A measurement of the transverse momenta of partons,and of jet fragmentation as a function of √s in p-p collisions

A large solid-angle apparatus consisting of a superconducting solenoid magnet, cylindrical drift chambers and two arrays of lead-glass counters was used to examine particles associated with a high transverse momentum trigger in p-p collisions with three √s values at the CERN ISR. The trigger was given by energy deposition in lead-glass arrays centred at 90°. The trigger transverse momentum range covered was 3 < $\text{p}{}_{\mathrm{<mtext>T\; trig</mtext>}}\text{< 11}\text{GeV}\text{c}$. Results are given for p_out for both individual charged particles, and also for the sum of charged particle momenta in the hemisphere opposite to the trigger. Mean values are then deduced for the parton transverse momentum k_T, and for the jet fragmentation momentum j_T.     

A measurement of high-pT correlations in 340 GeV/c pp and 280 GeV/cπ−p reactions

We have measured correlations between single high-p_T(1.5<p_T<3.5 GeV/c) trigger particles on one side of the beam line and groups of particles entering a calorimeter on the opposite side of the beam line. The mean transverse momentum measured in the calorimeter is found to increase with the trigger-particle transverse momentum. The coplanarity of the events increases with trigger-particle transverse momentum. We have compared our data with the predictions of a phenomenological four-jet model. To fit our data we find that we must give large (0.9 GeV/c) mean transverse momenta to the constituents of the initial hadrons.     

Production of large p⊥ single particles and multiparticle systems (JETS) in K−p interactions at 110 GeV/c

Differential cross sections of single particles and multiparticle systems produced in K^?p interactions at 110 GeV/c are presented. At large values of transverse momentum (p_⊥) we find the multiparticle cross section to be an order of magnitude larger than that for single particles. This and other features of our data are consistent with results obtained at 200 GeV/c, that have been interpreted as evidence of a new dynamical mechanism in hadron-hadron interactions. However, similar features are observed in a K^?p experiment at 16 GeV/c.     

Return of the volcano: PHENIX azimuthal correlations 62.4 GeV Au+Au

As in previous analyses at √s _NN =200 GeV., correlations in azimuthal angles between inclusive charge particles at intermediate transverse momentum (p _T=1.0?4.0) GeV are studied at √s _NN =62.4 GeV. The di-jet correlations reveal similar modification as in 200 GeV. Specifically large modification, including the “volcano” or “cone” structure, persists in the awayside correlation.     

Transverse momenta of high-η charged particles emitted in Au+Au collisions

This work demonstrates that the mean transverse momentum of charged particles at large pseudo-rapidities can be reliably derived from measurements of the complete charged-particle multiplicity distributions and using information from measurements of p _T spectra at mid-rapidity by applying energy conservation requirements. As an example, the mean p _T of charged particles emitted at η=4.6 is found to be 〈p _T 〉=0.305 GeV/c for the 0–3% most central Au+Au collisions at $\sqrt {s_{NN} } = 130$ GeV.     

Hadron fragmentation at high energies and quark constituents

The systematics of particle ratios in high-energy pp collisions suggest that the same constituent partons are active in the production of particles at small and large transverse momentum p_T. We relate various features of the pion spectra at small p_T in the fragmentation region and in the central region of pp collisions to corresponding features observed in ep and en collisions assuming that the dissociation of the proton into quark partons is the common underlying process.     

Cross sections and charged multiplicity distributions for π−p and K−p interactions at 147 GeV/c

The results presented in this paper were obtained from a 105 000 frame exposure of the FNAL Hybrid Proportional Wire Chamber-30 inch Bubble Chamber System, in a tagged beam of 147 GeV/c negative particles. Elastic, total and topological cross sections were obtained for both π^?p and K^?p interactions. Comparisons with other data, taken with various beam particles over large momentum intervals, show good agreement with KNO scaling, and similarity in the scaling behavior of σ_n for the different beam particles.     

Trigger bias in large pT reactions

We explore how particle multiplicities in large transverse momentum reactions are affected by the way in which the detection apparatus is triggered. For example, we predict that the multiplicity of particles accompanying a large p_T hadron is increased when it is required that there be a second large p_T hadron in the opposite hemisphere. The mechanism responsible for this effect is shown also to make correlations between pairs of large p_T pions produced on opposite sides depend only weakly on their charges.We include a list of further experimental tests, feasible with available apparatus, that are suggested by the two-jet picture of large p_T reactions.     

