Search results for "Functional analysis"
showing 10 items of 1059 documents
Observation of Two NewΞb−Baryon Resonances
2015
Two structures are observed close to the kinematic threshold in the Ξb0π- mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0fb-1, recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content bds are expected in this mass region: the spin-parity JP=(1/2)+ and JP=(3/2)+ states, denoted Ξb′- and Ξb∗-. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m(Ξb′-)-m(Ξb0)-m(π-)=3.653±0.018±0.006MeV/c2, m(Ξb∗-)-m(Ξb0)-m(π-)=23.96±0.12±0.06MeV/c2, Γ(Ξb∗-)=1.65±0.31±0.10MeV, where the first and second uncertainties are statistical and systema…
Electromagnetic form factors of the nucleon in a relativistic quark pair creation model
2001
We study the effects of the | qqq q\bar{q} > component of the hadronic wave function on the description of the electromagnetic structure of the nucleon. Starting with a qqq baryonic wave function which describes the baryonic and mesonic low energy spectrum, the extra q\bar{q} pair is generated through a relativistic version of the 3P_0 model. It is shown that this model leads to a renormalization of the quark mass that allows one to construct a conserved electromagnetic current. We conclude that these dynamical relativistic corrections play an important role in reproducing the Q2 dependence of the electromagnetic form factors at low Q^2.
Search for pentaquarks states in Z decays
2004
Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L. upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Θ(1535)+·BR(Θ(1535)+→pK S0)<6.2×10-4, N Ε(1862)-·BR(Ε(1862)-→Ε -π-)<4.5×10-4, N Ε(1862)0·BR(Ε(1862)0→Ε -π+)<8.9×10-4, N Θc(3100)0·BR(Θc(3100) 0→D*-p)<6.3×10-4, N Θc(3100)0·BR(Θc(3100) 0→D-p)<31×10-4. © 2004 Elsevier B.V. All rights reserved.
Dirac operator spectrum in the linear σ model
2003
Abstract The spectrum of the Dirac operator for the linear σ Model with quarks in the large Nc approximation is presented. The spectral density can be related to the chiral condensate which is obtained using renormalization group flow equations. For small eigenvalues, the Banks-Casher relation and the vanishing linear correaction are recovered. The spectrum beyond the low energy regime is discussed.
A plausible explanation of ϒ(10860)
2019
We show that a good description of the ¿(10860) properties, in particular the mass, the e + e ¿ leptonic widths and the ¿ + ¿ ¿ ¿(ns) (n=1,2,3) production rates, can be obtained under the assumption that ¿(10860) is a mixing of the conventional ¿(5s) quark model state with the lowest P¿ wave hybrid state. © 2019 The Author(s)
Scalar quark searches in $e^+ e^-$ collisions at $\sqrt{s}$ = 181-184 GeV
1998
Searches for scalar top, scalar bottom and degenerate scalar quarks have been performed with data collected with the ALEPH detector at LEP. The data sample consists of 57 pb^-1 taken at sqrt{s} = 181-184 GeV. No evidence for scalar top, scalar bottom or degenerate scalar quarks was found in the channels tilde{t} --> c chi, tilde{t} --> b l snu, tilde{b} --> b chi, and tilde{q} --> q chi. From the channel tilde{t} --> c chi a limit of 74 GeV/c^2 has been set on the scalar top quark mass, independent of the mixing angle. This limit assumes a mass difference between the stop and the chi in the range 10-40 GeV/c^2. From the channel tilde{t} --> b l snu the mixing-angle-indepen…
Heavy quark spin symmetric molecular states from D¯(*)Σc(*) and other coupled channels in the light of the recent LHCb pentaquarks
2019
We consider the ${\overline{D}}^{(*)}{\mathrm{\ensuremath{\Sigma}}}_{c}^{(*)}$ states, together with $J/\ensuremath{\psi}N$ and other coupled channels, and take an interaction consistent with heavy quark spin symmetry, with the dynamical input obtained from an extension of the local hidden gauge approach. By fitting only one parameter to the recent three pentaquark states reported by the LHCb Collaboration, we can reproduce the three of them in base to the mass and the width, providing for them the quantum numbers and approximate molecular structure as $1/{2}^{\ensuremath{-}}$ $\overline{D}{\mathrm{\ensuremath{\Sigma}}}_{c}$, $1/{2}^{\ensuremath{-}}$ ${\overline{D}}^{*}{\mathrm{\ensuremath{…
Instanton induced quark dynamics and the pentaquark
2004
We analyze the existence of the exotic $\Theta^+$ from the perspective of instanton induced quark dynamics. The 't Hooft interaction gives strong attraction in specific channels of the triquark $ud\bar s$ and diquark $ud$ configurations. In particular it leads to a light $ud\bar s$ triquark cluster, with the mass around $750 {\rm MeV}$, in the I=0, $S=1/2$ and color 3 configuration, and a light $ud$-diquark configuration, with mass $440 {\rm MeV}$, in the I=0, S=0 and color {$\bar{3}$} configuration. If we consider the pentaquark as a bound state of such triquark and diquark configurations in a relative L=1 state we obtain good agreement with the data. The small width of $\Theta^+$ has a na…
Is the spectrum of highly excited mesons purely coulombian?
2008
We show that a static central potential may provide a precise description of highly excited light unflavoured mesons. Due to string breaking this potential becomes of chromoelectric type at sufficiently large quark-antiquark distances giving rise to a coulombian spectrum. The same conclusion can be inferred for any other meson sector through a straightforward extension of our analysis.
Quark structure of the $$\chi _{\mathrm{c}}(3P)$$ and X(4274) resonances and their strong and radiative decays
2020
AbstractWe calculate the masses of $$\chi _{\mathrm{c}}(3P)$$χc(3P) states with threshold corrections in a coupled-channel model. The model was recently applied to the description of the properties of $$\chi _{\mathrm{c}}(2P)$$χc(2P) and $$\chi _{\mathrm{b}}(3P)$$χb(3P) multiplets (Ferretti and Santopinto in Phys Lett B 789:550, 2019]. We also compute the open-charm strong decay widths of the $$\chi _{\mathrm{c}}(3P)$$χc(3P) states and their radiative transitions. According to our predictions, the $$\chi _{\mathrm{c}}(3P)$$χc(3P) states should be dominated by the charmonium core, but they may also show small meson-meson components. The X(4274) is interpreted as a $$c {{\bar{c}}}$$cc¯$$\chi …