Abstract
In the positron–electron annihilation process, finite deviations from the standard calculation based on Fermi’s golden rule are suggested in recent theoretical work. This paper describes an ...experimental test of the predictions of this theoretical work by searching for events with two photons from positron annihilation of energy larger than the electron rest mass ($511\,{\rm keV}$). The positrons came from a ${\rm {}^{22}Na}$ source, tagging the third photon from the spontaneous emission of ${\rm {}^{22}{Ne}^*}$ de-exitation to suppress backgrounds. Using the collected sample of $1.06\times 10^{7}$ positron–electron annihilations, triple coincidence photon events in the signal-enhanced energy regions are examined. The observed number of events in two signal regions, $N^{\rm SR1}_{\rm obs}=0$ and $N^{\rm SR2}_{\rm obs}=0$, are, within the current precision, consistent with the expected number of events, $N^{\rm SR1}_{\rm exp}=0.86\pm0.08({\rm stat.})^{+1.85}_{-0.81}({\rm syst.})$ and $N^{\rm SR2}_{\rm exp}=0.37\pm 0.05({\rm stat.})^{+0.80}_{-0.29}({\rm syst.})$ from Fermi’s golden rule, respectively. Based on the $P^{(d)}$ modeling, a 90% CL lower limit on the photon wave packet size is obtained.
Radiation-tolerant n+-in-p silicon sensors were developed for use in very high radiation environments. Novel n+-in-p silicon strip and pixel sensors and test structures were fabricated, tested and ...evaluated, in order to understand the designs implemented. The resistance between the n+ implants (interstrip resistance), the electric potential of the p-stop, and the punch-through-protection (PTP) onset voltage were measured before and as a function of fluence after irradiation. The technology computer-aided design (TCAD) simulations were used to understand the radiation damage and fluence dependence of the structures. The decrease in the interstrip resistance is a consequence of increased leakage current. The decrease in the electric potential of the p-stop results from a build-up of positive charge in the silicon–silicon oxide interface. The decrease and subsequent increase in the PTP onset voltages results from the interface charge build-up and an increase in acceptor states.
The intrinsic decay rate of orthopositronium formed in SiO2 powder is measured using the direct 2γ correction method such that the time dependence of the pick-off annihilation rate is precisely ...determined using high energy-resolution germanium detectors. As a systematic test, two different types of SiO2 powder are used with consistent findings. The intrinsic decay rate of orthopositronium is found to be 7.0396±0.0012(stat)±0.0011(sys) μs−1, which is consistent with previous measurements using SiO2 powder with about twice the accuracy. Results agree well with a recent O(α2) QED prediction, varying 3.8–5.6 experimental standard deviations from other measurements.
Planar geometry silicon pixel and strip sensors for the high luminosity upgrade of the LHC (HL-LHC) require a high bias voltage of 1000V in order to withstand a radiation damage caused by particle ...fluences of 1×1016 1MeVneq/cm2 and 1×1015 1MeVneq/cm2 for pixel and strip detectors, respectively. In order to minimize the inactive edge space that can withstand a bias voltage of 1000V, edge regions susceptible to microdischarge (MD) should be carefully optimized. We fabricated diodes with various edge distances (slim-edge diodes) and with 1–3 multiple guard rings (multi-guard diodes). AC coupling insulators of strip sensors are vulnerable to sudden heavy charge deposition, such as an accidental beam splash, which may destroy the readout AC capacitors. Thus various types of punch-through-protection (PTP) structures were implemented in order to find the most effective structure to protect against heavy charge deposition. These samples were irradiated with 70MeV protons at fluences of 5×1012 1MeVneq/cm2–1×1016 1MeVneq/cm2. Their performances were evaluated before and after irradiation in terms of an onset voltage of the MD, a turn-on voltage of the PTP, and PTP saturation resistance.
