Low Q2 Research Articles

LOW Q2 KAON ELECTROPRODUCTION

A measurement of the H(e, e′ K+) reaction was performed at Hall A, TJNAF as part of the hypernuclear experiment E94-107. Data was taken at very low Q2 (~ 0.07 ( GeV /c)2) and W = 2.2 GeV . Kaons were detected along the direction of [Formula: see text], the momentum transferred by the incident electron (θCM = 6°). These measurements provide data about the Σ0/Λ ratio which drops rapidly with Q2, the angular dependence of the cross sections as Q2 → 0, and the dependence of the cross section with respect to Q2 ,W and θCM. The dependence of the cross section at very forward angles has been poorly known. Available models are inadequate to describe the results. The measurement of the elementary cross section will constrain models for the elementary reaction which are inadequate to describe these results. It is also a key ingredient in the hypernuclear spectroscopy studies performed at the same kinematics. Details of the calculations and results will be shown.

Role of mesons in the electromagnetic form factors of the nucleon

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as “charge distributions,” nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment–theory comparisons.15 MoreReceived 29 January 2010DOI:https://doi.org/10.1103/PhysRevC.82.045211©2010 American Physical Society

Design and verification of a 10-bit 1.2-V 100-MSPS D/A IP core based on a 0.13-μm low power CMOS process

Based on a low supply voltage curvature-compensated bandgap reference and central symmetry Q2 random walk NMOS current source layout routing method, a 1.2-V 10-bit 100-MSPS CMOS current-steering digital-to-analog converter is implemented in a SMIC 0.13-μm CMOS process. The total consumption is only 10 mW from a single 1.2-V power supply, and the integral and differential nonlinearity are measured to be less than 1 LSB and 0.5 LSB, respectively. When the output signal frequency is 1–5 MHz at 100-MSPS sampling rate, the SFDR is measured to be 70 dB. The die area is about 0.2 mm2.

Low Q2 proton structure function, using gluon and pseudoscalar meson clouds in the constituent quark framework

The idea of the meson cloud approach in the chiral quark model has been extended to include a gluon cloud in order to model the parton densities in the nucleon, based on the constituent quark framework. The splitting functions of a quark to quark–meson and quark–gluon at low Q2 values are used to obtain parton densities in the constituent quark approach. The phenomenological constituent model is employed to extract the parton distributions in the proton. Since we have access to the parton densities at low Q2, we are able to obtain the F2(x, Q2) structure function at low Q2 values. The result is in good agreement with the available experimental data and some theoretical models. To confirm the validity of our calculations, the fraction of the total momentum of the proton which is carried by gluons at high Q2 and the Gottfried sum rule are computed. The results are in good agreement with those expected.

Valence quark contributions for theγN→P11(1440)form factors

Using a covariant spectator quark model we estimate valence quark contributions to the F1*(Q2) and F2*(Q2) transition form factors for the gamma N -> P11(1440) reaction. The Roper resonance, P11(1440), is assumed to be the first radial excitation of the nucleon. The present model requires no extra parameters except for those already fixed by the previous studies for the nucleon. Our results are consistent with the experimental data in the high Q2 region, and those from lattice QCD. We also estimate the meson cloud contributions, focusing on the low Q2 region, where they are expected to be dominant.

Constraining WIMP magnetic moment from CDMS II experiment

We consider a degenerate or a nearly degenerate dark matter sector where a sizable magnetic moment of a (almost) Dirac type neutral dark matter candidate N is anticipated. Then, due to soft photon exchange, the cross-section in direct detection of N can be enhanced at low Q2 region. We discuss the implication of this type of models in view of the recent CDMS II report.

Deviations from NLO QCD evolution in inclusive HERA data

We search for deviations from next-to-leading order QCD evolution in HERA structure function data. We compare to data predictions for structure functions in the small x region, obtained by evolving backwards to low Q2 the results of a parton fit performed in the large Q2 region, where fixed-order perturbative QCD is certainly reliable. We find evidence for deviations which are qualitatively consistent with the behaviour predicted by small x perturbative resummation, and possibly also by non-linear evolution effects, but incompatible with next-to-next-to-leading order corrections.

