2011 QCD and High Energy Interactions - Rencontres de Moriond ...

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Figure 3: The invariant mass distribution for B + c → J/ψ(µ + µ − ) π + (left) and B + → J/ψ K + (right) candidates,
with the fit results superimposed. The blue solid line represents the total fit function, the red dashed line the
signal contribution, the green dashed line the combinatorial background contribution. For the B + → J/ψ K +
mass distribution, the red solid line represents the background from Cabibbo-suppressed B + → J/ψ π + decays.
The analysis has been performed in the fiducial region B pT > 4 GeV/c and B pseudo-rapidity
η ∈ [2.5;4.5] using 32.5 pb−1 of integrated luminosity. The B + c and B+ selection criteria have
been chosen to be as similar as possible to reduce the systematic uncertainties on Rc +. The
number of B + c and B + have been extracted from a fit to the J/ψ π and J/ψ K invariant mass
distributions (see Figure 3). In both cases a Gaussian shape has been used for the signal and
an exponential shape has been used for the combinatorial background. The non-combinatorial
background from the Cabibbo suppressed decay B + → J/ψ π + has also been taken into account.
Since the B + c production spectrum and lifetime are poorly known, the efficiency has been evaluated
from Monte Carlo simulation in bins of B pT and η to reduce the dependence on theoretical
models. The measured Rc + in the fiducial region is Rc + = (2.2 ± 0.8 ± 0.2)% where the first
uncertainty is statistical and the second is systematic. A model dependant approach obtained
with the B + c generator BCVEGPY 10 (i.e. a complete LO α 4 s
PDF gives R model-dependant
c +
6 Conclusions
= (1.4 ± 0.4 ± 0.1)%.
calculation) and the CTEQ6LL 11
With the 2010 data the differential production cross-sections of J/ψ and Υ(1S) and the production
cross-section of double J/ψ and B + c (relative to B + ) have been measured with the LHCb
detector. The results are in good agreement with the theoretical calculations and the observation
of the B + c looks very promising for future measurements.
References
1. The LHCb Collaboration, A.A. Alves et al, JINST 3, S08005 (2008).
2. The LHCb Collaboration, R. Aaij et al, arXiv:1103.0423v1 [hep-ex].
3. The LHCb Collaboration, R. Aaij et al, Phys. Lett. B 694, 209 (2010).
4. The LHCb Collaboration, R. Aaij et al, CERN-LHCb-CONF-2011-009.
5. A.V. Berezhnoy et al, arXiv:1101.5881v1 [hep-ph].
6. The LHCb Collaboration, R. Aaij et al, CERN-LHCb-CONF-2011-016.
7. K. Wang, Y.Q. Ma, K.T. Chao, private communication.
8. The CMS Collaboration, arXiv:1012.5545v1.
9. The LHCb Collaboration, R. Aaij et al, CERN-LHCb-CONF-2011-017.
10. Chao-Hsi Chang, Jian-Xiong Wang, Xing-Gang Wu, Comput.Phys.Commun. 175, 624
(2006).
11. J. Pumplin et al, JHEP 0207, 012 (2002).