Characteristics of π−-meson multiplicity distributions in central collisions of12C and16O with nuclei at a momentum of 4.5 GeV/c per incident nucleon

Multiplicities of π^?-mesons from central collisions of¹²C and¹⁶O(4.5 GeV/c/n momentum) with several target nuclei were studied in a streamer chamber experiment. The parameter η=(〈n _? ² 〉?〈n_?〉²)/〈n_?〉 was determined for several samples of events characterized by different values of Θ _ch — the “vetoangle” for emission of the projectile charged fragments. The value of η is shown to decrease when the projectile mass number increases from 12 to 16 and to decrease significantly when Θ _ch increases from 0° to 4°, whereas it remains nearly constant when Θ _ch increases further to 14°. The results are compared with predictions of some theoretical models.     

Multiplicity distributions in e+e− annihilations at petra energies

Measurements of the charged multiplicities for hadron production in e⁺e^? annihilation in the center of mass energy range 9–32 GeV have been made. The average charged multiplicity has an energy dependence much stronger than ln s and similar to that reported for pp collisions. Quantitative differences are observed in the magnitude of both the average multiplicity 〈n_ch〉 and the dispersion D_ch for e⁺e^? and pp interactions at the same center of mass energy. 〈n_ch〉 and the ratio 〈n_ch/D_ch in e⁺e^? annihilations are significantly larger than in pp collisions and are found to be in overall agreement with QCD predictions. KNO scaling is seen to be satisfied.     

General features ofK + d interactions at 70 GeV/c

We have studied 70 GeV/cK ⁺ d interactions from about 10 K events. The inelastic cross-section for three or more prongs is found to be (28.9±0.4) mb. From odd-and even-prong topologies we have extracted topological break-up ofK ⁺ n interactions by taking into account spectator corrections, rescattering effects and Glauber screening. The rescattering fraction is found to be 0.06±0.01 which is substantially different from pion and proton interactions. Combining ourK ⁺ n data with other existing π^± n andp ^±n we find〈n _ch 〉 ^ph ?〈n _ch 〉 ^hn =0.33±0.04 andD/〈n _ch 〉=0.529±0.003.     

Target mass dependence of charged particle multiplicity inp-nucleus interactions

The shower particle multiplicity (〈n _s 〉) in thep-nucleus interactions for different targets, in the incident energy range of ～6–500 GeV has been studied. The variation of multiplicity parameters with target mass (A) or with number of interactions that the incident hadron suffers inside the nucleus (v _A ) and with the changed particle multiplicity inp-p interactions (〈n _ch〉) has been examined in the light of the various models of multiparticle production. The present analysis favours the hydrodynamical model though some other models can not be conclusively ruled out.     

Partition temperature and fireballs of hadron-proton collisions

A geometric property is considered to relate the impact parameterb ofhh collision at a given \(\sqrt s \) to the partition temperatureT _p of producedn _ch pions. It is based on the overlapping of two Lorentz contracted fireballs (FB) associated to the primary hadrons, as is described in the partition temperature model (PTM), assuming for the FB radiusR=r(3n _ch/2)^1/3. For \(\bar p\) p collisions at \(\sqrt s \) = 540 GeV analyzed by the authors of the PTM,r=0.70±0.03 fm consistent with the pion radius, the computedT _p agree with their results for variousn _ch. The energy dependence ofT _p for \(\bar p\) p from \(\sqrt s \) = 13.8 to 900 GeV is accounted for by assuming the FB velocity with respect to the c.m.s., to behave likepp, i.e., β _F =1?λ with λ=2 〈P _⊥〉/λ〈P _∥〉 and \(\bar b = 0.98fm\) . Remarks are made on the relationship betweenT _p and the conventional temperature determined by 〈P _⊥〉 in terms of the Lorentz factor of the FB.     

