Elliptic flow of thermal photons in relativistic nuclear collisions

We predict the transverse momentum (p(T)) dependence of elliptic flow of thermal photons for Au + Au collisions at the BNL Relativistic Heavy Ion Collider. We model the system hydrodynamically, with a thermalized quark-gluon plasma at early times followed by hadronization and decoupling. Photons are emitted throughout the expansion history. Contrary to hadron elliptic flow, which increases monotonically with p(T), the elliptic flow nu2(p(T)) of thermal photons is predicted to first rise and then fall again. Photon elliptic flow at high p(T) reflects the quark momentum anisotropy at early times when it is small, while at low p(T) it mirrors the large pion momentum anisotropy during the late hadronic emission stage. An interesting structure is predicted at intermediate p(T) approximately 0.4 GeV/c, where photon elliptic flow reflects the momenta and the (compared to pions) reduced nu2 of heavy vector mesons in the late hadronic phase.     

Measurement of identified and inclusive photon second-harmonic parameter and implications for direct photon production in [FORMULA: SEE TEXT] Au+Au

The azimuthal distribution of identified pi0 and inclusive photons has been measured in [FORMULA: SEE TEXT] Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (nu2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1-6 GeV/c. An attempt is made to extract nu2 of direct photons.     

Photon polarization as a probe for quark–gluon plasma dynamics

Prospects of measuring polarized photons emitted from a quark–gluon plasma (QGP) are discussed. In particular, the detection of a possible quark spin polarization in a QGP using circularly polarized photons emitted from the plasma is studied. Photons leave the QGP without further interaction and thus provide a primary probe for quark polarization within the QGP. We find that photon polarization cannot solely arise due to a possible QGP momentum space anisotropy, but may be enhanced due to it. In particular, for oblate momentum distributions and high photon energies, quark polarization is efficiently transfered to photon polarization. The role of competing sources of polarized photons in heavy-ion collisions is discussed.     

Spectral asymmetry and quantum field theory in curved spacetime

I discuss cosmological particle production in spaces with spectral asymmetry. A change in the amount of spectral symmetry sufficient to produce a level crossing will result in the creation of neutrino pairs rather than neutrino, antineutrino pairs; the net excess of fermions being given by the number of level crossing. A symmetric Bianchi IX model is treated in detail and for large initial anisotropy the number of neutrinos produced is ($\text{1}\text{256}$) exp 12β₊ where β₊ is a measure of the initial anisotropy. The relation of this phenomenon to chiral anomalies and to the Atiyah-Patodi-Singer index theorem for manifolds with boundary is described. The effect of spectral asymmetry on photons is discussed and it is shewn that no level crossing can occur.     

Double-spin asymmetries in the cross section of \rho^0 and \phi production at intermediate energies

Double-spin asymmetries in the cross section of electroproduction of and mesons on the proton and deuteron are measured at the HERMES experiment. The photoabsorption asymmetry in exclusive electroproduction on the proton exhibits a positive tendency. This is consistent with theoretical predictions that the exchange of an object with unnatural parity contributes to exclusive electroproduction by transverse photons. The photoabsorption asymmetry on the deuteron is found to be consistent with zero. Double-spin asymmetries in and meson electroproduction by quasi-real photons were also found to be consistent with zero; the asymmetry in the case of the meson is compatible with a theoretical prediction which involves knockout from the nucleon. Received: 11 February 2003 / Published online: 11 June 2003     

New constraints on neutrino physics from BOOMERANG data

We have performed a likelihood analysis of the recent data on the cosmic microwave background radiation anisotropy from the BOOMERANG experiment. These data place a strong upper bound on the radiation density present at recombination. Expressed in terms of the equivalent number of neutrino species the 2sigma bound is N(nu)相似文献   

