1. Magnetic Field Task 24.02.2008 Dietrich Liko

2. Overview A lot of progress in the last two weeks I try to summarize the status Discussion on additional B field sensors Proposal to review the magnet measurements It was noted that its difficult to access the measurements

3. Discrepancy of the Magnetic Field The magnetic field simulation based on TOSCA had discrepancies to the true field outside the yoke Flux loop did not provide reliable information New input from the CRAFT data Several analysis show the effect Further information is derived from B sensors

4. Using Muons from Cosmics S. Bolognesi

5. B sensor measurements A number of sensors are available Some in the barrel Some in the forward A number of these sensors has been analyzed by Sorina Very difficult to access and process these measurements See her presentation later today

6. Where is the flux? 3.8T field, Bz flux through Z=0 plane TOSCA Hall Probes Flux Loops Tracks CRAFT Martijn Mulders

7. Progress in the field map Slava has studied several possible modifications of the model He has found an problem that can explain some of the observed differences Details see his presentation later today Results in a significantly improved map TCMB12MB23MB34 Old MapCRAFT-7%-24 %- 25% Old MapB Sensor- 6%-13%-24%-27% New MapB Sensor+5%-2%-8%-9%

8. Do we need a second simulation ? Some time ago the possible need for a second simulation of the field with a different simulation program was discussed (e.g. using ANSYS or similar) Several technical aspects Clearly an independent method is always an excellent crosscheck Currently we have observed significant progress with the TOSCA simulation We will have to check the effect of the new field map on the tracks Many arguments for a second simulation hold also if the TOSCA map is improved Its clear that such a simulation is considerable work. It will not happen by chance, but due to some decision.

9. Magnetic Field Lines Plot by Martijn. Can be used to identify interesting areas

10. Do we need more B field sensors ? We had some discussions on the possibility to install new sensors In general its difficult and one cannot simply ask for sensors everywhere A particular interest in studying a possible effect in Φ Should be most pronounced in the endcaps My understanding: A number of new sensors have been ordered (32)

11. Φ asymmetries The field parametrization in CMSSW is only one sector Φ asymmetry is assumed New model has significant Φ asymmetries Not really a surprise From 8% in the barrel to 50% in the endcap Up to now the effect has not been observed in the data

12. Access to measurements It has been noted that access to the measurements is somehow difficult Gigi has proposed to review the procedures I have prepared a proposal as a starting point for discussion See attachment in the agenda Sorina will discuss in some more details Basic idea is that measurements should be as automatic as possible and accessible in a central calibration database. One should follow the standard CMS procedure

13. Hall Sensors A large number of sensors are available Can be read automatically and it should work like that Requires integration in the detector control system (PVSS) to record data and transmit results Operational details (infrastructure) has to be understood

14. NMR Probes NMR probes can be read out permanently, if the noise stays at acceptable level. Automatic reading the NMR probes above 3 T fails because of too high gradient of the field across the NMR probe coils area. This would beat somehow the whole purpose … As reading the central field is obligatory, one has to see what part can be realized automatically and at which point a protocol for manual intervention has to be defined. Prior proposal for automatic readout https://edms.cern.ch/document/868689/1 https://edms.cern.ch/document/868689/1

15. Flux Loops Only the data collected during fast dump is of interest A special setup is required Effort to automatize would be significant Results have been questionable up to now Hardware intervention would be required to investigate the system We have to see if we “abandon” the system or aim for a long term upgrade