Search

We have for the first time identified e + e − -pairs produced by strongly varying electromagnetic fields in distant SPt collisions at 200 GeV/u projectile energy at the CERN-SPS. The differential cross section for the mass range 10 MeV/ c 2 ≤ m ee ≤ 100 MeV/ c 2 and the polar angle range 141 mrad ≤ θ e ≤ 260 mrad agrees well with a lowest-order perturbation QED-calculation.

Few reported studies describe normal values from 24-hour ECG (Holter) recordings of small breed dogs.To investigate influence of breed, age, sex, body weight, degree of recording artifact, and mitral valve prolapse (MVP) on Holter recordings of 3 breeds of small dogs that have differing predispositions for myxomatous mitral valve disease. The study also assessed if heart rate (HR) at clinical examination (HRex) was associated with HR during Holter monitoring and evaluated the reproducibility of Holter variables.Fifty clinically healthy, privately owned dogs of the breeds Cavalier King Charles Spaniel (CKCS), Wire-haired Dachshund (wD), or Cairn Terrier (CT).Prospective, longitudinal observational study. Dogs were recruited for clinical examination, echocardiography, and Holter monitoring. In 8 CKCS, Holter recordings were performed twice with a 7-day interval. Arrhythmia and heart rate variability (HRV) analysis (time and frequency domain analysis) were performed on Holter recordings.Fifteen out of 27 Holter derived variables were significantly associated with breed (P.03), but not with age (P.7), sex (P.2), body weight (P.7), degree of recording artifact (P.4), or MVP (P.6). During Holter recording, minimum (P = .0001) and mean HR (P = .0001) were higher in CKCS compared with wD. CKCS had significantly lower values than wD, CT, or both in 10 out of 13 HRV variables (P.03). Minimum and mean HR during Holter recording were correlated with HRex (r = 0.55, P = .0003). HR and time domain variables had a coefficient of variation10%.There is an influence of breed on Holter-derived variables in 3 breeds of small dogs. Arrhythmia and HRV analysis can be performed on 24-hour ambulatory ECG (Holter) recordings. Arrhythmia analysis includes HR measurements and identification of arrhythmias.

A silicon drift detector of circular geometry giving unambiguously the radial and azimuthal coordinates of particle's interaction point for events with high multiplicity is part of the experimental set up of the NA45 experiment at CERN SPS. The paper reviews the characteristics of the detector and of its assembly among the other detectors of the experiment. The first experimental results showing the performance of the detector in term of resolution and its effectiveness in reconstructing the position of the event are reported.

The CERES/NA45 experiment at CERN uses a silicon pad detector with 64 ring shaped pads for first level triggering on minimum bias proton-nucleus as well as on high multiplicity ion-ion collisions. In addition, the counter serves as a multiplicity detector to estimate the energy density obtained in the collision. The design and performance of the pad counter in the laboratory and under real beam conditions together with the first level trigger electronics are reported.

To evaluate the use of decreasing differential function (DF) as an indication for surgery in children with congenital hydronephrosis followed according to a flow chart with repeated renography and ultrasonography.The hospital records of consecutive children (0-12 years old) who underwent an Anderson-Hynes pyeloplasty between 1993 and 2000 were reviewed. Follow-up was recommended according to a flow chart, with isotope renography and ultrasonography at 1, 3 and 6 months, and at 1 (2), 3 and 5 years of age. The diagnosis and follow-up were often at the referring hospital. The criteria for surgery included a decrease in renographic DF of10% of DF, and a DF of42%, breakthrough pyelonephritis despite antibiotic prophylaxis, pain or an anterior-posterior pelvic diameter of50 mm.Fifty-two children with unilateral hydronephrosis were included; eight had surgery because of decreasing DF of the hydronephrotic kidney. Seven children had a prenatal diagnosis. Only one of these eight children was managed according to the recommended procedures for follow-up. In two and possibly three children there was significant irreversible kidney damage since the initial renography before surgery. In one child the initial renography was at 15 months and the DF was10%. There was a functional improvement after surgery in three children.Few children undergo surgery for decreasing DF of the hydronephrotic kidney in this study. Failure to adhere to the follow-up schedule was common; this may jeopardize kidney function when using decreasing DF as a criterion for surgery. Therefore, not complying (by medical staff or the patient) with the follow-up should be considered when using expectant management for asymptomatic hydronephrosis. The serious consequences for renal function of not complying with follow-up can be avoided by surgery if the patient risks renal functional deterioration, by close cooperation with medical staff at referring hospitals, and by close follow-up at an early age with renography and ultrasonography.

