High-luminosity Collider Research Articles

A CVD diamond beam telescope for charged particle tracking

Chemical vapor deposition (CVD) diamond is a radiation-hard sensor material that may be used for charged particle tracking near the interaction region in experiments at high-luminosity colliders. The goal of the work described in this paper is to investigate the use of several detector planes made of CVD diamond strip sensors for charged particle tracking. Toward this end, a tracking telescope composed entirely of CVD diamond planes has been constructed. The telescope was tested in muon beams, and its tracking capability has been investigated.

Beam extraction studies at 900 GeV using a channeling crystal

Luminosity-driven channeling extraction has been observed for the first time in a 900 GeV study at the Fermilab Tevatron. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multi-turn extraction was found to increase significantly the efficiency of the process. The beam extraction efficiency was about 25%. Studies of time dependent effects found that the turn-to-turn structure was governed mainly by accelerator beam dynamics. An investigation of a pre-scatterer using the accelerator flying wire system showed that a fiber could produce a significant extracted flux, consistent with expectations. Based on these results, it is feasible to construct a parasitic 5-10 MHz proton beam from the Tevatron collider.

Performance of GEM detectors in high intensity particle beams

We describe extensive tests of Double Gas Electron Multiplier (GEM) and Triple GEM detectors, including large size prototypes for the COMPASS experiment, exposed to high intensity muon, proton and pion beams at the Paul Scherrer Institute and at CERN. The measurements aim at detecting problems possibly appearing under these harsh operating conditions, the main concern being the occurrence of discharges induced by beam particles. Results for the dependence of the probability for induced discharges on the experimental environment are presented and discussed. Implications for the application of GEM detectors in experiments at high luminosity colliders are illustrated.

Investigation of vacuum polarization in t-channel radiative Bhabha scattering

We discuss the possibility of a precision measurement of vacuum polarization in t-channel radiative Bhabha scattering at a high luminosity collider. For illustration, the achievable precision is estimated for the BaBar experiment at PEP-II and for the OPAL experiment at LEP.

Overview: silicon vertex detectors and trackers

Performance requirements for Si tracking detectors for high-luminosity collider experiments are discussed. The radiation hardness of Si sensors and front-end electronics for the readout of Si detectors is reviewed. Some typical experimental results on radiation hardness are presented. The basic ingredients needed for the construction of Si trackers are described. Some performance results are shown. A very short discussion of mechanical support structures and alignment methods is given.

The decay τ→3 πντ as a probe of the mechanism of dynamical chiral symmetry breaking

The decays τ→3 π+ ν τ are analyzed at one loop order in the framework of Generalized Chiral Perturbation Theory, in order to test the sensitivity to the size of spontaneous chiral symmetry breaking parameters, contained in the S-wave. The latter, due to a kinematical suppression, at threshold, of the P-wave, is relatively large enough to be detectable at high-energy machines, through azimuthal left-right asymmetries. This quantity (for the π − π − π + mode), integrated from threshold to Q 2=0.35 GeV 2, varies from (17±3)% in the standard case of large condensate up to (40±5)% in the extreme case of tiny condensate. The feasibility of such measurement at high luminosity colliders (e.g., CLEO) is discussed. This method provides an independent cross-check of forthcoming experimental determination of the two-light-flavor chiral condensate, based on low-energy ππ scattering.

Quality control of GEM detectors using scintillation techniques

Non-destructive quality control of microstructures at the manufacturing stage is an important issue in the foreseen use of huge numbers of such gaseous detectors in the future high luminosity colliders. In this work we report on the use of the scintillation light emitted by the avalanches in GEM channels for checking defects in the foils. The test system is described and data on the relative efficiency of several gaseous mixtures are presented. The foil images obtained with a low-noise CCD system are analysed and compared with the optical images obtained with an industrial inspection system of high magnification. The validity of this test method is established and possible extensions of its use are discussed.

Continuous electron cooling for high-luminosity colliders

The prospects to use continuous electron cooling for increasing luminosity and quality of collider experiments, involving nuclei/nucleons, are discussed briefly. Possible sets of collider parameters are presented.

