Cosmic Muons and the Cosmic Challenge. data taken with B 3.5Tesla, red lines are reconstructed chamber segments

Transcription

1 Cosmic Muons and the Cosmic Challenge data taken with B 3.5Tesla, red lines are reconstructed chamber segments 0

2 Preamble Warning: Data analyzed in this talk are just a few days old, so all interpretations still preliminary Before looking at any data: BIG BIG thanks to all people involved in making Cosmic Challenge possible! Making the detector work (need 30 people to turn on CMS), doing shifts, copying the data, developing the software so fast that we can analyze data now, and many other tasks Challenge on all levels 1

3 Outline Reconstruction of Cosmic Muons with the Drift-Tube Chambers Comparing Data with Cosmic Simulation Looking at Single Chambers and Combining Them to Form Muon-Tracks 2

4 Cosmic Challenge 2006 (MTCC) the Cosmic Challenge is a crucial test of the CMS detector as a whole first real CMS data with B field turned on, dress rehearsal for LHC!!! phase 1 is now completed, enormous data-taking effort: recorded >30M trigger in various run configurations (13M@3.8T) Bon/Boff, just Drift Tube chambers or global MTCC setup readout, test runs emphasis is on testing the magnet (we ran on 4T!!!) and detector alignment, but if real data are recorded, we should look at them and test the full DAQ-chain + new software!!! For more info on muon status see talk from Kerstin: Hall almost empty since CMS is closed! 3

5 Detector Setup MB4 MB4 MB3 MB2 MB1 Drift Tube chamber: ϕ-superlayer θ-superlayer HCAL active sectors ϕ-superlayer sector 10 wheel YB+2 and YB+1 fully instrumented in this sector or t c e 11 s only instrumented in wheel YB CSC-chambers in endcap + some ECAL and tracker modules 4

6 Reconstruction of Hits the Drift Chamber and its electronics (Time-to-Digital-Converter) is a time measuring device very precise clock with Δt < 0.3 ns assumption: constant drift velocity x hit = v drift (t T 0 ) T 0 offset (arrival time of muon, delays of signal ) has to be determined combine hits from several cells to fit track segment no correct T0 no H 4μ 5

7 Drift Time Spectra all data are from global Boff run 2255 and global Bon run 2377 (B 3.5T) also have a cosmic Monte Carlo test sample (100000ev), thanks to Carsten Hof!!! drift times are the basic units of our DT chambers: 380ns T0-offset in the world of Monte Carlo life is easy, no noise 6

8 Incident Angle after combining cell hits from ϑ- and φ-superlayers we can reconstruct 3D chamber segments, then look at their properties Global CMS coordinate system: y incident angle x z z-axis points along the beamline incident angle is the true zenith angle of the cosmic muon 7

9 Incidene Angle with and without B-field look at incident angle in horizontal MB3, sector10, wheel YB+1 trigger-configurations are different in both runs, could also cause this shift bump is only reconstruction effect due to left-right ambiguity of hits in any case, effect of B-field on angular distribution is not huge! 8

10 Lessons Learned in Comparing Data and MC since some time cosmic muon generator existed in CMS wehavecosmicdata compare with Monte Carlo expectation angular distributions in data and MC showed huge differences problem with the old generator was discovered (things like this will happen all day during LHC ) we included a corrected and improved cosmic generator in CMSSW, based on generator provided by Thomas Hebbeker from LEP times 9

11 Data and New Cosmic MC compare angular distributions of new cosmic MC with data, here for horizontal MB2, sector 10, wheel YB+2 (data normalized to MC) with new MC agreement looks fine still: in MC only approximate modelling of trigger conditions (simply counting hits in chambers), this also assumes 100% trigger-efficiency more MC statistics with bigger sample 10

12 Residuals of Chamber Segments good quantity to check CMSSW reconstruction and quality of segments are residuals: distance between reconstructed cell hits and fitted segments compare Boff/Bon data and cosmic MC in MB3, sector 10, wheel YB+1 we can reconstruct cosmics also with Bon, data and MC comparable 11

13 Definition of StandAlone-Muon and Angles we can combine segments from DTs to form muon-track (Kalman filter) wedefine: SA-muon = track where 2 chambers contribute it is possible to access track-information at innermost and outermost hit track-fit (SA-muon) Global CMS coordinate system: y MB1 innermost measurement MB2 ϑ-superlayer φ-superlayer φ SA x ϑ SA MB3 outermost measurement 2D-segment in theta combined 2D-segment in phi z ϑ SA = 0 means track along the beamline (z) 12

14 Reconstructing Cosmic Muon Tracks all is still under development in CMSSW, so reconstructing tracks not easy little hits in inclined sector 11 as not in trigger 2D-info from ϑ-superlayer 2D-info from both φ-superlayers beampipe still, SA-reco works, also with Bon! 13

15 Cosmic Reconstruction is Special cosmics in general cross CMS outside origin have to modify default reconstruction code, remove vertex constraints MB1 MB2 MB3 sector 10 wheel YB+1 MB4 MB4 sector 10 wheel YB+2 MB1 MB2 MB3 MB4 wheelyb+2 contributing less (similar effect in MC) reconstruction effect? Remaining vertex constraint? In Boff data YB+2 contributes more 14

16 N Some Rough Estimates Estimate performance of Standalone Reco: require events with >6 hits in both φ-sls of MB2 and MB3 in sector 10, wheel YB+1/YB+2 (similar to DT-only trigger) events likely to have track N eventwithsatrack eventwithdt onlytrigger ( Boff Data) 55% eventwithdt onlytrigger ( BonData) 51% despite assumptions in MC, performance of SA-reco similar in data and MC track-fit similar with and without magnetic field Comparing trigger-rates in Bon-data and cosmic MC: N N eventwithsatrack eventwithdt onlytrigger ( BonMC) 48% cosmic generator predicts total muon flux determine rate of DT-only trigger: L1-rate(cosmic MC, Bon) < 160 Hz compare to B=3.5T data run: L1-rate(data, 3.5T) 40 Hz similar scale N N eventwithsatrack 15

17 Angular Distributions of SA-Muons look at track-parameters at innermost muonstation, e.g. φ-angle: (data normalized to MC) muons from muons from straight above have straight above have ϕ=270 ϕ = -90 φ-distribution looks reasonable, both in data and in cosmic MC again, effect of magnetic field does not change shape much in data 16

18 Angular Resolution of SA-Tracks in MC we know generated angle muon has to cross detector to reach bottom sectors generated long tails 13.6 MeV Δθ 330 = GeV reconstructed difference between gen. and rec. angle is well compatible with multiple scattering 17 in φ-angle σ 50 due to B-field!

19 Measuring the Transverse Momentum we have B-field, we have SA-tracks be brave and look at momentum: (data normalized to MC) note that maximum > 0 GeV, minimal momentum of cosmics! nice agreement between data and MC, general shape makes sense for cosmics RMS shows that measurment is not very exact, but it s cosmics! postive mean reflects energy loss 18

20 Outlook cosmics and the Cosmic Challenge are the ideal reharsal prior to LHC, at all levels of CMS huge statistics of data with and without B-field, waiting to be analyzed using reconstruction of new CMSSW possible to look at single DT-chambers and even fit StandAlone-tracks comparisons with cosmic MC show reasonable agreement still not tried to combine with other subdetectors yet volunteers? 19

21 Cosmic Challenge is a success! The detector and magnet are working!!! 20

22 Backup Slide 21