1 Physics with a Vertex Detector at the Linear Collider Overview VXD at SLD at the Z 0 Physics at Higher Energy VXD for the ILC Dave Jackson Oxford University/RAL Osaka University September 2004

2 The SLC; the First Linear Collider SLAC linear collider operated at c.o.m energy ~91 GeV on the Z 0 resonance (like LEP I) SLC was built in the 80’s within the existing SLAC linear accelerator Operated precision Z 0 measurements - established LC concepts - e- beam polarization ~75%

3 Physics at the Z 0 Need to consider: e- e+ f f Z0Z0 e- e+f f   (e+e- → ff )  |M Z + M  | 2  Z 0 → qq ~70% Z 0 → l+l- ~10% Z 0 → ~20%

4 SLDLEP (VXD2) 150, ,000, (VXD3) 400,000x4 550,00016,000,000 Need to benefit from SLC polarized e- beam and precise SLD Vertex Detector

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6 Z 0 → 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

7 M P T > 2 gives a very pure b-tag M P T (GeV/c 2 ) MBMB MDMD ‘P T Corrected Vertex Mass’ Apply a kinematic correction to M VTX to partially recover effect of missing neutral particles: P T miss B-tag purity vrs efficiency curve by sliding M P T cut

8 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

9 Quark and Lepton Asymmetries

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12 Above the Z 0 resonance Around √s ~ 91 GeV e+e- →  / Z 0 → qq or l+l- Measure cross-sections and asymmetries Above √s ~ 161 GeV e+e- →  / Z 0 → W+W- cross-sections, W mass and couplings Above √s ~ 182 GeV e+e- →  / Z 0 → Z 0 Z 0 cross-sections and anomalous couplings Above √s ~ 200 GeV e+e- →  / Z 0 → Z 0 H 0 ? New physics, Higgs, SUSY, extra dimensions ?

13 Production of Z 0 pairs at LEPII The OPAL event display shows two Z 0 decays: Z 0 →  +  - Z 0 → qq

14 LEP2 limit M higgs > GeV. LEP Higgs search – Maximum Likelihood for Higgs signal at m H = GeV with overall significance (4 experiments) ~ 2  Direct search for Standard Model Higgs at LEP II

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

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17 International Linear Collider c.o.m energy 500 GeV – 1 TeV SLC e+e+ e-e- ~30 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

18 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

19 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)

20 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 MHMH Higgs self couplings Measures Higgs potential shape independent of Higgs mass measurement. Determination of  and M H 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.

21 → t t √ √ → W W √ → Z h √ √ → Zhh √ SUSY CP √ √ A FB (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)

22 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, ~8x10 8 pixels in total Thin detector, target thickness < 0.1% X 0 / 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

23 Column parallel CCD and readout chip “Classic CCD” Readout time  N  M/F out N M N Column Parallel CCD Readout time = N/F out 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)

24 Bump-bonded CPC1-CPR1 assembly Bump bonding performed by VTT (Finland) Connecting to CCD channels effective pitch of 20  m possible by staggering of solder bumps

25 ISIS-based detector Signals 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 plans Design 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.

26 Thin-ladder development Track resolution σ in rz and rφ for 5 layers of 0.064% X 0 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 M bb jet-jet combinatorial background) How can ladders be made as thin and mechanically stable as possible? 7 μm μm

27 Thin detectors Standard CCD 20 μm sensitive region 300 μm Si substrate (support) Stabilise with tension 20 μm sensitive region 40 μm Si substrate Potentially most thin option, but… FEA (Finite Element Analysis)–, maximum deflection ~1mm transverse bowing effects

28 Ripple size: about 160 microns Consider tensioned Be substrate Layer thickness  0.09% X 0 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 -60 o C

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

30 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

31 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

32 Impact Parameter Resolution SGV (Simulation a Grande Vitesse)

33 P T miss Vertex reconstructed with SLD algorithm The ‘P T Corrected Vertex Mass’ M P T is the main parameter for jet flavour tagging Apply a kinematic correction to M VTX to partially recover effect of missing neutral particles:

34 Vertex Charge Reconstruction comparison of reconstructed Qsum distributions for the different generator level charges SGV ILC study SLD B-B- B0B0 B+B+

35 Charge Purity vrs b-tag Efficiency For three detector configurations: standard detector: 5 layers, layer thickness % X 0, 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% (M Pt > 2.0 GeV):  b = 6%,  (b) = 2% Result underlines preference for a small beam pipe radius

36 Java Analysis Studio (JAS3) Java version of ZVTOP (by Wolfgang Walkowiak) M P T and other Vertex properties provide usual flavour tagging variables Can non-vertex information (eg calorimeter) aid the performance ? Consider highest energy π 0 in jet, using MC truth Combine vertex plus neutral inputs with a Neural Network (cjnn by Saurav Pathak) M P b-jets M P c-jets GeV/c 2 T T Z 0 → bb and cc events, with SiD detector simulation

37 π 0 from B π 0 from IP Momentum Parallel to Vertex Axis / GeV Momentum Transverse to Vertex Axis / GeV Kinematic Properties of the highest energy π 0 in 45 GeV Jets

38 Preliminary Neural Network Study 2 Inputs M PT (Vertex) Momentum (Vertex) M PT (Vertex + π 0 ) Energy of π 0 4 Inputs Effect of adding highest energy π 0 information: Small increase in b-tag efficiency (~1%) Reduce b-jet background to c-tag by a relative 10–25%

39 b-tag efficiency in multijet event environment: dependence on angle between jets studied tag dependence on jet energy is found to be more significant e + e Zh e + e Zhh Physics Studies with JAS3 b-tag efficiency jet-jet angle jet momentum Zhh events

40 Summary Precise 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 ILC LCFI is studying design of the vertex detector including: CCD sensors and readout Thin ladder R&D Physics Studies to optimise geometry All part of the Global ILC Collaboration