Single transverse spin asymmetry of prompt photon production

We study the single transverse spin asymmetry of prompt photon production in high energy proton–proton scattering. We include the contributions from both the direct and fragmentation photons. While the asymmetry for direct photon production receives only the Sivers type of contribution, the asymmetry for fragmentation photons receives both the Sivers and Collins types of contributions. We make a model calculation for quark-to-photon Collins function, which is then used to estimate the Collins asymmetry for fragmentation photons. We find that the Collins asymmetry for fragmentation photons is very small, thus the single transverse spin asymmetry of prompt photon production is mainly coming from the Sivers asymmetry in direct and fragmentation photons. We make predictions for the prompt photon spin asymmetry at RHIC energy, and emphasize the importance of such a measurement. The asymmetry of prompt photon production can provide a good measurement for the important twist-three quark–gluon correlation function, which is urgently needed in order to resolve the “sign mismatch” puzzle.     

高能核-核碰撞中直接光子各向异性的数值模拟研(英文)

通过计算给出了在LHC能区非对心核 核碰撞中由椭圆流ν₂ 表示的高横动量直接光子的方位角不对称性。该高横动量光子是由喷注与热密介质相互作用而辐射出来的。光子椭圆流与强子椭圆流ν₂ 相差π/2的相位, 是直接光子椭圆流中负值的来源。同时, 计算表明LHC能区直接光子ν₂随粒子横动量p_T的变化趋势与RHIC上的实验结果一致, 但LHC能区较RHIC能区有更低的直接光子流ν₂ 值, 且ν₂ 值由负到正对应的转换p_T值更高。这表明在LHC能区喷注淬火效应更为明显, 表面发射的直接光子对光子椭圆流的贡献份额增强。The azimuthal anisotropy of high p_T direct photons is investigated by using the coefficient of elliptic flow ν₂ in non-central nucleus-nucleus collision at LHC energies. These photons come from radiation induced by the interaction between jet and hot/dense medium. The azimuthal anisotropy of high p_T direct photons is investigated by using the coefficient of elliptic flow ν₂ in non-central nucleus-nucleus collision at LHC energies. These photons come There is π/2 difference between direct photons and hadrons for the azimuthal elliptic flow ν₂. Such photons are the main source of the negative part of ν₂ for direct photons. The dependence of the direct photon ν₂ on the transverse momentum p_T at LHC energy is found to be consistent with the experimental results at RHIC energy. Furthermore, we find that the value of the direct photon ν₂ at LHC energy is smaller than that at RHIC energy. The value of the transverse momentum at which the direct photon ν₂ changes from negative value to positive at LHC is higher than that at RHIC. It’sfound the enhanced jet quenching effect and enhanced contribution for the elliptic flow ν₂ of the direct photons emitted from surface at LHC energy.     

Nondipole parameters of TDCS for electron impact ionization and drag current

A comprehensive study is undertaken of angular distributions of electron knock-out from atomic targets by fast electrons with a small transfer of momentum. The general expressions for the parameters of the triple differential cross-section of impact ionization in the optical limit are derived. The calculated parameters are compared with those of the angular distribution of electrons ejected from an atom in the process of photoionization. In these processes, when the multipole transitions are involved, the one-to-one correspondence between the photoionization and impact ionization parameters disappears. The nondipole transitions lead to the backward/forward asymmetry of the angular distribution of ejected electrons that is absent in the dipole approximation for ionization by both fast electrons and photons. Using the He atom as an example, the character of the asymmetry for these two processes is qualitatively different and the backward/forward asymmetry results in macroscopic directed motion of secondary electrons accompanying the passing of a fast electron beam through gas or plasma. The general formulas for this drag current are derived and applied to gaseous He.     

5-10 GeV neutrinos from gamma-Ray burst fireballs

A gamma-ray burst fireball is likely to contain an admixture of neutrons. Inelastic collisions between differentially streaming protons and neutrons in the fireball produce nu(&mgr;) (nu;(&mgr;)) of approximately 10 GeV as well as nu(e) (nu;(e)) of approximately 5 GeV, which could produce approximately 7 events/year in km(3) detectors, if the neutron abundance is comparable to that of protons. Photons of approximately 10 GeV from pi(0) decay and approximately 100 MeV nu;(e) from neutron decay are also produced, but will be difficult to detect. Photons with energies less, similar1 MeV from shocks following neutron decay produce a characteristic signal which may be distinguishable from the proton-related MeV photons.     

