We report a measurement of the half-life of the 136Xe two-neutrino double-β decay performed with a novel direct-background-subtraction technique. The analysis relies on the data collected with the ...NEXT-White detector operated with 136Xe-enriched and 136Xe-depleted xenon, as well as on the topology of double-electron tracks. With a fiducial mass of only 3.5 kg of Xe, a half-life of 2.34$_{-0.46}^{+0.80}$(stat)$_{-0.17}^{+0.30}$(sys)×1021yr is derived from the background-subtracted energy spectrum. The presented technique demonstrates the feasibility of unique background-model-independent neutrinoless double-β-decay searches.
Abstract
Background
Heart failure (HF) admission is a serious event in the follow up of patients with chronic coronary syndromes (CCS). Stratification schemes have been described for predicting this ...end-point but none of them has been externally validated.
Purpose
To develop point-scores for predicting incident HF admission with data from previous studies, to perform an external validation in an independent prospective cohort study, and to compare their discriminative ability for this event.
Methods
We performed a literature review searching for prospective studies including patients with CCS, excluding patients with HF at baseline, with data on HF admission incidence in follow up and predictive variables. If undescribed previously, scores were developed including those variables independently associated with this outcome, and score points were assigned based in the relative magnitude of the coefficients of Cox regression models. The resulting scores were validated and their discriminative ability compared in a prospective, monocentric, 17-years cohort study, that included consecutive outpatients with CCS.
Results
Four studies were included: two post-hoc analysis of clinical trials (CARE and PEACE) and two observational registries (CORONOR and CLARIFY). The validation cohort included 1212 patients (mean age 67±11 years, 74% male) followed for up to 17 years (median 12 years, p25–75 5–15 years), with 171 patients suffering at least one HF admission in follow-up. The proportions of the variables needed for scores calculation available in the database of the study were 75% (6/8), 88% (15/17), 100% (8/8) and 85% (17/20) respectively, for each of these study-derived scores. Discriminative ability for predicting HF admission was statistically significant for all (C-statistic 0.72, 95% CI 0.68–0.75, p<0.0005; 0.72, 95% CI 0.68–0.76, p<0.0005; 0.73, 95% CI 0.69–0.76, p<0.0005; and 0.69, 95% CI 0.65–0.73, p<0.0005 for CARE, PEACE, CORONOR and CLARIFY scores, figure 1) and paired comparison among them were all non-significant except for CORONOR and CLARIFY scores (p=0.03). The CORONOR score (Age each year 2 points, ejection fraction each percentage point −1 point, hypertension 11 points, diabetes 10 points, atrial fibrillation 14 points, body mass index each kg/m2 unit 1 point, symptomatic angina 11 points and multivessel disease 7 points) identified subgroups of patients with 12 years-HF admission free survival probabilities of 97%, 87 and 62% (p<0.0005, first, second and third tertile of the score, figure 2).
Conclusions
All tested scores showed significant discriminative ability for predicting incident HF admission in this independent validation study. Their discriminative ability was similar, except that CORONOR score performed significantly better than CLARIFY score.
Funding Acknowledgement
Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The work for this paper was funded by the Andalusian Society of Cardiology through anunconditional grant from Astra Zeneca. ROC curves for HF predictive scoresHF free survival by CORONOR score
A
bstract
The NEXT experiment aims at searching for the hypothetical neutrinoless double-beta decay from the
136
Xe isotope using a high-purity xenon TPC. Efficient discrimination of the events ...through pattern recognition of the topology of primary ionisation tracks is a major requirement for the experiment. However, it is limited by the diffusion of electrons. It is known that the addition of a small fraction of a molecular gas to xenon reduces electron diffusion. On the other hand, the electroluminescence (EL) yield drops and the achievable energy resolution may be compromised. We have studied the effect of adding several molecular gases to xenon (CO
2
, CH
4
and CF
4
) on the EL yield and energy resolution obtained in a small prototype of driftless gas proportional scintillation counter. We have compared our results on the scintillation characteristics (EL yield and energy resolution) with a microscopic simulation, obtaining the diffusion coefficients in those conditions as well. Accordingly, electron diffusion may be reduced from about 10 mm/
m
for pure xenon down to 2.5 mm/
m
using additive concentrations of about 0.05%, 0.2% and 0.02% for CO
2
, CH
4
and CF
4
, respectively. Our results show that CF
4
admixtures present the highest EL yield in those conditions, but very poor energy resolution as a result of huge fluctuations observed in the EL formation. CH
4
presents the best energy resolution despite the EL yield being the lowest. The results obtained with xenon admixtures are extrapolated to the operational conditions of the NEXT-100 TPC. CO
2
and CH
4
show potential as molecular additives in a large xenon TPC. While CO
2
has some operational constraints, making it difficult to be used in a large TPC, CH
4
shows the best performance and stability as molecular additive to be used in the NEXT-100 TPC, with an extrapolated energy resolution of 0.4% at 2.45 MeV for concentrations below 0.4%, which is only slightly worse than the one obtained for pure xenon. We demonstrate the possibility to have an electroluminescence TPC operating very close to the thermal diffusion limit without jeopardizing the TPC performance, if CO
2
or CH
4
are chosen as additives.
