recent results from atlas in beauty and charm physics · [] introduction to b às lltransitions []...
TRANSCRIPT
Recent results from ATLAS in beauty and
charm physicsHeather Russell, McGill UniversityOn behalf of the ATLAS CollaborationLake Louise Winter Institute, 10 – 16 February 2019
[] introduction to b à s ll transitions
[] overview of ATLAS B(s) à !+!- measurement
[] overview of ATLAS Bd0 à K*!+!- angular analysis
[] prospects for future B-physics measurements on ATLAS
2
Overview
Lake Louise Winter Institute 2019Heather Russell, McGill University
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/BPhysPublicResultsAll public ATLAS B-physics results:
3
Some background: b à sℓ+ℓ- transitions
Lake Louise Winter Institute 2019Heather Russell, McGill University
b s
µ+
µ−
t
γ, Z0
W−b s
µ+
µ−ν
W− W+
tNO flavour-changing neutral currents at tree level in the SM – but can be created with box diagrams/loop diagrams
b s
µ+
µ−ν
H− H+
t
3
Some background: b à sℓ+ℓ- transitions
Lake Louise Winter Institute 2019Heather Russell, McGill University
b s
µ+
µ−
d̃i
γ, Z0
χ̃0b s
µ+
µ−
d̃i
H0
g̃
b s
µ+
µ−
t
γ, Z0
W−
b s
µ+
µ−Z ′
b s
µ+
µ−ν
W− W+
tNO flavour-changing neutral currents at tree level in the SM – but can be created with box diagrams/loop diagrams
New physics can enter at tree, loop, or box-level:
4
B(s) à !+!- andBd0 à K*!+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
t
tZ0
b
s
W+
µ+
µ�
"#$ b s
µ+
µ−
t
γ, Z0
W−"%$d d_ _ &∗$
Both Bs à !+!- andBd0 à K*!+!- decays are suppressed in the Standard Model:
ℬ(Bs → !+!-) = (3.65 ± 0.23) ×10−9
ℬ(Bd → !+!-) = (1.06 ± 0.09) ×10−10 ℬ(Bd➝K*!+!-) = (1.02 ± 0.09) × 10−6
Loop suppressedCKM-suppressedHelicity suppressed
Loop suppressedCKM-suppressed
4
B(s) à !+!- andBd0 à K*!+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
t
tZ0
b
s
W+
µ+
µ�
"#$ b s
µ+
µ−
t
γ, Z0
W−"%$d d_ _ &∗$
Both Bs à !+!- andBd0 à K*!+!- decays are suppressed in the Standard Model:
Low-rate processes can be significantly modified by small BSM effects
Indirectly sensitive to BSM particles at mass scales up to 10 TeV – far beyond the reach of direct searches
Simultaneous branching ratiomeasurement of processesB0s à !+!- and B0d à !+!-
5
Measurement of B(s) à !+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
Measured relative to well-known decay mode
Simultaneous branching ratiomeasurement of processesB0s à !+!- and B0d à !+!-
5
Measurement of B(s) à !+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
Measured relative to well-known decay mode
Signal yield in Bd or Bs channel
Simultaneous branching ratiomeasurement of processesB0s à !+!- and B0d à !+!-
5
Measurement of B(s) à !+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
Measured relative to well-known decay mode
Signal yield in Bd or Bs channel
Fiducial acceptance*efficiency for B0 dimuon system
Simultaneous branching ratiomeasurement of processesB0s à !+!- and B0d à !+!-
5
Measurement of B(s) à !+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
Measured relative to well-known decay mode
Signal yield in Bd or Bs channel
Fiducial acceptance*efficiency for B0 dimuon system
Fiducial acceptance*efficiency and signal yield for J/"K+ system
Simultaneous branching ratiomeasurement of processesB0s à !+!- and B0d à !+!-
5
Measurement of B(s) à !+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
Measured relative to well-known decay mode
Signal yield in Bd or Bs channel
Fiducial acceptance*efficiency for B0 dimuon system
Fiducial acceptance*efficiency and signal yield for J/"K+ system
ratio of hadronisation probabilities of a b-quark into B+ vs. B0 (B0
s).