Mitral valve prolapse (MVP) is a fundamental feature of myxomatous mitral valve disease in the dog. In humans, primary MVP is associated with increased platelet reactivity. In Cavalier King Charles Spaniels (CKCS), a breed predisposed to myxomatous mitral valve disease, there is a high prevalence of hypomagnesemia and platelet anomalies, such as thrombocytopenia and macrothrombocytosis. The objective of this study was to evaluate platelet aggregation responses in CKCS and to determine the relationship between the platelet aggregation response and serum magnesium concentration, MVP, mitral regurgitation (MR), and platelet count. In 19 CKCS with MVP and 7 control dogs (not CKCS), the platelet aggregation response to 3 different agonists was compared. The CKCS with100,000 platelets/microL (n = 10) had a significantly higher maximum aggregation response with regard to all tested agonists than the CKCS with100,000 platelets/microL (n = 9) and control dogs (n = 7). The CKCS with100,000 platelets/microL had a platelet aggregation response similar to the control dogs. There was no correlation between degree of MVP and platelet aggregation response. Platelet diameter increased (P = .006) and serum magnesium concentration decreased (P = .04) with lower platelet concentration. In conclusion, CKCS with MVP appeared to separate into 2 groups--1 group with100,000 platelets/microL, normal platelet aggregation, low serum magnesium concentration, and enlarged platelets, and another group with100,000 platelets/microL, increased platelet aggregation, and normal serum magnesium concentration and platelet size.

The plasma urea:creatinine ratio (U:C ratio) is known to be elevated in cases of upper gastrointestinal bleeding. Almost all patients with haematemesis have upper gastrointestinal (or generalized) bleeding so that in this study we characterized the diagnostic power of the U:C ratio in patients with stools containing altered blood without haematemesis in the hope that this simple laboratory test (used in conjunction, perhaps, with clinical data) might reduce the number of patients subjected to an unrewarding gastroscopy or colonoscopy. Of 76 cases seen in a provincial and a metropolitan hospital, 42 and 34 patients had upper and lower gastrointestinal bleeding, respectively. Fifty-four per cent of those with upper gastrointestinal bleeding and none of those with lower gastrointestinal bleeding had U:C ratios above 110 on admission. However, a discriminating level of 90 is considered to be more suitable, judged by the quadratic uncertainty score. At this level the odds for upper gastrointestinal bleeding were 15:1.

One hundred ninety consecutive Dachshunds2 years of age, including 18 families consisting of both parents and 4 or more offspring, were examined clinically and echocardiographically to study the epidemiology and inheritance of mitral valve prolapse (MVP) and other signs of myxomatous mitral valve disease in the dog. From video-recorded echocardiograms, MVP severity, jet size (color Doppler), and leaflet thickness were assessed. With regard to murmur intensity and each of these 3 echocardiographic measurements. the inheritance and the influence of age, gender, coat type, body weight, degree of obesity, heart rate, and thorax dimensions were evaluated. MVP severity correlated positively with age (P.0001) and heart rate (P = .002), negatively with thorax circumference (P = .0005), and was related to coat type (P = .006). MVP severity progressed faster in males than in females (P = .0002). The other measures of disease severity (jet size, leaflet thickness, and murmur intensity) also correlated positively with age (all P.0001). When compared in pairs, all 4 measures of disease severity correlated significantly with one other. Pedigree analyses did not disclose agreement with simple Mendelian models, but high disease prevalence made interpretation difficult. Mean parental MVP severity correlated significantly with MVP severity in the offspring (P = .03). The epidemiology of MVP in Dachshunds resembles that of MVP in humans, MVP severity correlates significantly with other measures of the degree of myxomatous mitral valve disease, and MVP is an inherited condition in Dachshunds. A polygenic mode of inheritance is suggested.

