Quentin Ingram

Experimental results obtained at the CERN Super Proton Synchrotron on the structure-function ratio F2n/F2p in the kinematic range 0.004<x<0.8 and 0.4<Q2<190 GeV2, together with the structure function F2d determined from a fit to published data, are used to derive the difference F2p(x)-F2n(x). The value of the Gottfried sum F(F2p-F2n)dx/x=0.240±0.016 is below the quark-parton-model expectation of 1/3.Received 23 January 1991DOI:https://doi.org/10.1103/PhysRevLett.66.2712©1991 American Physical Society

The muon-proton and muon-deuteron inclusive deep inelastic scattering cross sections were measured in the kinematic range 0.002 < × < 0.60 and 0.5 < Q2 < 75 GeV2 at incident muon energies of 90, 120, 200 and 280 GeV. These results are based on the full data set collected by the New Muon Collaboration, including the data taken with a small angle trigger. The extracted values of the structure functions F2p and F2d are in good agreement with those from other experiments. The data cover a sufficient range of y to allow the determination of the ratio of the longitudinally to transversely polarised virtual photon absorption cross sections, R = σLσT, for 0.002 < × < 0.12. The values of R are compatible with a perturbative QCD prediction; they agree with earlier measurements and extend to smaller x.

We present a new determination of the nonsinglet structure function ${\mathit{F}}_{2}^{\mathit{p}}$ - ${\mathit{F}}_{2}^{\mathit{n}}$ at ${\mathit{Q}}^{2}$=4 ${\mathrm{GeV}}^{2}$ using recently measured values of ${\mathit{F}}_{2}^{\mathit{d}}$ and ${\mathit{F}}_{2}^{\mathit{n}}$/${\mathit{F}}_{2}^{\mathit{p}}$. A new evaluation of the Gottfried sum is given, which remains below the simple quark-parton model value of 1/3.

The proton and deuteron structure funtions F2p and F2d were measured in the kinematic range 0.006 < x < 0.6 and 0.5 < Q2 < 75 GeV2, by inclusive deep inelastic muon scattering at 90, 120, 200 and 280 GeV. The measurements are in good agreement with earlier high precision results. The present and earlier results together have been parametrised to give descriptions of the proton and deuteron structure functions F2 and their uncertainties over the range 0.006 < x < 0.9.

We present the structure function ratios measured in deep inelastic muonnucleus scattering at a nominal incident muon energy of 200 GeV The kinematic range is covered. For values of x less than 0.002 both ratios indicate saturation of shadowing at values compatible with photoabsorption results.

Results are presented for F2d/F2p and Rd − Rp from simultaneous measurements of deep inelastic muon scattering on hydrogen and deuterium targets, at 90, 120, 200 and 280 GeV. The difference Rd − Rp, determined in the range 0.002 < x < 0.4 at an average Q2 of 5 GeV2, is compatible with zero. The x and Q2 dependence of F2d/F2p was measured in the kinematic range 0.001 < x < 0.8 and 0.1 < Q2 < 145 GeV2 with small statistical and systematic errors. For x > 0.1 the ratio decreases with Q2.

Results are presented on the ratio of neutron and proton structure functions, F2n/F2p, deduced from deep inelastic scattering of muon from hydrogen and deuterium. The data, which were obtained at the CERN muon beam at 90 and 280 GeV incident energy, cover the kinematic range x = 0.002−0.80 and Q2 = 0.1−190 GeV2. The measured structure function ratios have small statistical and systematic errors, particularly at small and intermediate x. The observed Q2 dependence in the range x = 0.1−0.4 is stronger than predicted by perturbative QCD. From the present data together with results from other experiments it is suggested that the twist-four coefficient for the proton is smaller than that for the neutron for x larger than 0.2.

The elastic scattering of positive pions by deuterium has been studied at seven energies between 82 MeV and 292 MeV laboratory kinetic energy in the angular range between 30° and 130° (lab). The results are compared to recent relativistic three-body calculations.

Exclusive ϱ0 and φ muoproduction on deuterium, carbon and calcium has been studied in the kinematic range 2< Q2< 25 GeV2 and 40 < ν < 180GeV. We discuss the Q2 dependence of the cross sections, the transverse momentum distributions for the vector mesons, the decay angular distributions and, in the case of the ϱ0, nuclear effects. The data for 0 production are compatible with a diffractive mechanism. The distinct features of φ production are a smaller cross section and less steep pt2 distributions than those for the 0 mesons.

