The fundamental building blocks of the proton-quarks and gluons-have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and ...their dynamics give rise to the quantum bound state of the proton and its physical properties, such as its spin
. The two up quarks and the single down quark that comprise the proton in the simplest picture account only for a few per cent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force
. An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter-antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions in which a matter-antimatter quark pair annihilates. In this picture of quark-antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, given that their masses are very similar and small compared to the mass of the proton
. Here we provide evidence from muon pair production measurements that these distributions are considerably different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momenta. These results are expected to revive interest in several proposed mechanisms for the origin of this antimatter asymmetry in the proton that had been disfavoured by previous results
, and point to future measurements that can distinguish between these mechanisms.
The SeaQuest spectrometer at Fermilab Aidala, C.A.; Arrington, J.R.; Ayuso, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2019, Letnik:
930, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium ...and solid nuclear targets. The primary physics program uses the Drell–Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.
Evidence for a flavor asymmetry between the $\bar{u}$ and $\bar{d}$ quark distributions in the proton has been found in deep-inelastic scattering and DrellYan experiments. The pronounced dependence ...of this flavor asymmetry on x (fraction of nucleon momentum carried by partons) observed in the Fermilab E866 Drell-Yan experiment suggested a drop of the $\bar{d}$(x)/$\bar{u}$(x) ratio in the x > 0.15 region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for $\bar{d}$(x)/$\bar{u}$(x) in the large x region up to x = 0.45 using the 120 GeV proton beam. Two different methods for extracting the Drell-Yan cross section ratios, σpd/2σpp, from the SeaQuest data give consistent results. The $\bar{d}$(x)/$\bar{u}$(x) ratios and the $\bar{d}$(x)- $\bar{u}$(x) differences are deduced from these cross section ratios for 0.13 < x < 0.45. The SeaQuest and E866/NuSea $\bar{d}$(x)/$\bar{u}$(x) ratios are in good agreement for the x≲0.25 region. The new SeaQuest data, however, show that $\bar{d}$(x) continues to be greater than $\bar{u}$(x) up to the highest x value (x = 0.45). The new results on $\bar{d}$(x)/$\bar{u}$(x) and $\bar{d}$(x)-$\bar{u}$(x) are compared with various parton distribution functions and theoretical calculations.
The fundamental building blocks of the proton—quarks and gluons—have been known for decades. However, we still have an incomplete theoretical and experimental understanding of how these particles and ...their dynamics give rise to the quantum bound state of the proton and its physical properties, such as its spin1. The two up quarks and the single down quark that comprise the proton in the simplest picture account only for a few per cent of the proton mass, the bulk of which is in the form of quark kinetic and potential energy and gluon energy from the strong force2. An essential feature of this force, as described by quantum chromodynamics, is its ability to create matter–antimatter quark pairs inside the proton that exist only for a very short time. Their fleeting existence makes the antimatter quarks within protons difficult to study, but their existence is discernible in reactions in which a matter–antimatter quark pair annihilates. In this picture of quark–antiquark creation by the strong force, the probability distributions as a function of momentum for the presence of up and down antimatter quarks should be nearly identical, given that their masses are very similar and small compared to the mass of the proton3. Here we provide evidence from muon pair production measurements that these distributions are considerably different, with more abundant down antimatter quarks than up antimatter quarks over a wide range of momenta. These results are expected to revive interest in several proposed mechanisms for the origin of this antimatter asymmetry in the proton that had been disfavoured by previous results4, and point to future measurements that can distinguish between these mechanisms.
The SeaQuest Spectrometer at Fermilab Collaboration, SeaQuest; Aidala, C A; Arrington, J R ...
arXiv (Cornell University),
02/2019
Paper, Journal Article
Odprti dostop
The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium ...and solid nuclear targets. The primary physics program uses the Drell-Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.
