Engineering topics

Buchanan, E.

Publications and source records attributed to Buchanan, E..

At least 55 records · Page 3

DOE OSTI2017

Measurement of the $J/ψ$ pair production cross-section in pp collisions at $\sqrt{s}=13$ TeV

The production cross-section of $J/ψ$ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 279 ±11 pb -1 . The measurement is performed for $J/ψ$ mesons with a transverse momentum of less than 10 GeV/$c$ in the rapidity range 2.0 < $y$ < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/ψ$ pair are measured and compared to theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Observation of η c ( 2 S ) → p p ¯ and search for X ( 3872 ) → p p ¯ decays

The first observation of the decay η c ( 2 S ) → p p ¯ is reported using proton–proton collision data corre-sponding to an integrated luminosity of 3.0fb –1 recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The η c (2S) resonance is produced in the decay B + →[$c\bar{c}$]K + . The product of branching fractions normalised to that for the J/ψ intermediate state, $\mathscr{R}_{η_{c}(2S)}$, is measured to be $\mathscr{R}_{η_{c}(2S)}$ ≡ $\frac{\mathscr{B}(B^{+}→η_{c}(2S)K^{+})×\mathscr{B}(η_{c}(2S)→ p\overline{p})}{\mathscr{B}(B^{+}→ J/ψ K^{+})×\mathscr{B}(J/ψ →p\overline{p})}$ = (1.58±0.33±0.09)×10 –2 , where the first uncertainty is statistical and the second systematic. No signals for the decays B + → X(3872)(→$p\overline{p}$)K + and B + →ψ(3770)(→$p\overline{p}$)K + are seen, and the 95% confidence level upper limits on their relative branching ratios are found to be $\mathscr{R}_{X(3872)}$ < 0.25 ×10 –2 and $\mathscr{R}_{ψ(3770)}$ < 0.10. In addition, the mass differences between the η c (1S)and the J/ψ states, between the η c (2S)and the ψ(2S)states, and the natural width of the η c (1S)are measured as M J/ψ – M ηc(1S) = 110.2±0.5 ±0.9 MeV, M ψ(2S) – M ηc(2S) = 52.5±1.7±0.6 MeV, Γ ηc(1S) = 34.0±1.9±1.3MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the B s 0 → μ + μ - Branching Fraction and Effective Lifetime and Search for B 0 → μ + μ - Decays

A search for the rare decays $B^0_s$→$μ$ + $μ$ - and B 0 →$μ$ + $μ$ - is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb -1 . An excess of $B^0_s$→$μ$ + $μ$ - decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be $B$($μ$ + $μ$ - )=(3.0 ± $0.6^{+0.3}_{-0.2}$) × 10 -9 , where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s$→$μ$ + $μ$ - effective lifetime, τ($B^0_s$→($μ$ + $μ$ - ) = 2.04 ± 0.44 ± 0.05 ps, is reported. No significant excess of B 0 →($μ$ + $μ$ - decays is found, and a 95% confidence level upper limit, $B$(B 0 →($μ$ + $μ$ - ) < 3.4 × 10 -10 , is determined. All results are in agreement with the standard model expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Study of J / ψ Production in Jets

The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z$($J/ψ$)≡$p$ T ($J/ψ$)/$p$ T (jet), is measured using jets with $p$ T (jet) > 20 GeV in the pseudorapidity range 2.5 < $η$(jet) < 4.0. The observed $z$($J/ψ$) distribution for $J/ψ$ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the $p$ T fraction carried by prompt $J/ψ$ mesons in jets at any experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Study of the $D^0p$ amplitude in $Λ_b^0$ → $D^0pπ^-$ decays

An amplitude analysis of the decay $Λ_b^0$ → $D^0pπ^-$ is performed in the part of the phase space containing resonances in the $D^0p$ channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb -1 of $pp$ collisions recorded by the LHCb experiment. The spectrum of excited $Λ^+_c$ states that decay into $D^0p$ is studied. The masses, widths and quantum numbers of the $Λ_c$(2880) + and $Λ_c$(2940) + resonances are measured. The constraints on the spin and parity for the $Λ_c$(2940) + state are obtained for the first time. A near-threshold enhancement in the $D^0p$ amplitude is investigated and found to be consistent with a new resonance, denoted the $Λ_c$(2860) + , of spin 3/2 and positive parity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Observation of Five New Narrow Ω c 0 States Decaying to Ξ c + K -