Search for direct single-photon production at large pT in photon-proton collisions at √s = 62.4 GeV

As part of a study of large p_T phenomena in photon-proton collisions at the CERN ISR, a search for direct single photon production has been performed. A statistical division of the data sample into the fraction consistent with single photon and the fraction due to multiphoton decays of neutral hadrons is accomplished by measuring the average conversion probability for the sample in a one radiation length thick converter. The fraction of the sample attributable to direct single photon production is 〈γ/all〉 = 0.074 ± 0.012 for 6 GeV/c < p_T 10 GeV/c, and 〈γ/all〉 = 0.26 ± 0.04 for p_T > 10 GeV/c, with an additional systematic uncertainty of ±0.05 for both values.     

Isospin conservation and “poisson-like” multiplicity distributions

Data on charged particle multiplicities and on the production of neutral particles are used to calculate a lower bound on the dispersion of the distribution of the total number of particles in the final state of hadron-hadron collisions. It is shown that this bound is an approximately linear function of 〈n_ch〉, the mean of the number n_ch of charged particles in the final state. It is argued that this rules out the possibility that the production of particles can be described by a single “Poisson-like” mechanism, no matter what isospin conserving hypothesis is used. It is also argued that such models will inevitably fail to reproduce the available data on the mean number of neutrals produced when n_ch is known.     

Cosmic ray results on the A dependence of multiplicity and angular distributions in proton nuclear interactions above 100 GeV

A calorimeter-spark chamber system was used to collect data on several hundred proton-nucleus interactions above 100 GeV using targets of C, Al, Fe, Sn and Pb. The average charged prong multiplicity is found to depend on atomic mass number as 〈n_c〉 = 〈n_c〉(p-p)A^x where x = 0.129 ± 0.004, with the dominant increase in multiplicity occuring in the backward (p-p c.m.) hemisphere. The value of x shows no significant energy dependence.     

The missing mass squared dependence of the average charged particle multiplicity in the reaction K+p → KoX++ from 5–16 GeV/c

The average charged particle multiplicity, 〈n_ch(M_X²)〉, in the reaction K⁺p→K^oX⁺⁺ is studied as a function of the mass squared, M_X², of the recoil system X and also as a function of the K^o transverse momentum, p_T, at incident momenta of 5.0, 8.2 and 16.0 GeV/c. The complete data samples yield distributions which are not independent of c.m. energy squared, s, They exhibit a linear dependence on log (M_X²_X/M_o²)[M_o²=1 GeV²] with a change in slope occurring for M_X²≈s/2, and do not agree with the corresponding distributions of 〈n_ch〉 as a function of s for K⁺ p inelastic scattering. Sub-samples of the data for which K^o production via beam fragmentation, central production and target fragmentation are expected to be the dominant mechanisms show that, within error, the distribution of 〈n_ch(M_X²)〉 versus M_X² is independent of incident momentum for each sub-sample separately. In particular in the beam fragmentation region the 〈n_ch(M_X²)〉 versus M_X² distribution agrees rather well with that of 〈n_ch〉 versus s for inelastic K⁺p interactions. The latter result agrees with recent results on the reactions pp → pX and π^?p → pX in the NAL energy range. Evidence is presented for the presence of different production mechanisms in these separate regions.     

Quasielastic nucleon and hyperon production by neutrinos and antineutrinos with energies below 30 GeV

The cross sections of neutrino and antineutrino quasielastic reactions \(vn \to \mu ^ - p,\bar vp \to \mu ^ + n,\bar vp \to \mu ^ + \Lambda\) were studied in the neutrino energy range between 3 and 30 GeV. In comparison withV-A theory axial mass parameters ofM _A =(1.06±0.05±0.14) GeV/c² from neutrino andM _A =(0.71±0.10±0.20) GeV/c² from antineutrino data were found. The total cross-section for the hyperon production process can be described byM _A =1.0 GeV/c².     

