arXiv subjects

P. Camerini

Publications and source records attributed to P. Camerini.

23 records · Page 2Linked to original sources

arXiv2005

pi+- p differential cross sections at low energies

Differential cross sections for pi- p and pi+ p elastic scattering were measured at five energies between 19.9 and 43.3 MeV. The use of the CHAOS magnetic spectrometer at TRIUMF, supplemented by a range telescope for muon background suppression, provided simultaneous coverage of a large part of the full angular range, thus allowing very precise relative cross section measurements. The absolute normalisation was determined with a typical accuracy of 5 %. This was verified in a simultaneous measurement of muon proton elastic scattering. The measured cross sections show some deviations from phase shift analysis predictions, in particular at large angles and low energies. From the new data we determine the real part of the isospin forward scattering amplitude.

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arXiv2005

The pi -> pi pi process in nuclei and the restoration of chiral symmetry

The results of an extensive campaign of measurements of the pi -> pi pi process in the nucleon and nuclei at intermediate energies are presented. The measurements were motivated by the study of strong pi pi correlations in nuclei. The analysis relies on the composite ratio C_{pi pi}^A, which accounts for the clear effect of the nuclear medium on the (pi pi) system. The comparison of the C_{pi pi}^A distributions for the (pi pi)_{I=J=0} and (pi pi)_{I=0,J=2} systems to the model predictions indicates that the C_{pi pi}^A behavior in proximity of the 2m_pi threshold is explainable through the partial restoration of chiral symmetry in nuclei.

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arXiv2004

General properties of the pion production reaction in nuclear matter

The pion production reaction $π^+ \to π^+π^{\pm}$ on $^{45}Sc$ was studied at incident pion energies of $T_{π^{+}}$ = 240, 260, 280, 300, and 320 MeV. The experiment was performed using the $M11$ pion-channel at TRIUMF, and multiparticle events, ($π^+,π^+π^{\pm}$) and ($π^+,π^+π^{\pm}p$), were detected with the CHAOS spectrometer. Results are reported in the form of both differential and total cross sections, and are compared to theoretical predictions and the reaction phase space. The present investigation of the T-dependence of the $π^+ A \to π^+π^{\pm} A'$ reaction complements earlier examinations of the A-dependence of the reaction, which was measured using $^{2}H$, $^{4}He$, $^{12}C$, $^{16}O$, $^{40}Ca$, and $^{208}Pb$ targets at $\sim$280 MeV. Some general properties of the pion-induced pion production reaction in nuclear matter will be presented, based on the combined results of the two studies.

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arXiv2001

$π\to ππ$ results in nuclei

The Crystal Ball ($CB$) collaboration at $BNL$ has recently presented results regarding a study of the $π^- A \to π^0π^0 A^\prime$ reaction on $H, D, C, Al$ and $Cu$, using a nearly 4$π$ detector. Similar results, but for the $π^+ A \to π^+π^{\pm} A^\prime$ reaction on $^{2}H$, $^{12}C$, $^{40}Ca$, and $^{208}Pb$, have been published earlier by the $CHAOS$ collaboration at $TRIUMF$. In this Brief Report a comparison of the results of the two measurements is made, which shows that the $CHAOS$ and $CB$ data share relevant common features. In particular, the increase in strength as a function of A seen in the near-threshold $π^+ π^-$ invariant mass spectra reported by the $CHAOS$ group, is also seen in the $π^0 π^0$ CB data, when the results from the two groups are compared in a way which accounts for the different acceptances of the two experiments.

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arXiv2000

The $ππ$ interaction in nuclear matter from a study of the $π^+ A \to π^+ π^{\pm} A'$ reactions

The pion-production reactions $π^+ A \to π^+π^{\pm} A'$ were studied on $^{2}H$, $^{12}C$, $^{40}Ca$, and $^{208}Pb$ nuclei at an incident pion energy of $T_{π^{+}}$=283 MeV. Pions were detected in coincidence using the CHAOS spectrometer. The experimental results are reduced to differential cross sections and compared to both theoretical predictions and the reaction phase space. The composite ratio $\cal C$$_{ππ}^A$ between the $π^{+}π^{\pm}$ invariant masses on nuclei and on the nucleon is also presented. Near the $2m_π$ threshold pion pairs couple to $(ππ)_{I=J=0}$ when produced in the $π^+\to π^+π^-$ reaction channel. There is a marked near-threshold enhancement of $\cal C$$_{π^+π^-}^A$ which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. Furthermore, the behaviour of $\cal C$$_{π^+π^-}^A$ is well described when the restoration of chiral symmetry is combined with standard P-wave renormalization of pions in nuclear matter. On the other hand, nuclear matter only weakly influences $\cal C$$_{π^+π^+}^A$, which displays a flat behaviour throughout the energy range regardless of $A$.

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