r lambert, cerncern cpv, 18th june 20101 flavour-specific asymmetry and lhcb robert w. lambert on...
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R Lambert, CERN CERN CPV, 18th June 2010 1
Flavour-specific asymmetryand LHCb
Robert W. Lambert
On behalf of the LHCb collaboration
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Introduction
D exclusive asymmetry hep-ex 0904.3907
D Inclusive asymmetry hep-ex 1005.2757
What can we do at LHCb?
R Lambert, CERN CERN CPV, 18th June 2010 2
00 XDB ss
... bb
-31.41.5- 10 (syst)] 9.1(stat) 1.7[ s
fsa
-310 (syst)]46.12.51(stat) 57.9[ bA
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Literature
Reading material: LHCb
– CERN-LHCb-2007-054 Public note from old Monte Carlo– CERN-THESIS-2008-045 Paul’s Thesis– CERN-THESIS-2009-001 Rob’s Thesis– CERN-THESIS-2010-076 Ken’s Thesis
Theory– hep-ph 0406300 U. Nierste – hep-ph 0612167 [JHEP] A. Lenz, U. Nierste– hep-ph 0605028 [PRL] Y. Grossman et al.– hep-ph 0604112 [PRL] Z. Ligeti et al.
Other measurements– hep-ex 0505017 [PRD] Belle– hep-ex 0202041 [PRL] Babar– hep-ex 0101006 [PRL] Cleo– Note 9015 CDF inclusive
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Outline
1. Theory .. from an experimentalist
2. Experimental Status
3. Complications at LHCb
4. Why LHCb?
5. Measurements at LHCb
6. Real data highlights
7. Outlook and Prospects
8. Conclusions
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Flavour-specific decays Favoured/Allowed Not allowed at tree Through mixing
Flavour specific asymmetry, afs, parameterises CPV in mixing
R Lambert, CERN CERN CPV, 18th June 2010 5
Flavour-specific asym.
fBBfBB
fBBfBBtAa
qqqq
qqqqqfs
qfs
0000
0000
oror
oror)(
ss DB0
0sB
sD
fBq 0
fBB qq 00
fBq 0
ss DB0
DBd0
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The whole shebang
Three different parameters fully constrain b-mixing
afs is very small in the standard model
R Lambert, CERN CERN CPV, 18th June 2010 6
)(
)(
2)(
)(0
0
0
0
tB
tBiM
tB
tB
dt
di
q
qqq
q
q
q
qqfs Ma
12
12Im ,2,arg2 1212
1212
qqL
qHqq
qqq
LqHq MMMm
M
5
4
104.01.2
101.10.5
SMs
fs
SMdfs
a
a
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Discovery Potential
afs is sensitive to new physics (NP): Sensitive to loop contributions Sensitive to new CPV phases
If we allow a single NP phase in the mixing
R Lambert, CERN CERN CPV, 18th June 2010
0sB
0sB?
7
sinRecosIm12
12
12
12SM
SM
SM
SMNP
MMa
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sinRecosIm12
12
12
12SM
SM
SM
SMNP
MMa
Discovery Potential
afs is sensitive to new physics (NP): Sensitive to loop contributions Sensitive to new CPV phases
If we allow a single NP phase in the mixing
R Lambert, CERN CERN CPV, 18th June 2010
0sB
0sB?
8
SMfsa
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afs is sensitive to new physics (NP): Sensitive to loop contributions Sensitive to new CPV phases
If we allow a single NP phase in the mixing
Up to 200-times the SM ... but ... (4x10-3)< D measurement
sinRecosIm12
12
12
12SM
SM
SM
SMNP
MMa
Discovery Potential
R Lambert, CERN CERN CPV, 18th June 2010
0sB
0sB?
