Hadronic Mass Spectrum Research Articles

Improving extractions of|Vcb|andmbfrom the hadronic invariant mass moments of semileptonic inclusiveBdecay

We calculate the hadronic tensor for inclusive semileptonic B decay to O(alpha_s). This allows O(alpha_s Lambda_{QCD}/mb) corrections to hadronic invariant mass observables to be directly evaluated with experimentally required cuts on phase space. Several moments of phenomenological interest are presented to O(alpha_s Lambda_{QCD}/mb) and O(Lambda_{QCD}^3/mb^3), allowing a consistent extraction of the HQET parameters up to O(Lambda_{QCD}^3/mb^3) and the b quark mass with theoretical error ~ 50 MeV. The hadronic invariant mass spectrum is examined with a general moment to obtain observables that test the theoretical error estimate assigned to these parameters; in particular, fractional moments that directly test the OPE for inconsistencies in the hadronic invariant mass spectrum are reported. The mb Lambda_{QCD}/mc^2 expansion present for fractional moments of the hadronic invariant mass spectum is discussed and shown to introduce a numerically suppressed uncertainty of O(mb^4 Lambda_{QCD}^4/mc^8).

Towards the unified description of light and heavy hadrons in the bag model approach

Mass spectra of ground state hadrons containing u-, d-, s-, c- quarks as well as some lightest hadrons containing b-quarks are calculated on the basis of a slightly modified bag model. The center-of-mass motion corrections are incorporated using a wavepacket projection with Gaussian parametrization of the distribution amplitude. We use running coupling constant and also allow the effective quark mass to be scale-dependent. The impact of these modifications on the hadron mass spectrum is investigated. A comparison of the predicted mass values with the experimental data demonstrates that the modified bag model is sufficiently flexible to provide a satisfactory description of light and heavy hadrons (mesons and baryons) in a single consistent framework.

Subleading shape function contributions to the hadronic invariant mass spectrum inB¯→Xulν¯ldecay

We study the O(Lambda/mb) corrections to the singly and doubly differential hadronic invariant mass spectra d\Gamma/dsH and d\Gamma/dsH dq^2 in b -> u decays, and discuss the implications for the extraction of the CKM matrix element |Vub|. Using simple models for the subleading shape functions, the effects of subleading operators are estimated to be at thefew percent level for experimentally relevant cuts. The subleading corrections proportional to the leading shape function are larger, but largely cancel in the relation between the hadronic invariant mass spectrum and the photon spectrum in B -> X_s \gamma. We also discuss the applicability of the usual prescription of convoluting the partonic level rate with the leading light-cone wavefunction of the b quark to subleading order.

Interactions of heavy stable hadronising particles

In this article, we study the interactions of stable, hadronizing new states, arising in certain extensions of the Standard Model. A simple model, originally intended for stable gluino hadrons, is developed to describe the nuclear interactions of hadrons containing any new colour triplet or octet stable parton. Hadron mass spectra, nuclear scattering cross sections and interaction processes are discussed. Furthermore, an implementation of the interactions of heavy hadrons in GEANT 3 is presented, signatures are studied, and a few remarks about possible detection with the ATLAS experiment are given.

Strings on pp-waves and Hadrons in (softly broken) Script N = 1 gauge theories

We study the Penrose limit of Type IIB duals of softly broken N=1 SU(N) gauge theories in four dimensions, obtained as deformations of the Maldacena-Nunez and Klebanov-Strassler backgrounds. We extract the string spectrum on the resulting pp-wave backgrounds and discuss some properties of the conjectured dual gauge theory hadrons, the so called "Annulons". The string zero-point energy on the light-cone is nontrivial, due to the loss of linearly realized worldsheet supersymmetry, and negative, even in the unbroken supersymmetric case. This causes the appearance of non-perturbative corrections to the hadronic mass spectrum. We briefly discuss the thermodynamic behavior of these string models, calculating the corresponding Hagedorn temperatures.

Study of spectral moments in semileptonic decays of the b hadron with the DELPHI detector at LEP

The measurement of the moments of hadronic mass spectrum and of lepton energy spectrum based on a sample of semileptonic decays of the b hadron selected from Z 0 → b b events recorded with the Delphi detector at LEP, are presented. These results are interpreted in terms of constraints on the quark masses and on the b-quark kinetic energy value.

