Wim De Boer

Comparison of grand unified theories with electroweak and strong coupling constants measured at LEP

Abstract Using the renormalization group equations one can evolve the electroweak and strong coupling constants, as measured at LEP, to higher energies in order to test the ideas of grand unified theories, which predict that the three coupling constants become equal at a single unification point. With data from the DELPHI Collaboration we find that in the minimal non-supersymmetric standard model with one Higgs doublet a single unification point is excluded by more than 7 standard deviations. In contrast, the minimal supersymmetric standard model leads to good agreement with a single unification scale of 1016.0±0.3 GeV. Such a large scale is compatible with the present lower limits on the proton lifetime. The best fit is obtained for a SUSY scale around 1000 GeV and limits are derived as function of the strong coupling constant. The unification point is sensitive to the number of Higgs doublets and only the minimal SUSY model with two Higgs doublets is compatible with GUT unification, if one takes the present limits on the proton lifetime into account.

Consistency checks of grand unified theories

Abstract The world averaged values of the electroweak and strong couplings and the lower limits on the proton lifetime are used for consistency checks of grand unified theories (GUTs). It is confirmed that new physics outside the standard model (SM) is required to obtain unification of the electroweak and strong forces. Such new physics could come from the minimal supersymmetric extension of the SM, which provides unification consistent with the present limits on the proton lifetime, but also non-supersymmetric models based on additional split multiplets show similar unification properties. The results can be summarized as constraints on the slope differences of the coupling constants. These conditions have to be satisfied by any unified model having a single threshold at about 1 TeV, but cannot distinguish between them. Only future experiments will be able to do so.

Radiation hardness of diamond and silicon sensors compared

The radiation hardness of silicon charged particle sensors is compared with single crystal and polycrystalline diamond sensors, both experimentally and theoretically. It is shown that for Si- and C-sensors, the NIEL hypothesis, which states that the signal loss is proportional to the Non-Ionizing Energy Loss, is a good approximation to the present data. At incident proton and neutron energies well above 0.1 GeV the radiation damage is dominated by the inelastic cross section, while at non-relativistic energies the elastic cross section prevails. The smaller inelastic nucleon-carbon cross section and the light nuclear fragments imply that at high energies diamond is an order of magnitude more radiation hard than silicon, while at energies below 0.1 GeV the difference becomes significantly smaller.

Simulation of beam induced lattice defects of diamond detectors using FLUKA

Abstract Diamond is more and more used as a detector material for particle detection. One argument for diamond is its higher radiation hardness compared to silicon. Since various particles have different potentials for radiation damage at different energies, a scaling rule is necessary for the prediction of radiation damage. For silicon detectors the non-ionising energy loss (NIEL) is used for scaling the effects of different particles. A different way of predicting the radiation damage is based on the Norget–Robinson–Torrens theorem to predict the number of displacements per atom (DPA). This provides a better scaling rule since recombination effects are taken into account. This model is implemented in the FLUKA Monte Carlo simulations package for protons, neutrons and pions. We compare simulation results of NIEL and DPA for diamond and silicon material exposed to protons, neutrons and pions for a wide range of energies.

Diamond thin film detectors for beam monitoring devices

Diamonds offer radiation hard sensors, which can be used directly in primary beams. Here we report on the use of a polycrystalline CVD diamond strip sensor as beam monitor of heavy ion beams with up to ∼10 9 lead ions per bunch. The strips allow for a determination of the transverse beam profile to a fraction of the pitch of the strips, while the timing information yields the longitudinal bunch length with a resolution of the order of a few mm.

Severe signal loss in diamond beam loss monitors in high particle rate environments by charge trapping in radiation‐induced defects