9
5101.2 3100.4
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Experimental Status
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B-factories
Babar, Belle, Cleo all use the di-muon sample Know the initial state (4S) Time-integrated number-counting of di-muons Possible muon detector asymmetry is important to measure
R Lambert, CERN CERN CPV, 18th June 2010 11
bb
c
m-
n
310)5.51.1(
)(
factbdfs
dfsSL
a
aNN
NNA
lXlbbNNc b
m-
n
hep-ph 0605028
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Exclusive measurement
D have also made an exclusive measurement Search for the full decay chain in the data Requires full reconstruction Flavour-tagging provides extra information Lower and more easily understood backgroundsx Extra detector asymmetryx Lower statistics
R Lambert, CERN CERN CPV, 18th June 2010 12
Bs
Bs
Ds+
m-
n
3-1.41.5-
00
00
10 (syst)] 9.1(stat) 1.7[
sfs
sfs
ss
ssSL
a
afBfB
fBfBA
hep-ex 0904.3907
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CDF Inclusive
CDF use only the di-muon sample Don’t know the initial state (pp) Time-integrated number-counting Possible muon detector asymmetry is important to measure
R Lambert, CERN CERN CPV, 18th June 2010 13
bb
c
m-
n
c b
m-
n
3-10 (syst)]8.69.0(stat) 0.8[
582.0418.0
)(
b
dfs
sfs
b
A
aaNN
NNA
lXlbbNN
2fact-b using10) 9(ip).0 (syst)6.1 (stat)1.20.2( s
fsa
Note 9015
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New D inclusive
R Lambert, CERN CERN CPV, 18th June 2010 14
bb
c
m-
n
c b
m-
n
D used primarily the di-muon sample Don’t know the initial state (pp) Time-integrated number-counting Possible muon detector asymmetry is important to measure
2fact-b using
3-
10)75.046.1(
10 (syst)]46.12.51(stat) 57.9[
506.0494.0
)(
sfs
b
dfs
sfs
b
a
A
aaNN
NNA
lXlbbNN
hep-ex 1005.2757
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New D inclusive
Key Systematics (it’s difficult to be inclusive!) Kaons decaying in-flight Punch-through of hadrons to muons
Key methods Rely on real data, cross-check with well-tuned Monte Carlo Use the inclusive single muon sample to get extra information Reverse magnets to remove most detector asymmetry Do many many cross-checks in different phase-space regions
Result, 3.2 s !
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45.06.0 103.2
SM % 0.3) 1( bA
hep-ex 1005.2757
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Summary
Before the New D Inclusive Measurement A lot of measurements All consistent with SM +/- 1%
The New D Inclusive Measurement First evidence of departure from the SM Statistics-limited, so may improve over the next year
A lot of theory interest , so, how will LHCb help?
... The situation is significantly more complicated ...
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Complications
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The simple formula
qqb
q
qqp
qfs
qc
qfsq
fs S
B
t
tmaatA
22/cosh
cos
2222)(
10-3 -> 10 -5
ff
fftAqfs
)(
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R Lambert, CERN CERN CPV, 18th June 2010 19
The simple formula
Polluting asymmetries are much larger than afs
Detector asymmetry dc ~(10-2)
Production asymmetry dp ~(10-2)
Background asymmetry db ~(10-3)
qqb
q
qqp
qfs
qc
qfsq
fs S
B
t
tmaatA
22/cosh
cos
2222)(
1/
/
1)(
)(
1)(
)(
0
0
SB
SB
IN
IN
f
f
b
p
i
ic
10 -2 10 -2 10 -310-3 -> 10 -5
Very Complicated
ff
fftAqfs
)(
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LHCb
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Detector Asymmetry, dc
Matter detector hadronic interactions are asymmetric
Magnet divides +/- charge, allowing +/- detector asymmetry We need to reverse the magnet regularly
R Lambert, CERN CERN CPV, 18th June 2010 21
MC Asymmetry in Muons
Left Right
+ve -ve
After 4Tm Magnet
Kaon PDG cross-section
PDG
0
20
40
60
80
100
120
0.1 1 10 100 1000
momentum in lab frame Plab / GeV c
had
ron
ic c
ross
-sec
tio
n /
mb. K-, p
K+, p
-1
Kaon interaction cross-section
K- pK+ p
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LHC
R Lambert, CERN CERN CPV, 18th June 2010 22
An amazing machine
Unfortunately also not CP symmetric
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Production Asymmetry, dp
LHC is a proton-proton collider: not CP-symmetric
LHCb is at high rapidity where production asymm. are largest
There is never a simple control channel to measure dp
R Lambert, CERN CERN CPV, 18th June 2010 23
-0.020
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
0 50 100 150 200 250 300 350
Energy, E / GeVP
rod
uc
tio
n A
sy
mm
etr
y,
p
dp (B0 and B0)
Valence QuarkScattering
PYTHIA
Explicitly asymmetric at LHC
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Why LHCb?
