1. Backgrounds inc. W+jets, same sign combinations, QCD, many with higher x- sects. Fast simulation background studies (cc, bb) near to completion. A Feasibility Study on Measuring a Strange Sea Momentum Asymmetry in the Proton – Laura Gilbert u, d distributions in the proton predicted to be almost flavour symmetric within pQCD, but not measured that way. Could be similar for s, s. Look for W + D * signal: Preliminary study performed on DC2 fast simulation. Currently working on completing with full simulation (DC3) but limited by amount of data currently available. Should find zero asymmetry in Monte-Carlo from accepted PDFs. Work out CL on limits of null hypothesis Much progress made on validation and analysis of DC3 W NLO samples oW selection: An isolated electron, |η| 25GeV, ETmiss > 25GeV oKπ + bachelor pion os→W-D*+; s→W+D*-: oSign of πB will be anticorrelated with sign of W. s(x) s(x) - s(x) Asymmetry predictions from meson cloud model. Note x<0.01 for Ws at LHC so tricky to measure?

2. Motivation: Quark Asymmetries in the Proton u, d distributions in the proton predicted to be almost flavour symmetric within pQCD. 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: 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.

3. MCM would seem to imply a strange momentum fraction asymmetry too. MCM would seem to imply a strange momentum fraction asymmetry too. 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. 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

4. 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.

5. Detecting a Strange Sea Asymmetry Signal: W+D* e-e- ν D *+ jet KπKπ c s g d d π+π+ D0D0 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.

6. Analysis Technique Select W candidate. Select W candidate. 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) Add soft (prompt) pion to reconstruct D *+. Add soft (prompt) pion to reconstruct D *+. Signal has opposite sign combinations of W, π B. Signal has opposite sign combinations of W, π B. D 0 flight length: cτ=123μm. D 0 flight length: cτ=123μm. 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

7. 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 - ~211k events, cross section 8.4nb, luminosity 33pb - 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 + )