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Higgs Physics at the Large Hadron Collider

Higgs Physics at the Large Hadron Collider. Markus Schumacher, Bonn University. WE Heraeus Seminar, „New Event Generators“, Dresden, January 2006. Outline. the SM Higgs Mechanism and Status of Search SM Higgs Phenomenology and Environment at LHC Discovery Potential for SM Higgs Boson

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Higgs Physics at the Large Hadron Collider

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  1. Higgs Physics at theLarge Hadron Collider Markus Schumacher, Bonn University WE Heraeus Seminar, „New Event Generators“, Dresden, January 2006

  2. Outline • the SM Higgs Mechanism and Status of Search • SM Higgs Phenomenology and Environment at LHC • Discovery Potential for SM Higgs Boson • Investigation of the Higgs Boson Profile • Phenomenology of SUSY Higgs bosons • Discovery Potential for MSSM Higgs bosons • Discriminating the SM from Extended Higgs Sectors • Conclusion and Outlook Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  3. The Higgs Mechanism in the Nut Shell The problem: • consistent description of nature seems to be based on gauge symmetry • SU(2)LxU(1) gauge symmetry  no masses for W and Z and fermions • „ad hoc“ mass terms spoil • renormalisibility  no precise calculation of observables • high energy behaviour  e.g. WLWL scattering violate unitarity (probability interpretation) at ECM ~ 1.2 TeV massive gauge bosons: 2 transverse + 1 longitudinal d.o.f. massless gauge bosons: only 2 transverse d.o.f. Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  4. The Higgs Mechanism in the Nut Shell Scalar boson restores unitarity if gHWW ~ MW s  const=f(MH) The „standard“ solution: • new doublet of complex scalar fields (4 d.o.f.) • with appropiately choosen potential V • vacuum spontaneously breaks gauge symmetry • one new particle: the Higgs boson H F =v+H (+ 3 d.o.f. for longitudinal components of W and Z) Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  5. Mass generation and Higgs couplings: F = v+H x • Interaction of particles withv=247 GeV v =247 GeV gf effective mass = friction of particles with omnipresent „Äther“ fermion x x 2 mf ~ gfv Yukawa coupling MV ~ gvgauge coupling g gauge W/Z boson • Interaction of particles withHiggs H Higgs gf Fermions gf ~ mf / v W/Z Bosons: gV ~ MV / v 2 fermion v Higgs x 2 g gauge VVH coupling ~ vev only present after EWSB breaking !!! W/Z boson 1 unknown parameter in SM: the mass of the Higgs boson Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  6. Higgs Boson Decays in SM bb WW ZZ tt cc tt gg gg HDECAY: Djouadi, Spira et al. for M<135 GeV: H  bb, tt dominant for M>135 GeV: H  WW, ZZ dominant tiny: H  gg also important Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  7. What do we know about the Higgs boson mass? • Theory: from unitarity requirement  MH <~ 1TeV „triviality“  upper bound vacuum stability  lower bound if LNew=MPlanck  130 < MH<180 GeV • Direct search at LEP: MH<114.4 excluded at 95% CL Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  8. What do we know about the Higgs boson mass? • Indirect: from EW precision measurements (LEP,SLD, TEVATRON …): Corrections depend on masses of heavy particles: top, Higgs MH < 186 GeV (EW fit only) at 95% CL ,mtop=172.7 GeV MH<219 GeV incl. direct search SM prefers light Higgs boson Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  9. Status of SM Higgs Searches at the TEVATRON Expected sensitivity: 95% CL exclusion up to 130 GeV with 4fb-1 per experiment 3 sigma evidence up to 130 GeV with 8fb-1 per experiment Current sensitivity:: Cross section limits at level of ~ 10 x SM cross section Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  10. Higgs Physics at the LHC • discovery of 1 neutral scalar Higgs boson (determination of mass, spin, CP) • discrimination between SM and extended Higgs sectors direct observation of additional Higgs bosons determination of Higgs profile: deviations from SM prediction • > 1 neutral Higgs boson • charged Higgs boson • exotic decay modes • e.g. H invisible • 4) … … … • mass • quantum numbers: • spin and CP • BRs, total width, couplings • self coupling at SLHC Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  11. pp collisions at the Large Hadron Collider LHC SPPS • LHC: proton proton collisions at ECM = 14 TEV, start in 2007 • - low luminosity running: 1(2)x1033 /(cm2 s) 10(20) fb-1/year • 2 to 3 overlapping events • - high luminosity running: 1034/(cm2 s)  100 fb-1/year • ~ 20 overlapping events every 25 ns Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  12. AToroidal LHC ApparatuS Compact Muon Solenoid • el.