We report the first measurement of the fraction of J/ψ mesons coming from B-meson decay (FB→J/ψ) in p+p collisions at s=510 GeV. The measurement is performed using the forward silicon vertex detector ...and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of J/ψ due to B-meson decays from prompt J/ψ. The measured value of FB→J/ψ is 8.1%±2.3%(stat)±1.9%(syst) for J/ψ with transverse momenta 0<pT<5 GeV/c and rapidity 1.2<|y|<2.2. The measured fraction FB→J/ψ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The bb¯ cross section per unit rapidity dσ/dy(pp→bb¯) extracted from the obtained FB→J/ψ and the PHENIX inclusive J/ψ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean B hadron rapidity y=±1.7 in 510 GeV p+p collisions, is 3.63−1.70+1.92 μb. It is consistent with the fixed-order-next-to-leading-logarithm calculations.
In addition to its biological function, the stability of a protein is a major determinant for its applicability. Unfortunately, engineering proteins for improved functionality usually results in ...destabilization of the protein. This so-called stability–function trade-off can be explained by the simple fact that the generation of a novel protein functionor the improvement of an existing onenecessitates the insertion of mutations, i.e., deviations from the evolutionarily optimized wild-type sequence. In fact, it was demonstrated that gain-of-function mutations are not more destabilizing than other random mutations. The stability–function trade-off is a universal phenomenon during protein evolution that has been observed with completely different types of proteins, including enzymes, antibodies, and engineered binding scaffolds. In this review, we discuss three types of strategies that have been successfully deployed to overcome this omnipresent obstacle in protein engineering approaches: (i) using highly stable parental proteins, (ii) minimizing the extent of destabilization during functional engineering (by library optimization and/or coselection for stability and function), and (iii) repairing damaged mutants through stability engineering. The implementation of these strategies in protein engineering campaigns will facilitate the efficient generation of protein variants that are not only functional but also stable and therefore better-suited for subsequent applications.
PHENIX reports differential cross sections of μμ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in p+p collisions at s =200 GeV at forward and backward ...rapidity (1.2<|η|<2.2). The μμ pairs from $c\bar{c}, b\bar{b}$, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and pT. The azimuthal opening angle correlation between the muons from $c\bar{c}$ and $b\bar{b}$ decays and the pair-pT distributions are compared to distributions generated using pythia and powheg models, which both include next-to-leading order processes. The measured distributions for pairs from $c\bar{c}$ are consistent with pythia calculations. The $c\bar{c}$ data present narrower azimuthal correlations and softer pT distributions compared to distributions generated from powheg. The $b\bar{b}$ data are well described by both models. The extrapolated total cross section for bottom production is 3.75±0.24(stat)±$_{0.50}^{0.35}$(syst)±0.45(global) μb, which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy and is approximately a factor of 2 higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of ϕ(1020)-meson production at forward rapidity in p+p collisions at s=510 GeV via the dimuon ...decay channel. The partial cross section in the rapidity and pT ranges 1.2<|y|<2.2 and 2<pT<7 GeV/c is σϕ=2.28±0.09(stat)±0.14(syst)±0.27(norm)×10−2 mb. The energy dependence of σϕ (1.2<|y|<2.2,2<pT<5 GeV/c) is studied using the PHENIX measurements at s=200 and 510 GeV and the Large Hadron Collider measurements at s=2.76 and 7 TeV. The experimental results are compared to various event generator predictions (PYTHIA6, PYTHIA8, PHOJET, AMPT, EPOS3, AND EPOS-LHC).
We report the first measurement of the full angular distribution for inclusive J/ψ→μ+μ− decays in p+p collisions at s=510 GeV. The measurements are made for J/ψ transverse momentum 2<pT<10 GeV/c and ...rapidity 1.2<y<2.2 in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient λθ is strongly negative at low pT and becomes close to zero at high pT, while the azimuthal coefficient λϕ is close to zero at low pT, and becomes slightly negative at higher pT. The frame-independent coefficient λ˜ is strongly negative at all pT in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.
We report that during 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of ...transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized p+p collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in p+p collisions predicts only a moderate atomic-mass-number (A) dependence. In contrast, the asymmetries observed at RHIC in p+A collisions showed a surprisingly strong A dependence in inclusive forward neutron production. The observed asymmetry in p+Al collisions is much smaller, while the asymmetry in p+Au collisions is a factor of three larger in absolute value and of opposite sign. Lastly, the interplay of different neutron production mechanisms is discussed as a possible explanation of the observed A dependence.
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