87 research outputs found

    Production of highly-polarized positrons using polarized electrons at MeV energies

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    The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-ZZ target. Positron polarization up to 82\% have been measured for an initial electron beam momentum of 8.19~MeV/cc, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.Comment: 5 pages, 4 figure

    Trust as a daily defense against collective disease threats

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    Although the isolated threat of disease often motivates people to avoid others, people need the help and cooperation of others to protect themselves against pandemic disease threats. Therefore, the fear of contracting a highly contagious virus like COVID-19 should motivate people to believe that they can in fact count on the help and cooperation of others for protection. Trusting in others provides the basis to anticipate their cooperation. Therefore, we expected a greater daily threat of contracting COVID-19 to motivate people to trust more in others, providing needed assurance that others would keep them safe from harm. We obtained 4 daily diary samples involving 2794 participants who provided in excess of 18,000 daily observations within the first three months of the COVID-19 pandemic. Each day, we tracked (1) disease threat, captured daily by personal concerns about COVID-19 and infection totals in the nearest most populous city, and (2) trust in others, captured daily by expressions of trust in intimates, collective caregivers (e.g., President, Congress), and strangers. Participants in two samples completed 2-month follow-ups. Integrative analyses of the daily diaries revealed that people trusted more in intimates and collective caregivers on days they had greater (vs. less) reason to be concerned about COVID-19. Further integrative analyses of the follow-up data revealed that participants who were initially more likely to trust in others on days when COVID-19 cases in nearby communities spread more rapidly later reported greater confidence that others would keep them safe from harm. That is, they evidenced greater physical, interpersonal, and collective security in social connection than participants who were initially less likely to defensively trust in others on such occasions. The present findings suggest that ecological threats may dynamically motivate people to trust others more than they otherwise would, providing optimism that collectively-faced crises may motivate social cooperation when it is most needed

    A New Measurement of the π0\pi^0 Radiative Decay Width

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    High precision measurements of the differential cross sections for π0\pi^0 photoproduction at forward angles for two nuclei, 12^{12}C and 208^{208}Pb, have been performed for incident photon energies of 4.9 - 5.5 GeV to extract the π0→γγ{\pi^0 \to \gamma\gamma} decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ{\pi^0 \to \gamma\gamma} decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14 (stat.)±0.17 (syst.) eV\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.Comment: 4 pages, 5 figure

    Pursuing Safety in Social Connection Regulates the Risk-Regulation, Social-Safety and Behavioral-Immune Systems

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    A new goal-systems model is proposed to help explain when individuals will protect themselves against the risks inherent to social connection. This model assumes that people satisfy the goal to feel included in safe social connections—connections where they are valued and protected rather than at risk of being harmed—by devaluing rejecting friends, trusting in expectancy–consistent relationships, and avoiding infectious strangers. In the hypothesized goal system, frustrating the fundamental goal to feel safe in social connection sensitizes regulatory systems that afford safety from the risk of being interpersonally rejected (i.e., the risk-regulation system), existentially uncertain (i.e., the social-safety system), or physically infected (i.e., the behavioral-immune system). Conversely, fulfilling the fundamental goal to feel safe in social connection desensitizes these self-protective systems. A 3-week experimental daily diary study (N = 555) tested the model hypotheses. We intervened to fulfill the goal to feel safe in social connection by repeatedly conditioning experimental participants to associate their romantic partners with highly positive, approachable words and images. We then tracked how vigilantly experimental versus control participants protected themselves when they encountered social rejection, unexpected behavior, or contagious illness in everyday life. Multilevel analyses revealed that the intervention lessoned self-protective defenses against each of these risks for participants who ordinarily felt most vulnerable to them. The findings provide the first evidence that the fundamental goal to feel safe in social connection can co-opt the risk-regulation, social-safety, and behavioral-immune systems as independent means for its pursuit

    Looking for Safety in all the Right Places: When Threatening Political Reality Strengthens Family Relationship Bonds

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    Elections and pandemics highlight how much one’s safety depends on fellow community members, a realization that is especially threatening when the collective perceives political realities inconsistent with one’s own. Two longitudinal studies examined how people restored safety to social bonds when everyday experience suggested that fellow community members inhabited inconsistent realities. We operationalized consensus political realities through the negativity of daily, nation-wide social media posts mentioning President Trump (Studies 1 and 2), and the risks of depending on fellow community members through the pending transition to a divided Congress during the 2018 election season (Study 1), and escalating daily U.S. COVID-19 infections (Study 2). On days that revealed people could not count on fellow community members to perceive the same reality of President Trump’s stewardship they perceived, being at greater risk from the judgment and behavior of the collective community motivated people to find greater happiness in their family relationships

    A Moth to a Flame? Fulfilling Connectedness Needs Through Romantic Relationships Protects Conspiracy Theorists Against COVID-19 Misinformation

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    Conspiracy theorists’ unpopular opinions likely make them more apprehensive about interactions with others, frustrating their need to belong. Therefore, they may be susceptible to believing misinformation because evidence that others share their beliefs provides “social proof” that they can expect interactions with others to be positive and rewarding. The present research examined whether alternatively fulfilling the need for social connection through romantic relationships could protect conspiracy theorists against COVID-19 misinformation. In a 3-week daily diary study (N = 555), experimental participants implicitly learned to associate their romantic partners with positive experiences (by repeatedly pairing their partner with highly positive and approachable stimuli, McNulty et al., 2017). We then assessed how much participants trusted individuals they might normally distrust, as a manipulation check, and how much participants tuned their daily personal beliefs and behavior to match the U.S. public's daily susceptibility to COVID-19 misinformation. Participants high on conspiratorial thinking trusted fellow community members more in the experimental than control condition. Participants high on conspiratorial thinking in the experimental condition were also less likely to treat the U.S. public's greater daily susceptibility to COVID-19 misinformation as proof that they could discount the virus. The present findings suggest that rewarding romantic connections might be leveraged to limit conspiracy theorists’ susceptibility to believing public skepticism about COVID-19

    Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF

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    The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at the Fermilab Long-Baseline Neutrino Facility (LBNF) is described
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