118387288
Global flow of glasma in high energy nuclear collisions
Abstract We discuss the energy flow of the classical gluon fields created in collisions of heavy nuclei at collider energies. We show how the Yang–Mills analog of Faradayʼs Law and Gaussʼ Law predicts the initial gluon flux tubes to expand or bend. The resulting transverse and longitudinal structure of the Poynting vector field has a rich phenomenology. Besides the well-known radial and elliptic flow in transverse direction, classical quantum chromodynamics predicts a rapidity-odd transverse flow that tilts the fireball for non-central collisions, and it implies a characteristic flow pattern for collisions of non-symmetric systems A + B . The rapidity-odd transverse flow translates into a directed particle flow v 1 which has been observed at RHIC and LHC. The global flow fields in heavy ion collisions could be a powerful check for the validity of classical Yang–Mills dynamics in high energy collisions.
119188205
Initial Conditions with Flow from a McLerran Venugopalan model with Transverse Dynamics
Using a recursive solution of the Yang-Mills equation, we calculate analytic expressions for the gluon fields created in ultra-relativistic heavy ion collisions at small times τ. We have worked out explicit solutions for the fields and the energy momentum tensor up to 4th order in an expansion in τ. We generalize the McLerran-Venugopalan model to allow for a systematic treatment of averaged charge densities μ2 that vary as a function of transverse coordinates. This allows us to calculate radial, elliptic and directed flow of gluon fields. Our results can serve as initial conditions for hydrodynamic simulations of nuclear collisions that include initial flow.
119258817
Ward identity implies recursion relations in Yang-Mills theory
The Ward identity in gauge theory constrains the behavior of the amplitudes. We discuss the Ward identity for amplitudes with a pair of shifted lines with complex momenta. This will induce a recursion relation identical to BCFW recursion relations at the finite poles of the complexified amplitudes. Furthermore, according to the Ward identity, it is also possible to transform the boundary term into a simple form, which can be obtained by a new recursion relation. For the amplitude with one off-shell line in pure Yang-Mills theory, we find this technique is effective for obtaining the amplitude even when there are boundary contributions.
119276990
Heavy quarkonium production through the semi-exclusive $e^+e^-$ annihilation channels round the $Z^0$ peak
Within the framework of the non-relativistic QCD, we present a detailed discussion on the heavy quarkonium production at the leading order in $\alpha_s$ at a $e^+ e^-$ collider with the collision energy around the $Z^0$ peak. Quarkonia are produced through the semi-exclusive channels $e^{+}e^{-} \rightarrow |H_{Q\bar{Q}}\rangle +X$ with $X=Q\bar{Q}$ or $gg$, where $Q$ indicates a heavy quark (respectively $b$ or $c$). It is noted that in addition to the color-singlet 1S-level quarkonium states, the 2S and 1P color-singlet states and the color-octet $|(Q\bar{Q})[1^3S_1^{({\bf 8})}]g\rangle$ state also provide sizable contributions. The heavy quarkonium transverse momentum and rapidity distributions for the $e^+ e^-$ collision energy $E_{cm}=m_Z$ are presented. For both charmonium and bottomonium production via the $Z^0$ propagator, there is approximate "spin degeneracy" between the spin-triplet and spin-singlet quarkonium states. Uncertainties for the total cross sections are estimated by taking $m_c=1.50\pm0.15$ GeV and $m_b=4.90\pm0.15$ GeV. Around $E_{cm}=m_{Z}$, due to the $Z^0$-boson resonance effect, total cross sections for the channels via the $Z^0$-propagator become much larger than the channels via the virtual photon propagator. We conclude that, in addition to the $B$ factories as BaBar and Belle and the hadronic colliders as Tevatron and LHC, such a super $Z$-factory will present an excellent platform for studying the heavy quarkonium properties.
118607013
Permutation relations of generalized Yangian Invariants, unitarity cuts, and scattering amplitudes
A bstractWe find a permutation relation among the generalized Yangian Invariants — two Yangian Invariants with adjacent external lines exchanged are related by a simple kinematic factor — which is shown to be equivalent to U(1) decoupling and Bern-Carrasco-Johansson (BCJ) relation at the level of maximal helicity violating (MHV) amplitudes. We propose using unitarity cuts to study nonplanar amplitudes and to systematically reconstruct the integrands of nonplanar MHV amplitudes, up to a rational function which vanishes under all possible unitarity cuts. This is made possible with the newly found permutation relations by converting nonplanar on-shell diagrams into planar ones. As explicit examples the construction of one-loop double-trace MHV amplitudes of 4- and 5-point interactions are presented using on-shell diagrams. The kinematic factors and the resultant planar diagrams are carefully dealt with using the unitarity cut conditions. The first next-to-MHV amplitudes are addressed using generalized unitarity cuts. Their leading singularities can be identified as residues of the Grassmanian integrals. These examples also serve to demonstrate the power of the newly found relation of the generalized Yangian Invariants.
123396645
Calibration and performance of the AMS-02 time of flight detector in space
AMS-02 is a high energy particle detector deployed in May 19, 2011 on board of the International Space Station (ISS) where it is expected to be in operation for the ISS lifetime of at least a decade. The main goal of AMS-02 is the detection of cosmic rays and gammas from the GeV to the TeV energy region to search for anti-matter, dark matter and understanding the origin of the cosmic rays. The AMS-02 time of flight (TOF) detector provides the trigger to experiment and allows precise measurements of the cosmic rays velocity and charge magnitude from hydrogen to iron and above. With the data set acquired during the first two and a half years of operation in space, a precise time-dependent calibration for time, velocity and charge measured by the TOF had been developed. The TOF calibration methods are described and the AMS-02 TOF performance in space is presented. (C) 2014 Elsevier B.V. All rights reserved.
138378034
PERFORMANCES OF THE AMS-02 ELECTROMAGNETIC CALORIMETER