Impact parameter and beam energy dependence for azimuthal asymmetry of direct photons and free protons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have calculated the impact parameter and beam energy dependence for azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coeffcient v2, of direct photons and the corresponding free protons in intermediate energy heavy-ion collisions. It is further shown the anti-correlated azimuthal asymmetry between direct photons and free protons.     

Essay: 3rd Award 2004: Charge Conjugation and Lense-Thirring Effect—A New Asymmetry

This essay presents a new asymmetry that arises from the interplay of charge conjugation and Lense-Thirring effect. When applied to Majorana neutrinos, the effect predicts oscillations in gravitational environments with rotating sources. Parameters associated with astrophysical environments indicate that the presented effect is presently unobservable for solar neutrinos. But, it will play an important role in supernovae explosions, and carries relevance for the observed matter-antimatter asymmetry in the universe.     

Flow with photon multiplicity detector: Past and future

Measurements of azimuthal distribution of inclusive photons using the fine granularity pre-shower photon multiplicity detector (PMD) at CERN SPS are used to obtain anisotropy in the azimuthal distributions. These results are used to estimate the anisotropy in the neutral pion distributions. The results are compared with results of charged particle data, both for first order and second order anisotropy. Assuming the same anisotropy for charged and neutral pions, the anisotropy in photons is estimated and compared with the measured anisotropy. The effect of neutral pion decay on the correlation between the first order and the second order event plane is also discussed. Data from PMD can also be used to estimate the reaction plane for studying any anisotropy in particle emission characteristics in the ALICE experiment at the large hadron collider (LHC). In particular, we show that using the event plane from the PMD, it will be possible to measure the anisotropy inJ/Ψ absorption (if any) in the ALICE experiment.     

236U and 238U fission induced by linearly polarized photons in the region of a giant dipole resonance

The asymmetry Σ in ²³⁶U and ²³⁸U photofission induced by linearly polarized photons obtained by passing electrons through a silicon crystal under conditions close to the conditions of planar channeling is measured. This asymmetry is found to depend on the mass of the nucleus. The measured asymmetry is compared with data from other studies performed either with a polarized or an unpolarized photon beam. It is shown that the asymmetry value cannot be explained by a dominant role of any of the dipole fission channels, but that it is in accord with the currently prevalent idea that E1 transitions play the most important part in the energy region under investigation. It is assumed that the asymmetry Σ is sensitive to the relative height of the inner and the outer hump of the fission barrier, and this is manifested in the distinctions between the asymmetry values for nuclei having the same Z.     

Compact soft x-ray microscope using a gas-discharge light source

We report on a soft x-ray microscope using a gas-discharge plasma with pseudo spark-like electrode geometry as a light source. The source produces a radiant intensity of 4 x 10(13) photons/(sr pulse) for the 2.88 nm emission line of helium-like nitrogen. At a demonstrated 1 kHz repetition rate a brilliance of 4.3 x 10(9) photons/(microm2 sr s) is obtained for the 2.88 nm line. Ray-tracing simulations show that, employing an adequate grazing incidence collector, a photon flux of 1 x 10(7) photons/(microm2 s) can be achieved with the current source. The applicability of the presented pinch plasma concept to soft x-ray microscopy is demonstrated in a proof-of-principle experiment.     

