Observation of the Bottomonium Ground State in the Decay Y(3S) to ynb Page: 6 of 7
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> 10_,__,__,,_,,__,__,____ ,, ,, ,, from the fit is 147/113 1.3. Finally Figure 2(c) shows
the data points with all components except the Yb signal
500 (a) subtracted, overlaid with the Yb signal PDF. The fitted Yb
signal yield is 19200 2000 2100 events, where the first
400 error is statistical and the second systematic. A total
systematic uncertainty of 11% is estimated by varying
300 the Breit-Wigner width in the Yb PDF to 5, 15, and 20
MeV, setting the ISR T(1S) component to 1 o- of the
200 nominal rate, and varying the PDF parameters fixed in
the fit by 1 -. The largest contribution (10%) is from
100 the nb width variation.
The nb signal significance is estimated using the ratio
S . . . , ,,log(Lmax/Lo), where Lmax and Lo are the likelihood val-
8.5 0.6 0.7 0.8 0.9 1 1.1 ues obtained from the nominal fit and from a fit with the
E7 (GeV) Yb PDF removed, respectively. Fits have been performed
where the parameters entering the systematic uncertain-
10000 ties have been varied within their errors. Data have then
8000 (b) been fitted with all parameters simultaneously moved by
one standard deviation in the direction of lower signifi-
6000 cance. This conservative approach yields a signal signif-
icance greater than 10 standard deviations.
4000 As a cross check, we also perform a fit where the yield
of the ISR T(1S) component is left free, and we obtain
2000 24800 2300 events for this component. This is consistent
0 , ' + with the estimate using the below-T(4S) data and pro-
- + + -'+ vides an important validation of the XbJ(2P) line shape
-2000 parameterization. The yield and peak position of the Y
0.5 0.6 07 08 0.9 1.1 signal from this fit are unchanged.
Ey (GeV) The E, signal peak value from the fit is 917.4 2. MeV.
We apply a photon energy calibration shift of 3.8 2.0
8000 ,MeV, obtained by comparing the fitted position of the
XbJ(2P) peak to the known PDG value. After including
6000 (c) an additional systematic uncertainty of 1.3 MeV from
the fit variations described above, we obtain a value of
E, 921.2+z.8 2.4 MeV for the Yb signal.
The Yb mass derived from the E, signal is M(nb)
9388.9iia 2.7 MeV/c2. Using the PDG value of
2000 -9460.3 0.3 MeV/c2 for the T(1S) mass, we determine
the T(1S)-Yb mass splitting to be 71.4-2- 2.7 MeV/c2.
o The value we measure for the splitting is larger than
most predictions based on potential models , but rea-
-2000 - sonably in agreement with predictions from lattice calcu-
- - Ilations . The mass splitting between the T(1S) and
-4000 ' ' ' the Yb(1S) is a key ingredient in many theoretical cal-
.5~~~~ ~ (Ge07 0.V)9 1 . culations. The precision of our measurement will allow,
E7 (GeV) among others, a more precise determination of the lattice
spacing  and new precision determinations of a8 .
We estimate the branching fraction by correcting the
G. 2: (a) Inclusive photon spectrum in the region 0.50 < signal yield with the reconstruction efficiency (E) from
< 1.1 GeV. The component PDFs determined from the fit simulated signal MC events, and then dividing it by the
e overlaid on the data points. A prominent xbJ(2P) peak is number of T(3S) events in the data sample. The branch-
arly seen. The dashed line corresponds to the non-peaking ing fraction of the decay T(3S) -- nb is found to be
ckground component. (b) Inclusive photon spectrum af-
subtracting the non-peaking background, with PDFs for (4.8 0.5 1.2) x 10-4, where the first uncertainty is sta-
1(2P) peak (solid), ISR T(1S) (dot), 96 signal (dash) and tistical and the second systematic. The systematic uncer-
e sum of all three (solid). (c) Inclusive photon spectrum tainty of 25% comes from uncertainties in the signal yield
er subtracting all components except the n9 signal. The (11%) and E (22%). The latter is obtained by comparing
CB function shape describes the data points well.
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Aubert, B. Observation of the Bottomonium Ground State in the Decay Y(3S) to ynb, article, July 11, 2008; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc895669/m1/6/: accessed January 18, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.