arXiv subjects

Sasa Prelovsek

Publications and source records attributed to Sasa Prelovsek.

At least 55 records · Page 3Linked to original sources

arXiv2015

X(3872) and Y(4140) using diquark-antidiquark operators with lattice QCD

We perform a lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc \bar du$, $\bar cc(\bar uu+\bar dd)$ and $\bar cc \bar ss$, where the later two can mix with $\bar cc$. This simulation with $N_f=2$ and $m_π=266$ MeV aims at the possible signatures of four-quark exotic states. We utilize a large basis of $\bar cc$, two-meson and diquark-antidiquark interpolating fields, with diquarks in both anti-triplet and sextet color representations. A lattice candidate for X(3872) with I=0 is observed very close to the experimental state only if both $\bar cc$ and $D\bar D^*$ interpolators are included; the candidate is not found if diquark-antidiquark and $D\bar D^*$ are used in the absence of $\bar cc$. No candidate for neutral or charged X(3872), or any other exotic candidates are found in the I=1 channel. We also do not find signatures of exotic $\bar cc\bar ss$ candidates below 4.3 GeV, such as Y(4140). Possible physics and methodology related reasons for that are discussed. Along the way, we present the diquark-antidiquark operators as linear combinations of the two-meson operators via the Fierz transformations.

hep-lat↗

arXiv2015

Study of the $Z_c^+$ channel using lattice QCD

Recently experimentalists have discovered several charged charmonium-like hadrons $Z_c^+$ with unconventional quark content $\bar cc\bar d u$. We perform a search for $Z_c^+$ with mass below $4.2~$GeV in the channel $I^G(J^{PC})=1^+(1^{+-})$ using lattice QCD. The major challenge is presented by the two-meson states $J/ψ\, π$, $ψ_{2S}π$, $ψ_{1D}π$, $D\bar D^*$, $D^*\bar D^*$, $η_cρ$ that are inevitably present in this channel. The spectrum of eigenstates is extracted using a number of meson-meson and diquark-antidiquark interpolating fields. For our pion mass of 266~MeV we find all the expected two-meson states but no additional candidate for $Z_c^+$ below $4.2~$GeV. Possible reasons for not seeing an additional eigenstate related to $Z_c^+$ are discussed. We also illustrate how a simulation incorporating interpolators with a structure resembling low-lying two-mesons states seems to render a $Z_c^+$ candidate, which is however not robust after further two-meson states around $4.2~$GeV are implemented.

hep-lat↗

arXiv2014

Study of the Zc+ channel in lattice QCD

Several charged charmonium-like hadrons called $Z_c$ have been recently discovered by different experiments. In contrast to conventional hadrons these contain at least two valence quarks and antiquarks ($\bar{c}c\bar{d}u$). We perform a lattice QCD simulation of the $I^G(J^{PC})=1^+(1^{+-})$ channel including all relevant two-meson operators under 4.3 GeV: $J/ψπ$, $ψ_{2S}π$, $ψ_{1D}π$, $D \bar{D}^*$, $D^* \bar{D}^*$, $η_c ρ$ as well as additional diquark anti-diquark operators. In our $N_f = 2$ simulation with pion mass at 266 MeV we are able to identify all two-meson levels within the energy region of interest. However we find no additional level identifiable as a candidate for $Z_c$.

hep-lat↗

arXiv2014

Hadron Spectroscopy

Recent results on the hadron spectroscopy from lattice QCD are reviewed with emphasis on the meson sector and in particular on quarkonium-like $XYZ$ states. I report on the first rigorous treatment of the near-threshold states $X(3872)$ and $D_s^0(2317)$, and the lattice searches for $Z_c^+(3900)$, $X(4140)$ and double-charm tetraquark states. Meson resonances in light, strange and charm sector are reviewed, where the resonances masses as well as the strong decay widths are reported. The first lattice QCD simulation of two coupled-channels is discussed.

hep-lat↗

arXiv2014

$DK$ and $D^* K$ scattering near threshold

We study the three $D_s$ quantum channels $J^P = 0^+$, $1^+$ and $2^+$ where experiments have identified the charm-strange states $D^*_{s0} (2317)$, $D_{s1}(2460)$, $D_{s1}(2536)$ near the $DK$ and $D^*K$ thresholds, and $D^*_{s2}(2573)$. We consider correlation functions for sets of $\overline q q$ operators and, for $J^P = 0^+$, $1^+$, also the $DK$ and $D^*K$ meson-meson interpolators and determine for these cases values of the elastic scattering amplitude. Constructing the full set of correlators requires propagators which connect any pair of lattice sites. For one ensemble of gauge configurations ($32^3\times 64$, $m_π\approx 156$ MeV) a stochastic distillation variant is employed and for another ensemble ($16^3\times 32$, $m_π\approx 266$ MeV) we use the full distillation method. Both, $D^*_{s0} (2317)$ and $D_{s1}(2460)$, are found as bound states below threshold, whereas $D_{s1}(2536)$, and $D^*_{s2}(2573)$ are identified as narrow resonances close to the experimental masses.

