Hadronic Sector Research Articles

Exact [formula omitted] symmetry solving the supersymmetric flavor problem

The exact discrete flavor symmetry, S3 in the hadronic sector and S3×Z2 in the leptonic sector, which has been recently found, is introduced in a supersymmetric extension of the standard model. We investigate the supersymmetric flavor problem, and explicitly find that thanks to the flavor symmetry the dangerous FCNC processes and CP-violating phases are sufficiently suppressed.

GUT relation in neutrino-induced flavor physics in SUSY SU(5) GUT

In the SUSY SU(5) GUT with the right-handed neutrinos, the neutrino Yukawa coupling induces the flavor-violating mass terms for the right-handed down squarks and left-handed sleptons, and they lead to imprint on the flavor physics in the hadronic and leptonic sectors. In this Letter we study CP violation in Bd0 and Bs0, which is induced by the tau-neutrino Yukawa coupling. In particular, we notice the correlation of the CP asymmetries in Bd0→φKs (SφKs) and Bs0→J/ψφ (SJ/ψφ) with other observables, such as Br(τ→μγ), the muon EDM (dμ), and the mixing-induced CP asymmetry in Bd0→Ms0γ (Absg), since they have a common origin of the CP and flavor violation. The measurements are expected to play a significant role for consistency check of the SUSY SU(5) GUT. The hierarchical right-handed neutrino masses make the correlation better. We find that the current bound on Br(τ→μγ) constrains the allowed region for SφKs in this model.

Lattice results relevant to the CKM matrix determination

A brief discussion of the recent lattice studies of the quantities that are relevant to the Standard Model description of CP-violation in the hadronic sector is presented.

Meson lifetimes, decays, mixing and CPV in FOCUS

In recent years charm physics has encountered renovated interest; the excellent quality of the data and high statistics allow for unprecedented sensitivity and sophisticated studies never possible before. Investigation of decay dynamics in both the hadronic and semileptonic sectors reveals manifestation of quantum mechanical interference and phase effects that allow probing FSI and possible CPV effects. Lifetime measurements at a level of 1% or better can shed light onto the non-spectator contribution to the charm decays, and mixing could represent a possible window to new physics. It is in this context that the results selected from the Focus experiment here have to be accommodated.

Hadronic entropy enhancement and low density QGP

Recent studies show that for central collisions the rise in the incident energy from AGS to RHIC decreases the value of the chemical potential in the hadron-QGP phase diagram. Thus, the formation of QGP at RHIC energies in central collisions may be expected to occur at very small values of the chemical potential. Using many different relativistic mean-field hadronic models (RMF) at this regime we show that the critical temperature for the hadron-QGP transition is hadronic model independent. We have traced back the reason for this and conclude that it comes from the fact that the QGP entropy is much larger than the hadronic entropy obtained in all the RMF models. We also find that almost all of these models present a strong entropy enhancement in the hadronic sector coming from the baryonic phase transition to a nucleon–antinucleon plasma. This result is in agreement with the recent data obtained in the STAR collaboration at RHIC where a rich proton–antiproton matter was found.

Simple formulas forsin2θefflept,MW,Γl,and their physical applications

The calculation of the partial widths of the Z boson in the effective scheme is discussed. Simple formulae for Sin^2 theta_eff^lept, M_W, and Gamma_l in the on-shell, MS, and effective renormalization schemes are presented. Their domain of validity extends to low M_H values probed by current experiments, and to the range of Delta alpha_hadr results from recent calculations. Physical applications of these formulae are illustrated. A comparative analysis of the above mentioned schemes is presented. The paper includes a discussion of the discrepancy of the Sin^2 theta_eff^lept values derived from the leptonic and hadronic sectors and of the shortcomings of theoretical error estimates of Sin^2 theta_eff^lept based solely on those affecting M_W.

Polarization observables in elastic electron deuteron scattering including parity- and time-reversal-violating contributions

The general formalism for polarization observables in elastic electron deuteron scattering is extended to incorporate parity and time reversal violating contributions. Parity violating effects arise from the interference of $\gamma$ and $Z$ exchange as well as from the hadronic sector via a small parity violating component in the deuteron. In addition we have allowed for time reversal invariance violating contributions in the hadronic sector. Formal expressions for the additional structure functions are derived, and their decomposition into the various multipole contributions are given explicitly.

Strangeness in lattice QCD

The status of lattice calculations in the light hadron sector is reviewed.Special emphasis is given to recent lattice determinations of the mass ofthe strange quark. The impact of non-perturbative renormalization andcontrol over lattice artefacts on the attainable precision is discussed indetail. Furthermore, the influence of dynamical quark effects is assessed.

Three-body analysis of incoherent η-photoproduction on the deuteron in the near threshold region

A three-body calculation of the reaction γd→ ηnp in the energy region from threshold up to 30 MeV above has been performed. The primary goal of this study is to assess the importance of the three-body aspects in the hadronic sector of this reaction. Results are presented for the η-meson spectrum as well as for the total cross section. The three-body results differ significantly from those predicted by a simple rescattering model in which only first-order ηN- and NN-interactions in the final state are considered. The major features of the experimental data are well reproduced although right at threshold the rather large total cross section could not be explained.

