Steven Blusk, Syracuse University -- 1 Update on Global Alignment Steven Blusk Syracuse University.

Steven Blusk, Syracuse University -- 1

Update on GlobalAlignment

Steven BluskSyracuse University


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

1) Internal Alignment of the VELO (first halves, then to each other)2) Internal alignment of T-Stations (IT, OT and IT-to-OT)3) Relative alignment of VELO to T-Stations4) Alignment of TT to VELO-T Station system5) Alignment of ECAL & HCAL to tracking system6) Alignment of MUON to tracking system7) 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 AlignmentAfter internal alignment of each, there are in principle 9 global transformations between the two systems:

3 translations (X,Y,Z) 3 rotations () 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: X: Mean of XVELO-XT at Zmag. Y: Mean of YVELO-YT at Zmag.Z: Mean of (XVELO-XT)/tanX

VELO at Zmag. : Mean of tanY

VELO- tanYT.

: Mean of tanXVELO- tanX

T

: Mean difference in azimuthal angle VELO-T at Zmag. Zscale: Mean of (tanX

VELO- tanXT) / tanX

VELO


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:

o p > 20 GeV/c (no p cut for B=0, for the moment)o VELO angles < 100 mrado 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

No Zmag,since nobending

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

All meansare consistentwith zero !

All meansare consistentwith zero !


1 mm X Shift of VELO: B=0

No Zmag,since nobending

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<X>=(942±31) m<X>=(942±31) m

All other meansconsistentwith zero !



5 mm Y Shift of VELO: B=0

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<Y>=(4981±55) m<Y>=(4981±55) m




1 cm Z Shift of VELO: B=0

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<Z>=(1.25±0.12) cm<Z>=(1.25±0.12) cm




2 mrad Z-RotationVELO: B=0

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<>=(2.03±0.16) mrad<>=(2.03±0.16) mrad




Results with Perfect Geometry: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

All meansconsistentwith zero !

All meansconsistentwith zero !

<>=(0.47±0.31) mrad<>=(0.47±0.31) mrad


1 mm X Shift of VELO: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<X>=(1036±23)m<X>=(1036±23)m




5 mm Y Shift of VELO: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<Y>=(5049±71) m<Y>=(5049±71) m




1 cm Z Shift of VELO: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<Z>=(1.07±0.11) cm<Z>=(1.07±0.11) cm




2 mrad Z-RotationVELO: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

<>=(2.56±0.30) mrad<>=(2.56±0.30) mrad




Several ShiftsVELO: B=Nom

ZmagSlopeY

X at Zmag Y at Zmag

at Zmag Z

InX= - 250 mOut: X= - (249±23) m

InY= 250 mOut: Y= (188±50) m

In= 2 mradOut: = (2.38±0.33) m InZ = 4 mm

Out: Z = (3.1±1.1) mm


SummarizingParameter

VariedInputValue

B=0Rec. value

B=NomRec. value

X 1 mm ( 0.94±0.04 ) mm ( 1.04±0.02 ) mm

Y 5 mm ( 4.98±0.05 ) mm ( 5.05±0.08 ) mm

Z 1 cm ( 1.25±0.12 ) mm ( 1.07±0.11 ) mm

2 mrad ( 2.03±0.16 ) mrad ( 2.56±0.30 ) mrad

X

Y

Z

-0.25 mm

+0.25 mm

4.0 mm

2 mrad

-

( 0.25 ±0.23 ) mm

( 0.19 ±0.05 ) mm

( 3.1 ± 1.1 ) mm

( 2.38±0.33 ) mrad

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


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 and 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…

Steven Blusk, Syracuse University -- 1 Update on Global Alignment Steven Blusk Syracuse University.

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