1. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 0 Linear Collider Flavour Identification (LCFI) - Part 1 - S. Hillert (Oxford) on behalf of the LCFI collaboration Bristol U, Lancaster U, Liverpool U, Oxford U, RAL PPRP open session, London, 8 th September 2004  Overview  Physics Studies  Thin Ladder R & D

2. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 1 Introduction  There is consensus in the High Energy Physics community that a TeV scale e + e - linear collider (LC) has the first priority for the next major particle accelerator, to operate with significant overlap with the LHC: “Reviews … point … to the conclusion that there is fundamentally new physics in the energy range just beyond the reach of existing colliders.” (ICFA statement ’99) “The LC will extend the discoveries [to be made at the LHC] and provide a wealth of measurements that are essential for giving a deeper understanding of their meaning” (LC consensus document, 2004)  With the decision on the accelerator technology announced on 20 August, world wide R&D effort will increase in speed and international collaboration will intensify to reach a final design of the accelerator and the detectors.  “This is an extremely significant milestone. … The UK should take a leading role in this one-off, global machine” (Ian Halliday)

3. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 2 The detector at the ILC  Compared to physics at the LHC, events at the ILC will be much cleaner; much lower rates and background, known initial state;  Combining information from different subdetectors, we attempt to fully understand the basic physics process on an event by event basis.  Requirements: continual, triggerless readout hermeticity highly granular tracking and calorimetry, both inside a coil providing a high B-field to resolve jets in multijet topologies vertex resolution for flavour identification

4. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 3 Application of a particle flow algorithm permits resolution of events into the jets corresponding to the underlying quarks. Use of the vertex detector permits us to distinguish the jets generated by heavy quarks. An example: e + e -  t t a typical e + e -  t t event: b e+e+ e-e- t t W W+W+ b e.g. c q’ s q q e.g. s c

5. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 4 Vertex detector contribution to event reconstruction The most interesting new processes (Higgs, SUSY, …) will be rich in heavy quarks.  Vertex topology and effective mass of decay products allows us to distinguish between b and c jets.  Vertex charge allows us to distinguish between quark and anti-quark: b and b or c and c.

6. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 5 The LCFI R&D program  The linear collider flavour identification (LCFI) collaboration formed in 1998.  Since then we have carried out an extremely successful R&D program, aimed at finding viable solutions for building a vertex detector whatever the machine choice would turn out to be.  The prototypes of sensors and readout chips developed by the end of the current funding period would already have covered the major design specifications required by the warm technology.  For the cold option, now chosen, we have developed two baseline designs, one of which only emerged end of last year (cf. talk by Konstantin Stefanov).  The evaluation of which of these will be better matched to the requirements will need further intensive R&D in close collaboration with international partners in academic institutes and industry.  The LCFI program covers three closely connected areas of R&D: physics studies, thin ladder R&D and detector development. The remainder of the presentation will summarise our progress and future plans in each of these fields.

7. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 6 LCFI Physics studies  base, from which R&D goals are defined: How far do detector parameters like pixel size, ladder thickness, beam pipe radius, readout time etc. need to be pushed for the measurements planned at the LC? What performance do the parameters which are technically achievable yield?  SLD experience: vertex detector is a powerful tool, crucial for LC physics goals; besides b tagging it will allow high purity charm tagging (cf e.g. ICHEP’04 contribution 12- 0438)  provides a handle to unique physics in the TeV regime, complementary to LHC, e.g. precision measurement of branching ratios in Higgs decays via vertex charge reconstruction: distinguishing between b and b, c and c  suppression of combinatorial background in multi-jet events  asymmetries: parity of Higgs boson; CP asymmetries in SUSY processes Bristol U Lancaster U Oxford U RAL

8. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 7 Detector dependence of vertex charge reconstruction “standard detector” characterised by :  good angular coverage (cos  = 0.96)  proximity to IP, large lever arm: 5 layers, radii from 15 mm to 60 mm  minimal layer thickness ( 0.064 % X 0 ) to minimise multiple scattering  excellent point resolution (3.5  m) standard detector is compared to  degraded detector: beam pipe radius 25 mm, 4 layers only; factor 2 worse point resolution  improved detector: factor 4 less material, factor 2 better point resolution Vertex charge reconstruction studied in at, select two-jet events

9. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 8 Definition of vertex charge and of Pt-corrected mass  need to find all stable B decay chain tracks – procedure:  run vertex finder ZVTOP: the vertex furthest away from the IP (‘seed’) allows to define a vertex axis  reduce number of degrees of freedom  cut on L/D, optimised for each detector configuration, used to assign tracks to the B decay chain  by summing over these tracks obtain Q sum (charge), P T vtx (transverse momentum), M vtx (mass)  vertex charge  Pt-corrected mass used as b-tag parameter

10. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 9 Vertex charge: results conclusions:  purity flat out to efficiency of ~ 70% for standard detector  significant detector dependence: at  b = 70% (M Pt > 2.0 GeV):  b = 6%,  (b) = 2%  result underlines the need for a small beam pipe radius, previously indicated by impact parameter resolution (  LCWS ’04 result)  presented at Durham International LC Workshop 1- 4 September

11. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 10 Further improvement of tools  objected oriented frameworks, notably JAS3, will replace BRAHMS in the medium term, but have not yet reached the maturity required to work on the questions that need to be answered now  in the meantime, use fast MC program SGV (Simulation a Grande Vitesse): well-tested, flexible code includes ZVTOP package  complete, flexible neural network package has recently been developed at Bristol: improve on vertex charge result (e.g. by using a reconstruction similar to an optimised procedure developed for SLD) extend studies to different energies and to flavour tagging; results from this new tool expected soon

12. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 11 Physics studies: future plans  The physics studies are currently gaining momentum.  They are essential for the decisive phase of our R&D program which we entered with the decision on the accelerator technology: Emphasis will shift from an idealised optimisation of the vertex detector alone to the evaluation of tradeoffs between parameters of different subdetectors as well as the accelerator. Different aspects of the global physics needs, such as hermeticity of the forward calorimetry and degraded jet-energy resolution due to  conversions in vertexing and tracking detectors, will require compromises, for which input from a vertexing point of view will be needed.  When joining one of the LC protocollaborations, LCFI is well suited to contribute not only the vertex-detector system, but also the expertise needed to extract from its data the physics, for which that detector is crucial.

13. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 12 Thin ladder development  concentric barrels of the vertex detector consist of ladders comprising 1-2 CCDs substrate for mechanical support readout chips to process and sparsify the data  ladders attached to Be support shell  requirements: little material ( ~ 0.1 % X 0 ), positional stability  initial idea: unsupported silicon under tension; tests on thinned processed silicon showed bowing across the width of the ladder  not considered any longer Bristol U Oxford U RAL e2V

14. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 13 Semi-supported silicon: introduction  silicon, attached by adhesive pads to thin substrate, e.g. Beryllium, stabilised by tension  difference in expansion coefficient between silicon and substrate can have serious consequences  studied both by FEA and by measurements on physical models  LCFI developed purpose-built laser ranging device (left), allowing rapid ladder scans at micron precision; setup enclosed in cryostat

15. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 14 Semi-supported silicon: results  example: 30  m Si, 250  m Beryllium, 200  m thick glue pillars (silicone elastomer): good qualitative agreement between measurement (left) and FEA simulation (right)  below silicon thickness of ~ 50  m, compressive load from Be substrate causes strong buckling  interest in other substrate materials: carbon fibre composites, ceramics, foams

16. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 15  The thin ladder development is an inexpensive, but complex field of R&D.  The effects of internal stresses in processed silicon require further investigation: Studies of a silicon-sellotape assembly modelling these effects are underway. Samples of large area thin CCDs supplied by e2V, will allow further measurements.  Linked to studies of these effects are open questions regarding attachment to substrate. By the time the detector is going to be built, it may be possible to replace the pads of adhesive by advanced microstructures, which keep the silicon under tension:  In the longer term, studies will expand from the central part of ladders to the ladder ends. This topic will be closely connected to the development of drive electronics to fit on the ladder end, linked by requirements on the material budget and on cooling. Thin ladders: future plans

17. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 16 study based on single pions, generated using SGV Impact parameter resolution impact parameter in R  at track perigee  increasing material budget has moderate effect, but  performance strongly suffers when beam-pipe radius is increased detector geometries: standard detector: 5 layers (each 0.064 % X 0 ) at radii 15 mm to 60 mm double layer thickness beam-pipe with Ti-liner (0.07 % X 0 ) 4 layers at radii 25 mm to 60 mm Additional Material ~ Additional Material ~ Additional Material

18. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 17 Definition of L/D  seed vertex (ZVTOP vertex candidate furthest from IP) used to define the vertex axis  consider all tracks initially passed to ZVTOP and assign those to B decay chain, which at point of closest approach to the vertex axis have T < 1 mm: cleaning cut, only small effect (L/D)min < L/D < 2.5: main cut, optimised for each detector configuration independently Additional Material ~ Additional Material ~ Additional Material

19. Sonja Hillert, University of Oxford PPRP open session: LCFI, London, 8 th September 2004 p. 18 Improvement since LCWS – 1 MC: B _ + MC: neutral B hadrons comparison of reconstructed Qsum distributions for the different generator level charges LCWS new Additional Material ~ Additional Material ~ Additional Material