Strange Sea Asymmetry Analysis: Update

Strange Sea Asymmetry Analysis: Update Laura Gilbert 18/09/07

s W g c g c s W Branching ratios: D*+→D0π+ 67.7% D0 → K- π+ 3.8% c→D* 25.5% c→e 9.6% Reminder: D* Analysis • Select W candidate • Reconstruct D0→K-π+ • D0 vertex displaced. • Add prompt (soft) pion. • Consider 3 sign correlations: (K- with π+, K- with πB+, πB+ with e-) • Plot reconstructed D*-D0 mass difference = 145.4MeV Asymmetry: Plot as a function of rapidity

Reminder: D* Analysis Complete list of Cuts: 1 electron with pT>25GeV, |η|<2.4 MET>25GeV Two oppositely signed tracks: assign one K, one π. pT(K)>1.5GeV, pT(π)>1GeV Third track: assign bachelor πB, pT(πB)>0.5GeV πB charge opposite to e, opposite to K Reconstructed D0 mass within 40MeV of true. Track cuts: Signed lxy of vertex >0.35 πB impact parameter significance d0/σ(d0)<3 (99% sanity cut) d0(π)* d0(K)<0 mm2 (π, K have oppositely signed IPs) Impact parameter of reconstructed D0 > 0.2mm W selection

Signal: Results Reconstructed Unsmeared Real D*s No. signal events =86±22 No “real” D*s in window = 76 No. W- events = 45 ±14 No “real” D*s = 40 No. W+ events = 41 ±13 No “real” D*s = 36 (NB. 90% of real passing D*s have pT > 8GeV. Relevant later…)

Signal: W→eν • Comphep: cross sections without cuts • qg→W-c ≈ 10900pb, qg→W+c ≈ 10250pb • Which implies: • σ (qg→e-νe Kππ) ≈ 0.823pb • σ (qg→e+νe Kππ) ≈ 0.773pb q c q W- e- νe g • Comphep: Applying cuts • pT(e)>25GeV • |η(e)|<2.5 • pT(c)>8GeV • |y(c)|<2.5 • pT(νe) >25GeV • Bσ(W-,cuts)=0.136pb • Bσ(W+,cuts)=0.132pb • (ie. 17% of signal events pass these cuts) Inherent 1.5% asymmetry NB: around 30% of these numbers pass real selection

Electroweak Backgrounds W→τν: Additional signal Z→ee Z→ττ WW WZ ZZ

Signal: W→τν s c s ντ W- ντ g τ- W- e- νe • Comphep: cross sections without cuts • qg→W-c ≈ 10900pb • qg→τ-ντ c ≈ 1140pb B(W→τ-ντ)=10.74% • qg→ e-νeντντ c ≈ 5x10-5pb B(τ- →e- νeντ)=17.84% • Logic suggests ≈ 200pb instead • Comphep: Applying cuts gives cross section 3.3 x10-6pb (ie. 6.5% pass cuts) • pT(e-)>25GeV • |η(e-)|<2.5 • pT(c)>8GeV • |y(c)|<2.5 • pT(ντ+ ντ+νe) >25GeV ??

Signal: W→τν Mc@NLO with ATLFAST: 3 million of each W-, W+. 0.9 W+ events and 2.0 W- events pass cuts, ~3 total, <~8 at 95%CL. • Comphep: assume something is wrong. Work from expected un-cut cross section of 200pb. • Apply cut efficiency of 6.5% and branching ratio B(c→D*→D0πB, D0→K π) = 0.7% • Each of W-→τ-ν, W+→τ+ν would then contribute ~< 9 signal events per fb-1. s c s ντ W- ντ g τ- W- e- νe

Background: Z→ee MC@NLO with ATLFAST: (2 million events: Lepton Filter applied so one electron required pT(e)>10GeV, |η(e)|<2.7 ) Without MpT>25GeV cut 18 events pass per fb-1 (allow more than one electron) With MpT>25GeV cut 0 events pass per fb-1. Would we lose more electrons in full simulation? c c c e- Z g e+ Lost→MET • Comphep: • Cuts: σ(cg→e-e+c) = 31.9pb • pT(e-)>25GeV, pT(e+)>25GeV • |η(e-)|<2.5 AND/OR |η(e+)|<2.5 • |y(c)|<2.5 • pT(c)>8GeV • < 22 events/fb-1 (inc BRs)

Background: Z→ττ Z→ττ probably negligible when compared with Z→ee results… would be good to check properly with Comphep. c c c e+ νe g W+ Z ντ τ+ τ- Lost→MET • Comphep: cross sections without cuts, same issue • cg→Zc ≈ 2000pb • cg→τ-τ+ c ≈ 60pb B(Z→ τ-τ+ )=3.37% • cg→ e+νeνττ- c ≈ 14x10-7pb B(τ- →e- νeντ)=17.84% • Logic suggests ≈ 11pb instead

Backgrounds: WW, WZ, ZZ W→eν=10.72% W→cX=33.6% Z→ee=3.36% Z→cc=11.81% c→Kππ=0.07% • These sum to <4 event /fb-1 (~5% of signal) with *no cuts* applied

Signal and Electroweak Backgrounds: Summary W→eν: Signal: 84±22 events/fb-1 W→τν: Signal: <8 events/fb-1 (95% CL) Z→ee: < 3 events/fb-1 pass cuts 95% CL Z→ττ: < 1 event /fb-1 likely WW: <1 event /fb-1 WZ: <<1 event /fb-1 ZZ: <<1 event /fb-1

Further work: other backgrounds QCD backgrounds: D* + fake W: Sample 5802 dijet + fake electron (W, Z, t, γ). σ=191μb bb: MC@NLO tt: MC@NLO cc: Pythia? Not available at NLO W + cc (bb), Z + cc (bb): in current samples, mainly removed by ET cuts. Should consider pileup and missing jets

Strange Sea Asymmetry Analysis: Update