Narrow Decay Width Research Articles

Effect of divertor plasma-facing materials and drift on the power decay width in the scrape-off layer and divertor on EAST

The narrow power decay width λ q may lead to high heat flux density to the divertor target, which is one of the most severe challenges for future fusion devices. EAST has upgraded its lower graphite (C) divertor to a tungsten (W) one, and it is important to reveal the dependence of λ q on the divertor condition. In the present work, SOLPS-ITER is applied to estimate the effect of various conditions [C/W plasma facing material (PFM), with/without drift] on λ q of EAST in attached divertor regime. The simulation results confirm that the power decay width of the upstream λ q,SOL, divertor λ q,OT, and private-flux region (PFR) S OT all depend on the PFMs and drifts. However, the effect of PFM on λ q,SOL is slight, while it has a significant influence on λ q,OT and S OT. In the upstream, positive correlation between λ q,SOL and is obtained, and the simulation is in qualitative agreement with the two-point model. Both λ q,SOL and λ q,OT in without drift case are larger than that of with drift case. The regression of simulation results is obtained, showing a strong positive correlation between SOL collisionality , power radiation friction in divertor region f rad,OD and λ q,OT. Thus, the C PFM with intrinsic impurity has the largest λ q,OT. In the PFR, S OT with drift is smaller than that of without drift. Moreover, the combination of more D atoms accumulation and stronger E p × B drift lead to larger S OT in W PFM case than that of C PFM case.

QED exponentiation for quasi-stable charged particles: the e^-e^+rightarrow W^-W^+ process

All real and virtual infrared singularities in the standard analysis of the perturbative Quantum Electrodynamics (like that of Yennie–Frautschi–Suura) are associated with photon emissions from the external legs in the scattering process. External particles are stable, with the zero decay width. Such singularities are well understood at any perturbative order and are resummed. The case of production and decay of the semi-stable neutral particles, like the Z-boson or the tau -lepton, with the narrow decay width, Gamma /M ll 1, is also well understood at any perturbative order and soft-photon resummation can be done. For an absent or loose upper cut-off on the total photon energy omega , production and decay processes of the semi-stable (neutral) particles decouple approximately and can be considered quasi-independently. In particular, the soft-photon resummation can be done separately for the production and the decay, treating a semi-stable (neutral) particle as stable. QED interference contributions between the production and decay stages are suppressed by the Gamma /M factor. If experimental precision omega is comparable with or better than Gamma /M, these interferences have to be included. In the case of omega ll Gamma decoupling of production and decay does not work any more and the role of semi-stable particles is reduced to the same role as that of other internal off-shell particles. So far, consistent treatment of the soft photon resummation for semi-stable charged particles like the W^pm bosons is not available in the literature, and the aim of this work is to present a solution to this problem. Generally, this should be feasible because the underlying physics is the same as in the case of neutral semi-stable resonances—in the limit of Gamma /M ll 1 the production and decay processes for charged particles also necessarily decouple due to long lifetime of intermediate particles. Technical problems to be solved in this work are related to the fact that semi-stable charged particle are able to emit photons. Practical importance of the presented technique to the e^+e^-rightarrow W^+W^- process at the Future electron–positron Circular Collider (FCC-ee) is underlined.

Ω baryon spectrum and their decays in a constituent quark model

Combining the recent developments of the observations of $\mathrm{\ensuremath{\Omega}}$ sates we calculate the $\mathrm{\ensuremath{\Omega}}$ spectrum up to the $N=2$ shell within a nonrelativistic constituent quark potential model. Furthermore, the strong and radiative decay properties for the $\mathrm{\ensuremath{\Omega}}$ resonances within the $N=2$ shell are evaluated by using the masses and wave functions obtained from the potential model. It is found that the newly observed $\mathrm{\ensuremath{\Omega}}(2012)$ resonance is most likely to be the spin-parity ${J}^{P}=3/{2}^{\ensuremath{-}}$ $1P$-wave state $\mathrm{\ensuremath{\Omega}}({1}^{2}{P}_{3/{2}^{\ensuremath{-}}})$, it also has a large potential to be observed in the $\mathrm{\ensuremath{\Omega}}(1672)\ensuremath{\gamma}$ channel. Our calculation shows that the $1P$-, $1D$-, and $2S$-wave $\mathrm{\ensuremath{\Omega}}$ baryons have a relatively narrow decay width of less than 50 MeV. Based on the obtained decay properties and mass spectrum, we further suggest optimum channels and mass regions to find the missing $\mathrm{\ensuremath{\Omega}}$ resonances via the strong and/or radiative decay processes.

