Spin Effects in High Energy Fragmentation Processes

Recent measurements, in particular those on $\Lambda$ polarization and spin alignment of vector mesons in $e^+e^-$ annihilation at LEP, and those on the azimuthal asymmetry at HERA, have attracted much attention on the spin effects in high energy fragmentation processes. In this talk, we make a brief introduction to the different topics studied in this connection and a short summary of the available data. After that, we present a short summary of the main theoretical results that we obtained in studying these different topics. The talk was mainly based on the publications [5-9] which have been finished in collaboration with C.Boros, Liu Chun-xiu and Xu Qing-hua.Comment: Plenary talk given at the 3rd Circum-Pan-Pacifc Symposium on High Energy Spin Physics, October 2001, 8 pages, 4 figure

IceCube Events from Heavy DM decays through the Right-handed Neutrino Portal

The recently observed IceCube PeV events could be due to heavy dark matter (DM) decay. In this paper, we propose a simple DM model with extra $U(1)_X$ gauge symmetry and bridge it with standard model particles through heavy right-handed neutrino. The Dirac fermion DM $\chi$ with mass ~5 PeV can dominantly decay into a dark Higgs ($\phi$), the SM Higgs ($h$) and a neutrino ($\nu$). If the lifetime of $\chi$ is ~O($10^{28}$) sec, the resulting neutrino flux can fit data consistently. The neutrino flux from $\chi \rightarrow \phi h \nu$ in our model is softer than the one predicted from $\chi \rightarrow \nu h$, for example. We also discuss a possible mechanism to produce DM with the right relic abundance.Comment: 17 pages, 5 figures, references added, minor changes, published versio

Neutrino factory in stages: Low energy, high energy, off-axis

We discuss neutrino oscillation physics with a neutrino factory in stages, including the possibility of upgrading the muon energy within the same program. We point out that a detector designed for the low energy neutrino factory may be used off-axis in a high energy neutrino factory beam. We include the re-optimization of the experiment depending on the value of theta_13 found. As upgrade options, we consider muon energy, additional baselines, a detector mass upgrade, an off-axis detector, and the platinum (muon to electron neutrino) channels. In addition, we test the impact of Daya Bay data on the optimization. We find that for large theta_13 (theta_13 discovered by the next generation of experiments), a low energy neutrino factory might be the most plausible minimal version to test the unknown parameters. However, if a higher muon energy is needed for new physics searches, a high energy version including an off-axis detector may be an interesting alternative. For small theta_13 (theta_13 not discovered by the next generation), a plausible program could start with a low energy neutrino factory, followed by energy upgrade, and then baseline or detector mass upgrade, depending on the outcome of the earlier phases.Comment: 23 pages, 10 (color) figures. Minor clarifications and changes. Final version to appear in PR

Hidden Charged Dark Matter and Chiral Dark Radiation

In the light of recent possible tensions in the Hubble constant $H_0$ and the structure growth rate $\sigma_8$ between the Planck and other measurements, we investigate a hidden-charged dark matter (DM) model where DM interacts with hidden chiral fermions, which are charged under the hidden SU(N) and U(1) gauge interactions. The symmetries in this model assure these fermions to be massless. The DM in this model, which is a Dirac fermion and singlet under the hidden SU(N), is also assumed to be charged under the U(1) gauge symmetry, through which it can interact with the chiral fermions. Below the confinement scale of SU(N), the hidden quark condensate spontaneously breaks the U(1) gauge symmetry such that there remains a discrete symmetry, which accounts for the stability of DM. This condensate also breaks a flavor symmetry in this model and Nambu-Goldstone bosons associated with this flavor symmetry appear below the confinement scale. The hidden U(1) gauge boson and hidden quarks/Nambu-Goldstone bosons are components of dark radiation (DR) above/below the confinement scale. These light fields increase the effective number of neutrinos by $\delta N_{\rm eff}\simeq 0.59$ above the confinement scale for $N=2$, resolving the tension in the measurements of the Hubble constant by Planck and Hubble Space Telescope if the confinement scale is $\lesssim 1$ eV. DM and DR continuously scatter with each other via the hidden U(1) gauge interaction, which suppresses the matter power spectrum and results in a smaller structure growth rate. The DM sector couples to the Standard Model sector through the exchange of a real singlet scalar mixing with the Higgs boson, which makes it possible to probe our model in DM direct detection experiments. Variants of this model are also discussed, which may offer alternative ways to investigate this scenario.Comment: 20 pages, 4 figures; v2: version accepted for publication in PL

The Role of Microenvironment Reagent Solubility on Reaction Kinetics of 4-Nitrophenol Reduction

The Role of Microenvironment Reagent Solubility on Reaction Kinetics of 4-Nitrophenol Reduction Michael Zeevi1 with Andrew Harrison1 and Christina Tang, PhD1 1Department of Chemical and Life Science Engineering, VCU School of Engineering Introduction: Nanoparticles are of increasing interest due to their high surface area to volume ratio, as well as that they enable fine-tuning of the reaction microenvironment. Through flash nanoprecipitation, core-shell polymer nanoreactors were formed by directed self-assembly. Using the reduction of 4-nitrophenol as a model reduction reaction, we investigated the effect of reagent solubility in the nanoreactor microenvironment’s on nanoreactor kinetics. Methods: The standard reaction was conducted at room temperature, with a 1000-fold excess of sodium borohydride in a quartz cuvette for real-time in situ­ UV-Vis analysis. Reagent concentrations were varied to examine the resulting effect on the calculated reaction rate constant. Reagent solubility limits in the nanoreactor microenvironment were estimated from solubility measurements in solvents with similar Hansen solubility parameters. Ethanol was chosen to represent the hydrophilic poly(ethylene) glycol phase and chloroform was chosen to represent the hydrophobic polystyrene phase. The hydrophilic phase had a visual absorbance at nm, and thus UV-Vis spectrometry was used to determine the saturation concentration. 1H NMR analysis with chloroform-D containing an internal standard (v/v TMS 0.03%) was used to measure the reagent solubility in the hydrophobic phase. Results: 4-nitrophenol solubility in ethanol was determined by UV-Vis spectrometry to be . The solubility in chloroform-D was determined by 1H NMR to be . When 4-nitrophenol concentration is varied independently of sodium borohydride, an inverse relationship is observed with respect to the rate constant. However, when 4-nitrophenol and sodium borohydride concentrations are varied concurrently, no change is witnessed in the rate constant above the standard reaction concentration. Conclusions: This experiment demonstrated that the rate of reaction in polystyrene core nanoreactors is not dependent on the reagent concentrations above the standard concentration. Solubility in each phase was measured in an effort to explain this behavior. The differences in solubility observed between the hydrophobic and hydrophilic phases may serve to explain this behavior if the interior, hydrophobic phase is saturated by 4-nitrophenol at the standard concentration. Future work should include study of concentrations at lower values than the standard concentration to determine when a change in the observed rate constant occurs.https://scholarscompass.vcu.edu/uresposters/1287/thumbnail.jp