arXiv subjects

S. Narison

Publications and source records attributed to S. Narison.

At least 55 records · Page 3Linked to original sources

arXiv2010

On the nature of the X(3872) from QCD

We have studied some possible four-quark and molecule contents of the X(3872) using double ratios of sum rules, which are more accurate than the usual simple ratios often used in the literature for getting the hadron masses. We found that the different structures (\bar 3-3 and \bar 6-6 tetraquarks and D-D^{(*)} molecule) lead to the same prediction for the mass (within the accuracy of the method), indicating that the alone prediction of the X mass may not be sufficient to reveal its nature. In doing these analyses, we also find that (within our approximation) the use of the \bar{MS} running {\bar m}_c(m_c^2), rather than the on-shell mass, is more appropriate to obtain the J/ψand X meson masses. Using vertex sum rules to roughly estimate the X(3872) hadronic and radiative widths, we found that the available experimental data does not exclude a λ-J/ψ-like molecule current.

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arXiv2010

sigma and f_0(980) substructures from gamma-gamma to pi-pi, J/psi, phi radiative and D_s semi-leptonic decays

Using an improved "analytic K-matrix model", we reconsider the extraction of the sigma/f_0(600) and f_0(980) gamma-gamma widths from gamma-gamma to pi-pi scatterings data of Crystal Ball and Belle. Our main results are summarized in Tables 3 and 4. The averaged sigma "direct width" to gamma-gamma is 0.16(3) keV which confirms a previous result of [1] and which does neither favour a large four-quark (diquark-antidiquark) nor a molecule nor a pure \bar qq component. The "direct width" of the f_0(980) of 0.28(2) keV is much larger than the four-quark expectation but can be compatible with a \bar ss or gluonium component. We also found that the rescattering part of the amplitude is relatively large indicating an important contribution of the meson loops in the determination of the gamma-gamma total widths. This is mainly due to the large couplings of the sigma and f_0(980) to pi-pi and/or \bar KK, which can also be due to a light scalar gluonium with large OZI violating couplings but not necessary to a four-quark or molecule state. Our average results for the total (direct+rescattering) gamma-gamma widths: Gamma_sigma^{tot}= 3.08(82) keV, Gamma_{f_0}^{tot}= 0.16(1) keV} are comparable with the ones from dispersion relations and PDG values. Using the parameters from QCD spectral sum rules, we complete our analysis by showing that the production rates of unmixed scalar gluonia sigma_B(1) and G (1.5-1.6) agree with the data from J/ψ, phi radiative and D_s semi-leptonic decays.

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arXiv2010

The sigma and f_0(980) from K_e4+pi-pi, gamma-gamma scatterings, J/psi, phi to gamma sigma_B and D_s to l nu sigma_B

We extract the pole positions, hadronic and gamma-gamma widths of sigma and f_0(980, from pi-pi and gamma-gamma scattering data using an improved analytic K-matrix model. Our results favour a large gluon component for the sigma and a \bar ss or/and gluon component for the f_0(980) but neither a large four-quark nor a molecule component. Gluonium sigma_B production from J/psi, phi radiative and D_s semi-leptonic decays are also discussed.

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arXiv2010

Doubly heavy Baryons from QCD Spectral Sum Rules

We consider the ratios of doubly heavy baryon masses using Double Ratios of Sum Rules (DRSR), which are more accurate than the usual simple ratios used for getting hadron masses. Our results are comparable with the ones from potential models. The Xi^*_{QQ}-Xi_{QQ} splittings seem to behave like 1/M_Q and can only allow the electromagnetic decay Xi^*_{QQ} to Xi_{QQ}+gamma but not to Xi_{QQ}+ pi. Our results also show that the SU(3) mass-splittings are (almost) independent of the spin of the baryons and behave approximately like 1/M_Q, which could be understood from the QCD expressions of the corresponding two-point correlator. Our results can improved by including radiative corrections to the SU(3) breaking terms and can be tested, in the near future, at Tevatron and LHCb.