Formula omitted] a new symmetry possibly realizing in hadron spectroscopy

Starting from the multi-local Klein–Gordon equations with Lorentz-scalar squared-mass operator we give a covariant quark representation of the general composite mesons and baryons with definite Lorentz transformation property. The phenomenologically observed hadron mass spectra is pointed out to satisfy possibly the approximate symmetry under the U(12) transformation group of light constituent quarks. Here U(12)⊃ U(4) DS ⊗SU(3) F , and U(4) DS is a homogeneous Lorentz transformation group for Dirac spinors, while SU(3) F is the flavor unitary group. This symmetry predicts the existence of new type of chiral mesons and baryons out of the conventional level classification scheme: typical ones are for light q q ̄ system the scalar σ- and axial-vector a 1-nonets to be assigned as relativistic S-wave states, while for light-quark–baryon-system the Roper resonance N(1440) (J P= 1 2 +) and the Λ(1405) (J P= 1 2 −) with comparatively light mass to be assigned as the ground states.

Novel fat-link fermion actions

The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators of the fermion action are constructed using smeared links. The simulations are performed on a 16 3 × 32 lattice with a lattice spacing of a = 0.125 fm. We compare actions with n = 4 and 12 smearing sweeps with a smearing fraction of 0.7. The n = 4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative O ( a) improvement.

Hadron masses from novel fat-link fermion actions

The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement, including a reduced exceptional configuration problem.

Exploration of sea quark effects in two-flavor QCD with the O( a)-improved Wilson quark action

We explore sea quark effects in the light hadron mass spectrum in a simulation of two-flavor QCD using the nonperturbatively O( a)-improved Wilson fermion action. In order to identify finite-size effects, light meson masses are measured on 12 3 × 48, 16 3 × 48 and 20 3 × 48 lattices with a ∼ 0.1 fm. On the largest lattice, where the finite-size effect is negligible, we find a significant increase of the strange vector meson mass compared to the quenched approximation. We also investigate the quark mass dependence of pseudoscalar meson masses and decay constants and test the consistency with (partially quenched) chiral perturbation theory.

Type I superconductivity upon monopole condensation in Seiberg–Witten theory

We study the confinement scenario in N=2 supersymmetric SU(2) gauge theory near the monopole point upon breaking of N=2 supersymmetry by the adjoint matter mass term. We confirm claims made previously that the Abrikosov–Nielsen–Olesen string near the monopole point fails to be a BPS state once next-to-leading corrections in the adjoint mass parameter taken into account. Our results shows that type I superconductivity arises upon monopole condensation. This conclusion allows us to make qualitative predictions on the structure of the hadron mass spectrum near the monopole point.

MODEL INDEPEDENT EXTRACTIONS OF |Vub| FROM INCLUSIVE B DECAYS

We discuss the possibility of extracting |Vub| from various spectra of inclusive B decays, without large systematic errors which usually arise from having to model the Fermi motion of the heavy quark. This strategy can be applied to the electron energy spectrum, as well as the hadronic mass spectrum. Modulo violation of local hadron-parton duality, the theoretical error in the extraction is estimated to be less than 10%.

Hadronic invariant mass spectrum inB→Xulνdecay with a lepton energy cut

We discuss the implications of charged lepton energy cut to the hadronic invariant mass spectrum in charmless semileptonic B decays. Charged-lepton energy cut is inevitable in order to remove secondary leptonic events such as b -> c, tau -> l, and to identify the chaged leptons at detectors experimentally. We consider three possible lepton energy cuts, E_l^{cuts} = 0.6,1.5,2.3 GeV, and found that with the most probable cuts E_l^{cut} = 1.5 GeV and M_X^{max} = 1.5~(1.86) GeV, 45 ~ 60 % ~(58 ~ 67 %) of decay events survive. Therefore, B -> X_u l nu decay events can be efficiently distinguished from B -> X_c l nu decay events. We also discuss the possible model dependence on the results.

Strongly coupled ’t Hooft model on the lattice

We study the strong coupling limit of the one-flavor and two-flavor massless 't Hooft models, $large-{\cal N}_c$-color $QCD_2$, on a lattice. We use staggered fermions and the Hamiltonian approach to lattice gauge theories. We show that the one-flavor model is effectively described by the antiferromagnetic Ising model, whose ground state is the vacuum of the gauge model in the infinite coupling limit; expanding around this ground state we derive a strong coupling expansion and compute the lowest lying hadron masses as well as the chiral condensate of the gauge theory. Our lattice computation well reproduces the results of the continuum theory. Baryons are massless in the infinite coupling limit; they acquire a mass already at the second order in the strong coupling expansion in agreement with the Witten argument that baryons are the $QCD$ solitons. The spectrum and chiral condensate of the two-flavor model are effectively described in terms of observables of the quantum antiferromagnetic Heisenberg model. We explicitly write the lowest lying hadron masses and chiral condensate in terms of spin-spin correlators on the ground state of the spin model. We show that the planar limit (${\cal N}_c\longrightarrow \infty$) of the gauge model corresponds to the large spin limit ($S\longrightarrow \infty$) of the antiferromagnet and compute the hadron mass spectrum in this limit finding that, also in this model, the pattern of chiral symmetry breaking of the continuum theory is well reproduced on the lattice.