Strong and radiative decays of the low-lying D -wave singly heavy baryons

The strong and radiative decays of the low-lying $\lambda$-mode $D$-wave $\Lambda_{c(b)}$, $\Sigma_{c(b)}$, $\Xi_{c(b)}$, $\Xi_{c(b)}'$, and $\Omega_{c(b)}$ baryons are studied in a constituent quark model. Our calculation shows the following: (i) The missing $\lambda$-mode $D$-wave $\Omega_{c(b)}$, $\Lambda_{b}$, and $\Xi_{b}$ baryons have a relatively narrow decay width of a few MeV or a few tens of MeV and their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiments. (ii) The $\lambda$-mode $1D$-wave excitations in the $\Sigma_{c(b)}$ and $\Xi_{c(b)}'$ families appear to have a relatively broad width of $\sim 50-200$ MeV.Most of the $1D$-wave states have large decay rates into the $1P$-wave heavy baryons via the pionic or kaonic strong decay processes, which should be taken seriously in future observations. (iii) Both $\Lambda_c(2860)$ and $\Xi_c(3050)$ seem to favor the $J^P=3/2^+$ excitation $|^2D_{\lambda\lambda} \frac{3}{2}^+ \rangle$ of $\bar{\mathbf{3}}_F$, while both $\Lambda_c(2880)$ and $\Xi_c(3080)$ may be assigned as the $J^P=5/2^+$ excitation $|^2D_{\lambda\lambda} \frac{5}{2}^+ \rangle$ of $\bar{\mathbf{3}}_F$. The nature of $\Xi_c(3050)$ and $\Xi_c(3080)$ could be tested by the radiative transitions $\Xi_c(3055)^0\to \Xi_c(2790)^0 \gamma$ and $\Xi_c(3080)^0 \to \Xi_c(2815)^0 \gamma$, respectively.

Strong and radiative decays of the low-lying S - and P -wave singly heavy baryons

The strong and radiative decays of the low-lying $S$- and $P$-wave $\Lambda_{c(b)}$, $\Sigma_{c(b)}$, $\Xi_{c(b)}$, $\Xi_{c(b)}'$ and $\Omega_{c(b)}$ baryons are systematically studied in a constituent quark model. We find that the radiative decay mode $\Lambda_b^0\gamma$ could be very useful for us to establish the missing neutral states $\Sigma_b^{0}$ and $\Sigma_b^{*0}$. Our calculation shows that most of those missing $\lambda$-mode $P$-wave singly heavy baryons have relatively narrow decay width of less than 30 MeV. Their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiment. Configuration mixings between the $J^P=1/2^-$ states $|^2P_{\lambda} \frac{1}{2}^- \rangle$ and $|^4P_{\lambda} \frac{1}{2}^- \rangle$ of the $\mathbf{6}_F$ multiplet are discussed. The $\Xi_c(2930)^0$ state seems to favor the mixed state $|\Xi_c'~ P_{\lambda}\frac{1}{2}^-\rangle_2$ with $J^P=1/2^-$. The $\Sigma_c(2800)$ resonance may be assigned to $|\Sigma_c~ ^2P_{\lambda} \frac{3}{2}^- \rangle$ with $J^P=3/2^-$ or $|\Sigma_c~ ^4P_{\lambda} \frac{5}{2}^- \rangle$ with $J^P=5/2^-$. In general, the excitations of $|^2P_{\lambda} \frac{3}{2}^- \rangle$ and $|^4P_{\lambda} \frac{5}{2}^- \rangle$ of the $\mathbf{6}_F$ multiplet have similar strong decay properties. In order to to identify them, angular distributions of their decays in either strong decay modes or radiative transitions should be needed.

Tetraquark and two-meson states at large N_{mathrm {c}}

Considering four-point correlation functions of color-singlet quark bilinears, we investigate, in the large-N_{mathrm {c}} limit of QCD, the subleading diagrams that involve, in the s-channel of meson–meson scattering amplitudes, two-quark–two-antiquark intermediate states. The latter contribute, together with gluon exchanges, to the formation, at the hadronic level, of two-meson and tetraquark intermediate states. It is shown that the two-meson contributions, which are predictable, in general, from leading-order N_{mathrm {c}}-behaviors, consistently satisfy the constraints resulting from the 1/N_{mathrm {c}} expansion procedure and thus provide a firm basis for the extraction of tetraquark properties from N_{mathrm {c}}-subleading diagrams. We find that, in general, tetraquarks, if they exist in compact form, should have narrow decay widths, of the order of N_{mathrm {c}}^{-2}. For the particular case of exotic tetraquarks, involving four different quark flavors, two different types of tetraquark are needed, each having a preferred decay channel, to satisfy the consistency constraints.

