Material description in LHCb


This page is to collect information about the knowledge on the material uncertainty / description for the different subdetectors of LHCb.


Silicon Trackers

In the IT, the mass agrees between data and simulation for the boxes at the 2 % level. That is a solid measurement i.e- putting things on scales and doing the calculation in MC. The cables and supports are a bit harder to estimate (have to extrapolate from small pieces and makes assumptions about where they are) but 5 % is quoted. For the TT there are no numbers, but there is no why the module weight should not agree at the 2 % level as for IT. For TT the inactive material aside from the modules is easier to describe so 5 % is certainly a conservative estimate.

Outer Tracker

The weight of one OT module is known to about 1%, (8240 +- 80 g to be precise), and the total weight of a module is consistent with the estimated sum of all individual components. So not only the weight is well known, also the material composition.



Beam pipe


Text for publication "Measurement of the track reconstruction efficiency at LHCb"

"The 10% uncertainty is used as a conservative upper limit and is composed as follows: for the VELO a calculation in "Performance of the LHCb Vertex Locator (arxiv:1405.7808)" shows an uncertainty on the material budget of 6%. No direct measurements exist for the T and TT stations. However, weight measurements for the Inner Tracker for the silicon sensors and the detector boxes give an accuracy of 2%, while an agreement of 5% is reached for the cables and the support structure, as written in "Estimation of the material budget of the inner tracker, CERN-LHCb-2008-054" and "Survey of the Cables of the Inner Tracker, CERN-LHCb-2008-055". The Outer Tracker modules have been weighted and this measurement is precise to about 1% (as in "A Study of the Material in an Outer Tracker Module, CERN-LHCb-20014-114"). Furthermore, the sum of the weights of the individual components of a module adds up to the total weight of a module within the uncertainties. Taking into account that some level of detail is missing in the detector description in the simulation, an uncertainty of 5% is assumed for the outer tracker. Weight measurements for the sensor modules and the insulation material of TT have been performed. Given the detail of the detector description ("TT detector description and implementation of the survey measurements, CERN-LHCb-2008-061") an uncertainty of 5% on the material budget is well justified. The beam-pipe was implemented in the software following the design drawings, where a precision better than 10% for all pieces was confirmed following measurements after production. The solid radiator (aerogel) and the gas radiator (C4F10) contribute more than two-third of the material budget for the RICH1 detector, as written in "LHCb RICH1 Engineering Design Report, CERN-LHCb-2004-121"). The amount of aerogel is known up to 2% and the differences between 2011 and 2012 are accounted for in the simulation. The density of the C4F10 was monitored, with the RMS of the distribution being about 1%. The other components of RICH1 have a smaller contribution to the interaction length. The overall uncertainty of 10% for the full material budget was then chosen to also take uncertainties on the GEANT4 cross-sections and additional uncertainties, coming from simplified descriptions of the detector elements in the simulation, into account."


The statements are put together from discussions with the involved people via email, so no guarantee they can be found word-by-word in public documents.

-- MichelDeCian - 2014-11-14

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Topic revision: r2 - 2014-12-12 - MichelDeCian
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