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2016-03-29
10:51
$B0 \to Ds^{(*)}Ds^{(*)}$ and outlook of $B0 \to D^{(*)}D$ at LHCb
Reference: Poster-2016-531
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Belloli, Nicoletta

The measurement of the inclusive branching fraction of $B0s \to Ds^{(*)+} Ds^{(*)-}$ decay together with its contribution to the determination of $\Delta \Gamma{s}/ \Gamma {s}$ are presented. The branching fraction value is compatible with results from previous experiments, improving the world average. The $B0 \to D^+D^-$ and $B0 \to D^*D^{(*)}$ decays are used to measure the parameters associated with $CP$ Violation in those channels; while the analysis associated to the second channel is at an initial stage the first one is almost concluded, the values obtained for the sensitivity on the $CP$ observables show that LHCb can rival the results obtained by previous experiments.

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Conference - LHC students poster session
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2016-03-29
10:13
Prospects for |V$_{ub}$| measurements at LHCb
Reference: Poster-2016-530
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Stefkova, Slavomira

Precise measurements of the quark coupling strength, $|V_{ub}|$, the least well known CKM element, allow a strong test of the unitarity of the CKM matrix. Previous measurements using exclusive and inclusive methods have resulted in values of $|V_{ub}|$ which are 3$\sigma$ apart. The first measurement of $|V_{ub}|$ at LHCb confirmed this tension using the $\Lambda^{0}_{b} \rightarrow p \mu^{-} \overline{\nu}$ decay. This strengthens the motivation to measure this quantity using different channels, one of them being purely leptonic decay $B^{+} \rightarrow \mu^{+} \mu^{-} \mu^{+} \nu$, which benefits from LHCb's very good muon identification ability. This mode had never been observed before. With recent lattice QCD calculations, LHCb can also constrain $|V_{ub}|$ using the $B^{0}_s \rightarrow K^{+} \mu^{-} \overline{\nu}$ decay where the theoretical uncertainty is significantly smaller.

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Conference - LHC students poster session
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2016-03-22
13:59
LHCb measurements of $J/\psi$, and open charm cross-sections at $\sqrt{s}=13$TeV
Reference: Poster-2016-529
Created: 2016. -1 p
Creator(s): Muller, Dominik; Komarov, Ilya

Prompt $J/\psi$, $J/\psi$ from $b$-hadrons and prompt charm meson production is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$TeV at the LHCb detector with first application of a novel data streaming technique (Turbo steam). Cross-section measurements are performed as a function of the transverse momentum $p_T$ and the rapidity $y$ of the mesons in the region $p_T<15$GeV$/c$ and $2.0<y<4.5$. Obtained results were compared with expectations from QCD calculations. The ratios of the cross-sections with respect to Run 1 measurements are also determined. Comparison of the measured ratios values with theoretical predictions provided a new sensitive test of the QCD calculations.

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LHCb Poster
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2016-03-18
15:46
Soft QCD and pA physics, with a focus on the ridge at LHCb
Reference: Poster-2016-528
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Dreimanis, Karlis

The LHCb experiment is a forward spectrometer originally designed for study of b and c hadron decays. However, it can be used in a much wider spectrum of physics analyses. The poster presented here highlights a few studies from the extensive range of soft QCD and heavy-ion physics analyses performed at the LHCb. A particular emphasis is placed on the observation of the two-particle angular correlations, so-called ridge effect, in the forward region. The results presented here serve as one of numerous examples of LHCb being a proven multi-purpose detector in the forward region.

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LCHb poster
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2016-03-16
14:23
LHCb New algorithms for Flavour Tagging at the LHCb experiment
Reference: Poster-2016-527
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Fazzini, Davide

The Flavour Tagging technique allows to identify the B initial flavour, required in the measurements of flavour oscillations and time-dependent CP asymmetries in neutral B meson systems. The identification performances at LHCb are further enhanced thanks to the contribution of new algorithms.

