Minutes of the FMD workshop,  29- May-2001, CERN.

By Jens Jørgen Gaardhøje, NBI.

 

 

Agenda 29-05-2001:

 

1. Approval of agenda and minutes of last meeting

2.FMD overview. JJG                                               (13.05-13.30)

3.Si-FMD Background simulations. A. Maievskaia                         (13.30-13.50)

4.Si-FMD mult. response. A.Karpechev                     (13.50-14.10)

5.Si-FMD FE and RO electronics. B.S.Nielsen                        (14.10-14.35)

6.Si Prototype. A. Angelis                                        (14.35-15.00)

7.PMD design. Y. Viyogi                                             (15.00-15.20)

8.FMD reaction plane/flow  simulations S. Raniwala                  (15.20-15.40)

9.Integration. L. Leistam                                           (15.40-16.30)

BREAK                                   

10.T0 design options/summary from morning

    V.Grigoriev/ H. Trzaska/G. Feofilov/ Chris Fabjan                 (16.50-17.30)

 

11.V0 and role in trigger J.Y.Grossiord/L. Montano                 (17.30-18.00)

12.Summary- Conclusions,

Recommendations for ALICE Forum,   TB and MB. JJG+All                 (18.00-18.45)

13.AOB

 

 

Minutes:

 

  1. The minutes from the previous meeting in February (29-02-2001) were approved without comments.

 

  1. JJG presented the current design status of the Si-FMD. The salient issues were the high background from secondaries in the most forward detectors, and the role of the Si-FMD in the trigger. It was proposed to abandon the Si4 detector located at 630cm from the IP to the left side, which sees a background of about 300-500 % of the primary signal due to interactions in the beam pipe. This downscoping will reduce the pseudorapidity coverage from approx. 1.5-6 to approx. 1.5-5.3. It was pointed out also by Chris Fabjan that it would be desirable to move the Si3 detector to larger distances (approx. 345 cm from the IP) so that this detector, the left T0 and V0, and also the PMD could be mechanical mounted together on a common support structure. The possibility to optimize the pseudorapidity coverage by decreasing the inner radius of the detectors to 3.5 cm and adjusting detector wafer size and distance to IP was discussed and will be pursued. It was also proposed to not to pursue further considerations regarding the inclusion of the Si-FMD in the LVL 0 and 1 trigger, due to the difficulties related to producing a useful hardware trigger signal within the  approx. 80 ns defined by the trigger group. It was pointed out that the V0 detector can easily provide this functionality within the required time limits in a much simpler fashion. The segmentation of the individual wafers was discussed. The segmentation was proposed to be (at least) 128 strips/wafer leading to an average occupancy per strip of the order of 2-4. The issue of the integration of the Si1, Si2, T0-R and V0-R detectors with the ITS frame was discussed. Detailed work is needed here (See also item 9).

 

  1. Alla Maievskaia presented new simulations of the occupancy of the various detector elements, which evidenced the high background in the elements at small angles. A discussion ensued regarding the design of the beam pipe, flanges, pumps etc. It was recommended that the integration group should continue detailed studies and work to reduce the amount of material in the path of the Si detectors as much as possible. New simulations for the new inner radius and new detector placements should be undertaken for the next meeting.

 

  1. A. Karpechev showed studies of the multiplicity response of the proposed system, in particular under various assumptions regarding the of-line grouping of various detector segments and an analysis of the multiplicity starting from the deposited energy The overall conclusion appears to be that the multiplicity resolution is better than 10%  and thus within the design goals for the system.

 

  1. Børge Svane Nielsen reported on the studies of existing suitable radiation-hard front-end(FE) and RO electronic system for the Si-FMD. Two FE chips are retained as interesting for this project. The Viking-RICH chips from IDEAS, Norway and the Hal-25 chip used for the ALICE Si-drift detectors. Both chips may require modifications for the present implementation in order to match the required strip capacitances, gain and dynamic range, number of channels etc. BSN and JJG have visited the IDEAS company in Oslo and started concrete discussions of performance and price. It appears that a modified Viking chip can do the job. IDEAS can also deliver hybrids, handle the gluing to the sensors , bond and provide test of the assembled wafers with a factory guarantee. A test readout system is available for prototyping. It appears that the HAL 25 chip may be more difficult to adapt (dynamic range). It also appears that the HAL25 preamplifier shaping time is so long (ms) that the chip may not be able to handle the necessary rate for this high occupancy  application. These issues should  be explored until the next meeting, so that a choice of technology can be made and so that the project may proceed to initial tender and prototyping. Paolo suggested to consider two layer bonding  for the inner rings of Si1,2 where it is difficult to connect sensors and hybrid cards.