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arXiv2010

Mass-splittings of doubly heavy baryons in QCD

We consider (for the first time) the ratios of doubly heavy baryon masses (spin 3/2 over spin 1/2 and SU(3) mass-splittings) using double ratios of sum rules (DRSR), which are more accurate than the usual simple ratios often used in the literature for getting the hadron masses. In general, our results agree and compete in precision with potential model predictions. In our approach, the alpha_s corrections induced by the anomalous dimensions of the correlators are the main sources of the Xi^*_{QQ}- Xi_{QQ} mass-splittings, which seem to indicate a 1/M_Q behaviour and can only allow the electromagnetic decay Xi^*_{QQ} to Xi_{QQ}+ gamma but not to Xi_{QQ}+ pi. Our results also show that the SU(3) mass-splittings are (almost) independent of the spin of the baryons and behave approximately like 1/M_Q, which could be understood from the QCD expressions of the corresponding two-point correlator. Our results can improved by including radiative corrections to the SU(3) breaking terms and can be tested, in the near future, at Tevatron and LHCb.

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arXiv2010

The sigma and f_0(980) from Ke4 + pi-pi scatterings data

We systematically reconsider, within an improved "analytic K-matrix model", the extraction of the sigma = f_0(600) and f_0(980) masses, widths and hadronic couplings using new Ke4 = K-->pi-pi e nu_e data on pi-pi phase shift below 390 MeV and different sets of pi-pi--> pi-pi / K-K scatterings data from 400 MeV to 1.4 GeV. Our results are summarized in Tables 1, 2 and 5. In units of MeV, the complex poles are: M_sigma=452(12) - i 260(15) and M_f=981(34) -i 18(11), which are comparable with some recent high-precision determinations and with PDG values. Besides some other results, we find: |g_{sigma K+K-}|/|g_{sigma pi+pi-}|=0.37(6) which confirms a sizeable g_{sigma K+K-} coupling found earlier, and which disfavours a large pi-pi molecule or four-quark component of the sigma, while its broad pi-pi width (relative to the one of the rho-meson) cannot be explained within a \bar qq scenario. The narrow pi-pi width of the f_0(980) and the large value: |g_{f K+K-}|/|g_{f pi+pi-}|=2.59(1.34), excludes its pure (\bar uu+\bar dd) content. A significant gluonium component eventually mixed with \bar qq appears to be necessary for evading the previous difficulties.

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arXiv2009

SU(3) mass-splittings of heavy-baryons in QCD

We extract directly (for the first time) the charmed (C=1) and bottom (B=-1) heavy-baryons (spin 1/2 and 3/2) mass-splittings due to SU(3) breaking using double ratios of QCD spectral sum rules (QSSR) in full QCD, which are less sensitive to the exact value and definition of the heavy quark mass, to the perturbative radiative corrections and to the QCD continuum contributions than the simple ratios commonly used for determining the heavy baryon masses. Noticing that most of the mass-splittings are mainly controlled by the ratio kappa= <\bar ss>/<\bar dd> of the condensate, we extract this ratio, by allowing 1 sigma deviation from the observed masses of the Xi_{c,b} and of the Omega_c. We obtain: kappa=0.74(3), which improves the existing estimates: κ=0.70(10) from light hadrons. Using this value, we deduce M_{Omega_b}=6078.5(27.4) MeV which agrees with the recent CDF data but disagrees by 2.4 sigma with the one from D0. Predictions of the Xi'_Q and of the spectra of spin 3/2 baryons containing one or two strange quark are given in Table 2. Predictions of the hyperfine splittings Omega*_Q- Omega_Q and Xi*_Q-Xi_Q are also given in Table 3. Starting for a general choice of the interpolating currents for the spin 1/2 baryons, our analysis favours the optimal value of the mixing angle b= (-1/5 -- 0) found from light and non-strange heavy baryons.

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arXiv2009

Duality between QCD Perturbative Series and Power Corrections

We elaborate on the relation between perturbative and power-like corrections to short-distance sensitive QCD observables. We confront theoretical expectations with explicit perturbative calculations existing in literature. As is expected, the quadratic correction is dual to a long perturbative series and one should use one of them but not both. However, this might be true only for very long perturbative series, with number of terms needed in most cases exceeding the number of terms available. What has not been foreseen, the quartic corrections might also be dual to the perturbative series. If confirmed, this would imply a crucial modification of the dogma. We confront this quadratic correction against existing phenomenology (QCD (spectral) sum rules scales, determinations of light quark masses and of α_s from τ-decay). We find no contradiction and (to some extent) better agreement with the data and with recent lattice calculations.

