# Measurement of the $D_s^+ - D_s^-$ production asymmetry in 7 TeV pp collisions

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## Abstract

Heavy quark production in 7 TeV centre-of-mass energy pp collisions at the LHC is not necessarily flavour symmetric. The production asymmetry, A_P, between Ds+ and Ds- mesons is studied using the \phi\pi(+/-) decay mode in a data sample of 1.0/fb collected with the LHCb detector. The difference between \pi+ and \pi- detection efficiencies is determined using the ratios of fully reconstructed to partially reconstructed D*(+/-) decays. The overall production asymmetry in the Ds rapidity region 2.0 to 4.5 with transverse momentum larger than 2 GeV is measured to be A_P=(-0.33 +/- 0.22 +/- 0.10)%. This result can constrain models of heavy flavour production.

## Figures and captions

 Production of $c\overline{c}$ quark pairs in a $pp$ collision via gluons. Ds-thy.pdf [58 KiB] HiDef png [264 KiB] Thumbnail [59 KiB] *.C file Distributions of mass differences in partial reconstruction for (a) RS $m(\pi ^+ _{s} K ^- \pi ^+\pi ^- )-m( K ^- \pi ^+\pi ^- )$ and (b) WS $m(\pi ^+ _{s} K ^+ \pi ^+\pi ^- )-m( K ^+ \pi ^+\pi ^- )$ candidates, for magnet up data. The (green) dotted line shows the signal, the (red) dashed line the background, and the (blue) solid line the total. The fit shapes are defined in Appendix A. mag_0_[..].pdf [87 KiB] HiDef png [320 KiB] Thumbnail [61 KiB] *.C file Distributions of the mass difference $\Delta m_{\text{full}}$ for (a) RS and (b) WS events using magnet up data. The (green) dotted line shows the signal, the (red) dashed line the background, and the (blue) solid line the total. The fit shapes are defined in Appendix B. mag_0_[..].pdf [67 KiB] HiDef png [223 KiB] Thumbnail [47 KiB] *.C file Distribution of fully reconstructed signal candidates for magnet up data as a function of pion (a) $p$ and (b) $p_{\rm T}$ . Contro[..].pdf [115 KiB] HiDef png [184 KiB] Thumbnail [40 KiB] *.C file Relative detection efficiency in bins of detected pion momentum: (red) circles represent data taken with magnet polarity up and (blue) squares show data taken with magnet polarity down. Only statistical errors are shown. relati[..].pdf [39 KiB] HiDef png [142 KiB] Thumbnail [45 KiB] *.C file Relative efficiency averaged over magnet up and magnet down samples versus pion $p$ and $p_{T}$. p_slic[..].pdf [56 KiB] HiDef png [96 KiB] Thumbnail [27 KiB] *.C file Azimuthal angle distribution of $\epsilon(\pi^+)/\epsilon(\pi^-)$ for magnet up data (red circles) and magnet down data (blue squares), and their average (black diamonds) for (a) pion momentum $220$ GeV. effici[..].pdf [43 KiB] HiDef png [168 KiB] Thumbnail [46 KiB] *.C file Invariant mass distributions for (a) $K ^+ K ^- \pi ^+$ and (b) $K ^- K ^+ \pi ^-$ candidates, when $m(K^+K^-)$ is within $\pm$20 MeV of the $\phi$ mass, for the dataset taken with magnet polarity down. The shaded areas represent signal, the dashed line the background and the solid curve the total. Ds_mas[..].pdf [46 KiB] HiDef png [388 KiB] Thumbnail [69 KiB] *.C file (a) $D ^{\pm}_ s$ rapidity distribution (b) $D ^{\pm}_ s$ $p_{T}$ distribution for background subtracted magnet up data. The statistical uncertainty on the number of events in each bin is smaller than the line thickness. Ds_Pt_[..].pdf [71 KiB] HiDef png [123 KiB] Thumbnail [29 KiB] *.C file Observed production asymmetry $A_{\rm P}$ as a function of (a) y, and (b) $p_{\rm T}$ . The errors shown are statistical only. Ap_total.pdf [77 KiB] HiDef png [115 KiB] Thumbnail [30 KiB] *.C file Animated gif made out of all figures. PAPER-2012-009.gif Thumbnail

## Tables and captions

 Event yields for partial and full reconstruction. Table_1.pdf [52 KiB] HiDef png [114 KiB] Thumbnail [17 KiB] tex code Fitted numbers of $D_s^{\pm}$ events for both magnet up and down data. Table_2.pdf [49 KiB] HiDef png [73 KiB] Thumbnail [11 KiB] tex code $A_{\rm P}$ (%) shown as a function of both $y$ and $p_{\rm T}$ . Table_3.pdf [34 KiB] HiDef png [59 KiB] Thumbnail [11 KiB] tex code

Created on 15 June 2019.Citation count from INSPIRE on 15 June 2019.