1. 1 Strange Sea Asymmetry Analysis: Update Laura Gilbert 18/09/07

2. 2 Reminder: D* Reminder: D* Analysis Select W candidate Reconstruct D 0 →K - π + D 0 vertex displaced. Add prompt (soft) pion. Consider 3 sign correlations: (K - with π +, K - with π B +, π B + with e - ) Consider 3 sign correlations: (K - with π +, K - with π B +, π B + with e - ) Plot reconstructed D*-D0 mass difference = 145.4MeV Plot reconstructed D*-D0 mass difference = 145.4MeV s g W c cg W s Branching ratios: D* + →D0π + 67.7% D0 → K - π+ 3.8% c→D* 25.5% c→e 9.6% Asymmetry: Plot as a function of rapidity

3. 3 Reminder: D* Reminder: D* Analysis Complete list of Cuts: Complete list of Cuts: 1 electron with pT>25GeV, |η| 25GeV, |η|<2.4 MET>25GeV MET>25GeV Two oppositely signed tracks: assign one K, one π. pT(K)>1.5GeV, pT(π)>1GeV Two oppositely signed tracks: assign one K, one π. pT(K)>1.5GeV, pT(π)>1GeV Third track: assign bachelor π B, pT(π B )>0.5GeV Third track: assign bachelor π B, pT(π B )>0.5GeV π B charge opposite to e, opposite to K π B charge opposite to e, opposite to K Reconstructed D0 mass within 40MeV of true. Reconstructed D0 mass within 40MeV of true. Track cuts: Track cuts: Signed lxy of vertex >0.35 Signed lxy of vertex >0.35 π B impact parameter significance d0/σ(d0)<3 (99% sanity cut) π B impact parameter significance d0/σ(d0)<3 (99% sanity cut) d0(π)* d0(K)<0 mm 2 (π, K have oppositely signed IPs) d0(π)* d0(K)<0 mm 2 (π, K have oppositely signed IPs) Impact parameter of reconstructed D0 > 0.2mm Impact parameter of reconstructed D0 > 0.2mm W selection

4. 4 Signal: Results 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 Reconstructed Unsmeared Real D*s (NB. 90% of real passing D*s have pT > 8GeV. Relevant later…)

5. 5 Signal: W→eν q g W-W- c q νeνe e-e- Comphep: cross sections without cuts qg→W - c ≈ 10900pb, qg→W + c ≈ 10250pb Which implies: σ (qg →e - ν e Kππ) ≈ 0.823pb σ (qg →e + ν e Kππ) ≈ 0.773pb Comphep: Applying cuts pT(e)>25GeV |η(e)|<2.5 pT(c)>8GeV |y(c)|<2.5 pT(ν e ) >25GeV Bσ(W -,cuts)=0.136pb Bσ(W +,cuts)=0.132pb (ie. 17% of signal events pass these cuts) qNo. W - signal events / fb -1 No. W + signal events / fb -1 sum136132 d139 s123 b0.1 Inherent 1.5% asymmetry NB: around 30% of these numbers pass real selection

6. 6 Electroweak Backgrounds W→τν: Additional signal W→τν: Additional signal Z→ee Z→ee Z→ττ Z→ττ WW WW WZ WZ ZZ ZZ

7. 7 Signal: W→τν s g W-W- c s W-W- ντντ τ-τ- ντντ νeνe e-e- Comphep: cross sections without cuts qg→W - c ≈ 10900pb qg → τ - ν τ c ≈ 1140pb B(W→ τ - ν τ )=10.74% qg → e - ν e ν τ ν τ c ≈ 5x10 -5 pb B( τ - → e - ν e ν τ )=17.84% Logic suggests ≈ 200pb instead Comphep: Applying cuts gives cross section 3.3 x10 -6 pb (ie. 6.5% pass cuts) pT(e - )>25GeV |η(e - )|<2.5 pT(c)>8GeV |y(c)|<2.5 pT(ν τ + ν τ + ν e ) >25GeV ??

8. 8 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. s g W-W- c s W-W- ντντ τ-τ- ντντ νeνe e-e- 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*→D 0 π B, D 0 →K π) = 0.7% W - →τ - ν, W + →τ + ν would then contribute ~< 9 signal events per fb -1. Each of W - →τ - ν, W + →τ + ν would then contribute ~< 9 signal events per fb -1.

9. 9 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? 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) c g Z c c e-e- e+e+ Lost→MET

10. 10 Comphep: cross sections without cuts, same issue cg→Zc ≈ 2000pb cg → τ - τ + c ≈ 60pb B(Z→ τ - τ + )=3.37% cg → e + ν e ν τ τ - c ≈ 14x10 -7 pb B( τ - → e - ν e ν τ )=17.84% Logic suggests ≈ 11pb instead Background: Z→ ττ Z→ττ probably negligible when compared with Z→ee results… would be good to check properly with Comphep. Z→ττ probably negligible when compared with Z→ee results… would be good to check properly with Comphep. c g Z c c τ+τ+ τ-τ- W+W+ ντντ νeνe e+e+ Lost→MET

11. 11 Backgrounds: WW, WZ, ZZ Total HERWIG xsect σ (pb) Branching Ratio Bfractional cross section σxB (pb) No. events /fb -1 WW70 2(W→eν,W→cX c→Kππ) =5.04x10 -5 3.5x10 -3 3.5 WZ27 (W→eν, Z→cc) + (W→cX, Z→ee) c→Kππ =1.68x10 -5 4.5x10 -4 0.45 ZZ11 2(Z→ee, Z→cc, c→Kππ) =5.56x10 -6 6.1x10 -5 0.061 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

12. 12 Signal and Electroweak Backgrounds: Summary W→eν: Signal: 84±22 events/fb -1 W→eν: Signal: 84±22 events/fb -1 W→τν: Signal: <8 events/fb -1 (95% CL) W→τν: Signal: <8 events/fb -1 (95% CL) Z→ee: < 3 events/fb -1 pass cuts 95% CL Z→ee: < 3 events/fb -1 pass cuts 95% CL Z→ττ: < 1 Z→ττ: < 1 event /fb -1 likely WW: WW: <1 event /fb -1 WZ: WZ: <<1 event /fb -1 ZZ: ZZ: <<1 event /fb -1

13. 13 Further work: other backgrounds QCD backgrounds: D* + fake W: Sample 5802 dijet + fake electron (W, Z, t, γ). σ=191 μb 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 Should consider pileup and missing jets