what we measure
DESCRIPTION
Measurement of associated charm production in W final states at s=7TeV J. Alcaraz , I. Josa , J. Santaolalla (CIEMAT, Madrid) VHF working meeting. 1. What we measure. Our signal. - PowerPoint PPT PresentationTRANSCRIPT
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