Time-like proton form factor measurement with P̄ANDA

The electromagnetic probe is an excellent tool to investigate the structure of the nucleon. The nearly 4π detector PANDA, will allow to make a precise determination of the electromagnetic form factors of the proton in the time-like region with unprecedented precision. In the one-photon exchange approximation, the center of mass unpolarized differential cross section of the reaction p̄p → e+e− is a linear combination of the squared moduli of the electric GE and magnetic GM proton form factors. The precise measurement of the angular distribution over almost full angular range then directly gives these quantities. At present only two experiments have provided the ratio R = |GE|/|GM| but with large statistical uncertainties. It is shown that with strict PID cuts and a kinematic fit, the dominant background, p̄p → π+π−, can be supressed to much less than 1% of the signal, without affecting the extraction of the ratio R. P̄ANDA will therefore offer a unique opportunity to measure the ratio with a precision ranging from <1% at low q2 up to 30% for q2 = 14 (GeV/c)2.

Measurement of the inclusive ep scattering cross section at low Q2 and x at HERA

A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV^2 < Q^2 < 12 GeV^2, and low Bjorken x, 5x10^-6 < x < 0.02. The result is based on two data sets collected in dedicated runs by the H1 Collaboration at HERA at beam energies of 27.6 GeV and 920 GeV for positrons and protons, respectively. A combination with data previously published by H1 leads to a cross section measurement of a few percent accuracy. A kinematic reconstruction method exploiting radiative ep events extends the measurement to lower Q^2 and larger x. The data are compared with theoretical models which apply to the transition region from photoproduction to deep inelastic scattering.

A concept for the experimental determination of the nucleon electric to magnetic form factor ratio at very low Q2

Stationary target measurements of the nucleon form factors have been performed with high precision down to Q2 of ∼ 0.01 GeV2 for protons (GEp) and down to ∼ 0.1 GeV2 for neutrons (GMn). Conventional extraction using cross section and polarization measurement cannot be extended to very low values of Q2 due to inherent experimental limitations. We present a proposal for a new approach to a measurement, using colliding beams, which will extend the range of possible measurement at low Q2 by several orders of magnitude over stationary target limits.

A 3D‐QSAR Study of Celebrex‐Based Pdk1 Inhibitors Using Comfa Method

AbstractA 3D‐QSAR study of celebrex‐based compounds of PDK1 inhibitors using comparative molecular field analysis (CoMFA) was carried out. The structures of the compounds were obtained using quantum chemistry calculation. CoMFA calculations for a number of grouped subsets of compounds gave q2 values of correlation in the range from 0 to 0.8. The low q2 values should be mainly due to the narrow span of biological activity. Calculations for several subsets of 11–13 compounds gave high q2 values, with 0.5–0.8. Factors affecting the results of the calculations are discussed. Calculated results with high q2 values suggest that further chemical modifications of the compounds could lead to enhanced activity and could be an aid in the design of celebrex‐based cancer drugs.

HADRON PHYSICS AT ELSA

Excitation of the nucleon at low Q2 and energies up to several GeV reveals clearly measurable structures that indicate the existance of resonances. A major goal of experiments carried out at the accelerator facility ELSA in Bonn/Germany is to explore this resonance structure, which gives valuable input to models describing the QCD structure of the nucleon. Resonance contributions for nuclear reaction channels, such as single pion, two pion and eta production from the experiments can be given using the Bonn-Gatchina partial wave analysis1. The talk at the conference MESON 2008 in Krakow gave an overview of results from experiments at ELSA and plans for the near future.

On the perturbative stability of the QCD predictions for the ratio R=F L /F T in heavy-quark leptoproduction

We analyze the perturbative and parametric stability of the QCD predictions for the Callan–Gross ratio, R(x,Q 2)=F L /F T , in heavy-quark leptoproduction. We consider the radiative corrections to the dominant photon–gluon fusion mechanism. In various kinematic regions, the following contributions are investigated: exact NLO results at low and moderate Q 2≲m 2, asymptotic NLO predictions at high Q 2≫m 2, and both NLO and NNLO soft-gluon (or threshold) corrections at large Bjorken variable x. Our analysis shows that large radiative corrections to the structure functions F T (x,Q 2) and F L (x,Q 2) cancel each other in their ratio R(x,Q 2) with good accuracy. As a result, the NLO contributions to the Callan–Gross ratio are less than 10% in a wide region of the variables x and Q 2. We provide compact LO predictions for R(x,Q 2) in the case of low x ≪1. A simple formula connecting the high-energy behavior of the Callan–Gross ratio and low-x asymptotics of the gluon density is derived. It is shown that the obtained hadron-level predictions for R(x→0,Q 2) are stable under the DGLAP evolution of the gluon distribution function. Our analytic results simplify the extraction of the structure functions F 2 (x,Q 2) and F 2 (x,Q 2) from measurements of the corresponding reduced cross sections, in particular at DESY HERA.

