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There are many motivations for adding simultaneously acquired MR images to PET scanning. The most straight forward are, superior registration of MR and PET images, the addition of morphological detail when there is non-rigid motion and for pre-clinical studies simultaneous imaging could lead to a significant reduction in the time that animals are required to be anesthetised. In addition simultaneous MR has the potential to provide accurate motion correction for PET image reconstruction. For functional imaging simultaneous acquisition is required to assess the subject in the same physiological state, such as acute stroke studies. The elimination of the additional radiation associated with combining CT with PET, by providing anatomic detail with MR, would be a crucial advantage for cancer screening. Combining the two instruments necessitates some engineering tradeoffs, especially associated with the use of the highly developed photomultiplier tube (PMT) used for light amplification, because of its incompatibility with strong magnetic fields. Our approach is to provide a split in the magnet and gradients to locate the magnetic sensitive components, the PMTs, in regions of low magnetic field, leaving only the essential PET components, the scintillator blocks, in the strong magnetic field region. The crystals are coupled to the PMTs by extending the optical fibres. A further advantage accrues by moving the PET electronics out of the region seen by the MR radio-frequency (RF) and gradient coils as electromagnetic interference effects between the PET and MR systems, which could cause artefacts in either modality, are eliminated. Here we describe a preliminary evaluation of the system, which is essentially a microPET Focus-120 located in a 1T split magnet, and compare its performance to previous microPET instruments.

As evidenced by the success of PET-CT, there are many benefits from combining imaging modalities into a single scanner. The combination of PET and MR offers potential advantages over PET-CT, including improved soft tissue contrast, access to the multiplicity of contrast mechanisms available to MR, simultaneous imaging and fast MR sequences for motion correction. In addition, PET-MR is more suitable than PET-CT for cancer screening due to the elimination of the radiation dose from CT.A key issue associated with combining PET and MR is the fact that the performance of the photomultiplier tubes (PMTs) used in conventional PET detectors is degraded in the magnetic field required for MR. Two approaches have been adopted to circumvent that issue: retention of conventional, magnetic field-sensitive PMT-based PET detectors by modification of other features of the MR or PET system, or the use of new, magnetic field-insensitive devices in the PET detectors including avalanche photo-diodes (APDs) and silicon photomultipliers (SiPMs).Taking the former approach, we are assembling a modified microPET® Focus 120 within a gap in a novel, 1T superconducting magnet. The PMTs are located in a low magnetic field (~30mT) through a combination of magnet design and the use of fiber optic ‘bundles’.Two main features of the modified PET system have been tested, namely the effect of using long fiber optic bundles in the PET detector, and the impact of magnetic field upon the performance of the position sensitive PMTs.The design of a modified microPET®-MR system for small animal imaging is completed, and assembly and testing is underway.

In an experiment with the 30-inch Hybrid Spectrometer at Fermilab we have obtained the inclusive and semi-inclusive production cross sections of the ϱ0 meson using a conventional background subtraction technique. Production cross sections for the ϱ0 are derived as a function of the Feynman scaling variablex, and the transverse variablespt2 andEt=(pt2+M2)1/2. The longitudinal distributions are compared with the (1−x) dependence of the proton and meson valence quark structure functions, using various forms of recombination and fragmentation models. The transverse distributions are compared with thermodynamic models. We give density matrix elements for the ϱ0 production from pions in the extreme forward region.

Results on the production cross sections ofW andZ bosons detected in the UA2 experiment are given based on a large sample ofW→eν andZ→e+e− decays. The measured cross sections are σWe = 660±15(stat)±37(syst)pb, σZe = 70.4±5.5(stat)±4.0(syst)pb and their ratioR=9.38−0.72+0.82(stat)±0.25(syst). In the framework of the Standard Model, the measured value ofR is used to determine the total width of theW, Γ(W)=2.30±0.19(stat)±0.06(syst) GeV.

Multiplicity distributions of charged particles produced in non single-diffractive collisions between protons and antiprotons at centre of mass energies of 200 and 900 GeV are presented. The data were recorded in the UA5 streamer chambers at the CERN Collider, which was operated in a pulsed mode between the two energies. A new method to correct for acceptance limitations and inefficiencies based on the principle of maximum entropy has been used. Multiplicity distributions in full phase space and in intervals of pseudorapidity are presented in tabular form. The violation of KNO scaling in full phase space found by the UA5 group at an energy of 546 GeV is confirmed also at 200 and 900 GeV. The shape of the 900 GeV distribution in full phase space is narrower in the peak region than at 200 GeV but exhibits a pronounced high multiplicity tail. The negative binomial distribution fits data at 200 GeV in all pseudorapidity intervals and in small intervals at 900 GeV. In large intervals at 900 GeV, however, the negative binomial distribution. Fits to the partially coherent laser distribution are also presented as well as comparisons with predictions of the Dual Parton, the Fritiof and the Pythia models.

