15/6/2006Gaia Lanfranchi - LNF-INFN1 Why do we have to measure efficiencies in the Muon Detector? Muon Software Meeting, June 15th G. Lanfranchi LNF-INFN

15/6/2006Gaia Lanfranchi - LNF-INFN2 In the past days I had a very interesting exchange with Giovanni (Carboni) about my work on the efficiency measurements. He asked me to clarify several points about my job – and more or less I have already done - and actually I wanted to give more details about it today. But in the last - yesterday evening - I got the impression that there is an opinion that efficiencies measurement is NOT a crucial point to be studied at the beginning of data taking since: 1)“It does not have any impact on LHCb physics performance so it can be neglected during reconstruction…” 2) “ Our detector is so simple that we dont need to measure such information during data taking in order to provide it to data reconstruction (i.e. we could simply rely on its design performance …)” So I changed my talk because, before proceeding doing other work, I need to clarify to myself WHY I am spending so much energy & time in doing this study. And I will try to do it by asking the following “basic” questions……… Introduction:

15/6/2006Gaia Lanfranchi - LNF-INFN3 1)Which kind of impact have the MWPC efficiencies on LHCb physics performance? Will they have an impact only in “catastrophic cases” that can be simply monitored via ECS? 2) Do we need to measure an efficiency map in the LHCb Muon System? Or, in other words, how does the Muon Detector performance depend on the MWPCs efficiency? 3) Is our detector really “so simple and common”? Outline of the Talk: Today I will spend my talk to answer to these questions. I will discuss all the other (technical and not technical) questions related to my work in the Muon Commissioning Meeting of July 5 th.

15/6/2006Gaia Lanfranchi - LNF-INFN4 Which impact have the efficiencies on LHCb physics performance? 1) L0 Trigger: L0 efficiency MUST be > 95% in 20 ns time window (LHCb TDR)  ε (L0) = ε(M1RX) x ε(M2RX) x ε(M3RX) x ε(M4RX) x ε(M5RX)  chambers efficiency MUST be > 99% in 20 ns time window in all regions/stations for ~1368 chambers covering a sensitive area of 435 m 2. J/ψ  μμ μ L0 muon  if one station (or a part of it) is 90% efficient (instead of 99%) the L0 efficiency will be 85%...and this certainly cannot be considered a “catastrophic case” that can be seen by a simple ECS monitoring…..

15/6/2006Gaia Lanfranchi - LNF-INFN5 2) Offline Muon ID: J/ψ  μμ Ks  ππ μ π The Muon ID efficiency plateau is 98%:  All physics analyses assume this number.  this value is valid ONLY IF the efficiencies of the M2-M3-M4-M5 stations are > 99%.  If one station (or a part of it) has an efficiency of 90% this value becomes 87%.  All physics performance must be re-evaluated… ε ~ 98% ε ~ 87% MuonID efficiency vs P (GeV/c)

6 How much the Muon Detector performance depend on MWPC efficiency (I)? The efficiency is evaluated in 20 ns time window  The efficiency STRONGLY depends on the time spectrum.  The time spectrum STRONGLY depends on the Gain.  The Gain depends on a lot of things (HV,P,T, geometry, bubbles..) M.Anelli et al. LHCb-Muon M. Anelli et al., IEEE 53 (2006) 330 Time Window Double-gap time spectrum for 3 different HV values measured with MIPs at CERN Test beam, October 2003.

