R.J. Homer

Experimental comparison of Jψ production by π±, K±, p and p̄ beams at 39.5 GeV/c

Abstract Measurements have been made of relative production cross sections of the J ψ by π±, K±, p and p at 39.5 GeV/c incident on copper. J ψ production rates from π−, K− and p are similar. The J ψ relative particle/anti-particle production cross sections for x>0 are σ(π + ) σ(π − )=(0.87±0.14) , σ(K+)/σ(K−)=(0.85±0.5) and σ( p ) σ( p )=(0.15 ±0.08) . The small p/p cross section ratio disagrees with models of J/ψ production by gluon amalgamation.

A measurement of the A-dependence of the J/ψ cross section by comparing data on hydrogen and tungsten targets at 39.5 GeV/c

Abstract J/ψ production on hydrogen and tungsten targets has been compared at 39.5 GeV/ c and the variation of the A -dependence of the J/ψ cross section as a function of p t 2 and x F has been measured. The A -dependence parameter, α, rises with increasing p t 2 and falls with increasing x F . Both effects are shown not to be due to the Fermi motion of nucleons in the tungsten nucleus.

Irradiation studies of multimode optical fibres for use in ATLAS front end links

The radiation tolerance of three multimode optical fibres has been investigated to establish their suitability for the use in the front-end data links of the ATLAS experiment. Both gamma and neutro ...

Experimental results on J/ψ production by π±, K±, p and p incident on hydrogen at 39.5 GeV/c

Abstract J/ ψ production at 40 GeV/ c by π ± , K ± , p and p incident on hydrogen has been studied and results compared with those obtained on tungsten in the same experiment. On hydrogen, J/ψ cross-section ratios relative to π − have been measured to be (for x F > 0) σ(π − ) : σ(π + ) : σ( p ) : σ( p ) = 1 : (0.78 ± 0.09) : (0.83 ± 0.35) : (0.07 ± 0.04) . The suppression of the proton induced cross sections shows the importance of calence quark-antiquark fusiin J/ψ production at this energy (i.e. M J 2 / ψ / s =0.13).

System tests of radiation hard optical links for the ATLAS semiconductor tracker

A prototype optical data and Timing Trigger and Control transmission system based on LEDs and PIN-diodes has been constructed. The system would be suitable in terms of radiation hardness and radiat ...

Production of muon pairs in the continuum region by 39.5 GeV/c π±, K±, p and p¯ beams incident on a tungsten target

Abstract Inclusive dimuon production by 39.5 GeV/ c π ± , K ± , p and p¯ is described for masses greater than 2.0 GeV/ c 2 . The π − , π + and (π − − π + ) continuum cross-sections exceed the naive Drell-Yan predictions by a factor ∼2.4. The pion valence structure function has been measured and is consistent with a corresponding measurement at 200 GeV/ c .

A study of the reactions π+p→ K+∑+ and K−p→π−∑+ at 10 GeV/c

Abstract For the first time, the reactions π+p→K+∑+ and K−p→π−∑+ have been studied in the same apparatus. This has been done at an adequately high momentum (10.1 GeV/c) to allow a check of the prediction of exchange degeneracy, that the differential cross sections should be converging at high energy. We have measured the cross section for momentum transfers t between tmin and t = −0.3 (GeV/c)2. We find that for both reactions the differential cross section shows an exponential fall, with no deviations right in to t =tmin (where some other experiments have shown a dip in the cross section). Furthermore, we find the magnitude of the differential cross sections to be closely similar at t = 0, with a ratio R= ( d σ d t) t=0 ( K − p →π − ∑ + ) ( d σ d t) t=0 (π + p → K + ∑ + However, the slope for the positive reaction is about 19% steeper than that for the negative reaction.

A study of the line reversed hypercharge exchange reactions π+p → K+Σ+(1385) and K−p → π−Σ+(1385) at 10 GeV/c

Abstract We present results on the differential cross-sections for the reactions π+p → K+Σ+(1385) and K−p → π−Σ+(1385) at 10 GeV/c. For the first time, the same equipment has been used in measuring both reactions, in order to obtain good relative normalization. In the region of low t (tmin to −0.3 (GeV/c)2) the two differential cross-sections have similar shape, and show a sharp forward dip indicating a dominant helicity flip contribution. However, the magnitudes of the cross-sections are significantly different, indicating substantial exchange degeneracy breaking. We find the ratio of the integrated cross-sections for the reactions K−p → π−Σ+(1385) and π+p → K+Σ+(1385) over the range −0.3

Radiation hardness and lifetime of VCSELs and PIN photodiodes for use in the ATLAS SCT

This paper reports the radiation hardness of optical components to be used in the binary readout of one of the next generation of detectors in high energy physics. The optical components will have to sustain a total ionizing dose of 500 kGy and a 1 MeV equivalent neutron fluence of 1015 n cm-2. Emitters of VCSEL type have been chosen and have shown a shift of 1 mA in the laser threshold current after irradiation, but are still suitable for our purpose. The epitaxial Si PIN photodiode receivers have an acceptable 30% drop in responsivity providing a higher reverse bias is applied. Speed and lifetime of both components appear to be unaffected by the radiation damage. Temperature characteristics showing differences from un- irradiated materials will be also presented.

An experimental test of exchange degeneracy in the hyperchange exchange reactions π+p→K+Σ+and K−→π−Σ+

Abstract For the first time, the line reversed reactions π + p→K + Σ + and K − p→ π − Σ + have been studied in the same apparatus. We present the differential cross sections and polarizations over a large t range and at two momenta, 7.0 and 10.1 GeV/ c . The differential cross sections as a function of t are shown for the first time to cross over. Going from the lower to the higher momentum, the differences in cross section between the two reactions diminish at low | t | by about a factor 2. We find large polarizations of opposite sign for the two reactions. The momentum dependence, presented in the form of α eff ( t ) for the t range 0 to −2 (GeV/ c ) 2 , is compared with the expectations from the K ∗ −K ∗∗ trajectory.