VHF working meeting, 4 Oct 2011 1

   Measurement of Measurement of associated charm associated charm

production in W final production in W final states at states at s=7TeV s=7TeV

J. Alcaraz J. Alcaraz, I. Josa, , I. Josa, J. SantaolallaJ. Santaolalla(CIEMAT, Madrid)(CIEMAT, Madrid)

VHF working meetingVHF working meeting

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What we measureWhat we measure

In “W+c”, the W production proceeds predominantly via “gluon + s-quark”: g + s cc + s c + W”.

Direct access to s quark PDF

Our signal1

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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 d

What we measureWhat we measure Other W+c contributions

2

Cabibbo suppresed d is valence quark

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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

What we measureWhat we measure Other W+c contributions

2

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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

Data sampleData sample Our data3

Will work since W+b sample is small enough

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We use MADGRAPH as our reference (with 2010 data we used POWHEG instead)

List of MC samples used in the analysis:

MC samplesMC samples Our MC4

2011 PileUp conditions

New samples

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How we measure itHow we measure it 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)

Selection1

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How we measure itHow we measure it W inclusive selection Jet Seleccion

Selection1

Dominant backgrounds

Largely Reduced withNew cuts

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How we measure itHow we measure it W inclusive selection Jet Seleccion

Selection1

Dominant backgrounds

Largely Reduced withNew cuts

We finally plot the b-discriminator of the most significant jet

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Simple Secondary Vertex High Efficiency discriminator DSSVHE = log(1+decayLengthSignificance)

SENSITIVITY TO SIGNAL AND BACKGROUNDS

WW++ WW--

How we measure itHow we measure it c-tag discriminator

2Same procedure as in 2010

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Negative vertices help to constrain the light-quark contribution below the charm signal peak

Cross checks with TCHE discriminant (see later)

WW++WW--

How we measure itHow we measure it Fit the DSSVHE

distribution

3

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ResultsResults The fit1

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

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WW++WW--

ResultsResults Output of the fit2

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ResultsResults Ratios2

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)

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Systematics for charm charge ratioSystematics for charm charge ratio

Similar procedure to 2010 analysis

In progress

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Systematics for charm ratioSystematics for charm ratio

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Other plotsOther plots

W boson transverse mass

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Other plotsOther plots

Pt of jet # jets

Better agreement than in2010 analysis (POWHEG)

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Other plotsOther plots

Jet charged multiplicity

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Other plotsOther plots

Jet eta

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Other plotsOther plots

# of tracks per vertex

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Other discriminantsOther discriminants

TCHE discriminator

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Other discriminantsOther discriminants

SV high purity

Largely reduces light contribution. However, it also reduces signal contribution. Light contribution is in principle under control.

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To do list and important remarks for 2011 dataTo 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.

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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.

CONCLUSIONSCONCLUSIONS