 

  1. Aris Angelis reported on the Athens prototype effort. A segmented (16 sector) Si detector has been purchased from Canberra and has been delivered. A test FE circuit based on conventional (not integrated) circuitry has been developed. It was discussed whether this system could be ported to radiation hard highly integrated form. In view of the complexity of such a project and the tight timescales (the full system must be installed in ALICE in early 2005) this does not seem to be a desirable avenue. It was discussed how the Greek groups could utilize their electronics expertise in the final project. A possibility is a direct contribution to the  RO system (ADC’s- VME – DAQ intefacing). The Athens groups will discuss this internally for the next meeting.

 

  1. Yogendra Viyogi reported news from the PMD group. The integration of the Left FMD detectors (Si3 etc..) with the PMD was discussed. The PMD group has looked closely at the beam line situation and explored various options (Al, Al-Be, longer Be ) for the beam pipe. A placement at d=350cm for all forward left detectors seem feasible. The various groups should keep in close contact on these issues.

 

  1. Sudhir Raniwala presented simulations of the sensitivity of the present Si configuration for flow studies (directed and elliptic). It was pointed out that the sensitivity to f.ex. V2 depends markedly on the azimuthal segmentation and that it would be desirable with an increased segmentation in phi for the Si detectors. The segmentation is currently 16 for the inner rings and 24 for the outer rings. The Si-FMD group will revisit the segmentation in connection with the optimization of the geometry and coverage.

 

  1. Lars Leistam showed current plans for the beam pipe and ideas related to the integration of the FMD detectors with the ITS. It is clear that the mounting of the FMD detectors in the conical volumes on either side of the ITS poses a difficult challenge. Detailed work on this issue should commence ASAP. A detailed plan for the sequence of steps associated with the installation must be worked out. LL and the integration group will study the beam line further and attempt to reduce the amount of material in the path of the FMD detectors as much as possible. A major concern is also the background from ITS cables. The contribution from this source (f.ex in radiation lengths) is unknown and must be evaluated. The cooling requirements of the FMD detectors were discussed. Preliminary figures for the power requirements of the Si wafers were presented based on Viking chips. It appears that the total energy release in the FE electronics is low (5-10W). Thus cooling needs are small. In any case, the Si detectors need to be operated in a dry environment wherefore a small N2 flow will be required.  The amount of cables from the FMD detectors were discussed. The VIKING chip system requires about 20 (HV, multiplexed signal,  and control) cables. However, chips can be daisy-chained and output signals multiplexed so the total number of cables is limited. The T0 detector  (12 PM’s on either side) will generate its HV in generators on the detector so the number of  cables is also small.

 

  1. A main issue was the choice of technology for the T0 detectors. A pre-meeting had taken place in the morning and Chris Fabjan reported on the discussions on behalf of the proponents of various systems (MCP- G. Feofilov, radiator-PM by V. Grigoriev). It is recognized that the MCP system would need significant additional R&D work in order to be brought to a stage were it can be considered as a realistic option. It was felt that this  is not realistic in view of  the time scale of the entire project. On the other hand, the radiator-PM solution can provide the necessary fast timing required for the main ALICE T0 trigger and adequate efficiency with existing and proven technology.  The discussion continued under item 12 after dinner. It was then decided to recommend to the TB, the Forum and the MB that the T0 radiator/PM option be retained as the baseline option for ALICE. It also turns out that the funding of this detector is now assured via the Jyvaeskyla group (Trzaska et al.). The Finnish and Russian groups will collaborate on this project and bring it rapidly to the prototyping stage. A two-arm T0 is needed for good vertex for runs where TPC an pixels are absent.

 

  1.  Jean Yves Grossiord presented the status of the V0 detector. The detector will be built in a collaboration between the groups from Lyon and Mexico. V0 is now adapted in size to match the occupancy of the Si detectors providing desirable redundancy. It was pointed out that the V0 detectors, now that the Si detectors need not deliver a LVL 0 or 1 trigger, must provide the main on line LVL 0 multiplicity trigger. The necessary trigger scheme will be developed for discussion at the next meeting.

 

  1. The main decisions from the meeting are as follows:

 

-Abandon Si4.

-Position Si3 together with T0-L, V0-L and PMD in a common group at about 350 cm

 from the IP.

-Optimize the geometry of Si1,2,3 for best pseudorapidity coverage.

-The electronics for the Si-FE must be frozen soon so that realistic prototyping can

 commence.

-The beam pipe layout must be optimized and material strongly reduced to suppress the

 production of secondaries.

-The integration with the ITS must proceed to a detailed level ASAP and the material

 budget of its cables evaluated.

-Abandon the Si-FMD as a participant in the low level trigger.

-The two arm T0-radiator/PM option is selected as the baseline detector for providing a fast

 T0 trigger signal in LVL 0. Trigger scheme must be explored and developed in detail.

-The V0 detector will provide the main LVL 0 trigger multiplicity selection. Trigger scheme

  must be explored in detail.

  

  1.  Nothing.

 

PS: These recommendation were subsequently presented by JJG at the Technical Board and at the ALICE forum, and by FB at the Collaboration Board on behalf of the management board. The decisions were endorsed at all meetings.