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Physics with a Vertex Detector at

the Linear Collider

Overview

• VXD at SLD at the Z0

• Physics at Higher Energy

• VXD for the ILC

Dave JacksonOxford University/RAL

Osaka University

September 2004

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The SLC; the First Linear Collider

SLAC linear collider operated at c.o.m energy ~91 GeV on the Z0 resonance (like LEP I)

SLC was built in the 80’s within the existing SLAC linear accelerator

Operated 1989-98 - precision Z0 measurements - established LC concepts - e- beam polarization ~75%

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Physics at the Z0

Need to consider:

e-

e+

f

f

Z0 e-

e+ f

f

(e+e- → ff ) |MZ + M|2

Z0 → qq ~70%

Z0 → l+l- ~10%

Z0 → ~20%

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SLD LEP

1993-95 (VXD2)

150,000 1989-96 4,000,000

1996-98 (VXD3) 400,000 x4

550,000 16,000,000Need to benefit from SLC polarized e- beam and precise SLD Vertex Detector

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Z0 → bb event at SLD

Precise tracking allows reconstruction of

secondary vertices from B and D hadron

decays and tagging of b and c-quark flavoured jets

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MPT > 2 gives a very pure b-tag

MPT (GeV/c2)

MBMD

‘PT Corrected Vertex Mass’

Apply a kinematic correction to MVTX to

partially recover effect of missing neutral

particles:

PTmiss

B-tag purity vrs efficiency curve

by sliding MPT cut

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The left-right forward-backward asymmetry in b-tagged events

SLD

Vertex charge is used here to identify B+ or B- decays and hence the b or b-quark jet direction

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Quark and Lepton Asymmetries

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Above the Z0 resonance

Around √s ~ 91 GeV e+e- → /Z0 → qq or l+l-

Measure cross-sections and asymmetriesAbove √s ~ 161 GeV e+e- → /Z0 → W+W-

cross-sections, W mass and couplingsAbove √s ~ 182 GeV e+e- → /Z0 → Z0Z0

cross-sections and anomalous couplingsAbove √s ~ 200 GeV e+e- → /Z0 → Z0H0 ?

New physics, Higgs, SUSY, extra dimensions ?

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Production of Z0 pairs at LEPII

The OPAL event display shows two Z0

decays:

Z0 → +-

Z0 → qq

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LEP2 limit Mhiggs > 114.1 GeV.

LEP Higgs search – Maximum Likelihood for Higgs signal at mH = 115.6 GeV with overall significance (4 experiments) ~ 2

Direct search for Standard Model Higgs at LEP II

15e+e- c.o.m. energy

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International Linear Collider c.o.m energy 500 GeV – 1 TeV

SLC

e+

e-

~3

0 km ILC

The ITRP recommends that the linear collider be based on super-conducting rf technology (from Exec. Summary)

This recommendation is made with the understanding that we are recommending a technology, not a design. We expect the final design to be developed by a team drawn from the combined warm and cold linear collider communities, taking full advantage of the experience and expertise of both (from the Executive Summary).

We submitted the Executive Summary to ILCSC & ICFA at the Beijing Conference

http://www.interactions.org/pdf/ITRPexec.pdf

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Time scale

ILCSC (International Linear Collider Steering Committee):

2004 technology recommendation (confirmed by ITRP)

Establish Global Design Initiative / Effort (GDI/E)

2005 CDR for Collider (incl. first cost estimate)

2007 TDR for Collider (Technical Design Report)

2008 site selection

2009 construction could start (need approval of funding but not yet major spending !)

2015 LC and Detector ready for Physics

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Study the `Higgs boson’ (or its surrogate) and understand what it really is. The SM Higgs mechanism is unstable; find and explore the required new physics sector…

•Supersymmetry

•New gauge bosons

•Extra Dimensions

(Also a rich program of study of the top quark, QCD, precision EW measurements, etc.)

Detector to be designed for the Main ILC physics themes:

In general ILC and LHC both needed to

explore new high energy phenomena (compare history of

proton/e+e- colliders)

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Need to determine experimentally that Higgs couplings to fermions are indeed proportional to mass. SM couplings differ from Susy couplings.