The interaction of 47.5 (±0.5) MeV positive pions with douterons was studied using a scintillation counter telescope as the pion spectrograph. With an energy resolution sufficient to separate the elastic from inelastically scattered pions, the system was used to measure the cross sections for these reactions as well as the non-radiative pion capture process over the angular range of 22.5°–157.5°. The scattering results are well-fitted by recent theoretical calculations provided appropriate pion-nucleon phase shifts are used. The protons from the non-radiative capture reaction are fitted by a differential cross section of the form: dσ/dΩ ∝ A + cos2 θ, with A = 0.31 ± 0.03.

We present results on inelastic J/ψ production from muon interactions with hydrogen and deuterium at an incident muon energy of 280 GeV. The measured cross section ratio per nucleon for muon-induced Jψ production in deuterium and hydrogen was found to be R(D2/H2) = 1.01±0.15. The colour singlet model is shown to provide a good description of the observed differential cross section apart from a normalisation factor. The comparison between the observed cross section and the colour singlet model prediction allows the extraction of the gluon structure function G(x) of the nucleon. The momentum fraction x of the nucleon carried by the gluon is measured in the range of x = [0.02, 0.30]. The normalised gluon distribution of free nucleons thus found can be parametrised as xG(x) = 12 (η+1) (1−x)η, withη=5+-9(sta.).

The Q2 dependence of the structure functions F2p and F2d recently measured by the NMC is compared with the predictions of perturbative QCD at next-to-leading order. Good agreement is observed, leading to accurate determinations of the quark and gluon distributions in the range 0.008 ⩽ × ⩽ 0.5. The strong coupling constant is measured from the low x data; the result agrees with previous determinations.

The energy resolution of the barrel part of the CMS Electromagnetic Calorimeter has been studied using electrons of 20 to 250 GeV in a test beam. The incident electron's energy was reconstructed by summing the energy measured in arrays of 3 × 3 or 5 × 5 channels. There was no significant amount of correlated noise observed within these arrays. For electrons incident at the centre of the studied 3 × 3 arrays of crystals, the mean stochastic term was measured to be 2.8% and the mean constant term to be 0.3%. The amount of the incident electrons' energy which is contained within the array depends on its position of incidence. The variation of the containment with position is corrected for using the distribution of the measured energy within the array. For uniform illumination of a crystal with 120 GeV electrons a resolution of 0.5% was achieved. The energy resolution meets the design goal for the detector.

Results are reported for the elastic scattering of π+ and π− by 16O and 40Ca between 115 MeV and 240 MeV. Large differences between the π+ and π− cross sections are observed up to large angles which are substantially explained by simple Coulomb effects.

We present results on J/ψ production in muon interactions with tin and carbon targets at incident muon energies of 200 and 280 GeV. The ratio of cross sections per nucleon for J/ψ production on tin and carbon, R(Sn/C), is studied as a function of pT2, z and x. We find an enhancement for coherent J/ψ production Rcoh(Sn/C) = 1.54 ± 0.07, a suppression for quasielastic production Rqe(Sn/C) = 0.79 ± 0.06 and for inelastic production Rin(Sn/C) = 1.13 ± 0.08. The inelastic cross section ratio can be interpreted within the Colour Singlet model as an enhancement of the gluon distribution in tin with respect to that in carbon. The dependence of the ratio on z and pT2 can explain the discrepancy between the results obtained in previous experiments.

We present the energies, widths, and cross sections of the isovector monopole resonance in nuclei between $^{40}\mathrm{Ca}$ and $^{208}\mathrm{Pb}$ excited by the (${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${\ensuremath{\pi}}^{0}$) reactions. We also give results for the giant dipole resonance. Both resonances exhaust the same substantial fraction of the cross section calculated in a random-phase, distorted-wave impulse-approximation model. No isovector quadrupole resonance was observed.