-mag.calorimetry: H2 photons, HZZ 4 electrons • mass resolutions: gg: 0.7 to 1.5 % 4e: 1.3 to 1.8% • m-spectrometer + tracking det.: HZZ 4 muons • mass resolution: 0.6 to 1.1 % • vertex + tracking detectors: ttH, Hbb • b-tagging performance • overall calorimetry: Htt, HWWlnln, VBF prod. • missing E. resolution, hermiticity, forward jets  calorimetry to h = 5 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  13. Production of the SM Higgs Boson at LHC Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  14. QCD corrections and Knowledge of Cross Sections e.g.: Gluon Gluon Fusion • K = sNNLO/sLO~2 • Ds = 15% from scale variations • error from PDF uncertainty ~10% • Caveat: scale variations may • underestimate the uncertainties! Harlander et al. • ttH: K ~ 1.2 Ds~ 15% WH/ZH: K~1.3 to1.4 Ds~7% • VBF: K ~ 1.1 Ds~ 4% + uncertainties from PDF (5 to 15%) • but: rarely MC at NLO avaiable (except gluon gluon fusion) • background: NLO calculations often not avaiable  need background estimate from data • ATLAS: use K=1 and LO MC for signal and background for now • CMS: apply K-factor for GGF production a. „guestimated“ K for BG Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  15. Cross sections for background processes l  q q W W q H p p q l  Background: mainly QCD driven q q q p p q Signal: often electroweak interaction  photons, leptons, … • overwhelming background • trigger: 10-7 reduction on leptons, photons, missing E Higgs 150 GeV: S/B <= 10-10 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  16. Considerations for Discovery Channel Choice • efficient trigger (need photon, lepton, muon, …)  no fully hadronic final states: eg. GGF, VBF: Hbb • reconstruction of Higgs boson mass possible? yes: Hgg, ZZ, tt no: HWW • background suppressable and controlable - good signal-to-background ratio, small BG uncertainty - estimate from data possible (sidebands, control samples) - some channels: shape prediction from MC • evaluation of discovery potential: stable cross section prediction and MC generator avaiable • MC studies with fast detector simulation • key performance numbers from full sim.: b/tau/jet/el./g/m ID, isolation, jet veto, mass resolutions, trigger, … • both collaborations plan updated evaluation with current software, newest detector layout and MC event generators within next year Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  17. H 2 Photons • signature: two highPtg • background: irreducible pp gg+x • reducible ppgj, (jj), … • exp issues (mainly for ECAL): • g, jet separation • energy scale, energy + angular resolution • conversions/dead material • mass resolution sM/M= 0.7% dead material: (un)converted g underlying event: vtx constraint CMS 100fb-1 NLO precise background estimate from sidebands (O(0.1%)) expected S/BG ~ 1/10 LO  NLO: increase of S/ÖB ~ 5060% Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  18. Gluon Fusion: H ZZ(*)4 Leptons CMS • signature: 4 high pt isolated leptons 1(2) dilepton mass ~ MZ • irreducible BG: ZZ  mass reconstruction • reducible BG: tt, Zbb  4 leptons  rejection via lepton isolation and b-veto CMS 100fb-1 NLO • good mass resolution sM: <~1% • small and flat background  easy estimate from data Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  19. Gluon Fusion: H WW  ln ln • signature: - 2 high pt leptons + large missing ET - lepton spin corrleations - no mass peak  transverse mass ATLAS M=170GeV 30fb-1 transverse mass • BG: WW, WZ, tt • lepton iso., missing E resolution • jet (b-jet) veto against tt Dührssen, prel. • BG estimate in data from DFll • NLO effect on spin corr.  ggWW contribution signal like DFll Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  