Linear Collider Vertex Detector R&D

1

Natalie RoeUCSC Linear Collider WorkshopJune 27-29, 2002

Linear Collider Vertex Detector R&D

2 N. Roe LBNL LC Workshop 6/28/02

R&D: General Goals & Strategy

R&D should be undertaken to mitigate risk and ensure a project will succeed Technical risk for new, unproven techniques or

significant extensions of existing methods Schedule risk for long-lead development or

procurementsR&D strategy: identify areas of technical or

schedule risk with biggest physics impact Focus on most critical areas needing early R&D

investment to ensure the project’s success and to maximize the physics reach


What type of R&D is required for LC Detectors?

Hard to argue schedule risk at this stage… There is time for new technical developments with

significant physics impactFirst step is to write down machine constraints

and physics-driven requirements Next, devise a focused R&D plan to address the

technical issues associated with the requirements that: • a) have biggest physics impact, and• b) are most challenging


Requirements for an LC Vertex Detector

Accelerator-related requirements, such asBeam-pipe radius, thickness, machine stayclearRadiation levels & background ratesEvent rate and time structure of collisionsetc.

Physics requirements, eg vertex flavor tagging, driven by:Impact parameter resolutionTwo-track/two-hit separationEfficiency, fake track rateSolid angle coverageetc.


Quantifying Requirements: Accelerator constraints

Machine design is not yet finalized Detailed design studies exist for several machines -

consider worst case parameters

Experience suggests conservative assumptions eg, radiation levels generally get worse with more realistic machine studies, bkgds go up etc.

Critical design areas may require iteration with accelerator experts, additional efforts on machine simulations


Quantifying Requirements: Accelerator constraints I

Beam pipe radius: determined by beamstrahlung and synchrotron radiation backgrounds. Present thinking: NLC: r = 1 cm for z = ± 2.5 cm, then increases to 2.2 cm Tesla: r = 1.4 cm

Radiation & background rates: Tesla:

beam-beam e+e- pairs produce 0.03 hits/mm2/BX, resulting in ~20kRad/yr ionizing radiation for B= 4T and r = 1.5 cm

Neutron fluence ~ 109 1 MeV neutrons/cm2/yr NLC:

beam-beam e+e- pairs produce 3 hits/mm2/train =0.015 hits/mm/BX at B=3T and r = 1.2 cm

Neutron fluence estimates vary from 107 to 1011 n/cm2/year Maruyama - 2.3 x 109 n/cm2/year

What about beam gas backgrounds?


NLC Bkgds

B=6T, no crossing angleB= ?See talk this morning by Maruyama


Quantifying Requirements: Accelerator constraints II

Time Structure & Event Rates

Layer 1 hit occupancies (bkgd dominated): At NLC 190 x 0.015 hits/mm2/BX = 2.85 hits/mm2/train = 1 x 10-3

occupancy for 20x20um pixels => read out between bunch trains At Tesla 2820 x 0.030 hits/mm2/BX = 84.5 hits/mm2/train = 3.4 % occ

for 20x20 um pixel => readout during train

A

B

C

Tesla500 Tesla800 NLCA 200 ms 250 ms 8.3msB 337 ns 176ns 1.4 nsC 950 us 860us 266 nsC/B 2820 4886 190C/BA 14kHz 19.5kHz 23kHzL(1034) 3.4 5.8 2.0


Reality Check: NLC vs Tesla background rates

Tesla = 0.03 hits/mm2/BX at 4T, r=1.5 mm NLC = 0.015 hits/mm2/BX at 3T, r=1.2 mm Why are NLC bkgds lower with smaller B field and radius? Bkgds/BX should be proportional to lumi/BX

Tesla: 3.4x1034 / 14kHz NLC: 2x1034 / 23kHz Factor of 3 lower lumi/BX at NLC => compensated for by

lower B and r More detailed comparisons needed, eg compare rates at same

B field and radius. Understand beamgas and synchrotron backgrounds and

compare


Quantifying Requirements: Accelerator constraints III

Beam pipe thickness (scale: 100 um of Si ~ 0.1%X0): Tesla studies assume a beampipe of ~ 0.25 mm Be = 0.07%X0

Matches first detector layer thickness of 0.06% X0

NLC studies: assumptions ranging from 0.160 - 0.180 mm Be (?) NLC beampipe has stepped radius from 1.2 -> 2.4 cm to avoid

backgrounds - does this create problems with showering?