Pentaquark states in a diquark–triquark model

The diquark-triquark model is used to explain charmonium-pentaquark states, i.e., $P_c(4380)$ and $P_c(4450)$, which were observed recently by the LHCb collaboration. For the first time, we investigate the properties of the color attractive configuration of a triquark and we define a nonlocal light cone distribution amplitude for pentaquark states, where both diquark and triquark are not pointlike, but they have nonzero size. We establish an effective diquark-triquark Hamiltonian based on spin-orbital interaction. According to the Hamiltonian, we show that the minimum mass splitting between $\frac{5}{2}^+$ and $\frac{3}{2}^-$ is around $100$~MeV, which may naturally solve the challenging problem of small mass splitting between $P_c(4450)$ and $P_c(4380)$. This helps to understand the peculiarities of $P_c(4380)$ with a broad decay width whereas $P_c(4450)$ has a narrow decay width. Based on the diquark-triquark model, we predict more pentaquark states, which will hopefully be measured in future experiments.

Interpretations of the ATLAS diboson anomaly

Recently, the ATLAS Collaboration recorded an interesting anomaly in diboson production with excesses at the diboson invariant mass around 2 TeV in boosted jets of all the WZ, W+W−, and ZZ channels. We offer a theoretical interpretation of the anomaly using a phenomenological right-handed model with extra W′ and Z′ bosons. Constraints from narrow total decay widths, dijet cross sections, and W/Z+H production are taken into account. We also comment on a few other possibilities.

Decay widths of ground-state and excitedΞbbaryons in a nonrelativistic quark model

Decay processes of ground and excited bottom baryons are studied in the ${}^{3}{P}_{0}$ nonrelativistic quark model with all model parameters fixed in the sector of light quarks. Using as an input the recent mass of ${\ensuremath{\Xi}}_{b}$ and the theoretical masses of ${\ensuremath{\Xi}}_{b}^{*}$ and ${\ensuremath{\Xi}}_{b}^{\ensuremath{'}}$, narrow decay widths are predicted for the ground-state bottom baryons ${\ensuremath{\Xi}}_{b}^{*}$ and ${\ensuremath{\Xi}}_{b}^{\ensuremath{'}}$. The work predicts large decay widths, about $100$ MeV for the $\ensuremath{\rho}$-type orbital excitation states of ${\ensuremath{\Xi}}_{b}$.

New Heavy-Light Mesons Q

We succeed in reproducing the = 1 B mesons B1(5720), B ∗ 2 (5745), and B ∗ s2(5839) that were recently reported by D0 and CDF, using our semi-relativistic quark potential model, which also succeeds in predicting the mass spectra of the narrow DsJ , as well as broad D∗ 0(0 ) and D′ 1(1 ) particles observed a couple of years ago. The mass of higher excited states ( = 1, 2) of B and Bs mesons, which have not yet been observed, is also predicted to first order in p/mb with the internal quark momentum p and the b quark mass mb. We find that the corresponding BsJ are below the BK/B ∗K threshold and should have narrow decay widths, contrary to most other predictions. Also, already established states ( = 0 and = 1) of D, Ds, B, and Bs heavy mesons are simultaneously reproduced in good agreement with experimental data, within one percent accuracy. To calculate these D/Ds and B/Bs heavy mesons, we use different values of the strong coupling, αs and α b s, respectively.

A New Candidate for Non-Strangeness Pentaquarks:N*(1675)

We study a new nucleon resonance fromphotoproduction, which was observed at √ s = 1675 MeV with a narrow decay width (∼ 10 MeV) by the Tohoku LNS group as well as the GRAAL collaboration. Using an effective Lagrangian approach, we compute differential cross sections for the � photoproduction. In addition to N � (1675,1/2 ± ,3/2 ± ), we employ six other nucleon resonances, i.e. N � (1520,1535,1650,1675,1710,1720) and vector meson exchanges which are the most relevant ones to this reaction process. As a result, we can reproduce the GRAAL data qualitatively well and observe obvious isospin asymmetry between the transition magnetic moments of N � (1675): µnn� ≫ µpp�, which indicates that the newly found nucleon resonance may be identified as a non-strange pentaquark state.

X(3872)→J/ψπ+π− and X(3872)→J/ψπ+π−π0 decay widths from QCD sum rules

Abstract New spectroscopy from the B factories, the advent of CLEO-c and the BES upgrade renewed the interest in charmonia. Among the new measurements, the state X ( 3872 ) has received special attention due to its unexpected properties. Its structure has been studied with different theoretical approaches, most of them being able to reproduce the measured mass. A further test for the theoretical descriptions of the X ( 3872 ) is to explain its narrow decay width. In this work we address the decays X → J / ψ π + π − π 0 and X → J / ψ π + π − , using QCD sum rules with the hypothesis that X is a four quark state.

