Measurement of the F2 structure function in deep inelastic e+^{+}p scattering using 1994 data from the ZEUS detector at HERA

We present measurements of the structure function \Ft\ in e^+p scattering at HERA in the range 3.5\;\Gevsq < \qsd < 5000\;\Gevsq. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At \qsd < 35 \;\Gevsq the range in x now spans 6.3\cdot 10^{-5} < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q^2 above 1000 GeV^2 the x range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic urray, W

Comparison of ZEUS data with standard model predictions for e+p→e+Xe^+ p \rightarrow e^+ X scattering at high xx and Q2Q^2

Using the ZEUS detector at HERA, we have studied the reaction e(+)p --> e(+)X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1993 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2. two events are observed while 0.145 +/- 0.013 events are expected, A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q(2) cut. For x > 0.55 and y > 0.75, four events are observed where 0.91 +/- 0.08 events are expected, A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q(2) > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region

Measurement of Elastic ϕ\phi Photoproduction at HERA

The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+} \phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \ \rm{GeV^2}$has been studied with the ZEUS detector at HERA. The differential$\phi$photoproduction cross section$d\sigma/dt$has an exponential shape and has been determined in the kinematic range$0.1<|t|<0.5 \ \rm{GeV^2}$and$60 < W < 80 \ \rm{GeV}$. An integrated cross section of$\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$$\rm{\mu b}$has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both$\sigma_{\gamma p \rightarrow \phi p}$and the slope of the$t$distribution. The$\phi$decay angular distributions are consistent with$s$-channel helicity conservation. From lower energies to HERA energies, the features of$\phi$ photoproduction are compatible with those of a soft diffractive process.Comment: 23 pages, including 6 post script figure

Examining the Psychobiology of Callous-Unemotional Traits

Callous-unemotional (CU) traits (e.g., lack of empathy, deficient guilt/remorse, and shallow affect) are a risk factor for delinquent behavior. Youth high in CU traits exhibit a range of cognitive and emotional deficits, such as fearlessness, insensitivity to punishment, and reward dependency, that predispose them to antisocial behavior and justice system involvement. This two-part dissertation study sought to better understand how CU traits predispose youth to delinquent behavior by examining the hormones thought to underlie these emotional and cognitive deficits. Employing a sample of 55 justice-involved male youth recruited from an ongoing longitudinal study of first-time juvenile offenders, Study One examined the association between CU traits, adverse experiences (prior exposure to violence and hostile parent-child relationships), and cortisol and alpha-amylase reactivity. The results indicate that individuals with elevated levels of CU traits exhibit lower cortisol reactivity than their counterparts. However, they exhibited the same pattern of alpha-amylase reactivity. In addition, prior adversity did not moderate the association between CU traits and either indicator of stress reactivity. Study Two tested whether cortisol and testosterone mediated the association between CU traits, reward and punishment sensitivity, and risk taking. Unfortunately, the study was underpowered and could not determine whether there was a direct or indirect association between CU traits, risk taking, or reward/punishment sensitivity. However, the study provided evidence that individuals with high CU traits exhibited the same pattern of testosterone reactivity as their counterparts. Taken together, the results of the two studies suggest youth with elevated levels of CU traits exhibit a pattern of stress reactivity that may contribute to their behavior. Future research should continue to explore the relation between stress reactivity, CU traits, and other aspects of antisocial behavior, such as aggression and retaliation

