Probing the Weak Boson Sector in γe→Ze\gamma e\rightarrow Ze

We study possible deviations from the standard model in the reaction $\gamma e\rightarrow Ze$ at a 500 GeV $e^+e^-$ collider. As a photon source we use a laser backscattered photon beam. We investigate the most general $\gamma Z\gamma$ and $\gamma ZZ$ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving, $h^\gamma_1$ and $h^Z_1$, and two are CP-violating, $h^\gamma_2$ and $h^Z_2$. We present analytical expressions of the helicity amplitudes for the process $\gamma e\rightarrow Ze$ for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the ($h^\gamma_1,h^Z_1$) plane at the 90\% confidence level. We then show how the angular correlation of the $Z$ decay products can be used to extract detailed information on the anomalous (especially CP-violating) $\gamma Z\gamma$ and $\gamma ZZ$ couplings.Comment: Latex, 25 pages, 12 figures (not included). One compressed postscript file including all the figures available at ftp://ftp.kek.jp/kek/preprints/TH/TH-420/kekth420.ps.g

Measuring the Higgs boson parity at a Linear Collider using the tau impact parameter and tau --> rho nu decay

We demonstrate that a measurement of the impact parameter in one-prong tau decay can be useful for the determination of the Higgs boson parity in the H/A --> tau tau; tau --> rho nu decay chain. We have estimated that for a detection set-up such as TESLA, use of the information from the tau impact parameter can improve the significance of the measurement of the parity of the Standard Model 120 GeV Higgs boson to 4.5 sigma, and in general by factor of about 1.5 with respect to the method where this information is not used. We also show that the variation in the assumption on the precision of the measurement of the impact parameter and/or pi's momenta does not affect the sensitivity of the method. This is because the method remains limited by the type of twofold ambiguity in reconstructing the tau momentum.Comment: 12 pages, 12 figures, LaTe

Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field

The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg spins in an arbitrarily oriented magnetic field is exactly solved using the spin-rotation transformation and the transfer-matrix method. It is shown that the low-temperature magnetization process depends basically on a spatial orientation of the magnetic field. A sharp stepwise magnetization curve with a marked intermediate plateau, which emerges for the magnetic field applied along the easy-axis direction of the Ising spins, becomes smoother and the intermediate plateau shrinks if the external field is tilted from the easy-axis direction. The magnetization curve of a polycrystalline system is also calculated by performing powder averaging of the derived magnetization formula. The proposed spin-chain model brings an insight into high-field magnetization data of 3d-4f bimetallic polymeric compound Dy(NO_3)(DMSO)_2Cu(opba)(DMSO)_2, which provides an interesting experimental realization of the ferrimagnetic chain composed of two different but regularly alternating spin-1/2 magnetic ions Dy^{3+} and Cu^{2+} that are reasonably approximated by the notion of Ising and Heisenberg spins, respectively.Comment: 11 pages, 6 figure

Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{\gamma,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(\alpha_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.

Measuring the Higgs boson's parity using tau --> rho nu

We present a very promising method for a measurement of the Higgs boson parity using the H/A -> tau^+ tau^- --> rho^+ nu rho^- nu --> pi^+ pi^0 nu pi^- pi^0 nu decay chain. The method is both model independent and independent of the Higgs production mechanism. Angular distributions of the tau decay products which are sensitive to the Higgs boson parity are defined and are found to be measurable using typical properties of a future detector for an e^+ e^- linear collider. The prospects for the measurement of the parity of a Higgs boson with a mass of 120 GeV are quantified for the case of e^+ e^- collisons of 500 GeV center of mass energy with an integrated luminosity of 500 fb^-1. The Standard Model Higgsstrahlung production process is used as an example.Comment: 10 pages, 4 figures, LaTeX, version of Phys. Lett.