Probing a Very NarrowZ′Boson with CDF and D0 Data

The CDF and D0 data of nearly 475 pb(-1) in the dilepton channel is used to probe a recent class of models, Stueckelberg extensions of the standard model (StSM), which predict a Z' boson whose mass is of topological origin with a very narrow decay width. A Drell-Yan analysis for dilepton production via this Z' shows that the current data put constraints on the parameter space of the StSM. With a total integrated luminosity of 8 fb(-1), the very narrow can be discovered up to a mass of about 600 GeV. The StSM Z' will be very distinct since it can occur in the region where a Randall-Sundrum graviton is excluded.

A new [formula omitted] resonance in the [formula omitted] reaction

We study the η-photoproduction focusing on the new nucleon resonance which was observed at s=1675MeV with a narrow decay width (∼10MeV) in the recent GRAAL experiment. Using an effective Lagrangian approach, we compute differential cross sections for the η-photoproduction. In addition to N∗(1675), we employ three other nucleon resonances, i.e., N∗(1535), N∗(1650) and N∗(1710), and vector meson exchanges which are the most relevant ones to this reaction process. As a result, we can reproduce the GRAAL data qualitatively well and observe obvious isospin asymmetry between the transition magnetic moments of N∗(1675): μγnn∗≫μγpp∗.

Role of Large Gluonic Excitation Energy for Narrow Width of Penta-Quark Baryons in QCD String Theory

We study the narrow decay width of low-lying penta-quark baryons in the QCD string theoryin terms of gluonic excitations. In the QCD string theory, the penta-quark baryon decays via a gluonic-excited state of a baryon and meson system, where a pair of Y-shaped junction and anti-junction is created. Since lattice QCD shows that the lowest gluonic-excitation energy takes a large value of about 1 GeV, the decay of the penta-quark baryon near the threshold is considered as a quantum tunneling process via a highly-excited state (a gluonic-excited state) in the QCD string theory. This mechanism strongly suppresses the decay and leads to an extremely narrow decay width of the penta-quark system.

A study of [formula omitted] in lattice QCD

We investigate the mass spectrum of the pentaquark baryon ( udud s ¯ ) in quenched lattice QCD with exact chiral symmetry. Using 3 different interpolating operators, we measure the 3 × 3 correlation matrix and obtain the eigenvalues A ± ( t ) with ± parity. For odd parity states, A − ( t ) deviates from pure exponential decay even at large t , which implies that it cannot be a resonance with narrow decay width, thus is ruled out as a candidate of Θ + ( 1540 ) . For even parity states, they behave like usual resonances seen in quenched lattice QCD, and the mass of the lowest lying J P = 1 / 2 + state is determined to be 1583 ± 121 MeV.

Pentaquark Baryons in String Theory

The recently observed pentaquark baryons $\Theta^{+}$ and $\Xi^{--}$ are studied in the dual gravity theory of QCD. By developing a general formulation useful for studying the branched string web in a curved space, simple mass formulae of the pentaquark baryons are derived in the Maldacena prototype model for supersymmetric QCD and a more realistic model for ordinary QCD. Even though the approximations adopted here in deriving these formulae are extremely naive, the predicted values of the masses do not differ significantly from their experimental values. We thus conclude that this approach is promising for the purpose of obtaining a description of the observed masses of pentaquarks and of their extremely narrow decay widths. With the aim of constructing more reliable mass formulae, a preliminary sketch is given of how spin, the hyperfine interaction and parity are considered in the string picture.

THE CHARMED STRANGE MESON SYSTEM

Motivated by the recent surprising discovery of two new meson states with [Formula: see text] quark content but unexpectedly low masses and narrow total decay widths, we work out, in a nonrelativistic potential-model approach developed already some two decades ago, the predictions for the energy levels of the corresponding charm–anti-strange quark bound states. In spite of the fact that this simple quark model reproduces the mass spectrum of the previously observed hadrons remarkably well, we are led to the conclusion that, without considerable modifications, both the new states do not fit into this framework.

Search for narrow dibaryon resonances by the pd → pdX and pd → ppX reactions

Dibaryons which have a very narrow decay width, called super-narrow dibaryons, are searched for by the p + d scattering at E p = 295 MeV. The experiment was carried out at the Research Center for Nuclear Physics employing a two-arm magnetic spectrometer. A good mass resolution of 0.95 MeV and background free condition have been achieved. No resonance has been observed in the mass region of 1896–1914 MeV. The upper limits of the dibaryon production cross section have been determined.

SEARCH FOR SUPER-NARROW DIBARYON RESONANCES BY THE pd → pdX AND pd → ppX REACTIONS

Dibaryons which have a very narrow decay width, called super-narrow dibaryons, are searched for by the p+d scattering at Ep = 295 MeV . The experiment was carried out at the Research Center for Nuclear Physics employing a two-arm magnetic spectrometer. A good mass resolution of 0.95 MeV and background free condition have been achieved. No resonance has been observed in the mass region of 1896–1914 MeV. The upper limits of the dibaryon production cross section have been determined.