Forward W + c, b-jet and Top Measurements with LHCb

Inclusive c and b-jet tagging algorithms have been developed to utilize the excellent secondary vertex reconstruction and resolution capabilities of the LHCb detector. The validation and performance of these tagging algorithms are reported using the full run 1 LHCb dataset at 7 and 8 TeV. Jet-tagging has been applied to muon+jet final states to measure both the W+c,b-jet charge asymmetries and the ratios of W+c,b-jet to W+jet and W+jet to Z+jet production. The forward top production cross-section is also measured using the muon+b-jet final. All results are found to be consistent with standard model predictions.Comment: 8 pages, 5 figures, presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 201

Z→ττZ \to \tau\tau and W→τντW \to \tau\nu_\tau Cross-Sections at the LHC

Measurements of the $Z \to \tau\tau$ and $W \to \tau\nu_\tau$ cross-sections at the LHC with data taken at $\sqrt{s} = 7$ TeV are reported for the ATLAS, CMS, and LHCb experiments. All results are found to agree with the Standard Model.Comment: 4 pages, 1 figur

Soft QCD Measurements at LHCb

Studies in the forward region of charged particle multiplicity and density, as well as energy flow, are presented. These measurements are performed using data from proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the LHCb detector. The results are compared to predictions from a variety of Monte Carlo event generators and are used to test underlying event and hadronization models as well as the performance of event generator tunes in the forward region.Comment: 6 pages, 10 figure

WW and ZZ Production in the Forward Region with LHCb

Results for $W$ and $Z$ boson production from $pp$ collisions at $\sqrt{s} = 7$ TeV in the LHCb experiment are presented. Due to LHCb's unique forward acceptance in pseudorapidity of $2.0 \leq \eta \leq 4.5$ these results are a test of the Standard Model in the forward region, and can be used to better constrain parton density functions in the low $x$ kinematic regime.Comment: 4 pages, 6 figures, PANIC1

Electroweak and Higgs Measurements Using Tau Final States with the LHCb Detector

Spin correlations for tau lepton decays are included in the Pythia 8 event generation software and the spin correlations for the decays of tau leptons produced from electroweak and Higgs bosons are calculated. Decays of the tau lepton using sophisticated resonance models are included in Pythia 8 for all channels with experimentally observed branching fractions greater than 0.04%. The mass distributions for the decay products of these channels are validated and the technical implementation of these decays is described. A measurement of the inclusive Z to di-tau cross-section using 1.0 inverse fb of data from pp collisions at sqrt(s) = 7 TeV collected with the LHCb detector is presented. Reconstructed final states containing two muons, a muon and an electron, a muon and a charged hadron, or an electron and a charged hadron are selected as candidates. The cross-section for Z bosons with a mass between 60 and 120 GeV decaying into tau leptons with pseudo-rapidities between 2.0 and 4.5 and transverse momenta greater than 20 GeV is measured to be 72.3 +- 3.5 +- 2.9 +- 2.5 pb. The first uncertainty is statistical, the second uncertainty is systematic, and the third is to due the integrated luminosity uncertainty. Limits on the production of neutral Higgs bosons decaying into tau lepton pairs with pseudo-rapidities between 2.0 and 4.5 are set at a 95% confidence level using the same LHCb dataset. A model independent upper limit on the production of neutral Higgs bosons decaying into tau leptons is set and ranges between 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs boson mass of 250 GeV. An upper limit on tan-beta in the CP-odd Higgs mass and tan-beta plane is set for the mh-max scenario of the minimal supersymmetric model and varies from 34 for a CP-odd Higgs boson mass of 90 GeV to 70 for a CP-odd Higgs boson mass of 140 GeV.Comment: PhD thesis, 255 page

Disentangling Heavy Flavor at Colliders

We propose two new analysis strategies for studying charm and beauty quarks at colliders. The first strategy is aimed at testing the kinematics of heavy-flavor quarks within an identified jet. Here, we use the SoftDrop jet-declustering algorithm to identify two subjets within a large-radius jet, using subjet flavor tagging to test the heavy-quark splitting functions of QCD. For subjets containing a $J / \psi$ or $\Upsilon$, this declustering technique can also help probe the mechanism for quarkonium production. The second strategy is aimed at isolating heavy-flavor production from gluon splitting. Here, we introduce a new FlavorCone algorithm, which smoothly interpolates from well-separated heavy-quark jets to the gluon-splitting regime where jets overlap. Because of its excellent ability to identify charm and beauty hadrons, the LHCb detector is ideally suited to pursue these strategies, though similar measurements should also be possible at ATLAS and CMS. Together, these SoftDrop and FlavorCone studies should clarify a number of aspects of heavy-flavor physics at colliders, and provide crucial information needed to improve heavy-flavor modeling in parton-shower generators.Comment: 22 pages, 14 figures; v2: updated figures with new z_tag condition, references and discussion adde

Inclusive Dark Photon Search at LHCb

We propose an inclusive search for dark photons $A'$ at the LHCb experiment based on both prompt and displaced di-muon resonances. Because the couplings of the dark photon are inherited from the photon via kinetic mixing, the dark photon $A' \to \mu^+ \mu^-$ rate can be directly inferred from the off-shell photon $\gamma^* \to \mu^+ \mu^-$ rate, making this a fully data-driven search. For Run 3 of the LHC, we estimate that LHCb will have sensitivity to large regions of the unexplored dark-photon parameter space, especially in the 210-520 MeV and 10-40 GeV mass ranges. This search leverages the excellent invariant-mass and vertex resolution of LHCb, along with its unique particle-identification and real-time data-analysis capabilities.Comment: 5+5 pages, 5 figures; v2: approximate version to appear in PRL, enlarged figure at en

Measurements of long-range near-side angular correlations in √sNN = 5 TeV proton-lead collisions in the forward region

Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of √sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.National Science Foundation (U.S.

Discovering True Muonium at LHCb

We study the potential of the LHCb experiment to discover, for the first time, the $\mu^+\mu^-$ true muonium bound state. We propose a search for the vector $1^3S_1$ state, $\mathcal{T\!M}$, which kinetically mixes with the photon and dominantly decays to $e^+e^-$. We demonstrate that a search for $\eta \to \gamma \mathcal{T\!M}$, $\mathcal{T\!M}\to e^+e^-$ in a displaced vertex can exceed a significance of 5 standard deviations assuming statistical uncertainties. We present two possible searches: an inclusive search for the $e^+e^-$ vertex, and an exclusive search which requires an additional photon and a reconstruction of the $\eta$ mass.Comment: 12 pages, 5 figures; v2: edits from comments and review, matched to PRD versio