Seesaw-constrained minimal supersymmetric standard model, solution to the supersymmetricCPproblem, and a supersymmetric explanation ofε′/ε

We analyze CP violation in the supersymmetric standard model (MSSM) embedded minimally into a left-right symmetric gauge structure with the seesaw mechanism for neutrino masses. With the plausible assumption of universal scalar masses it is shown that CP violation in the hadron sector of the MSSM is described by a single phase residing in the supersymmetry breaking Lagrangian. This improves the CP properties of the MSSM by providing a natural solution to the SUSY CP problem. Furthermore, $\epsilon'/\epsilon$ vanishes in this model above the seesaw scale; extrapolation to the weak scale then leads to a prediction in agreement with the NA31 and the recent KTeV observations. The electric dipole moment of the neutron is naturally suppressed, we estimate its magnitude to be about $4 \times 10^{-29}$ ecm. Additional predictions include a tightly constrained super particle spectrum and vanishingly small CP asymmetries in the $B$ meson system.

Up–down unification, neutrino masses, and rare lepton decays

In a recent paper, we showed that tree level up–down unification of fermion Yukawa couplings is a natural consequence of a large class of supersymmetric models. They can lead to viable quark masses and mixings for moderately large values of tan β with interesting and testable predictions for CP violation in the hadronic sector. In this letter, we extend our discussion to the leptonic sector focusing on one particular class of these models, the supersymmetric left–right model with the seesaw mechanism for neutrino masses. We show that fitting the solar and the atmospheric neutrino data considerably restricts the Majorana–Yukawa couplings of the leptons in this model and leads to predictions for the decay τ→ μ+ γ, which is found to be accessible to the next generation of rare decay searches. We also show that the resulting parameter space of the model is consistent with the requirements of generating adequate baryon asymmetry through lepton-number violating decays of the right-handed neutrino.

U(1)textures and lepton flavor violation

U(1) family symmetries have led to successful predictions of the fermion mass spectrum and the mixing angles of the hadronic sector. In the context of the supersymmetric unified theories, they further imply a non-trivial mass structure for the scalar partners, giving rise to new sources of flavor violation. In the present work, lepton flavor non-conserving processes are examined in the context of the minimal supersymmetric standard model augmented by a U(1)-family symmetry. We calculate the mixing effects on the \mu-> e\gamma and \tau -> \mu\gamma rare decays. All supersymmetric scalar masses involved in the processes are determined at low energies using two loop renormalization group analysis and threshold corrections. Further, various novel effects are considered and found to have important impact on the branching ratios. Thus, a rather interesting result is that when the see-saw mechanism is applied in the (12 X 12)-sneutrino mass matrix, the mixing effects of the Dirac matrix in the effective light sneutrino sector are canceled at first order. In this class of models and for the case that soft term mixing is already present at the GUT scale, tau -> \mu \gamma decays are mostly expected to arise at rates significantly smaller than the current experimental limits. On the other hand, the $\mu \ra e \gamma$ rare decays impose important bounds on the model parameters, particularly on the supersymmetric scalar mass spectrum. In the absence of soft term mixing at high energies, the predicted branching ratios for rare decays are, as expected, well below the experimental bounds.

SU(3) breaking and hidden local symmetry

We study the various existing implementations of SU(3) breaking in the hidden local symmetry model for the low energy hadronic sector following a mechanism originally proposed by Bando, Kugo and Yamawaki (BKY). We pay particular attention to Hermiticity and current conservation. Following this, we present a new method for including symmetry breaking effects which preserves the BKY mass relation among vector mesons. Symmetry breaking (SB) necessarily requires a transformation of the pseudoscalar fields, which, following BKY, we refer to as field renormalization. We examine the consequences of propagating this through all Lagrangian terms including the anomalous ones. We thus explore the consequences of these various SB schemes for both charged and neutral pseudoscalar decay constants as measured in weak and anomalous decays respectively.

Sin 2θefflep from hadronic final states

The different techniques used to access sin 2 θ eff lep in the hadronic sector is presented with a summary of the results obtained by the LEP experiments. The LEPI average in this sector is sin 2 θ eff lep = 0.23225 ± 0.00035. The main sources of uncertainties in the experimental measurements are reviewed with a special attention to the forward backward b asymmetry.

Third generation familons,Bfactories, and neutrino cosmology

We study the physics of spontaneously broken family symmetries acting on the third generation. Massless familons (or Majorons) $f$ associated with such broken symmetries are motivated especially by cosmological scenarios with decaying tau neutrinos. We first note that, in marked contrast with the case for the first two generations, constraints on third generation familon couplings are poor, and are, in fact, non-existent at present in the hadronic sector. We derive new bounds from $B^0$--$\bar{B}^0$ mixing, $B^0 \to l^+ l'^-$, $b\to s\nu\bar{\nu}$, and astrophysics. The resulting constraints on familon decay constants are still much weaker than those for the first and second generation. We then discuss the promising prospects for significant improvements from searches for $\tau\to l f$, $B\to (\pi, K) f$, and $b\to (d,s) f$ with the current CLEO, ARGUS, and LEP data. Finally, we note that future constraints from CLEO III and the $B$ factories will probe decay constants beyond 10^8 GeV, well within regions of parameter space favored by proposed scenarios in neutrino cosmology.

