The quantum numbers of the X(3872) meson are determined to be J(PC)=1(++) based on angular correlations in B(+)→X(3872)K(+) decays, where X(3872)→π(+)π(-)J/ψ and J/ψ→μ(+)μ(-). The data correspond to ...1.0 fb(-1) of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J(PC)=2(-+) is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.
We document the hidden costs of a popular nudge and show how these costs distort policy making when neglected. In a field experiment with a charity, we find reminders increasing intended behavior ...(donations), but also increasing avoidance behavior (unsubscriptions from the mailing list). We develop a dynamic model of donation and unsubscription behavior with limited attention. We test the model in a second field experiment which also provides evidence that the hidden costs are anticipated. The model is estimated structurally to perform a welfare analysis. Not accounting for hidden costs overstates the welfare effects for donors by factor ten and hides potential negative welfare effects of the charity.
•Hidden costs of nudges can be problematic when neglected.•Reminders increase intended behavior, but also unintended, negative reactions.•Reducing the frequency has positive, long-term effects for receivers and charity.•When evaluating nudges, more rigorous welfare calculations need to be made.
A
bstract
We report the measured transverse momentum (
p
T
) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy
s
N
N
=
5.02
TeV in the kinematic range ...of 0
.
15
< p
T
<
50 GeV/
c
and |
η
|
<
0
.
8. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at
s
N
N
=
2.76
TeV, as well as in p-Pb collisions at
s
N
N
=
5.02
TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For central collisions, the
p
T
spectra are suppressed by more than a factor of 7 around 6–7 GeV/
c
with a significant reduction in suppression towards higher momenta up to 30 GeV/
c
. The nuclear modification factor
R
pPb
, constructed from the pp and p-Pb spectra measured at the same collision energy, is consistent with unity above 8 GeV/
c
. While the spectra in both pp and Pb-Pb collisions are substantially harder at
s
N
N
=
5.02
TeV compared to 2.76 TeV, the nuclear modification factors show no significant collision energy dependence. The obtained results should provide further constraints on the parton energy loss calculations to determine the transport properties of the hot and dense QCD matter.
The crowding-out effects predict that offering monetary incentives to complete a task might negatively affect task performance because the monetary rewards crowd out non-monetary sources of value ...that people derive from task completion. In this study, we revisit a well-known field experiment by Gneezy and Rustichini (2000) that provides evidence for crowding-out effects in the context of prosocial behavior. We test the robustness of these effects using a larger sample and adjust the experiment's design to better elucidate the role of non-monetary incentives in prosocial behavior. Specifically, we assigned 245 pairs of high school students to different incentives for collecting donations for charity: low monetary incentives (1 % of total donations collected), high monetary incentives (10 % of total donations collected), non-monetary incentives (enhanced task importance and public recognition), or no external incentives. We made it explicit to the students that the monetary incentives were funded by the researchers, not the charities. In line with crowding-out effects and Gneezy and Rustichini's (2000) findings, our results show that low monetary incentives elicit lower performance (collected donations) compared with the absence of external incentives. Importantly, non-monetary incentives elicit higher performance compared with either monetary incentives or the absence of external incentives.
Recent pT-integrated cross-section measurements of the ground-state charm mesons and baryons, D0, D+, D+s, Λ+c, and Ξ0c, are used to evaluate the charm fragmentation fractions and production cross ...section per unit of rapidity at midrapidity (|y|<0.5), in pp collisions at √s=5.02 TeV at the LHC. The latter is dσc¯c/dy||y|<0.5=1165±44(stat)+134−101(syst) μb. These measurements were obtained for the first time in hadronic collisions at the LHC, including the charm baryon states, recently measured by ALICE at midrapidity. The charm fragmentation fractions differ significantly from the values measured in e+e− and ep collisions, providing evidence of the dependence of the parton-to-hadron fragmentation fractions on the collision system, indicating that the assumption of their universality is not supported by the measured cross sections. An increase of a factor of about 3.3 for the fragmentation fraction for the Λ+c with a significance of 5σ between the values obtained in pp collisions and those obtained in e+e− (ep) collisions is reported. The fragmentation fraction for the Ξ0c was obtained for the first time in any collision system. The measured fragmentation fractions were used to update the c¯c cross sections per unit of rapidity at |y|<0.5 at √s=2.76 and 7 TeV, which are about 40% higher than the previously published results. The data were compared with perturbative-QCD calculations and lie at the upper edge of the theoretical bands.
Tax evasion is a pervasive problem in many countries. In particular, some developing countries do not collect even half of what they would if taxpayers complied with the written letter of the law. ...The academic literature has not been oblivious to the need to explain why people pay (or do not pay) taxes. However, the empirical literature has not yet reached consensus. This paper reports the results of a large field experiment that tried to affect compliance by influencing property tax taxpayers' beliefs regarding the levels of enforcement, reciprocity, and peer-effects of the tax system in a municipality in Argentina. Results indicate that those taxpayers that received the deterrence message have a higher probability (almost 5 percentage points) to comply than the taxpayers in the control group. No average effects are found for the other two treatments. However, this average effects masks important results. After receiving the reciprocity and the peer-effects messages, the probability of compliance increased for some taxpayers but it decreased for others according to their underlying distribution of beliefs. The evidence in this paper advances the state of knowledge, may help to reconcile some of the results in the literature, and provides the basis for advancing policies and research on tax compliance in developing countries.
The strong nuclear interaction is probed at short-distance and high-momenta using new measurements of the $^{12}$C$(e,e'p)$ and $^{12}$C$(e,e'pn)$ reactions, at high-$Q^2$ and $x_B>1$. The data span ...a missing-momentum range of 300-850 MeV/c and is predominantly sensitive to the dominant proton-neutron short-range correlated (SRC) pairs and complements previous $^{12}$C$(e,e'pp)$ measurements. The data are well reproduced by theoretical calculations using the Generalized Contact Formalism with both chiral and phenomenological nucleon-nucleon ($NN$) interaction models. This agreement, observed here for the first time, suggests that the measured high missing-momentum protons up to $850$ MeV/c belonged to SRC pairs. The measured $^{12}$C$(e,e'pn)$ / $^{12}$C$(e,e'p)$ ratio is consistent with a decrease in the fraction of proton-neutron SRC pairs with increasing missing-momentum. This confirms the transition from an isospin-dependent tensor $NN$ interaction at $\sim 400$ MeV/c to an isospin-independent scalar interaction at high-momentum around $\sim 800$ MeV/c.
We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is ...broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α5) with negligible numerical uncertainty. The electroweak contribution is suppressed by (mμ∕MW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α2) and is due to hadronic vacuum polarization, whereas at O(α3) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aμSM=116591810(43)×10−11 and is smaller than the Brookhaven measurement by 3.7σ. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future – which are also discussed here – make this quantity one of the most promising places to look for evidence of new physics.
•In an artefactual field experiment, we study physicians’ response to incentives.•Physicians’ behavior is compared with medical and non-medical students in the lab.•All subject groups provide more ...services under fee-for-service compared to capitation.•Our findings are robust regarding subjects’ gender, age, and personal traits.
We analyze how physicians, medical students, and non-medical students respond to financial incentives from fee-for-service and capitation. We employ a series of artefactual field and conventional lab experiments framed in a physician decision-making context. Physicians, participating in the field, and medical and non-medical students, participating in lab experiments, respond to the incentives in a consistent way: Significantly more medical services are provided under fee-for-service compared to capitation. The intensity by which subjects respond to incentives, however, differs by subject pool. Our findings are robust regarding subjects’ gender, age, and personality traits.
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