(from LHCb)
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
backgrounds from partially reconstructed Bà!!X decays
6
B(s) à !+!-: backgrounds I
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
Missing energy from ”X” tracks not included in reconstructed vertex means mB appears lower
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
1
10
210
310
Even
ts /
40 M
eV ATLAS Simulation-1 = 13 TeV, 26.3 fbs X-µ +µ ®b
decayscB
Semi-leptonic decays
-µ +µ ® s0B
-µ +µ ® 0B
backgrounds from partially reconstructed Bà!!X decays
6
B(s) à !+!-: backgrounds I
Lake Louise Winter Institute 2019Heather Russell, McGill University
Submitted to JHEP, arXiv:1812.03017
4800 5000 5200 5400 5600 5800Mass of two misidentified muons [MeV]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Even
ts /
40 M
eV
h h'®Total B
±
p± K® 0B-K+ K® s
0B
-p+p ® 0B
±
K±p ® s0B
ATLAS Simulation-1 = 13 TeV, 26.3 fbs
Blinded region
Missing energy from ”X” tracks not included in reconstructed vertex means mB appears lower
fully hadronic semileptonicpeaking B à hh’
e.g. B à "+ "-
"± à !±#e.g. B à !+ # "-
"± à !±#
true muons, but not produced promptly in the decay of a B meson.
hadron misidentification
[also backgrounds from muons from fake MS tracks combined with real hadronic ID tracks]
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
02
4
6
81012
14
16
18
Even
ts /
40 M
eV
ATLAS-1 = 13 TeV, 26.3 fbs
0.4163 < BDT <= 1
2015-2016 data
Total fit
Continuum background
X background-µ +µ ®b
Peaking background-µ +µ ® 0 + B-µ +µ ® s
0B
7
B(s) à !+!-: backgrounds II
Lake Louise Winter Institute 2019Heather Russell, McGill University
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
0
10
20
30
40
50
60
70
Even
ts /
40 M
eV
ATLAS-1 = 13 TeV, 26.3 fbs
0.3312 < BDT <= 0.4163
2015-2016 data
Total fit
Continuum background
X background-µ +µ ®b
Peaking background-µ +µ ® 0 + B-µ +µ ® s
0B
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
0
20
40
60
80
100
120
140
Even
ts /
40 M
eV
ATLAS-1 = 13 TeV, 26.3 fbs
0.2455 < BDT <= 0.3312
2015-2016 data
Total fit
Continuum background
X background-µ +µ ®b
Peaking background-µ +µ ® 0 + B-µ +µ ® s
0B
4800 5000 5200 5400 5600 5800Dimuon invariant mass [MeV]
0
100
200
300
400
500
600
700
Even
ts /
40 M
eV
ATLAS-1 = 13 TeV, 26.3 fbs
0.1439 < BDT <= 0.2455
2015-2016 data
Total fit
Continuum background
X background-µ +µ ®b
Peaking background-µ +µ ® 0 + B-µ +µ ® s
0B
1- 0.8- 0.6- 0.4- 0.2- 0 0.2 0.4 0.6BDT output
00.020.040.060.08
0.10.120.140.160.180.2
Frac
tion
of e
vent
s / 0
.05
ATLAS Simulation MC-µ +µ ® s0B
Continuum bkg MC MCcB
X MC-µ +µ ®b MC
(s)0Semi-leptonic B
Increasing BDT response
Combinatorial backgrounddisentangled using a BDT with three categories of variables relating to:
Submitted to JHEP, arXiv:1812.03017
(b) the muons
(c) the rest of the event
(a) the B vertex
8
B(s) à !+!-: results
Lake Louise Winter Institute 2019Heather Russell, McGill University
[limits are diagonal ovals because the mass resolution is insufficient to resolve the two signals]
Submitted to JHEP, arXiv:1812.03017Unbinned maximum likelihood fit to m(!!) in each of the 4 BDT bins
Signal yield result:Ns = 80 ± 22, Nd = −12 ± 20
Most stringent limit to date!
