The ATLAS B-Physics programme
description
Transcript of The ATLAS B-Physics programme
The ATLAS B-physics programmeJames R Catmore ([email protected])
1/14
ATLAS & the LHC
Triggering
B-physics programme
The ATLAS B-Physics programme
James R Catmore
ATLAS group, University of Lancaster
United Kingdom
Institute of Physics HEPP Conference 2005, Dublin, Republic of Ireland
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Overview of ATLAS
Weight: 7000 tonnes
Radius: 11m
Length: 46m
Muon chambers
Barrel toroid
Inner detector
EM calorimeterForward calorimeter
Hadronic calorimeter
End-cap toroid
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
The LHC Environment
• pp collisions: 14 TeV centre of mass energy • Luminosity:
– 2007: 100 days @ 0.5 x 1033 cm-2s-1 Tuning– 2008-2009: 200 days @ 2 x 1033 cm-2s-1 “Low”– 2010+: 1034 cm-2s-1 “High”– Drops by factor ~2 during 10 hour run
• 1 proton bunch crossing every 25ns– 4.6/23 pp collisions/crossing @ low/high luminosity– ~1% of pp collisions produce a bb pair
• At luminosity 2 x 1033 cm-2s-1 – bb events produced with rate of 106 Hz– 10Hz output to permanent storage for B-physics
so highly selective and adaptable B-physics
trigger required
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
The ATLAS Trigger System
Calorimeters
Muon Systems
Tracking
Pipeline memory
LVL1
Read-out buffers
LVL2
Event Builder
Distributed storage & analysis
(“Grid”)
Event filter
Region of interest data
1 GHz interaction rate
75 kHz 1 kHz 100 Hz
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
B-physics trigger strategies
As luminosity drops during the run, more triggers are turned on
Trigger LVL1 Example channels
Di-muon
L 2.1033
(L ≈ 1034)
2 muons
pT > 5 GeV (barrel)
3 GeV (end-caps)
Bd→ J/ψ(μμ)K0S
Bs→ J/ψ(μμ)φ
B→μμ B→K0*μμ B→μμ
Λb→Λ0 J/ψ(μμ) Λb→Λ0 μμ
EM+μ
L < 2.1033
1 muon
pT > 6 GeV
1 EM cluster
ET > 2GeV
Bd→ J/ψ(μμ)K0S+ b→ eX
Bd→ J/ψ(ee)K0S + b→ μX
Bd→K0* Bs→+ b→ μX
Hadronic
L < 2.1033
1 muon
pT > 6 GeV
1 jet cluster
ET > 2GeV
Bs→Ds(φ(KK))π
Bs→Ds (φ(KK)) a1(ρ0π+)
B+ → K+K+- Bd → +-
(+ b→ μX)
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
The current ATLAS B-physics studies
Event type Channel Physics motivationsDecays to charm Bd→ J/ψ(μμ)K0
S
Bs→ J/ψ(μμ)φ Bs→ J/ψ(μμ)η
sin 2β and test of CPV from NP
ΔΓS, φS - test of CPV from NP
Λb→Λ0 J/ψ(μμ)
Bc+→ J/ψ(μμ)π+
QCD: production polarization, test of CPV
QCD, heavy-heavy decays, VcbV
Rare decays Bs→μμ Bd→μμ
Bd→K0*μμ ; Bs→φμμ
Bd→K0*γ ; Bs→φγ
Λb→Λ0 μμ
Branching ratio
Branching ratio, AFB,
B.R., angular studies; CPV
Branching ratio, AFB
Hadronic
channels
Bs→Dsπ, Bs→Dsa1
Bd→ππ
B+ → K+K+-
Bs oscillation; Vts/Vtd
CP violation, decay parameters
Branching ratio, test of NP
NLO QCD: b-production
B →l + B+→ J/ψ(μμ)K+
B+→J/ψ(μμ)K0* , Bs→ J/ψ(μμ)b-cross section and b-b correlations
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Bs meson physics
• B mesons mix:
• Mixing parameters:
– ΔMs Bs→Dsπ, Bs→Dsa1
– ΔΓs , φs Bs→ J/ψ(μμ) φ, Bs→ J/ψ(μμ) η
,s
,s
The ATLAS B-physics programmeJames R Catmore ([email protected])
