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Baszczyk, M.

Publications and source records attributed to Baszczyk, M..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Observation of the Decays Λ b 0 → χ c 1 p K - and Λ b 0 → χ c 2 p K -

The first observation of the decays Λ$^0_b$ → $χ$ c1 $pK$ - and Λ$^0_b$ → $χ$ c2 $pK$ - is reported using a data sample corresponding to an integrated luminosity of 3.0 fb -1 , collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: $$\frac{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}=0.242 ± 0.014 ± 0.013 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}= 0.248 ± 0.020 ± 0.014 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}= 1.02 ± 0.10 ± 0.02 ± 0.05$$ where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $Χ_{c1}$ → $Jψγ$ and $Χ_{c2}$ → $Jψγ$ decays. Using both decay modes, the mass of the Λ$^0_b$ baryon is also measured to be $m$ Λ$^0_b$ = 5619.44 ± 0.28 ± 0.26 MeV/$c$ 2 , where the first and second uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

First Observation of a Baryonic B s 0 Decay

We report the first observation of a baryonic $B$$_s^0$ decay, $B$$_s^0$ → $p$$\bar{Λ}$$K$ - , using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb -1 . The branching fraction is measured to be $B$($B$$_s^0$ → $p$$\bar{Λ}$$K$ - ) + $B$($B$$_s^0$ → $\bar{p}$$Λ$$K$ + ) = [5.46±0.61±0.57±0.50($B$)±0.32($f$ s /$f$ d )]×10 -6 , where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the $B$ 0 →$p$$\bar{Λ}$$π$ - decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of $b$-quark hadronization probabilities $f$ s /$f$ d .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of the B + → D * – K + π + decay

The B + →D* – K + π + decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb –1 . A clear signal is observed, and the ratio of its branching fraction to that of the B + →D* – π + π + normalization channel is measured to be B(B + →D* – K + π + )/B(B + →D* – π + π + )=(6.39±0.27±0.48)×10 –2 , where the first uncertainty is statistical and the second is systematic. This is the first observation of the B + →D* – K + π + decay.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the C P Violation Parameter A Γ in D 0 → K + K - and D 0 → π + π - Decays

Asymmetries in the time-dependent rates of D 0 →K + K - and D 0 →$π$ + $π$ - decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of 3 fb -1 . The asymmetries in effective decay widths between $D$ 0 and $\bar{D}$ 0 decays, sensitive to indirect $CP$ violation, are measured to be A $Γ$ (K + K - ) = (-0.30 ± 0.32 ± 0.10) × 10 -3 and A $Γ$ ($π$ + $π$ - ) = (0.46 ± 0.58 ± 0.12) × 10 -3 , where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $CP$ violation and improve on the precision of the previous best measurements by nearly a factor of two.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of the decay $Λ^0_b$ → $pK$ - $μ$ + $μ$ - and a search for $CP$ violation

A search for $CP$ violation in the decay $Λ^0_b$ → $pK$ - $μ$ + $μ$ - is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb -1 . The $Λ^0_b$ → $pK$ - $μ$ + $μ$ - decay is observed for the first time, and two observables that are sensitive to different manifestations of $CP$ violation are measured, $ΔΑ$ CP $\equiv$ $ΔΑ$ CP ($Λ^0_b$ → $pK$ - $μ$ + $μ$ - ) - $ΔΑ$ CP ($Λ^0_b$ → $pK$ - $J/Ψ$) and a C P T &#x005E;<!-- ^ --> - o d d , where the latter is based on asymmetries in the angle between the $μ$ + $μ$ - and $pK$ - decay planes. These are measured to be &#x0394;<!-- Δ --> A C P = ( &#x2212;<!-- - --> 3.5 &#x00B1;<!-- ± --> 5.0 ( s t a t ) &#x00B1;<!-- ± --> 0.2 ( s y s t ) ) &#x00D7;<!-- × --> 10 &#x2212;<!-- - --> 2 , a C P T &#x005E;<!-- ^ --> - o d d = ( 1.2 &#x00B1;<!-- ± --> 5.0 ( s t a t ) &#x00B1;<!-- ± --> 0.7 ( s y s t ) ) &#x00D7;<!-- × --> 10 &#x2212;<!-- - --> 2 , and no evidence for $CP$ violation is found

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for the Decays B s 0 → τ + τ - and B 0 → τ + τ -

A search for the rare decays $B^0_s$→$τ$ + $τ$ - and $B$ 0 →$τ$ + $τ$ - is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb -1 collected in 2011 and 2012. The $τ$ leptons are reconstructed through the decay $τ$ - →$π$ - $π$ + $π$ - $ν$ $τ$ . Assuming no contribution from B 0 →$τ$ + $τ$ - decays, an upper limit is set on the branching fraction $B$($B^0_s$→$τ$ + $τ$ - ) < 6.8×10-3 at the 95% confidence level. If instead no contribution from $B^0_s$→$τ$ + $τ$ - decays is assumed, the limit is $B$($B$ 0 →$τ$ + $τ$ - ) < 2.1×10 -3 at the 95% confidence level. These results correspond to the first direct limit on $B$($B^0_s$→$τ$+$τ$-) and the world's best limit on $B$($B$ 0 →$τ$ + $τ$ - ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for CP violation in the phase space of D 0 → π + π – π + π – decays

A search for time-integrated CP violation in the Cabibbo-suppressed decay D 0 → π + π – π + π – is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for P-even CP asymmetries and, for the first time, is extended to probe the P-odd case. Using proton–proton collision data corresponding to an integrated luminosity of 3.0 fb –1 collected by the LHCb detector at centre-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (4.6±0.5)% in the P-even case, and marginally consistent with a p-value of (0.6±0.2)% in the P-odd case, corresponding to a significance for CP non-conservation of 2.7 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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

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.

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