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Register a new userResonance Structure in the $gammagamma$ Invariant Mass Spectrum in $p$C- and $d$C-Interactions
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Kh. U. Abraamyan
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Along with $pi^0$ and $eta$ mesons, a resonance structure in the invariant mass spectrum of two photons at $M_{gammagamma}= 360 pm 7 pm 9$ MeV is observed in the reaction $d Ctogamma + gamma +X$ at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are $Gamma = 63.7 pm 17.8$ MeV and $sigma_{gammagamma}=98pm24^{+93}_{-67} {rm mu b}$, respectively. The collected statistics amount to $2339 pm 340$ events of $1.5cdot 10^6$ triggered interactions of a total number $sim 10^{12}$ of $d$C-interactions. This resonance structure is not observed in $p$C collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed.
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A new resonance structure at M = 355 pm 6 pm 9 MeV is observed in the invariant mass spectrum of two gamma-quanta produced in the reaction d + C => gamma + gamma + x at momentum 2.75 GeV/c per nucleon. Preliminary estimates of its width and cross section are Gamma = 41 pm 12 MeV and sigma_{gamma-gamma} = 0.6 mkb. The collected statistics is 2680 pm 310 events of 1.5 10^6 triggered interactions of a total number 3 10^{12} dC-interactions.
The use of nuclear transparency effect of pi^{-}-mesons in proton, and deuteron induced interactions with carbon nuclei at 4.2A GeV/c, to get information about the properties of nuclear matter, is presented in this work. Half angle (theta_{1/2}) technique is used to extract information on nuclear transparency effect. The theta_{1/2} divides the multiplicity of charged particles into two equal parts depending on their polar angle in the lab. frame in pp interactions. Particles with angle smaller than (incone particles) and greater than (outcone particles) theta_{1/2} are considered separate. The average values of multiplicity, momentum and transverse momentum of the pi^{-}-mesons are analyzed as a function of a number of identified protons in an event. We observed evidences in the data which could be considered as transparency effect. For quantitative analysis, the results are compared with cascade model. The observed effects are categorized into leading effect transparency and medium effect transparency. The transparency in the latter case could be the reason of collective interactions of grouped nucleons with the incident particles.
The neutron yield in $^{12}$C(d,n)$^{13}$N and the proton yield in $^{12}C(d,p)^{13}$C have been measured by deuteron beam from 0.6 MeV to 3 MeV which is delivered from a 4-MeV electro static accelerator bombarding on the thick carbon target. The neutrons are detected at $0degree$, $24degree$, $48degree$ and the protons at $135degree$ in the lab frame. The ratios of the neutron yield to the proton one have been calculated and can be used as an effective probe to pin down the resonances. The resonances are found at 1.4 MeV, 1.7 MeV, 2.5 MeV in $^{12}C(d,p)^{13}$C and at 1.6 MeV, 2.7 MeV in $^{12}$C(d,n)$^{13}$N. This method provides a way to reduce the systematic uncertainty and helps to confirm more resonances in compound nuclei.
We have investigated the heaviest one-neutron halo candidate C-19 nucleus. Few-body model calculations of cross section angular distributions for the C-19(p,d)C-18 reaction, together with the test calculations carried out for the C-17(p,d)C-16 reaction, at a low incident energy are presented for different possible halo-neutron configurations. We show that there is a clear distinction between in particular $ell_{n}=0$ and $ell_{n}=2$ halo transfers. The sensitivity of the cross sections to the assumed C-19 single neutron separation energy is discussed.
Azimuthal correlations between the same type of particles (protons or pions) in the target fragmentation region was studied in d, He, C + C, Ta (4.2 AGeV/c), C + Ne, Cu (4.5AGeV/c) and p + C, Ta (10 GeV/c) interactions. The data were obtained from the SKM-200-GIBS streamer chamber and from Propane Bubble Chamber (PBL-500) systems utilized at JINR. Study of multiparticle azimuthal correlations offers unique information about space-time evolution of the interactions. Azimuthal correlations were investigated by using correlation function C($Deltaphi$)=dN/d($Deltaphi$), where $Deltaphi$ represents the angle between the sums of transverse momenta vectors for particles emitted in the forward and backward hemispheres. For protons a back-to back (negative) azimuthal correlations were observed in the above mentioned interactions. The absolute values of the correlation coefficient $|xi|$ -- the slope parameter of C($Deltaphi$), strongly depend on the mass number of the target ($A_T$) nuclei in the nucleon-nucleus and nucleus-nucleus collisions. Namely, $|xi|$ -- decreases with increase of $A_T$ in p+C and p+Ta collisions, while $|xi|$ decreases from d+C up to C+Ne and then almost does not change with increase of $A_P$, $A_T$ in (d+He)Ta, C+Cu and C+Ta collisions. For pions a back-to-back correlations were obtained for a light targets (C, Ne), and a side-by-side (positive) correlations for a heavy targets (Cu, Ta). The $|xi|$ insignificantly changes with increase of the momenta per nucleon and almost does not change with increase of $A_P$ and $A_T$. Models, used for description of the data -- the Ultra relativistic Quantum Molecular Dynamic (UrQMD) and Quark-Gluon String Model (QGSM), satisfactorily describe the obtained experimental results.
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