Encuestas a trabajadores

A wide range of systematic effects impact this analysis; for example, variations in the energy

response may shift 8_{B background events into and out of the hep energy region of interest}

in a box analysis, affecting the background estimate, or errors in cross sections may change the interpretation of event rates in terms of fluxes. These may generally be classified in two categories: normalization uncertainties, which affect the overall rate of events of a particular class, and shape uncertainties, which change the how the events are distributed in one or more observable dimensions. Table 6.4 provides an overview of the parameters considered in this analysis.

6.6 Summary of Systematic Uncertainties

Parameter Variation Correlated

Live time _§6.3.1

Energy scale _§7.3

Energy resolution _§7.3

Vertex accuracy 2.9%

Vertex resolution 2.5 cm

Instrumental cut sacrifice _§8.1.1 X

8_Bν e spectrum §6.6 X ν Mixing parameters _§2.3 X Atm. ν flux _§6.2.4 Eν >100 MeV 10% X Eν <100 MeV 25% X Cross sections CCν₋d 1.2% X Atm. ν CCQE 25% (_§6.2.4) X Atm. ν other 30% (_§6.2.4) X 15.1 MeV γ 100% (_§6.2.4) X Atm. nmultiplicity 7% (_§6.2.4) X

Table 6.4: Systematic uncertainties. “Correlated” means that the parameter is assumed to

6.6 Summary of Systematic Uncertainties

Live Time A small uncertainty in the live time (the period of time the detector was fully online and collecting data) is derived by comparing live times calculated by using the global 10 MHz system clock and by using randomly-triggered (pulsed GT) data, and also considering the uncertainty due to electronics effects and burst cuts; see e.g. Reference [45]. The fractional live time uncertainties used in this analysis are taken from previous SNO publications using the same or similar data sets, per Section 6.3.1.

Energy Systematics The reconstruction-related systematics are understood through the use of calibration sources, specifically the16N source (5 MeV) at the low end, thepT source

(19.8 MeV, Phase I only) near thehependpoint, and a sample of Michel electrons extracted

from data on the high-energy end; the 8B-like 8Li source data is used a cross-check and a

high-statistics sample with which to search for unexpected tails in the energy response. The estimation of energy systematics is detailed in Chapter 7. For Phases I and II, the FTP vertex fitter is used, while FTN is chosen for Phase III. The RSP energy estimator is used for all three phases. For more details on vertex and energy reconstruction, see Section 5.6.

Vertex Reconstruction Systematics As with the energy estimation, uncertainties in the reconstructed position and direction can distort observed spectra and shift events into or out of the analysis window. These uncertainties have been estimated based on comparison of calibration data and Monte Carlo for previous SNO publications; I have used values from Reference [48].

Instrumental Cut Sacrifice The low-level instrumental background cuts described in Section 6.3.2.1 unfortunately will also remove a small number of signal events. This cannot be estimated using Monte Carlo, since instrumental backgrounds are not modeled in the simulation. Instead, an estimate of the sacrifice is based on calibration source data.

6.6 Summary of Systematic Uncertainties

While most past efforts have focused on the energy range relevant to 8B oscillation

analysis, in the preparation of Reference [15] an estimation was made for higher energies (up to 35 MeV) using a combination of16N,8Li,pT, and laser source data. The instrumental cut sacrifice was fit with a quadratic function, as shown in Figure 6.4. This result is used for the present analysis, and assumed to apply to all three phases.

It is clear that the fit is poor at the high-energy side, specifically the high-energy laser data. The systematic error shown in the figure is about 3% up 8.5 MeV and increasing thereafter to a maximum 11% at 40 MeV. For the present analysis, the errors beyond 8.4 MeV are increased such that the maximum at 40 MeV is 25%, more representative of the

spread in calibration data. A simple linear scaling is used to expand the uncertainty σ,

where

σ(T >8.4 MeV)_→(1.0 + 0.0394_·(T ₋8.4))σ.

8_{B ν}

e Spectrum Shape The best measurement of the energy spectrum for 8Bβ+ decay neutrinos [85] is inferred from a positron energy spectrum, which is in turn inferred from a

measurement of8Be decayαenergies. The difficulty of the measurement and the corrections

in each step result in an effective energy scale uncertainty in P(Eν). This energy shift is modeled as a distortion in the shape of the spectrum, and Monte Carlo events are reweighted according to the parent neutrino energy. The distortion is shown in Figure 6.5.

Solar Neutrino Oscillation Parameters The oscillation parameters relevant for so- lar neutrinos, ∆m2₁₂,θ12, and θ13, have been tightly constrained by recent global analyses

combining the results of solar neutrino observatories, KamLAND, and short-baseline exper- iments. For this analysis the parameter values recommended by the Particle Data Group [28] are used; these are also summarized in Section 2.3. Values are sampled within their respective uncertainties in order to propagate this systematic.

6.6 Summary of Systematic Uncertainties

Figure 6.4: Signal sacrifice due to instrumental background cuts, as measured in the Phase I

6.7 Corrections to Data and Monte Carlo