Observer variation in diagnosing mild mitral regurgitation in dogs by cardiac auscultation was assessed by having 6 veterinarians with different levels of experience examine 57 Cavalier King Charles Spaniels. Comparisons with color Doppler echocardiography and phonocardiography were made, and the effects of 2 physical maneuvers on the auscultatory findings were evaluated. Using mildly diseased dogs, interobserver agreement in diagnosing the presence or absence of left-sided murmurs ranged from 63% to 88%. The agreement with phonocardiography (range, 53-91%) increased with the amount of observer experience. The 2 most experienced observers could discern soft ejection murmurs from regurgitant murmurs and were able to diagnose 89% of the dogs with regurgitant jets larger than 30% of the left atrial area. In general, less experienced observers diagnosed most jets larger than 50%. In many dogs with small jets, no murmur was found by auscultation and phonocardiography. The audibility of mild regurgitation was significantly reduced in dogs that were difficult to auscultate. Early systolic murmurs were typical of mild regurgitation, whereas holosystolic murmurs typified severe regurgitation. In a few dogs, late systolic murmurs alternated with holosystolic murmurs. Systolic clicks were found phonocardiographically in 18 dogs with mild to moderate regurgitation, but the audibility apparently was low. In many mildly affected dogs, physical maneuvers increased murmur intensity. Thus, some form of dynamic auscultation might facilitate the diagnosis of mild regurgitation. Auscultatory findings in mild regurgitation appear to depend on observer experience, circulatory status, and how difficult the dog is to auscultate.

Traditionally, patients with non-invasive bladder tumours are evaluated every three months in the first year(s) after primary resection. In a randomised controlled design we evaluated the consequences of doubling the follow-up intervals for patients with non-invasive bladder tumours (Ta) grade I and II without concomitant urothelial dysplasia. The patients were allocated to one of the two regimens: Regimen I: follow-up every three months for the first two years, every sixth month in the third year and thereafter once a year. Regimen II: every sixth month the first year, and once a year thereafter. Follow-up examinations were usually performed by transabdominal ultrasound, but cystoscopy was performed once a year in all patients. Of the 97 evaluable patients, three patients in regimen I and one patient in regimen II progressed in relation to stage and/or grade in the study period. No patient died from the tumour disease. There was no difference with regard to recurrence and progression between the two groups.

In a joint experiment the TAPS and CERES collaborations have studied the production of the neutral mesons $\pi^\circ,\eta$ and $\omega$ in 450 GeV p-Be and p-Au collisions at the CERN SPS. The mesons were identified by their $\pi^\circ\rightarrow\gamma\gamma$ , $\eta\rightarrow\gamma\gamma$ , and $\omega\rightarrow\pi^\circ\gamma$ decay modes. The cross sections were measured down to very low $p_T$ ( $\geq$ 20 MeV/c) near mid-rapidity ( $3.0 < y < 4.0$ ). The $\eta$ and $\omega$ cross sections are smaller than expected from extrapolations of earlier data to low $p_T$ . Integrated over all $p_T$ , the ratios $\eta/\pi^\circ$ and $\omega$ / $\pi^\circ$ are lower by about 25% compared to previously published values. The reduction may be attributed to the large number of low $p_T$ pions from decays of heavier mesons. In addition, we have studied the dependence of neutral meson production on the mass of the nuclear target and find it in good agreement with previous measurements of charged mesons.

