Central Detector Research Articles

Track based alignment procedure for the CBM silicon tracking detector

The CBM (Compressed Baryonic Matter) experiment at FAIR is being designed for the study of the QCD phase diagram in the region of the high baryon chemical potential at relatively moderate temperatures. The Silicon Tracking System (STS) is the central detector for momentum reconstruction of the produced charged particles in the CBM experiment. It consists of 8 layers of altogether ∼ 900 double sided silicon micro strip sensors. Limited mechanical precision(> 100μm) during the mounting, temperature differences during the experiment, influence of the applied magnetic field result in misalignment to the detector component positions. Therefore, the intrinsic spatial resolution(∼ 20μm) of the detector components has to be recovered by a track based alignment method. In this conference paper, the current status of implementation of the alignment algorithm is presented. For this work, the GBL (General broken line) track refit model is employed to create the necessary input data structure to provide the input to the standalone PEDE part of the χ2 minimization based MILLEPEDE II alignment algorithm.

Thermal reliability analysis of the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy, precisely measure oscillation parameters and study solar neutrinos, supernova neutrinos and geo-neutrinos, etc. The central detector (CD) of JUNO has 20,000 tons liquid scintillator as target mass, which contains inside a huge acrylic sphere with inner diameter of 35.4 m, supported by a stainless steel structure. The whole structure of CD will be installed inside a cylindrical water pool, and the acrylic sphere will be submerged in the center of water pool. The operating temperature of CD is designed to be 21 °C as long as over 20 years, which is determined by the mechanical requirement of the structure and physics consideration. For this operating temperature, a special cooling system will be used to maintain the temperature inside the water pool. The main structure of CD is composed of acrylic and stainless steel, and they have much different thermal expansion coefficients, strengths and life times. Change in temperature may affect the safety of CD. As part of reliability analysis, the effect of cooling system failure on the CD is considered, and finite element method is used in our thermal calculation. In this article, the temperature fields before and after cooling system failure are calculated and analyzed, and the temperatures of different locations of water pool after cooling system failure are compared and discussed in detail.

Status of the Jiangmen Underground Neutrino Observatory

The Jiangmen Underground Neutrino Observatory (JUNO) is a next generation multipurpose antineutrino detector currently under construction in Jiangmen, China. The central detector, containing 20 kton of a liquid scintillator, will be equipped with ∼18 000 20 inch and 25 600 3 inch photomultiplier tubes. Measuring the reactor antineutrinos of two powerplants at a baseline of 53 km with an unprecedented energy resolution of 3%/√︀E(MeV), the main physics goal is to determine the neutrino mass hierarchy within six years of run time with a significance of 3–4q. Additional physics goals are the measurement of solar neutrinos, geoneutrinos, supernova burst neutrinos, the diffuse supernova neutrino background, and the oscillation parameters sin2 O12, Δm212, and |Δm2ee| with a precision <1%, as well as the search for proton decays. The construction is expected to be completed in 2021.

Photoproduction of charged final states in ultraperipheral collisions and electroproduction at an electron-ion collider

Ultra-peripheral collisions (UPCs) of relativistic ions are an important tool for studying photoproduction at high energies. Vector meson photoproduction is an important tool for nuclear structure measurements and other applications. A future electron-ion collider (EIC) will allow additional studies, using virtual photons with a wide range of $Q^2$. We propose a significant expansion of the UPC and EIC photoproduction physics programs to include charged final states which may be produced via Reggeon exchange. We consider two examples: $a_2^+(1320)$, which is a conventional $q\overline q$ meson, and the exotic $Z_c^+(4430)$ state (modeled here as a tetraquark). The $Z_c^+(4430)$ cross-section depends on its internal structure, so photoproduction can test whether the $Z_c^+(4430)$ is a tetraquark or other exotic object. We calculate the rates and kinematic distributions for $\gamma p\rightarrow X^+n$ in $pA$ UPCs and $ep$ collisions at an EIC and in UPCs. The rates are large enough for detailed studies of these final states. Because the cross-section for Reggeon exchange is largest near threshold, the final state rapidity distribution depends on the beam energies. At high-energy colliders like the proposed LHeC or $pA$ collisions at the LHC, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to mid-rapidity, within reach of central detectors.

