The quark structure of the f2 (1270) meson has, for many years, been assumed to be a pure quark-antiquark (qq) resonance with quantum numbers JPC = 2++. Recently, it was proposed that the f2 (1270) ...is a molecular state made from the attractive interaction of two ρ mesons. Such a state would be expected to decay strongly to final states with charged pions due to the dominant decay ρ → π+π−, whereas decay to two neutral pions would likely be suppressed. Here, we measure for the first time the reaction γp → π0π0p, using the CEBAF Large Acceptance Spectrometer detector at Jefferson Lab for incident beam energies between 3.6 and 5.4 GeV. Differential cross sections, dσ/dt, for f2 (1270) photoproduction are extracted with good precision due to low backgrounds and are compared to theoretical calculations.
The first results on the σLT' structure function in exclusive π0p electroproduction at invariant masses of the final state of 1.5 GeV < W < 1.8 GeV and in the range of photon virtualities 0.4 GeV2 < ...Q2 < 1.0 GeV2 were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments deter- mined from the σLT' structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries in π0p electroproduction extend the opportunities for the extraction of the nucleon resonance electroexcitation amplitudes in the mass range above 1.6 GeV.
The integrated cross sections of the
ep
→
e
π
+
n
,
ep
→
e
π
0
p
,
ep
→
eK
+
Λ, and
ep
→
eK
+
Σ
0
reactions are evaluated in the energy range of nucleon resonance excitation at photon virtualities
Q
...2
from 5 to 12 GeV
2
. These exclusive channels will be explored at photon virtualities
Q
2
> 5 GeV
2
for the first time in future experiments with the CLAS12 detector. The cross-section evaluation is based on the extrapolation of exclusive contributions to the inclusive structure functions
F
1
and
F
2
from a region of
Q
2
< 5 GeV
2
, in which the experimental data are available, to the region of higher
Q
2
. This evaluation of cross sections is of particular importance in the development of the program of experiments with the CLAS12 detector for studying the structure of the ground and excited nucleon states, which may reveal the dynamics of strong interactions in the nonperturbative regime.
This White Paper aims at highlighting the important benefits in the science reach of the EIC. High luminosity operation is generally desirable, as it enables producing and harvesting scientific ...results in a shorter time period. It becomes crucial for programs that would require many months or even years of operation at lower luminosity.
The double-polarization observable $E$ was studied for the reaction $\gamma p\to p\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator ...Facility and the longitudinally-polarized frozen-spin target (FROST). The observable was measured from the charged decay mode of the meson, $\omega\to\pi^+\pi^-\pi^0$, using a circularly-polarized tagged-photon beam with energies ranging from the $\omega$ threshold at 1.1 to 2.3 GeV. A partial-wave analysis within the Bonn-Gatchina framework found dominant contributions from the $3/2^+$ partial wave near threshold, which is identified with the sub-threshold $N(1720)\,3/2^+$ nucleon resonance. To describe the entire data set, which consisted of $\omega$ differential cross sections and a large variety of polarization observables, further contributions from other nucleon resonances were found to be necessary. Here, with respect to non-resonant mechanisms, $\pi$ exchange in the $t$-channel was found to remain small across the analyzed energy range, while pomeron $t$-channel exchange gradually grew from the reaction threshold to dominate all other contributions above $W \approx 2$ GeV.
We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off 4He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV ...longitudinally polarized electron beam incident on a pressurized 4He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling 4He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e4 He $~\to~e'p'γ'X')$ asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only 4He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.
We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off $^4$He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV ...longitudinally polarized electron beam incident on a pressurized $^4$He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling $^4$He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent ($e^4$He$~\to~e'$$^4$He$'\gamma'$) beam spin asymmetries compared to those observed on the free proton, while the incoherent ($e^4$He$~\to~e'$p$'\gamma'$X$'$) asymmetries exhibit a 30$\%$ suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only $^4$He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.
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