KTeV e'/e plots
Updated March 6, 2003.
[e'/e Results]
"Measurements of Direct CP Violation, CPT Symmetry,
and Other Parameters in the Neutral Kaon System"

beamline.eps
Top view of the KTeV beamline, showing the BeO target, absorbers, collimating system, Mask Anti, and regenerator. The common absorber is a 7.62 cm thick Pb slab followed by a 52.3 cm slab of beryllium. The movable absorber is a 45.7 cm slab of beryllium that alternates beam positions once every minute along with the regenerator. The crossover absorber is a 2 m thick iron slab. Note the different horizontal and vertical scales.


detector.eps
Top view of the KTeV (E832) detector. The evacuated decay volume extends to z = 159m.


dccell.eps
Drift chamber hexagonal cell geometry showing six field wires (open circles) around each sense wire (solid dots). The vertical dashed lines denote the boundaries of the ``offsetcells'' used in the trackseparation cut. For example, two offsetcells are between tracks 1 and 2.


sod.eps
Deviation of the sum of drift distances (SOD) from the nominal cell size of 6.35 mm, for the yviews using a sample of K>pi^{+}pi^{} decays. The arrows indicate the + 1mm requirement for a good hitpair. The data are shown as dots. The histogram is the Monte Carlo (MC) prediction .


csilayout.eps
Beamline view of the KTeV CsI calorimeter, showing the 868 larger outer crystals and the 2232 smaller inner crystals. Each beam hole size is 15 x 15 cm^2 and the two beam hole centers are separated by 0.3m.


eopreslin.eps
(a) E/p distribution based on electrons from K_{L}>pi e nu decays, where E is the energy measured in the CsI calorimeter and p is the momentum measured in the spectrometer;
(b) electron energy resolution vs. momentum (dots) obtained by subtracting the tracking resolution, shown by the smooth curve, from the E/presolution;
(c) E/pmean vs. momentum before the linearity correction is applied.


regdiagram.eps
(a) Diagram of the regenerator and (b) magnified view of the downstream end of the regenerator. PMTs are not shown. The dimension of each element is given in the figure. The kaon beam enters from the left. Vertical arrows above the lead and scintillator show the effective edge locations for K>pi^{0}pi^{0} and K>pi^{+}pi^{} decays; the width of each arrow indicates the uncertainty.


rcma.eps
(a) Transverse layout for one of five photon veto detectors between the regenerator and the vacuumwindow. The square aperture size varies, but is roughly 1 meter.
(b) MA photon veto detector (z=123 m). The two MA beam hole sizes are 9 x 9 cm^2 and their centers are separated by 20 cm. For both detectors the shaded region indicates the active veto area. The PMTs are at the outer edges of each detector.


cadiagram.eps
The Collar Anti (CA) is shown as the two shaded ``pictureframe'' regions that cover the inner 60\% (1.50 cm) of the CsI crystals surrounding the beam holes. The neutral beams go into the page, and the two beamhole centers are separated by 30 cm. Wavelength shifting fibers transmit the scintillation light to PMTs at the edges of the calorimeter.


mass.eps
Invariant mass distributions for (a) vacuumbeam pi^{+}pi^{}, (b) regeneratorbeam pi^{+}pi^{}, (c) vacuumbeam pi^{0}pi^{0}, (d) regeneratorbeam pi^{0}pi^{0}. All other analysis cuts are applied. The vertical arrows indicate the accepted mass range.


pt2diagram.eps
Illustration of the transverse momentum, $\vec{p}_T$, for a kaon that scatters in the regenerator and then decays at the point labeled ``decay vertex.'' The line connecting the target to R_{reg} represents the kaon trajectory upstream of the regenerator, $\vec{p}$ is the measured momentum of the pi^{+}pi^{} system, and z_{reg} is the distance from the target to the downstream end of the regenerator.