Charged particle and π0 multiplicity distributions and the annihilation properties of\bar p p interactions at 70 GeV/c

The elastic and inelastic \(\bar p\) p cross sections at 70 GeV/c have been determined in an experiment performed at CERN using BEBC equipped with a TST. The topological cross sections were measured and the moments of the inelastic multiplicity distribution are 〈n _c 〉=6.16±0.09, 〈n _c 〉/D=2.04±0.05 andf ₂ ^cc =2.97±0.03. The average number of Dalitz pairs per inelastic event is (3.12±0.09)×10^?2. Assuming that these all arise from π⁰ decay the average π⁰ multiplicity is \(\langle n_{\pi ^0 } \rangle = 2.71 \pm 0.14\) . The \(\bar p\) p?pp cross section differences lead to an annihilation cross section σ _A = 4.42±0.41 mb and the moments of the annihilation multiplicty distribution are 〈n _A 〉=8.0±0.3, 〈n _A 〉/D=2.5±0.2 andf ₂ ^A?? =?1.4±0.3. An independent check of σ _A was made by investigating fast forward charged and neutral secondary interactions in the TST and in the surrounding neon-hydrogen mixture, and gives a value σ _A = 5.0±1.6 mb. The ratio of fast \(\bar n\) to \(\bar p\) production in non-annihilation interactions at 70 GeV/c is found to be 0.45±0.11.     

Analysis of topological cross sections in pp interactions at 22.4 GeVc

The multiplicity distribution for 11558 events in $\text{p}\text{p}$ interactions at 22.4 $\text{GeV}\text{c}$ was analyzed. The average charged multiplicity 〈n_ch〉 for inelastic events was found to be 4.69 ±0.05 and $\text{〈n}{}_{\mathrm{ch}}\text{〉}\text{D=2.04 ± 0.05}$. The early KNO scaling of normalized topological cross sections has been tested.     

Charged multiplicity distributions in pd and π+d interactions at 195 GeV/c

Topological inelastic cross-sections and average multiplicities for pd and π⁺d interactions at 195 GeV/c, are obtained from an exposure of the NAL 30″ proportional wire chamber-bubble chamber hybrid system to a positive π⁺/p beam. We find that 〈n_c〉_pn = 7.67 ± 0.25, and 〈n_c〉_π⁺n = 7.56 ± 0.30, yielding a negative multiplicity difference between pn and pp of 0.50 ± 0.14, and that σ_n(pp) is approximattely interleaved between σ_n?1(pn).     

Investigation of the decay rate for71Ge in chemical compounds and calibration of the Mössbauer isomer shift of the 67 keV γ-transition of73Ge

Changes of the radioactive decay rate of⁷¹Ge (T _1/2=11.43 days) have been studied experimentally for⁷¹Ge in some compounds of bivalent and quadrivalent germanium. Relative changes Δλ/λ of the electron capture probability have been measured, and the chemical changes Δρ(0) of the electron density at the germanium nuclei have been determined from these measurements. Values for the Mössbauer isomer shift calibration constants for the 67 keV γ-transition of⁷³Ge have been estimated:C=δ/Δρ(0)=(0.061±0.020) mm·s^?1/a.u., Δ〈r ²〉=(21±7)·10^?3 fm², ΔR/R=(6.9±2.3)·10^?4.     

Remarks on the charged multiplicity of hadronic Z0(91) decays

The charged multiplicity distribution of hadronic decays of Z ⁰ from LEP and those of inclusive $e^{+}+e^{-}?ghtarrow h{?erline h} at E_{? cm}=14 {? to} 60 {? GeV}$ at E _cm = 14 to 61 GeV are analyzed using a Poisson-type distribution for photon statistics, due to Scully-Lamb. Its two parameters are expressed in terms of 〈n〉 and f ₂ = 〈n(n ? 1)〉 ? 〈n〉² of the data in order to perform no-free-parameter fits. It is found that f₂ behaves like $E_{? cm}^{a}$ with a = 2.01 ± 0.11, whereas C ₂ = 〈n ²〉/〈n〉² ～ E _cm with ΔC ₂/ΔE _cm = (1.81 ± 0.14)·10^?3.     