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Conference 125th LHCC Meeting
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2016-03-09
17:06
Measurement of the ${B^0_s \to \phi \phi}$ branching fraction and angular analysis of ${B^0_{(s)} \to \phi \pi^{+}\pi^{-}}$.
Reference: Poster-2016-526
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Morris, Adam

Using 3~fb$^{-1}$ of $pp$ collisions collected by the LHCb detector at $\sqrt{s} = 7$ and 8~TeV, the $B_s^0 \to \phi \phi$ branching fraction is measured to be \[ \mathcal{B}(B^0_s \to \phi \phi) = \left[ 1.84 \pm 0.05 (\mathrm{stat}) \pm 0.07 (\mathrm{syst}) \pm 0.11 (f_s/f_d) \pm 0.12 (\mathrm{norm}) \right] \times 10^{-5}. \] A search for the decay $B^0 \to \phi \phi$ is also made. No signal is observed, and an upper limit on the branching fraction is set as \[ \mathcal{B}(B^0 \to \phi \phi) < 2.8 \times 10^{-8}. \] The rare decays $B_s^0 \to \phi \pi^+ \pi^-$ and $B^0 \to \phi \pi^+ \pi^-$ are observed for the first time. The branching fractions in the range $400<m(\pi^+ \pi^-)<1600$~MeV/$c^{2}$ are measured to be \[ \mathcal{B}(B_s^0 \to \phi \pi^+ \pi^-) = \left[ 3.37 \pm 0.20 (\mathrm{stat}) \pm 0.16 (\mathrm{syst}) \pm 0.34 (\mathrm{norm}) \right] \times 10^{-6} \] \[\mathcal{B}(B^0 \to \phi \pi^+ \pi^-) = \left[ 1.58 \pm 0.18 (\mathrm{stat}) \pm 0.35 (\mathrm{syst}) \pm 0.13 (\mathrm{norm}) \right] \times 10^{-7}. \] An amplitude fit is performed to extract the following exclusive branching fractions: \[ \mathcal{B}(B_s^0 \to \phi f_0(980) \to \phi \pi^+ \pi^-) = \left[ 1.12 \pm 0.16 (\mathrm{stat}) ^{+0.07}_{-0.14} (\mathrm{syst}) \pm 0.11 (\mathrm{norm}) \right] \times 10^{-6} \] \[ \mathcal{B}(B_s^0 \to \phi f_2(1270) \to \phi \pi^+ \pi^-) = \left[ 0.55 \pm 0.10 (\mathrm{stat}) ^{+0.18}_{-0.05} (\mathrm{syst}) \pm 0.06 (\mathrm{norm}) \right] \times 10^{-6}. \] Evidence is found for the decay $B_s^0 \to \phi \rho^0$. An upper limit on the branching fraction is set as \[ \mathcal{B}(B_s^0 \to \phi \rho^0) < 4 \times 10^{-7}. \]

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LHCb poster
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2016-03-08
15:35
Jet Flavour Tagging and Top Production at LHCb
Reference: Poster-2016-525
Created: 2016. -1 p
Creator(s): Khurewathanakul, Chitsanu

Top quark production in the forward region in proton-proton collisions is observed for the first time. The $W+b$ final state with $W\rightarrow \mu\nu$ is reconstructed using muons with a transverse momentum, $p_{\rm T}$, larger than 25 GeV in the pseudorapidity range $2.0 < \eta < 4.5$. The $b$ jets are required to have $50 < p_{\rm T} < 100$ GeV and $2.2 < \eta < 4.2$, while the transverse component of the sum of the muon and $b{-}$jet momenta must satisfy $p_{\rm T} > 20$ GeV. The algorithm was developed to select $b{-}$ and $c{-}$quark jets. The efficiency for identification a $b(c)$ jet is about 65% (25%) with a probability for misidentifying a light-parton jet of 0.3% for jets with $p_{\rm T} > 20$ GeV. The results are based on data corresponding to integrated luminosity of 1.0 and 2.0 fb$^{-1}$ collected at the center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are \begin{align*} \sigma\text{(top)[7 TeV]} \;=\; 239 \pm 53 \;\text{(stat)} \pm 33 \;\text{(syst)} \pm 24 \;\text{(theory) fb},\\ \sigma\text{(top)[8 TeV]} \;=\; 289 \pm 43 \;\text{(stat)} \pm 40 \;\text{(syst)} \pm 29 \;\text{(theory) fb}. \end{align*} These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order Standard Model predictions.

