1. Study of DC3 Fully Simulated W→eν Samples with an eye to Strange Sea Asymmetry Analysis Laura Gilbert, University of Oxford 20/09/06 Many thanks to: Jeff Tseng, Amanda Cooper-Sarkar, Tony Weidberg, Chris Hayes

2. OUTLINE 1)Motivation: quark asymmetries in the proton 2)Technique for strange sea analysis 3)Analysis sample: W→eν e W reconstruction W reconstruction Conclusions Conclusions

3. Motivation: Quark Asymmetries in the Proton u, d distributions in the proton predicted to be almost flavour symmetric within pQCD. MNC measured the flavour nonsinglet structure function [F p 2 (x,Q 2 ) − F n 2 (x,Q 2 )]. → large (~30%) violation of Gottfried sum rule: d/u Confirmed by the NA51, E866 and HERMES. Meson Cloud model (MCM) seems most successful in explaining observations. Various theoretical models proposed. Meson Cloud model (MCM) seems most successful in explaining observations.

4. A symmetric s/s distribution is often assumed, but not established theoretically or experimentally. A symmetric s/s distribution is often assumed, but not established theoretically or experimentally. MCM would seem to imply a strange momentum fraction asymmetry too. MCM would seem to imply a strange momentum fraction asymmetry too. Signal & Cao showed that incorporating asymmetric distribution into the MCM can reduce NuTeV anomaly (measured sin 2 θ W of 3σ above accepted value, reduced to 2σ by MCM). Signal & Cao showed that incorporating asymmetric distribution into the MCM can reduce NuTeV anomaly (measured sin 2 θ W of 3σ above accepted value, reduced to 2σ by MCM). Possible Strange Sea Momentum Asymmetry? In the MCM the proton oscillates into virtual mesons/baryons In the MCM the proton oscillates into virtual mesons/baryons sea q/qbar are in different environments carrying different momenta. sea q/qbar are in different environments carrying different momenta. d u u q q du u oscillates q du uq

5. A note on measuring strange sea asymmetries at ATLAS Likely to be hard to see at ATLAS: Likely to be hard to see at ATLAS: s(x) s(x) - s(x) Physics Letters B 381 (1996) 317-324: Brodsky & Ma Calculations from Meson Cloud Model – 2-body wavefunctions [Gaussian (thick) and power-law (thin)] Ws at LHC sensitive to small x regime (<0.01). Difficult to probe.

6. An isolated electron, η 25GeV. ETmiss>25GeV. Kπ(ππ)(π0) + bachelor pion s→W-D*+; s→W+D*-: Sign of πB will be anticorrelated with sign of W. Detecting a Strange Sea Asymmetry Signal: W+D* e-e- ν D *+ jet KπKπ c s g d d π+π+ D0D0 W-W-

7. Analysis Technique Select W candidate ( Select W candidate ( isolated electron, |η| 25GeV, ETmiss>25GeV) Reconstruct D 0 →K - π + (also D 0 →K - π + π 0, D 0 →K - π + π - π + π 0 etc) Reconstruct D 0 →K - π + (also D 0 →K - π + π 0, D 0 →K - π + π - π + π 0 etc) D 0 flight length: cτ=123μm so vertex displaced. D 0 flight length: cτ=123μm so vertex displaced. Add prompt (soft) pion. Add prompt (soft) pion. Signal has opposite sign combinations of W, π B. Signal has opposite sign combinations of W, π B. Backgrounds inc. same sign combinations, QCD. Backgrounds inc. same sign combinations, QCD. Should find zero asymmetry in Monte-Carlo from accepted PDFs. Work out CL on limits of null hypothesis Should find zero asymmetry in Monte-Carlo from accepted PDFs. Work out CL on limits of null hypothesis

8. Preliminary ATLFAST search DC2 sample (A4) of W→eν e at NLO. DC2 sample (A4) of W→eν e at NLO. One electron track with Pt>25GeV, missing Et>25GeV, η 25GeV, missing Et>25GeV, η<2.5 ~211k events, cross section 8.4nb, luminosity 33pb -1 ~211k events, cross section 8.4nb, luminosity 33pb -1 D* selection cuts D* selection cuts Pt of Kaon candidate > 1.5GeV, pion pt > 1.0GeV (combined to D 0 ) Pt of Kaon candidate > 1.5GeV, pion pt > 1.0GeV (combined to D 0 ) Pt of batchelor pion > 0.9GeV Pt of batchelor pion > 0.9GeV Atlfast - unsmearedAtlfast - smeared Mass (K - π + π B + ) - Mass(K - π + ) Mass difference plots: Mass (K - π + π B + ) - Mass(K - π + )

9. Current Sample: W→e - ν @ NLO W→e - ν from MC@NLO, full sim 47800 events currently available (reconstructed in 11.0.42, using CBNTs, DC3 generation, 005250) W→e - ν from MC@NLO, full sim 47800 events currently available (reconstructed in 11.0.42, using CBNTs, DC3 generation, 005250) Generated cross section is 8.4nb (cf. 30nb for W→lν: TDR). Luminosity (for 50k events) is 9.5pb -1. Generated cross section is 8.4nb (cf. 30nb for W→lν: TDR). Luminosity (for 50k events) is 9.5pb -1. Cuts applied at any stage are listed on top right of slide. Cuts applied at any stage are listed on top right of slide. All truth plots are normalised to weighting of simulated data. All truth plots are normalised to weighting of simulated data.

