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Register a new userObservation of New Resonance Structure in the Invariant Mass Spectrum of Two gamma-Quanta in dC-Interactions at Momentum 2.75 GeV/c per Nucleon
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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.
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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.
Along with $pi^0$ and {eta} mesons, a resonance structure in the invariant mass spectrum of two photons at M{gamma}{gamma} = 360 pm 7 pm 9 MeV is observed in the reaction d + C rightarrow {gamma} + {gamma} + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are {Gamma} = 64 pm 18 MeV and $sigma_{gammagamma}$ = 98 pm 24 {mu}b, respectively. The collected statistics amount to 2339 pm 340 events of 1.5 cdot 10^6 triggered interactions of a total number ~ 10^12 of dC-interactions. The results on observation of the resonance in the invariant mass spectra of two $pi^0$ mesons are presented: the data obtained in the d + C rightarrow {gamma} + {gamma} reaction is confirmed by the d + C rightarrow $pi^0$ + $pi^0$ reaction: $M_{pi^0pi^0}$ = 359.2 pm 1.9 MeV, {Gamma} = 48.9 pm 4.9 MeV; the ratio of Br(Rrightarrow{gamma}{gamma}) / Br(Rrightarrow$pi^0pi^0$) = (1.8 {div} 3.7)cdot10^-3.
First searches for the coherent dissociation of relativistic oxygen nuclei into four a particles are reported. It is shown that reactions of this type are characterized by a significantly lower decay temperature than the conventional multifragmentation of residual projectile nuclei. The momentum spectra and correlations of a panicles are not reproduced by the simple statistical model of direct fragmentation. The possibility that the oxygen nucleus undergoing fragmentation acquires a nonzero angular momentum in the collision process is discussed.
The transverse-momentum distributions and correlation characteristics of relativistic $alpha$ particles from the coherent dissociation of a carbon nucleus into three $alpha$ particles at 4.5 GeV/$c$ are studied in lead-enriched emulsion. Comparative analysis of data obtained in ordinary and lead-enriched emulsion stacks is performed. It is shown that the statistical model of rapid fragmentation does not describe the momentum and correlation characteristics of a $alpha$ particles in the rest frame of the carbon nucleus. The estimated decay temperature of $^{12}$C is weakly dependent on the target atomic mass. It is shown that the carbon nucleus undergoing fragmentation acquires angular momentum in the collision.
Nuclear fragments emitted at 3.5 degrees in 12C fragmentation at 0.6 GeV/nucleon have been measured. The spectra obtained are used for testing the predictions of four ion-ion interaction models: INCL++, BC, LAQGSM03.03 and QMD as well as for the comparison with the analytical parametrization in the framework of thermodynamical picture of fragmentation.
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