7 How much the Muon Detector efficiency depend on MWPC performance (II)? Double gap efficiency and pad cluster size vs HV M.Anelli et al. LHCb-Muon M. Anelli et al., IEEE 53 (2006) The useful working region is ~ 150 V (the working point is ~ 2600 V) - Gain variation of ~100% (~20%) corresponds to a HV variation ~100 V (~35 V). - Gain variations – at fixed HV – can be induced by external factors (like T or P) and by geometrical tollerances (ex. panel planarity).  they can cause an efficiency drop Working Point

8 Gain Variations due to Geometrical Parameters: M. Anelli et al., IEEE 53 (2006) 330 Measurements performed at LNF show that over 58 chambers we have a double-gap gain variation of ~ 30% simply due to geometry. Inside the same chamber we have a gain spread of ~20% due to panel planarity (~100 μm planarity tolerance over 5000 cm 2 of sensitive area). If we put the same HV value to these chambers there will be some of them at the boundary of the working region and a “potential” efficiency drop…. These two chambers at the same HV have a Gain difference of 100% simply due to the geometry

15/6/2006Gaia Lanfranchi - LNF-INFN9 Problem of the bubbles in the panels: (C. Forti, LHCb week, Plenary Meeting, June 2th) “In a fraction of the panels we observed a “bubble”. The cause is not well understood, also because: - it appears mainly after months, even > 1 yr - the fraction of these panels is ~0.7%” The presence of such a bubble will modify dramatically the efficiency in the “defecting” zone…..We MUST know which are the chambers and logical pads that will be affected by that!

15/6/2006Gaia Lanfranchi - LNF-INFN10 Gain variations induced by Temperature and Pressure variations:  2 degrees temperature variation (over 20 degrees, P=constant) produce a single-gap gain variation of ~ 10%  20 mbar pressure variation (at T=constant) produces ~10% gain variation

15/6/2006Gaia Lanfranchi - LNF-INFN11 We will be certainly smart enough to correct all the gain variations by varying the HV but, if we want to keep the design performance, we certainly need to know which efficiencies will come out after corrections. To measure an efficiency map is UNAVOIDABLE ! What we need to discuss is: 1)How often do we need to measure this map? 2)Do we need to measure efficiency per logical pad or it is enough per chamber? If we measure efficiency per chamber we cannot identify bubbles or geometry defects inside a chamber…. 3) Which is the accuracy required? Are 100 events per chamber/logical pad enough? Do we need to measure an efficiency map (I)?

15/6/2006Gaia Lanfranchi - LNF-INFN12 With the present trigger lines at the initial luminosity of L ~ 2x10 31 cm -2 s -1 we would need (see my talk, Muon Meeting May 31th): ~ 3000 hours to collect 100 events per logical channel in M1R1 ~ hours to collect 100 events per chamber in the more external chambers of M5R4 If we assume a useful running time of 12 hours per day this means: -221 days to collect 100 events per logical channel in M1R days to collect 100 events per chamber in M5R4 In this period the Gain (and therefore the efficiencies) could be changed hundreds of times…. What do we think about? Do we think that it is fine? What will we tell to the Collaboration ? How can we measure an efficiency map ?

15/6/2006Gaia Lanfranchi - LNF-INFN13 Is our detector a “very common” and “simple” Muon Detector? I will show you some slides from a Seminar that Werner Riegler has done at CERN on March 16 th about “Gaseous detectors” at LHC experiments”. You will see in the next 4 slides that – if we exclude the RPCs – the LHCb Muon Detector is the most demanding Gaseous Detector of the four LHC experiments as far as regard timing performance (i.e. efficiency performance in 20 ns, i.e. trigger efficiency). followed by the ATLAS Thin Gap Chamber (TGC) and the CMS Cathode Strip Chambers (CSC). All the other Gaseous Detector are used only for position measurements.

15/6/2006Gaia Lanfranchi - LNF-INFN14 Time resolution ~ 5 ns

15/6/2006Gaia Lanfranchi - LNF-INFN15 Time resolution: ~ 3.5 ns

15/6/2006Gaia Lanfranchi - LNF-INFN16 Time resolution of the 4-gaps: ~ 3 ns

15/6/2006Gaia Lanfranchi - LNF-INFN17

15/6/2006Gaia Lanfranchi - LNF-INFN18 Please, send me all the technical questions that you have about my last presentation at the Muon Meeting (Giovanni already has done it..) so that I can prepare detailed answers for the next Muon Commissioning Meeting in July 5 th.