Critical point of N f =3 QCD from lattice simulations in the canonical ensemble
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Li, Anyi↗
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Excited-state spectroscopy of triply bottom baryons from lattice QCD
Here, the spectrum of baryons containing three b quarks is calculated in nonperturbative QCD, using the lattice regularization. The energies of ten excited bbb states with J P = 1/2 + , 3/2 + , 5/2 + , 7/2 + , 1/2 – , and 3/2 – are determined with high precision. A domain-wall action is used for the up, down, and strange quarks, and the bottom quarks are implemented with nonrelativistic QCD. The computations are done at lattice spacings of a ≈ 0.11 fm and a ≈ 0.08 fm, and the results demonstrate the improvement of rotational symmetry as a is reduced. A large lattice volume of (2.7 fm) 3 is used, and extrapolations of the bbb spectrum to realistic values of the light sea-quark masses are performed. All spin-dependent energy splittings are resolved with total uncertainties of order 1 MeV, and the dependence of these splittings on the couplings in the nonrelativistic QCD action is analyzed.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Baryon masses and axial couplings in the combined 1/N c and chiral expansions
Not Available
Cordón, A. Calle↗
Toward the excited isoscalar meson spectrum from lattice QCD
We report on the extraction of an excited spectrum of isoscalar mesons using lattice QCD. Calculations on several lattice volumes are performed with a range of light quark masses corresponding to pion masses down to about ~400 MeV. The distillation method enables us to evaluate the required disconnected contributions with high statistical precision for a large number of meson interpolating fields. We find relatively little mixing between light and strange in most J PC channels; one notable exception is the pseudoscalar sector where the approximate SU(3) F octet, singlet structure of the η, η' is reproduced. We extract exotic J PC states, identified as hybrid mesons in which an excited gluonic field is coupled to a color-octet qqbar pair, along with non-exotic hybrid mesons embedded in a qq¯-like spectrum.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Charmed and light pseudoscalar meson decay constants from four-flavor lattice QCD with physical light quarks
We compute the leptonic decay constants f D+ , f Ds , and f K+ , and the quark-mass ratios m c =m s and m s =m l in unquenched lattice QCD using the experimentally determined value of f π+ for normalization. We use the MILC Highly Improved Staggered Quark (HISQ) ensembles with four dynamical quark flavors -- up, down, strange, and charm -- and with both physical and unphysical values of the light sea-quark masses. The use of physical pions removes the need for a chiral extrapolation, thereby eliminating a significant source of uncertainty in previous calculations. Four different lattice spacing ranging from a ≈ 0:06 fm to 0:15 fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are f D+ = 212:6(0:4)$(^{+1.0}_{-1.2})$ MeV, f Ds = 249:0(0:3)$(^{+1.1}_{-1.5})$ MeV, and f Ds /f D+ = 1:1712(10)$(^{+29}_{-32})$, where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately two to four times smaller than those of the most precise previous lattice calculations. We also obtain f K+ / f π+ = 1:1956(10)$(^{+26}_{-18})$, updating our previous result, and determine the quark-mass ratios m s /m l = 27:35(5)$(^{+10}_{-7})$ and m c /m s = 11:747(19)$(^{+59}_{-43})$. When combined with experimental measurements of the decay rates, our results lead to precise determinations of the CKM matrix elements !Vus! = 0:22487(51)(29)(20)(5), !Vcd! = 0:217(1)(5)(1) and !Vcs! = 1:010(5)(18)(6), where the errors are from this calculation of the decay constants, the uncertainty in the experimental decay rates, structure-dependent electromagnetic corrections, and, in the case of !Vus!, the uncertainty in |Vud|, respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Charmed bottom baryon spectroscopy from lattice QCD
In this study, we calculate the masses of baryons containing one, two, or three heavy quarks using lattice QCD. We consider all possible combinations of charm and bottom quarks, and compute a total of 36 different states with J P = 1/2 + and J P = 3/2 + . We use domain-wall fermions for the up, down, and strange quarks, a relativistic heavy-quark action for the charm quarks, and nonrelativistic QCD for the bottom quarks. Our analysis includes results from two different lattice spacings and seven different pion masses. We perform extrapolations of the baryon masses to the continuum limit and to the physical pion mass using SU(4|2) heavy-hadron chiral perturbation theory including 1/m Q and finite-volume effects. For the 14 singly heavy baryons that have already been observed, our results agree with the experimental values within the uncertainties. We compare our predictions for the hitherto unobserved states with other lattice calculations and quark-model studies.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Excited meson radiative transitions from lattice QCD using variationally optimized operators