Results are presented on the difference in R, the ratio of longitudinally to transversely polarised virtual photon absorption cross sections, for the deuteron and the proton. They are obtained by comparing the ratio of cross sections for the deep inelastic scattering of muons from deuterium and hydrogen targets at 90 and 280 GeV incident energy. The results cover the range x=0.01–0.30, at an average Q2 of 9 GeV2. The measured difference Rd-Rp shows no significant x dependence and is compatible with zero, as well as with expectations from perturbative QCD. We use the same method to obtain the difference RCa-RC from cross section ratios measured on carbon and calcium targets at 90 and 200 GeV incident energy.

The avalanche photodiodes, developed by Hamamatsu Photonics in collaboration with CMS, which are to be used to read out the lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter, are described. The procedures taken to ensure their long-term reliability in the radiation environment expected in CMS are outlined, as well as the studies made to verify the very high reliability required.

The electromagnetic calorimeter of the CMS experiment at CERN's Large Hadron Collider will use 122 400 Avalanche Photodiodes from Hamamatsu Photonics. The design of this APD type is the result of a long R&D program performed by Hamamatsu Photonics and the CMS collaboration. The APD parameters including the behavior under irradiation are discussed in view of our application.

Results are presented for six nuclei from Be to Pb on the structure function ratios F2A/F2C(x) and their A dependence in deep inelastic muon scattering at 200 GeV incident muon energy. The data cover the kinematic range 0.01 < x < 0.8 with Q2 ranging from 2 to 70 GeV2. The A dependence of nuclear structure function ratios is parametrised and compared to various models.

The structure function ratiosF 2 C /F 2 Li ,F 2 Ca /F 2 Li andF 2 Ca /F 2 C were measured in deep inelastic muonnucleus scattering at an incident muon energy of 90 GeV, covering the kinematic range 0.0085<x<0.6 and 0.8<Q 2<17GeV2. The sensitivity of the nuclear structure functions to the size and mean density of the target nucleus is discussed.

Quasielastic production of J/ψ mesons has been measured in muon interactions with hydrogen, deuterium, carbon and tin targets at incident muon energies of 200 and 280 GeV. The hydrogen and deuterium data were used to study the transverse momentum distribution of the J/ψ's. These data have been analysed together with previously published ϱ0 data in the framework of the vector meson dominance model. The radii of the Jψ and the ϱ0 as well as the total J/ψ-N and ϱ0-N cross sections were deduced. From the tin and carbon data the ratio of the quasielastic J/ψ production cross sections, Rqe(Sn/C), has been extracted and found to be less than unity. In the Glauber approach this suppression can be related to the J/ψ absorption probability in nuclei. The suppression is also compared to those predicted by various colour transparency models.

We have studied transverse momentum distributions for exclusiveρ 0 muoproduction on protons and heavier nuclei at 2<Q 2<25 GeV2. TheQ 2 dependence of the slopes of thep 2 andt′ distributions is discussed. The influence of the non-exclusive background is investigated. Thep 2 -slope for exclusive events is 4.3±0.6±0.7 GeV−2 at largeQ 2. Thep 2 spectra are much softer than inclusivep 2 spectra of leading hadrons produced in deep inelastic scattering.

A search for possible structure in the energy spectrum of forward going protons from the 12C(π+, 3p)X reaction was undertaken. The measurement was done for π+ momenta of 355, 375, and 405 MeV/c. No narrow (less than 20 MeV) structure was found. A broad structure corresponding to a quasi-free scattering of the pion before capture, superimposed on a continuum background, was observed. The data indicate that additional free nucleons or light products are usually present in the final state.

The photo detectors of the CMS electromagnetic calorimeter have to operate in a rather hostile environment, in a strong magnetic field of 4 T and under unprecedented radiation levels. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 62,000 lead tungstate crystals in the barrel part of the calorimeter. After a 6 year long R&D work Hamamatsu Photonics produces APDs with a structure that is basically radiation hard. Only a few percent of the delivered APDs are weak due to defects at the surface caused by dust particles in the production process. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of 60Co irradiations and annealing under bias of all APDs and irradiations with hadrons on a sampling basis.

Avalanche Photodiodes (APD) with improved characteristics were developed by Hamamatsu Photonics for the Electromagnetic Calorimeter of the CMS experiment. This report presents measurements of the latest generation of APDs, which are capable to operate at high gains (∼2000).