Considerable resources are devoted to the follow-up of patients with superficial bladder tumors. Traditionally these patients are evaluated every three months in the first year(s) after the primary resection. In a randomised controlled design we evaluated the consequences of doubling the follow-up intervals for patients with non-invasive bladder tumors (Ta) with none of the following risk factors: concomitant urothelial dysplasia, tumor gradeII, early recurrence. The patients were allocated to one of two follow-up regimens: Regimen I: follow-up every three months for the first two years and every six months in the third year, thereafter once a year. Regimen II: Every six months for the first year and once a year thereafter. At most of the follow-up visits the bladder was examined by transabdominal ultrasound. Cystoscopy was performed in all patients once a year. The data from the 97 patients were evaluable. Three patients in regimen I and 1 patient in regimen II progressed in grade and/or stage in the observed period. No patient died of his tumor disease. There was no difference with regard to recurrence, progression and tumor-related death between the two groups. The total number of follow-up visits in regimen II was reduced by 37.5% (P = 0.0016) compared to regimen I. The number of patients specific follow-up visits with a recurrent tumor present was increased by 65% (P = 0.0475). In the future we will follow this selected group of patients with non-invasive bladder tumors as described.

The CERES experiment (CErenkov Ring Electron Spectrometer) studies the production of low mass e + e − pairs in proton-proton, proton-nucleus and nucleus-nucleus interactions at the CERN SPS. The CERES spectrometer, has a novel design based on two Ring Imaging Cherenkov (RICH) counters, and it operates close to its design specifications. Data were recorded with 200 GeV u sulfur beam and 450 GeV proton beam. The analysis is in progress. We have extracted first e + − -pairs samples for p+Be, p+Au and S+Au collisions. In addition other physics topics were addressed. Inclusive photon spectra were measured in S+Au interactions. No excess over known hadronic sources was found within our present systematic error of 11%. Results on high p i charged pion spectra are presented up to 4 GeV c . We also studied the production of e + e − -pairs m the strong electromagnetic fields of very peripheral S+Pt collisions. The data are well described by a first-order perturbative QED-calculation.

We have measured the inclusivepT spectra of soft photons produced at central and backward rapidities in 450 GeV/cp-Be collisions down to 1 MeV/c in transverse momentum. In the region 1

In a double-blind, placebo-controlled multicentre study, the effect of luteinizing-hormone-releasing-hormone (LHRH) in 141 boys was analysed after 4-week treatment period with 0.4 mg LHRH nasal spray or placebo nasal spray three times daily. Data from 123 boys was analysed, with 62 boys in the treatment group and 61 in the placebo group. Full response i.e. the testis at the bottom of the scrotum on both sides in boys with bilaterally undescended testes, was found in six patients, one of them in the placebo group [Therapeutic gain of LHRH with 95% CI: 8.1% (0.1-16.6%, P = 0.12)]. Only in these boys could surgery be avoided. Considering the number of testes (and not the number of boys) a significant effect was found on at least one testis in 25% of boys with bilaterally undescended testes [Therapeutic gain with 95% CI: 24.0% (13.2-34.8%, P = 0.001)]. In unilateral undescended testes, the LHRH treatment showed no effect (P = 1.00). The inclusion of retractile testes did not affect our results. In our opinion LHRH has a limited place in treatment of the non-descended testis.

We have measured the production of one and two large transverse momentum hadrons in pp and pp interactions in the range 2 < pT < 6 GeV/c for the central rapidity region |y| < 0.9 at s = 63 and 31 GeV. No statistically significant difference between pp and pp collisions is observed. The results are in accordance with lowest order QCS perturbative calculations and rule out a large contribution of Constituent Interchange Model (CIM), di-quark of quark-fusion subprocesses in this kinematic range.

We have measured the production of prompt positrons in pp collisions at √s = 63 GeV and y = 0 in the pT interval 0.12

Low-transverse-momentum photon production at the CERN ISR is compared in high- and low-multiplicity events. High-transverse-energy pp collisions and low-multiplicity ..cap alpha cap alpha.. and pp collisions are studied. Relative photon-to-charged-track production is found to be the same in pp minimum bias, ..cap alpha cap alpha.. minimum bias, and pp high-transverse-energy collisions, to within 15%. No low-P/sub T/ excess is seen; the limits are dominated by systematic uncertainties.

