Martin zur Nedden, HU Berlin 1 WS 2007/08: Physik am LHC Kap 4: Heavy Quarks Physics Introduction and overview Measurement of heavy quarks Production of

Martin zur Nedden, HU Berlin 1WS 2007/08: Physik am LHC

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


Motivation

● Exploring the Big Band

– Quark-Gluon-Plasma (LHC: ALICE)

● Test of symmetry of forces

– CP-violation

● Kosmology

– dark Matter

● Structure of strong and weak

interaction

– Strong coupling constant

– Quark-Mixing-Matrix

● Search for new Physic (Beyond Standard Model)

– Precission measurements

Heavy Quarks are improtant tools for:


Quarks and Leptons

Masses in MeV

0

-1

+2/3

-1/3

CHARGE

the top-Quark mass Is huge (175 GeV) …


• “Hidden” Flavours: States wiht Quarks and corresponding Antiquarks• Analogy to Positronium• Spectroskopy of strong Interaction• c-Quarks: and excited states (Ψ’, χc, etc.)• b-Quarks: and excited states (Y’, Y’’, etc.)

• “Open” Flavours: States with other (light) Quarks/Antiquarks• c-Quarks: • b-Quarks:

• 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 • b c + μ + υμ : well measurable impact parameter

Particles with heavy Quarks

ccJ /

bb

etc. ,,0 dcDucD

etc. ,,, 00 ubBsbBdbB s


Decays of heavy Quarks

hadronic decay semi-leptonic decay

decay into a CP-Eigen state:

without B0 - Oscillation with B0 - Oscillation


Methods of b-tagging

momentum of myons relativ to Jet-Axix: ptrel

based on Jet (calorimeter) and MYON information: b-Jet

Decay length of B-hadrons:

track- und vertex-information necessary:

pp bb X J/ψ XY XY

measurement of secundary vertices

semi leptonic b quark decay

pp B+B- XY


Reconstruction of decay vertices

experiment D0 (Tevatron): Zbb


Production of heavy Flavours

ij

FRijFjFi dxdxppxfxf 2122

212

22

1 ),,,(ˆ),(),(

Production in hadronic interaction

Parton-Density Fuctions Partonic cross section

Hadronization:formation of hadrons withheavy quarks

faktorisation


Reconstruction of the Decay Length

decay length in the lab-system:

L = c t ß γ


Impact-Parameter in b-flavourd Jets


ATLAS Inner Detector (ID)

The Inner Detector (ID) is organized into four sub-systems:

Pixels (0.8 108 channels)Silicon Tracker (SCT)

(6 106 channels)Transition Radiation Tracker (TRT)

(4 105 channels)Common ID items


b-Reconstruktion from 2-Muon events


b production-cross section at TEVATRON


Pseudo-Proper time of the J/ψ


J/ψ for B-Hadron Identification at CDF


Search for Toponium…


Discovery of the top-Quark

1995 at TEVATRON in Proton-Antiproton interactions


Top-Decay Channels

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


Observation in the Muon-Channel

Lepton + Jet channel:1 L + 2 J + 2 b-J + 1 MET


Observation in the Electron-Channel

2 Lepton channel:2 L + 2 b-J + 2 MET


Observation based on Jets

Jet channel:4 J + 2 b-J


Top-Event-Displays von D0 (Tevatron)

2 with Jets

with 4 Jets


Top-Eventdisplays of D0 (Tevatron)

e wiht 4 Jets

e with Jets


Example of a 2-myon Event


Signal/Background in top/Anti-top production

Top events are multi jet events


Top mass reconstruction


Mean Value of the Top-Mass (TEVATRON)


Cross Section Measurement


Mean Value of Top-Production Cross Section


• big bb productions-XS: ~ 500 µb (~ 1 bb pairs per 100 p-p collisions)

• high tt production-XS: ~830 pb (~ 80.000.000 tt pairs per year)

– LHC is a top-factory– important tool for detector- calibration and trigger comissioning

• Luminosity phases:– 2008: ~ 100 pb-1

– 2009: 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)

Heavy Quarks at LHC


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/() )

measurements of rare B-decays (Bd K* , Bd K* , Bs , Bs , Bs , B )

• Focus on physics topics that will not be accessible for the B-factories mainly Bs, baryon and double heavy flavour hadrons (Bs Ds , Bs J/() , b J/0 , …)


Trigger Strategies for B-Physics

• limited bandwidth for B-triggers: highly efficient and selective trigger needed.• c- and b-events contain mostly low pT particles:

challenge to trigger on those events• many b-decays contain J/ψ :

useful for calibration, optimization and understanding of detector, trigger as well as B-physics

• 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 -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(π)π)

• EM RoI: for e/ final states (e.g. J/ψ → ee, K*γ, γ)

• 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() , rare decays (B → , B K0*μμ), double semi leptonic decays

all single-

all di-

h (hadron)b (beauty)c (charm)J/

ATLAS rates for 14 TeV and 1033cm-2s-1


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 effectsdetermination of the |Vtd| and |Vts|

some of the rare decays as background to other rare decays(for example Bd0+- as bkg for Bd,s+- )

Searches: Rare B-Decays

Bsμ+μ-


Example: ATLAS offline analysis for Bs

Cuts B0s signal BG (bbX)

pT>6 GeV, ΔR<0.9 50 events 6.0×106 events

Mcut (Mμμ = MBs+140

-70 MeV) 0.77 2×10-2

Isolation cut:no charged tracks with pT > 0.8 GeV in cone < 15 degrees

0.36 5×10-2

Lxy/(Lxy)>11, 2<15

(transverse decay length)vertex fit with pointing to primary vertex constraint

0.4 < 0.7×10-4

All cuts 7 20±12

Expected signal v.s. inclusive bbμμX background

Background: lcl lBlBB ,,0

KKBKBBB sdsd ,,, 000


Projected upper limits: Bs

totalBs

bgs

nnNBBr

L2

,0

extraction of upper limit on Br(Bs μμ) (from 7 signal and (20±12) background events)

ATLAS experiment expects to reachthe sensitivity of SM prediction

Still factor of 10 aboveThe measurement of Bsμμ is still feasible at nominal LHC luminosity 1034cm-2s-1.

This would mean 100 fb-1 just in one year.

Tevatron projection


Top-Decay channels

bWt )JetJet( qqW

)Lepton( miss

ElW l

charakteristic Signal:Lepton + missing energy

only Jets in final state:dominant BG from QCD-multijet-events


Top – Physics at LHC/ATLAS

● measurement of the top-Quark mass– using mt = mjjb (mjj = mW)

● pairproduction of top-Quarks– Tag via leptons and ET

miss

● decay of top-Quarks– Branching ratios / coupplings– rare decays: t g//Z q (q=u,c: FCNC)

● Single top-Production● ideal “standard-candel”

– Detekctor calibration and trigger optimization


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-Fusiont-Kanal

Direkte Produktion,Wt-Prozess

W*-Prozesss-Kanal


Connection of W- and Top-Masse

Documents

Martin zur Nedden, HU Berlin 1 WS 2007/08: Physik am LHC Kap 4: Heavy Quarks Physics Introduction and overview Measurement of heavy quarks Production of