Motivation Fact: The multi-generational structure of the quark doublets requires explanation and could herald compositeness. Under hypothesis of compositeness, deviation from point-like behavior would likely manifest in third generation. Conclusion: g  bb may exhibit desired deviant behavior. Explore b quark dijet mass as a possible signature. Problem ~100:1 QCD:bb Solutions m tagging 2nd VTX tagging Impact parameter CDF: PRL 82 (1999) 2038 Fit to CDF qQCD calculation

m-tagged Jet Cross-section eT Trigger Eff ePV Primary Vertex Eff ej Jet Eff em m Eff fbm Frac b  m (Pt > 4 GeV) fBm Frac B  m (Pt > 4 GeV) L Luminosity Dpt Pt bin width sb b cross-section sB BKD cross-section Correlated Jet + m (Pt > 5 GeV) Given the simplicity of the calculation, there are few likely sources of the excess seen in p13. These could conceivably be N m JES (central value) Resolution (i.e. smearing) p13

p14 Analysis Summary Inclusive m-tagged jet corrJCCB (0.5 cone jets) Standard Jet quality cuts, Standard JET Triggers Jet tagged with MEDIUM muon (more on this later) DR(m, jet) < 0.5 |yjet| < 0.5 JES 5.3 Long term goal was b-jet xsec. Difficult due to no data-driven determination of b-fraction.

p14 Skimming Start with CSG QCD skim Turn into TMBTrees (40M events…on disk) Skim on Trees Remove bad runs (CAL, MET, SMT, CFT, JET, Muon) Remove events w/o 2 jets Use Ariel d0root_ based package SKIM 1:  1 leading jet has ~ MEDIUM m (P(m) > 4 GeV) SKIM 2:  1 leading jet has ~ loose SVT

p14 All Data: CSG Skims Bad runs & lumblk removed in luminosity. Only bad run removed in event counts for skims. Up until Run 193780 (07-JUN), V12.37.

Trigger Turn On Jet Trigger Collinear muon |yjet| < 0.5 Luminosity weighted Statistics uncorrelated poisson (wrong, of course) JES corrected (5.3)

f Distribution of MEDIUM m-tagged jets (+ mycuts) f(jet+m) These cuts clearly improve the fake m rate. Some residual fake m’s must persist. How many? CHF should be higher for punch through jets?

Closer Look Suspicious JT45_TT Pt(m) 4.5-5.0 4.0-4.5 Pt(m)

What is now a muon? Medium muon (as defined by mID group) At least one scintillator hit in BC. Pt(central track) > 5 GeV |Pt(central) – Pt(global)| < 15 GeV Rejected if 4.25 < f (muon) < 5.15 AND |h(detector)| < 1.1 m A layer cal jet Fake m from punch-through In a jet environment is an issue

Efficiency/Fraction Summary Detail Value eT Trigger Eff 1.000 ePV Primary Vertex Eff 0.84 ± 0.005 em m Eff [0.37 ± 0.05] 0.41 ± 0.05 ej Jet Eff 0.99 ± 0.01 fBm Frac B  m (Pt > 4 GeV) Pt dependent fbm Frac b  m (Pt > 4 GeV)

m JES Definitions Required identically 2 jets Pt(jet 3, uncor) < 8 OR third jet doesn’t pass jet QC One jet contains muon, the other doesn’t. | Df | > 2.84 Imbalance variable: Independent variable:

JES v5.3 STD JES 5.3 gives a 3.8% offset for m-tagged jets. It is independent of Pt (75-250 GeV). Maybe higher above that. Need to rebin and revisit the idea that the muon Pt may be mis-measured. Same plot when scaling the m-tagged jets by 3.8%.

JES v5.3 Energy Resolution (Fixed)

Fitting Functions Variable Value Error N 9.56 × 107 1.7 × 106 a 3.195 0.004 b 5.61 0.04 Variable Value Error N1 7.62 0.32 k1 16.90 1.26 N2 3.28 0.60 k2 36.33 3.23

Extraction of Correction Factors “normal” exponential

Point by Point Unsmearing Factors “normal” Exponential Unsmearing Error small ~5% for Pt > 100 GeV

PtRel at High Pt PtRel muon jet

Fitting to HF fraction

Systematic Error Breakdown

MC Comparison Pythia using standard DØ MC. NLO uses NLO++ (CTEQ6L) From Pythia, find fraction of jets tagged with muons (HF only). Multiply NLO cross-section by Pythia muon-fraction. This is effectively the NLO k factor.

Status DØNote and Conference note to EB025 Residual small bug in code (should have only a few percent effect). JES error must be reduced to use this before setting limits on new physics.