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arXiv2009

Gluonium nature of the sigma/f_0(600) from its coupling to KK

We extract the K+K- couplings of the isoscalar scalar mesons sigma/f_0(600) and f_0(980) from pi pi to pi pi / K K scatterings and found: |g_{sigma K+K-}|/ |g_{sigma pi+pi-}|= 0.8 and |g_{f_0 K+K-}|/ |g_{f_0 pi+pi-}|= 1.7. These results, together with the tiny "direct" gamma gamma width of the sigma and its large hadronic width, are a strong indication for the gluonium/glueball nature of the sigma-meson, as predicted by QCD spectral sum rules (QSSR) + some low-energy theorems (LET), while some other assignements (pi pi molecule, tetraquark state and ordinary qq meson) do not satisfy simultaneously these requirements from the data. These properties suggest that the sigma can be a scalar meson associated to the U(1)V conformal anomaly like is the eta'-meson for the U(1)A anomaly.

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arXiv2008

Can one measure C-odd asymmetry in e+e- --> pi+pi-

C-odd asymmetry can be studied from an accurate measurement of the angular distribution due to the interference between the S- and P-waves in e+e- --> pi+ pi- at order alpha^3. The asymmetry is dominated by the pion rescattering diagram which is enhanced by the presence of the ln(s/m^2_e), and is quite large (10% at theta=30^0 and sqrt{s} < M_{f_2}) compared to alpha/pi=0.3%. This process can also be used for alternatively measuring the size of the rescattering term and the phase of the S-wave amplitude, but does not help to solve the present discrepancy between the hadronic spectral functions from e+e- and tau-decay data.

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arXiv2008

Two-photon width and gluonic component of sigma/f_0(600)

We analyse data on pi pi and gamma gamma scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: pi^+ pi^-) and their subsequent annihilation or through a ``direct'' transition into photons. Our analysis confirms the rather large total radiative width of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV but suggests its dominance by the pi pi rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, (0.13 \pm 0.05) keV, and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.

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arXiv2008

Glueball nature of the sigma/f_0(600) from pi-pi and gamma-gamma scatterings

We estimate the I=0 scalar meson sigma/f_0(600) parameters from pi-pi and gamma-gamma scattering data below 700 MeV using an improved analytic K-matrix model. A fit of the hadronic data gives a complex pole mass M_sigma= 422-i290 MeV, while simultaneous best fits of the gamma-gamma to pi+pi-, pi0pi0 data give a direct width of (0.13+-0.05)keV, a rescattering component of (2.7+-0.4)keV and a total (direct+rescattering) width of (3.9+-0.6)keV. "Running" these results to the physical real axis, the small "direct" gamma-gamma and the large hadronic widths at the "on-shell" mass are compatible with QCD spectral sum rules (QSSR) and some low-energy theorems (LET) expectations for an unmixed lowest mass glueball/gluonium sigma_B of a mass around 1 GeV and a large OZI-violation decay into pi-pi.

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arXiv2007

Can the gamma-gamma processes reveal the nature of the sigma ?

We reanalyse the gamma-gamma scattering data and conclude that in the mass region below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can be largely explained by the one pion exchange process with pi-pi rescattering. The radiative width of the sigma is estimated and a model dependent separation into contributions from direct gamma-gamma decay and decay through rescattering is obtained. We confront these findings with QCD spectral sum rule (QSSR) predictions and conclude that the sigma can have a large gluonium component in its wave function.

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arXiv2006

Can the X(3872) be a 1^{++} four-quark state?