The ratio of hadronic p+/p- production has been studied in the target fragmentation region of p+p, p-p,K+p andp p collisions at 147 GeV/c beam momentum. The difference between this ratio in the p+p and p-p data is less than at lower energies but still present. No difference exists anymore for the p+/p- ratio at this energy betweenK+p andpp collisions. Exclusion of diffraction dissociation and resonance production does not change the main conclusions. The energy dependence of the ratio for p+p and p-p collisions gives evidence for a universal asymptotic ratio for all beams. Thept-dependence at low-pt is in agreement with the expectation from geometrical correlation of the valence quarks.

The transverse momentum distributions ofW andZ bosons produced in collisions at are examined. Comparisons are made with QCD predictions, and good agreement is found. The fraction ofW bosons produced withpT>25 GeV is found to be 3.8±0.6(stat)−1.3+0.9(syst)%.

New data are presented on charged particle pseudorapidity distributions for inelastic events produced at c.m. energies $$\sqrt s $$ =200 and 900 GeV. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode. The rise of the central density ?(0) at energies up to $$\sqrt s $$ =900 GeV has been studied. A new form of central region scaling is found involving the density?n(0) for charged multiplicityn, namely that the scaled central density?n(0)/?(0) expressed as a function ofz=n/ is independent ofs. Scaling in the fragmentation region holds to 10–20%, and the small amount of scalebreaking observed here could be accommodated within the framework suggested by Wdowcyk and Wolfendale to account for both accelerator and cosmic ray data.

Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=s900/s200)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimatesine1(200 GeV) this measurement ofR leads tosine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofse1/stot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln2s dependence. Comparisons are made with different fits to the total cross section energy dependence.

A detailed analysis ofKs0 production in |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheKs0 production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity.

We present data on two-particle pseudorapidity and multiplicity correlations of charged particles for non single-diffractive at c.m. energies of 200, 546 and 900 GeV. Pseudorapidity correlations interpreted in terms of a cluster model, which has been motivated by this and other experiments, require on average about two charged particles per cluster. The decay width of the clusters in pseudorapidity is approximately independent of multiplicity and of c.m. energy. The investigations of correlations in terms of pseudorapidity gaps confirm the picture of cluster production. The strength of forward-backward multiplicity correlations increases linearly with ins and depends strongly on position and size of the pseudorapidity gap separating the forward and backward interval. All our correlation studies can be understood in terms of a cluster model in which clusters contain on average about two charged particles, i.e. are of similar magnitude to earlier estimates from the ISR.

A study of the two-jet mass spectrum measured with the UA 2 calorimeter has revealed a signal from hadronic decays ofW andZ bosons above a large background. Production and decay properties of the signal have been measured. The combined production cross-section σ·B(W, Z → two jets) is 9.6±2.3 (stat.)±1.1 (syst.) nb, compared with an expectation of 5.8 nb calculated to order αs2. A limit on the production cross-section of additional heavy vector bosons decaying into two jets is given as a function of the boson mass.

Cross-sections for diffractive particle production and pseudorapidity distributions of the decay products of diffractive states are presented. The data were obtained with the UA 5 streamer chamber detector at the CERNpp Collider operated in a new pulsed mode yieldingpp interactions at c.m. energies of 900 and 200 GeV. Data recorded with a special trigger designed to select a sample of events enriched in single-diffractive interactions clearly favour apt-limited fragmentation of diffractive states. The cross-section for single-diffractive particle production ? was found to be 7.8±0.5±1.1 mb at 900 GeV and 4.8±0.5±0.8 mb at 200 GeV (first error statistical, second systematic). From the pseudorapidity distribution of diffractive states we deduce the average number of charged particles to be 6.5±1.0 at 900 GeV and 4.1±1.1 at 200 GeV. Furthermore we report on our estimates for the cross-section of double-diffractive particle production at both Collider energies.

We have studied the reactionspp?ppp+p-,K+p?K+pp+p-p, p+p? p+,pp+p- and p-p ?p+p- at 147 GeV/c using the 30-inch Fermilab hybrid system. All four reactions were detected with the same apparatus and analyzed in the same way. The energy dependence of the channel cross section was found to beAp-0.6+B for thepp reaction andAp-1+B for the other three. About 90% of the cross section at 147 GeV/c can be accounted for by either beam or target diffraction. Some of the remaining cross section may come from double Pomeron exchange reactions which we tried to isolate. We have tested the hypothesis of a factorizable Pomeron and our data indicates a violation of this hypothesis. We show that the 3p mass enhancement in the mass region 1.2–1.4 GeV is diffractively produced in the p± beam reactions. Fourprong, four-constraint and six-prong, four-constraint cross sections are reported.

The gross features of the data are reviewed and the momentum tensor components, , and are studied. Evidence for coplanarity effects is observed. A probabilistic method to search for jets is proposed. The jets found by this method are seen to be similar to highpT jets frompp interactionse+e- annihilations andvp interactions. The effect of subtracting the leading particles and the effect of lowpT diffractive and non diffractive components are investigated.