Forward pixels – on tracking at higher η in CMS

Frank MeierUniversity of Nebraska-Lincoln

Januar 23, 2015

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Introduction

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Introduction

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Overview

Introduction

Phase-I forward pixelsPhase-I: Motivation

Phase-II forward pixels

Very forward pixelsSimulationsSensor R&D:HardwareConclusions

Conclusions

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Phase-I forward pixels

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Phase-I forward pixels

The upgrade is foressen to be installed at YETS2016

I Baseline: L = 2 · 1034 cm−2s−1 @ 25 ns → 50 PU withnegligible efficiency loss

I Tolerate: L = 2 · 1034 cm−2s−1 @ 50 ns → 100 PU withreduced performance

I Survive integrated luminosity of 500 fb−1

I Evolutionary upgradeI Robustify tracking: 4 instead of 3 hits; from 2 to 3 disks

(can compensate point losses in strips)6 / 40

Phase-I: Motivation

Requirements (TDR)I Running at 50 or more pile-up, same or better than current

detector in low pile-up (PU)I Maintain or improve the high efficiencies and low fake ratesI Maintain or improve the track impact resolutions and vertex

resolutions

I Maximize 4-pixel-hit coverage over an η range of ±2.5

I No increase of material in the tracking volume; Minimizedegradation due to radiation damage

I Reuse patch panel and off-detector cables and fibers

I Have one FPix module type, simplifying production andmaintenance

I Be compatible with the new smaller diameter beam pipe

I Switch to 2-phase CO2 cooling, target −25◦C

I Install during a slightly extended year-end technical stop

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Phase-I forward pixels

Plots show expected fluence in innermost disk:

Comparison based on x-rays.

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Phase-I forward pixels

Comparing old and new for efficiency:

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Phase-I forward pixels

Improvements in impact parameter resolution:

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Phase-I forward pixels

New design reduced mass

Biggest impact: optimized cabling, end-flange of barrel, cooling

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Phase-I forward pixels

B-tagging efficiency

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Phase-I forward pixels

One physics example: H → ZZ → 4`Analysis does:

1. trigger on di-lepton

2. kinematic reconstruction of 2 Zs from isolated di-leptons

3. reconstruct invariant mass of H

Plot on next slide shows a cut flow-chart to emphasize on cutsthat make the biggest improvement

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Phase-I forward pixels

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Phase-I forward pixels

Where are we?

I FPix passed CD reviews (critical decision), production canstart

I Final pre-production of modules end of February

I Module production seems to work

I Mechanics starts now as well

Want to emphasize on some module manufacturing issues

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Phase-I forward pixels

102Delivery of BBM

101Deliveryof HDI

103Glueing of

HDI to BBM

104Wirebonding

105Encapsulation

106Final inspectionand shipping

107Reworking

206Electrical

acceptancetest module

204Electrical

acceptancetest HDI

203IV test

202Visual

inspection201

Visualinspection

205Visual

inspection module

208Electrical

acceptancetest BBM

207Pull testing

of wirebonds

This is the workflow at UNL.The second production center,Purdue, differs slightly

We use a semi-automatedmanufacturing process using arobotic gantry, a Delvotecwirebonder and some testequipment

Bare modules (sensor + ROC)are made at a commercialvendor (RTI), as well as theHDI (Compunetics)

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Phase-I: Motivation

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Phase-I forward pixels

https://www.youtube.com/watch?v=ofdntTIwKY4

Beware: it is not an action movie. . .18 / 40

Phase-I forward pixels

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Phase-II forward pixels

I Phase-II is beyond about 2023

I 10× more instantaneous luminosity, even more PU

I Major challenge

I Simply said: what layer 1 of the barrel is in Phase-I wouldbecome the outer layers and new technology will be neededfor innermost layer(s)

I will focus on some very forward studies and will briefly come backto this at the end

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Very forward pixelsI VFPix effort studies optins in high pseudorapidity tracking

using optimised pixels (2.5 < |η| < 4.0)I Worked on three areas:

I Simulation: Explore physics potential and resolution impactby studying different strawmans and pixel cell geometries

I Sensor R&D: Explore potential of other pixel sizes thancurrently in use

I Hardware: Finish up the construction of a precision telescope(from a PIRE project)

I Will flash status on all three areas.I Baseline layout from TP:

z [mm]0 500 1000 1500 2000 2500

r [m

m]

0

200

400

600

800

1000

1200

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

1.8

2.0

2.2

2.5η

this proposal

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Very forward pixels

Latest proposal (strawman 5):

Observe: Extended inner layer, two types of modules. Has insertionalready in mind.

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Simulations

Results from TkLayout studies:

Strawman 0: TP; Strawman 5: Previous slide.Pixel size is 75 × 100µm2. Estimated resolutions were (assumingdigitized analog pulse-height and charge sharing based onmounting angle/B-field):

FPix/VFPix: 6.8 × 28µm2

BPix: 6.8 × 14.8µm2

Details: https://twiki.cern.ch/twiki/bin/view/CMS/VFPix

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Simulations

This already allows to justify the importance of a well-chosenenvelope.

I Conical geometry performs better than cylindrical

I Keep in mind: there is a strip tracker around this volume

I For a good pT measurement, three points need to bemeasured to good precision:

I Why do we need good pT ? Think of calorimetry and particleflow

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Simulations

Results from TkLayout studies:

Strawman 4, similar to 5Observe: To establish charge of a track, a good pT resolutionmatters, even one is tempted to optimize on z resolution

NB: pT resolution comes from lever arm and hit resolution, zresolution dominated by distance to first hit

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SimulationsHow to recover z resolution?

layer closer to BS

layer further away

Overlap helps. Some we get in the disks “for free”, somedownstream.

The resolution studies already have some assumptions on zresolution beyond just the local pixel resolution.

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SimulationsHot off the press: Resolution studies using PixelAV (courtesyMorris Swartz)

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Simulations

Next steps here:

I Use this information in TkLayout simulation

I Have to deal with clusters of size 30. . . – but we already havesome ideas how to handle this

I ROC: psi46 architecture can be translated into more advancedtechnologies. I.e. 110 nm offers reduction of pixel cell by factor5, good for pixels of size 60× 90µm2. Would allow forevolutionary design.

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Simulations

Results from Delphes using resolution data from TkLayout:

Details: See TWiki, table of presentations.

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Simulations

Results from Delphes using resolution data from TkLayout:

Details: See TWiki, table of presentations.

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Sensor R&D:

30

0 µ

m

50 µm

60

0 µ

m

25 µm

I All our pixel geometriesused same area

I Want to study resolutionusing some clever metallayer routing

I Made a sensor designgood for current Psi46pixel, available spring2015Disadvantage: increasedcapacitance, of course

I Will have 300 × 50µm2

and 600 × 25µm2

geometries

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Hardware

I We work on external triggering and soft TBM for the DTB

I Build a telescope based on PIRE project

I Uses thinned-down strip sensors with 25µm pitch

I APC128 chip with analog readout

I Telescope had some issues with signal quality. Improving thatto get decent S/N

I Should be ready in spring 2015

I Target resolution: ≈ 1µm

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Conclusions

I Established simulation chain

I Resolution studies show very nice results

I One physics case studies with clear benefit from VFPix

I More physics channels in the come

I Hardware studies will soon start as well

I Telescope should be available for beam tests

I Will keep you updated

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Conclusions

I Phase-I forward pixel ongoing and on track

I For Phase-II, I’ve shown some studies we did for very forwardtracking

I Efforts ongoing

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