Analysis of stability against rotation of a spherical shell structure subjected to buoyancy

The main structure of the central detector at the Jiangmen Underground Neutrino Observatory (JUNO) is a spherical shell structure, which has a giant acrylic spherical shell connected to a stainless-steel (SS) reticulated shell with 590 SS rods. The acrylic spherical shell is submerged into water and filled with detection liquid and prone to rotation subjected to considerable buoyancy. The stability against rotation of this super-deep underground spherical shell structure needs to be fully investigated. In this study, an effective and practical method consisting of parametric analysis and optimization procedure is proposed to improve the stability against rotation. Specifically, two indicators, namely, the critical loading multiplier and the rotation angle, are proposed to evaluate the stability against rotation of the acrylic spherical shell in linear and nonlinear stability analyses, respectively. Then, parametric analysis is performed to assess the sensitivity of the stability against rotation to four parameters of interest (i.e., rod outer end constraints, liquid level difference, disc spring stiffness, and rod deviation). Based on the obtained parametric analysis results, the liquid level difference and disc spring stiffness are finally selected as design variables for the subsequent optimization process to further improve the stability against rotation. An efficient scheme combining design variable discretization and exhaustive method is adopted to identify the optimal variable values at which the acrylic spherical shell has good stability against rotation. The results indicate that the proposed method is efficient and effective for optimization of stability against rotation of such super-deep underground spherical shell structure. The proposed method is practical and easy to use for structural designers, and provides an efficient approach to the stability design of such rod-connected spherical shell structures.

Timing detectors for forward physics

The use of precise time-of-flight (ToF) detectors for measurements of diffractive and electromagnetic processes in proton-proton collisions is discussed. The performance of background rejection exploiting the ToF measurements of the forward protons is derived. The influence of additional timing measurements delivered by the central detectors is presented and the possible gain is studied.

The Jiangmen Underground Neutrino Observatory (JUNO)

The Jiangmen Underground Neutrino Observatory (JUNO) is an experiment under construction in China with the primary goal of determining the neutrino mass hierarchy (MH) with reactor anti-neutrinos. The JUNO detector system consists of a central detector, an active veto system and a calibration system. The central detector is a 35 m diameter transparent acrylic sphere containing a 20 kton liquid scintillator neutrino target. A primary photo-detection system consisting of 18,000 large (20” diameter) dynode and micro-channel plate photomultipliers surrounds the central detector. A second interlaced photo-detection system is made of 25,600 small (3” diameter) photomultipliers working in the single photo-electron regime for the reactor anti-neutrino detection. The detector is designed to achieve an unprecedented energy resolution of 3% @1MeV and an absolute energy scale uncertainty better than 1%. A veto system, consisting of a water Cherenkov detector and a top tracker, is used help maximally remove cosmogenic backgrounds. Due to its unprecedented scale and precision, JUNO will be an exceptional multipurpose detector with a rich physics program in neutrino oscillation, geo-neutrinos, astrophysical neutrinos and the search for physics beyond the Standard Model (sterile neutrinos, dark matter, proton decay and others).

Study on the Fracture Properties of the PMMA Structure for the JUNO Central Detector

Polymethyl methacrylate (PMMA) is increasingly used in building structures nowadays. PMMA materials utilized in structures have different fracture property compared with those used in aircrafts or biomedical equipment. Single-edge-notch bending (SENB) tests were firstly carried out at various temperatures (−40°C, −20°C, 0°C, 20°C, and 40°C) to determine the KIC values of base PMMA materials and connected areas. The crack-resisting capacity of PMMA plate is subsequently studied. The fracture property of the PMMA joint for the Jiangmen Underground Neutrino Observatory (JUNO) central detector is investigated. The results show that base PMMA material has higher KIC values than connected area. The KIC of base PMMA material is lowest at 20°C and highest at −20°C, while that of connected area is lowest at 40°C and highest at −40°C. For the PMMA joint of the JUNO detector, the cracks perpendicular to the X axis are more disadvantageous than those perpendicular to the Z axis. The stress intensity factors (SIFs) at the crack front of the embedded crack decrease with the increase of embedded depth. Due to the presence of two parallel surface or embedded cracks, the SIFs at the crack front decrease.

