Tracking resolution 9th December 2016 1 Material for tracking - - PowerPoint PPT Presentation

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9th December 2016

Tracking resolution

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9th December 2016

Material for tracking seminar

intrinsic pt resolution for equidistant measurement resolution in case of correlated errors Nef vs Np

• e.g Space charge distortion, Time response function
• requirement for the precision of calibration

approximate formulas - intrinsic pt resolution in case of combined (non equidistant) pt measurement

• consideration for the TPC+ITS+TRD diferent fmuctuation scenarios

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9th December 2016

q/pt resolution. T rack-let update

Global fjt with the Ntr track-lets and global fjt with the Ntr x Ncl space points - similar performance

• In T
• y Simulation example space points assumed to be independent

→ Nefallf=Ntr x Ncl Track-let position resolution for Ncl independent clusters Curvature resolution at limit of high Neff

Alice TPC - Numerical simulation In the case of N equidistant measurement q/pt resolution Gluckstern [NIM 24 (1963) 381] (for N>10)

Ntr track-lets (15 in example) Ncl space points per tracklet (8 in example)

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9th December 2016

TPC q/pt resolution. Track-let update

Number of efective point Nef reduced by correlation between measurement ( Nef!=Npoints) T rack-let consideration

• Speed-up track fjt (e.g 6 Kalman propagate and Update instead of 159)
• Possibility to account for correlation.
• track-let length longer than correlation length
• Approximation of analytical formulas for non equidistant measurement

Track-let position resolution for Ncl independent clusters Curvature resolution at limit of high Neff

Alice TPC - Numerical simulation In the case of N equidistant measurement q/pt resolution Gluckstern [NIM 24 (1963) 381] (for N>10)

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9th December 2016

Nef in case of correlated measurement. Examples.

TPC Space charge distortion example

• Nef ~Nall/Ncorr=159/20~8

ALICE TRD TRF example

• Nef= Nall/Ncorr=20/6 ~ 3.

Distortion due space charge p3 - scale parameter 3.7 cm Time response function (TRF) correlating (ALICE TRD) Helix fjt for correlated measurement

pad-row ∆ (cm)

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9th December 2016

Space charge fmuctuation

Signifjcant relative fmuctuation of the space charge Limit cases:

• big volume limit 1/(Fµtrack)<<2 → σ/µ~sqrt(1/NEvents
• small volume limit 1/(Fµtrack)>>2 → σ/µ~1/s*sqrt(1/Ntrack

Run 2 O(20-30%) for pp and Pb (small volume limit) - consistent with measurement Run3 Pb-Pb O(2-5%)

Expected relative fluctuation

• f space charge originating

at volume

Run2 scenario Small ion hotspot Ion integration time ~ 0.1 s S ~ 3x3 cm Rin~83 cm Rout~245cm Volume fraction F = 0.00017

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9th December 2016

Space charge fmuctuation

Expected relative fluctuation

• f space charge

Signifjcant relative fmuctuation of the space charge Limit cases:

• big volume limit 1/(Fµtrack)<<2 → σ/µ~sqrt(1/NEvents)
• small volume limit 1/(Fµtrack)>>2 → σ/µ~sqrt(1/Ntrack

Run 2 O(20-30%) for pp and Pb (small volume limit) - consistent with measurement Run3 Pb-Pb O(2-5%)

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9th December 2016

Combined pt resolution. T

• y MC

Combined pt resolution signifjcantly better than TPC only

• High distortion limit - q/pt resolution fully determined by ITS and TRD
• Close to TPC nominal resolution - linear scaling of q/pt resolution as

function of TPC σrφ

Small TPC σrφ limit Hight SC distortion σrφ limit Nominal TPC σrφ resolution

ITS TPC TRD ITS Ntr 6 layers σrφef ~ 0.01 cm TPC Ntr - 159 layers TRD Ntref 6 layers σrφef ~ 0.05 cm Toy MC setup