8/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
• Aim: measurement of ΔГs and φs
• S → V V decay so three final state helicity configurations:
• To extract φs we must separate out the helicity amplitudes → angular analysis: 3 angles in inner detector
J/J/ψψ φφBB00
SS
BB00SS
μμ++μμ--
KK++KK--
A┴ A║ A0…so final state is made up of linear combinations of helicity amplitudes which are CP-eigenstates with different parities
p pB0
S
K+J/
- φ
1
2
The ATLAS B-physics programmeJames R Catmore ([email protected])
9/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
Accurately modelled by EvtGen
The ATLAS B-physics programmeJames R Catmore ([email protected])
10/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
• Experimental technique:
– Identify BS→J/ψφ decays, collect angular distribution
– Fit distribution against theoretical expression to extract the parameters, using a Maximum Likelihood Estimator
– Magnitudes and forms of εtag, εrec ,, ρ, b estimated with simulation
– Correlations between parameters are of critical importance
0
0
2211
2211
1
min
0
0
)(,,
)(,,
t
trectagrectag
it
irectagirectagN
idttdttbetWtW
dtttbetWtWL
i
i
The ATLAS B-physics programmeJames R Catmore ([email protected])
11/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
The ATLAS B-physics programmeJames R Catmore ([email protected])
12/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
xs - φs region
Allowed by Standard Model (updated 2003)
New physics: Left-right symmetric model (NP-LR)Fleischer, Ball, 2000
ATLAS (3yr @ 1033cm-2s-1)
Statistics: 300 000
LHCb (5yr @ 5 x 1032cm-2s-1) performance as given in 2000
Statistics: 240 000
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Rare Decays
• FCNC processes b→d, b→s
– forbidden at tree level: occur at lowest order as loops
– sensitive to deviations from S.M.
e.g. B→μμ
Signal
Bs→μ+μ-
Signal
Bd→μ+μ-
BG
1 yr
1034cm-2s-192 14 660
3 yrs
1033cm-2s-127 4 93
ATLAS measurement
Combing the two samples:
4.3σ significance for Br(Bs→μμ)
95% C.L. upper limit for Br(Bd→μμ) = 3x10-10
Standard Model:Br(Bd→μμ) ≈ 1.5 x 10-10
Br(Bs→μμ) ≈ 3.5 x 10-9
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Conclusions
• ATLAS is well placed to perform a diverse range of precise measurements on B-physics events
• A flexible trigger strategy will allow efficient use of beam-time
• Precise measurements to test sensitivity of CPV or other NP indicators in charm and charmless decays will be carried out
• In rare muonic decays already after 1yr @ 1034cm-2s-1 sensitivity down to BR ~ 3 x 10-10
• Rare semi-muonic and rare radiative decays: statistics allow the testing of the sensitivity of angular distributions to NP
• QCD tests: b-quark, b-b production, origin of b polarization, doubly HF production mechanisms (Bc)
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Additional Slides
The ATLAS B-physics programmeJames R Catmore ([email protected])
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ATLAS & the LHC
Triggering
B-physics programme
Is it a B or a B? (Tagging)
b/b? b/b?
Signal B/B-meson
Jet charge tag
b/b? b/b?