Measurement of Leptonic Structure Functions with the L3 detector at LEP

We report on a measurement of dimuon events obtained in a sample of single-tagged two photon events, at low Q2, between 0.2 GeV2 and 0.85 GeV2. The data were recorded by the L3 detector at LEP at center of mass energies between 189 GeV and 206 GeV. Production cross-sections and the leptonic structure functions will be presented.

Charged pion form factor betweenQ2=0.60and2.45 GeV2. II. Determination of, and results for, the pion form factor

The charged pion form factor, Fπ(Q2), is an important quantity that can be used to advance our knowledge of hadronic structure. However, the extraction of Fπ from data requires a model of the 1H(e,e'π+)n reaction and thus is inherently model dependent. Therefore, a detailed description of the extraction of the charged pion form factor from electroproduction data obtained recently at Jefferson Lab is presented, with particular focus given to the dominant uncertainties in this procedure. Results for Fπ are presented for Q2=0.60−2.45 GeV2. Above Q2=1.5 GeV2, the Fπ values are systematically below the monopole parametrization that describes the low Q2 data used to determine the pion charge radius. The pion form factor can be calculated in a wide variety of theoretical approaches, and the experimental results are compared to a number of calculations. This comparison is helpful in understanding the role of soft versus hard contributions to hadronic structure in the intermediate Q2 regime.4 MoreReceived 11 July 2008DOI:https://doi.org/10.1103/PhysRevC.78.045203©2008 American Physical Society

Determination of the effective strong coupling constant [formula omitted] from CLAS spin structure function data

We present a new extraction of the effective strong coupling constant αs,g1(Q2). The result agrees with a previous determination and extends the measurement of the low and high Q2 behavior of αs,g1(Q2) that was previously deduced from sum rules. In particular, it experimentally verifies the lack of Q2-dependence of αs,g1(Q2) in the low Q2 limit. This fact is necessary for application of the AdS/CFT correspondence to QCD calculations. We provide a parameterization of αs,g1(Q2) that can equivalently be used to parameterize the Q2-dependence of the generalized Gerasimov–Drell–Hearn and Bjorken sums.

Effect of Dispersion Condition of Calcium Carbonate on the Crystallization and Melting Behavior of Polypropylene/CaCO3 Nanocomposites

Polypropylene/calcium carbonate (PP/CaCO3) nanocomposites were prepared by melt compounding (C-1) and novel compounding process (C-2), respectively. Scanning electronic microscope (SEM) results illustrated that CaCO3 nanoparticles were well dispersed at nanoscale in C-2, whereas the nanoparticles were mostly aggregate in C-1. Differential scanning calorimetry (DSC) measurements indicated the onset crystallization temperature was increased by 11.4°C and the supercooling wasdecreased by 13.68°C in C-2. A faster crystallization rate, a higher melting point, and a higher degree of crystallization in C-2 were also detected. Polarization light microscope (PLM) photographs showed the spherulites sizes of C-2 were 60 mm, whereas common spherulites with an average size of about 200 mm were observed in both pure PP and C-1. These phenomena demonstrated that the well-dispersed CaCO3 nanoparticles could result in heterogeneous nucleation effect on PP even at quite low loading Q2 (1.5% wt.).

Two-Photon-Exchange andγZ-Exchange Corrections to Parity-Violating Elastic Electron-Proton Scattering

Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and gammaZ-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of gammaZ exchange is in general larger than that of TPE, especially at low momentum transfer Q2</=1 GeV2. Their combined effects on the values of G(E)s + beta G(M)s [corrected] extracted in recent experiments can be as large as -40% in certain kinematics.

The low Q2 behavior of the extended Gerasimov-Drell-Hearn sum rule

The low Q2 behavior of the extended Gerasimov-Drell-Hearn sum rule

Experimental determination of the effective strong coupling constant

We present a first attempt to experimentally extract an effective strong coupling constant that we define to be a low Q2 extension of a previous definition by S. Brodsky et al. following an initial work of G. Grunberg. Using Jefferson Lab data and sum rules, we establish its Q2-behavior over the complete Q2-range. The result is compared to effective coupling constants inferred from different processes and to calculations based on Schwinger–Dyson equations, hadron spectroscopy or lattice QCD. Although the connection between the experimentally extracted effective coupling constants and the calculations is not established it is interesting to note that their behaviors are similar.