20. ttH with Hbb • signature: 1 lepton, missing energy 6 jets of which 4 b-tagged • reducible BG: tt+jets, W+jets  b-tagging irreducible BG: ttbb  reconstruct mass peak • exp. issue: full reconstruction of ttH final state  combinatorics !!! need good b-tagging + jet / missing energy performance ATLAS • mass resolution sM: ~ 15% • 50% correct bb pairings • very difficult background estimate from • data with exp. uncertainty ~ O(10%) •  normalisation from side band •  shape from „re-tagged“ ttjj sample 30 fb-1 S/BG ~ 1/6 only channel to see Hbb Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  21. Vector Boson Fusion: ppqqH Higgs Decay Forward tagging jets Jet f h Jet • signature: • 2 forward jets with • large rapidity gap - only Higgs decay products • in central part of detector Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  22. Vector Boson Fusion: ppqqH • 2 forward tagging jets with rapidity gap: • theory questions: • jet distributions at NLO? • esp. direction of 3rd jet? efficieny of central jet veto? • need NLO MC generator for signal and BG influence of underlying evt? h Dh • experimental issues: forward jet reconstruction jet-veto fake rate due to pile up ATLAS ATLAS High Lumi Low Lumi pT>20GeV h Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  23. Weak Boson Fusion: HWWllnn (lnqq) • signature: tagging jets + - 2 high pt leptons + large missing ET - lepton spin corrleations (spin10) - no mass peak  transverse mass • backgrounds: tt, Wt, WWjj, ... central jet veto, b-veto ATLAS • S/BG ~ 3.5/1 • D BG ~10% shape from MC normalisation from side bands in MT and Dfll HWWe 10 fb-1 MH=160 GeV CMS 60 fb-1 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  24. Vector Boson Fusion: H tau tau  ll 4 n or l had 3 n • signature: tagging jets + - 2 high pt leptons (1 l, 1 tau) + large missing ET - mass reconstruction despite 4 (3) n in collinear approximation • backgrounds: tt,Zjj central jet veto reconstruction of mtt large boost of tau  tau, lepton, neutrino directions same mass resolution ~ 10% (5 % from acollinear approximation) dominated by missing E. resolution Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  25. Vector Boson Fusion: H tau tau  ll 4 n or l had 3 n lepton lepton lepton hadron Httem 30 fb-1 ATLAS 30 fb-1 expected BG uncertainty ~ 5 to 10% for MH > 125 GeV: flat sideband for MH < 125 normalisation from Z peak, but shape? channel so far only studied für MH>110 GeV: how far down sensitive? mass determination possible? Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  26. Vector Boson Fusion, Htt: estimate of BG shape from data • Idea: jjZmmandjjZttmm • look almost the same, esp. in calos •  same missing energy • only m momenta different • Method: select Z mm events randomise mmomenta apply „normal“ mass reco. promising prel. results from ongoing diploma thesis in BN (M. Schmitz) PTmiss,final (GeV) Mtt (GeV) Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  27. Discovery Potential for light SM Higgs boson excluded by LEP • for GGF: raise of significance by ~ 50% from LO to NLO • results for cut based analysis  improvement by multivariate methods Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  28. Discovery Potential for light SM Higgs boson excluded by LEP For MH>330 GeV also: VBF: H  ZZ  llnn VBF: WW  lnqq • discovery from LEP exclusion until 1 TeV • from combination of search channels with 15 fb-1 of well understood data • with individual search channels with 30 fb-1 of well understood data Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  29. Measurement of Higgs Boson Mass • Direct from mass peak: HggHbbHZZ4l • “Indirect” from Likelihood fit to transverse mass spectrum: HWWlnln WHWWWlnlnln • Uncertainties considered: ATLAS i) statistical ii) absolute energy scale 0.1 (0.02) % for l,g,1% for jets iii) 5% on BG + signal for HWW VBF with Htt or WW not studied yet ! DM/M: 0.1% to 1% Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  30. Spin and CP Quantum Numbers: 0 even in SM • observation of Hgg or ggH rules out Spin=1 (Young theorem) • sensitivity through spin correlations of Higgs decay products  one possibility HZZ4 leptons • f:angle btw. decay planes