ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 0 The Vertex Detector in the LDC Concept Sonja Hillert (Oxford) on behalf of the LCFI collaboration A Vertex Detector for the ILC Workshop at Ringberg Castle ~ 28 – 31 May 2006 Vertex detector requirements and differences in the 3 concepts Vertex charge reconstruction for performance evaluation Comparison of different detector designs Effects not yet included in simulation The LCFI Vertex Package – Plans and Status Summary

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 1 At the ILC, the most stringent requirements on the vertex detector are common to all the concepts. In part they are given by the machine: readout at least at effectively 50 s intervals excellent point resolution / small pixel size adequate radiation hardness Other requirements result from physics needs: hermeticity / good angular coverage (to cos = 0.96) proximity to the IP / small radius of innermost detector layer minimal material amount, as far as possible evenly distributed over layer low power consumption to permit gas cooling Requirements for the ILC vertex detector

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 2 Detector concepts differ in overall size and therefore in B-field and inner radius of the vertex detector. Other differences are not necessarily related to global detector design: SiD: short barrel and forward disks LDC: long barrel and tracking from additional silicon detectors in forward region Differences between vertex detectors of the 3 concepts 250 mm 15 mm 60 mm 100 mm LDC vertex detector SiD vertex detector design concept (Norman Graf)

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 3 Vertex charge reconstruction in the 40% of cases where b quark hadronises to charged B-hadron quark sign can be determined by vertex charge – good performance indicator for vertex detector probability of mis-reconstructing vertex charge is small for both charged and neutral cases neutral vertices require charge dipole procedure from SLD still to be developed for ILC need to find all stable tracks from B decay chain: define seed axis cut on L/D (normalised distance between IP and projection of track POCA onto seed axis) tracks that form vertices other than IP are assigned regardless of their L/D

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 4 Energy and polar angle dependence impurity is given by probability 0 of reconstructing neutral B hadron as charged degradation at large cos : multiple scattering of oblique tracks in detector material, loss of tracks at detector edge effects more strongly seen at lower jet energy (jet cone is broader and more low momentum tracks multiple scattering more severe) results obtained with SGV fast MC

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 5 Comparing detector with different inner layer radii 250 mm 15 mm 60 mm 100 mm 8 mm 25 mm e+e- BEAM importance of small beam pipe radius demonstrated by recent study of probability 0 for reconstructing neutral hadron as charged (Snowmass 2005) can be translated into luminosity factor: factor by which luminosity would have to be varied to reach same statistical significance as for standard detector (plot: processes requiring vtx chg for 2 jets)

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 6 Comparison with SiD & GLD vertex detectors: Results material at the end of SiD short barrel staves compromises performance at large cos GLD performance affected by larger beam pipe radius compared to LDC detector 50 (August 05)

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 7 Sensitivity to other parameters since vertex charge performance is sensitive to multiple scattering need to keep layer thickness small (target 0.1 % X 0 ) also strong dependence on momentum cut (track selection) – this depends critically on tracking performance: track finding capability background rates linking across subdetector boundaries should push all these parameters to their limits, as all these effects will eventually add up in the real detector

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 8 A future optimised full MC simulation and reconstruction will need to reliably model pair background cluster shapes (different for signal and pair background: also transverse component) time / position correlation (different for different sensor technologies) dependence on any non-uniformities in material distribution, effect of conical beam-pipe pattern recognition, leading to detailed understanding of tracking precision, track finding inefficiency, incorrect hit association, fake tracks non-Gaussian tails on track errors track linking between sub-detectors reconstruction of K s and ILC community will need to look at all these items in detail to arrive at reliable conclusions regarding detector performance. Effects not yet included T Woolliscroft (Liverpool U)

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 9 The LCFI Vertex Package The LCFI collaboration is working hard to provide a C++ based Vertex Package comprising the vertex finder ZVTOP, NN-based flavour tagging and vertex charge reconstruction. To make our code available to the community and to profit from future improvements of the ILC software frameworks, this package will be provided in the form of MARLIN processors with input / output in LCIO format. For part of the output, we have proposed the introduction of a new Vertex class into LCIO: currently under discussion in the LCIO developers group, for more information see the ILC forum at Performance will be checked using SGV. Parts for which FORTRAN code exists will be cross-checked against the FORTRAN version. Improvements of the code are guided by comparison to MC information. Coding / validation is making good progress – release envisaged this summer

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 10 interface SGV to internal format interface LCIO to internal format input to LCFI Vertex Package output of LCFI Vertex Package interface internal format to SGV interface internal format to LCIO ZVRESZVKIN ZVTOP: vertex information track attachment assuming c jet track attachment assuming b jet track attachment for flavour tag find vertex- dependent flavour tag inputs find vertex charge find vertex- independent flavour tag inputs neural net flavour tag