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Why LHCb?
LHCb is a dedicated, precision, b-physics experiment
More statistics: we’re in the forward region, and at LHC
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Being Timely
Proper Time: LHCb Velo precise down to 35 fs!
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Being Precise
Particle ID: separation handled by dedicated subdetectors
Two RICHes, Calorimetry and Muon system
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RICH 1(Vertical)
RICH 2(Horizontal)
MA
GN
ET
TT
T1-T
3
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Being Exclusive
Our forte: exclusive, reconstructed, b-decays
In particular, time-dependent measurements
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Monte-Carlo!
~100k Ds in 5 fb-1 ~100k Ds in 0.05 fb-1
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Measurements
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Measurements
Inclusive
Exclusive
Subtraction method
combine and
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... bb
00 XDB ss
00 XDBd
ss DB0
00 XDB ss 00 XDBd
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Inclusive at LHCb
Channel
Measured by D (see earlier)
Complications Physics! Production asymmetry: N(b)≠N(anti-b) [in acceptance] PYTHIA predicts dp(b) =
Mitigating factors None, difficult to interpret this measurement
R Lambert, CERN CERN CPV, 18th June 2010 31
... bb
2
dfs
sfsb aa
A
3103.04.3
45.06.0 103.2
SM
~108 per fb-1
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Inclusive at LHCb
Channel
Measured by D (see earlier)
Complications Physics! Production asymmetry: N(b)≠N(anti-b) [in acceptance] PYTHIA predicts dp(b) =
Mitigating factors None, difficult to interpret this measurement
R Lambert, CERN CERN CPV, 18th June 2010 32
... bb
3103.04.3
45.06.0 103.2
SM
~108 per fb-1
2
dfs
sfsb aa
A
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Hadronic at LHCb
Channel
R Lambert, CERN CERN CPV, 18th June 2010 33
KKDB ss0 ~105 per fb-1
CERN-THESIS-2008-045
CERN-LHCb-2007-017
Monte-Carlo!
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Hadronic at LHCb
Channel
Measures
Complications Must fix either dc or dp in the fit – (db can be fit beforehand)
Mitigating factors Detector asymmetry small ~10-4 Fit afs and dp. – With excellent proper time resolution (35 fs)
R Lambert, CERN CERN CPV, 18th June 2010 34
ssb
s
s
sp
sfs
sc
sfss
fs S
B
t
tmaatA
22/cosh
cos
2222)(
KKDB ss0
CERN-THESIS-2008-045
CERN-LHCb-2007-054
~105 per fb-1
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Hadronic at LHCb
Channel
Measures
Complications Must fix either dc or dp in the fit – (db can be fit beforehand)
Mitigating factors Detector asymmetry small ~10-4 Fit afs and dp. – With excellent proper time resolution (35 fs)
R Lambert, CERN CERN CPV, 18th June 2010 35
ssb
s
s
sp
sfs
sc
sfss
fs S
B
t
tmaatA
22/cosh
cos
2222)(
KKDB ss0
CERN-THESIS-2008-045
CERN-LHCb-2007-054
~105 per fb-1
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Semi-leptonic
Channel (q = s/d)
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00 XDB qq ~106 per fb-1
CERN-LHCb-2007-054
Monte-Carlo!
00 XDB ss
00 XDBd
Monte-Carlo!