Q:angle btw. leptons and Z in Z rest frame (Gottfried Jackson angle) Higgs rest frame 100 fb-1 L (T) ratio of longitudinal (tranverse) polarised Z bosons Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  31. Spin and CP Quantum Numbers: discrimination power q f • discrimination dominated by q for masses> 250 GeV • seperation power > 2 s for all spin, CP hypothesis and MH>200 GeV • currently under study: • - NLO effects • - verification with full sim. + all BGs • - lower masses HZZ* q f q f • alternative methods: decay: Htt via spin correlations production: i) ttH angle between t,t,H ii) VBF Df btw. tagging jets Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  32. Determination of Higgs boson couplings Born level couplings: Fermions gf = mf / v W/Z Bosons: gV = 2 MV / v x H x 2 Loop induced effective couplings: (sensitive to new physics) Photon: gg = gW “+“ gt “+“… Gluon: gg = gt “+“ gb “+“… • couplings in productionsHx= const x GHx and decay BR(Hyy) = GHy / Gtot • experiment: rate = Nsig+NBG Nsig= L x efficiency x sHx x BR  need to know: luminosity, efficiency, background prod decay GHX GHy 2 partial width:GHz ~ gHz sHx x BR ~ Gtot • tasks: - disentangle contribution from production and decay • - determine Gtot Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  33. Ratio of Partial Widths  • ratios of BRs = ratios of G = ratios of g, if only Born level couplings e.g.  13 analysis used 9 fit parameters: including various exp. and theo. errors all rates can be expressed by those 9 parameters H WW chosen as reference as best measured for MH>120 GeV For 30fb-1 worse by factor 1.5 to 2 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  34. Total Decay Width GH • for MH>200 GeV, Gtot>1GeV  measurement from peak width in ZZ4 l • for MH<200 GeV, Gtot<< mass resolution  no direct determination  have to use indirect constraints onGtot • lower limit from observable rates: Gtot > GW+GZ+Gt+Gg+.... • upper limit needs input from theory: mild assumption: gV<gVSM valid in models with only Higgs doublets and singlets rate(VBF, HWW) ~ GV2 / Gtot < (GV2 in SM)/ Gtot  Gtot< rate/(GV2 in SM) Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  35. Absolute couplings with gV < gVSM constraint • Ginvfor undetactable decays e.g. c, gluons,new • coupling to W, Z, t, b, t Dührssen et al. • Gphoton (new), Ggluon (new): non SM contribution to loops Dührssen et al. Dg/g = ½ D(g2)/g2 Dg/g = ½ D(g2)/g2 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  36. Motivation forSupersymmetryfrom Higgs Sector 2 2 DMH2 = a(MSM-MSUSY) • “solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ? • Higgs problem in SM: • large corrections to the mass of the Higgs-Boson W W 2 + DMH2 = aL2 =aMPlanck H H  natural value ~ MPl  electroweak fit MH~O(100GeV) • SUSY solution: • partner with spin difference by ½ cancel divergence exactly if same M • SUSY broken in nature, but hierarchy still fine if MSUSY~1 TeV c+ H H - c- • SUSY breaking in MSSM: • parametrised by 105 additional parameters • too many  constrained MSSM with 5 additional parameters Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  37. The MSSM Higgs sector in a tiny Nut Shell • SUSY: 2 Higgs doublets  5 physical bosons real MSSM: 2 CP even h, H, 1 CP odd A, charged H+, H- • at Born level 2 parameters: tanb, m A mh < MZ • large loop corrections from SUSY breaking parameters mh < 133 GeV for mtop=175 GeV, MSUSY=1TeV • corrections depend on 5 SUSY parameters: Xt, M0 , M2, Mgluino, m fixed in the benchmark scenarios e.g. MHMAX scenario  maximal Mh conservative LEP exclusion • gMSSM = xgSM • no coupling of A to W/Z • small a small BR(htt,bb) • large b large BR(h,H,Att,bb) a = mixing btw. CP-even neutral Higgs bosons Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  38. Discovery Potential in the tanb versus MA Plane main questions for LHC: • At least 1 Higgs boson observable in the entire parameter space? • How many Higgs bosons can be observed? • Can the SM be discriminated from extended Higgs sectors? • LEP tanb exclusion: no exclusion for mt larger ~183 GeV ! • TEVATRON: so far exclusion for tanb > 50 MA<200GeV Mtop=174.3 GeV • ATLAS: calculations with FeynHiggs • CMS: HDECAY