Bioinvasions and Globalization synthesises our current knowledge of the ecology and economics of biological invasions, providing an in-depth evaluation of the science and its implications for ...managing the causes and consequences of one of the most pressing environmental issues facing humanity today. Emergent zoonotic diseases such as HIV and SARS have already imposed major costs in terms of human health, whilst plant and animal pathogens have had similar effects on agriculture, forestry, fisheries. The introduction of pests, predators and competitors into many ecosystems has disrupted the benefits they provide to people, in many cases leading to the extirpation or even extinction of native species. This timely book analyzes the main drivers of bioinvasions - the growth of world trade, global transport and travel, habitat conversion and land use intensification, and climate change - and their consequences for ecosystem functioning. It shows how bioinvasions impose disproportionately high costs on countries where a large proportion of people depend heavily on the exploitation of natural resources. It considers the options for improving assessment and management of invasive species risks, and especially for achieving the international cooperation needed to address bioinvasions as a negative externality of international trade. Available in OSO: http://www.oxfordscholarship.com/oso/public/content/biology/9780199560158/toc.html Contributors to this volume - N. A. Aravind; Stas Burgiel; Milan Chytry; Christopher Costello; Katharina Dehnen-Schmutz; Martin Drechsler; Eli Fenichel; Peyton Ferrier; David Finnoff; K. N. Ganeshaiah; Liba Pejchar Goldstein; Vojtěch Jarošik; Karin Johst; Gladwin Joseph; Ramesh Kannan; Reuben P. Keller; Ann Kinzig; Mark A. Lewis; David M. Lodge; Mark Lonsdale; Carol McSweeney; Harold Mooney; Mark New; Ralf Ohlemuller; Charles Perrings; Stephen Polasky; Alexei Potapov; Petr Pyšek; David M. Richardson; R. Uma Shaanker; R. David Simpson; Michael Springborn; Chris D. Thomas; Julia Touza; Brian W. van Wilgen; Mark Williamson
As the global climate changes, there are concomitant changes in global biological productivity. This book is devoted to the assessment of terrestrial Net Primary Productivity ("the total amount of ...energy acquired by green plants during photosynthesis, minus the energy lost through respiration"--APDS&T, pp. 1457). The book is comprised of three major sections. The first section is a review of the processes that operate globally to influence productivity--these are the initial conditions of any model of primary productivity. The second section is comprised of chapters that assess the contribution of particular ecosystems to global productivity. The final major section contains chapters of a synthetic nature that describe attempts to model global productivity. This book should appeal to both ecologists and environmental scientists.
Evidence for a flavor asymmetry between the $\bar u$ and $\bar d$ quark
distributions in the proton has been found in deep-inelastic scattering and
Drell-Yan experiments. The pronounced dependence of ...this flavor asymmetry on
$x$ (fraction of nucleon momentum carried by partons) observed in the Fermilab
E866 Drell-Yan experiment suggested a drop of the $\bar d\left(x\right) / \bar
u\left(x\right)$ ratio in the $x > 0.15$ region. We report results from the
SeaQuest Fermilab E906 experiment with improved statistical precision for $\bar
d\left(x\right) / \bar u\left(x\right)$ in the large $x$ region up to $x=0.45$
using the 120 GeV proton beam. Two different methods for extracting the
Drell-Yan cross section ratios, $\sigma^{pd} /2 \sigma^{pp}$, from the SeaQuest
data give consistent results. The $\bar{d}\left(x\right) /
\bar{u}\left(x\right)$ ratios and the $\bar d\left(x\right) - \bar
u\left(x\right)$ differences are deduced from these cross section ratios for
$0.13 < x < 0.45$. The SeaQuest and E866/NuSea $\bar{d}\left(x\right) /
\bar{u}\left(x\right)$ ratios are in good agreement for the $x\lesssim 0.25$
region. The new SeaQuest data, however, show that $\bar d\left(x\right)$
continues to be greater than $\bar u\left(x\right)$ up to the highest $x$ value
($x = 0.45$). The new results on $\bar{d}\left(x\right) /
\bar{u}\left(x\right)$ and $\bar{d}\left(x\right) - \bar{u}\left(x\right)$ are
compared with various parton distribution functions and theoretical
calculations.
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