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Semi-leptonic
Channel (q = s/d)
Measures
Complications Missing neutrino makes proper-time resolution worse (≥120 fs?) Detector asymmetry large and difficult to measure
Mitigating factors Lots of statistics, but this makes dc even more important
R Lambert, CERN CERN CPV, 18th June 2010 37
00 XDB qq
qqb
q
qqp
qfs
qc
qfsq
fs S
B
t
tmaatA
22/cosh
cos
2222)(
CERN-LHCb-2007-054
~106 per fb-1
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Semi-leptonic
Channel (q = s/d)
Measures
Complications Missing neutrino makes proper-time resolution worse (≥120 fs?) Detector asymmetry large and difficult to measure
Mitigating factors Lots of statistics, but this makes dc even more important
R Lambert, CERN CERN CPV, 18th June 2010 38
00 XDB qq
qqb
q
qqp
qfs
qc
qfsq
fs S
B
t
tmaatA
22/cosh
cos
2222)(
CERN-LHCb-2007-054
~106 per fb-1
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The subtraction method
Take Bs/Bd with the same final states ( =KK p m) Background asymmetry: 2D fit in mass spectra Production asymmetry: fit with proper-time dependence Detector asymmetry: the same in each decay…
Do a simultaneous time-dependent fit
Measure the difference between Bs and Bd
Very comparible to the D measurement, but orthogonal to it!
R Lambert, CERN CERN CPV, 18th June 2010 39
f
22
)()(,dfs
sfsc
dfsc
sfsds
fs
aaaaA
45.06.0 105.2
SM
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The subtraction method
Take Bs/Bd with the same final states ( =KK p m) Background asymmetry: 2D fit in mass spectra Production asymmetry: fit with proper-time dependence Detector asymmetry: the same in each decay…
Do a simultaneous time-dependent fit
Measure the difference between Bs and Bd
Very comparible to the D measurement, but orthogonal to it!
R Lambert, CERN CERN CPV, 18th June 2010 40
f
22
)()(,dfs
sfsc
dfsc
sfsds
fs
aaaaA
45.06.0 105.2
SM
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Real data highlights
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R Lambert, CERN 42CERN CPV, 18th June 2010
m-
PV
SV
TV
Bs
Ds+
+,K+,K-
EVT: 49700980RUN: 70684
LHCb Preliminary
mm
Real Data Bs
~800 mb-1
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R Lambert, CERN 43CERN CPV, 18th June 2010
PV
SV
Bd
D+
K-,K+,+
TV
m-
EVT: 141526660RUN: 70666
LHCb Preliminary
mm
Real Data Bd
~800 mb-1
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All D(s)->KKp
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n.b. Selection with no requirement for a muon (need ~40 nb-1)
~2.6 nb-1
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R Lambert, CERN CERN CPV, 18th June 2010 45
Sensitivities and Outlook
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Sensitivity estimates
Full MC used to tune toy MC
Massive toy MC studies done in: CERN-LHCb-2007-054 CERN-THESIS-2008-045 CERN-THESIS-2009-001
Scaled to: Latest Monte Carlo efficiencies s(bb) = 500 mb
R Lambert, CERN CERN CPV, 18th June 2010 46
Stat. Error (500 mb)
100 pb-1 1fb-1
afss (Ds p) 2.1 x10-2 6.8 x10-3
DAfs (Dq mn) 2.0 x10-3 6.3 x10-4
All MC predictions!!Real data will be worse
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Current Results
R Lambert, CERN CERN CPV, 18th June 2010 47
fs
fs
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After 1fb-1 of LHCb
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AssumeAb central valueand no NP in Bd
fs
fs
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c.f. J/Y F
R Lambert, CERN CERN CPV, 18th June 2010 49
hep-ph 0612167
Directly Measure sin fs
s(fs) = 0.05c in 1 fb-1
Effectively Measures
s() = 0.5c in 1 fb-1
But they constrain NP differently Effective power enhanced NB physical limit of afs is at 4x10-3 < current D result!
/0 JBs
sfsa
sinRecosIm12
12
12
12
MMCurrent measurements (pre D0 paper)
Red : Dms
Yellow: DGs
Black: fs
Blue: afs
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Combining D
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D and CDF
-2bs=fs
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FPCP 2010
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D and CDF
(add my own personal merging)
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FPCP 2010
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Conclusion
D have made an astounding new measurement (3.2 s!)
At LHCb the environment is more hostile, concentrate on:
Low detector asymmetry, great proper time resolution
Detector and production asymmetries fitted with the data
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ss DB0
Stat. Error (500 mb)
100 pb-1 1fb-1
afss (Ds p) 2.1 x10-2 6.8 x10-3
DAfs (Dq mn) 2.0 x10-3 6.3 x10-4
sfsa from
dsfsA, from 00 XDB qq
All MC predictions!!Real data will be worse
-310 (syst)]46.12.51(stat) 57.9[ bA
(a)
(b)
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End
Backups are often required
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Cereal loops
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Now in bitesize-chunks!