Not Available
Shultz, Christian J.↗
$|V_{ub}|$ from $B\to\pi\ell\nu$ decays and (2+1)-flavor lattice QCD
We present a lattice-QCD calculation of the B → πℓν semileptonic form factors and a new determination of the CKM matrix element |V ub |. We use the MILC asqtad (2+1)-flavor lattice configurations at four lattice spacings and light-quark masses down to 1/20 of the physical strange-quark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hard-pion and SU(2) limits. We employ a model-independent z parametrization to extrapolate our lattice form factors from large-recoil momentum to the full kinematic range. We introduce a new functional method to propagate information from the chiral-continuum extrapolation to the z expansion. We present our results together with a complete systematic error budget, including a covariance matrix to enable the combination of our form factors with other lattice-QCD and experimental results. To obtain |V ub |, we simultaneously fit the experimental data for the B → πℓν differential decay rate obtained by the BABAR and Belle collaborations together with our lattice form-factor results. We find |V ub |=(3.72±0.16) × 10 –3 , where the error is from the combined fit to lattice plus experiments and includes all sources of uncertainty. Our form-factor results bring the QCD error on |V ub | to the same level as the experimental error. We also provide results for the B → πℓν vector and scalar form factors obtained from the combined lattice and experiment fit, which are more precisely determined than from our lattice-QCD calculation alone. Lastly, these results can be used in other phenomenological applications and to test other approaches to QCD.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Isovector and isoscalar tensor charges of the nucleon from lattice QCD
We present results for the iso-vector and flavor diagonal tensor charges $g$$^{u−d}_{T}$, $g$$^{u}_{T}$, $g$$^{d}_{T}$, and $g$$^{s}_{T}$ needed to probe novel tensor interactions at the TeV scale in neutron and nuclear β-decays and the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The lattice QCD calculations were done using nine ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2+1+1 dynamical flavors. These ensembles span three lattice spacings a ≈ 0.06, 0.09 and 0.12 fm and three quark masses corresponding to the pion masses M π ≈ 130, 220 and 310 MeV. Using estimates from these ensembles, we quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, volume and light quark masses for the connected contributions. The final estimates of the connected nucleon (proton) tensor charge for the iso-vector combination is $g$$^{u−d}_{T}$ = 1.020(76) in the MS scheme at 2 GeV. The additional disconnected quark loop contributions needed for the flavor-diagonal matrix elements are calculated using a stochastic estimator employing the truncated solver method with the all-mode-averaging technique. We find that the size of the disconnected contribution is smaller than the statistical error in the connected contribution. This allows us to bound the disconnected contribution and include it as an additional uncertainty in the flavor-diagonal charges. After a continuum extrapolation, we find $g$$^{u}_{T}$ = 0.774(66), $g$$^{d}_{T}$ = −0.233(28) and $g$$^{u+d}_{T}$ = 0.541(67). The strangeness tensor charge, that can make a significant contribution to the neutron EDM due to the large ratio ms/mu,d, is $g$$^{s}_{T}$ = 0.008(9) in the continuum limit.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Rho resonance parameters from lattice QCD
We perform a high-precision calculation of the phase shifts for $\pi$-$\pi$ scattering in the I = 1, J = 1 channel in the elastic region using elongated lattices with two mass-degenerate quark favors ($N_f = 2$). We extract the $\rho$ resonance parameters using a Breit-Wigner fit at two different quark masses, corresponding to $m_{\pi} = 226$MeV and $m_{\pi} = 315$MeV, and perform an extrapolation to the physical point. The extrapolation is based on a unitarized chiral perturbation theory model that describes well the phase-shifts around the resonance for both quark masses. We find that the extrapolated value, $m_{\rho} = 720(1)(15)$MeV, is significantly lower that the physical rho mass and we argue that this shift could be due to the absence of the strange quark in our calculation.