Study of the out-of-plane emission of protons and light fragments in symmetric heavy-ion collisions

Midrapidity protons from²⁰⁹Bi+²⁰⁹Bi collisions were measured with the Kaon Spectrometer at SIS at incident energies of E _Lab /A=400, 700 and 1000 MeV. Additionally, light fragments were analysed at 400 MeV. We have investigated the azimuthal emission pattern of the particles relative to the reaction plane as function of transverse momentum, bombarding energy and impact parameter. We observe an enhanced emission of particles perpendicular to the reaction plane at all bombarding energies. The ratio of the number of particles emitted out-of-plane/in-plane increases strongly with the particles transverse momentum. The anisotropy decreases with increasing beam energy. Composite particles show a much stronger effect than protons.     

Charged particle production at the CERN ISR as a function of transverse momentum

Experimental results are presented on the production of charged particles in inclusive reactions at ISR energies. The data have been taken as function of transverse momentum p_t at the fixed x-values of 0.08, 0.16 and 0.32. The behaviour of the p_t-distributions for the different particles is discussed.     

Study of charged and neutral multiplicities associated with large transverse momentum π0's in proton-proton collisions

A streamer chamber detector surrounding an intersection region of the CERN ISR was triggered on large transverse momentum π⁰'s by means of an array of lead-glass counters. The directions of all charged particles and photons converted in lead-oxide plates inside the streamer chamber were measured. Data were taken at c.m.s. energies of 45, 53 and 63 GeV around two production angles of the high-p_Tπ⁰ (90° and 53°). The total charged multiplicity associated with large transverse momentum π⁰'s is presented for the first time. Associated photon multiplicities are given for different phase-space regions. The data are compared with two extreme models, a simple jet model and a cluster model which describes normal inelastic events. The cluster model agrees much better with the data.     

Angular correlations in proton-proton collisions producing a high transverse momentum π0

In an experiment at the CERN ISR, a streamer chamber detector surrounding one of the intersection regions was triggered on large transverse momentum π⁰'s by means of an array of lead-glass counters. The directions of charged particles and γ rays converted in lead-oxide plates inside the streamer chamber were measured. Data were taken at c.m. energy of √s = 53 GeV at two production angles of the high p_Tπ⁰ (90° and 53°). They indicate an enhancement of particles mostly in the hemisphere opposite to the π⁰. In the 53° data, a shift of this enhancement towards rapidities opposite to the rapidity of the π⁰ and confined to a ±30° azimuthal region around the collision plane is observed. In addition, a short-range angular correlation is evidenced between the high p_Tπ⁰ and the other collisions products (photons or charged particles). Two-particle correlations between charged particles produced in association with the high p_Tπ⁰ are found similar to those     

Highp T hadrons as leading particles in jets produced at the ISR

The density of charged particles near a single highp _T trigger particle in proton-proton collisions has been studied with the SFM detector at the CERN-ISR. It is shown that:—the secondaries cluster in a jet-like manner about the trigger particle; —the momentum distributions in this trigger jet can be unambiguously separated from the spectator background distributions;—the momentum distributions in this trigger jet can be unambiguously separated from the spectator background distributions;—the momentum component transverse to the jet direction is exponentially damped;—the width of the transverse distributions increases with the momentum component along the jet;—the fractional longitudinal momentum density depends strongly on the trigger transverse momentum and scales with \(x_T = {{2p_T } \mathord{\left/ {\vphantom {{2p_T } {\sqrt s }}} \right. \kern-0em} {\sqrt s }}\) . All these findings support the hard constituent scattering origin of highp _T hadrons.     

Multiplicity dependence of particle spectra: A peripheral phase-space description with application to 19 GeV/c pp reactions

As an attempt to describe the overall features of spectra of particles produced in hadronic interactions at high energy, we propose a peripheral phase-space model which incorporates restricted transverse momenta to the outgoing particles as well as a leading particle effect. Simulating proton-proton interactions at 19 GeV/c beam momentum, we examine the effect of modifying Monte-Carlo generated events by a matrix element containing a factor (?bp_⊥²) for each outgoing particle and an exponential damping exp (at) in the momentum transfer to each of the final baryons. With a fixed set of cut-off constants, we give a survey of spectral shapes obtained for particles of different types, pions, kaons, nucleons and hyperons. In particular, the generated longitudinal spectra are shown to have a distinct dependence on multiplicity. A comparison is carried out with existing data on 19 GeV/c pp interactions obtained by the Scandinavian Bubble Chamber Collaboration.     