Higgs fermion couplings

With vertex reconstruction can distinguish b, c, light quark jets: and measure BRs into various particles.

BR

MH

Higgs self couplings

Measures Higgs potential shape independent of Higgs mass measurement. Determination of and MH gives new constraint on SM.

Study ZHH production and decay to 6 jets (4 b’s). Cross section is small; premium on very good jet energy resolution and b-jet tagging.

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→ t t √ √

→ W W √

→ Z h √ √

→ Zhh √

SUSY CP √ √

AFB(Z/) √ √

h bb, h cc

Linear Collider Physics examples

Tags needed

b-jets c-jets Vertex Detector design

determines b/c-jet tagging and physics performance

Physics environment more varied than SLD/LEP

for Physics Studies: Physics generator + Detector simulation + Reconstruction code

Physics Process

e+e-

(Standard Model, Higgs, SUSY, Other BSM)

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To reconstruct secondary vertices for excellent b and c-jet flavour tagging

5 layers of CCDs at radii 15, 26, 37, 48 and 60 mm; 120 CCDs, ~8x108 pixels in total

Thin detector, target thickness < 0.1% X0 / layer; Close to the interaction point

Collaboration of five UK institutes (Bristol U, Lancaster U, Liverpool U, Oxford U and RAL) studying Vertex Detector Design for the ILC

Linear Collider Flavour Identification (LCFI)

Three research areas:

Electronics

Thin Ladders

Physics Studies

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Column parallel CCD and readout chip

“Classic CCD”Readout time

NM/Fout

N

M

N

Column Parallel CCD

Readout time = N/Fout

Clocking rate required for ILC stimulated concept of ‘column parallel’ operation

Main LCFI R&D: development of sensors and their dedicated readout chip (CPR)

first CCD (CPC1) received April 2003, CPR1 in June 2003: excellent standalone performance of both devices

first assembly of CPC1-CPR1 (start January 2004) using wire bonds: proof of principle of reading CPC with CPR

detailed tests of first bump-bonded assembly (ongoing since May 2004)

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Bump-bonded CPC1-CPR1 assembly

Bump bonding performed by VTT (Finland)

Connecting to CCD channels effective pitch of 20m possible by staggering of solder bumps

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ISIS-based detectorSignals of 1000 e- to be amplified & read; so far envisaged 20 readouts / bunch train

SLC experience: may be impossible due to beam–related RF pickup started to investigate alternative architecture: variant of Image Sensor with In-situ Storage (ISIS)

in each pixel: linear CCD with 20 elements, each storing charge collected during 1 time slice, shifted on at 50 μs intervals

during 200 ms between bunch trains: transfer of stored signals to local charge sensing circuits in pixel, column-parallel readout at moderate rate, e.g. 1MHz

Future plansDesign of next generation of CCD and CPR near conclusion

CPC2 to comprise following features:

3 different sizes, including ‘full length’ devices to be tested at frequencies of few MHz

ISIS test structure for proof of principle: 16x16 cells on an x-y-pitch of 160 m x 40 m

CPR2 characteristics to include:

on-chip cluster finding, allowing sparsified readout

Future evaluation will show, which of our two baseline detector designs – CPCCDs or ISIS – will be better matched to the requirements.

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3 2

44

/sinp

Thin-ladder development

Track resolution σ in rz and rφ for 5 layers of 0.064% X0 each

All B decay tracks required to get best b/c separation and correct B or D hadron charge (needed to measure asymmetries and useful in reducing Mbb jet-jet combinatorial background)

How can ladders be made as thin and mechanically stable as possible?

