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First Look at Global Alignment of LHCb Detector

First Look at Global Alignment of LHCb Detector. Forewords. The goal here is to obtain a relative alignment of the entire LHCb detector Other groups are working on the internal alignment of subdetectors. Here, we are only interested in global transformations between detectors.

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First Look at Global Alignment of LHCb Detector

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  1. First Look at Global Alignment of LHCb Detector

  2. Forewords • The goal here is to obtain a relative alignment of the entire LHCb detector • Other groups are working on the internal alignment of subdetectors. • Here, we are only interested in global transformations between detectors. • Taking VELO and T stations, one could have: • Relative misalignment in X, Y, or Z with respect to the assumed value (3). • Rotation around the Z axis of one subdetector relative to the other (1) • Rotation around X,Y axis (or shearing) of one sub-detector wrt the other (2). • Different Z scale between one subdetector and the other (1). • Tracking alignment is the starting place, since all other subdetectors require an aligned tracking system.

  3. LHCB Detector XZ Plane, Bend plane YZ Plane, “non”-bend Strategy: Match upstream and downstream segments at the magnet center. Extract relativealignment between the two subdetectors

  4. Magnet OFF/ON Data • Magnet OFF data will be a critical first step to decouple B field/material effects from geometry. • Magnet OFF data can be used to extract all 7 relative alignment parameters. • Magnet ON data can only provide 5 (DX, DY, DZ, Dfz , Shear in Y) • Shear in X and Z scale only change the reconstructed bend angle • ~no change in track c2, for example • Magnet ON data more difficult • Let’s start there…

  5. Need Center of the Magnet • Assume dipole magnet gives a px kick at the effective center of the magnet. • The effective center is simply the intersection point of the upstream and downstream segments. • In general though, the effective center depends on both the VELO and T angles ( and |p| ) • To reduce this dependence, which becomes large for large angles (and low momenta), we use tracks with: • P >10 GeV/c • VELO X & Y slopes less than 100 mrad • T-station slopes less than 200 (100) mrad in X (Y) view • Isolation not required at this stage, but can be explored if necessary. • Must reconstruct VELO tracks and seed tracks independently so notto bias the result. Not the default way to obtain tracks… All simulations shown are 5K Min Bias events

  6. Center of Magnet – Perfect Alignment <Zcen> (cm) QxVELO (rad) (cm)

  7. Corrections to Y slope For a perfect dipole withfield along Y, pY does notchange, but, the angle does,since pZ changes… Correct Qy(T-stations)for change in pZ…

  8. DqY Zcen DY DX Df DZ Perfect Alignment Dq=(0.010.01) mrad Zcen= 526.6 cm DX=(-2921) mm DY=(-639) mm Df=DX/Ymag DZ=DX/qX Df=(0.30.2) mrad DZ=0.3 cm In all cases, P3is the mean of thedistribution, andis the relevant parameter

  9. Perfect Alignment I am still working onthis…but keep the ~(3-4) mmshift in RAM…

  10. DqY Zcen DY DX Df DZ Z Shift by 10 mm Dq=(-0.020.01) mrad Zcen= 526.7 cm DX=(322) mm DY=(-4340) mm Df=(0.30.2) mrad DZ=1.3 cm

  11. Z Shift by 10 mm Some mystery herewhy Y view doesn’tprovide Z shift.(needs further investigation)Maybe some bad fits…

  12. DqY Zcen DY DX Df DZ 5 mm X Shift Dq=(0.030.01) mrad Zcen= 526.0 cm Positive and neg.slopes produceseparate peaks DX=(-504025) mm DY=(2548) mm Df=(0.3XX) mrad DZ=1.3 cm, but…. Resolutiondegraded

  13. DqY Zcen DY DX Df DZ 2 mm X Shift Dq=(0.20.02) mrad Zcen= 526.6 cm DX=(-196922) mm DY=(2644) mm DZ=0.26 cm Df=(0.80.2) mrad ?

  14. DqY Zcen DY DX Df DZ 1 mm X Shift Dq=(0.02??) mrad Zcen= 526.6 cm DX=(-102622) mm DY=(4339) mm Df=(-0.20.2) mrad ? DZ=0.20 cm

  15. DqY Zcen DY DX Df DZ 5 mm Y Shift Dq=(0.020.02) mrad Zcen= 526.7 cm DX=(2028) mm DY=(-504853) mm Df=(XXXX) mrad DZ=0.7 cm ? Resolutiondegraded,bad fit… Fit quality?

  16. DqY Zcen DY DX Df DZ 2 mrad Z Rotation Dq=(0.00.01) mrad Zcen= 526.7 cm DX=(221) mm DY=(2940) mm Df=(2.10.2) mrad DZ=0.3 cm

  17. Summary • X, Y Translations and Z rotations “reliably” determined, with 5K events. A 0.3 cm bias in Z shift is still under investigation.Obtain resolutions of about: • DX: 20 mm, DY: 40 mm, DZ:1 mm, DQZ:0.2 mrad (Did not simulate Z-stretching or compression (yet)) • This level of statistics at the right level for determining the global alignment parameters. • Will generate magnet OFF simulate data next. • Need to understand this bias.. • Need to move to ROOT for final package..

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