Helicity structure in low- and intermediate-energy weak interaction

We report on the status of the measurements of the longitudinal polarization of positrons emitted by polarized 107In and 12N nuclei. Present results yield a lower limit of 306 GeV/c 2 (90 % CL) for the mass of a possible W gauge boson with predominantly right-handed couplings, if interpreted in the framework of the manifest left-right symmetric model. In addition, the helicity structure of the weak interaction is discussed on the basis of experimental results at low and intermediate energies in the leptonic, semileptonic and hadronic sectors. Whereas in the minimal manifest left-right symmetric extension of the Standard Model the results from collider experiments are superior to results from other experiments, experiments in the three sectors of the weak interaction yield complementary information on the helicity structure of the interaction if interpreted in general left-right symmetric models.

Finite Temperature Effects on Electromagnetic Probes of Quark–Gluon Plasma

Effects of temperature dependence of hadronic form factors on the electromagnetic probes of Quark–Gluon Plasma (QGP) have been looked into. It has been observed that in the kinematic domain thought to be most relevant for Quark–Gluon Plasma diagnostics with electromagnetic probes (M ~ 1–4 GeV ), the space–time integrated emission rates (i.e. count rates) of dileptons and photons from the hot hadronic sector are not very sensitive to the finite temperature corrections of the form factors.

Parity violation in quasifree electron scattering off the deuteron

For deuteron electroweak disintegration, parity violating effects are investigated which arise from the interference of γ and Z exchange as well as from the hadronic sector via a small parity violating component in the deuteron. The general formalism for the differential cross section and polarization observables of electromagnetic deuteron disintegration is extended to incorporate parity violating contributions. Formal expressions for the additional structure functions and derived. Results are presented for these parity violating structure functions for quasifree kinematics neglecting final state interaction and two-body effects. Both types of parity violating contributions to the asymmetry of the inclusive reaction with respect to longitudinally polarized electrons are evaluated. The one from parity violating deuteron components is negligible over the whole range of momentum transfers considered.

A Novel State for Kaon Condensation

An SU(2)-invariant hadronic sector of the Kaplan-Nelson model is analyzed to find an energetically improved variational ground state of neutral nucleonic matter which consists of nucleons and kaons. Our state yields a vanishing expectation value of the K- field and a finite three-body correlation (ntpK-). The variational problem of finding the ground state is solved almost analytically. It is shown that the solution consisting of equal numbers of neutrons, protons and K- together with KO(or KG) in excess suppresses the kinetic term of the kaon and results in a remarkable improvement of the variational energy. 953 1. Kaon condensation in the Kaplan-Nelson (KN) modeP) is due mainly to the sig­ nificance of the sigma term EKN in reducing the effective kaon mass in medium. The term EKN is dominated by a3 in the KN-model and provides a large attractive force between the kaon and nucleon in the s-wave state. Variational calculations which utilize the time-dependent classical K--field have been performed.l)~l1) They show that kaons start to condense at a few times the normal nuclear matter density for EKN = 2 ' 3m7r • For the ground state I~) of a given Hamiltonian H, however, we have i(O) = (~I[B, HJI~) = 0 where B is any field operator. In fact, in a simple model which consists of terms quadratic in mesonic and baryonic fields,12) the author explicitly constructed a state with (K-) = 0 that has a lower energy than the coherent state with (k-) =1: o. In this paper, we construct a variational state which is an eigenstate of the electric charge and gives a vanishing expectation value of K- and a nonvanishing three-body correlation (ntpK-). We then apply these to the KN-model and evaluate the energy of dense nuclear matter. 2. The effective lagrangian of the KN-model is expressed in terms of the usual meson and baryon fields U and B as

Lepton pairs from thermal mesons

We study the net dielectron production rates from an ensemble of thermal mesons, using an effective Lagrangian to model their interaction. The coupling between the electromagnetic and the hadronic sectors is done through the vector meson dominance approach. For the first time, a complete set of light mesons is considered. We include contributions from decays of the type $V(P)\ensuremath{\rightarrow}P(V)+{e}^{+}{e}^{\ensuremath{-}}$, where $V$ is a vector meson and $P$ is a pseudoscalar, as well as those from binary reactions $P+P$, $V+V$, and $V+P\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$. Direct decays of the type $V\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ are included and shown to be important. We find that the dielectron invariant mass spectrum naturally divides into distinct regions: in the low mass domain the decays from vector and pseudoscalar mesons form the dominant contribution. The pion-pion annihilation and direct decays then pick up and form the leading signal in an invariant mass region that includes the $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ complex and extends up to the $\ensuremath{\varphi}$. Above the invariant mass $M\ensuremath{\approx}1$ GeV other two-body reactions take over as the prominent mechanisms for lepton pair generation. These facts will have a quantitative bearing on the eventual identification of the quark-gluon plasma.