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2016-03-08
15:18
R(D*) and other tauonic decays at LHCb
Reference: Poster-2016-524
Created: 2016. -1 p
Creator(s): Betti, Federico

The measurement of the branching fraction ratio $\mathcal{R}(D^{*}) \equiv \mathcal{B}(\overline{B}^0 \to D^{*+}\tau^{-}\overline{\nu}_{\tau})/\mathcal{B}(\overline{B}^0 \to D^{*+}\mu^{-}\overline{\nu}_{\mu})$ is performed using a sample of proton-proton collision data corresponding to 3.0 $\text{fb}^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The chosen tau decay mode is $\tau^{-} \to \mu^{-}\overline{\nu}_{\mu}\nu_{\tau}$. A multidimensional fit to kinematic distributions of the candidate $\overline{B}^0$ decays gives $\mathcal{R}(D^{*}) = 0.336 \pm 0.027(stat) \pm 0.030 (syst)$. This result, which is the first measurement of this quantity at a hadron collider, is $2.1$ standard deviations larger than the value expected from lepton universality in the Standard Model. An ongoing analysis aiming at measuring the $\mathcal{B}(\overline{B}^0 \to D^{*+}\tau^{-}\overline{\nu}_{\tau})$ branching fraction through three-prong tau decays is expected to give competitive results with the published one.

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2016-03-04
13:55
LHCb - Measurement of the branching fraction ratio $\cal{B}$ $(B_{c}^{+} \to \psi(2S)\pi^+)$ / $\cal{B}$ $(B_{c}^{+} \to {J}\psi\pi^+)$ at LHCb
Reference: Poster-2016-523
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): An, Liupan

Using the $pp$ collision data collected by LHCb at center-of-mass energies $\sqrt{s} \, = 7 \, {\rm TeV} \,$ and $8 \, {\rm TeV} \,$, corresponding to an integrated luminosity of $3 \, \mathrm{fb}^{-1} \,$, the ratio of the branching fraction of the $B_{c}^{+} \to \psi(2S)\pi^+$ decay relative to that of the $B_{c}^{+} \to J/\psi\pi^+$ decay is measured to be ${0.268 \pm 0.032\mathrm{\,(stat)} \pm 0.007\mathrm{\,(syst)} \pm 0.006\,(\mathrm{BF}) }$. The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainties on the branching fractions of the $J/\psi \to \mu^{+}\mu^{-}$ and $\psi(2S) \to \mu^{+}\mu^{-}$ decays. To enhance the signal significance with limited $B_{c}^{+}$ statistics, the boosted decision tree selection is used to separate the signal and background effectively. The systematic uncertainties are discussed extensively. This measurement is consistent with the previous LHCb result, and the statistical uncertainty is halved.

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LHCb poster
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2016-03-04
13:27
LHCb - Novel Muon Identification Algorithms for the LHCb Upgrade
Reference: Poster-2016-522
Keywords:  LHCb
Created: 2016. -1 p
Creator(s): Cogoni, Violetta

The present LHCb Muon Identification procedure was optimised to guarantee high muon detection efficiency at the istantaneous luminosity $\mathcal{L}$ of $2\cdot10^{32}$~cm$^{-2}$~s$^{-1}$. In the current data taking conditions, the luminosity is higher than foreseen and the low energy background contribution to the visible rate in the muon system is larger than expected. A worse situation is expected for Run III when LHCb will operate at $\mathcal{L} = 2\cdot10^{33}$~cm$^{-2}$~s$^{-1}$ causing the high particle fluxes to deteriorate the muon detection efficiency, because of the increased dead time of the electronics, and in particular to worsen the muon identification capabilities, due to the increased contribution of the background, with deleterious consequences especially for the analyses requiring high purity signal. In this context, possible new algorithms for the muon identification will be illustrated. In particular, the performance on combinatorial background rejection will be shown, together with the extrapolations in upgrade conditions.

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LHCb poster
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