0 1 2 3 4 5 6 7
]9- [10)- µ +µ ® s0BB(
0.2-
0
0.2
0.4
0.6
0.8
1
1.2
]9- [1
0)-
µ +µ
® 0B
B(
SM
ATLAS 2015-2016 data
Run 1 + 2015-2016 data
Likelihood contours for ) = 2.3, 6.2, 11.8Lln(D-2
8
B(s) à !+!-: results
Lake Louise Winter Institute 2019Heather Russell, McGill University
[limits are diagonal ovals because the mass resolution is insufficient to resolve the two signals]
Submitted to JHEP, arXiv:1812.03017Unbinned maximum likelihood fit to m(!!) in each of the 4 BDT bins
Signal yield result:Ns = 80 ± 22, Nd = −12 ± 20
Most stringent limit to date!
0 1 2 3 4 5 6 7
]9- [10)- µ +µ ® s0BB(
0.2-
0
0.2
0.4
0.6
0.8
1
1.2
]9- [1
0)-
µ +µ
® 0B
B(
SM
ATLAS Run 1 data
2015-2016 data
Run 1 + 2015-2016 data
Likelihood contours for ) = 2.3, 6.2, 11.8Lln(D-2
8
B(s) à !+!-: results
Lake Louise Winter Institute 2019Heather Russell, McGill University
[limits are diagonal ovals because the mass resolution is insufficient to resolve the two signals]
Submitted to JHEP, arXiv:1812.03017Unbinned maximum likelihood fit to m(!!) in each of the 4 BDT bins
Signal yield result:Ns = 80 ± 22, Nd = −12 ± 20
Most stringent limit to date!
0 1 2 3 4 5 6 7
]9- [10)- µ +µ ® s0BB(
0.2-
0
0.2
0.4
0.6
0.8
1
1.2
]9- [1
0)-
µ +µ
® 0B
B(
SM
ATLAS 2015-2016 data
Run 1 + 2015-2016 data
LHCb Run 1 + partial Run 2 data
Likelihood contours for ) = 2.3, 6.2, 11.8Lln(D-2
8
B(s) à !+!-: results
Lake Louise Winter Institute 2019Heather Russell, McGill University
[limits are diagonal ovals because the mass resolution is insufficient to resolve the two signals]
Submitted to JHEP, arXiv:1812.03017Unbinned maximum likelihood fit to m(!!) in each of the 4 BDT bins
Signal yield result:Ns = 80 ± 22, Nd = −12 ± 20
Most stringent limit to date!
9
Angular analysis of Bd0 à K*!+!-
Lake Louise Winter Institute 2019Heather Russell, McGill University
JHEP 10 (2018) 047, arXiv:1805.04000
Full differential angular distribution:
Angular coefficients Sihave large uncertainties
è study ratios to minimize theory uncertainties
q2 = (dilepton invariant mass)2fraction of longitudinally polarised K* mesons
0 2 4 6 8 10 12 14
]2 [GeV2q
[MeV]µµpKm5000 5200 5400 5600
Even
ts /
40 M
eV
0
1000
2000
3000
4000
5000ATLAS
-1 = 8 TeV, 20.3 fbsDataTotal Fit ModelSignalCombinatorial
L(2S) y ® bL +(2S) Ky ® +B(2S) K*y ® sB
10
Bd0 à K*!+!-: event selection
Lake Louise Winter Institute 2019Heather Russell, McGill University
[MeV]µµpKm5000 5200 5400 5600
Even
ts /
40 M
eV
0
10000
20000
30000
40000
50000ATLAS
-1 = 8 TeV, 20.3 fbsDataTotal Fit ModelSignalCombinatorial
L y J/® bL + Ky J/® +B K*y J/® sB
" (resonance removed from analysis)
Signal regionq2 # [0.04, 6]\[0.98, 1.1] GeV2
Analysis performed in q2 bins:[0.04, 2.0], [2.0, 4.0], [4.0, 6.0]
[0.04, 4.0], [1.1, 6.0][0.04, 6.0]
Four reconstructed objects:K $ ! !