A
bstract
The measurement of the internal
222
Rn activity in the NEXT-White detector during the so-called Run-II period with
136
Xe-depleted xenon is discussed in detail, together with its ...implications for double beta decay searches in NEXT. The activity is measured through the alpha production rate induced in the fiducial volume by
222
Rn and its alpha-emitting progeny. The specific activity is measured to be (38.1 ± 2.2 (stat.) ± 5.9 (syst.)) mBq/m
3
. Radon-induced electrons have also been characterized from the decay of the
214
Bi daughter ions plating out on the cathode of the time projection chamber. From our studies, we conclude that radon-induced backgrounds are sufficiently low to enable a successful NEXT-100 physics program, as the projected rate contribution should not exceed 0.1 counts/yr in the neutrinoless double beta decay sample.
A
bstract
Natural radioactivity represents one of the main backgrounds in the search for neutrinoless double beta decay. Within the NEXT physics program, the radioactivity- induced backgrounds are ...measured with the NEXT-White detector. Data from 37.9 days of low-background operations at the Laboratorio Subterráneo de Canfranc with xenon depleted in
136
Xe are analyzed to derive a total background rate of (0.84
±
0.02) mHz above 1000 keV. The comparison of data samples with and without the use of the radon abatement system demonstrates that the contribution of airborne-Rn is negligible. A radiogenic background model is built upon the extensive radiopurity screening campaign conducted by the NEXT collaboration. A spectral fit to this model yields the specific contributions of
60
Co,
40
K,
214
Bi and
208
Tl to the total background rate, as well as their location in the detector volumes. The results are used to evaluate the impact of the radiogenic backgrounds in the double beta decay analyses, after the application of topological cuts that reduce the total rate to (0.25
±
0.01) mHz. Based on the best-fit background model, the NEXT-White median sensitivity to the two-neutrino double beta decay is found to be 3.5
σ
after 1 year of data taking. The background measurement in a Q
ββ
±
100 keV energy window validates the best-fit background model also for the neutrinoless double beta decay search with NEXT-100. Only one event is found, while the model expectation is (0.75
±
0.12) events.
A
bstract
In experiments searching for neutrinoless double-beta decay, the possibility of identifying the two emitted electrons is a powerful tool in rejecting background events and therefore ...improving the overall sensitivity of the experiment. In this paper we present the first measurement of the efficiency of a cut based on the different event signatures of double and single electron tracks, using the data of the NEXT-White detector, the first detector of the NEXT experiment operating underground. Using a
228
Th calibration source to produce signal-like and background-like events with energies near 1.6 MeV, a signal efficiency of 71
.
6
±
1
.
5
stat
±
0
.
3
sys
% for a background acceptance of 20
.
6
±
0
.
4
stat
±
0
.
3
sys
% is found, in good agreement with Monte Carlo simulations. An extrapolation to the energy region of the neutrinoless double beta decay by means of Monte Carlo simulations is also carried out, and the results obtained show an improvement in background rejection over those obtained at lower energies.
Within the framework of xenon-based double beta decay experiments, we propose the possibility to improve the background rejection of an electroluminescent Time Projection Chamber (EL TPC) by reducing ...the diffusion of the drifting electrons while keeping nearly intact the energy resolution of a pure xenon EL TPC. Based on state-of-the-art microscopic simulations, a substantial addition of helium, around 10 or 15 %, may reduce drastically the transverse diffusion down to 2.5 mm/m from the 10.5 mm/m of pure xenon. The longitudinal diffusion remains around 4 mm/m. Light production studies have been performed as well. They show that the relative variation in energy resolution introduced by such a change does not exceed a few percent, which leaves the energy resolution practically unchanged. The technical caveats of using photomultipliers close to an helium atmosphere are also discussed in detail.
