Kap 4: Heavy Quarks Physics

Transcription

1 Kap 4: Heavy Quarks Physics Introduction and overview Measurement of heavy quarks Production of Heavy Quarks at TEVATRON: b-selection methods Cross section measuremtens Top search and mass measurement at TEVATRON Heavy quarks at LHC BSM searches with rare B-decays Top physics at LHC 1

2 Motivation Heavy Quarks are improtant tools for: Exploring the Big Band Test of symmetry of forces CP-violation Kosmology Quark-Gluon-Plasma (LHC: ALICE) dark Matter Structure of strong and weak interaction Strong coupling constant Quark-Mixing-Matrix Search for new Physic (Beyond Standard Model) Precission measurements 2

3 Quarks and Leptons CHARGE Masses in MeV the top-quark mass Is huge (175 GeV) /3-1/3 3

4 Particles with heavy Quarks Hidden Flavours: States wiht Quarks and corresponding Antiquarks Analogy to Positronium Spectroskopy of strong Interaction c-quarks: J / Ψ = cc and excited states (Ψ, χc, etc.) b-quarks: Υ= bb and excited states (Y, Y, etc.) Open Flavours: States with other (light) Quarks/Antiquarks c-quarks: D = cu, D = cd, etc. 0 b-quarks: + B 0 = b d, Bs0 = b s, B + = b u, etc. no bound states wiht top-quarks Decay channels J/Ψ, Υ e+e-, μ+μ- : easy to reconstruct B0 J/Ψ + X : well measurable decay length well measurable impact parameter b c + μ + υμ : 4

5 Decays of heavy Quarks semi-leptonic decay hadronic decay decay into a CP-Eigen state: without B0 - Oscillation with B0 - Oscillation 5

6 Methods of b-tagging momentum of myons relativ to Jet-Axix: ptrel based on Jet (calorimeter) and MYON information: b-jet pp B+B- µ XY semi leptonic b quark decay Decay length of B-hadrons: track- und vertex-information necessary: pp bb X J/ψ XY µµ XY measurement of secundary vertices 6

7 Reconstruction of decay vertices experiment D0 (Tevatron): Z bb 7

8 Production of heavy Flavours σ = 2 2 ˆ f i ( x1, µ ) f j ( x2, µ )σ ij ( p1, p2, µ R, µ F )dx1dx2 ij 2 F 2 F Parton-Density Fuctions Partonic cross section Hadronization: formation of hadrons with heavy quarks faktorisation Production in hadronic interaction 8

9 Reconstruction of the Decay Length decay length in the lab-system: L=ctßγ 9

10 Impact-Parameter in b-flavourd Jets 10

11 ATLAS Inner Detector (ID) The Inner Detector (ID) is organized into four sub-systems: Pixels ( channels) Silicon Tracker (SCT) (6 106 channels) Transition Radiation Tracker (TRT) (4 105 channels) Common ID items 11

12 b-reconstruktion from 2-Muon events 12

13 b production-cross section at TEVATRON 13

14 Pseudo-Proper time of the J/ψ 14

15 J/ψ for B-Hadron Identification at CDF 15

16 Search for Toponium 16

17 Discovery of the top-quark 1995 at TEVATRON in Proton-Antiproton interactions 17

18 Top-Decay Channels Top production at TEVATRON dominated by quark antiquark processes, At LHC by gluon-gluon interactions, decay channels are the same. 18

19 Observation in the Muon-Channel Lepton + Jet channel: 1 L + 2 J + 2 b-j + 1 MET 19

20 Observation in the Electron-Channel 2 Lepton channel: 2 L + 2 b-j + 2 MET 20

21 Observation based on Jets Jet channel: 4 J + 2 b-j 21

22 Top-Event-Displays von D0 (Tevatron) µ with 4 Jets 2 µ with Jets 22

23 Top-Eventdisplays of D0 (Tevatron) eµ with Jets e wiht 4 Jets 23

24 Example of a 2-myon Event 24

25 Signal/Background in top/anti-top production Top events are multi jet events 25

26 Top mass reconstruction 26

27 Mean Value of the Top-Mass (TEVATRON) 27

28 Cross Section Measurement 28

29 Mean Value of Top-Production Cross Section 29

30 Heavy Quarks at LHC big bb productions-xs: ~ 500 µb (~ 1 bb pairs per 100 p-p collisions) high tt production-xs: ~830 pb (~ tt pairs per year) LHC is a top-factory important tool for detectorcalibration and trigger comissioning Luminosity phases: 2008: ~ 100 pb : more than 1 fb-1 at an available luminosity of 1033 cm-2 s-1 (~10 fb-1 per year) design: High -Luminosität: 1034 cm-2s-1 (~100 fb-1 per year) 30