Guo, Dehua↗
Particle formation and ordering in strongly correlated fermionic systems: Solving a model of quantum chromodynamics
In our paper we study a (1+1)-dimensional version of the famous Nambu–Jona-Lasinio model of quantum chromodynamics (QCD2) both at zero and at finite baryon density. We use nonperturbative techniques (non-Abelian bosonization and the truncated conformal spectrum approach). When the baryon chemical potential, μ, is zero, we describe the formation of fermion three-quark (nucleons and Δ baryons) and boson (two-quark mesons, six-quark deuterons) bound states. We also study at μ=0 the formation of a topologically nontrivial phase. When the chemical potential exceeds the critical value and a finite baryon density appears, the model has a rich phase diagram which includes phases with a density wave and superfluid quasi-long-range (QLR) order, as well as a phase of a baryon Tomonaga-Luttinger liquid (strange metal). Finally, the QLR order results in either a condensation of scalar mesons (the density wave) or six-quark bound states (deuterons).
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Study of excited Ξ c states decaying into Ξ c 0 and Ξ c + baryons
Here, with a data sample of 980 fb - 1 of e + e - annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy e + e - collider, we discuss the results of a study of excited Ξ c states that decay, via the emission of photons and/or charged pions, into Ξ c 0 or Ξ c + ground state charmed-strange baryons. We present new measurements of the masses of all members of the Ξ c ' , Ξ c ( 2645 ) , Ξ c ( 2790 ) , Ξ c ( 2815 ) , and Ξ c ( 2980 ) isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First Monte Carlo analysis of fragmentation functions from single-inclusive e + e - annihilation
Here, we perform the first iterative Monte Carlo (IMC) analysis of fragmentation functions constrained by all available data from single-inclusive $e^+ e^-$ annihilation into pions and kaons. The IMC method eliminates potential bias in traditional analyses based on single fits introduced by fixing parameters not well contrained by the data, and provides a statistically rigorous determination of uncertainties. Our analysis reveals specific features of fragmentation functions using the new IMC methodology and those obtained from previous analyses, especially for light quarks and for strange quark fragmentation to kaons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Λ c + → φ p π 0 and branching fraction measurement of Λ c + → K - π + p π 0
We have investigated the Cabibbo-suppressed decay Λ c + → φ p π 0 in e + e - collisions using a data sample corresponding to an integrated luminosity of 915 fb - 1 . The data were collected by the Belle experiment at the KEKB e + e - asymmetric-energy collider running at or near the Υ ( 4 S ) and Υ ( 5 S ) resonances. No significant signal is observed, and we set an upper limit on the branching fraction of B ( Λ c + → φ p π 0 ) < 15.3 × 10 - 5 at 90% confidence level. The contribution of nonresonant Λ c + → K + K - p π 0 decays is found to be consistent with zero, and the corresponding upper limit on its branching fraction is set to be B ( Λ c + → K + K - p π 0 ) NR < 6.3 × 10 - 5 at 90% confidence level. We also search for an intermediate hidden-strangeness pentaquark decay P s + → φ p . We see no evidence for this intermediate decay and set an upper limit on the product branching fraction of B ( Λ c + → P s + π 0 ) × B ( P s + → φ p ) < 8.3 × 10 - 5 at 90% confidence level. Finally, we measure the branching fraction for the Cabibbo-favored decay Λ c + → K - π + p π 0 ; the result is B ( Λ c + → K - π + p π 0 ) = ( 4.42 ± 0.05 ( stat ) ± 0.12 ( syst ) ± 0.16 ( norm ) ) % , which is the most decisive measurement to date.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Nonperturbative comparison of clover and highly improved staggered quarks in lattice QCD and the properties of the Φ meson
