Update on global alignment steven blusk syracuse university
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Update on Global Alignment Steven Blusk Syracuse University. Preface. The LHCb detector alignment will require several steps. A sensible scenario is: Internal Alignment of the VELO (first halves, then to each other) Internal alignment of T-Stations (IT, OT and IT-to-OT)

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Update on Global Alignment Steven Blusk Syracuse University

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Update on global alignment steven blusk syracuse university

Update on GlobalAlignmentSteven BluskSyracuse University


Preface

Preface

  • The LHCb detector alignment will require several steps. A sensiblescenario is:

    • Internal Alignment of the VELO (first halves, then to each other)

    • Internal alignment of T-Stations (IT, OT and IT-to-OT)

    • Relative alignment of VELO to T-Stations

    • Alignment of TT to VELO-T Station system

    • Alignment of ECAL & HCAL to tracking system

    • Alignment of MUON to tracking system

    • Alignment of RICH to tracking system

The internal alignment tasks are being addressed by various groups.

Here, I present a plan and details for Step 3.

Simulations consistent of 5000 event samples of min bias usingGauss v22r1, Boole v10r3, Brunel v28r2


Relative velo to t station alignment

Relative VELO-to-T-Station Alignment

  • After internal alignment of each, there are in principle 9 global transformations between the two systems:

    • 3 translations (X,Y,Z)

    • 3 rotations (a,b,g)

    • 3 scale factors (Xscale, Yscale, Zscale )

  • In practice, Xscale, Yscale are highly constrained by the interwire/strip spacing. Therefore there are realistically 7 global parameters between the two systems.

  • Align the VELO to the T-Stations by matching segments at the center of the magnet (Zmag).. Pattern recognition done independently in each system.

  • They can all be measured using MAGNET OFF data:

    • DX: Mean of XVELO-XT at Zmag.

    • DY: Mean of YVELO-YT at Zmag.

    • DZ: Mean of (XVELO-XT)/tanqXVELO at Zmag.

    • Da: Mean of tanqYVELO-tanqYT.

    • Db: Mean of tanqXVELO-tanqXT

    • Dg: Mean difference in azimuthal angle fVELO-fT at Zmag.

    • Zscale: Mean of (tanqXVELO-tanqXT) / tanqXVELO


Method details

Method Details

  • We use a single kick approximation to the field, where the kickoccurs at the effective center of the magnet (Zmag).

    • This is only an approximation, and in general Zmag is a function of the track’s X,Y slopes and momentum.

    • To minimize dependence, we can require high momentum, low angle trackssince we are only seeking global alignment parameters. We require:

      • p > 20 GeV/c (no p cut for B=0, for the moment)

      • VELO angles < 100 mrad

      • TX-seed angle < 200 mrad (Ty–seed constrained since Py ~unchanged)

  • Zmag is determined using simulation, with “perfect geometry” and field045.cdf. We map out using the straight line intersection of T-seed and VELO tracks:

    • Zmag = 526.7 cm, and has a mild dependence on X angle.

      • We correct for it, but it’s not critical to determine global offsets.

    • Correction to Y-slope in T-Station for change in Pz.


Results with perfect geometry b 0

Results with Perfect Geometry: B=0

No Zmag,since nobending

DSlopeY

Zmag

All meansare consistentwith zero !

DX at Zmag

DY at Zmag

DZ

Dg at Zmag


1 mm x shift of velo b 0

1 mm X Shift of VELO: B=0

No Zmag,since nobending

DSlopeY

Zmag

<DX>=(942±31) mm

DX at Zmag

DY at Zmag

All other meansconsistentwith zero !

DZ

Dg at Zmag


5 mm y shift of velo b 0

5 mm Y Shift of VELO: B=0

DSlopeY

Zmag

<DY>=(4981±55) mm

DX at Zmag

DY at Zmag

All other meansconsistentwith zero !

DZ

Dg at Zmag


1 cm z shift of velo b 0

1 cm Z Shift of VELO: B=0

All other meansconsistentwith zero !

DSlopeY

Zmag

DX at Zmag

DY at Zmag

<DZ>=(1.25±0.12) cm

DZ

Dg at Zmag


2 mrad z rotation velo b 0

2 mrad Z-RotationVELO: B=0

All other meansconsistentwith zero !

DSlopeY

Zmag

DX at Zmag

DY at Zmag

<Dg>=(2.03±0.16) mrad

DZ

Dg at Zmag


Results with perfect geometry b nom

Results with Perfect Geometry: B=Nom

DSlopeY

Zmag

DX at Zmag

DY at Zmag

<Dg>=(0.47±0.31) mrad

All meansconsistentwith zero !

DZ

Dg at Zmag


1 mm x shift of velo b nom

1 mm X Shift of VELO: B=Nom

DSlopeY

Zmag

<DX>=(1036±23)mm

DX at Zmag

DY at Zmag

All other meansconsistentwith zero !

DZ

Dg at Zmag


5 mm y shift of velo b nom

5 mm Y Shift of VELO: B=Nom

DSlopeY

Zmag

<DY>=(5049±71) mm

DX at Zmag

DY at Zmag

All other meansconsistentwith zero !

DZ

Dg at Zmag


1 cm z shift of velo b nom

1 cm Z Shift of VELO: B=Nom

All other meansconsistentwith zero !

DSlopeY

Zmag

DX at Zmag

DY at Zmag

<DZ>=(1.07±0.11) cm

DZ

Dg at Zmag


2 mrad z rotation velo b nom

2 mrad Z-RotationVELO: B=Nom

All other meansconsistentwith zero !

DSlopeY

Zmag

DX at Zmag

DY at Zmag

<Dg>=(2.56±0.30) mrad

DZ

Dg at Zmag


Several shifts velo b nom

Several ShiftsVELO: B=Nom

DSlopeY

Zmag

In: DX= - 250 mm

Out: DX= - (249±23)mm

In: DY= 250 mm

Out: DY= (188±50)mm

DX at Zmag

DY at Zmag

In: Dg = 2 mrad

Out: Dg = (2.38±0.33)mm

In: DZ = 4 mm

Out: DZ = (3.1±1.1) mm

DZ

Dg at Zmag


Summarizing

Summarizing

Still need to check rotations around X,Y axes and Z-scale but don’t expect any surprises


Conclusions

Conclusions

  • Matching at the center of magnet appears to provide robustestimate of relative alignment between VELO and T-Stations.

  • 5000 min bias events gives reasonably good precision on offsets(Scale by 1/N to get a given precision)

  • Still need to check Da and Db and Z-scale, but don’t expectany surprises.

  • Document in progress. Full description of LHCb alignment needsto be put together. This is one piece of it.

  • Migrate (PAW) code to ROOT-based GaudiAlgorithm.

Many thanks again to Matt , Eduardo, Juan and Marco Cattaneo for lots of help with software issues…


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