31 General Strategy for B Physics at LHC General-purpose experiments for discoveries: main emphasis on high-pt physics beyond the Standard Model B-physics programme depending on stages of the LHC operation: Huge b-hadron production statistics allow precise measurements of their properties Theoretical descriptions of heavy flavoured hadrons need input from LHC Precision measurements already achievable after one year of data taking Inclusive production cross section measurement in the initial phase Measurements extending the discovery potential for BSM physics measurements of CP violation parameters that are predicted to be small in the SM (e.g in Bs J/ψφ(η) ) measurements of rare B-decays (Bd K*γ, Bd K*µµ, Bs φγ, Bs φµµ, Bs γµµ, B µµ ) Focus on physics topics that will not be accessible for the B-factories mainly Bs, baryon and double heavy flavour hadrons (Bs Dsπ, Bs J/ψφ(η), Λb J/ψΛ0, ) 31

32 Trigger Strategies for B-Physics ATLAS µ rates for 14 TeV and 10 cm s limited bandwidth for B-triggers: highly efficient and selective trigger needed. c- and b-events contain mostly low pt particles: h (hadron) all single-µ challenge to trigger on those events b (beauty) many b-decays contain J/ψ : c (charm) useful for calibration, optimization and understanding of J/Ψ detector, trigger as well as B-physics 33 B-trigger is based on single- and di-muons in final state BR ~ 10 %, but clean signature at early level in trigger and give flavour tag lower lumi (< 2*1033 cm-2s-1) LVL1 single µ-trigger with additional LVL1 signature or a jet in calorimeter at LVL2 use LVL1 Regions of Interest (RoI) to seed LVL2 reconstruction: Jet RoI: for hadronic final states (e.g. Bs Ds(φπ)π) -2-1 all di-µ EM RoI: for e/γ final states (e.g. J/ψ ee, K*γ, φγ) Muon RoI: to recover di-muon final-states in which second muon was missed at LVL1 LVL1 di-muon trigger high lumi (>2x1033 cm-2s-1) LVL1 di-μ trigger B J/ψ(µµ), rare decays (B µµ, B K0*μμ), double semi leptonic decays 32

33 Searches: Rare B-Decays b d, s transitions (FCNC) are forbidden at the tree level in SM and occur at the lowest order through one-loop-diagrams penguin and box Main points to study: good test of SM and its possible extensions information of the long-distance QCD effects determination of the Vtd and Vts some of the rare decays as background to other rare decays (for example Bd π0µ+µ- as bkg for Bd,s µ+µ- ) Bs μ+μ- 33

34 Example: ATLAS offline analysis for Bs µµ Expected signal v.s. inclusive bb μμx background Cuts B0s signal BG (bb µµx) pt>6 GeV, ΔRµµ< events events < ±12 Mµµcut (Mμμ = MBs MeV) Isolation cut: no charged tracks with pt > 0.8 GeV in cone θ < 15 degrees Lxy/σ(Lxy)>11, χ2<15 (transverse decay length) vertex fit with pointing to primary vertex constraint All cuts Background: B 0 π µ +ν µ, B + µ + µ l +ν l, Bc µ + µ l +ν l Bd0 π 0 µ + µ, Bs0 µ + µ γ, Bd Kπ, Bs KK 34

35 Projected upper limits: Bs µµ extraction of upper limit on Br(Bs μμ) ( Br B µ µ 0 s + (from 7 signal and (20±12) background events) N ( n, nbg ) ) 2σ Bs L αε total ATLAS experiment expects to reach the sensitivity of SM prediction Tevatron projection Still factor of 10 above The measurement of Bs μμ is still feasible at nominal LHC luminosity 1034cm-2s-1. This would mean 100 fb-1 just in one year. 35

36 Top-Decay channels ± t W b ± W qq ( Jet + Jet ) W ± lν l ( Lepton + E miss ) charakteristic Signal: Lepton + missing energy only Jets in final state: dominant BG from QCD-multijet-events 36

37 Top Physics at LHC/ATLAS measurement of the top-quark mass pairproduction of top-quarks using mt = mjjb (mjj = mw) Tag via leptons and ETmiss decay of top-quarks Branching ratios / coupplings rare decays: t g/γ/z q (q=u,c: FCNC) Single top-production ideal standard-candel Detekctor calibration and trigger optimization 37

38 Single-Top Produktion direkte Bestimmung der Kopplungsstärke des t-w-b Vertex: W-Gluon-Fusion: sensitiv auf Modifikationen der Kopplungen des top-quarks an andere SM-Teilchen Wt: sensitiv auf FCNC W*: sensitiv auf neue, schwere W -Bosonen wesentlich geringerer Anteil an der top-produktion bei LHC W-Gluon-Fusion t-kanal Direkte Produktion, Wt-Prozess W*-Prozess s-kanal 38

39 Connection of W- and Top-Masse 39