All must be in the fiducial tracking volume of ATLAS: |%| < 2.5
m(K $) # [846, 946] MeV (K* mass)m(K$!!) # [5.150, 5.7] GeV (B0 mass)
Important - tracks come from thesame location: B0 vertex χ2/n.d.f. < 2
&(2s)J/&
Control regions:extract mass and width of B0
J/& &(2s)
[MeV]µµpKm5200 5400 5600
Even
ts /
25 M
eV
0
10
20
30
40-1 = 8 TeV, 20.3 fbsATLAS
2 [4.0, 6.0] GeVÎ 2S5 fold, q
DataTotal Fit ModelSignalBackground
11
Bd0 à K*!+!-: angular fit results
Lake Louise Winter Institute 2019Heather Russell, McGill UniversityLqcos
0 0.2 0.4 0.6 0.8 1
Even
ts /
0.04
0
10
20
30-1 = 8 TeV, 20.3 fbsATLAS
2 [4.0, 6.0] GeVÎ 2S5 fold, qDataTotal Fit ModelSignalBackground
Kqcos 1- 0.5- 0 0.5 1
Even
ts /
0.08
0
10
20
30
40
50-1 = 8 TeV, 20.3 fbsATLAS
2 [4.0, 6.0] GeVÎ 2S5 fold, qDataTotal Fit ModelSignalBackground
[rad]f0 1 2 3
pEv
ents
/ 0.
04
0
10
20
30-1 = 8 TeV, 20.3 fbsATLAS
2 [4.0, 6.0] GeVÎ 2S5 fold, qDataTotal Fit ModelSignalBackground
", #K, #L fit simultaneously in each q2 bin:[shown: 4 < q2 < 6 GeV2]
0 5 10 15]4c/2 [GeV2q
1-
0.5-
0
0.5
15'P
(1S)
y/J
(2S)
y
LHCb dataBelle data
ATLAS dataCMS data
SM from DHMVSM from ASZB
12
Bd0 à K*!+!-: results
Lake Louise Winter Institute 2019Heather Russell, McGill University
0 2 4 6 8 10]2 [GeV2q
1-
0.5-
0
0.5
1
1.5
2
5P'
DataCFFMPSV fittheory DHMVtheory JC
ATLAS -1 = 8 TeV, 20.3 fbs
0 2 4 6 8 10]2 [GeV2q
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8LF
DataCFFMPSV fittheory DHMVtheory JC
ATLAS -1 = 8 TeV, 20.3 fbs
Tension in higher q2 bins amongst most measurements:
NB: uses LHCb data!
13
Looking forward – HL-LHC
Lake Louise Winter Institute 2019Heather Russell, McGill University
0 2 4 6 8 10]2 [GeV2q
1-
0.5-
0
0.5
1
1.5
2
5P' ATLAS JHEP 10 (2018) 047
CFFMPSV fittheory DHMVtheory JC
6µ10µATLAS HL 6 (stat. only)µ10µATLAS HL
ATLAS Preliminary-1 = 14 TeV, 3000 fbs
Projections from Run 1 dataµµ K*®B
Upgraded inner tracker, higher statistics allow much higher precision on BR measurement
ATL-PHYS-PUB-2019-003
2 3 4 5 6]-9 ) [10-µ +µ ® s
0B( B
0.1-
0
0.1
0.2
0.3
0.4
0.5
0.6]-9
) [1
0- µ + µ
® 0B(
B
ATLAS Simulation Preliminary-µ+µ ® (s)
0Bworking point x60 Run1 statistics stat + syst
stat onlySM prediction
ATL-PHYS-PUB-2018-005
Expect dramatically reduced uncertainties on Bd0 à K*!+!-parameters, even after accounting for harsher muon pT thresholds
[] B(s) à !+!- measurement presents most stringent B à !+!- limit to date
[] Bd0 à K*!+!- angular analysis, compatible
with results from other experiments
[] run 4 HL-LHC prospects show promising improvement in sensitivity
[] look forward to results with the full 140 fb-1
run 2 dataset14
Conclusions
Lake Louise Winter Institute 2019Heather Russell, McGill University
0 1 2 3 4 5 6 7
]9- [10)- µ +µ ® s0BB(
0.2-
0
0.2
0.4
0.6
0.8
1
1.2
]9- [1
0)-
µ +µ
® 0B
B(
SM
ATLAS Run 1 data2015-2016 dataRun 1 + 2015-2016 dataLHCb Run 1 + partial Run 2 data