hep-lat↗

arXiv2014

Exotic and conventional mesons from lattice

Recent results on meson spectroscopy from lattice QCD are reviewed. The emphasis is on interesting states near thresholds like $Z_c^+(3900)$, $X(3872)$ and $D_{s0}^*(2317)$. Another focus is on the meson resonances in light, strange and charm sector, where the resonance masses as well as the strong decay widths are extracted from the lattice.

hep-lat↗

arXiv2014

K pi scattering and the K* decay width from lattice QCD

K* mesons and in particular the K*(892) were frequently addressed in lattice simulations, but always while ignoring that the K*(892) decays strongly. We present an exploratory extraction of the masses and widths for the K* resonances by simulating K pi scattering in p-wave with I = 1/2 on the lattice. The K pi system with total momenta P = 2*pi/L e_z, 2*pi/L (e_x + e_y) and 0, that allows the extraction of phase shifts at several values of K pi relative momenta, is studied. A Breit-Wigner fit of the phase renders a K*(892) resonance mass m^{lat} = 891 +/- 14 MeV and the K*(892) -> K pi coupling g^{lat} = 5.7 +/- 1.6 compared to the experimental values m^{exp} = 892 MeV and g^{exp} = 5.72 +/- 0.06, where g parametrizes the K* -> K pi width. When extracting the phase shift around the K*(1410) and K2*(1430) resonances we take into account the mixing of p-wave with d-wave and assume that the scattering is elastic in our simulation. This gives us an estimate of the K*(1410) resonance mass m^{lat} = 1.33 +/- 0.02 GeV compared to m^{exp} = 1.414 +/- 0.0015 GeV assuming the experimental K*(1410) -> K pi coupling. We contrast the resonant I = 1/2 channel with the repulsive non-resonant I = 3/2 channel, where the phase is found to be negative and small, in agreement with experiment.

hep-lat↗

arXiv2014

Axial resonances a1(1260), b1(1235) and their decays from the lattice

The light axial-vector resonances $a_1(1260)$ and $b_1(1235)$ are explored in Nf=2 lattice QCD by simulating the corresponding scattering channels $ρπ$ and $ωπ$. Interpolating fields $\bar{q} q$ and $ρπ$ or $ωπ$ are used to extract the s-wave phase shifts for the first time. The $ρ$ and $ω$ are treated as stable and we argue that this is justified in the considered energy range and for our parameters $m_π\simeq 266~$MeV and $L\simeq 2~$fm. We neglect other channels that would be open when using physical masses in continuum. Assuming a resonance interpretation a Breit-Wigner fit to the phase shift gives the $a_1(1260)$ resonance mass $m_{a1}^{res}=1.435(53)(^{+0}_{-109})$ GeV compared to $m_{a1}^{exp}=1.230(40)$ GeV. The $a_1$ width $Γ_{a1}(s)=g^2 p/s$ is parametrized in terms of the coupling and we obtain $g_{a_1ρπ}=1.71(39)$ GeV compared to $g_{a_1ρπ}^{exp}=1.35(30)$ GeV derived from $Γ_{a1}^{exp}=425(175)$ MeV. In the $b_1$ channel, we find energy levels related to $π(0)ω(0)$ and $b_1(1235)$, and the lowest level is found at $E_1 \gtrsim m_ω+m_π$ but is within uncertainty also compatible with an attractive interaction. Assuming the coupling $g_{b_1ωπ}$ extracted from the experimental width we estimate $m_{b_1}^{res}=1.414(36)(^{+0}_{-83})$.

