A large ungated TPC with GEM amplification Berger, M.; Ball, M.; Fabbietti, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2017, Letnik:
869
Journal Article
Recenzirano
Odprti dostop
A Time Projection Chamber (TPC) is an ideal device for the detection of charged particle tracks in a large volume covering a solid angle of almost 4π. The high density of hits on a given particle ...track facilitates the task of pattern recognition in a high-occupancy environment and in addition provides particle identification by measuring the specific energy loss for each track. For these reasons, TPCs with Multiwire Proportional Chamber (MWPC) amplification have been and are widely used in experiments recording heavy-ion collisions. A significant drawback, however, is the large dead time of the order of 1 ms per event generated by the use of a gating grid, which is mandatory to prevent ions created in the amplification region from drifting back into the drift volume, where they would severely distort the drift path of subsequent tracks. For experiments with higher event rates this concept of a conventional TPC operating with a triggered gating grid can therefore not be applied without a significant loss of data. A continuous readout of the signals is the more appropriate way of operation. This, however, constitutes a change of paradigm with considerable challenges to be met concerning the amplification region, the design and bandwidth of the readout electronics, and the data handling. A mandatory prerequisite for such an operation is a sufficiently good suppression of the ion backflow from the avalanche region, which otherwise limits the tracking and particle identification capabilities of such a detector. Gas Electron Multipliers (GEM) are a promising candidate to combine excellent spatial resolution with an intrinsic suppression of ions. In this paper we describe the design, construction and the commissioning of a large TPC with GEM amplification and without gating grid (GEM-TPC). The design requirements have driven innovations in the construction of a light-weight field-cage, a supporting media flange, the GEM amplification and the readout system, which are presented in this paper. We further describe the support infrastructure such as gas, cooling and slow control. Finally, we report on the operation of the GEM-TPC in the FOPI experiment, and describe the calibration procedures which are applied to achieve the design performance of the device.
Simulation of space-charge effects in an ungated GEM-based TPC Böhmer, F.V.; Ball, M.; Dørheim, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2013, Letnik:
719
Journal Article
Recenzirano
A fundamental limit to the application of Time Projection Chambers (TPCs) in high-rate experiments is the accumulation of slowly drifting ions in the active gas volume, which compromises the ...homogeneity of the drift field and hence the detector resolution. Conventionally, this problem is overcome by the use of ion-gating structures. This method, however, introduces large dead times and restricts trigger rates to a few hundred per second. The ion gate can be eliminated from the setup by the use of Gas Electron Multiplier (GEM) foils for gas amplification, which intrinsically suppress the backflow of ions. This makes the continuous operation of a TPC at high rates feasible.
In this work, Monte Carlo simulations of the buildup of ion space charge in a GEM-based TPC and the correction of the resulting drift distortions are discussed, based on realistic numbers for the ion backflow in a triple-GEM amplification stack. A TPC in the future p¯anda experiment at FAIR serves as an example for the experimental environment. The simulations show that space charge densities up to 65fCcm−3 are reached, leading to electron drift distortions of up to 10mm. The application of a laser calibration system to correct these distortions is investigated. Based on full simulations of the detector physics and response, we show that it is possible to correct for the drift distortions and to maintain the good momentum resolution of the GEM-TPC.
First measurement of dE/dx with a GEM-based TPC Böhmer, F.V.; Ball, M.; Dørheim, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2014, Letnik:
737
Journal Article
Recenzirano
In this work we present the first measurement of the specific energy loss (dE/dx) and an analysis of the resulting charged-particle identification (PID) capabilities of a large-scale TPC with ...GEM-based gas amplification. The data has been recorded inside the FOPI spectrometer at GSI, Germany, using reactions of 1.7GeV/c pions impinging on a carbon target.
In the specific energy loss spectrum clear bands for pions, kaons, protons and deuterons are observed. The specific energy loss resolution is studied as a function of the total particle momentum and as a function of the track length. It is found to be ~15%, consistent with expectations.
Previous Mendelian randomization (MR) studies on 25-hydroxyvitamin D (25(OH)D) and cancer have typically adopted a handful of variants and found no relationship between 25(OH)D and cancer; however, ...issues of horizontal pleiotropy cannot be reliably addressed. Using a larger set of variants associated with 25(OH)D (74 SNPs, up from 6 previously), we perform a unified MR analysis to re-evaluate the relationship between 25(OH)D and ten cancers. Our findings are broadly consistent with previous MR studies indicating no relationship, apart from ovarian cancers (OR 0.89; 95% C.I: 0.82 to 0.96 per 1 SD change in 25(OH)D concentration) and basal cell carcinoma (OR 1.16; 95% C.I.: 1.04 to 1.28). However, after adjustment for pigmentation related variables in a multivariable MR framework, the BCC findings were attenuated. Here we report that lower 25(OH)D is unlikely to be a causal risk factor for most cancers, with our study providing more precise confidence intervals than previously possible.