Likelihood contours for ) = 2.3, 6.2, 11.8Lln(D-2
0 5 10 15]4c/2 [GeV2q
1-
0.5-
0
0.5
15'P
(1S)
y/J
(2S)
y
LHCb dataBelle data
ATLAS dataCMS data
SM from DHMVSM from ASZB
2 3 4 5 6]-9 ) [10-µ +µ ® s
0B( B
0.1-
0
0.1
0.2
0.3
0.4
0.5
0.6]-9
) [1
0- µ + µ
® 0B(
B
ATLAS Simulation Preliminary-µ+µ ® (s)
0Bworking point x60 Run1 statistics stat + syst
stat onlySM prediction
Backup
Variable Description
pBT
Magnitude of the B candidate transverse momentum�!pT
B.
�2
PV,DV xy Compatibility of the separation�!�x between production (i.e. associated PV) and decay (DV)
vertices in the transverse projection:�!�xT ·⌃ �1
��!�xT
·�!�xT, where ⌃��!�xT
is the covariance matrix.
�Rflight Three-dimensional angular distance between�!p B
and�!�x:
p↵2D
2 + (�⌘)2
|↵2D | Absolute value of the angle in the transverse plane between�!pT
Band�!�xT.
Lxy Projection of�!�xT along the direction of
�!p BT
: (�!�xT ·�!pT
B)/|�!pTB |.
IP3D
B Three-dimensional impact parameter of the B candidate to the associated PV.
DOCAµµ Distance of closest approach (DOCA) of the two tracks forming the B candidate (three-dimen-
sional).
��µµ Azimuthal angle between the momenta of the two tracks forming the B candidate.
|d0 |max-sig. Significance of the larger absolute value of the impact parameters to the PV of the tracks
forming the B candidate, in the transverse plane.
|d0 |min-sig. Significance of the smaller absolute value of the impact parameters to the PV of the tracks
forming the B candidate, in the transverse plane.
Pmin
LThe smaller of the projected values of the muon momenta along
�!pTB
.
I0.7 Isolation variable defined as ratio of |�!pTB | to the sum of |�!pT
B | and the transverse momenta of
all additional tracks contained within a cone of size �R =p
(��)2 + (�⌘)2 = 0.7 around the
B direction. Only tracks matched to the same PV as the B candidate are included in the sum.
DOCAxtrk DOCA of the closest additional track to the decay vertex of the B candidate. Only tracks
matched to the same PV as the B candidate are considered.
Nclose
xtrkNumber of additional tracks compatible with the decay vertex (DV) of the B candidate with
ln( �2
xtrk,DV)<1. Only tracks matched to the same PV as the B candidate are considered.
�2
µ,xPVMinimum �2
for the compatibility of a muon in the B candidate with any PV reconstructed in
the event.
15
B(s) à !+!-: BDT variables
Lake Louise Winter Institute 2019Heather Russell, McGill University
Number of signal events insufficient to fit the full angular distribution è trigonometric folding used to reduce the number of fit parameters
Perform multiple fits, extracting FL, S3, and one Si per fit[Use FL, S3 results with lowest systematic uncertainty]
Example: for S5, transform:
Note: cannot extract S6 (AFB) or S9 in this manner
16
Bd0 à K*!+!-: parameter extraction
Lake Louise Winter Institute 2019Heather Russell, McGill University
Asymmetric, so cancel in folding:
sin(ϕ)sin(2θL)cos(θL)