hep-lat↗

arXiv2014

Coupled channel analysis of the rho meson decay in lattice QCD

We employ a variational basis with a number of $\bar{q}q$ and $ππ$ lattice interpolating fields with quantum numbers of the $ρ$ resonance to extract the discrete energy spectrum in a finite volume. In the elastic region, this spectrum is related to the phase shift of the continuum scattering amplitude by Lüscher's formula and the relation allows the extraction of resonance parameters from the spectrum calculation. The simulations are performed at three different total momenta of the coupled $\bar q q-ππ$ system, which allows us to extract the p-wave scattering phase at five values of pion relative momenta near the resonance region. The effective range formula describes the phase-shift dependence nicely and we extract the resonance mass $m_ρ=792(7)(8)$ MeV and the coupling $g_{ρππ}=5.13(20)$ at our $m_π\simeq 266 $MeV. The coupling $g_{ρππ}$ is directly related to the width of the $ρ$ meson and our value is close to the value derived from the experimental width. The simulations are performed using dynamical gauge configurations with two mass-degenerate flavors of tree-level improved clover-Wilson fermions. Correlation functions are calculated using the recently proposed distillation method with Laplacian Heaviside (LapH) smearing of quarks, which enables flexible calculations, in many cases with unprecedented accuracy.

hep-lat↗

arXiv2014

$D_{s}$ mesons with $DK$ and $D^{*}K$ scattering near threshold

$D_s$ mesons are studied in three quantum channels ($J^P=0^+$, $1^+$ and $2^+$), where experiments have identified the very narrow $D_{s0}^*(2317)$, $D_{s1}(2460)$ and narrow $D_{s1}(2536)$, $D_{s2}^*(2573)$. We explore the effect of nearby $DK$ and $D^*K$ thresholds on the subthreshold states using lattice QCD. Our simulation is done on two very different ensembles of gauge configurations (2 or 2+1 dynamical quarks, Pion mass of 266 or 156 MeV, lattice size $16^3\times 32$ or $32^3\times 64$). In addition to $\bar{q}q$ operators we also include meson-meson interpolators in the correlation functions. This clarifies the identification of the states above and below the scattering thresholds. The ensemble with $m_π\simeq 156~$MeV renders the $D_{s1}(2460)$ as a strong interaction bound state 44(10)MeV below $D^*K$ threshold, which is in agreement with the experiment. The $D_{s0}^*(2317)$ is found 37(17)MeV below $DK$ threshold, close to experiment value of 45MeV. The narrow resonances $D_{s1}(2536)$ and $D_{s2}^*(2573)$ are also found close to the experimental masses.

hep-lat↗

arXiv2013

$D_{s0}^*(2317)$ Meson and $D$-Meson-Kaon Scattering from Lattice QCD

The scalar meson $D_{s0}^*(2317)$ is found 37(17)MeV below DK threshold in a lattice simulation of the $J^P=0^+$ channel using, for the first time, both DK as well as $\bar sc$ interpolating fields. The simulation is done on $N_f=2+1$ gauge configurations with $m_π\simeq 156 $MeV, and the resulting $M_{D_{s0}^*}-\tfrac{1}{4}(M_{D_s}+3M_{D_s^*})=266(16)$ MeV is close to the experimental value 241.5(0.8)MeV. The energy level related to the scalar meson is accompanied by additional discrete levels due to DK scattering states. The levels near threshold lead to the negative DK scattering length $a_0=-1.33(20)$ fm that indicates the presence of a state below threshold.

hep-lat↗

arXiv2013

Charmonium-like states from scattering on the lattice

Three charmonium-like states were studied using lattice QCD. The candidate for X(3872) was found slightly below DD* threshold in the channel with J^PC=1^++ and I=0, where cc as well as DD* and $J/ψω$ interpolating operators were used. A charmonium-like channel with J^PC=1^+- and I=1 was also studied, as the recently discovered Z_c^+(3900) might reside there. Here $J/ψπ$ and DD* scattering states were found, but no candidate for the Z_c^+(3900). We present also preliminary results for the J^PC=0^++ charmonium channel, where cc, DD and $J/ψω$ interpolating operators were used. A candidate for a resonance, chi_c0^', that couples to DD in J^PC=0^++ was found.

hep-lat↗

arXiv2013

Lattice QCD review of charmonium and open-charm spectroscopy

Lattice QCD results on the spectroscopy of charmonium(like) states and open charm mesons are reviewed. Near-threshold states X(3872) and D_{s0}^*(2317) were treated rigorously for the first time and the searches for Z_c^+(3900), X(4140) and $cc\bar u\bar d$ were carried out. The first simulations of the resonances with charm quarks have been performed, including the determination of their strong decay widths. Spectroscopy of highly excited charmed, charmonium and hybrid states has been calculated.

