Search Results (13 total)

Previous research [S. J. Pollock , Phys. Rev. ST Phys. Educ. Res. 3, 1 (2007)] showed that despite the use of interactive engagement techniques, the gap in performance between males and females on a conceptual learning survey persisted from pretest to post-test at the University of Colorado at Boulder. Such findings were counter to previously published work [M. Lorenzo , Am. J. Phys. 74, 118 (2006)]. This study begins by identifying a variety of other gender differences. There is a small but significant difference in the course grades of males and females. Males and females have significantly different prior understandings of physics and mathematics. Females are less likely to take high school physics than males, although they are equally likely to take high school calculus. Males and females also differ in their incoming attitudes and beliefs about physics. This collection of background factors is analyzed to determine the extent to which each factor correlates with performance on a conceptual post-test and with gender. Binned by quintiles, we observe that males and females with similar pretest scores do not have significantly different post-test scores (p>0.2). The post-test data are then modeled using two regression models (multiple regression and logistic regression) to estimate the gender gap in post-test scores after controlling for these important prior factors. These prior factors account for about 70% of the observed gender gap. The results indicate that the gender gap exists in interactive physics classes at our institution but is largely associated with differences in previous physics and math knowledge and incoming attitudes and beliefs.

While it is well known which curricular practices can improve student performance on measures of conceptual understanding, the sustaining of these practices and the role of faculty members in implementing these practices are less well understood. We present a study of the hand-off of Tutorials in Introductory Physics [McDermott and Schaffer (Prentice-Hall, Upper Saddle River, NJ, 2002)] from initial adopters to other instructors at the University of Colorado, including traditional faculty not involved in physics educational research. The study examines the impact of implementation of tutorials on student conceptual learning across ten first-semester, and seven second-semester courses, for 15 faculty members over 13 semesters, and includes roughly 5000 students. It is possible to demonstrate consistently high, and statistically indistinguishable, student learning gains for different faculty members; however, such results are not the norm and appear to rely on a variety of factors. Student performance varies by faculty background—faculty involved in, or informed by physics education research, consistently post higher student learning gains than less-informed faculty. Student performance in these courses also varies by curricula used—all semesters in which the research-based Tutorials and learning assistants are used have higher student learning gains than those semesters that rely on nonresearch-based materials and do not employ learning assistants.

Previous research [Lorenzo , Am. J. Phys. 74, 118 (2006)] demonstrated that the difference in performance between male and female students can be reduced and even eliminated, in consistent fashion, by using interactive engagement techniques in the introductory physics classroom. The present paper describes similar studies in a different, large research university and finds that the use of interactive engagement techniques does not necessarily reduce the gender gap. Furthermore, in the environments studied, there is a gap in learning gains between male and female students (p<0.01) whether partially or fully interactive classroom techniques are used. Our findings suggest that engaging students in interactive educational environments is not sufficient to reduce the gender gap, and we find instances where despite significant learning gains by all students, the gender gap is increased. There is indication that there are both student and instructor effects that impact the gender gap, which are the subjects of ongoing studies.

We report a detailed study of the implementation of Tutorials in Introductory Physics at a large-scale research institution. Based on two successive semesters of evaluation, we observe students’ improved conceptual mastery (force and motion concept evaluation median normalized gain 0.77, N=336), albeit with some student discontent. We replicate the results of original studies of tutorial effectiveness and document how and why these results occur. Additionally, using the Colorado Learning Attitudes about Science Survey we measure the support of students’ expertlike beliefs about learning physics in our environment. We examine this implementation from a viewpoint that emphasizes varying contextual levels of this implementation, from students’ engagement in individual tasks, to the situations in which these tasks are embedded, to the broader classroom, departmental, and educational structures. We document both obvious and subtle features that help ensure the successful implementation of these reforms.

Parity violating electron nucleus scattering is a clean and powerful tool for measuring the spatial distributions of neutrons in nuclei with unprecedented accuracy. Parity violation arises from the interference of electromagnetic and weak neutral amplitudes, and the Z⁰ of the standard model couples primarily to neutrons at low Q². The data can be interpreted with as much confidence as electromagnetic scattering. After briefly reviewing the present theoretical and experimental knowledge of neutron densities, we discuss possible parity violation measurements, their theoretical interpretation, and applications. The experiments are feasible at existing facilities. We show that theoretical corrections are either small or well understood, which makes the interpretation clean. The quantitative relationship to atomic parity nonconservation observables is examined, and we show that the electron scattering asymmetries can be directly applied to atomic parity nonconservation because the observables have approximately the same dependence on nuclear shape.

We examine isospin breaking in the nucleon wave functions due to the u-d quark mass difference and the Coulomb interaction among the quarks, and their consequences on the nucleon electroweak form factors in a nonrelativistic constituent quark model. The mechanically induced isospin breaking in the nucleon wave functions and electroweak form factors are exactly evaluated in this model. We calculate the electromagnetically induced isospin admixtures by using first-order perturbation theory, including the lowest-lying resonance with nucleon quantum numbers but isospin 3/2. We find a small (≤ 1%), but finite correction to the anomalous magnetic moments of the nucleon stemming almost entirely from the quark mass difference, while the static nucleon axial coupling remains uncorrected. Corrections of the same order of magnitude appear in charge, magnetic, and axial radii of the nucleon. The correction to the charge radius in this model is primarily isoscalar, and may be of some significance for the extraction of the strangeness radius from, e.g., elastic forward angle parity violating electron-proton asymmetries, or elastic ⁴He(e,e′) experiments.

There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.

We calculate the neutrino and antineutrino elastic scattering cross section on unpolarized deuterons at energies from a few MeV to several GeV and squared momentum transfers up to 5 GeV². These cross sections can be used to deduce the unknown weak SU(2) isoscalar and SU(3) flavor-scalar axial-vector coupling to nucleons. This observable can be related to the strangeness axial-vector matrix element in the absence of QCD radiative or isospin-violating corrections. We show that the unknown weak magnetic vector coupling may also be gleaned from these measurements. We use different techniques at different energies, including light-cone impulse approximation at the highest energies, and show that they connect smoothly to each other.

We consider the effect of strong-vertex form factors on the gauge invariance of Born diagrams for the pion photoproduction reaction. The minimal-substitution prescription of Ohta for the electromagnetic current operator in pion photoproduction yields the same result as the simplest Born approach for one particular invariant amplitude. This is incompatible with recipes that multiply the Born amplitude by an overall form factor.

We consider elastic electroweak lepton-deuteron scattering as a means to extract information on both vector and axial-vector isoscalar currents, and thus the strange- (and heavier-) quark content of the deuteron. Parity violation in electron-deuteron scattering is examined in some detail. Numerical estimates are made, using a simple model when required, to find the sensitivity to strange-quark components of the various form factors. We find that backward angles are in general best to isolate axial-vector and magnetic vector components. Figures of merit relevant to future experiments are given, using existing limits on s-quark contributions to nucleon form factors where possible.

We consider popular extensions of the standard model which include new heavy Z⁰ gauge bosons, and examine their effect on parity violation in elastic electron-proton scattering at intermediate energies. These extensions all involve an effective low-energy symmetry group SU(3)_C⊗SU(2)_L ⊗U(1)_Y⊗(U)1_Y’. In several special cases motivated by grand unified theories based on SO(10) and E₆, we find that a parity measurement with an accuracy of a few percent would raise the existing mass bounds on a heavy Z⁰, and would reduce the range of allowed mixing angles by as much as a factor of 5. In some cases, the lower bound on a heavy Z⁰ mass would be raised by more than 100 GeV over current limits.