The beam condition monitoring leakage (BCML) system is a beam monitoring device in the compact muon solenoid (CMS) experiment at the large hadron collider (LHC). As detectors 32 poly-crystalline (pCVD) diamond sensors are positioned in rings around the beam pipe. Here, high particle rates occur from the colliding beams scattering particles outside the beam pipe. These particles cause defects, which act as traps for the ionization, thus reducing the charge collection efficiency (CCE). However, the loss in CCE was much more severe than expected from low rate laboratory measurements and simulations, especially in single-crystalline (sCVD) diamonds, which have a low initial concentration of defects. After an integrated luminosity of a few corresponding to a few weeks of LHC operation, the CCE of the sCVD diamonds dropped by a factor of five or more and quickly approached the poor CCE of pCVD diamonds. The reason why in real experiments the CCE is much worse than in laboratory experiments is related to the ionization rate. At high particle rates the trapping rate of the ionization is so high compared with the detrapping rate, that space charge builds up. This space charge reduces locally the internal electric field, which in turn increases the trapping rate and recombination and hence reduces the CCE in a strongly non-linear way. A diamond irradiation campaign was started to investigate the rate-dependent electrical field deformation with respect to the radiation damage. Besides the electrical field measurements via the transient current technique (TCT), the CCE was measured. The experimental results were used to create an effective deep trap model that takes the radiation damage into account. Using this trap model, the rate-dependent electrical field deformation and the CCE were simulated with the software SILVACO TCAD. The simulation, tuned to rate-dependent measurements from a strong radioactive source, was able to predict the non-linear decrease of the CCE in the harsh environment of the LHC, where the particle rate was a factor 30 higher.

Severe signal loss in diamond beam loss monitors in high particle rate environments by charge trapping in radiation-induced defects

The beam condition monitoring leakage (BCML) system is a beam monitoring device in the compact muon solenoid (CMS) experiment at the large hadron collider (LHC). As detectors 32 poly-crystalline (pCVD) diamond sensors are positioned in rings around the beam pipe. Here, high particle rates occur from the colliding beams scattering particles outside the beam pipe. These particles cause defects, which act as traps for the ionization, thus reducing the charge collection efficiency (CCE). However, the loss in CCE was much more severe than expected from low rate laboratory measurements and simulations, especially in single-crystalline (sCVD) diamonds, which have a low initial concentration of defects. After an integrated luminosity of a few corresponding to a few weeks of LHC operation, the CCE of the sCVD diamonds dropped by a factor of five or more and quickly approached the poor CCE of pCVD diamonds. The reason why in real experiments the CCE is much worse than in laboratory experiments is related to the ionization rate. At high particle rates the trapping rate of the ionization is so high compared with the detrapping rate, that space charge builds up. This space charge reduces locally the internal electric field, which in turn increases the trapping rate and recombination and hence reduces the CCE in a strongly non-linear way. A diamond irradiation campaign was started to investigate the rate-dependent electrical field deformation with respect to the radiation damage. Besides the electrical field measurements via the transient current technique (TCT), the CCE was measured. The experimental results were used to create an effective deep trap model that takes the radiation damage into account. Using this trap model, the rate-dependent electrical field deformation and the CCE were simulated with the software SILVACO TCAD. The simulation, tuned to rate-dependent measurements from a strong radioactive source, was able to predict the non-linear decrease of the CCE in the harsh environment of the LHC, where the particle rate was a factor 30 higher.

Indirect Dark Matter Signals from EGRET and PAMELA compared

Dark Matter annihilation (DMA) may yield an excess of gamma rays and antimatter particles, like antiprotons and positrons, above the background from cosmic ray interactions. The excess of diffuse Galactic Gamma Rays from EGRET shows all the features expected from DMA. The new precise measurements of the antiproton and positron fractions from PAMELA are compared with the EGRET excess. It is shown that the charged particles are strongly dependent on the propagation model used. The usual propagation models with isotropic propagation models are incompatible with the recently observed convection in our Galaxy. Convection leads to an order of magnitude uncertainty in the yield of charged particles from DMA, since even a rather small convection will let drift the charged particles in the halo to outer space. It is shown that such anisotropic propagation models including convection prefer a contribution from DMA for the antiprotons, but the rise in the positron fraction, as observed by PAMELA, is incompatible wit...

Indirect evidence for WIMP annihilation from diffuse galactic gamma rays

The EGRET excess in the diffuse galactic gamma ray data above 1 GeV shows all the features expected from Dark Matter WIMP Annihilation: a)it is present and has the same spectrum in all sky directions, not just in the galactic plane. b) The intensity of the excess shows the

Description of Radiation Damage in Diamond Sensors Using an Effective Defect Model

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