Examining the Psychobiology of Callous-Unemotional Traits

Callous-unemotional (CU) traits (e.g., lack of empathy, deficient guilt/remorse, and shallow affect) are a risk factor for delinquent behavior. Youth high in CU traits exhibit a range of cognitive and emotional deficits, such as fearlessness, insensitivity to punishment, and reward dependency, that predispose them to antisocial behavior and justice system involvement. This two-part dissertation study sought to better understand how CU traits predispose youth to delinquent behavior by examining the hormones thought to underlie these emotional and cognitive deficits. Employing a sample of 55 justice-involved male youth recruited from an ongoing longitudinal study of first-time juvenile offenders, Study One examined the association between CU traits, adverse experiences (prior exposure to violence and hostile parent-child relationships), and cortisol and alpha-amylase reactivity. The results indicate that individuals with elevated levels of CU traits exhibit lower cortisol reactivity than their counterparts. However, they exhibited the same pattern of alpha-amylase reactivity. In addition, prior adversity did not moderate the association between CU traits and either indicator of stress reactivity. Study Two tested whether cortisol and testosterone mediated the association between CU traits, reward and punishment sensitivity, and risk taking. Unfortunately, the study was underpowered and could not determine whether there was a direct or indirect association between CU traits, risk taking, or reward/punishment sensitivity. However, the study provided evidence that individuals with high CU traits exhibited the same pattern of testosterone reactivity as their counterparts. Taken together, the results of the two studies suggest youth with elevated levels of CU traits exhibit a pattern of stress reactivity that may contribute to their behavior. Future research should continue to explore the relation between stress reactivity, CU traits, and other aspects of antisocial behavior, such as aggression and retaliation

The Differential Influence of Absent and Harsh Fathers on Juvenile Delinquency

Father absence has been identified as a key contributor to juvenile delinquency. As a result, many politicians and community leaders are making the effort to re-engage fathers. However, it is possible that merely the presence of fathers is not, in itself, a substantial protective factor and, in some cases, can even be more detrimental than father absence. The present study (a) examines differential effects of absent fathers and harsh fathers on delinquent behavior, and (b) determines whether these fathers have an effect on youth behavior after accounting for the mother-child relationship. This study employs a diverse (48.4% Black, 37.3% Latino, 12.6% White, and 1.7% other race) sample of first-time male juvenile offenders who identified their father as absent (N=291) or harsh (N=58). Results indicate that youth with harsh fathers reported committing a greater number of offenses and using a greater number of substances than youth with absent fathers. This difference exists even after controlling for the quality of the mother-child relationship. Implications of these findings for future research and delinquency prevention programs are discussed

Aspirations, expectations and delinquency: the moderating effect of impulse control

Although prior research finds a robust link between delinquent behavior and expectations, or an adolescent’s perceived likelihood of obtaining one’s future goals, fewer studies have evaluated aspirations, or the perceived importance of achieving one’s goals. In addition, few studies consider how individual traits such as impulsivity affect the degree to which expectations and aspirations motivate or deter delinquent behavior. We contribute to this body of research by evaluating the independent effects of expectations and aspirations, and the aspiration-expectation gap (i.e., strain) on delinquent behavior during the year following an adolescent’s first arrest using a large (N = 1117), racially/ethnically diverse sample of male adolescents (46.55% Latino, 35.81% Black, 14.95% White, and 2.69% Other race). In addition, we considered how impulse control interacts with expectations, aspirations, and strain to motivate behavior. Our results indicated that both aspirations, expectations and strain uniquely influence criminal behavior. Importantly, aspirations interacted with impulse control, such that aspirations affected delinquency only among youth with higher impulse control. Our findings suggest that aspirations may only influence behavior if youth also have the psychosocial capabilities to consider their future aspirations when behaving in the present

The differential influence of absent and harsh fathers on juvenile delinquency

Researchers have identified father absence as a contributor to juvenile delinquency. Consequently, politicians and community leaders are making efforts to re-engage fathers. However, it is possible that the presence of fathers is not, in itself, a substantial protective factor and, in some cases, can even be more detrimental than father absence. Employing a diverse sample of male juvenile offenders in the U.S. (ages 13–17), the present study examined the differential effects of absent fathers and harsh fathers on delinquency. Results indicated that youth in the harsh-father group engaged in more offending behaviors and used more substances than youth in the absent-father group. This difference remained even after controlling for the mother-child relationship. Implications of these findings for future research and delinquency prevention programs are discussed