1. Aras Papadelis, NIKHEF Jaarvergadering 19/12/06 1 Fresh results from the LHCb Vertex Locator test beam Aras Papadelis Ann Van Lysebetten, Anne Keune, Eddy Jans, Hans de Vries, Martin van Beuzekom, Thijs Versloot, Tjeerd Ketel

2. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 2/17 ACDC, No ordinary test beam Test beam = R&D ? Not always! The VELO Alignment Challenge & Detector Commissioning (ACDC): ¼ of the real VELO in SPS 400GeV proton beam Final hardware and Experimental Control System (ECS) Operation in vacuum with CO 2 cooling Real LHCb firmware and software (event building, clustering, tracking, vertexing, alignment, online monitoring) - A FULL SYSTEM TEST - A DRESS REHEARSAL - THE FIRST STEPS OF THE COMMISSIONING

3. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 3/17 Beam z y x VELO in North Area, November 2006 ( 4 weeks ago!!!)

4. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 4/17 Targets 8 targets 200/300 micron Pb- coins Emulate open and closed VELO R =2.5 mm R =1 mm

5. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 5/17 Recabling in the name of physics Straight Tracks Interactions in silicon Angled TracksSome More Vertices Target

6. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 6/17 Online monitoring X Y # Online high level monitor  For example, see the beam spot in real time!

7. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 7/17 First tracks in the “real” VELO ● From LHCb event display - Panoramix

8. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 8/17 Software alignment ● Important part of the ACDC – demonstrate that the alignment software works with real data. Spacepoint y-residuals

9. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 9/17 Vertex analysis ● 35 M events from target runs on tape (1.5 TB) ● Low purity of sample  ~ 30000 useful target vertices. ● To reconstruct vertices every step in the software chain has to work. ● 1 st analysis focused on 4 targets (2 closed VELO + 2 open VELO) The data is very fresh (4 weeks since test beam) so the analysis results are preliminary!

10. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 10/17 The VELO locates a vertex! 2-track vertex event in Panoramix Seen “almost” online! 4 mm Al vacuum trolley wall Target cylinder

11. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 11/17 The vertices from the vacuum trolley proved very useful during data taking. Their XY distribution used as hit map during test beam. Offline we might use vertices in the trolley to unfold the beam profile. The vertex landscape z/mm x/mm y/mm “Closed VELO” targets

12. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 12/17 Vertex z ● We can clearly reconstruct the z positions of the targets and silicon sensors. ● E particle < 1 GeV ● Targets far from first silicon Vertex resolutions are not LHC-like but worse z y x

13. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 13/17 X slice Edges in X-Y X/mm Y/mm Fit sum of two error functions (integral of gaussians) to central X and Y to find target edges Y slice x/mm y/mm

14. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 14/17 Edge fits – “closed VELO” targets Red marker and rings = metrology result Blue markers = fitted edges and centre

15. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 15/17 Edge fits – “open VELO” targets Red marker and rings = metrology result Blue markers =fitted edges and centre

16. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 16/17 Analysis results so far ● Preliminary results! ● X-Y resolution is ~ 150 (closed) – 300(open)  m. ● Differences between metrology and reconstructed edges. Something to investigate! Still space for improvement. ● Move to more sophisticated fit method. ● More data on tape to look at! ● Compare with simulation Most important result at the moment: - The VELO software and hardware is there and it works! We see vertices!

17. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 17/17 Summary In 2006 the VELO group conducted a system test (ACDC) in the SPS beam where hardware and software was commissioned in preparation for the LHC start 2007. One of the crucial exercises was to show the ability to reconstruct the xy positions of vertices from targets. 2007 will be a very exciting year for the VELO: - finish assembly - installation in pit (May) - First beam in LHC (November) The battle of CERN Prevessin - Nov 2006 THE VELO IS PREPARED!

18. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 18/17 BACKUP SLIDES

19. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 19/17 Fitting with error functions ● A simple Gaussian fit the x/y distribution doesn’t give edges. ● But, assume that each vertex measurement is Gaussian  Vertex x/y distribution is sum of Gaussians  described by two Error functions. diameter centre edge σ Erf(1; 0.3)-Erf(3; 0.3) edge

20. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 20/17 Target positions scintillator 100mm 90 mm ≥3 hits in modules + scintillator hit 4 upstream targets4 downstream targets 8 targets in total, 2 x 4, 200μm and 300 μm 4 inner – 1mm radius 4 outer – 2.5mm radius. Emulate a half open VELO. X /mm Target 1 Target 2

21. Aras Papadelis, NIKHEFJaarvergadering 19/12/2006 21/17 A cool VELO MAIN LESSONS LEARNED The CO2 cooling method works. The cooling on the modules is sufficient. T < 0°C on sensors is no problem. CERN crane drivers don’t work after 5pm and weekends. CO2 batteries tend to need replacement by a crane driver after 5pm and on weekends. Cooling made at NIKHEF and operated by Ann Van Lysebetten & Eddy Jans