Heavy-Flavor Baryons b (*) (at the Tevatron) c (*) , c * BR( b - PowerPoint PPT Presentation

Heavy-Flavor Baryons Σ b (*) (at the Tevatron) Σ c (*) , Λ c * BR(Λ b ) Thomas Kuhr Hadron2011 16.06.2011

Tevatron: pp @ 1.96 TeV Tevatron: pp @ √s = 1.96 TeV Thomas Kuhr Hadron 2011, 16.06.2011 page 2

Tevatron Performance ~10 fb -1 recorded per experiment Thomas Kuhr Hadron 2011, 16.06.2011 page 3

Heavy Flavor Production at the Tevatron b b g b g g q b b b q b g g g b q q ➔ Huge bb cross section ✗ Background tracks from fragmentation ➔ Production of all heavy hadron → High combinatorial species in fragmentation background but Belle CDF ✗ inelastic cross section ~10 3 times larger than σ( bb) → Trigger Thomas Kuhr Hadron 2011, 16.06.2011 page 4

CDF and D0 Detectors CDF D0 ➔ Excellent mass resolution ➔ Large tracking and muon coverage ➔ Displaced track and ➔ Single + di-muon triggers di-muon triggers Thomas Kuhr Hadron 2011, 16.06.2011 page 5

B Baryon History ✔ Λ b observation 1991, UA1, PLB 273, 540 ✔ Σ b (*) observation 2007, CDF, PRL 99, 202001 ✔ Ξ b observation (D0, CDF), 2007, D0, PRL 99, 052001, 2007, CDF, PRL 99, 052002 ✔ Ω b observation 2008, D0, PRL 101, 232002 2009, CDF, PRD 80, 072003 Thomas Kuhr Hadron 2011, 16.06.2011 page 6

Current Knowledge Thomas Kuhr Hadron 2011, 16.06.2011 page 7

Σ b (*) States ➢ Isospin triplets ● Strong decay to Λ b π via p-wave ➔ Charged states observable via decay chain:  Σ b (*)+ → Λ b 0 π +  Λ b 0 → Λ c + π –  Λ c + → p K – π + Thomas Kuhr Hadron 2011, 16.06.2011 page 8

Σ b (*) Status ● First observed by CDF in 2007 with 1.1 fb -1 ● Significance of each peak ~ 3 σ ● Measurement of masses and hyperfine splitting: Motivation for update: ➢ Confirm observation ➢ Improve mass measurements ➢ Measure widths and isospin splitting Thomas Kuhr Hadron 2011, 16.06.2011 page 9

Σ b (*) Trigger and Selection p ● Trigger on a pair of Λ c displaced tracks K Λ b Σ b (*) π π π ● Vertex fit (with mass constraint) for Λ c , Λ b , and Σ b (*) ● Selection cuts on  Decay time, impact parameter, momentum ➔ Optimized on S/√(S+B) of Λ b signal Thomas Kuhr Hadron 2011, 16.06.2011 page 10

Σ b (*) Data Sample 6 fb -1 ➢ ~16k Λ b ● S/B ≈ 1.8 ➔ Real Λ b with random π Backgrounds: is dominant ● Combinatorial ● Partially or fully background reconstructed B for Σ b mesons and Λ b Thomas Kuhr Hadron 2011, 16.06.2011 page 11

Σ b (*) Fit ➢ Fit of Q = M( Λ b π ) – M( Λ b ) – M( π ) Background: ● Second order polynomial times ● Square root function (for threshold) Signal: ● Non-relativistic Breit-Wigner ● With variable width Γ = Γ 0 (p π / p π, 0 ) 3 (for p-wave decay) ● Convolved with double-Gaussian resolution function determined from MC Thomas Kuhr Hadron 2011, 16.06.2011 page 12

Σ b (*)– Mass Spectrum Significance: Comparison of  hypotheses for different numbers of peaks via Δ log(L) ➔ Two vs. one: 7.5 σ ➔ One vs. none: 10.0σ ➔ Two vs. none: 12.3σ Thomas Kuhr Hadron 2011, 16.06.2011 page 13

Σ b (*)+ Mass Spectrum Significance: Comparison of  hypotheses for different numbers of peaks via Δ log(L) ➔ Two vs. one: 7.2 σ ➔ One vs. none: 12.2σ ➔ Two vs. none: 14.0σ Thomas Kuhr Hadron 2011, 16.06.2011 page 14

Σ b (*) Results Talk by Igor Gorelov, tomorrow in Heavy Hadron session ● Systematics: momentum scale, resolution model, background model, fit bias, external input First Improved by measurements factor ≥ 2 Thomas Kuhr Hadron 2011, 16.06.2011 page 15

Λ b → J/ ψ Λ ● Very little known about flavor physics processes in b baryons ➔ For example b → s transitions are sensitive to new physics ➢ Λ b → J/ ψ Λ CDF Run I measurement:  f(b → Λ b ) BR( Λ b → J/ ψ Λ ) = (4.7 ± 2.3 ± 0.2) x 10 -5 Thomas Kuhr Hadron 2011, 16.06.2011 page 16