Here, we compare correlators for pseudoscalar and vector mesons made from valence strange quarks using the clover quark and highly improved staggered quark (HISQ) formalisms in full lattice QCD. We use fully nonperturbative methods to normalise vector and axial vector current operators made from HISQ quarks, clover quarks and from combining HISQ and clover fields. This allows us to test expectations for the renormalisation factors based on perturbative QCD, with implications for the error budget of lattice QCD calculations of the matrix elements of clover-staggered $b$-light weak currents, as well as further HISQ calculations of the hadronic vacuum polarisation. We also compare the approach to the (same) continuum limit in clover and HISQ formalisms for the mass and decay constant of the $\phi$ meson. Our final results for these parameters, using single-meson correlators and neglecting quark-line disconnected diagrams are: $m_{\phi} =$ 1.023(5) GeV and $f_{\phi} = $ 0.238(3) GeV in good agreement with experiment. These results come from calculations in the HISQ formalism using gluon fields that include the effect of $u$, $d$, $s$ and $c$ quarks in the sea with three lattice spacing values and $m_{u/d}$ values going down to the physical point.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Skewness and kurtosis of net baryon-number distributions at small values of the baryon chemical potential
In this paper, we present results for the ratios of mean (M B ), variance (σ$2\atop{B}$), skewness (S B ) and kurtosis (κ B ) of net baryon-number fluctuations obtained in lattice QCD calculations with physical values of light and strange quark masses. Using next-to-leading order Taylor expansions in baryon chemical potential we find that qualitative features of these ratios closely resemble the corresponding experimentally measured cumulants ratios of net proton-number fluctuations for beam energies down to √sNN ≥ 19.6 GeV. We show that the difference in cumulant ratios for the mean net baryon-number, M B /σ$2\atop{B}$ = χ$B\atop{1}$ (T, µ B )/χ$B\atop{2}$ (T, µ B ) and the normalized skewness, S B σ B = χ$B\atop{3}$ (T, µB)/χ2 (T, µB ), nat-urally arises in QCD thermodynamics. Moreover, we establish a close relation between skewness and kurtosis ratios, S B σ$B\atop{3}$/M B = χ$B\atop{3}$ (T, µ B )/χ$B\atop{1}$ (T,µ B ) and κ B σ$2\atop{B}$ = χ$B\atop{4}$ (T,μ B )/χ$B\atop{2}$ (T,μ B ), valid at small values of the baryon chemical potential.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Baryon-baryon interactions and spin-flavor symmetry from lattice quantum chromodynamics
Lattice quantum chromodynamics is used to constrain the interactions of two octet baryons at the SU(3) flavor-symmetric point, with quark masses that are heavier than those in nature (equal to that of the physical strange quark mass and corresponding to a pion mass of $\approx 806~\tt{MeV}$). Specifically, the S-wave scattering phase shifts of two-baryon systems at low energies are obtained with the application of L\"uscher's formalism, mapping the energy eigenvalues of two interacting baryons in a finite volume to the two-particle scattering amplitudes below the relevant inelastic thresholds. The values of the leading-order low-energy scattering parameters in the irreducible representations of SU(3) are consistent with an approximate SU(6) spin-flavor symmetry in the nuclear and hypernuclear forces that is predicted in the large-$N_c$ limit of QCD. The two distinct SU(6)-invariant interactions between two baryons are constrained at this value of the quark masses, and their values indicate an approximate accidental SU(16) symmetry. The SU(3) irreducible representations containing the $NN~({^1}S_0)$, $NN~({^3}S_1)$ and $\frac{1}{\sqrt{2}}(\Xi^0n+\Xi^-p)~({^3}S_1)$ channels unambiguously exhibit a single bound state, while the irreducible representation containing the $\Sigma^+ p~({^3}S_1)$ channel exhibits a state that is consistent with either a bound state or a scattering state close to threshold. These results are in agreement with the previous conclusions of the NPLQCD collaboration regarding the existence of two-nucleon bound states at this value of the quark masses.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