Multiple scattering in beampipe sets scale for thickness of first detector layer and for point resolution at low p

Radius and thickness of beampipe are critical inputs for vertex detector; think of beampipe as part of detector


Physics Requirements I

Flowdown of requirements:1) Science requirement: Precision on particular physics

quantities, eg error on Br(H-> cc)2) Performance requirement: high-level event parameter, eg

specified flavor tag purity at a given efficiency3) Detector requirement, eg impact parameter resolution or

tracking efficiency vs fake rate for a given detector subsystem

y A number of LC vertex detector studies have already been performed at all 3 levels.

y


Selected Previous Vertex Performance Studies

Sinev: http://blueox.uoregon.edu/~jimbrau/talks/IEEE-99/ieee99.pdf

Abe(ghost tracks): http://www.slac.stanford.edu/~toshi/LCDstudy/toshi_ghost.pdf

Schumm (vertex parameters): http://scipp.ucsc.edu/~schumm/talks/fnal2000/fnal2000_ag.ps

Oregon vertex detector parameters study: http://blueox.uoregon.edu/~jimbrau/LC/vxd-studies.PDF

Chou (H->cc): http://www-sldnt.slac.stanford.edu/nld/meetings/ChicagoJan2002/BRHccJan8.pdf

Potter et al (Higgs branching ratios ): http://www.slac.stanford.edu/econf/C010630/forweb/P118_potter.pdf

Iwasaki - top: http://www.slac.stanford.edu/~masako/LC_study/Chicago2002/Top.pdf

Walkowiak:http://www.slac.stanford.edu/~walkowia/lcd/talks/ chicago2002/lcChicago010802-1.pdf

LCFI studies : ( http://hep.ph.liv.ac.uk/~green/lcfi/home.html )


Physics Requirements II Impact parameter resolution:

Simplified formula for i.p. resolution in 2 layer device with measurements at r1,r2 and errors :

Dominated by resolution of first hit Multiple scattering dominates for low momenta; material in beampipe and first

detector layer must be minimized, along with radius of 1st hit Intrinsic point resolution dominates at high momenta - includes misalignment

effects

€

σ =r2 ⋅σ1

r2 −r1

⎛

⎝ ⎜ ⎞

⎠ ⎟ ⊕

r1⋅σ2

r2 −r1

⎛

⎝ ⎜ ⎞

⎠ ⎟

σ1,2 =σms⊕σ pt; σms=0.014⋅ r X0

sin3/2θ ⋅βcp


Impact Parameter Resolution Studies - Schumm

dR

(cm

)

M.S. dominated

Pt resolution dominated

10 um

2-3 um


Impact parameter study

resolution ladder thickness beampipe radius outer radius

http://scipp.ucsc.edu/~schumm/talks/fnal2000/fnal2000_ag.ps

B. Schumm

“Standard L2” = 1.2 cm beampipe, 160 um Be, 5 um resolution


How does i.p. resolution affect flavor tagging?

Compare i.p. resolution to typical impact parameters at LC For B decay products, i.p. ~ 300 um>>10 um

B-tagging should not depend strongly on pt resolution, beampipe radius or thickness

For charm decay products, i.p. ~ 80-100 umMight see mild dependence To correctly assign tracks to both b and c vertices to

determine charge or mass will be more challenging Needs a level 2/level 3 study


Study of Charm Tagging

Mild detector dependence: 15% change going from 10 um, 1.0%X0 to 1 um, 0.03%X0 detector

Beampipe radius = 1 cm What was the beampipe thickness? What bkgd levels?

A. Chou


MH = 140 GeV/c2 , s = 500 GeV, L = 500 fb-1

RINNER(cm) 1.2 2.4 1.2 2.4 1.2

hit res (m) 5.0 5.0 3.0 3.0 4.0

H bb 3.8% 3.8% 3.8% 3,8% 3.8%

H 10% 10% 10% 10% 10%

H cc 46% 47% 42% 46% 42%

H gg 23% 22% 22% 22% 22%

H WW* 3.5% 3.5% 3.5% 3.5% 3.5%

Error on Higgs BRs - Oregon Study

Error on Higgs branching ratios is essentially independent of radius and resolution, with mild dependence for H-> cc

http://blueox.uoregon.edu/~jimbrau/LC/vxd-studies.PDF

Potter, Brau, Iwasaki


Vertex R&D - paper studies & simulations

Write down assumptions for NLC/Tesla/JLC beampipe, backgrounds, radiation levels; compare/rationalize different results, get improved estimates if possible (=>run accelerator simulations)

Consider dependence of i.p. resolution on beampipe thickness as well as detector thickness; engineering study of beampipe construction?

Consider effects of material at large radius as well (cryostat can decouple vertex from outer tracking, reduce effective lever arm for tracking)

Consider design where L1 is special: thinner, faster readout, better resolution. (may want L2 also for backup)

Document a set of science-driven requirements (goals) for vertex detector performance, with a clear link from specific measurements to the required performance parameters.


R&D: Hands-on studies

Leading candidates: CCDs, hybrid pixels, active pixels … + time to develop new ideas!

General areas for R&D Radiation hardness Readout speed, especially in Tesla context Minimizing material thickness including mechanical

structures and beampipe


Summary

There are interesting vertex detector issues to address both in simulation and in hands-on R&D

To coordinate US efforts, please provide a brief description, list of participants and proposed budget

Should aim to cooperate on global level with international partners

Documents

Linear Collider Vertex Detector R&D