A study of final states with a large transverse momentum particle from proton-proton collisions at 24 GeV/c

Events with a large transverse momentum (>1 GeV/c) pion or nucleon have been selected from the data of a high-statistics pp bubble chamber experiment (√s=6.84 GeV). Only events in which all secondary particles could be identified were used. One finds that fewer pions are produced in the azimuthal hemisphere containing the large transverse momentum particle than in the opposite hemisphere. An indication for coplanarity is found. Most pions associated with a large transverse momentum pion are emitted with small absolute c.m. rapidities, whereas those associated with large transverse momentum nucleons show some back-to-back structure. Various results of this investigation are similar to those obtained at the ISR. Most of the findings are compatible with predictions from an independent emission model.     

Measurement of large transverse momentum positive particles produced at medium angles at √s = 52.5 GeV

The inclusive spectrum of positive particles has been measured at the ISR energy √s = 52.5 GeV as function of transverse momentum, p_T for large p_T values using the Split Field Magnet facility. The angular dependence of the distribution is observed and discussed in the range $\text{9° ? θ}{}^1\text{? 21°}$. An upper limit for the production of ? meson with p_T ? 3 GeV/c is derived from the same sample of data.     

Measurement of the polarization of positive muons produced in high-energy antineutrino interactions

The question whether scalar-type interactions contribute to weak interactions at large momentum transfer has been investigated by a measurement of the longitudinal polarization of positive muons produced in charged-current interactions of high-energy antineutrinos with iron. At an average momentum transfer <Q ²>=4 GeV² the muon spin is found to be oriented forward with respect to the muon momentum vector, with an average polarization of 1.10±0.24, consistent with positive helicity. A limit on scalar contributions of σ_{s, p}/σ_tot <7% at the 95% confidence level can be deduced. A search for violation of time reversal invariance which could manifest itself by a polarization component perpendicular to the muon production plane gave a limit of σ_tv/σ_tot <16% (95% c.l.). It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at large momentum transfers.     

Event-by-event search for charged-neutral fluctuations in Pb-Pb collisions at 158 A⋅GeV

We analyse the proton electromagnetic form factor ratioR(Q ² ) =QF ₂ (Q ² )/F ₁ (Q ² ) as a function of momentum transferQ ² within perturbative QCD. We find that the prediction for (R(Q ² ) at large momentum transferQ depends on the exclusive quark wave functions, which are unknown. For a wide range of wave functions we find thatQF ₂ F ₁ ～ const. at large momentum transfer, which is in agreement with recent JLAB data.     

Structure of final states with a high transverse momentum π0 in proton-proton collisions

We present a study of the final state structure in proton-proton collisions (√s = 53 GeV) where a large transverse momentum π⁰ (p_t > 2 GeV/c) is produced at an angle of 90°. Charged secondaries have been detected and momentum analysed in the split field magnet detector at the CERN Intersecting Storage Rings. The large angular coverage of this detector extends over ±2.5 units of rapidity and ±30° of azimuth with respect to the trigger π⁰, both towards and away from it. In each of these directions, where we observe similar strong correlations, we present charged particle distributions, in rapidity and momentum. In the hemisphere containing the trigger π⁰ we have measured the cross section for inclusive production of large transverse momentum ?^± mesons. In the opposite hemisphere the data exhibit several features predicted by hard scattering quark-parton models: coplanarity and short-range rapidity correlation for the large transverse momentum secondaries as well as a transverse momentum sharing distribution similar to that observed in deep inelastic electro-production and in e⁺e^? collisions.     

Inclusive processes at large transverse momenta

A general model for processes at large transverse momentum is constructed on the assumption that events with large transverse momentum particles posses short range correlations. It is shown that particle ratios and scaling properties are not sensitive to the detailed dynamics of large angle scattering, and also that the character of the inclusive spectrum can be understood in terms of (quasi-) elastic scattering.