We have measured the fivefold differential cross section ${d}^{5}$\ensuremath{\sigma}/d${\ensuremath{\Omega}}_{\ensuremath{\pi}}$d${\ensuremath{\Omega}}_{\ensuremath{\gamma}}$${\mathrm{dE}}_{\ensuremath{\gamma}}$ for the process ${\ensuremath{\pi}}^{+}$p\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$p\ensuremath{\gamma} with incident pions of energy 299 MeV. The angular regions for the outgoing pions (55\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\pi}}\mathrm{\ensuremath{\le}}95}$\ifmmode^\circ\else\textdegree\fi{}), and photons (${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\gamma}}=241\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\ifmmode\pm\else\textpm\fi{}10}$\ifmmode^\circ\else\textdegree\fi{}) in coplanar geometry are selected to maximize the sensitivity to the radiation from the magnetic dipole moment of the ${\ensuremath{\Delta}}^{++}$(1232) resonance. At low photon energies, the data agree with the soft-photon approximation to pion-proton bremsstrahlung. At forward pion angles the data agree with older data and with the latest theoretical calculations for 2.3${\ensuremath{\mu}}_{p}$\ensuremath{\le}${\ensuremath{\mu}}_{\ensuremath{\Delta}}$\ensuremath{\le}3.3${\ensuremath{\mu}}_{p}$. However at more backward pion angles where no data existed, the predictions fail.

The Hamamatsu Photonics S8148 large area Avalanche Photo Diodes (APD) were designed for the crystal electromagnetic calorimeter of the CMS setup at LHC in a close collaboration of Hamamatsu Photonics and CMS APD group (PSI, Northeastern University and University of Minnesota). All essential parameters of these devices are controlled by the producer and are fairly stable during the mass production, except the radiation hardness. To insure 99.9% reliability of APDs in the radiation hard environment of LHC, the CMS APD group had to invent a dedicated screening procedure. The details of this procedure and some results of the screening are discussed.

Avalanche Photodiodes (APDs) are now out of their infancy and are used in large numbers in the electromagnetic calorimeter of CMS where they have to stand the extremely hostile environment of LHC. This type—with smaller sensitive area and arranged in monolithic arrays—is an excellent candidate for the read out of scintillating crystals in medical imaging and a PET scanner operates already successfully since more than 3 years. We present the properties of the device used in CMS and possible improvements of the structure, which could open the door for new applications. Operating APDs at low temperatures or in Geiger mode will allow single photon counting and in future they could replace photomultiplier tubes.

The feasibility of using cosmic rays to make an intercalibration of the ECAL Supermodules before installation in CMS has been investigated. In a test with a single crystal a clear signal with a width of 15% rms was seen, with rates as expected. Simulations using a simplified detector geometry and a parameterisation of the vertical cosmic ray muon flux indicate that it is feasible to use the surrounding crystals as veto counters to ensure a longitudinal trajectory through the crystal, without introducing a large systematic error. The statistical error would be around 1% for one week of running.

Abstract Avalanche Photodiodes (APDs) are now out of their infancy and are used in large numbers in the electromagnetic calorimeter of CMS where they have to stand the extremely hostile environment of LHC. This type—with smaller sensitive area and arranged in monolithic arrays—is an excellent candidate for the read out of scintillating crystals in medical imaging and a PET scanner operates already successfully since more than 3 years. We present the properties of the device used in CMS and possible improvements of the structure, which could open the door for new applications. Operating APDs at low temperatures or in Geiger mode will allow single photon counting and in future they could replace photomultiplier tubes.

The response of the Avalanche Photo-diodes (APDs) installed in the CMS detector at the LHC to neutrons from 241AmBe and 252Cf sources is reported. Signals in size equivalent to those of up to 106 photo-electrons with the nominal APD gain are observed. Measurements with an APD with the protective epoxy coating removed and with the source placed behind the APD show that there is an important response due to recoil protons from neutron interactions with the hydrogen in the epoxy, in addition to signals from neutron interactions with the silicon of the diode. The effective gain of these signals is much smaller than the diode's nominal gain.