Absolute Intensities Measurements in the nu(4) + nu(5) Band of (12)C(2)H(2): Analysis of Herman-Wallis Effects and Forbidden Transitions

We measured absolute line intensities in two bands of (12)C(2)H(2) near 7.5 μm, namely the nu(4) + nu(5)(Sigma(+)(u))-0(Sigma(+)(g)) and nu(4) + nu(5)(Delta(u))-0(Sigma(+)(g)) bands, using Fourier transform spectroscopy with an accuracy estimated to be better than 2%. Using theoretical predictions from Watson [J. K. G. Watson, J. Mol. Spectrosc. 188, 78 (1998)], the observation of the forbidden nu(4) + nu(5)(Delta(u))-0(Sigma(+)(g)) band and the Herman-Wallis behavior exhibited by its rotational lines were studied quantitatively in terms of two types of interactions affecting the levels involved by the band: l-type resonance and Coriolis interaction. In the case of the nu(4) + nu(5)(Sigma(+)(u))-0(Sigma(+)(g)) band, the influence of l-type resonance is also confirmed. We also attributed the intensity asymmetry observed between the R and P branches of that latter band to a Coriolis interaction with l = 1 levels. We did not observe the nu(4) + nu(5)(Sigma(-)(u))-0(Sigma(+)(g)) band, consisting only of a Q branch, in agreement with Watson's prediction. Copyright 2000 Academic Press.     

Density-induced interchange of anisotropy axes at half-filled high Landau levels

We observe density-induced 90 degrees rotations of the anisotropy axes in transport measurements at half-filled high Landau levels in the two dimensional electron system, where stripe states are proposed ( nu = 9/2, 11/2, etc.). Using a field effect transistor, we find the transition density to be 2.9x10(11) cm(-2) at nu = 9/2. Hysteresis is observed in the vicinity of the transition. We construct a phase boundary in the filling factor magnetic field plane in the regime 4.4相似文献   

Measurement of isolated prompt photon production in photon-photon collisions at $\sqrt{s_{\rm ee}} = 183$-209 GeV

For the first time at LEP the production of prompt photons is studied in the collisions of quasi-real photons using the OPAL data taken at centre-of-mass energies between 183 GeV and 209 GeV. The total inclusive production cross-section for isolated prompt photons in the kinematic range of transverse momentum GeV and pseudorapidity is determined to be . Differential cross-sections are compared to the predictions of a next-to-leading-order (NLO) calculation.Received: 6 May 2003, Published online: 4 November 2003     

Probing MeV dark matter at low-energy e+e- colliders

It has been suggested that the pair annihilation of dark matter particles chi with mass between 0.5 and 20 MeV into e+e- pairs could be responsible for the excess flux (detected by the INTEGRAL satellite) of 511 keV photons coming from the central region of our Galaxy. The simplest way to achieve the required cross section while respecting existing constraints is to introduce a new vector boson U with mass M(U) below a few hundred MeV. We point out that over most of the allowed parameter space, the process e+e--->U(gamma), followed by the decay of U into either an e+e- pair or an invisible (nu(-)nu or chi(-)chi) channel, should lead to signals detectable by current B-factory experiments. A smaller, but still substantial, region of parameter space can also be probed at the Phi factory DAPhiNE.     

Plasma interactions with aminoacid (l-alanine) as a basis of fundamental processes in plasma medicine

Plasma interactions with l-alaine have been studied as a basis of fundamental processes in plasma medicine. The plasma interactions with l-alaine have been examined for investigations of molecular degradations induced by direct exposures with Ar plasma and exposures with UV–VUV photons emitted from the Ar plasma via chemical bonding states analyses using X-ray photoelectron spectroscopy (XPS). The direct Ar-plasma exposure resulted in significant degradations of COOH group and CNH₂ group. Separate experiments via irradiation with photons in UV and VUV regions from the Ar plasma showed that the molecular degradation via irradiation with photons in VUV region was much more significant than via irradiation with photons in UV region. These experiments have indicated that the causality of the molecular degradation of the l-alanine during the Ar plasma exposure is considered to be significant in the following order; ions > VUV photons > UV photons ～ meta-stable radicals. Furthermore, the exposure with Ar–O₂ mixture plasma resulted in insignificant change in the XPS C1s spectra for variation of the exposure time ranging from 30 s to 300 s, indicating that the surface etching process is much more considerable than the chemical degradation process.