The detailed shape of events triggered by a 1.7 sr hadron calorimeter is studied using charged track information in the Axial Field Spectrometer at the CERN ISR. With increasing transverse energy (ET) a large fraction of the events are seen to have a limited transverse momentum relative to the trigger direction. A comparison of the circularity of the events with a prediction of a QCD-motivated Monte Carlo model shows that at high ET the events originate predominantly from two-constituent scattering.

The production of direct photons has been measured relative to π 0 's in the rapidity range 2.00 y s = 63 GeV at the CERN Intersecting Storage Rings. The γ/π 0 ratio increases from ⪅2% at p T = 1.5 GeV/ c to ∼8% at p T = 4.25 GeV/ c , similar to the value observed near 90°. The results indicate no strong enhancement of single-photon production due to quark bremsstrahlung in this kinematic region.

Relative yields of $\ensuremath{\varphi}$ and charged $K$ mesons are measured as functions of charged multiplicity in the central rapidity region for $\mathrm{pp}$, $\mathrm{dd}$, $p\ensuremath{\alpha}$, and $\ensuremath{\alpha}\ensuremath{\alpha}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=3.15 \mathrm{and} 44$ GeV. No anomalous strange-particle production is observed in $\ensuremath{\alpha}\ensuremath{\alpha}$ reactions relative to $\mathrm{pp}$ even at large multiplicities corresponding to events comprising less than 3.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ of the inclusive cross section.

Production of rho ^{0}, K*^{0}, and phi have been measured in proton-proton collisions at the CERN Intersecting Storage Rings (ISR) at low p/sub T/ in the central region. The transverse mass spectra are well described by exp (-a mu /sub T/), with a=-6.4+or-0.2 GeV/sup -1/. The cross sections for d sigma /dy mod /sub y=0/ are 6.5+or-0.8+or-1.2 mb for rho ^{0}, 1.9+or-0.3+or-0.3 mb for K*^{0}, 1.9+or-0.3+or-0.3 mb for K*^{0}, and 0.60+or-0.12+or-0.13 mb for phi , where the first error is statistical and the second is systematic.

Calorimeter measurements of dσ de t for pp, dd, pα , and αα collisions at S nn =31.5 GeV are presented for the pseudorapidity interval | η cm | ⩽ 0.7, extending over eight decades to E t ⩾ 30 GeV. The data are compared with models that predict nuclear cross sections directly from pp data, under the assumption of independent nucleon scatters.

Measurements of charged particle multiplicity distributions in the central rapidity region in p-p and p-α, and α-α collisions are reported. They are better fitted to the “wounded nucleon” than to the “gluon string” model. The average transverse momenta, for all three reactions, are identical (and almost independent of multiplicity) up to very high multiplicities.

The production of inclusive prompt positrons in pp collisions at √ s = 63 GeV and θ cm = 90° has been measured over the p T interval 0.08 T GeV c . The e / π ratio rises from ∼ 2 × 10 −4 at p T = 0.9 GeV c to ∼ 1 × 10 −3 at p T = 0.1 GeV c . This is a factor of 6 higher than would be expected from the sum of hadronic bremsstrahlung and the semileptonic decay of charm.

The differential cross section for production of jets in pp interactions at y = 0 and p T from 6–12 GeV/ c has been measured at √ s = 45 GeV at the CERN Intersecting Storage Rings and compared with a previous measurement at √ s = 63 GeV. The data were obtained using a 2.1 sr hadron calorimeter which was triggered on transverse energy. The energy dependence of the jet cross section is well described by (1− x T ) m p T − n , with m = 10.6±1.0 and n = 5.3±0.2. The results are in good agreement with predictions obtained from a QCD-motivated model.

We have measured the production of direct photons, π 0 's, and η's in p p and pp collisions at √ s =53 GeV in the range 2≈ p T ≈6 GeV/ c for the central rapidity region | y | 0.4. No statistically significant difference between pp and pp interactions is observed.

Rapidity and charge distributions have been measured for central charged tracks in events at center-of-mass energy 63 GeV, triggered on a ..pi../sup 0/ near 11/sup 0/ with transverse momentum greater than 2.25 GeV/c. The observed distributions are consistent with parton-parton scattering models with a spin-one gluon, and inconsistent with the exchange of a spin-zero gluon.