Lepton tag from semi-leptonic decay
For Bd→ J/ψ(μ6μ3)K0S
Tagging efficiency εtag = 0.64
Wrong-tag fraction Wtag = 0.42
εtag(electron) = 0.012
εtag(muon) = 0.025
Wtag(electron) = 0.27
Wtag(muon) = 0.24Signal B/B-meson
The ATLAS B-physics programmeJames R Catmore ([email protected])
17/14
ATLAS & the LHC
Triggering
B-physics programme
Measuring sin(2β) with Bd→ J/ψ K0S
• Decay into a CP eigenstate (CP=-1)
• So far the study assumed no direct CP violation, the plan is to include it
2sinsin/ dsdmixCP KJBA
N
i
t
tii
it
ii
dttdttbetWtW
dtttbetWtWL
i
i
1 0
0
21
21
min
0
0
where W+ = Pdf (Bd→ J/ψK0S)
W- = Pdf (Bd→ J/ψK0S)
The ATLAS B-physics programmeJames R Catmore ([email protected])
18/14
ATLAS & the LHC
Triggering
B-physics programme
Measuring sin(2β) with Bd→ J/ψ K0S
• To achieve high sensitivity:– Triggers selecting J/ψ→μμ, J/ψ→ee– Combined tagging techniques: lepton tag and jet-charge tag
J/ψ→μ(6)μ(3) J/ψ→μ(6)μ(5) J/ψ→e(1)e(1)
No. of reconstructed events
Signal/Background
δstat[sin 2β]: lepton tag
δstat[sin 2β]: j.c. tag
δstat[sin 2β]: combined tag
490 000
23
0.023
0.015
0.0126
250 000
32
0.030
0.019
0.016
15 000
16
0.018
-
0.018
δstat[sin 2β] J/ψ→μ(6)μ(3) + J/ψ→e(1)e(1)
δstat[sin 2β] J/ψ→μ(6)μ(5)
δsystematic
0.010
0.016
0.005
3 years @ 1033 cm-2 s-1:
The ATLAS B-physics programmeJames R Catmore ([email protected])
19/14
ATLAS & the LHC
Triggering
B-physics programme
CP violation with Bd→π+π-
– Penguin diagrams contribute without suppression so large hadronic uncertainties
– Difficult to isolate the decay from other similar decays (Bd→K+π-, Bs→K+K-, Bs→K- π+, Λb→pπ-, Λb→pK-)
– Low branching ratio
• Maximum likelihood:
2sin d
mixCP BA
• Decay into a CP = +1 state:
MtAMtA
tt
ttA dir
CPmixCPCP
cossin
sin2coscos22sin;sinsin2T
PA
T
PA dir
CPmixCP
arg(P/T)
The ATLAS B-physics programmeJames R Catmore ([email protected])
20/14
ATLAS & the LHC
Triggering
B-physics programme
CP violation with Bd→π+π-
%0|| TP
%30|| TP
%100|| TP
The ATLAS B-physics programmeJames R Catmore ([email protected])
21/14
ATLAS & the LHC
Triggering
B-physics programme
Bs meson physics: ΔMs measurement
• Bs→Ds(φ(KK))π, Bs→Ds (φ(KK)) a1(ρ0π+) : B(t=0) = Bs
– p-(t), p+(t) = probability of decay in the state B(t) = Bs , B(t) = Bs
2cos
2cosh
22s
sst tMtetp
t
tM
tptp
tptptr
s
s
2cosh
cos
TheoryExperiment
1 year @ 1033 cm-2 s-1:
• Measurement highly dependent on the trigger scheme
• ΔMs determination not sensitive to value of ΔΓs with these channels
The ATLAS B-physics programmeJames R Catmore ([email protected])
22/14
ATLAS & the LHC
Triggering
B-physics programme
Physics with BS→J/ψφ
ATLAS LHCb
No of events 300 000 240 000
Proper time res. 0.063 ps 0.031 ps
Background ~15% ~3%
Tag efficiency 63% j.c. 40% lp & K
Wrong-tag 38% 30%
σstat: ΔГs,Гs
σstat: A┴, A║
σstat: φs(x=20)
σstat: φs(x=40)
12%, 0.7%
0.8%, 3%
0.03
0.05
9%, 0.6%
0.7%, 2%
0.02
0.03
The ATLAS B-physics programmeJames R Catmore ([email protected])
23/14
ATLAS & the LHC
Triggering
B-physics programme
More Rare Decays
Semi-muonic decays: Bd→μμK0*, Bd→μμφ
(a) Branching ratios: enhancement
from beyond the S.M.
(b) Forward-backward asymmetryb s
?
)cos(
0
1 )cos(
)cos(
1
0 )cos(
1)(
2
2
ddsd
d
ddsd
d
dsdsAFB
Three points: mean values of AFB in three q2/MB
2 experimental regions with error bars
SM
MSSM C7g >0
MSSM C7g <0
K*0
Bd