MICROPATTERNGASEOUSDETECTORS

▪ Abstract Introduced in 1988, microstrip gas chambers perform considerably better than classic multiwire detectors. Excellent localization, high rate capability, and good granularity make them attractive for charged-particle tracking at high-luminosity colliders, among other applications. The technology continues to improve; for example, substrates have been developed that prevent charge accumulations. Some problems persist, namely the slow degradation under sustained irradiation (aging) and the serious damage that can result from accidental discharges. New types of detectors aim at improving on these points; the microdot, micromegas, and gas electron multiplier detectors are promising examples. They are generally more reliable and cheaper.

FCNC top quark decays in the MSSM: a door to SUSY physics in high luminosity colliders?

We study the FCNC top quark decays t→ch in the framework of the MSSM, where h≡h0,H0,A0 is any of the supersymmetric neutral Higgs bosons. We include the leading set of SUSY-QCD and SUSY electroweak contributions. While the FCNC top quark decay into the SM Higgs boson has such a negligible rate that it will not be accessible to any presently conceivable accelerator, we find that there is a chance that the potential rates in the MSSM can be measured at the high luminosity colliders round the corner, especially at the LHC and possibly at a future LC, but we deem it difficult at the upgraded Tevatron. In view of the large SUSY-QCD effects that we find in the Higgs channels, and due to some discrepancies in the literature, we have revisited the FCNC top quark decay into gluon, t→cg, in our framework. We confirm that the possibility of sizeable rates does not necessarily require a general pattern of gluino-mediated FCNC interactions affecting both the LH and the RH sfermion sectors – the LH one being sufficient. However, given the present bounds on sparticle masses, the gluon channel turns out to lie just below the expected experimental sensibility, so our general conclusion is that the Higgs channels t→ch (especially the one for the light CP-even Higgs) have the largest potential top quark FCNC rates in the MSSM, namely of order 10−4.

Recent progress in GEM manufacturing and operation

The Gas Electron Multiplier (GEM) is a robust and ubiquitous device for the proportional amplification of electrons released in a gas by radiation, and can be used as a pre-amplification stage in a cascade of detectors. Using single and double GEM detectors with simple segmented printed circuits for signal read-out, we have achieved full efficiency of detection for minimum ionizing particles. With suitably configured readout electrodes, fast, two-dimensional localization and imaging of radiation has been demonstrated. Extended discharge studies confirm that multiple devices including a GEM amplifier can perform reliably in the harsh operating conditions expected at high luminosity colliders. Applications and developments of GEM detectors for the imaging of single photoelectrons are also briefly discussed.

The FINUDA superconducting magnet at DAΦNE

FINUDA is an experiment aiming at high resolution hypernuclear spectroscopy. It employs different types of detectors enclosed inside a large superconducting solenoid. It will operate on the new, high luminosity ( e + − e −) collider DAΦNE of the INFN Frascati National Laboratory. The solenoid operates at 2765 A maximum current corresponding to a magnetic field of 1.1 T. The inner dimensions are: 2.4 m length, 2.7 m diameter. The coil within its cryostat is enclosed inside an iron return yoke composed by a central barrel and two end-caps which can be opened to access the inner detectors. The magnetic field in the inner volume has been fully mapped for both main and minor components. The alignment of such a magnet on a machine as DAΦNE is a very crucial item, needing particular care.

Tracking with CVD diamond radiation sensors at high luminosity colliders

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

Beam tests of the gas electron multiplier

We describe the results of systematic measurements, carried out with single and double GEM detectors with printed circuit read-out and having an active area of 10×10 cm 2, both in the laboratory and in a high-energy charged particles beam at CERN. Using fast analog readout electronics, we demonstrate efficiencies for minimum ionizing particles close to 100%, with typical signal/noise ratios above 50 and up to 10 3 for the single and double GEM configuration, respectively, and a time resolution of 15 ns fwhm. Localization accuracies around 40 μm r.m.s. have been obtained for perpendicular tracks, degrading to 200 μm at 20° of incidence to the normal. Operated in a non-flammable gas mixture (argon–carbon dioxide), GEM detectors are robust, light and cheap to manufacture, and offer excellent performances and reliability suited for use in the harsh environments met at high luminosity colliders.