Taxane-based adjuvant chemotherapy is standard in node-positive (N+) early breast cancer (BC). The magnitude of benefit in intermediate-risk N+ early BC is still unclear. WSG-AGO epiribicine and ...cyclophosphamide (EC)-Doc is a large trial evaluating modern taxane-based chemotherapy in patients with 1–3 positive lymph nodes (LNs) only.
A total of 2011 BC patients (18–65 years, pN1) were entered into a randomized phase III trial comparing 4 × E90C600 q3w followed by 4 × docetaxel100 q3w (n = 1008) with the current standard: 6 × F500E100C500 q3w (n = 828) or C600M40F600 d1, 8× q4w (n = 175). Primary end point was event-free survival (EFS); secondary end points were overall survival (OS), toxicity, translational research, and quality of life. Central tumor bank samples were evaluable in a representative collective (n = 772; 40%). Ki-67 was assessed centrally in hormone receptor-positive disease as a surrogate marker for the distinction of luminal A/B-like tumors.
Baseline characteristics were well balanced between study arms in both main study and central tumor bank subset. At 59-month median follow-up, superior efficacy of EC-Doc versus FEC (a combination of 5-fluorouracil, epirubicin, and cyclophosphamide) was seen in EFS and OS: 5-year EFS: 89.8% versus 87.3% (P = 0.038); 5-year OS: 94.5% versus 92.8% (P = 0.034); both tests one-tailed. EC-Doc caused more toxicity. In hormone receptor-positive (HR)+ disease, only high-Ki-67 tumors (≥20%) derived significant benefit from taxane-based therapy: hazard ratio = 0.39 (95% CI 0.18–0.82) for EC-Doc versus FEC (test for interaction; P = 0.01).
EC-Doc significantly improved EFS and OS versus FEC in intermediate-risk BC (1–3 LNs) within all subgroups as defined by local pathology. In HR+ disease, patients with luminal A-like tumors may be potentially over-treated by taxane-based chemotherapy.
ClinicalTrials.gov, NCT02115204.
Employing the Bonn–Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5 GeV)+p→pK+Λ. This reaction might contain information about the kaonic cluster ...“ppK−” (with quantum numbers JP=0− and total isospin I=1/2) via its decay into pΛ. Due to interference effects in our coherent description of the data, a hypothetical K‾NN (or, specifically “ppK−”) cluster signal need not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectrum like pΛ. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a K‾NN cluster. At a confidence level of CLs=95% such a cluster cannot contribute more than 2–12% to the total cross section with a pK+Λ final state, which translates into a production cross-section between 0.7 μb and 4.2 μb, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.
We grew single-crystalline, single-phase CaKFe4As4 out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, ...elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc=35.0±0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8K≤T≤300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1-xKx)Fe2As2, suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as “optimal-doped” on a generalized, Fe-based superconductor, phase diagram. Furthermore, the anisotropic superconducting upper critical field, Hc2(T), of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ(T)=H$⊥\atop{c2}$/H$∥\atop{c2}$, for H applied perpendicular and parallel to the c axis, decreases from ≃2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of dH$∥\atop{c2}$/dT≃-44 kOe/K and dH$⊥\atop{c2}$/dT≃-109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥≃1/6 and short Ginzburg-Landau coherence lengths ξ∥(0)≃5.8Å and ξ⊥(0)≃14.3Å. Finally, the value of H$⊥\atop{c2}$(0) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.
A Time Projection Chamber for continuous readout Berger, M.; Berger-Chen, J. C.; Cusanno, F. ...
2013 IEEE Nuclear Science Symposium and Medical Imaging Conference (2013 NSS/MIC),
10/2013
Conference Proceeding
A Time Projection Chamber (TPC) with its 3-dimensional tracking and particle identification capabilities is a very powerful detector for high multiplicity events. TPCs are used for tracking in ...several experiments such as ALICE, STAR and many others. A drawback of such devices is the restriction to trigger rates of the order of 1 kHz due to the necessity of a gating grid which prevents ions produced in the amplification region of MWPCs from entering the drift volume. A GEM-TPC has been built which is the GEM-TPC with the largest active volume up to date. The detector has been commissioned with cosmics and particle beams at the FOPI experiment at GSI, and was employed for a physics measurement with a pion beam.
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