Top Spin Research Articles

Exact ground state and elementary excitations of the spin tetrahedron chain

We study the antiferromagnetic spin exchange models with $S=1∕2$ and $S=1$ on a one-dimensional tetrahedron chain by both analytical and numerical approaches. The system is shown to be effectively mapped to a decoupled spin chain in the regime of strong rung coupling, and a spin sawtooth lattice in the regime of weak rung coupling with spin $2S$ on the top row and spin $S$ on the lower row. The ground state for the homogeneous tetrahedron chain is found to fall into the regime of strong rung coupling. As a result, the elementary excitation for the spin-$1∕2$ system is gapless whereas the excitation for the spin-1 system has a finite spin gap. With the aid of the exact diagonalization method, we determine the phase diagram numerically and find the existence of an additional phase in the intermediate regime. This phase is doubly degenerate and is characterized by an alternating distribution of rung singlet and rung spin $2S$. We also show that the SU(3) exchange model on the same lattice has completely different kind of ground state from that of its SU(2) correspondence and calculate its ground state and elementary excitation analytically.

On the Chaotic Instability of a Nonsliding Liquid-Filled Top with a Small Spheroidal Base via Melnikov-Holmes-Marsden Integrals

Chaotic orientations of a top containing a fluid filled cavity are investigated analytically and numerically under small perturbations. The top spins and rolls in nonsliding contact with a rough horizontal plane and the fluid in the ellipsoidal shaped cavity is considered to be ideal and describable by finite degrees of freedom. A Hamiltonian structure is established to facilitate the application of Melnikov-Holmes-Marsden (MHM) integrals. In particular, chaotic motion of the liquid-filled top is identified to be arisen from the transversal intersections between the stable and unstable manifolds of an approximated, disturbed flow of the liquid-filled top via the MHM integrals. The developed analytical criteria are crosschecked with numerical simulations via the 4th Runge-Kutta algorithms with adaptive time steps.

The dependence of specularity behavior and thermal stability on capping layer thickness in spin valves

We investigated the dependence of capping layer thickness and composition on Mn diffusion and specular reflection behavior in top spin valves. The capping layer materials used included an amorphous ZrAl alloy that was oxidized completely when its thickness was 2nm, improving both the thermal stability and magnetoresistance ratio of the spin valves (SVs). Mn diffusion into the active sensing layer was inhibited markedly when the 2-nm-thick capping layer was present, as this oxide layer provides an oxygen potential gradient along which Mn diffuses preferentially. The thermal stability of a ZrAl-based SV proved greater than that of a traditional Ta-based SV owing to its interdiffusion-resistive microstructure, which provides both a smoother surface and a fine and dense microstructure that lacks crystallinity.

MIXED QCD AND WEAK CORRECTIONS TO $t\bar{t}$ PRODUCTION BY QUARK-ANTIQUARK ANNIHILATION

We report on our computation of the mixed QCD and weak corrections to [Formula: see text] including t, [Formula: see text] spin effects, in particular on single top spin asymmetries.

New method for reconstructing effective top quark spin

We propose a new method for reconstructing an effective spin direction of a semi-leptonically decayed top quark. The method is simple: for instance, it does not require the spin information of the antitop quark in a tt¯ event. The reconstructed effective spin is expected to be useful in hadron collider experiments. We demonstrate its usefulness in an analysis of the top decay vertex.

Mechanism of Racket Spin Performance in Tennis(Spin Performance Improvement by Lubrication of String Intersections with Super High Speed Video Analysis)

Players often say that some strings provide a better grip and more spin than others, but ball spin did not depend on string type, gauge or tension in the past laboratory experiment. There was no research work on the spin to uncover what is really happening during actual tennis impact owing to difficult experiment. This paper made clear the mechanism of top spin and its improvement by lubrication of strings according to the high speed video analysis. It also provided the more detailed explanations of spin behavior by comparison between a lubricant string racket and a famous 'Spaghetti strings racket' which was banned in 1978 by the International Tennis Federation since it used plastic spaghetti tubing over the strings to reduce friction resulting in the excessive spin on the ball. As the main strings stretch and slide side ways more, the ball is given more spin due to restoring force parallel to the string face when the main strings spring back and the ball is released from the strings. Furthermore, it showed that the more spin results in the reduction of shock vibrations of the wrist joint during impact.

Mixed QCD and weak corrections to top quark pair production at hadron colliders

The order αs2α mixed QCD and weak corrections to top quark pair production by quark–antiquark annihilation are computed, keeping the full dependence on the t and t¯ spins. We determine the contributions to the cross section and to single and double top spin asymmetries at the parton level. These results are necessary ingredients for precise standard model predictions of top quark observables, in particular of top-spin induced parity-violating angular correlations and asymmetries at hadron colliders.