We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White time projection chamber (TPC) and a dedicated setup. Detailed comparison with ...first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that is postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about10−2photon/e−cm−1bar−1at pressure-reduced electric field values of50Vcm−1bar−1to above3×10−1photon/e−cm−1bar−1at500Vcm−1bar−1. Above1.5kVcm−1bar−1, values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around1photon/e−cm−1bar−1, which is about 2 orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the “buffer” region, where keeping the electric field below the electroluminescence threshold does not suffice to extinguish secondary scintillation. The electric field leakage in this region should be mitigated to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path toward obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to20–50photons/e−cm−1.
A
bstract
Excellent energy resolution is one of the primary advantages of electroluminescent high-pressure xenon TPCs. These detectors are promising tools in searching for rare physics events, such ...as neutrinoless double-beta decay (
ββ
0
ν
), which require precise energy measurements. Using the NEXT-White detector, developed by the NEXT (Neutrino Experiment with a Xenon TPC) collaboration, we show for the first time that an energy resolution of 1% FWHM can be achieved at 2.6 MeV, establishing the present technology as the one with the best energy resolution of all xenon detectors for
ββ
0
ν
searches.
Abstract
Purpose
Women and men with stable coronary artery disease (sCAD) have different clinical features and management, but 1-year prognosis has been reported to be similar in large observational ...registries. The objective of the present study was to investigate the impact of female sex in the prognosis of the disease in the very long-term.
Methods
The CICCOR registry (“Chronic ischaemic heart disease in Cordoba”) is a prospective, monocentric, cohort study. From February 1, 2000 to January 31, 2004, all consecutive patients with sCAD attended at two outpatient cardiology clinics in a city of the south of Spain were included in the study and prospectively followed. Differential clinical features of women and men were described and the impact of female sex in long term prognosis was investigated.
Results
The study sample included 1268 patients, 337 women (27%) and 931 men (73% male). Women were older than men (70±9 versus 65±11 years, p<0.0005), more likely to have hypertension (72% versus 49%, p<0.0005) and diabetes (45% versus 26%), and less likely to be ex-smoker/active smoker (5%/2% versus 49%/9%, p<0.0005). They had more frequently angina in functional class ≥II (22% versus 17%, p=0.04) and atrial fibrillation (8% versus 5%, p=0.04), but had received less frequently coronary revascularization (32% versus 44%, p<0.0005). Prescription of statins (64% versus 68%, p=0.22), antiplatelets (89% versus 93%, p=0.07) and betablockers (67% versus 63%, p=0.28) at first visit was similar than men, but women received more frequently nitrates (78% versus 64%, p<0.0005), angiotensin-conversing enzyme inhibitors or receptor antagonists (56% versus 47%, p=0.004) and diuretics (41% versus 22%, p<0.0005). After up to 17 years of follow-up (median 11 years, IQR 4–15 years, with a total of 12612 patients-years of observation), probabilities of acute myocardial infarction (12% versus 14%, p=0.55) or stroke (14% versus 12%, p=0.40) at median follow up were similar for women and men. However, the risks of hospital admission for heart failure (22% versus 13%, p<0.0005) or cardiovascular death (35% versus 24%, p<0.0005) were significantly higher for women, with a non-significant trend to higher overall mortality (45% versus 39%, p=0.07). After multivariate adjustment, the risks of most events were similar for women and men (Hazard Ratios 95% confidence intervals: 0.79 0.55–1.14, p=0.21 for acute myocardial infarction; 0.89 0.61–1.29, p=0.54 for stroke; 1.13 0.82–1.57, p=0.46 for admission for heart failure; and 0.92 0.73–1.16, p=0.48 for cardiovascular death), with a non-significant trend to lower overall mortality (0.83 0.67–1.02, p=0.08).
Conclusion
Although women and men with sCAD presents a different clinical profile, and crude rates of hospital admissions for heart failure and cardiovascular death were higher in women, female sex was not an independent prognostic factor in this observational study with up to 17 years of follow-up.
Funding Acknowledgement
Type of funding source: None
PDF