► We have evaluated radiation tolerance of n-in-p sensors up to 1×1016 1MeVneq/cm2. ► Both n-bulk and p-bulk require a field width≥450μm in order to withstand 1000V. ► The MD onset voltage was found to be independent of the edge width. ► With increasing number of guard rings, bias voltage tolerance improved before irrad. ► BZ4D-5 (with full extension) performs the best among the samples.
Abstract
Standard calculations by Fermi’s golden rule involve approximations. These approximations could lead to deviations from the predictions of the standard model, as discussed in another paper. ...In this paper we propose experimental searches for such deviations in the two-photon spectra from the decay of the neutral pion in the process $\phi \rightarrow \pi^+ \pi^- \pi^0$ and in the annihilation of the positron from nuclear $\beta$ decay.
Toward High Luminosity LHC (HL-LHC), the whole ATLAS inner tracker will be replaced, including the semiconductor tracker (SCT) which is the silicon micro strip detector for tracking charged ...particles. In development of the SCT, integration of the detector is the important issue. One of the concepts of integration is the “super-module” in which individual modules are assembled to produce the SCT ladder.
A super-module prototype has been developed to demonstrate its functionality. One of the concerns in integrating the super-modules is the electrical coupling between each module, because it may increase intrinsic noise of the system. To investigate the electrical performance of the prototype, the new Data Acquisition (DAQ) system has been developed by using SEABAS. The electric performance of the super-module prototype, especially the input noise and random noise hit rate, was investigated by using SEABAS system.
We have been developing highly radiation-tolerant n+-in-p planar pixel sensors for use in the high-luminosity LHC. Novel n+-in-p structures were made using various combinations of the bias structures ...(punch-through or polysilicon resistor), isolation structures (p-stop or p-spray), and thicknesses (320μm or 150μm). The 1-chip pixel modules with thin FE-I4 pixel sensors were evaluated using test beams, before and after 2×1015neq/cm2 irradiation. The full depletion voltages were estimated to be 44±10V and 380±70V, in the non-irradiated and the irradiated modules, respectively. A reduction of efficiency was observed in the vicinity of the four pixel corners and underneath the bias rail after the irradiation. The global efficiencies were >99% and >95% in the non-irradiated and the irradiated modules, respectively. The collected charges were uniform in the depth direction at bias voltages well above the full depletion voltages. The encapsulation of vulnerable edges with adhesive or parylene prevented HV sparking. Bump bonding with the SnAg solder bumps was performed at HPK with 150μm- and 320μm-thick sensors and chips. No disconnection of bumps was observed after 10 thermal cycles between −40 and +50°C, with a temperature slew rate of >70K/min.
► Novel n+-in-p pixel sensors were made of punch-through/poly-Si biasing, p-stop/p-spray isolation, and 320/150μm thickness. ► The thin pixel modules were evaluated in testbeams, before and after 2×1015neq/cm2 irradiation. ► A reduction of efficiency was observed in the vicinity of four-corners of pixels and underneath the bias rail after irradiation. ► Encapsulating the vulnerable edges with adhesive or parylene achieved prevention of HV sparking up to 1000V. ► No disconnection of SnAg bump-bonds was observed in dummy modules after 10 thermal cycles with a slew rate of >70K/min.
A precise measurement of the analyzing power AN in proton–proton elastic scattering in the region of 4-momentum transfer squared 0.001<|t|<0.032 (GeV/c)2 has been performed using a polarized atomic ...hydrogen gas jet target and the 100 GeV/c RHIC proton beam. The interference of the electromagnetic spin-flip amplitude with a hadronic spin-nonflip amplitude is predicted to generate a significant AN of 4–5%, peaking at −t≃0.003 (GeV/c)2. This kinematic region is known as the Coulomb nuclear interference region. A possible hadronic spin-flip amplitude modifies this calculable prediction. We present the first precise result of the CNI asymmetry and shape as a function of t. Our data are well described by the CNI prediction with the electromagnetic spin-flip alone and do not support the presence of a large hadronic spin-flip amplitude.
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