Extracting | Vub| from the hadronic mass spectrum of inclusive B decays

Following a strategy introduced earlier by the authors, we show that it is possible to extract | V ub | from the cut hadronic mass spectrum of B decays without large systematic errors which usually arise from having to model the Fermi motion of the heavy quark. We present a closed form expression for | V ub |/| V ts | which is accurate up to corrections of order α s 2, α s ρ, ( Λ/ m b ) 2/ ρ, where ρ is the experimental cut ( s c / m b 2) on the hadronic mass used to veto charmed decays. Modulo duality violation errors, which are intrinsic to all inclusive predictions, we estimate the theoretical error in the extraction to be at the 5% level.

Resummed hadronic spectra of inclusiveBdecays

In this paper we investigate the hadronic mass spectra of inclusive $B$ decays. Specifically, we study how an upper cut on the invariant mass spectrum, which is necessary to extract ${V}_{\mathrm{ub}},$ results in the breakdown of the standard perturbative expansion due to the existence of large infrared logs. We first show how the decay rate factorizes at the level of the double differential distribution. Then, we present closed form expressions for the resummed cut rate for the inclusive decays $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}$ and $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{u}e\ensuremath{\nu}$ at next-to-leading order in the infrared logs. Using these results, we determine the range of cuts for which resummation is necessary, as well as the range for which the resummed expansion itself breaks down. We also use our results to extract the leading and next to leading infrared log contribution to the two loop differential rate. We find that for the phenomenologically interesting cut values, there is only a small region where the calculation is under control. Furthermore, the size of this region is sensitive to the parameter $\overline{\ensuremath{\Lambda}}.$ We discuss the viability of extracting ${V}_{\mathrm{ub}}$ from the hadronic mass spectrum.

A model independent determination of | Vub|

It is shown that measuring the lepton invariant mass spectrum in inclusive semileptonic B ̄ →X uℓ ν ̄ decay yields a model independent determination of | V ub |. Unlike the lepton energy and hadronic invariant mass spectra, nonperturbative effects are only important in the resonance region, and play a parametrically suppressed role when d Γ/d q 2 is integrated over q 2>( m B − m D ) 2, which is required to eliminate the charm background. Perturbative and nonperturbative corrections are presented to order α s 2 β 0 and Λ QCD 2/ m b 2, and the Λ QCD 3/ m b 3 corrections are used to estimate the uncertainty in our results. The utility of the B ̄ →X sℓ +ℓ − decay rate above the ψ(2 S) resonance is discussed.

B→Xulbar nul decay distributions to order αs

An analytic result for the O(alpha_s corrections to the triple differential B -> X_u l nu decay rate is presented, to leading order in the heavy-quark expansion. This is relevant for computing partially integrated decay distributions with arbitrary cuts on kinematic variables. Several double and single differential distributions are derived, most of which generalize known results. In particular, an analytic result for the O(alpha_s) corrections to the hadronic invariant mass spectrum is presented. The effects of Fermi motion, which are important for the description of decay spectra close to infrared sensitive regions, are included. The behaviour of perturbation theory in the region of time-like momenta is also investigated

Nuclear medium effects on invariant mass spectra of hadrons decaying in nuclei

Effects of nuclear medium on invariant masses of in-medium hadrons as reconstructed from their decay particles alone (here called quasi invariant masses) are examined. Such “inclusive” invariant masses are related to the average potential energies, and thus are not identified as medium-modified hadronic masses. Furthermore, a significant fraction of in-medium hadrons is subject to decay in correlation with surrounding nucleons, producing a broad pseudo peak at a lower mass in a quasi invariant mass spectrum, as calculated for ρ meson decays in high density medium and for proton decays in 16 O.

Inverse slope systematics in high-energy p+p and Au+Au reactions

We employ the Monte Carlo PYTHIA to calculate the transverse mass spectra of various hadrons and their inverse slopes T ∗ at m T − m=1.5–2 GeV in p+p reactions at s =200 GeV. Due to (multiple) minijet production T ∗ in general increases as a function of the hadron mass. Moreover, the T ∗(m) systematics has a “discontinuity” at the charm threshold, i.e. the inverse slope of D-mesons is much higher than that of non-charmed hadrons and even of the heavier Λ C baryon. The experimental observation of this characteristic behaviour in Au+Au collisions would indicate the absence of c-quark rescattering. In contrast, the assumption of thermalized partons and hydrodynamical evolution would lead to a smoothly increasing T ∗(m) , without discontinuity at the charm threshold. The degree of collective transverse flow, indicated by the slope of the T ∗(m) systematics, depends strongly on whether kinetic equilibrium is maintained for some time after hadronization or not.