Direct Observation of the Quantum Energy Gap in S = 1/2 Tetragonal Cuprate Antiferromagnets

Using an electron spin resonance spectrometer covering a wide range of frequency and magnetic field, we have measured the low energy excitations of the S=1/2 tetragonal antiferromagnets, Sr_{2}CuO_{2}Cl_{2} and Sr_{2}Cu_{3}O_{4}Cl_{2}. Our observation of in-plane energy gaps of order 0.1 meV at zero external magnetic field are consistent with a spin wave calculation, which includes several kinds of quantum fluctuations that remove frustration. Results agree with other experiments and with exchange anisotropy parameters determined from a five band Hubbard model.Comment: 4 pages, 3 figure

TauSpinner program for studies on spin effect in tau production at the LHC

Final states involving tau leptons are important components of searches for new particles at the Large Hadron Collider (LHC). A proper treatment of tau spin effects in the Monte Carlo (MC) simulations is important for understanding the detector acceptance as well as for the measurements of tau polarization and tau spin correlations. In this note we present a TauSpinner package designed to simulate the spin effects. It relies on the availability of the four-momenta of the taus and their decay products in the analyzed data. The flavor and the four-momentum of the boson decaying to the tau-tau+ or tau+- nu pair need to be known. In the Z/gamma* case the initial state quark configuration is attributed from the intermediate boson kinematics, and the parton distribution functions (PDF's). TauSpinner is the first algorithm suitable for emulation of tau spin effects in tau-embedded samples. It is also the first tool that offers the user the flexibility to simulate a desired spin effect at the analysis level. An algorithm to attribute tau helicity states to a previously generated sample is also provided.Comment: 13 pages, 6 figures New feature, an algorithm to attribute tau helicity states introduced in v

Integrable models and quantum spin ladders: comparison between theory and experiment for the strong coupling ladder compounds

(abbreviated) This article considers recent advances in the investigation of the thermal and magnetic properties of integrable spin ladder models and their applicability to the physics of real compounds. The ground state properties of the integrable two-leg spin-1/2 and the mixed spin-(1/2,1) ladder models at zero temperature are analyzed by means of the Thermodynamic Bethe Ansatz. Solving the TBA equations yields exact results for the critical fields and critical behaviour. The thermal and magnetic properties of the models are investigated in terms of the recently introduced High Temperature Expansion method, which is discussed in detail. It is shown that in the strong coupling limit the integrable spin-1/2 ladder model exhibits three quantum phases: (i) a gapped phase in the regime $H<H_{c1}$, (ii) a fully polarised phase for $H>H_{c2}$, and (iii) a Luttinger liquid magnetic phase in the regime $H_{c1}<H<H_{c2}$. The critical behaviour in the vicinity of the critical points is of the Pokrovsky-Talapov type. The temperature-dependent thermal and magnetic properties are directly evaluated from the exact free energy expression and compared to known experimental results for a range of strong coupling ladder compounds. Similar analysis of the mixed spin-(1/2,1) ladder model reveals a rich phase diagram, with a 1/3 and a full saturation magnetisation plateau within the strong antiferromagnetic rung coupling regime. For weak rung coupling, the fractional magnetisation plateau is diminished and a new quantum phase transition occurs. The phase diagram can be directly deduced from the magnetisation curve obtained from the exact result derived from the HTE. The thermodynamics of the spin-orbital model with different single-ion anisotropies is also investigated.Comment: 90 pages, 33 figures, extensive revisio

Novel ordering of an S = 1/2 quasi one-dimensional Ising-like anitiferromagnet in magnetic field

High-field specific heat measurements on BaCo2V2O8, which is a good realization of an S = 1/2 quasi one-dimensional Ising-like antifferomagnet, have been performed in magnetic fields up to 12 T along the chain and at temperature down to 200 mK. We have found a new magnetic ordered state in the field-induced phase above Hc ~ 3.9 T. We suggest that a novel type of the incommensurate order, which has no correspondence to the classical spin system, is realized in the field-induced phase.Comment: 4pages, 4figure