We study the production of identified charged particles in pp collisions at a c.m. energy of 63 GeV in events with an identified high-pT trigger particle. The measurements were performed at the CERN Intersecting Storage Rings using the Axial Field Spectrometer. Production ratios are presented as a function of pT in the range 2.5 to 8 GeV/c.

In this report we describe construction and performance of two identical units of electromagnetic shower counters which were installed in the axial-field spectrometer at the CERN-ISR in 1982 to provide improved detection of photons and electrons over a 1.3 sr solid angle of the AFS calorimeter. Thallium doped sodium-iodide in the form of small blocks served as an active shower material. Vacuum photodiodes and low-noise charge sensitive electronics were used for the deposited energy measurement and signal amplification. The stable performance of the detectors over a period of more than 18 months until the closure of the ISR has proven that vacuum photodiodes can reliably be utilized in highly modularized large scale detectors operating in a high magnetic field environment.

We have studied the inclusive production of the hadrons π±, K±, p, p , Λ, Λ , ρ and ⋉ in the central region at the ISR s = 53 GeV , in both pp and p p collisions. Differences are observed only for K±, p, and p production. We then study also correlations between low-pT pp and p p pairs in the two types of collisions, separating the contribution from baryon pair production and from the incident particles (stopping protons). We observe a positive correlation between two stopping protons; between the production of two pairs, and between a stopping proton and a pair production, there are negative correlations.

Calorimeters downstream of the intersection of pα and αα beams in the ISR have been used to study the hadronization of excited nucleons. These data extend and support the conclusions from previous studies of the A-dependence of particle multiplicities in ultrarelativistic p-nucleus collisions, which provided evidence that the proton hadronizes outside the nuclear volume.

Events with a large transverse energy in a calorimeter with full azimuthal coverage and |y

The properties of high-ET events produced inpp collisions at\(\sqrt s \)=63 GeV have been studied at the CERN Intersecting Storage Rings. The fragmentation of the jets is found to be very similar to that of jets produced ine+e− annihilation and at the SPS\(p\bar p\) collider. We measure an excess of soft particles compared withe+e− events and this underlying event is found to be sensitive to the trigger. ThepT balance between the jets is measured. The distribution of charges in the jets indicates that a substantial fraction of the jets originate from valence quarks.

The inclusive π0 production cross-section and the η/π0 ratio have been measured inpp collisions at\(\sqrt s = 63 GeV\) at the CERN Intersecting Storage Rings in the rapidity range 2.00

A uranium-scintillator sandwich electromagnetic calorimeter has been constructed for the detection of photons produced at small angles at the CERN ISR. The calorimeter was designed to have good energy and spatial resolution to resolve the two photons from π° decays up to a maximum energy of ∼ 25 GeV (PT ∼ 4.5 GeV/c). The longitudinal division into a front and back section provided information for discriminating between electromagnetic and hadronic showers. The mechanical design is described along with test beam results and the operation of the calorimeter in the ISR.

We present results obtained with a uranium/copper scintillator fine-sampling calorimeter with wavelength shifter readout. Test beam measurements made with e±, π± and protons in the momentum range 0.3–40 GeV/c are presented. The calorimeter achieves energy resolutions of σ(E) E = 0.36 √E and 0.16 √E for hadrons and electrons, respectively. The measured ratio of response for electrons to that for hadrons is 1.11, for energies of 2 GeV or more. The spatial resolution achieved for single particles at normal incidence is ∼1 cm for electromagnetic showers and ∼3 cm for hadronic showers. Operational experience over three years of running at the CERN ISR, including operation at very high luminosities (∼1.4×1032 cm−2 s−1) is described.

