What we measure

1. Measurement of associated charm production in W final states at s=7TeV J. Alcaraz, I. Josa, J. Santaolalla(CIEMAT, Madrid)VHF working meeting

2. 1 What we measure Our signal • In “W+c”, the W production proceeds predominantly via “gluon + s-quark”: g + s  cc + s  c + W”. Direct access to s quark PDF

3. 2 What we measure Other W+c contributions • Valence quark contribution for W-: g + d  cc + d  W- + c . • The anti-strange contribution of this process is even more suppressed since d-bar is not a valence quark. d is valence quark Cabibbosuppresed d d

4. 2 What we measure Other W+c contributions • Gluon splitting of the type: u + d  W+ + g  W+ + cc bar. Two c quarks in the final state. It will be part of our signal

5. 3 Data sample Our data • We use 2.2 fb-1 of LHC 2011 data • runA and runB, in the next step we will use 2 fb-1 of runA data • W  decay channel (no plans of using e data) • Data: • Selection of W bosons: follow the standard VBTF criteria to select a pure W sample • Enhancement of c jets: b-tagging discriminator Will work since W+b sample is small enough

6. 4 MC samples Our MC • We use MADGRAPH as our reference (with 2010 data we used POWHEG instead) • List of MC samples used in the analysis: 2011 PileUp conditions New samples

7. 1 How we measure it Selection • W  inclusive selection (same as in 2010) • Jet Seleccion, same as in 2010 except • SV mass lower than 2 GeV • Leptonic W jet systems’s mass lower than 300 GeV • Less than 2 jets above 40 GeV to reduce top backgrounds (less than 3 jets in 2010 analysis)

8. 1 How we measure it Selection • W  inclusive selection • Jet Seleccion Dominant backgrounds Largely Reduced with New cuts

9. 1 How we measure it Selection • W  inclusive selection • Jet Seleccion Dominant backgrounds Largely Reduced with New cuts • We finally plot the b-discriminator of the most significant jet

10. 2 How we measure it c-tag discriminator Same procedure as in 2010 W+ W- • Simple Secondary Vertex High Efficiency discriminator • DSSVHE = log(1+decayLengthSignificance) • SENSITIVITY TO SIGNAL AND BACKGROUNDS

11. 3 How we measure it Fit the DSSVHE distribution W+ W- • Negative vertices help to constrain the light-quark contribution below the charm signal peak • Cross checks with TCHE discriminant (see later)

12. 1 Results The fit • Fit to 3 components: light quarks, signal, top • Shape taken from MC • Different shape of contributions allows to have a good discriminant power. Ttbar and s-top have similar shape 'harder' than W+charm

13. 2 Results Output of the fit W+ W-

14. 2 Results Ratios • The efficiency includes the tagging efficiency, but also implicit corrections that bring the ratio to the MCFM expected definition at the parton level (acceptance effects, hadronization effects)

15. Systematics for charm charge ratio Similar procedure to 2010 analysis In progress

16. Systematics for charm ratio

17. Other plots W boson transverse mass

18. Other plots Pt of jet # jets Better agreement than in 2010 analysis (POWHEG)

19. Other plots Jet charged multiplicity

20. Other plots Jet eta

21. Other plots # of tracks per vertex

22. Other discriminants TCHE discriminator

23. Other discriminants SV high purity Largely reduces light contribution. However, it also reduces signal contribution. Light contribution is in principle under control.

24. To do list and important remarks for 2011 data • The use of MADGRAPH instead of POWHEG allows us to set a more restrictive cut in the #jets • We reduce top rel. backgrounds (not dominant now) • WplusJets MC sample seems to be wrongly normalized. A 10% increase in MC normalization was necessary to reach better agreement. • MC statistics start to be insufficient (same order as data). • W+1jet, W+2 jet… instead of W+jets • We are planning to change the way some systematics are assigned (the most critical ones) • In this presentation, 2.2 fb-1 of data were used. In the future we plan to restrict it to the 2 fb-1 of runA • We plan to use the muon charge information to better compute the efficiency.

25. CONCLUSIONS • We took a first look to 2011 data. Preliminary result were shown. • Everything worked out-of-the-box (except MC normalization of signal sample) • Big amount of data allow us to: • envisage new methods to improve our confidence on the analysis and to decrease the systematic uncertainties. • enter a systematic dominated era. • An analysis note (AN-11-381) is being redacted.