Searching for the odderon in ultraperipheral proton-ion collisions at the LHC

We explore the possibility of observing Odderon exchange in proton--ion collisions at the LHC, via the ultraperipheral photoproduction of C-even mesons. As well as the signal, we consider in detail the principle backgrounds, due to QCD--initiated production (i.e. double Pomeron exchange) and $\gamma\gamma$ fusion. We find that while the photon--initiated background is dominant at very small momentum transfer, this can be effectively removed by placing a reasonable cut on the transverse momentum of the produced meson. In the case of QCD--initiated production, we show this is in general strongly suppressed by the small probability of no additional particle production in the central detector, namely the survival factor. In some scenarios, this suppression is sufficient to permit the observation of Odderon exchange in Pb$-p$ collisions in a clean environment, or else to place bounds on this. We in addition identify the cases of $\pi^0$ and $\eta(548)$ production as particularly promising channels. Here, the QCD--initiated background is absent for $\pi^0$ due to isospin conservation and very small for $\eta(548)$ due to its dominantly flavour octet nature and odd parity.

Experimental determination of the “collimator monitoring fill factor” and its relation to the error detection capabilities of various 2D‐arrays

The collimator monitoring fill factor (CM-FF) introduced by Stelljes etal. (2017) and the FWHM fill factor (FWHM-FF) introduced by Gago-Arias etal. (2012) were determined using the measured photon fluence response functions of various 2D-arrays. The error detection capabilities of 2D-arrays were studied by comparing detector signal changes and local gamma index passing rates in different field setups with introduced collimation errors. The fill factor is defined as the ratio of the sensitive detector area and the cell area of a detector, defined by the detector arrangement on a 2D-array. Gago-Arias etal. calculated the FWHM-FF, using the FWHM² of a detector's fluence response function KM (x) as the sensitive detector area. For the CM-FF a sensitive detector width w(Δ mm, d%) is calculated. The sensitive detector width is the lateral extent of KM (x), lying inside the detector cell area, along which a collimator error of Δ mm yields a signal change exceeding a detection threshold of d%. The sensitive area for a single detector is calculated using w(Δ mm, d%)². The CM-FF is then calculated as the ratio of the sensitive area of a detector within its cell area and the detector cell area. The fluence response functions of the central detector of the OCTAVIUS 729, 1500, and 1000 SRS array (all PTW-Freiburg, Freiburg, Germany) and the MapCHECK 2 array (Sun Nuclear, Melbourne, US) were measured using a photon slit beam. The FWHM-FF and the CM-FF were calculated and compared for all 2D-arrays under investigation. The error detection capabilities of 2D-arrays in quadratic fields were studied by investigating the signal changes in the detectors adjacent to the collimator edge when changing the collimator position. The change in local gamma index passing rate with respect to the introduced collimator error was investigated for an ionization chamber and a diode array in quadratic and two intensity modulated fields. Values for the CM-FF and FWHM-FF were 1.0 and 0.35, respectively for the area of the liquid-filled 1000 SRS ionization chamber array with a detector to detector distance of 5mm and 0.32 and 0.04, respectively, for the MapCHECK 2 diode array. For the vented ionization chamber array OCTAVIUS 729 fill factors were calculated as CM-FF=0.59 and FWHM-FF=0.53, while the OCTAVIUS 1500 array yielded fill factors of CM-FF=0.77 and FWHM-FF=0.72. Signal changes in vented ionization chambers for collimator errors of 1mm surpassed those of diodes by a factor of 2 in quadratic fields. The gamma index passing rates in quadratic fields reflect those findings. In intensity modulated fields, the decline of the gamma index passing rate is bigger for the ionization chamber array compared to the diode array when introducing collimator errors. The calculated values of the CM-FF correlate with the signal changes in quadratic field setups with introduced collimator position errors of 1mm, while the FWHM-FF underestimates the error detection capabilities of 2D-arrays. An increased error detection capability of the ionization chamber array compared to diode array was observed in quadratic and intensity modulated fields.

Regulation of Thirst and Vasopressin Release.

Recent experiments using optogenetic tools facilitate the identification and functional analysis of thirst neurons and vasopressin-producing neurons. Four major advances provide a detailed anatomy and physiology of thirst, taste for water, and arginine-vasopressin (AVP) release: ( a) Thirst and AVP release are regulated by the classical homeostatic, interosensory plasma osmolality negative feedback as well as by novel, exterosensory, anticipatory signals. These anticipatory signals for thirst and vasopressin release concentrate on the same homeostatic neurons and circumventricular organs that monitor the composition of blood. ( b) Acid-sensing taste receptor cells (TRCs) expressing otopetrin 1 on type III presynaptic TRCs on the tongue, which were previously suggested as the sour taste sensors, also mediate taste responses to water. ( c) Dehydration is aversive, and median preoptic nucleus (MnPO) neuron activity is proportional to the intensity of this aversive state. ( d) MnPOGLP1R neurons serve as a central detector that discriminates fluid ingestion from solid ingestion, which promotes acute satiation of thirst through the subfornical organ and other downstream targets.