pt2datamcmaps.eps
pi^{+}pi^{} p_{T}^{2} distributions after all other K>pi^{+}pi^{} analysis cuts in (a) the vacuum beam and (b) the regenerator beam. The backgroundsubtracted data are shown as dots, and the histogram shows the MC prediction. The selection cut is shown by the arrows. The dotted histogram in the vacuum beam shows the MC prediction without the effects of wire inefficiency, delayed hits, and accidentals.


ringdatamc.eps
Vacuum and regenerator RING distributions for K>pi^{0}pi^{0} events after all other analysis cuts and after background subtraction. The data (MC) are shown by the dots (histogram). The vertical arrows show the signal selection of RING < 110 cm^2.


regmatch.eps
(a) Reconstructed K>pi^{0}pi^{0} zvertex near the regenerator edge for data (dots) using the K_{e3} electron calibration, and for MC (histogram).
(b) Same as (a) after the final energy scale adjustment is applied.
(c) DataMC difference in the reconstructed zvertex (meters) in 10 GeV kaon energy bins, before the final energy scale adjustment.


escale.eps
(a) The difference between the reconstructed data and MC neutral vertex at different locations within the decay region (1997 sample). The K>pi^{0}pi^{0} mode at z=125 m (solid dot) has a dataMC difference of zero by definition since the regenerator edge has been matched. The vacuumwindow pi^{0}pi^{0} crosscheck at z=159 m (solid dot) shows the largest discrepancy; the open circles and K_{L}>pi^{+}pi^{}pi^{0} band show other crosschecks. The hatched region shows the range of discrepancies covered by the assigned systematic uncertainty.
(b) The reconstructed pi^{0}pi^{0} vertex distribution relative to the vacuumwindow for data after matching the regenerator edge (dots), for the default MC (histogram), and for the MC shifted 2.46 cm downstream (dashed histogram).


cosct.eps
y vs. x distribution of the kaon trajectory projected back to the z position of the defining collimator in the vacuum beam. The sample shown here is after all K>pi^{+}pi^{} analysis cuts, except that the p_{T}^{2} cut is changed to P_{T}^{2} > 1000 MeV^{2}/c^{2}. The square bands correspond to the edges of the defining collimators.


tdk_rgsct.eps
Acceptancecorrected distribution of the number of regenerator beam K>pi^{+}pi^{} decays vs. the number of K_{S} lifetimes (t/tau_{S}), for kaon momenta between 40 and 50 GeV/c. The proper time t=0 corresponds to the downstream edge of the regenerator. The p_{T}^{2} ranges are indicated on the plot for each curve. The thick curve is for coherent K>pi^{+}pi^{} decays. The thin solid curve corresponds to small p_{T}^{2} and is mostly from diffractive scattering. The dashed curve is for large p_{T}^{2} events, which are due to both inelastic and diffractive scattering. The fluctuations are due to statistics. All K>pi^{+}pi^{} cuts except p_{T}^{2} have been applied. Backgrounds from collimator scattering and semileptonic decays have been subtracted.


pt2overlay.eps
Data p_{T}^{2} distribution after all other K>pi^{+}pi^{} selection cuts for (a) the vacuum beam and (b) the regenerator beam. The Monte Carlo predictions for the background components are overlaid. Events with p_{T}^{2} < 250 MeV^{2}/c^{2} (vertical arrow) are included in the final K>pi^{+}pi^{} sample.


ringoverlay.eps
Data RING distribution after all other K>pi^{0}pi^{0} selection cuts for (a) the vacuum beam and (b) the regenerator beam. The Monte Carlo predictions for the background components are overlaid. Events with RING < 110 cm^2 (vertical arrow) are included in the final K>pi^{0}pi^{0} sample.


zbkgneut.eps
K>pi^{0}pi^{0} backgroundtosignal (B/S) ratio vs. zvertex in 1 meter bins. The regenerator (vacuum) beam is represented by solid dots (crosses). The vertical arrow shows the location of the downstream edge of the regenerator.