7μm

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Thin detectorsStandard CCD20 μm sensitive region300 μm Si substrate (support)

Stabilise with tension

20 μm sensitive region40 μm Si substrate

Potentially most thin option, but…

FEA (Finite Element Analysis)–,maximum deflection ~1mmtransverse bowing effects

28 Ripple size: about 160 microns

Consider tensioned Be substrate

CCD brought down

Assembly after shim removal and curing

Beryllium substrate (250 μm)

Beryllium substrate with adhesive pads

Thinned CCD ( 20 μm)

Adhesive

Shims

1 mm

0.2mm

CCD brought down

Assembly after shim removal and curing

Beryllium substrate (250 μm)

Beryllium substrate with adhesive pads

Thinned CCD ( 20 μm)

Adhesive

Shims

1 mm

0.2mm

Layer thickness 0.09% X0

Silicone adhesive: (e.g. NuSil), excellent low temperature properties

Beryllium thermal contraction greater than for silicon

Finite Element Analysis:

60 μm Si: distortion only few μm

20 μm Si: distortion significant

At -60oC

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What about real silicon ?

XY stage for 2-dimensional laser profiling assembled

Resolution 1 μm

Models made from steel + unprocessed Si have been studied

CMM metrology system surveying a test ladder at RAL

30 μm silicon after cool down to -100C

To remove distortion of CCD considering use of substrate with better thermal matching to silicon such as carbon fibre material

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Could also replace beryllium by some foam material – whatever gives best stiffness for least radiation length, regardless of thermal expansion properties

A New Idea – Micromechanical Structures

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Aim at providing a guideline for vertex detector design, e.g. :

How close to the interaction point does the inner layer need to be ?

What layer thickness should be aimed at ? (multiple scattering)

How many layers are needed ?

Physics Studies

Performed in the context of R&D work of the LCFI collaboration

To answer these questions study for example:

• impact parameter resolution

• heavy flavour jet tagging and vertex charge reconstruction

• specific physics channels expected to be sensitive

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Impact Parameter Resolution

SGV (Simulation a Grande Vitesse)

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PTmiss

Vertex reconstructed with SLD algorithm

The ‘PT Corrected Vertex Mass’ MPT is the main parameter for jet flavour tagging

Apply a kinematic correction to MVTX to

partially recover effect of missing neutral particles:

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Vertex Charge Reconstructioncomparison of reconstructed Qsum distributions for the different generator level charges

SGV ILC study

SLD 1997-98B-

B0

B+

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Charge Purity vrs b-tag Efficiency

For three detector configurations:

standard detector: 5 layers, layer thickness 0.064 % X0, point resolution 3.5 μm

degraded detector: 4 layers, beam pipe radius 25 mm, factor 2 worse point resolution

improved detector: 5 layers, factor 4 less material, factor 2 better point resolution

at b = 70% (MPt > 2.0 GeV):

b = 6%, (b) = 2%

Result underlines preference for a small beam pipe radius

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Java Analysis Studio (JAS3)

    

Java version of ZVTOP (by Wolfgang Walkowiak)

MPT and other Vertex properties provide usual flavour tagging variables

Can non-vertex information (eg calorimeter) aid the performance ?

Consider highest energy π0 in jet, using MC truth

Combine vertex plus neutral inputs with a Neural Network (cjnn by Saurav Pathak)

MP b-jets

MP c-jets

GeV/c2

T

T

Z0 → bb and cc events, with SiD detector simulation

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π0 from B

π0 from IP

Mo

men

tum

Pa

ralle

l to

Ve

rte

x A

xis

/ G

eV

Momentum Transverse to Vertex Axis / GeV

Kinematic Properties of the highest energy π0 in 45 GeV Jets

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Preliminary Neural Network Study

2 InputsMPT (Vertex)

Momentum (Vertex)

MPT (Vertex + π0)

Energy of π0

4 Inputs

Effect of adding highest energy π0 information:

Small increase in b-tag efficiency (~1%)

Reduce b-jet background to c-tag by a relative 10–25%

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b-tag efficiency in multijet event environment: dependence on angle between jets studiedtag dependence on jet energy is found to be more significant

e+e Zh

e+e Zhh

Physics Studies with JAS3b

-tag

effi

cien

cy

jet-jet angle

jet momentum

Zhh events

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SummaryPrecise Vertex Detector was crucial for much of the physics at SLD (and LEP) Heavy flavour jet tagging will be crucial for analysis of new physics at the ILCLCFI is studying design of the vertex detector including: CCD sensors and readout Thin ladder R&D Physics Studies to optimise geometryAll part of the Global ILC Collaboration