QCD studies with e+e− annihilation data at 161 GeV

We have studied hadronic events produced at LEP at a centre-of-mass energy of 161 GeV. We present distributions of event shape variables, jet rates, charged particle momentum spectra and multiplicities. We determine the strong coupling strength to be α_s(161 GeV) = 0.101±0.005(stat.)±0.007(syst.), the mean charged particle multiplicity to be 〈n _ch〉(161 GeV) = 24.46 ± 0.45(stat.) ± 0.44(syst.) and the position of the peak in the ξ_p = ln(1/x _p) distribution to be ξ₀(161 GeV) = 4.00 ±0.03(stat.)±0.04(syst.). These results are compared to data taken at lower centre-of-mass energies and to analytic QCD or Monte Carlo predictions. Our measured value of α_s(161 GeV) is consistent with other measurements of α_s. Within the current statistical and systematic uncertainties, the PYTHIA, HERWIG and ARIADNE QCD Monte Carlo models and analytic calculations are in overall agreement with our measurements. The COJETS QCD Monte Carlo is in general agreement with the data for momentum weighted distributions like Thrust, but predicts a significantly larger charged particle multiplicity than is observed experimentally.     

Nuclear mass number dependence of inclusive pion production by pions and protons at 4.3GeV/c

The inclusive production of π⁺ for 0.4≤p_T<1.0 GeV/c in pion-nucleus and proton-nucleus collisions at 4.3 GeV/c was measured. A strong A-dependence of the cross sections at high p_T is observed to be persistent in the low energy region. The ratio of the cross sections for proton-nucleus and pion-nucleus collisions is also observed to be compatible with the quark-parton picture, for p_T>0.6 GeV/c.     

Inclusive electron production from heavy quarks in e+e− annihilation at 34.6 GeV center of mass energy

The production of electrons by bottom and charm hadrons has been studied in e⁺e^? annihilation at 34.6 GeV center of mass energy. It is observed that the b quark fragmentation function is peaked at large values of the scaling variable z with 〈z_b〉 = 0.84^{+0.15 + 0.15}_{?0.10 ? 0.11}. For c quarks 〈z_c〉 = 0.57^{+0.10 + 0.05}_{?0.09 ? 0.06} is observed. A forward-backward charge asymmetry of A = ?0.25 ± 0.22 was measured in b production.     

Factorial cumulant moments and correlation integrals in pp collisions at 400 GeV/c

The pseudorapidity distribution of charged particles produced in pp collisions at 400 GeV/c was measured by using LEBC films offered by CERN NA27 collaboration. The scaled factorial cumulant moments have been calculated. The results show that the second order cumulants have positive values, while the cumulants of higher order are consistent with zero except for the situation ofn _ch ≥ 4 events, where the third-order cumulants have positive values beyond the statistical uncertainties. It means that the observed increase of the higherorder factorial momentsF _q is almost due to the dynamical two-particle correlation in pp collisions at 400 GeV/c. The cumulant moments also have been calculated by star correlation integrals. It significantly reduced the statistical errors, especially for higher order cumulants. From Monte Carlo events with the same single particle spectrum and no correlations, we observed that for broad mixed-multiplicity distributions, a significant part ofK ₂ is coming from the single-particle fluctuation due to the fluctuating multiplicity.     

Gluon multiple scattering and the transverse momentum dependence of J/ψ production in nucleus-nucleus collisions

A J/ψ meson is mainly formed by gluon fusion for 200 GeV pp collisions. In reactions with nuclei the gluons (g) scatter off other nucleons (N) before fusing to a J/ψ, which thenshows additional transverse momentum p_T. Fitting the value of the parameter σ_gN〈p²_T〉_gN to describe the gluon multiple scattering effect in proton-nucleus data, we can reproduce the p_T distribution of J/ψ production in 200 GeV/A nucleus-nucleus collisions. The origin of the p_T distribution is traced to soft gluon radiation via the Sudakov form factor.