The $\Xi{^+_c}$$K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb -1 , collected by the LHCb experiment. The $\Xi{^+_c}$ is reconstructed in the decay mode $pK^-$$π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c$(3000)$^0$, $Ω_c$(3050)$^0$, $Ω_c$(3066)$^0$, $Ω_c$(3090)$^0$, and $Ω_c$(3119)$^0$. Measurements of their masses and widths are reported.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Evidence for the two-body charmless baryonic decay $$ {B}^{+}\to p\overline{\varLambda} $$

A search for the rare two-body charmless baryonic decay B + → p$-\atop{Λ}$ is performed with pp collision data, corresponding to an integrated luminosity of 3 fb -1 , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of B + →p$-\atop{Λ}$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the B + →K S 0 π + decay for normalisation, B(B + →p$-\atop{Λ}$=2.4$+1.0\atop{0.8}$±0.3 x 10 -7 )where the first uncertainty is statistical and the second systematic.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for long-lived scalar particles in B + → K + χ ( μ + μ – ) decays

A search for a long-lived scalar particle χ is performed, looking for the decay B + →K + χ with χ→μ + μ – in pp collision data corresponding to an integrated luminosity of 3 fb –1 , collected by the LHCb experiment at center-of-mass energies of √s = 7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250 < m(χ) < 4700 MeV/c 2 and lifetime 0.1 < τ(χ) < 1000 ps. Upper limits on the branching fraction B(B + →K + χ(μ + μ – )) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2 × 10 –10 and 10 –7 . These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for massive long-lived particles decaying semileptonically in the LHCb detector

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2 fb -1 , respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80 GeV/c 2 and lifetimes from 5 to 100ps are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23–198 GeV/c 2 range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurements of charm mixing and C P violation using D 0 → K ± π ∓ decays

Measurements of charm mixing and CP violation parameters from the decay-time-dependent ratio of D 0 →K + π – to D 0 →K – π + decay rates and the charge-conjugate ratio are reported. The analysis uses B¯→D* + μ – X, and charge-conjugate decays, where D* + →D 0 π + , and D 0 →K ∓ π ± . The pp collision data are recorded by the LHCb experiment at center-of-mass energies √s = 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb –1 . The data are analyzed under three hypotheses: (i) mixing assuming CP symmetry, (ii) mixing assuming no direct CP violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct CP violation and/or CP violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of D 0 →Kπ decays from a disjoint set of D* + candidates produced directly in pp collisions. In all cases, the data are consistent with the hypothesis of CP symmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the B ± production asymmetry and the C P asymmetry in B ± → J / ψ K ± decays

The B ± meson production asymmetry in pp collisions is measured using B + →¯D 0 π + decays. The data were recorded by the LHCb experiment during Run 1 of the LHC at center-of-mass energies of √s = 7 and 8 TeV. The production asymmetries, integrated over transverse momenta in the range 2 < p T < 30 GeV/c, and rapidities in the range 2.1 < y < 4.5 are measured to be A prod (B + ,√s = 7 TeV)=(–0.41±0.49±0.10)×10 –2 , A prod (B + ,√s = 8 TeV)=(–0.53±0.31±0.10)×10 –2 , where the first uncertainties are statistical and the second are systematic. These production asymmetries are used to correct the raw asymmetries of B + →J/ψK + decays, thus allowing a measurement of the CP asymmetry, A CP (B + →J/ψK + )=(0.09±0.27±0.07)×10 –2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the phase difference between short- and long-distance amplitudes in the ${{B} ^+} \!\rightarrow {{{K}} ^+} {\mu ^+\mu ^-} $ decay

A measurement of the phase difference between the short- and long-distance contributions to the B + →K + μ + μ - decay is performed by analysing the dimuon mass distribution. The analysis is based on pp collision data corresponding to an integrated luminosity of 3 fb -1 collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the B + →K + μ + μ - decay is modelled as a sum of relativistic Breit–Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the J /ψ and ψ(2 S ) resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, C 9 and C 10 , and the branching fraction of the short-distance component is measured.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Observation of B c + → D 0 K + Decays

Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb -1 , recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the $B_c^+$ → $D^0K^+$ decay is observed with a statistical significance of 5.1 standard deviations. By normalizing to $B^+$ → $\bar{D}^0π^+$ decays, a measurement of the branching fraction multiplied by the production rates for $B_c^+$ relative to B + mesons in the LHCb acceptance is obtained, $R_{D^0K}$ = ($f_c / f_u$) x $B$($B^+_c$ → $D^0K^+$) = ($9.3_{-2.5}^{+2.8}$ ± 0.6) × 10 -7 , where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B^+_c$ decay of this nature to be observed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the ratio of branching fractions and difference in CP asymmetries of the decays $B^+$ → $J/ψπ^+$ and $B^+$ → $J/ψK^+$

The ratio of branching fractions and the difference in $CP$ asymmetries of the decays $B^+$ → $J/ψπ^+$ and $B^+$ → $J/ψK^+$ are measured using a data sample of $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 3 fb -1 at centre-of-mass energies of 7 and 8 TeV. The results are B ( B + → J / ψ π + ) B ( B + → J / ψ K + ) = ( 3.83 ± 0.03 ± 0.03 ) × 10 − 2 , A C P ( B + → J / ψ π + ) − A C P ( B + → J / ψ K + ) = ( 1.82 ± 0.86 ± 0.14 ) × 10 − 2 , where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of $A^{CP}$ ($B^+$ → $J/ ψK^+$) provides the most precise estimate to date of $CP$ violation in the decay $B^+$ → $J/ψπ^+$, A C P ( B + → J / ψ π + ) = ( 1.91 ± 0.89 ± 0.16 ) × 1 0 − 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for decays of neutral beauty mesons into four muons

A search for the non-resonant decays B s 0 → μ + μ – μ + μ – and B 0 → μ + μ – μ + μ – is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of 1 and 2 fb –1 collected at centre-of-mass energies of 7 and 8 TeV, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at 95% confidence level are determined to be $\mathcal{B}$ (B$^{0}_{s}$→μ + μ – μ + μ – )< 2.5 × 10 –9 , (B 0 →μ + μ – μ + μ – )< 6.9 × 10 –10 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

The HPS electromagnetic calorimeter

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called "heavy photon". Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015-2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. Finally, the detector is a homogeneous calorimeter, made of 442 lead-tungsten (PbWO$_4$) scintillating crystals, each read-out by an avalanche photodiode coupled to a custom trans-impedance amplifier.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

Observation of the Annihilation Decay Mode B 0 → K + K –

A search for the B 0 → K + K - decay is performed using pp -collision data collected by LHCb. The data set corresponds to integrated luminosities of 1.0 and 2.0 fb -1 at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B^{0}_{s}$ → π + π - decay. The measured branching fractions are $\mathcal{B}$(B 0 → K + K - ) = (7.80 ± 1.27 ± 0.81 ± 0.21) × 10 -8 and $\mathcal{B}$(B$^{0}_{s}$ → π + π - ) = (6.91 ± 0.54 ± 0.63 ± 0.19 ± 0.40) × 10 -7 . The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the B 0 → K + π - branching fraction used as a normalization. For the $B^{0}_{s}$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into $B^{0}_{s}$ and $B^0$ mesons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of CP asymmetry in D 0 → K - K + decays

A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D 0 → K - K + is performed using pp collision data, corresponding to an integrated luminosity of 3 fb -1 , collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D *+ →D 0 π + and D* - →$\bar{D}$ 0 π - decays. The time-integrated CP asymmetry A CP (K - K + ) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D 0 →K - π + , D + →K - π + π + and D + →$\bar{K}$ 0 π + decays used as calibration channels. It is found to be A CP (K - K + )=(0.14±0.15 (stat)±0.10 (syst))%. A combination of this result with previous LHCb measurements yields A CP (K - K + )=(0.04±0.12 (stat)±0.10 (syst))%, A CP (π - π + )=(0.07±0.14 (stat)±0.11 (syst))%. These are the most precise measurements from a single experiment. The result for A CP (K - K + ) is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