Magnetic properties of spin valves with antiferromagnetic CrMnPt deposited at various Ar pressures

The dependence of the giant magnetoresistance (MR) ratio and exchange bias field (Hex) on the argon deposition pressure (PAr) of antiferromagnetic CrMnPt film for top spin valves was investigated. The MR ratio was enhanced from 5.0% to 8.3% as the PAr of CrMnPt film increased from 2to15mTorr. Hex also increased from 150to300Oe. These significant enhancements in the magnetic properties were correlated with microstructural changes and body-centered-tetragonal (bct) phase change reaction in the antiferromagnetic film. The bct phase change was promoted at high PAr because of the microstructural defects. The blocking temperature (TB) and the exchange anisotropy energy (Jex) were higher at high PAr owing to the promotion of bct phase change.

Effect of H2 sputter gas on interfacial mixing in spin valves

We introduced the use of hydrogen during the deposition of spin valves to achieve better control of interfacial mixing, especially for bottom spin valves (B-SV). The hydrogen was introduced during deposition of the CoFe or IrMn layer depending on whether it was a B-SV or a top spin valve (T-SV). The magnetoresistance ratio and Hex increased to 15% and 30%, respectively, when hydrogen (10vol%) was introduced for a B-SV. By contrast, the hydrogen effect for a T-SV was small. Using hydrogen (10vol%), the surface of the SV was smoother (1.01nm) than without hydrogen (1.94nm). In addition, the SV with hydrogen had a well-developed (111) texture and larger grains. By introducing hydrogen, we could control the microstructure and reduce the intermixing between CoFe and IrMn, especially for B-SVs.

Top quark pair production and decay at a polarized photon collider

Top quark pair production by (polarized) γγ collisions offers an interesting testing ground of the Standard Model and its extensions. In this Letter we present results for differential cross sections of top quark pair production and decay including QCD radiative corrections. We take into account the full dependence on the top quark spins. We give analytic and numerical results for single and double differential angular distributions of tt¯ decay products which are due to top quark polarizations and spin correlations in the intermediate state.

Can Video Games be Used to Predict or Improve Laparoscopic Skills?

Performance of laparoscopic surgery requires adequate hand-eye coordination. Video games are an effective way to judge one's hand-eye coordination, and practicing these games may improve one's skills. Our goal was to see if there is a correlation between skill in video games and skill in laparoscopy. Also, we hoped to demonstrate that practicing video games can improve one's laparoscopic skills. Eleven medical students (nine male, two female) volunteered to participate. On day 1, each student played three commercially available video games (Top Spin, XSN Sports; Project Gotham Racing 2, Bizarre Creations; and Amped 2, XSN Sports) for 30 minutes on an X-box (Microsoft, Seattle, WA) and was judged both objectively and subjectively. Next, the students performed four laparoscopic tasks (object transfer, tracing a figure-of-eight, suture placement, and knot-tying) in a swine model and were assessed for time to complete the task, number of errors committed, and hand-eye coordination. The students were then randomized to control (group A) or "training" (i.e., video game practicing; group B) arms. Two weeks later, all students repeated the laparoscopic skills laboratory and were reassessed. Spearman correlation coefficients demonstrated a significant relation between many of the parameters, particularly time to complete each task and hand-eye coordination at the different games. There was a weaker association between video game performance and both laparoscopic errors committed and hand-eye coordination. Group B subjects did not improve significantly over those in group A in any measure (P >0.05 for all). Video game aptitude appears to predict the level of laparoscopic skill in the novice surgeon. In this study, practicing video games did not improve one's laparoscopic skill significantly, but a larger study with more practice time could prove games to be helpful.

Next-to-leading order corrections to single top quark production and decay at the Fermilab Tevatron:s-channel process

We present a study of s-channel single top quark production at the upgraded Tevatron $p\bar{p}$ collider, including the next-to-leading order (NLO) QCD corrections to the production and the decay of the top quark. The "modified" narrow width approximation was adopted to preserve the spin of the top quark in its production and decay. We discuss the effect of the different $O(\alpha_s)$ contributions on the inclusive cross section as well as various kinematic distributions after imposing the relevant cuts to select s-channel single top signal events. In particular the $O(\alpha_s)$ decay contribution, while small in size, has a significant impact on several distributions. With the help of the best-jet algorithm to reconstruct the top quark we demonstrate that it is possible to study kinematical and spin correlations in s-channel single top events. We furthermore compare top quark spin measurements in two different basis and show how NLO corrections have to be taken into consideration in searches for the Higgs boson through $W^{\pm}H$ associated production at the Tevatron.

Maximizing the spin correlation of top quark pairs produced at the large hadron collider

The measurement of top quark spin correlation is an important tool for precise studies of top quark interactions. In this Letter I construct a quantization axis maximizing the spin correlation at the LHC within the Standard Model. Using this axis a spin correlation of 48% or even more, on applying additional cuts, can be reached. This represents a significant improvement compared to the helicity bases studied thus far.

