When an ultrarelativistic electron traverses two closely spaced foils, a radiation spectrum ‘resonance’ appears, arising from the photon formation length extending from one foil, across the gap and ...into the second foil. Several theoretical approaches yield quite different answers to the spectral location of this ‘resonance’, and we have therefore in the CERN NA63 collaboration addressed the question experimentally with a 178 GeV electron beam. The experimental technique used – where a variable gap separates two thin gold foils – allows for a direct measurement of a length that is closely related to the distance over which the photon formation takes place. These are the first measurements to observe the gap dependence of the energy of the ‘resonance’ in the radiation spectrum from a structured target on a truly macroscopic scale up to 0.5 mm. The results are compared with the theory of Baier and Katkov, with both the modified and unmodified theories of Blankenbecler as well as with a naïve, straightforward expectation. Surprisingly, the experiment shows a clear preference for the two latter, comparatively unsophisticated, approaches.
Experimental results for the radiative energy loss of 149, 207, and 287 GeV electrons in a thin Ir target are presented. From the data we conclude that at high energies the radiation length increases ...in accordance with the Landau-Pomeranchuk-Migdal (LPM) theory and thus electrons become more penetrating the higher the energy. The increase of the radiation length as a result of the LPM effect has a significant impact on the behavior of high-energy electromagnetic showers.
Experimental results for the radiative energy loss of 206 and 234 GeV electrons in 5–10 μm thin Ta targets are presented. An increase in radiation emission probability at low photon energies compared ...to a 100 μm thick target is observed. This increase is due to the formation length of the GeV photons exceeding the thickness of the thin foils, the so-called Ternovskii–Shul'ga–Fomin (TSF) effect. The formation length of GeV photons from a multi-hundred GeV projectile is through the TSF effect shown directly to be a factor 1010 longer than their wavelength.
Ageing in the LHCb outer tracker: Aromatic hydrocarbons and wire cleaning Tuning, N.; Bachmann, S.; Bagaturia, Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2011, Letnik:
656, Številka:
1
Journal Article
Recenzirano
The LHCb Outer Tracker straw tubes have shown to suffer from gain loss after irradiation in the laboratory at moderate intensities. Under irradiation an insulating layer is formed on the anode wire. ...The ageing is caused by contamination of the counting gas due to outgassing of the plastifier di-isopropyl-naphthalene in araldite AY103-1 used at construction. This paper presents irradiation results with and without the plastifier, together with the mass spectra of the glue samples. In addition, the effects of wire heating and large currents are presented.
Results are reported from an amplitude analysis of the B+ → D+D− K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at √s = 7, 8, and 13 TeV, corresponding to a total ...integrated luminosity of 9 fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D−K+ channel with masses around 2.9 GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2 χc2(3930) state.
A narrow pentaquark state, Pc(4312)+, decaying to J/ψp, is discovered with a statistical significance of 7.3σ in a data sample of Λb0→J/ψpK− decays, which is an order of magnitude larger than that ...previously analyzed by the LHCb Collaboration. The Pc(4450)+ pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, Pc(4440)+ and Pc(4457)+, where the statistical significance of this two-peak interpretation is 5.4σ. The proximity of the Σc+D¯0 and Σc+D¯*0 thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.
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