Anomalies in B Decays: A Sign of New Physics?
579
At the Rencontres de Moriond, 2019, LHCb presented new R K results [15]:
(1) the Run 1 data were reanalyzed using a new reconstruction selection method,
and (2) the Run 2 data were analyzed. The results are
R
new
K,Run 1 = 0.717
+0.083
−0.071 (stat)
+0.017
−0.016 (syst) ,
R K,Run 2 = 0.928
+0.089
−0.076 (stat) ±
+0.020
−0.017 (syst) .
(4)
Combining the Run 1 and Run 2 results gives
R K = 0.846
+0.060
−0.054 (stat)
+0.016
−0.014 (syst) .
(5)
The central value is closer to the SM prediction, but, due to the smaller errors,
the discrepancy with the SM is still ∼ 2.5σ .
LHCb has also measured
R K ∗ ≡
B( ¯
B → K ∗ μ + μ − )
B( ¯
B → K ∗ e + e − )
,
(6)
finding [16]
R K ∗ =
0.660
+0.110
−0.070 (stat) ± 0.024 (syst) , 0.045 q 2 1.1 GeV
2 ,
0.685
+0.113
−0.069 (stat) ± 0.047 (syst) , 1.1 q 2 6.0 GeV
2 .
Compared to SM predictions, these correspond to discrepancies of 2.4σ and
2.5σ .
At the Rencontres de Moriond, 2019, Belle announced its measurement of
R K ∗ [17]:
R K ∗ =
⎧
⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨
⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩
0.52
+0.36
−0.26 ± 0.05 , 0.045 q 2 1.1 GeV
2 ,
0.96
+0.45
−0.29 ± 0.11 , 1.1 q 2 6.0 GeV
2 ,
0.90
+0.27
−0.21 ± 0.10 , 0.1 q 2 8.0 GeV
2 ,
1.18
+0.52
−0.32 ± 0.10 , 15.0 q 2 19.0 GeV
2 ,
0.94
+0.17
−0.14 ± 0.08 , 0.045 q 2 .
Although the central values are closer to the SM predictions, the errors are
considerably larger than in the LHCb measurement.
• On average, older measurements of the branching ratio of B s → μ + μ − were in
agreement with the prediction of the SM [18–20]. However, a new measurement
by ATLAS disagrees with SM by 2.4σ [21]. Combining all results leads to
tension of ∼ 2σ with the SM.
There are therefore quite a few measurements of observables that are in disagreement with the predictions of the SM. All of these involve the decay b → sμ + μ − ,
579
At the Rencontres de Moriond, 2019, LHCb presented new R K results [15]:
(1) the Run 1 data were reanalyzed using a new reconstruction selection method,
and (2) the Run 2 data were analyzed. The results are
R
new
K,Run 1 = 0.717
+0.083
−0.071 (stat)
+0.017
−0.016 (syst) ,
R K,Run 2 = 0.928
+0.089
−0.076 (stat) ±
+0.020
−0.017 (syst) .
(4)
Combining the Run 1 and Run 2 results gives
R K = 0.846
+0.060
−0.054 (stat)
+0.016
−0.014 (syst) .
(5)
The central value is closer to the SM prediction, but, due to the smaller errors,
the discrepancy with the SM is still ∼ 2.5σ .
LHCb has also measured
R K ∗ ≡
B( ¯
B → K ∗ μ + μ − )
B( ¯
B → K ∗ e + e − )
,
(6)
finding [16]
R K ∗ =
0.660
+0.110
−0.070 (stat) ± 0.024 (syst) , 0.045 q 2 1.1 GeV
2 ,
0.685
+0.113
−0.069 (stat) ± 0.047 (syst) , 1.1 q 2 6.0 GeV
2 .
Compared to SM predictions, these correspond to discrepancies of 2.4σ and
2.5σ .
At the Rencontres de Moriond, 2019, Belle announced its measurement of
R K ∗ [17]:
R K ∗ =
⎧
⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨
⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩
0.52
+0.36
−0.26 ± 0.05 , 0.045 q 2 1.1 GeV
2 ,
0.96
+0.45
−0.29 ± 0.11 , 1.1 q 2 6.0 GeV
2 ,
0.90
+0.27
−0.21 ± 0.10 , 0.1 q 2 8.0 GeV
2 ,
1.18
+0.52
−0.32 ± 0.10 , 15.0 q 2 19.0 GeV
2 ,
0.94
+0.17
−0.14 ± 0.08 , 0.045 q 2 .
Although the central values are closer to the SM predictions, the errors are
considerably larger than in the LHCb measurement.
• On average, older measurements of the branching ratio of B s → μ + μ − were in
agreement with the prediction of the SM [18–20]. However, a new measurement
by ATLAS disagrees with SM by 2.4σ [21]. Combining all results leads to
tension of ∼ 2σ with the SM.
There are therefore quite a few measurements of observables that are in disagreement with the predictions of the SM. All of these involve the decay b → sμ + μ − ,