Λ b → J/ ψ Λ BR Measurement ● Trigger on muon pair or single muon ● Vertex fit for Λ , and Λ b ● Cascade decays like Σ → Λγ or Ξ 0 → Λπ 0 suppressed by requiring Λ vertex in Λ momentum direction ● Selection cuts on – Momentum, impact par., decay length ➔ Optimized on S/√(S+B) with S from MC and B from sidebands ➢ Normalized to B 0 → J/ ψ K S with K S → π + π – Thomas Kuhr Hadron 2011, 16.06.2011 page 17

Λ b → J/ ψ Λ Fit 6.1 fb -1 ● Signal: double Gaussian ● Background: 2 nd order polynomial ● Relative efficiency from MC ● ε = 2.37 ± 0.05 (stat.) Thomas Kuhr Hadron 2011, 16.06.2011 page 18

Λ b → J/ ψ Λ Result ● Systematic uncertainties: Fit model (5.6%), relative efficiency [B 0 decay model] (2.0%), cross-feed (2.3%), Λ b polarization (7.2%) ✔ Several cross-checks (sub-samples, data-MC comparisons) Factor ~3 improvement Submitted to PRD-RC arXiv:1105.0690 Thomas Kuhr Hadron 2011, 16.06.2011 page 19

Charm Baryons ● Σ c (*) : Isospin triplets J P =1/2 + : Σ c (2455), J P =3/2 + : Σ c (2520) ● Λ c * : Λ c o rbital excitations J P =1/2 – : Λ c (2595), J P =3/2 – : Λ c (2625) Thomas Kuhr Hadron 2011, 16.06.2011 page 20

Charm Baryons Trigger and Selection p ● Trigger on a pair of displaced tracks π Λ c ➔ ~50% from b hadron decays K Σ c (*) ● Selection of Λ c + → p K – π + Λ c * π Λ b π with Neural Network (NN) X ● Input variables: particle ID, decay time, decay angles, fit quality ➢ NN training on data only using sPlot technique Thomas Kuhr Hadron 2011, 16.06.2011 page 21

Charm Baryons Data Sample 5.2 fb -1 Σ c (*) candidates: ➔ Λ c + one π Λ c * candidates: ➔ Λ c + two π ➢ Σ c (*) and Λ c * selection with NN trained on data (sPlot) Thomas Kuhr Hadron 2011, 16.06.2011 page 22

Charm Baryon Spectra Λ c (2625) Σ c (2520) 0 Λ c (2595) Σ c (2455) 0 Fit of mass difference Σ c (*) : ΔM = M( Λ c π ) – M( Λ c )  Σ c (2520) ++ Λ c * : ΔM = M( Λ c ππ ) – M( Λ c )  Σ c (2455) ++ Thomas Kuhr Hadron 2011, 16.06.2011 page 23

Σ c (*) Fit Signal: ● nonrelativistic Breit-Wigner convolved with triple Gaussian resolution function Background: ● Combinatorial: 2 nd order polynomial from Λ c sideband, Gaussian for D * reflection for Σ c (*) 0 case ● Λ c with random π: 3 rd order pol. ● Λ c (2625) → Λ c ππ feed down: derived from Λ c (2625) → Λ c ππ yield Thomas Kuhr Hadron 2011, 16.06.2011 page 24

Σ c (*) Fit Projections Σ c (*) 0 → Λ c + π – Σ c (*) ++ → Λ c + π + Thomas Kuhr Hadron 2011, 16.06.2011 page 25

Σ c (*) Results ● Systematic uncertainties: resolution model, mass scale, fit model WA w/o CDF ➢ Masses and widths consistent with world averages Thomas Kuhr Hadron 2011, 16.06.2011 page 26

Λ c * Fit Signal: ● Threshold effect in Λ c *+ → Σ c 0,++ π +,– taken into account by mass dependent width ● Pion coupling constant h 2 Background: ● Combinatorial: 2 nd order polynomial from Λ c sidebands ● Λ c with random pions: 2 nd order polynomial ● Σ c with random pion: threshold function according to Σ c line shape Thomas Kuhr Hadron 2011, 16.06.2011 page 27

Λ c (2625) Result ● Δ M (MeV/c 2 ) = 341.65 ± 0.04 ± 0.12 ● Γ (MeV/c 2 ) < 0.97 @ 90% CL (PDG: < 1.9) ➢ Significantly improved precision Thomas Kuhr Hadron 2011, 16.06.2011 page 28

Λ c (2595) Threshold Effect ➢ Λ c line shape not described by normal Breit-Wigner  Increase of χ 2 from Fit w/o threshold 227 to 286 effect (for ndf=206) ➔ Discrepancy only observable because of high statistics ● Additional systematic uncertainty due to Σ c parameters Thomas Kuhr Hadron 2011, 16.06.2011 page 29

Λ c (2595) Result ● Δ M = (305.79 ± 0.14 ± 0.20) MeV/c 2 ● h 2 2 = 0.36 ± 0.04 ± 0.07 ➢ Significantly improved precision Submitted to PRD arXiv:1105.5995 ➢ Predicted threshold effect confirmed ➔ Leads to significantly smaller mass Thomas Kuhr Hadron 2011, 16.06.2011 page 30

Summary Factor ~2 improvement Expected improvements First measurement of width and in PDG tables isospin splitting Factor ~3 Factor ~3 improvement improvement Mass shift by threshold effect First direct h 2 measurement Thomas Kuhr Hadron 2011, 16.06.2011 page 31