Act now and getyour first 105 decays free!
New Physics inspecial boxes!
Afs DG and Dms in every box!
Two excitingflavours!
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Nomenclature
A decay to a given state which cannot be reached by the anti-flavour state (at tree level) = flavour-specific
CP-violating asymmetry in mixing, manifests directly in flavour-specific decays = Afs/afs flavour-specific asymmetry
Since this is most readily observed in semi-leptonic decays it is also referred to as Asl
a final state of given flavour. its charge conjugate.
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f f
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After 1fb-1 of LHCb
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LHCb measurement cuts at right-angles really depends what the value is, and if there is NP!
current favoured value Ab central value and no NP in Bd
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Detector Asymmetry, dc
Magnet divides +/- charge, allowing +/- asymmetry
by reversing magnet in D0: dc reduced from 3% -> ~0.1%
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Asymmetry from Long Muon Tracks Reconstructed in MC
Left Right
-ve +ve
Left Right
+ve -ve
Before 4Tm Magnet After 4Tm Magnet
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Detector Asymmetry, dc
Matter detector hadronic interactions are asymmetric
Dominant systematic at order 1%
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Kaon PDG cross-section
PDG
0
20
40
60
80
100
120
0.1 1 10 100 1000
momentum in lab frame Plab / GeV c
had
ron
ic c
ross
-sec
tio
n /
mb. K-, p
K+, p
-1
Kaon interaction cross-section
K- pK+ p
Resultant charge asymmetry (MC)
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Systematics (1)
1. Detector asymmetry • Expect second order, so < 10-4
• Know the magnitude in real data from the pi momentum spectra• Detect any bias by binning in momentum• Correct with MC: Assuming the magnet is reversed!!
2. Production asymmetry• Separate using the time-dependence• Detect large bias from this by binning in eta• Measure production asymmetry, possible but very coarse
3. Background asymmetry • Fit simultaneously, simply, in the B-mass spectrum
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ss DB0
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Systematics (2)
1. Detector asymmetry only second order, so < 10-4
• Know the magnitude in real data from the daughter momenta• Detect any bias by binning in momentum• Correct with MC: Assuming the magnet is reversed!!
2. Production asymmetry• Separate using the time-dependence • Detect large bias from this by binning in eta• Measure in can help quantify any bias
3. Background asymmetry • Suppressed by the effective B/S < 0.1, in the signal region• Fit simultaneously, 2D fit, in the B-mass and D-mass spectra• Cancel detector-related part also, only production remains• Detect bias by binning in eta
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00 XDB qq
ss DB0
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The subtraction method
Take Bs/Bd with the same final states ( =KK p m)
All production asymmetry is in x2/x3, just throw it away
Measure the difference between Bs and Bd
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f
2211,
dfs
sfs
dsdsfs
aaxxA
45.0
6.0 105.2 SM
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Subtraction method
Channel (q = s/d)
Measures
Complications Requires weak constraints on DG and Dm
Mitigating factors Production asymmetry fit simultaneously Detector asymmetry cancelled
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00 XDB qq
2
dfs
sfs
fs
aaA
45.0
6.0 105.2 SM
CERN-THESIS-2009-001
KKDqCERN-LHCb-2007-054
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Production Asymmetry
Tuned Pythia samples
*=standard decays, †=Stable Bd+Bs
Asymmetries agree with generic bb events
dp x1000 Min Bias (10M)* bb – inclusive (10M)* (20M) †
Pions -(4.23±0.16) -(2.16±0.09) -(2.27±0.07)
Kaons -(17.0±0.5) -(7.73±0.26) -(8.2±0.2)
Muons -- +(2.0±1.2) +(1.0±0.9)
Ds -- -(1.6±1.1) -(1.6±1.1)
Bs -- -(1.9±1.3) -(1.5±0.8)
Bd -- -(3.2±0.7) -(3.2±0.4)
00ds BB