Measurement of associated charm production in W final states at sqrt(s) = 7 TeV - INSPIRE

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Measurement of associated charm production in W final states at sqrt(s) = 7 TeV

CMS

Collaboration

Mar 10, 2013

36 pages

Report number:

CMS-PAS-SMP-12-002

Experiments:

CERN-LHC-CMS

View in:

CERN Document Server

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Abstract:

We present a detailed study of the associated production of a W boson and one c-quark jet in pp collisions at a center-of-mass energy of 7 TeV. The analysis has been conducted with a data sample corresponding to a total integrated luminosity of

5~\textrm{fb}^{-1}

, collected by the CMS detector at the LHC. Candidates of W bosons are identified through their decay into a charged lepton (muon or electron) and a neutrino, in the pseudorapidity range

|\eta^{\ell}|<2.1

. The W + c measurements are performed for charm jets in the kinematic region

p_T^{jet}>25

GeV,

|\eta^{jet}|<2.5

and for two different thresholds of transverse momentum of the lepton from the W decay. Using hadronic and inclusive semileptonic decays of charm hadrons, we measure the following total cross sections:

\sigma(\mathrm{pp} \rightarrow \mathrm{W+c + X}) \times {\cal B}(\mathrm{W} \rightarrow \ell\nu ) = 107.7 \pm 3.3~(\rm {stat.}) \pm 6.9~(\rm {syst.})~\textrm{pb}~(p_T^\ell>25 ~\textrm{GeV})

and

\sigma(\mathrm{pp} \rightarrow \mathrm{W+c + X}) \times {\cal B}(\mathrm{W} \rightarrow \ell\nu ) = \phantom{0}84.1 \pm 2.0~(\rm {stat.}) \pm 4.9~(\rm {syst.})~\textrm{pb}~(p_T^\ell>35 ~\textrm{GeV}),

and the cross section ratios:

\frac{\sigma(\mathrm{pp} \rightarrow \mathrm{W^+ + \bar c +X})}{\sigma(\mathrm{pp} \rightarrow \mathrm{W^- + c + X})} = 0.954 \pm 0.025~(\rm {stat.}) \pm 0.001~(\rm {syst.}) ~ (p_T^\ell>25 ~\textrm{GeV})

and

\frac{\sigma(\mathrm{pp} \rightarrow \mathrm{W^+ + \bar c +X})}{\sigma(\mathrm{pp} \rightarrow \mathrm{W^- + c + X})} = 0.939 \pm 0.019~(\rm {stat.}) \pm 0.005~(\rm {syst.}) ~ (p_T^\ell>35 ~\textrm{GeV}).

These cross sections and cross section ratios provide important information on the strange and anti-strange quark parton density functions of the proton at the electroweak scale. Cross sections and cross section ratios are also measured differentially with respect the pseudorapidity of the lepton from the W decay. Results are compared with theoretical predictions at next-to-leading order using different parton distribution function sets. Whereas current theoretical predictions are in agreement with the measured

\mathrm{W} + \mathrm{c}

cross sections at the 10

\%

level, an analysis of data distributions sensitive to

\mathrm{W} + \mathrm{c\bar c}

and

\mathrm{W} + \mathrm{b\bar b}

backgrounds reveals large differences between Monte Carlo generators. In particular, simulations based on PYTHIA show a large deficit when compared with experimental observations in some specific kinematic configurations.

Note:

CMS Physics Analysis Summary - preliminary results

Data
p p: interaction
W: hadroproduction
W: leptonic decay
charm: associated production
charmed particle: decay modes
channel cross section: branching ratio: measured
cross section: ratio
p: strangeness
quark: distribution function

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