with SUBHPOLE up to now • no systematic uncertainties yet • 4 CP conserving benchmark scenarios considered: Carena et al. , Eur.Phys.J.C26,601(2003) • MHMAX 2) No mixing 3) Gluophobic 4) small a • conclusions the same due to to complementarity of search channels Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  39. Influence of Benchmark Scenarios • different Mh in same (tanb,MA) point  change of sensitive channels - FeynHiggs: maximum value 133 GeV - SUBHPOLE: (less corrections) 127 GeV • reduced couplings e.g. small a scenario •  small ghbb and ghtt •  reduced sensitivity discovery via • VBF, htt tth, hbb Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  40. Vector Boson Fusion: 30 fb-1 ATLAS preliminary h or H observable with 30 fb-1 studied for MH>110GeV at low lumi running Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  41. Small a scenario versus MHMAX Scenario, h: 30 fb-1 • small a: „hole“ covered by complementarity of search channels ATLAS preliminary ATLAS preliminary • remaining differences due to different Mh (11 GeV between MHMAX and small a ) • VBF, Htt: border at low tanb given by Mh=110 GeV contour • - tth, Hbb: significance decreasing rapidly with increasing Mh Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  42. Light Higgs Boson h 300 fb-1 30 fb-1 ATLAS preliminary ATLAS preliminary • large area covered by several channels •  sure discovery and parameter determination possible • small area uncovered @ mh ~ 95 GeV • VBF dominates observation • small area from bbh,Hmm for small Mh Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  43. CMS: Light Higgs Boson h Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  44. Heavy Neutral Higgs Bosons H and A • dominant production: bbH(A) • (NLO studies on the way: • how to handle correctly • bbH, gbbH, ggbbH) s ~ (tanb)2 • decay modes: H/Amm and H/Attenhanced with tan b tt: BR ~ 10 % dM ~ 12% mm: BR~ 0.04% dM ~ 1% • intense coupling regime: • only mm might resolve several mass states • exp. challenges: b-tag, tau-tag, Emiss res.  mass res. Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  45. H/A mm and tt H/Amm H/A tt  e m (only CMS) H/A tt  had had ATLAS 30fb-1 larger mass: also tt had. nhad. n trigger on hard tau jets Eff.(LV1TR)= 80% =95% offline selected evt. Tau ID: eff(tau)=55% rejection(QCD)=2500 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  46. Discovery Potenital for H and A ATLAS preliminary intermediate tanb region not covered by SM decay modes Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  47. Charged Higgs Bosons Production: • high mass: mH+-> mtop • low mass: mH+-< mtop • ggtt • ttH+-bW gbH+-t ggbtH+- contributes to NLO of gbtH+- avoid double counting correct handling of region around mtop • transition region around mtopand from 2to2 to 2to3 process needs revised experimental analysis, are MC generators ready? • decay modes: Htn (~100% below mtop, ~10% above) Htb (~90% above threshold) • running bottom quark mass used, Xsec for gbtH+- from T. Plehn‘s program Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  48. Charged Higgs Bosons ATLAS preliminary ATLAS ttbbWH+ Wqq H+-tn Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  49. Overall Discovery Potential: 300 fb-1 300 fb-1 • at least one Higgs boson observable for all parameters in all CPC benchmark scenarios • significant area where only lightest Higgs boson h is observable • can H SUSY decays or Higgs from SUSY decays • provide observation? • discrimination via h profile • determination? ATLAS preliminary similar results in other benchmark scenarios VBF channels , H/Att only used with 30fb-1 Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

  50. Higgs Decays to Gauginos e.g. H0 20 20  10 10+4l dominant background from SUSY • results for most optimistic scenarios shown  fine tuned • require small slepton masses for large BR(2  1 n leptons) • reduced sensitivity for other channels, consistent interpretation needed H0 20 20  4l+ETmiss gbtH+, H 2,30 1,2  3l+ETmiss Msleptons=250 GeV Msleptons = 110 GeV Markus Schumacher Higgs Physics at the LHC WE Heraues Seminar, Dresden, January 2006

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