Performance of a spaghetti calorimeter prototype with tungsten absorber and garnet crystal fibres

A spaghetti calorimeter (SPACAL) prototype with scintillating crystal fibres was assembled and tested with electron beams of energy from 1 to 5 GeV. The prototype comprised radiation-hard Cerium-doped Gd$_3$Al$_2$Ga$_3$O$_{12}$ (GAGG:Ce) and Y$_3$Al$_5$O$_{12}$ (YAG:Ce) embedded in a pure tungsten absorber. The energy resolution was studied as a function of the incidence angle of the beam and found to be of the order of $10\% / \sqrt{E} \oplus1\%$, in line with the LHCb Shashlik technology. The time resolution was measured with metal channel dynodes photomultipliers placed in contact with the fibres or coupled via a light guide, additionally testing an optical tape to glue the components. Time resolution of a few tens of picosecond was achieved for all the energies reaching down to (18.5 $\pm$ 0.2) ps at 5 GeV.Comment: 14 pages, 8 figures, published on NIM

Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Crystal Fibers for the LHCb Calorimeter Upgrade

The Large Hadron Collider beauty (LHCb) experiment is one of the four main particle detectors located at the Large Hadron Collider. After the high-luminosity upgrade of the accelerator, the expected radiation dose faced by the LHCb electromagnetic calorimeter will reach peak values of 1 MGy in the centermost part, an amount not tolerable by the currently employed Shashlik technology, which demands a novel radiation hard design. In addition, a time resolution of few tens of picoseconds and a cell lateral size of about 2 cm are planned for track reconstruction purposes by thecollaboration. In this article, the crystal spaghetti design was evaluated, a sampling geometry where scintillating crystal fibers are embedded in the dense absorbing material. The prototype was tested at CERN super proton synchrotron (SPS) with muons and electrons measuring an energy resolution of 3% for electrons at 20 GeV, tilting the prototype by $3^◦$ both horizontally and vertically with respect to the incident beam, and a time resolution of 79 ps. The results presented in this article show the feasibility of the design

SCINT2019

Pendin

Development of a Sampling Calorimeter for the LHCb Upgrade

Since 2008 the Large Hadron Collider (LHC) at CERN, Geneva, has offered the ideal testing ground to probe the scientific knowledge of the fundamental interactions. There, the LHCb experiment performs precision measurements of CP violation and rare decays of B hadrons. LHCb will be upgraded to run at a luminosity of $1.5\times10^{34} \ \text{cm}^{−2} \ \text{s}^{−1}$ . This will require a substantial modification of its current electromagnetic calorimeter due to high radiation doses in the central region and increased particle densities. This PhD thesis presents an innovative technological solution based on spaghetti calorimeters (SPACAL). The candidate scintillators include both radiation-hard inorganic crystal garnets, for the region with the highest radiation dose, and organic dyes in polystyrene or polysiloxane hosts. The R&D on scintillating materials individuated garnets radiation-hard up to 1 MGy with timing capabilities close to LYSO:Ce. Their composition was then tuned to reduce their decay time at the level of plastic scintillators, keeping competitive timing. Samples of polysiloxane scintillators were tested with promising results. Prototypes of SPACAL with lead or tungsten absorbers were produced and tested at DESY and CERN. The energy resolutions showed sampling and constant contributions of ∼ 10%/ $\sqrt{E} \oplus$ 1% in line with the current LHCb modules. The spatial resolutions reached below 1 mm, and time resolutions at the level of 15 ps at high energies. Moreover, time resolution was studied with several PMTs coupled to the scintillators in direct contact or via light guides, with or without optical glues. A Monte Carlo simulation framework was developed, validated with testbeam results, and used to optimise the prototypes. It relies on a hybrid approach to describe the transport of the optical photons, retaining the precision of ray tracing but reducing by orders of magnitude the computation time. The framework was employed to study the deterioration caused by the LHCb background to the time resolution of a SPACAL with tungsten absorber and inorganic crystals, giving further input to the scintillators R&D

Scintillation properties and timing performance of state-of-the-art Gd3_{3}Al2_{2}Ga3_{3}O12_{12}single crystals

Future colliders will set stringent requirements on the performance of detector materials in terms of timing and radiation hardness. Scintillating garnet crystals proved to satisfy the latter, while the former can be improved through technological developments. In this work, optical and scintillation properties of Cerium-doped Gd$_{3}$Al$_{2}$Ga$_{3}$O$_{12}$ (GAGG:Ce) single crystals were studied upon gamma radiation excitation. Several 2x2x3 mm 3 and 2x2x10 mm$^{3}$ samples from various producers were characterized in terms of light output, transmission, scintillation kinetics and coincidence time resolution (CTR). Light output was measured using a$^{137}$Cs radioactive source, ranging between 27900 and 49500 photons per MeV. Scintillation emission time profiles were measured with 511 keV gamma excitation, and the fastest samples displayed components below 70 ps rise time and 50 ns decay time. CTR was measured employing silicon photomultipliers (SiPMs) obtaining a best value of 87  ±  2 ps full width at half maximum, significantly improving on past state-of-the-art GAGG

Modeling Scintillation Kinetics and Coincidence Time Resolution in Heterostructured Scintillators

In the search for new materials and technologies to push the timing performances of time-of-flight positron emission tomography (TOF-PET) detectors, it is important to have a model capable of predicting the coincidence time resolution (CTR) of the system to be implemented. While for bulk standard scintillators, a model that takes into account the intrinsic properties of the material (and the characteristics of the photodetector) is already well established, it has never been experimentally validated for composite structures. As heterostructured scintillators–i.e., the combination of two or more materials with complementary properties–are emerging as a possible solution to the conflict between fast timing and high detection efficiency for TOF-PET detectors, such validation becomes necessary. In this work, by using a time-correlated single photon counting (TCSPC) setup capable of simultaneously recording the TCSPC signal and the scintillation pulse on an event-by-event basis, we experimentally demonstrate that the scintillation kinetics of heterostructures can be modeled as a linear combination of the scintillation kinetics of the materials that constitute the heterostructure itself. Based on these results, we develop an extension of well-established CTR analytical model which can be applied to heterostructured scintillators

Compositional engineering of multicomponent garnet scintillators: towards an ultra-accelerated scintillation response

Optical, luminescence and scintillation characteristics were studied in garnet-type GAGG single-crystal scintillators grown by the Czochralski method and heavily doped with a cerium activator and a magnesium codopant at different concentrations. Emission quenching due to the formation of closely spaced Ce–Mg pairs accelerating the photoluminescence and scintillation decays down to a few nanoseconds and substantial suppression of slower decay components are observed. We show that despite a significant decrease in the scintillation yield, the coincidence time resolution and the afterglow, which are the most critically important parameters of fast scintillators, exhibited by the heavily doped GAGG:- Ce,Mg are superior to those in the state-of-the-art scintillators. Due to the peculiar feature of the GAGG host to tolerate extremely high cerium and magnesium concentrations while still maintaining a bulk single crystal form, this scintillator has a great potential for high-count-rate applications in high energy physics experiments and industries with harsh operational environments, where a lower light yield can be tolerated