pzdata.eps
(a) zvertex distribution for reconstructed K>pi^{+}pi^{} decays for the vacuum beam (thick) and regenerator beam (thin histogram).
(b) zvertex distributions for reconstructed K>pi^{0}pi^{0} decays.
(c) Kaon momentum distributions for reconstructed K>pi^{+}pi^{} decays.
(d) Kaon momentum distributions for reconstructed K>pi^{0}pi^{0} decays.
All K>pi pi analysis cuts have been applied and background has been subtracted.


mczacc.eps
MC acceptance vs. zvertex (2 meter bins) for K>pi pi decays with momentum range 7080 GeV/c. The solid (dotted) histogram refers to the charged (neutral) decay mode as indicated on the plot.


vtxz.eps
Comparison of the vacuum beam z distributions for data (dots) and MC (histogram). The datatoMC ratios on the right are fit to a line, and the zslopes (see text) are shown. The neutral distributions are for the combined 1996+1997 samples; the charged distributions are for 1997 only.


intreg.eps
z decay distribution of K>pi^{+}pi^{} decays in the regenerator beam, for the restricted momentum range 4050 GeV/c. The MC prediction (dashed) is without the interference term that is proportional to ``2\rho \eta'' in Eq.~\ref{eq:dnreg_dt}.


crosscheck.eps
Re(e'/e) consistency checks. The first five data points correspond roughly to onemonth time periods. RegLeft and RegRight correspond to the two regenerator positions. Magnet+ and Magnet correspond to the two magnet polarities, with the K>pi^{0}pi^{0} sample common to both results. The uncertainties shown within each category are independent statistical errors.


epvspk.eps
Results of twelve independent fits in 10 GeV/c wide p bins for: (a) Re(e'/e) and (b) f_{}(70 GeV/c). Within each kaon momentum bin, Re(e'/e) and f_{}(70 GeV/c) are extracted from the same fit. Only statistical errors are shown. Each dashed line shows the average of all momentum bins.


rewgt.eps
(a) K>pi^{+}pi^{} track illumination in the DC1 yview for vacuum (dots) and regenerator (histogram) beams.
(b) The same track illumination after applying the weight factor to the vacuum beam. The vacuumtoregenerator beam ratios are shown for each case in (c) and (d); note the different vertical scales for the ratios.


kparvspk.eps
Kaon parameters as a function of kaon momentum and decay mode are shown for: (a) Delta m from pi^{+}pi^{}, (b) Delta m from pi^{0}pi^{0}, (c) tau_{S} from pi^{+}pi^{}, (d) tau_{S} from pi^{0}pi^{0}, (e) phi_{+}, and (f) Delta phi. Each dashed horizontal line is the average of all momentum bins, and the $\chi^2/$dof noted on each plot is for the consistency relative to the dashed line.


kparvstaus.eps
Dots (open circles) show the kaon parameter measurements using regenerator beam data with proper time less (greater) than three K_{S} lifetimes relative to the regenerator edge. For (a) Delta m and (b) tau_{S}, the charged and neutral mode results are shown separately. For each pair of measurements (dot and open circle), the error bars reflect statistical uncertainties and are independent. Each vertical dashed line shows the nominal result using all of the data.


regscat.eps
Regenerator scattering p_{T}^{2} distribution (solid curve) from a fit to acceptancecorrected K>pi^{+}pi^{} data. The normalization corresponds to the measured 0.074\% scatteringtocoherent background level in the charged decay mode. The hatched (clear) region shows the diffractive (inelastic) component. The total (diffractive + inelastic) scatteringtocoherent ratio is shown for K>pi^{+}pi^{} (solid) and K>pi^{0}pi^{0} (dashed). The 3\% chargedneutral difference reflects the additional 16\% suppression of inelastic scattering in the neutral mode analysis.


kparcorr.eps
1 sigma contours of statistical uncertainty (dashed) and total uncertainty (solid) for (a) Delta m tau_{S} fit (combined charged+neutral), and for (b)(d) correlations from the phi_{+} fit.


epecorr.eps
1\sigma contours of statistical uncertainty (dashed) and total uncertainty (solid) for Re(e'/e) vs. Im(e'/e) from the fit with no CPT assumptions related to phi_{+} and phi_{00}.

Send corrections to Taku Yamanaka.