3rd workshop in the 2nd European series of Linear Collider Detector workshops
Richard Dubois, SLAC
present state of North American simulations
The European effort is focussed on a high luminosity 500 GeV linear collider (LC) called TESLA, proposed by DESY. They have been charged with optimizing a baseline detector design to exploit the physics that a 500 fb-1/year machine could deliver.
The baseline detector design laid out in the Conceptual Design Report (CDR) consists of a tracking system composed of a pixel vertex detector, an intermediate tracker and a TPC. The EM calorimeter is Pb-scintillator; the Hadronic is Cu-scintillator, with the coil between them producing a 3 T field. There is to be a muon system which will act as a tail-catcher calorimeter. They also plan on an instrumented mask and luminosity monitor covering down to ~25 mrad, allowing a veto on beam electrons from 2g backgrounds.
About 130 people were registered for the conference, with 3 from the US and perhaps a couple from Japan. The meeting was held at the Frascati National Lab (LNF). The meeting was somewhat oversubscribed and there were several time conflicts on interesting talks in parallel sessions. Many of the talks have already been placed/scanned onto the web.Their next large workshop is scheduled for late March 1999 at Oxford, to be hosted by Phil Burrows. This workshop is seen as a tune-up for the big LCWS meeting in Sitges, outside of Barcelona, in May 1999. They are assuming that not everyone who presented at the European series of workshops would get time at the Barcelona meeting.
The workshop management stressed that, for Barcelona, people should stick to the CDR definition of the detector (partly as enforced by what's in BRAHMS) and use the provided simulation tools.
The main design issue discussed was in the area of the beampipe (going to 1 cm from 2). The consequences were increased B field (to 4T from 3 to sweep away more background) and its effect on the final quads and, of course, occupancy in the VXD. They did not have a solution for the masking at the smaller radius and were estimating occupancies of 700 hits/mm2.
There was also discussion of hermiticity. It was felt that at least a calorimetric veto must be possible down to as low an angle as can be achieved, perhaps 25 mrad. This implies an instrumented mask. There were comments that the endcaps would be compromised by cables and plumbing in any case.
There were questions about the need for the intermediate tracker, but if there was to be one, it would be a 3D device. There was a proposal for a TOF system, stated to help ID bunches in the bunch trains, tag cosmics and to assist in dealing with accelerator-induced muons. Resolutions at the 0.5 ns level were put forward.
The trigger folks were in accord with the Keystone recommendations: no trigger be applied and complete readout of all bunches be done. The 'trigger' to pass the bunch on would then be completely done in software. Their concern was volume of data, notably in the inner layer of the VXD. They were also concerned about leaving the VXD and TPC running ungated.
They have set up both fast-smear and full simulations. Their primary fast-smear package is called SIMDET, with a second equivalent one, SGV, in reserve. Their full simulation is called BRAHMS. SIMDET and SGV are fast and essentially just do 4-vector smearing. BRAHMS is a full GEANT3 description of the baseline TESLA detector. All their simulations are based on Fortran and existing tools (GEANT3, LEP reconstruction tools, etc).
BRAHMS is in the later stages of development and starting to gain momentum, and users. A few initial studies, mostly by the authors, were presented here. Most detector subsystems have been installed and hits are produced.
BRAHMS does have a first track fitter, which does not yet correctly handle multiple scattering; it does appear to reproduce the expected momentum resolution at high p. I believe the tracking code has been borrowed from L3.
They say they have rudimentary calorimeter clustering. At present there is no standard output format; it is being defined now. This standard format is important for bringing people on board with a common interface to the tools. It is not clear that the format proposed at the meeting has sufficient information in it to do really detailed studies. The MC history is sparse and calorimeter object descriptions terse.
The fast-smear MC's are in use for physics studies already. A new option to SIMDET is in the works which will adapt the H1 GFLASH shower parameterization to provide more realistic shower properties. Presumably this will be ready in the next couple of months.
They are just beginning to institute some form of code management, using CMZ/Patchy administered in AFS from DESY/Zeuthen. They will create a web interface, using TUOVI, for those who do not have AFS.
DESY/Zeuthen has embarked on a training exercise in OO. They are attempting to build an event display using LHC++ tools, notably OpenInventor and HEPVis, following on work done by L3. Initially, data input will come from C++-wrapped Fortran, and geometry definition from GEANT4's (G4) GEANT3 (G3) translator. They have some pretty pictures to show already of the detector design. OpenInventor is a commercial product which must be licensed.
No plans were mentioned for OO reconstruction.
A b02 release came out in October and the first production release is still due out in January '99. They have, without too much trouble, but not none, installed G4 on Linux using standard utilities: g++, CLHEP and gmake. One still must use the RogueWave (commercial) class library. It should run on most flavours of Unix and WindowsNT/98.
Object persistency is done via Objectivity (another commercial product). They supply conversion tools which will generate the C++ geometry code given a GEANT3 Zebra RZ file. The speaker had been unable to get G4 to successfully convert the BRAHMS geometry file.
Features of interest are:
Their scheme for generators is to use the Circe package for beamsstrahlung and feed that into Pythia, which is their workhorse generator. Pythia does not do polarization and will not. They use SUSYGEN, but it also does not do polarization nor beamsstrahlung nor ISR. I suggested they look at IsaJet, for which I believe beamsstrahlung and ISR is in the works. Output from the generator goes to an ASCII file based on /HEPEVT/.
It is expected that the proceedings of the European workshop series will be recorded separately for physics and detector issues as reports DESY 123 F and G. They are aiming at Barcelona to present results on their CDR design and then modify it to produce a costed detector design for the Technical Design Report that has been requested by DESY for June 2000. For that time frame, they are expecting well-oiled simulations that will allow defining a programme at both design energies (500 and 800 GeV) and to investigate the issue of one or two IPs.
There was a surprising (to me) amount of discussion of TESLA as a Z0 factory, producing up to 109 Z0/yr, and the issues involved in making sure that could happen. There was a talk from Nick Walker in which he gave an estimate of one shift to switch the machine from 500 GeV to 90 GeV. In this estimate he assumed that the controls system had been designed to accomodate such a shift. He ignored possible time delays due to background tuning after the changeover.
The Europeans seem to have selected a large number of reference reactions and look like they are overwhelming the people who are to supply the generators and event libraries for those reactions. These reactions form a comprehensive list of processes that could occur at the LC. I believe their intent is more to scope out the high luminosity physics with the fast MCs rather than use them to explore the detailed detector specifications using BRAHMS.
They are not yet in the mode of using the simulations to study the physics or detector parameters. Very few talks were given using these tools and most physics talks (that I saw) were from theorists. However, a few people are starting to use the tools and the fast simulators appear to be in good enough shape for physics requirements studies, while the full simulation is getting close. It is my impression that perhaps 5-10 young physicists are devoting significant time to the LC detector effort and they are the ones who will take up the simulations and create tools (probably adapted from LEP) going into the Oxford meeting. DESY-Zeuthen appears to be making an effort to be a centre of computing for the European efforts.
Ciao!
Last Modified: 01/13/04 12:46