Light absorption properties of the high quality linear alkylbenzene for the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton multi-purpose underground liquid scintillator detector designed to determine the neutrino mass hierarchy, and measure the neutrino oscillation parameters. The excellent energy resolution and the large fiducial volume anticipated for the JUNO detector offer exciting opportunities for addressing many important topics in neutrino and astro-particle physics. Linear alkylbenzene (LAB) will be used as the solvent for the liquid scintillation system in the central detector of JUNO. The light attenuation lengths of LAB should be comparable to the diameter of the JUNO detector, hence very good optical transparency is required. However, the presence of impurities in the LAB renders an intrinsic limit for the transparency. This work focuses on the study of the effects of organic impurities in the LAB, and their light absorption properties particularly in the wavelength region of 350–450 nm. We have prepared LAB samples and measured their light attenuation lengths. These samples were then analyzed by a gas chromatography–mass spectrometry (GC–MS), and the structure formulas of organic impurities were ascertained. These impurities’ light-absorption properties in the wavelength region of 350–450 nm were theoretically investigated with time-dependent density functional theory (TDDFT). The overall optical transparency of the LAB samples was studied, which would further help us in promoting the LAB preparation technique for the mass production thereof, thus improving the transparency of the high quality LAB samples in the near future.

Using monochromatic light to measure attenuation length of liquid scintillator solvent LAB

Linear alkylbenzene (LAB) will be used as solvent for the liquid scintillator in the central detector of Jiangmen Underground Neutrino Observatory. The sheer size of the detector imposes significant challenges and the necessity to further improve the optical transparency of high-quality LAB. In order to study high optical transparencies, we continuously improve our measurement setup and use monochromatic light to measure the attenuation lengths of LAB samples. Moreover, the effects of organic impurities on LAB samples are studied to understand their interaction mechanisms and further improve the optical transparency of LAB.

Upgrade of the ALICE central barrel tracking detectors: ITS and TPC

The ALICE Collaboration will undertake a major upgrade of the detector apparatus during the second LHC Long Shutdown LS2 (2019–2020) in view of the Runs 3 and 4 (2021–2029). The objective of the upgrade is two-fold: i) an improvement of the tracking precision and efficiency, in particular in the low-momentum range; ii) an improvement of the readout capabilities of the experiment, in order to fully exploit the luminosity for heavy ions envisaged after LS2. The first goal will be achieved by replacing the Inner Tracking System with a new tracker, composed of seven layers of silicon pixel detectors. The new tracker will be made up of about 25000 Monolithic Active Pixel Sensors with fast readout, resulting in a material thickness reduced to 0.3% (inner layers) – 1% (outer layers) of the radiation length and a granularity of 28×28μm2. The second goal will be achieved, among other measures, by replacing the readout chambers of the 90m3 Time Projection Chamber with Micro Pattern Gaseous Detectors. In particular, the new readout chambers will consist of stacks of 4 Gas Electron Multiplier foils combining different hole pitches. The upgraded detector will operate continuously without the use of a triggered gating grid. It will thus be able to record all Pb–Pb collisions at the LHC interaction rate of 50kHz.

Status of the parallelized JUNO simulation software

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment. It consists of a central detector, a water pool and a tracker placed on top. The central detector, which is used for neutrino detection, consists of a 20 kt liquid scintillator target and about 18,000 20-inch photomultiplier tubes (PMTs) to detect scintillation photons. Simulation software is an important part of the JUNO offline software. To speed up the simulation, a parallelized simulation framework has been developed based on the SNiPER framework and Geant4 version 10. The SNiPER task components are in charge of the event loop, which can run in sequential mode, Intel TBB mode and other modes. Based on SNiPER, the simulation framework and its underlying parallel libraries have been decoupled. However, parallelized simulation of correlated events is a challenge. In order to keep the correct event order, a component called global buffer is developed in SNiPER. In this paper, an overview of the parallelized JUNO simulation framework is presented. The global buffer is used in the parallelized event correlation simulation. An event generator produces events with timestamps in sequential mode. These events are put into the global buffer and processed by the detector simulation algorithms in different tasks. After simulation, the events are saved into ROOT files with a ROOT I/O service running in a dedicated thread. Finally, the software performance is presented.