10. Electron Selection Cuts At least one electron with transverse energy > 25GeV. At least one electron with transverse energy > 25GeV. Electron candidate has at least one matched track. Electron candidate has at least one matched track. |η| < 2.4. |η| < 2.4. IsEM flag = 0 (electron isolation cut). IsEM flag = 0 (electron isolation cut). - before cuts - after cuts Initially tracks associated with egamma candidates include kaons, pions, muons. After cuts only electrons and positrons remain.

11. ELECTRONS Electron ET - truth - full sim Cuts: ET(ele) > 25GeV At least one track matched IsEM=0 η(ele) < 2.4

12. ELECTRONS Identifying electrons with their partner in truth containers, matching (η,φ) space: If (ΔR<0.1) match is found Cuts: ET(ele) > 25GeV At least one track matched IsEM=0 η(ele) < 2.4

13. ELECTRONS Electron ET resolution: (sim-truth)/truth for matched sim:truth electron pairs. Cuts: ET(ele) > 25GeV At least one track matched IsEM=0 η(ele) < 2.4 ΔR<0.1 (matching sim to truth) Resolution: ~1.8%

14. ELECTRONS ET distribution of "wrong sign" electron candidates: - +ve charge electrons (from track q/p) - all electron candidates (for shape comparison) Cuts: ET(ele) > 25GeV At least one track matched IsEM=0 η(ele) < 2.4 Only 4 of these reconstructed e + have "Trk_truthpdg = 11", meaning only 4 are charge misidentified

15. ELECTRONS What are the wrong sign electrons? What are the wrong sign electrons? Not generated (except in eg pion decays, low momenta). Not generated (except in eg pion decays, low momenta). Tracks carry "truth id" of a positron, implies mostly not charge misidentified. (Do I understand Trk_ParticlePdg variable?) Tracks carry "truth id" of a positron, implies mostly not charge misidentified. (Do I understand Trk_ParticlePdg variable?) Probably hard brem or photon conversions in which one electron has significantly higher pT than the other. Probably hard brem or photon conversions in which one electron has significantly higher pT than the other. Only ever one electron/positron passing cuts per event Only ever one electron/positron passing cuts per event Check with HepVis… Check with HepVis…

16. Beampipe v-atlas view of an event with e+… Electron Neutrino Photon Pixel hits SCT hits TRT hits Photon conversion with one soft e? This electron produced with high η: probably lost Nothing particularly fishy going on (?) – count these as statistical errors in the same sign combinations.

17. MISSING ENERGY - truth: calculated from non- interacting particles - full sim: corrected, inc. muons Missing ET (cut on 25GeV to select Ws) Probably not properly calibrated? Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 MET>25GeV Cut on MET>25GeV

18. MISSING ENERGY Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 Jet η < 2.4 ΔR (e-jet) > 0.7 MET>25GeV Missing ET Resolution: Asymmetry reflecting right-shift of data w.r.t. truth Resolution: ~17%

19. MISSING ENERGY Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 MET>25GeV Missing ET Resolution: Expect this to vary with the ET of the rest of the event, barring the electron. Expect this to vary with the ET of the rest of the event, barring the electron. Total ET - electron jet ET (recoil)

20. Missing ET Resolution as a function of ΣE T (recoil): ΣE T = total E T -electron E T Error in MET resolution ≈ A(event recoil) B Expect MET resolution to increase with event recoil: power law. Expect MET resolution to increase with event recoil: power law. σ MET (ΣE T ) ≈ 0.10 (ΣE T ) 0.27 20GeV< ΣE T <30GeV90GeV< ΣE T <100GeV

21. MISSING ENERGY - truth - full sim Missing ET parallel to lepton Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 Jet η < 2.4 ΔR (e-jet) > 0.7 MET>25GeV

22. Missing ET perpendicular to lepton MISSING ENERGY Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 Jet η < 2.4 ΔR (e-jet) > 0.7 MET>25GeV

23. W RECONSTRUCTION - truth - full sim Cuts: Ptele > 25GeV At least one track matched IsEM=0 Electron η < 2.4 Jet η < 2.4 ΔR (e-jet) > 0.7 MET>25GeV W transverse mass reconstructed from Missing ET and highest ET electron: TDR: ATLFAST

24. Rapidity Distributions of Ws There should be a charge asymmetry between W +, W - rapidity distributions. There should be a charge asymmetry between W +, W - rapidity distributions. Ws produced with heavy quarks should be produced preferentially at central rapidities. Ws produced with heavy quarks should be produced preferentially at central rapidities. Leptons from electron decays continue to display the charge asymmetry. Leptons from electron decays continue to display the charge asymmetry. The W + sample half as large (errors): only 25100 events (same type of sample, run # 005254) The W + sample half as large (errors): only 25100 events (same type of sample, run # 005254)

25. Rapidity Distributions of Ws: generator level - all - heavy quarks - light quarks (~2.5 times more light than heavy) Hmm!

26. Pseudorapidity Distributions of electrons: reconstructed - all - heavy quarks - light quarks

27. Conclusions: There is enough CSC data to start looking in detail at W →eν events. There is enough CSC data to start looking in detail at W →eν events. Missing energy doesn’t seem best corrected to match truth, but behaves as expected. Missing energy doesn’t seem best corrected to match truth, but behaves as expected. High-energy positrons probably consistent with hard brem or conversions. High-energy positrons probably consistent with hard brem or conversions. Ws produced from heavy quark slightly more central than light as expected. Not clear whether this effect can be seen in the decay products. Ws produced from heavy quark slightly more central than light as expected. Not clear whether this effect can be seen in the decay products. W - distribution requires further investigation. W - distribution requires further investigation. Much more data will be needed for strange asymmetry study in full simulation. Much more data will be needed for strange asymmetry study in full simulation.