Summary of the UK HARP meeting of 7 April 2000 at Sheffield

Present: G.Barr, C.Booth, C.Buttar, R.Edgecock, A.Holmes, R.Nicholson
  1. Funding: We got funded! From Neville's mail, it seems we will get £55k (asked for £64k) for 2000/1. The main drop was in travel for which we are allocated £6k (asked for £12k+2k). We discussed methods of economising in this direction. It is not clear if we are allowed to supplement the travel money at all if we are able to economise elsewhere. To centralise management of the travel money, we agreed to check with Rob before organising travel.

  2. Target caps: The prototype target mounting cap was shown. This had already been shown at CERN by P. Soler in March. In principle, design with wall thickness of 0.2mm will be able to support the target weight, if this can be manufactured. Sheffield agreed to have a go at machining a prototype a bit thinner. We were encouraged by recent indications from CERN that the experiment is attempting to minimise the material close to the target. The plan is that each target has its own target cap which will be custom designed. Richard and Alan will work on a method of attaching the caps to the insertion tube.

  3. Test targets: We discussed the provision of two test targets.
    1. Set at 45 degrees to the incident beam direction (to obtain a good measurement at 90 degrees without severe reinteraction corrections) for one of the target materials (e.g. Al). It would need to be the same pure target as one of the standard targets.
    2. A "top-hat" target which is a uniform 2% of an interaction length except for a circular region at the centre of diameter 5mm which is 10% of an interaction length. This will allow us to derive the position of the target relative to the beam for alignment checks. This could be any material, e.g. brass.

  4. Beam layout: We discussed the beam layout as derived from a mail message from Lucie Linssen in March. As Lucie summarised, our plans from the proposal require too much space upstream of the TPC. An alternative scheme involving a drainpipe, or a series of rails, was conceived.

    The mail confused us about the positioning of the three beam chambers. The downstream one is mounted as close to the TPC as possible along with the beam trigger counter (and must be removed each time the trigger is changed. This unit is 0.3m long). The mail referred to the two upstream chambers being separated by about 1m which puts the second one closer to the third than the first. In our design discussions, we assumed that the second chamber could go quite close to the first and that the entire assembly of the two chambers is 0.57m thick (10 cm for each chamber and 37cm separation).

    We then worked with the remaining 1.4 m for the target changing gear (thereby allowing that the first two beam chambers would not be dismounted at each target change) for the new design. This is just enough space for the long targets. See Chris's diagram of all of this.

  5. Target mounting: It is thought (indeed this was already realised before the UK proposal) that the same mounting apparatus can be used for all the thin and the thick targets [unlike an earlier concept in which the inner trigger counters were removed for the thick target running]. Since the majority of the backward-going secondaries escape through the Sheffield mounting caps and not the long insertion tube, the insertion tube might be able to be made from aluminium rather than carbon fibre. [Giles is a bit nervous with carbon fibre pipes after the NA48 accident last November :-( ]. Alan will study how thick this would have to be. It is possible that Sheffield could manufacture it in the same way as the caps. (This needs further study!) We discussed whether the space occupied by drain-pipe needs to be vacuum during running. The physicists will think about this (extrapolation error due to multiple scattering and dE/dx).

  6. K2K target: The K2K target diameter (60mm at the downstream end and a flange of 78mm (checked on diagram) at the upstream end) now presents a problem, since we are using the same mounting scheme for all other targets. We need to discuss with K2K whether the width of the target needs to be maintained.

  7. We discussed whether to reduce the target diameter from 3cm to 2cm (the cryogenic targets will be only 2cm), however, we were concerned about the extrapolation accuracy of the beam chambers - for the analysis to be succesful, we will define a sample of primary tracks which we KNOW must have hit the target. We are concerned about the cryogenic targets and about the MINIBOONE target which is 1cm in diameter. One solution would be to decrease the resolution of the beam chambers (currently 2mm/SQRT(12)). Silicon anyone ?

  8. Target identification We discussed various schemes to ensure that the current target was correctly identified by the data acquisition system. Ideas included the use of bar codes on the target support cap, which would be swept passed a reader when a target was inserted. A microswitch, operated when a target was dismounted, could alert the slow-control computer that the currrent target was undefined.

  9. Next meeting: On the 2nd May at Sheffield.

Minutes by Giles Barr (+ CNB).