May 9, 2003
We have measured the nuclear transparency of the fundamental process $\gamma$ n $\to \pi^-$ p in $^4$He. These measurements were performed at Jefferson Lab in the photon energy range of 1.6 to 4.5 GeV and at $\theta^{\pi}_{cm}= 70^\circ$ and $90^\circ$. These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. The transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations which include the quantum chromodynamics phenomenon of color transparency.
Similar papers 1
March 23, 2023
The transparency of the hadrons produced in the $\gamma (n,p) \pi^-$ reaction in nuclei is calculated using the Glauber model modified by including the Fermi motion of the nucleon in the nucleus. Since the calculated results underestimates the measured transparency for $^4$He nucleus, the Glauber model is further modified by incorporating the short-range correlation of the nucleon and the color transparency of the hadron in the nucleus. The nuclear transparency of the $\gamma...
January 11, 2007
We present a relativistic and cross-section factorized framework for computing nuclear transparencies extracted from A(\gamma,\pi N) reactions at intermediate energies. The proposed quantummechanical model adopts a relativistic extension to the multiple-scattering Glauber approximation to account for the final state interactions of the ejected nucleon and pion. The theoretical predictions are compared against the experimental ^4He(\gamma,p \pi^-) data from Jefferson Lab. For ...
July 10, 2007
We have measured the nuclear transparency of the A(e,e' pi^+) process in ^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the super-ratio of $(\sigma_A/\sigma_H)$ from data to a model of pion-electroproduction from nuclei without pi-N final state interactions. The Q^2 and atomic number dependence of ...
August 17, 2012
Color transparency is the vanishing of nuclear initial or final state interactions involving specific reactions. The reasons for believing that color transparency might be a natural consequence of QCD are reviewed. The main impetus for this talk is recent experimental progress, and this is reviewed briefly.
October 25, 2007
A relativistic and quantum mechanical framework to compute nuclear transparencies for pion photo- and electroproduction reactions is presented. Final-state interactions for the ejected pions and nucleons are implemented in a relativistic eikonal approach. At sufficiently large ejectile energies, a relativistic Glauber model can be adopted. At lower energies, the framework possesses the flexibility to use relativistic optical potentials. The proposed model can account for the ...
August 28, 1996
Color transparency is the vanishing of initial and final state interactions, predicted by QCD to occur in high momentum transfer quasielastic nuclear reactions. For specific reactions involving nucleons, the initial and final state interactions are expected to be dominated by exchanges of pions. We argue that these interactions are also suppressed in high momentum transfer nuclear quasielastic reactions; this is ``chiral transparency". We show that studies of the $e ^3He \to ...
January 2, 2016
We argue that the observation of the color transparency effect in the semiexclusive $A(\pi^-,l^+ l^-)$ process is important for determining whether it is possible to extract the generalized parton distributions of the nucleon from the elementary reaction $\pi^- p \to l^+ l^- n$ at $p_{\rm lab}=15-20$ GeV/c at small $|t|$ and large invariant mass of the dilepton pair $l^+ l^-$. Assuming that the transverse size of the pionic $q \bar q$ pair in the hard interaction point is sim...
August 19, 2008
We investigate the early onset of pionic color transparency ($\pi$CT) observed at Jefferson Laboratory (JLAB) in semi--exclusive pion electroproduction reaction $A(e,e'\pi^+)$ off nuclei. In the present description the primary $\gamma^*p \to \pi^+ n$ interaction is described very well both for the longitudinal and the transverse polarizations. For the final state interactions a coupled--channel treatment of the interactions of transmitted hadrons allows to go beyond the Glaub...
September 22, 1995
The current status of the theory of and the experimental evidence for color transparency are reviewed. The problems with interpretation of quasielastic scattering on nuclei are discussed to some detail.
January 19, 1995
The Glauber approximation is used to calculate the contribution of nucleon correlations in high-energy $A(e,e'N)$ reactions. When the excitation energy of the residual nucleus is small, the increase of the nuclear transparency due to correlations between the struck nucleon and the other nucleons is mostly compensated by a decrease of the transparency due to the correlations between non detected nucleons. We derive Glauber model predictions for nuclear transparency for the dif...