Ultrasonic positioning system for the calibration of central detector

A thorough detector response calibration using radioactive sources is necessary for the Jiangmen Underground Neutrino Observatory. Herein, we discuss the design of a source positioning system based on ultrasonic technology, aiming for a 3-cm precision over the entire 35-m diameter detector sphere. A prototype system is constructed and demonstrated for the experiment.

Multi-scale Modeling for the Stress Analysis of Acrylic Joints in a Hybrid Structure

The central detector at the Jiangmen Underground Neutrino Observatory (JUNO) is a hybrid structure system consisting of an inner acrylic sphere and an outer stainless steel reticulated shell. The stress distributions of the acrylic joints must be accurately simulated to avoid “crazing”. To balance the accuracy and efficiency of the stress analysis, a multi-scale modeling method using mixed-dimensional coupling is proposed. A framework and a generalized procedure are developed to instruct the modeling and analysis. A multi-scale model consisting of a single refined acrylic joint and equipped with simplified joints is proposed and discussed. A comparison of the results using the multi-scale model with a cluster of 3 × 3 refined joints reveals that the difference is less than 5%, while the ratio of the computation resource cost and the time consumption is approximately only 1/7 and 1/5, respectively. The stress distributions of the acrylic joints in the central detector are obtained using the proposed multi-scale model.

Shielding the Earth Magnetic Field using Spherical Coils

The Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment consisting of 2 systems; central detector (CD) and veto systems. The CD is composed of thousands of photomultiplier tubes (PMTs) used to detect light signals from neutrino induced interactions with liquid scintillator inside the CD. Another set of PMTs is used as water Cherenkov detector, together with muon top tracker forming the veto system for background rejection [1]. However, the PMTs’ efficiency decreases when they are used in magnetic field. At JUNO’s construction site, the Earth Magnetic Field (EMF) is approximately 0.45 G [2]. Therefore, the PMTs of JUNO detector are necessary to be shielded from the EMF.This work aims to design current-carrying coils that generate magnetic field in the opposite direction to the EMF, thus, the two fields tend to cancel each other. We found that the magnetic field generated by the 32 circular coils forming a sphere of diameter 43.5 m can reduce the residual magnetic field to be lower than 10% of the EMF at the CD region and less than 20% at the veto region. Moreover, considering the secular change of the EMF’s inclination angle of approximately 2.87° over the 20 years of its operation, the coils can maintain the residual magnetic field both in the CD and the veto regions to be less than 10% and 20%, respectively.

357. iQA: Quality assurance management software in hospital radiology

Purpose iQA takes its bases on the necessity to share QA (Quality Assurance) radiologic information among different professionals such as physician as responsible of technology, technicians and medical physicists. Our medical physics department is involved in the QA of radiologic equipment on several hospitals in the Ferrara district. Methods and materials iQA is a web-based software with a client/server architecture achievable from different navigator browser. Each user has an account that allows to view and modify data according to his permission limited to his equipment. For each radiological center, the equipment (RX tube, workstation monitor, computed radiography (CR) and digital radiography (DR) detectors, magnetic resonance) are listed with their location and technical information. Details on QA protocols and reports, status of maintenance, final evaluation to clinical use are always available. In case of some parameters are out of tolerance an alert is provided to the user by e-mail. Results The use of iQA started from December 2017, after a training of each professional involved. From the beginning it results so useful to a real time monitoring of the equipment status. Conclusion The future developments see the implementation in iQA of the nuclear medicine, radiotherapy equipment and also a radioprotection module. It could be develop iQA mobile application to enhance the users feedback. Download : Download high-res image (201KB) Download : Download full-size image

EMF Shielding of One Set of Circular Coils with Slight Distortion

Jiangmen Undergroud Neutrino Observatory (JUNO) is a reactor antineutrino experiment with the main purpose for determining the neutrino mass hierarchy by precisely measuring the energy spectrum of nuclear reactor electron antineutrinos. The JUNO central detector consists of 20 kilotons an organic liquid scintillator filling the spherical CD or acrylic sphere whose diameter is 35.4 meters, surrounded by a water pool, approximately 18, 000 20″ and 25, 000 3″ photomultiplier tubes (PMTs) on the inner CD truss and 2,400 20″ Veto-PMT on the outer CD truss. The PMTs are very sensitive to external magnetic fields, the earth magnetic field (EMF) passing through the PMTs without any shielding would largely reduce the efficiency of the PMTs. In order to minimize the effect of EMF inside the detector, JUNO has been planing to use the DC coils to shield EMF, aiming at the residual EMF to less than 10 % on PMT areas.