This paper presents a large solid angle measurement of the positive pion absorption cross section on 4He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of Tπ+=70, 118, 162, and 239 MeV are 35±5, 52±4, 51±5, and 27±2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels.Received 2 September 1997DOI:https://doi.org/10.1103/PhysRevC.58.942©1998 American Physical Society

The photodetectors which read out the scintillation light generated in the lead tungstate crystals in the barrel part of the Compact Muon Solenoid (CMS) electromagnetic calorimeter are avalanche photodiodes (APDs). Scanning the APD's active area with a collimated light spot, the spatial uniformity of their quantum efficiency and gain has been measured at four different operating gains. Details of the APD surface structure are examined by scanning with a fine light spot. These details help to explain the difference between the bias voltage for a given gain when the full APD area is illuminated and when only the central part is illuminated.

Specially developed avalanche photodiodes (APDs) will be used to measure the light from the 61,200 lead tungstate crystals in the barrel part of the CMS electromagnetic calorimeter. To ensure the reliability over the lifetime of the detector, every APD is screened by irradiation and burn-in before it is accepted for CMS. As part of the establishment of the screening procedure and to determine its effectiveness, a large number of APDs were screened twice. The results of these tests suggest that the required reliability will be achieved.

We have studied the excitation function of the reaction 2H(π±, p)X at a fixed proton angle of 90° for several fixed proton momenta of the detected proton as a function of the incident pion energy. No signal was found for a previous candidate for a dibaryon resonance around a mass of 2.23 GeV. The general trend of the data is reproduced by a multiple scattering theory

Abstract

The light from the lead tungstate crystals of the barrel part of the CMS ECAL will be measured using avalanche photodiodes developed for the purpose by Hamamatsu Photonics in collaboration with CMS.The requirements for the diodes are described, and the performance achieved is summarised, with emphasis on the long-term reliability in the difficult high radiation conditions at CMS.

A precision measurement of the π± Total Cross Sections on Hydrogen and Deuterium by the classical transmission method is described. The experimental arrangement and analysis procedures are explained and preliminary results presented.

Results are presented for F-2(d)/F-2(p) and R(d) - R(p) from simultaneous measurements of deep inelastic muon scattering on hydrogen and deuterium targets, at 90, 120, 200 and 280 GeV. The difference R(d) - R(p), determined in the range 0.002 0.1 the ratio decreases with Q(2).

The Compact Muon Solenoid is one of two general purpose detectors currently being constructed for the Large Hadron Collider at CERN foreseen to begin data taking in 2007. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 61 200 lead tungstate crystals in the barrel part of the electromagnetic calorimeter of CMS. After a 8 years long R&D work Hamamatsu Photonics produces now APDs with a structure that is basically radiation resistant. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of an irradiation with 60Co and annealing under bias of all APDs and on a sampling basis only an irradiation with hadrons.

The lead tungstate crystals of the barrel part of the CMS electromagnetic calorimetar (ECAL) will be read out using avalanche photodiodes (APDs). To maintain performance of the CMS ECAL, the APDs must operate with a very high reliability for at least ten years in an extremely hostile environment. By measuring the dark current of APDs every 30 minutes over 72 days the stability of carefully selected APDs has been studied.

The CERN LHC experiment CMS has selected for the readout of the barrel crystal calorimeter a 5/spl times/5 mm/sup 2/ avalanche photodiode (APD) manufactured by Hamamatsu Photonics. In the detector we will equip each crystal with two APDs for a total of 122400 diodes. As the calorimeter will be almost completely inaccessible during the life of the detector, the assurance that they will survive with a high probability in the intense radiation field is an essential part of the of the APD qualification process. In this paper the properties of the APD selected will be described, as well as the procedures we have developed to assure their radiation hardness and reliability.

This paper presents a large solid angle measurement of the positive pion absorption cross section on ^4He and its decomposition into partial channels. A large fraction of the absorption cross section at incident pion kinetic energies of T_π+ =70, 118, 162, 239, and 330 MeV is due to multinucleon channels.

We have used the (π-,π0) charge-exchange reaction at 165-MeV kinetic energy to study the T + 1 component of the isovector monopole resonance (IVM). The nuclei 40Ca, 60Ni, 90Zr, 120Sn, 140Ce, and 208Pb were used as targets. We also observed the T + 1 component of the giant dipole resonance (GDR) in the lighter targets. The (π+,π0) reaction also yielded positive results for the T - 1 component of the IVM and GDR in 40Ca, 60Ni, and 90Zr.