Progress with diamond over-coated microstrip gas chambers

We describe recent observations and measurements with Micro-Strip Gas Chambers coated, after manufacturing, with a thin diamond-like layer in order to increase their rate capability. Compared to the more widely used solution consisting in coating the insulating support with a conductive layer before photo-lithography (the so-called undercoating), over-coating has the advantage of avoiding possible problems with adherence of metals to the layer, damages during the etching process and reduced quality of the artwork resulting from imperfections or dust inclusions in the layer. Early tests have however indicated that, possibly because of damages to the layer due to electron and ion bombardment during the avalanche process, irreversible structural modifications and fatal breakdown could be encountered at very high integral radiation fluxes. The present paper summarizes these results, and describes recent developments demonstrating that a better choice of the parameters of the over-coat may allow to withstand the radiation doses anticipated for LHC detectors with the intrinsically simpler over-coating solution. We discuss also several possible applications of the use of thin, controlled resistivity layers for other families of detectors used or in development for CERN's high luminosity collider.

Silicon tracking at high luminosity colliders

Future applications of silicon detectors at high luminosity colliders envision their use after fluences equivalent to 10/sup 14/-10/sup 15/ minimum ionizing particles/cm/sup 2/ (MIP/cm/sup 2/). This requires facing a number of special problems: large bias voltages on the detector, large leakage currents, and thermal instabilities. We present some of the relevant results on these problems as well as a brief review of some of the presently planned detectors.

The pipe-quadrupole, an alternative for high gradient interaction region quadrupole designs

In the design of interaction region (IR) quadrupoles for high luminosity colliders such as the LHC or a possible upgrade of the Tevatron, the radiation heating of the coil windings is an important issue. Two obvious solutions to this problem can be chosen. The first is to reduce the heat load by added shielding, increased cooling with fins or using Nb/sub 3/Sn to increase the temperature margin. The second solution eliminates the conductor from the areas with the highest radiation intensity, which are located on the symmetry-axes of the midplanes of the coils. A novel quadrupole design is presented, in which the conductor is wound on four half-moon shaped supports, forming elongated toroid sections. The assembly of the four shapes yields a quadrupole field with an active flux return path, and a void in the high radiation area. This void can be occupied by a liquid helium cooling pipe to lower the temperature of the windings from the inside. The coil layout, harmonic optimization and mechanical design are shown, together with the calculated temperature rise for the radiation load of the LHC interaction region quadrupoles.

Ionization cooling and muon collider

A short review of ionization cooling features, important for the preparation of muon beams for a high luminosity collider, is presented. Some new approaches to obtain ultimate efficiency of muon production, including polarized ones, as well as some practical limits, are considered briefly.

Fermilab R&D program in medium energy electron cooling

Fermilab began an R&D program in medium energy electron cooling in April 1995 with the object of cooling 8 GeV antiprotons in a new 3.3 km permanent magnet storage ring (Recycler) to be built in the same tunnel as the Main Injector (MI). The MI is to be completed in 1998, and it is planned to install the Recycler by the end of 1997 to reduce interference during the final rush of MI installation. Although the Recycler will employ stochastic cooling initially, its potential for contributing and order of magnitude to Tevatron collider luminosity is tied to electron cooling. The short time scale and Fermilab's limited familiarity with low energy electron beams has given rise to a two-phase development plan. The first phase is to build a cooling system based on an electron beam of ≥200 mA before the year 2000. The second phase of about three years is planned to reach an electron current of 2 A or more. This report describes the general scheme for high luminosity collider operation as well as the R&D plan and progress to date.

Neutron irradiation of CVD diamond samples for tracking detectors

Diamond may make an excellent substrate for a tracking device in the near future, especially at colliders like LHC, where extreme running conditions are expected (high rates and high radiation levels). We report on neutron irradiation of several CVD-diamond samples at the ISIS facility (Rutherford Appleton Laboratory), which provides a fast neutron spectrum similar to that expected in a high luminosity collider experiment like CMS. We measured beam-induced currents and charge collection of diamonds exposed to fluences in excess of 10 15 n/cm 2 (peaking at 1 MeV), which should be the maximum value of the ten years total fluence at the design LHC luminosity. Physical hypotheses for the interactions of neutrons on CVD-diamond are proposed.