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 11 The ZVTOP vertex finder two branches: ZVRES and ZVKIN (also known as ghost track algorithm) The ZVRES algorithm: tracks approximated as Gaussian ´probability tubes´ from these, a ´vertex function´ is obtained: 3D-space searched for maxima in the vertex function that satisfy resolubility criterion; track can be contained in > 1 candidate vertex iterative cuts on 2 of vertex fit and maximisation of vertex function results in unambiguous assignment of tracks to vertices has been shown to work in various environments differing in energy range, detectors used and physics extracted very general algorithm that can cope with arbitrary multi-prong decay topologies D. Jackson, NIM A 388 (1997) 247

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 12 The ZVKIN (ghost track) algorithm more specialised algorithm to extend coverage to b-jets in which one or both secondary and tertiary vertex are 1-pronged and / or in which the B is very short-lived; algorithm relies on the fact that IP, B- and D-decay vertex lie on an approximately straight line due to the boost of the B hadron should improve flavour tagging capabilities ZVRES GHOST SLD VXD3 bb-MC

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 13 tanh (M Pt / 5 GeV) joint probability uds c b Flavour tag Vertex package will provide flavour tag procedure developed by R. Hawkings et al (LC-PHSM ) and recently used by K. Desch / Th. Kuhl as default NN-input variables used: if secondary vertex found: M Pt, momentum of secondary vertex, and its decay length and decay length significance if only primary vertex found: momentum and impact parameter significance in R- and z for the two most-significant tracks in the jet in both cases: joint probability in R- and z (estimator of probability for all tracks to originate from primary vertex) will be flexible enough to permit user further tuning of the input variables for the neural net, and of the NN-architecture (number and type of nodes) and training algorithm b c

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 14 Status of C++ ZVTOP development ZVRES branch: coding completed, validation ongoing left: comparison of decay length reconstructed by C++ to the FORTRAN value right: comparison of C++ reconstructed to true track origin (iso = isolated tracks from ZVTOP) Ben Jeffery (Oxford U) MC track origin 2 vertices3 vertices prisecisoprisecteriso Primary B decay D decay Mark Grimes (Bristol U) coding of ZVKIN branch ongoing, determination of ghost track direction complete

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 15 Towards completion of the Vertex Package b c c (b bkgr) c b Z peak E CM = 500 GeV test of full chain of C++ ZVTOP with FORTRAN flavour tag and vertex charge imminent pure FORTRAN results (from SGV) show below: C++ code for calculation of inputs for flavour tag being written Vertex charge reconstruction for c-jets under development

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 16 Summary and outlook Stringent requirements from the accelerator on the one hand and from ILC physics on the other hand make the design of an ILC vertex detector very demanding. Careful modelling of all relevant aspects is necessary to arrive at reliable conclusions regarding requirements and performance achieved. Relaxing design targets prematurely could result in performance being severely compromised – targets for inner layer radius, layer thickness and momentum cutoff should be maintained. Realistic assessment of vertex detector performance and comparison of designs will be helped by the LCFI vertex package, providing vertex finding, flavour tag and vertex charge reconstruction – due to be released this summer. Output of our code crucially relies on the quality of the input – precise reconstruction of low momentum tracks particularly challenging, likely to influence design of FTD system. ILC community still has a long way to go for many aspects of the reconstruction.

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 17 Additional Material

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 18 Position of vertices wrt detector layers: percentages CM energy (GeV) inside beam pipe99.99 % % % % between layer 1 & layer % 0.48 % 4.48 % % between layer 2 & layer % 0.67 % 5.78 % between layer 3 & layer % 2.49 % between layer 4 & layer % 1.11 % outside vertex detector % 1.19 % CM energy (GeV) inside beam pipe95.39 % % % % between layer 1 & layer % 1.37 % 7.82 % % between layer 2 & layer % 0.34 % 1.46 % 9.03 % between layer 3 & layer % 0.27 % 0.43 % 4.32 % between layer 4 & layer % 0.23 % 0.21 % 2.10 % outside vertex detector 3.00 % 3.82 % 4.18 % 6.08 % MC-level secondary vertex MC-level tertiary vertex

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 19 quark b hadron B - B 0 vtx charge X -- X - X 0 X - X 0 X + Interpretation b 0.4(1- pm ) pm 1-2 pm 0 b-bar B 0 -bar B + X - X 0 X + X 0 X + X ++ b-bar 0.4(1- pm ) b quark sign selection

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 20 Vertex charge reconstruction

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 21 Increasing beam pipe thickness for standard detector difference in layer thickness between standard detector and 4-layer detector only small effect main difference between the detectors due to difference in inner layer radius

ILC VTX workshop at Ringberg, 29 th May 2006Sonja Hillert (Oxford)p. 22 Suggestion for a new Vertex class in LCIO a new vertex class could look like this: +~Vertex() +getMomentum() : const float* +getMass() : float +getCharge() : float +getPosition() : const FloatVec& +getCovMatrix() : const FloatVec& +getChi2() : float +getProbability() : float +getDistanceToPreviousVertex() : float +getErrorDistanceToPreviousVertex() : float +getParameters() : const LCParameters& +getTracks() : const TrackVec& +addTrack() : void +getPreviousVertex() : Vertex&