We use QCD spectral sum rules to test the nature of the meson X(3872), assumed to be an exotic four-quark (c\bar{c}q\bar{q}) state with J^{PC}=1^{++}. For definiteness, we work with the current proposed recently by Maiani et al [1], at leading order in α_s, consider the contributions of higher dimension condensates and keep terms which are linear in the light quark mass m_q. We find M_X=(3925+- 127) MeV which is compatible, within the errors, with he experimental candidate X(3872), while the SU(3) breaking-terms lead to an unusual mass-splitting M_{X^{s}}-M_X=- (61+-30) MeV. The mass-difference between the neutral states due to isospin violation of about (2.6-3.9) MeV is much smaller than the value (8+-3) MeV proposed in [1]. For the b-quark, we predict M_{X_b}= (10144+-106) MeV for the X_b(b\bar{b}q \bar{q}), which is much below the {\bar B}B* threshold in contrast to the {\bar B}B* molecule prediction [2], and for the X_b^s(b\bar{b}s \bar{s}), a mass-splitting M_{X^s_{b}}-M_{X_b}=-(121+-182) MeV. Our analysis also indicates that the mass-splitting between the ground state and the radial excitation of about (225~250) MeV is much smaller than in the case of ordinary mesons and is (within the errors) flavour-independent. We also extract the decay constants, analogous to f_π, of such mesons, which are useful for further studies of their leptonic and hadronic decay widths. The uncertainties of our estimates are mainly due to the ones from the c and b quark masses.

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arXiv2002

Tests of the nature and of the gluon content of the σ(0.6) from D and D_{s} semileptonic decays

We summarize the different features which show that QCD spectral sum rule analyses of the scalar two- and three-point functions do not favour the $\bar uu+\bar dd$ interpretation of the broad and low mass $σ(0.6)$ and emphasize that a measurement of the $D_s$ semileptonic decays into $ππ$ can reveal in a model-independent way its eventual gluon component $σ_B$. The analysis also implies that one expects an observation of the $K\bar K$ final states from the $σ_B$ which may compete (if phase space allowed) with the one from a low mass $\bar ss$ state assumed in the literature to be the SU(3) partner of the observed $σ(0.6)$ if the latter is a $\bar uu+\bar dd$ state

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arXiv2001

Hints on the power corrections from current correlators in x-space

We consider an interpretation of the recent lattice data on the current-current correlators in the x-space. The data indicate rather striking difference between (axial)vector and (pseudo)scalar channels which goes beyond the predictions of the standard non-perturbative models. We argue that if the difference is to be explained by power corrections, there is a unique choice of the form of the correction. We discuss the emerging picture of the power corrections.

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arXiv1998

Topological Charge Screening and the `Proton Spin' Beyond the Chiral Limit

The theory of the `proton spin' effect proposed in our earlier papers is extended to include the chiral SU(3) symmetry breaking and flavour mixing induced by non-vanishing quark masses in QCD. The theoretical basis is the derivation of exact, unified Goldberger-Treiman (GT) relations valid beyond the chiral limit. The observed suppression in the flavour singlet axial charge $a^0(Q^2)$ is explained by an anomalously small value for the slope of the singlet current correlation function $<0|T~\pl^\m J_{\m 5}^0 ~ \pl^\n J_{\n 5}^0 |0>$, a consequence of the screening of topological charge in the QCD vacuum. Numerical predictions are obtained by evaluating the current correlation functions using QCD spectral sum rules. The results, $a^0(Q^2) = 0.31 \pm 0.02$ and $\int dx ~g_1^p(x,Q^2) = 0.141 \pm 0.005$ (at $Q^2=10 \~\GV^2$), are in good agreement with current experimental data on the polarised proton structure function $g_1^p$.

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arXiv1997

Direct extraction of the chiral quark condensate and bounds on the light quark masses

We select sum rules from which one can extract directly reliable limits on the size of the chiral symmetry breaking light quark condensate $<\barψψ>$. Combined results from the nucleon and $B^*-B$ mass-splitting sum rules give a result compatible with the standard value: $<\barψψ> (1 GeV) \simeq (-229 MeV)^3$, through the determinations of the quark-gluon mixed condensate. The vector form factor of the $D\rar K^*lν$ semi-leptonic decay leads to the range $0.6\leq <\barψψ> (-229 MeV)^3 \leq 1.5$. The upper limit combined with the Gell-Mann-Oakes-Renner (GMOR) relation implies the interesting lower bound on the sum of light quark masses:$(m_u+m_d) (1 GeV) \geq$ 9.4 MeV, which combined with the ratio of light quark masses from chiral perturbation theory leads to $m_s (1 GeV) \geq (121\pm 12)$ MeV. The lower limit combined with the positivity of the $m_q^2$ contribution to the GMOR relation leads to the upper bound : $(m_u+m_d) (1 GeV) \leq$ 15.7 MeV, which is independent on the nature of chiral symmetry breaking.

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