Two body correlations between negative pions in pp interactions at 69 GeV/c

Correlations between two π^? in pp interactions at 69 GeV/c are presented in terms of longitudinal and transversal variables. The dominant feature is the existence of a strong shortrange positive correlation between the two π^? in the central region.     

Multiplicity of charged particles π− interactions on nuclei at 40 GeV/c

Multiparticle production in π^?-nucleus interactions at 40 GeV/c (Fifth Joint CERN-Serpukhov Experiment) has been studied using a spark-chamber technique at the Serpukhov accelerator. The mean multiplicities, the pseudorapidity distributions and the dispersion of the multiplicity distributions of charged particles produced on C, Al, Cu and Pb targets are presented. The data have been analysed, both subtracting and including secondary protons with p < 1 GeV/c. In the region of pseudorapidity η > 3.4 the average multiplicity is nearly independent of the size ($\text{ν}$) of the target nucleus, while it increases for η < 3.4. In the forward direction (η > 4) the mean multiplicity on nuclei is smaller than the mean multiplicity on hydrogen. The dependence upon $\text{ν}$ in the target fragmentation region is stronger when the emitted protons are included in the pseudorapidity distributions of the secondary particles. The dispersion of the multiplicity distributions for the different nuclear targets versus the mean multiplicity shows the same slope as found by the world statistics on hydrogen and by other experiments on nuclei at different energies. The results are compared with the predictions of the coherent tube model and with the soft hadron-nucleus collision model.     

Multiplicity distributions and double scattering effects in π−d interactions at 205 GeV

Multiplicity distributions of charged secondaries, σ_N(π^?d) are obtained. The effective multiplicities σ_N(π^?n) and σ_N(π^?p) are extracted using the measured spectator momentum. The probability of double scattering P_N is found to be independent of multiplicity.     

Real‐space analysis of radiation‐induced specific changes with independent component analysis

A method of analysis is presented that allows for the separation of specific radiation‐induced changes into distinct components in real space. The method relies on independent component analysis (ICA) and can be effectively applied to electron density maps and other types of maps, provided that they can be represented as sets of numbers on a grid. Here, for glucose isomerase crystals, ICA was used in a proof‐of‐concept analysis to separate temperature‐dependent and temperature‐independent components of specific radiation‐induced changes for data sets acquired from multiple crystals across multiple temperatures. ICA identified two components, with the temperature‐independent component being responsible for the majority of specific radiation‐induced changes at temperatures below 130 K. The patterns of specific temperature‐independent radiation‐induced changes suggest a contribution from the tunnelling of electron holes as a possible explanation. In the second case, where a group of 22 data sets was collected on a single thaumatin crystal, ICA was used in another type of analysis to separate specific radiation‐induced effects happening on different exposure‐level scales. Here, ICA identified two components of specific radiation‐induced changes that likely result from radiation‐induced chemical reactions progressing with different rates at different locations in the structure. In addition, ICA unexpectedly identified the radiation‐damage state corresponding to reduced disulfide bridges rather than the zero‐dose extrapolated state as the highest contrast structure. The application of ICA to the analysis of specific radiation‐induced changes in real space and the data pre‐processing for ICA that relies on singular value decomposition, which was used previously in data space to validate a two‐component physical model of X‐ray radiation‐induced changes, are discussed in detail. This work lays a foundation for a better understanding of protein‐specific radiation chemistries and provides a framework for analysing effects of specific radiation damage in crystallographic and cryo‐EM experiments.     

Speeding up Evolutionary Search by Small Fitness Fluctuations

We consider a fixed size population that undergoes an evolutionary adaptation in the weak mutation rate limit, which we model as a biased Langevin process in the genotype space. We show analytically and numerically that, if the fitness landscape has a small highly epistatic (rough) and time-varying component, then the population genotype exhibits a high effective diffusion in the genotype space and is able to escape local fitness minima with a large probability. We argue that our principal finding that even very small time-dependent fluctuations of fitness can substantially speed up evolution is valid for a wide class of models.     

The many faces of radiation‐induced changes

During diffraction experiments even cryo‐cooled protein crystals can be significantly damaged due to chemical and physical changes induced by absorbed X‐ray photons. The character and scale of the observed effects depend strongly on the temperature and the composition of crystals. The absorption of radiation energy results in incremental regular changes to the crystal structure, making its impact on the process of solving the structure strongly correlated with other experimental variables. An understanding of all the dependencies is still limited and does not allow for a precise prediction of the outcome of a particular diffraction experiment. Results are presented of diffraction experiments performed under different experimental conditions. The influence of temperature and crystal composition on different characteristics of radiation damage is analyzed. The observed effects are discussed in terms of their impact on data processing and phasing procedures.     

The nuclear response in high-energy hadron-nucleus interactions

In an experiment at the CERN Super Proton Synchrotron (SPS) studying hadron-nucleus interactions, slow particles which are mainly knockout protons were measured with an electronic detector. Their dependence on the target mass, incoming energy, and projectile is shown. We discuss the use of the number of protons as a measure for the number of interactions of the projectile and conclude that the emitted protons measure the impact parameter of the reaction.     

On statistical thermodynamics of multicomponent systems II

The equivalent neighbour (EN) model of interacting continuous spherically symmetric spins with the length equal or smaller than unity is solved exactly for all values of the spin dimensionality, D. A surprising result is that only for D 628 the system undergoes phase transitions at temperatures lower than those of the EN model of interacting spins with the hypercubic symmetry. In the D → ∞ limit the equation of state in zero field is derived analytically and gives the Landau type behaviour in the whole range of temperatures.     

Particle production in high-energy hadron-nucleus interactions

The pseudorapidity (η) distributions of fast particles (β>0.7) emitted in inelastic hadron interactions with carbon, copper and lead were measured for incoming energies from 50 to 150GeV at the CERN Super Proton Synchrotron. Their dependence on target mass (A) and projectile (h) obeys <v>-scaling as expected. Their energy dependence is in contrast with most model predictions.     

Diffractive dissociation of the beam particle in pp interactions at 32.1 GeVc

We report the results of a study of the reaction $\text{p}\text{p}\text{→}\text{p}\text{+}\text{x}\text{at}\text{32.1}\text{GeV}\text{c}$, where the recoiling proton has a small laboratory momentum. The reaction is studied in the 4.5 m Mirabelle bubble chamber at Serpukhov. We compare the diffractive dissociation of the incident antiproton to other incident particles.