hep-lat↗

arXiv2013

K pi scattering in moving frames

We extend our study of the $Kπ$ system to moving frames and present an exploratory extraction of the masses and widths for the $K^*$ resonances by simulating $Kπ$ scattering in p-wave with $I=1/2$ on the lattice. Using $Kπ$ systems with non-vanishing total momenta allows the extraction of phase shifts at several values of $Kπ$ relative momenta. A Breit-Wigner fit of the phase renders a $K^*(892)$ resonance mass and $K^*\to K π$ coupling compatible with the experimental numbers. We also determine the $K^*(1410)$ mass assuming the experimental $K^*(1410)$ width. We contrast the resonant $I=1/2$ channel with the repulsive non-resonant $I=3/2$ channel, where the phase is found to be negative and small, in agreement with experiment.

hep-lat↗

arXiv2013

Search for Z_c^+(3900) in the 1^+- channel on the lattice

Recently three experiments reported a discovery of manifestly exotic Z_c^+(3900) in the decay to J/psi pi+, while J and P are experimentally unknown. We search for this state on the lattice by simulating the channel with J^PC=1^+- and I=1, and we do not find a candidate for Z_c^+(3900). Instead, we only find discrete scattering states D D* and J/psi pi, which inevitably have to be present in a dynamical QCD. The possible reasons for not finding $Z_c^+$ may be that its quantum numbers are not $1^{+-}$ or that the employed interpolating fields are not diverse enough. Simulations with additional types of interpolators will be needed to reach a more definite conclusion.

hep-lat↗

arXiv2013

Evidence for X(3872) from DD* scattering on the lattice

A candidate for the charmonium(like) state X(3872) is found 11 +/- 7 MeV below the DD* threshold using dynamical Nf=2 lattice simulation with J^PC=1^++ and I=0. This is the first lattice simulation that establishes a candidate for X(3872) in addition to the nearby scattering states D D* and J/psi omega, which inevitably have to be present in dynamical QCD. We extract large and negative DD* scattering length a_0=-1.7 +/- 0.4 fm and the effective range r_0=0.5 +/- 0.1 fm, but their reliable determination will have to wait for a simulation on a larger volume. In I=1 channel, only the D D* and J/psi rho scattering states are found and no candidate for X(3872). This is in agreement with the interpretation that X(3872) is dominantly I=0, while its small I=1 component arises solely from the isospin breaking and is therefore absent in our simulation with m_u=m_d.

hep-lat↗

arXiv2012

K pi scattering for isospin 1/2 and 3/2 in lattice QCD

We simulate K pi scattering in s-wave and p-wave for both isospins I=1/2, 3/2 using quark-antiquark and meson-meson interpolating fields. We extract the elastic phase shifts delta at several values of the K-pi relative momenta. The resulting phases exhibit qualitative agreement with the experimental phases in all four channels. We express the s-wave phase shifts near threshold in terms of the scattering length and the effective range. Our K pi system has zero total momentum and is simulated on a single ensemble with two dynamical quarks, so results apply for mpi=266 MeV and mK=552 MeV in our simulation. The backtracking contractions in both I=1/2 channels are handled by the use of Laplacian-Heavyside smeared quarks within the distillation method. Elastic phases are extracted from the energy levels using Luscher's relations. In all four channels we observe the expected K(n)pi(-n) scattering states, which are shifted due to the interaction. In both attractive I=1/2 channels we observe additional states that are related to resonances; we attribute them to K_0^*(1430) in s-wave and K*(892), K*(1410) and K*(1680) in p-wave.

hep-lat↗

arXiv2012

Scattering phase shifts for two particles of different mass and non-zero total momentum in lattice QCD

We derive the relation between the scattering phase shift and the two-particle energy in the finite box, which is relevant for extracting the strong phase shifts in lattice QCD. We consider elastic scattering of two particles with different mass and with non-zero total momentum in the lattice frame. This is a generalization of the Luscher formula, which considers zero total momentum, and the generalization of Rummukainen-Gottlieb's formula, which considers degenerate particles with non-zero total momentum. We focus on the most relevant total momenta in practice, i.e. P=(2π/L) e_z and P=(2π/L) (e_x+e_y) including their multiples and permutations. We find that the P-wave phase shift can be reliably extracted from the two-particle energy if the phase shifts for l>=2 can be neglected, and we present the corresponding relations. The reliable extraction of S-wave phase shift is much more challenging since delta(l=0) is always accompanied by delta(l=1) in the phase shift relations, and we propose strategies for estimating delta(l=0). We also propose the quark-antiquark and meson-meson interpolators that transform according the considered irreducible representations.

hep-lat↗