving the $Z_b(10610)$ and $Z_b(10650)$ resonances. If confirmed by the data, this would be the first observation of transition from the $Z_b$ resonances to lower bottomonium with emission of a light meson state different from a single pion, which may provide a new input in understanding of the internal dynamics of these resonances.

hep-ph↗

arXiv2014

Y(4260) and Y(4360) as mixed hadrocharmonium

Recent BESIII data indicate a significant rate of the process $e^+e^- \to h_c π^+ π^-$ at the Y(4260) and Y(4360) resonances, implying a substantial breaking of the heavy quark spin symmetry. We consider these resonances within the picture of hadrocharmonium, i.e. of (relatively) compact charmonium embedded in a light quark mesonic excitation. We suggest that the resonances Y(4260) and Y(4360) are a mixture, with mixing close to maximal, of two states of hadrochamonium, one containing a spin-triplet $c \bar c$ pair and the other containing a spin-singlet heavy quark pair. We argue that this model is in a reasonable agreement with the available data and produces distinctive and verifiable predictions for the energy dependence of the production rate in $e^+e^-$ annihilation of the final states $J/ψππ$, $ψ' ππ$ and $h_c ππ$, including the pattern of interference between the two resonances.

hep-ph↗

arXiv2014

Bound state energy of a Coulomb impurity in gapped bilayer graphene: "Hydrogen atom with a Mexican hat"

Application of a perpendicular electric field induces a band gap in bilayer graphene, and it also creates a "Mexican hat" structure in the dispersion relation. This structure has unusual implications for the hydrogen-like bound state of an electron to a Coulomb impurity. We calculate the ground state energy of this hydrogen-like state as a function of the applied interlayer voltage and the effective fine structure constant. Unlike in the normal hydrogen atom, the resulting wavefunction has many nodes even in the ground state. Further, the electron state undergoes "atomic collapse" into the Dirac continuum both at small and large voltage.

cond-mat.mes-hall↗