Top quark spin correlations in theories with large extra dimensions at the CERN Large Hadron Collider

In theories with large extra dimensions, we study the top-spin correlations at the Large Hadron Collider. The $s$-channel process mediated by graviton Kaluza-Klein modes contributes to the top-antitop pair production in addition to the standard model processes, and affects the resultant top-spin correlations. We calculated the full density matrix for the top-antitop pair production. With the fundamental scale of the extra dimensional theory below 2 TeV, we find a sizable deviation of the top-spin correlations from the standard model one.

The effect of cyclic annealing treatments on magnetoresistance in IrMn‐pinned top and bottom spin valves

IrMn-pinned top spin valve (TSV) and bottom spin valve (BSV) films were prepared by DC magnetron sputtering onto thermally oxidized Si (111) substrates at room temperature under a magnetic field of above 100 Oe. The effect of cyclic annealing treatments on magnetoresistive and structural properties in the films was investigated. The exchange coupling field (Hex) of TSV and BSV is stabilized after the second annealing cycle and it is thought that these films reveal high thermal stability. The magnetoresistance (MR) ratio and Hex of TSV were 5.6% and 430 Oe, respectively. For BSV the Hex value (1180 Oe) is much higher while MR ratio (3.6%) is reduced with respect to TSV. The blocking temperatures of the TSV and BSV were 250 °C and 270 °C, respectively. The results concerning magnetic properties together with structural investigations suggest the Hex is mainly dependent on the quality of fcc (111) crystalline texture while MR is sensitive to both crystalline texture and interface roughness. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Top quark spin inepcollision

We revised the discussion on the degree of spin polarization of single top quarks produced via Wg fusion process in ep collision at TESLA+HERAp and CLIC+LHC energies in connection with our article in [Phys. Rev. D 69, 034016 (2004)]. For $e\stackrel{\ensuremath{\rightarrow}}{b}t\overline{\ensuremath{\nu}}$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. After combining properly the cross sections of ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{b}t\overline{\ensuremath{\nu}}$ and ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{g}t\overline{b}\overline{\ensuremath{\nu}}$ processes we find that 96% of the top quarks have their spins up in ${e}^{+}$-beam direction with the asymmetry of 0.92. Some of the spin fractions and asymmetries have been corrected 2--5 % when compared to the previous paper. Consequently, this Brief Report improves the results of the previous paper about the ideal basis for studying the top quark spin in ep collision.

Aerodynamics of spinning and non-spinning tennis balls

The aerodynamic properties of a tennis ball are obtained using wind tunnel measurements. In the first phase of this study, the drag coefficient of a variety of new and used non-spinning tennis balls was measured. The measurements were conducted in the Reynolds number range of 85×10 3< Re<250×10 3, which corresponds to a velocity range of 20< U<60 ms −1 (45< U<135 mph). The data for the new tennis balls revealed that all balls have similar drag coefficients, within the repeatability of the experiment. However, it was shown that a heavily worn ball exhibits a significant decrease in drag coefficient. A simple trajectory plot was used to illustrate the significance of this drop in C D, on a typical tennis stroke. It was shown that if the drag coefficient of the worn ball was reduced even further, then the ball would travel faster through the air, and give the receiver a significantly shorter time to react to the shot. In the second phase of this study, the drag and lift coefficients of new and used spinning tennis balls was measured. This testing was conducted by placing the ball inside the working section of the wind tunnel, held between two horizontal shafts. The ball was spun at rates up to 2750 rpm, which is representative of a typical top spin shot hit by a professional player. The data showed that the lift coefficient for all the new balls was identical. However, the lift coefficient was generally lower for the heavily worn ball compared with the new ball. A trajectory plot was calculated to illustrate the effect of the lower drag and lift coefficients of the worn ball, compared to the new ball. It was shown that the lift coefficient value has little effect on the reaction time of the receiver. It was also shown that a lower lift coefficient reduces the window of opportunity for the server because the player is less able to utilise the spin to control the shot to ensure that the ball both clears the net and also lands in the service box. This highlights the fact that it may not be in the manufacturers interest to produce a ‘faster’ tennis ball with a lower drag coefficient, because the ball may also have a lower lift coefficient, thus reducing the players ability to play certain strokes.

Top quark pair production and decay at hadron colliders

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.

Top quark pair production and decay at hadron colliders

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.

Top quark spin inepcollision

We discuss the degree of spin polarization of single top quarks produced via $Wg$ fusion process in $ep$ collision at TESLA+HERAp and CLIC+LHC energies $\sqrt{s}=1.6$ and 5.3 TeV. For $eb \to t \bar{\nu}$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. A description on how to combine the cross sections of $e^{+}b\to t\bar{\nu}$ and $e^{+}g\to t\bar{b}\bar{\nu}$ processes is given. $e^{+}$-beam direction is taken to be the favorite top quark spin decomposition axis in its rest frame and it is found to be comparable with the ones in $pp$ collision. It is argued that theoretical simplicity and experimental clearness are the advantage of $ep$ collision.