Search for Heavy, Right Handed Quarks in Dilepton + Jets + Large $\Ht$

• Contacts: Collin Wolfe, Sasha Paramonov, Steve Levy, Carla Pilcher, Henry Frisch
• Data: Run II, 1.2 fb^-1
• Documentation: Public Note PS

BPT Model:

• Reference: Bjorken, Pakvasa, Tuan: Yet Another Extension of the Standard Model: Oases in the Desert?, hep-ph/0206116
• Presented as a solution to the physics underlying the CKM matrix
• New, heavy quarks mix with the SM down-quark sector, leading to small off diagonal elements in the CKM matrix
• These quarks decay to light quarks and an EWK boson at a relative rate of $Q\rightarrow W:Z:H$ of 2:1:1.
• They're pair produced via QCD, just like \ttbar.
• The model is rather generic. Jon Rosner introduced them to explain the difference in the top and bottom masses (hep-ph/9907438); Carlos Wagner introduced similar quarks to explain the Forward-Backward Asymmetry result at LEP (hep-ph/0109097).
• The new quarks correspond naturally to the three families, with decays:
  • $D_i \rightarrow u_i W$
  • $D_i \rightarrow d_i Z$
  • $D_i \rightarrow d_i H$
  • where $i=d,s,b$
  • These have relative branching ratios for $W:Z:H$ of approximately $2:1:1$
• Note: If $D_d$ is the lightest of the heavy quarks, we would find a heavy quark decaying to a d quark, not a b quark.
• Down type quarks produced via qcd exactly like top, implies if the Higgs mass is less than the $D_d$ mass, we are producing the Higgs with strong cross section!

Other Models:

• Rosner: "Splitting between up type and down type quark masses via mixing with exotic fermions in E6", Phys.\ Rev.\ D {\bf 61}, 097303 (2000).
  • Model uses down-type quarks similar to BPT to explain mass quark mass differences. Phenomenology very similar to BPT model.
• Choudhury, Tait, and Wagner: "Beautiful mirrors and precision electroweak data," hep-ph/0109097
  • Model uses similar "Mirror Quarks" to explain the 2.9 sigma difference between the SM and measurement in Forward-Backward assymetry in Zbb decays.

Analysis strategy:

• The signal looks a lot like Top, so we look for it like Top:
  • We look for events with Two leptons, two high Et jets, and large HT
  • HT is the scalar sum of the transverse energies of all objects in the event including Missing Et (MET).
• After we define our signatures, we validate the data and quantities we cut on in several control regions. Quantities we cut on are:
  • NJet distribution
  • Et of the second highest Et jet in the event (sub-leading jet Et)
  • Ht
• After Verifying these distributions, we set a cross section limit for four masses of a new quark. We optimize cuts on the sub-leading jet Et and Ht for the expected limit.

Signatures
e-mu	one electron and one muon	At least 2 Jets
ss	either two electron or two muons with the same charge	At least 2 Jets
e-tau-met	one electron, one tau, and MET > 20 GeV.	At least 2 Jets
mu-tau-met	one muon, one tau, and MET > 20 GeV.	At least 2 Jets
ll-met	Two OS electrons or two OS muons, MET > 30 GeV	At least 2 Jets

Control Regions, Low Ht to remove any signal:
e-e	Verifies Z+jets in electrons
mu-mu	Verifies Z+jets in muons
e-mu	Verifes electron/muon fake rates
e-tau-met, mu-tau-met	Verifies tau id and tau fake rates
e-mu+btag with no cut on Ht	Verifies ttbar

Signal Region Cuts
$M_Q$	HT Cut (GeV)	2nd Jet Et Cut (GeV)
200	350	40
250	400	50
300	450	50
350	550	70

Plots and Tables:

Limit Plot
	Limit Plot PNG. pdf.
Control Region Plots
	Comparison of SM MC and Data in Ht in ee events. Linear Scale GIF. EPS.
	Comparison of SM MC and Data in Ht in ee events. Log Scale GIF. EPS.
	Comparison of SM MC and Data in Ht in mu-mu events. Linear Scale GIF. EPS.
	Comparison of SM MC and Data in Ht in mu-mu events. Log Scale GIF. EPS.
	Comparison of SM MC and Data in Me-mu in e-mu events. Linear Scale GIF. EPS.
	Comparison of SM MC and Data in Me-mu in e-mu events. Log Scale GIF. EPS.
Signal Region Plots
	HT in EMU events. PNG. PDF.
	NJet in EMU events. PNG. PDF.
	Sub-leading jet Et in EMU events. PNG. PDF.
	HT in ETAU events. PNG. PDF.
	NJet in ETAU events. PNG. PDF.
	Sub-leading jet Et in ETAU events. PNG. PDF.
	HT in MUTAU events. PNG. PDF.
	NJet in MUTAU events. PNG. PDF.
	Sub-leading jet Et in MUTAU events. PNG. PDF.
	HT in EEMET events. PNG. PDF.
	NJet in EEMET events. PNG. PDF.
	Sub-leading jet Et in EEMET events. PNG. PDF.
	HT in MUMUMET events. PNG. PDF.
	NJet in MUMUMET events. PNG. PDF.
	Sub-leading jet Et in MUMUMET events. PNG. PDF.
	HT in SS events. PNG. PDF.
	NJet in SS events. PNG. PDF.
	Sub-leading jet Et in SS events. PNG. PDF.
Event Displays of Highest Ht Events
	Event display of 864 GeV Ht e-mu event. GIF. EPS.
	Event display of 864 GeV Ht e-mu event. GIF. EPS.
	Event display of 864 GeV Ht e-mu event. jpg. EPS.
	Event display of 864 GeV Ht e-mu event. GIF. EPS.
	Event display of 864 GeV Ht e-mu event. GIF. EPS.