We have studied the processpp→γγ+X at\(\sqrt s = 63 GeV\) GeV in the central rapidity region. We report a positive signal at 96% C.L., a ratio γγ/e+e−=4.0±3.0 when the transverse momentum of each photon is above 2 GeV/c, and a cross-sectiondσ/dydMγγ=(5.5±2.7)×10−34 cm2/GeV when |y

We have studied the distribution of charged particles recoiling from high pT (> 3.5 GeV/c) direct photons and neutral pions in pp collisions at ?s = 63 GeV. One expects a different mixture of quark and gluon initiated jets in the two cases, with predominantly u-quark jets recoiling from direct photons. No significant differences are observed in our momentum range apart from the charge composition, with a larger positive to negative ratio for particles with pT > 1 GeV/c opposite direct photons than opposite ?0.

Measurements of the central multiplicity associated with high-p/sub t/ particles up to 2 GeV/c in p-p, p-..cap alpha.., and ..cap alpha..-..cap alpha.. collisions, and measurements of dsigma/dE/sub t/ are presented. The difference in associated multiplicity, n(p-..cap alpha..)-n(p-p), is independent of p/sub t/ while n(..cap alpha..-..cap alpha..)-n(p-p) rises with p/sub t/, providing new information on the ''anomalous'' p/sub t/ dependence of nuclear inclusive cross sections.

Calorimeters have been used to study the energy released in the fragmentation region of inelastic 15 GeV p  15 GeV p and 63 GeV α  63 GeV α collisions in correlation with high multiplicity in the central (pseudorapidity |η|< 1.7) region. Events with large central multiplicities (≳50 charged particles) may be simply interpreted as arising from independent inelastic collisions involving four nucleons in each α-particle

We present measurements of the αα elastic scattering differential cross section at √ s = 126 GeV in the range 0.05 ⩽ ‖ t ‖ c ) 2 . The data give an improved definition of the first cross section minimum at ‖ t ‖ = 0.098 (GeV/ c ) 2 and are consistent with theotheoretical models of nucleus-nucleus scattering. The αα total cross section obtained by extrapolation to the optical point is 280 ± 70 mb.

We present stdies of events triggered on two high-pT jets, produced inpp collisions at the CERN Intersecting Storage Rings (ISR) at\(\sqrt s \)=63 GeV, using a large solid angle calorimeter. The cross-section for producing two jets is measured in the dijet mass range 17–50 GeV/c2. A high-statistics sample of dijet events, where each jet has transverse energy above 10 GeV, is used to study the structure of jets and the associated event. We find the longitudinal fragmentation function to be similar to that of jets emerging frome+e− collisions but considerably harder than that observed at the Super Proton Synchrotron (SPS)\(p\bar p\) Collider. A steepening of the fragmentation function is observed when increasing the jet energy. Studies of the charge distribution in jets show that these predominantly originate from fragmenting valence quarks. The transverse energy and particle flows are presented as functions of the azimuthal distance from the jet axis.

We have searched for direct photons of low PT (≤1.0 GeV/c) at θc.m.=90° in pp collisions at √s =63 GeV. We used two independent methods: direct detection in NaI crystals and conversion to e+e− pairs. No signal is observed; the photon spectrum is well described by the decay of hadrons. The result is consistent with a direct low-PT photon signal reported at √s =12 GeV, but excludes a rapid growth of soft-photon production with √s .

We present results from a study of centrally produced mesons in 3 × 106 events with two small-angle protons at the CERN Intersecting Storage Rings. A high-statistics sample of exclusive pp → ppπ+π− events at √s = 63 GeV has been obtained, where the reaction mechanism is dominated by double pomeron exchange. Scalar or tensor glueballs may be produced by this process. The π+π− mass spectrum has a distinctive structure, and analysis shows that the data are dominantly S-wave up to 1600 MeV. The behaviour of the D-wave provides evidence for a 2++ resonance (M = 1480 ± 50 MeV, Γ = 150 ± 50 MeV) in addition to the f(1270). We also show data on exclusive K + K − , p p , and π + π − π + π − production, and on the analogous reaction αα → ααπ+π− at √s = 126 GeV. Flavour independence is suggested by the observation of approximately equal numbers of K+K− and π+π− pairs for mass above 1 GeV. The mass spectra are also apparently independent of √s (45, 63, 126 GeV) and incident particle type (p, α).