first year of bab - harvard universityusers.physics.harvard.edu/~morii/talks/moriond.pdffirst year...
TRANSCRIPT
EP-IIc B Factory —
ter
First Year of BABAR/P— Measuring CP Violation at an Asymmetri
Masahiro MoriiStanford Linear Accelerator Cen
SLAC
CP Violation in B0 Decays
atrix
ard Model?
, β, γ
rediction
ween direct androduces CP asymmetry
ACP ∆m t⋅( )sin=
First Year of BaBar/PEP-II Masahiro Morii
CP violation has been known for 36 years◆ Occurs naturally in the Standard Model ← the CKM m◆ Limited experimental constraints from KL decays
→ Is CP violation fully explained by the Stand
CP violation in B0 decays comes to the rescue
Asymmetry ACP is related to the CKM angles α◆ E.g. for (gold-plated decay)
→ Powerful probe to verify/disprove the SM p
B0
B0
CP eigenstate
Mixing
Decay ◆ Interference betmixed decays ptime-dependent
ACP t( )Γ B
0f CP→( ) Γ B
0f CP→( )–
Γ B0
f CP→( ) Γ B0
f CP→( )+-------------------------------------------------------------------------=
t = decay time
ACP 2βsin= B0
J/ψ KS→
SLAC
How We Measure CP Violation
fficiency
non-CP) decayes orB
0B
0
CP decay
First Year of BaBar/PEP-II Masahiro Morii
Step 1: Reconstruct a CP decay (e.g. B0 → J/ψ KS)✱ Low BR (5 x 10-5) → luminosity & detector e
Step 2: Tag the flavor of the other B0
✱ Leptons and kaons → particle identificationStep 3: Measure ∆z → t = ∆z/βγc
✱ Asymmetric collider (βγ = 0.56)✱ Vertex resolution → silicon vertex tracker
e- e+
B0
B0 (t = 0)
ϒ4S µ+
µ- J/ψπ+
π-KS∆z
ACP t( )Γ B
0f CP→( ) Γ B
0f CP→( )–
Γ B0
f CP→( ) Γ B0
f CP→( )+------------------------------------------------------------------------- ACP ∆m t⋅( )sin= =
} Tagging (determin
}
SLAC
PEP-II Storage Ring
peak scan
First Year of BaBar/PEP-II Masahiro Morii
9 GeV e- + 3.1 GeV e+ → βγ ∼ 0.56
First collision May 26, 1999
>1/2 design luminosity achieved
Design Achieved
Luminosity (cm-2s-1) 3 x 1033 1.7 x 1033
No. of bunches 1658 829
LER current (mA) 2140 960
HER current (mA) 610 750 ϒ4S
SLAC
PEP-II Integrated Luminosity
k
reded
ents
repair
First Year of BaBar/PEP-II Masahiro Morii
Current run continues through August 2000
→ accumulate 10 fb -1 on-pea
3.8 fb -1 delive3.2 fb -1 record
Detector improvem
Vacuum
SLAC
BABAR Detector
3.1GeV e+
Drift Chamberrtex Tracker
1.5T Solenoid
First Year of BaBar/PEP-II Masahiro Morii
9GeV e-
Instrumented Flux Return
Electromagnetic
DIRC
Silicon Ve
(Cerenkov)
Calorimeter
SLAC
Silicon Vertex Tracker (SVT)
Si detectora (●) reachedo
o 2 Mrad
First Year of BaBar/PEP-II Masahiro Morii
SVT Hit Resolution vs. Incident Track Angle
Monte Carlo - SP2
Layer 1 - Z View
(deg)
(µm
)
Data - Run 7925
BA B A R
Monte Carlo - SP2
Layer 1 - φ View
(deg)
(µm
)
Data - Run 7925
BA B A R
0
20
40
60
-50 0 50
0
20
40
60
-50 0 50
◆ 5 layer double-sided◆ Hit resolution in dat
design: ~15 µm at 0◆ Radiation hard up t
SLAC
Drift Chamber (DCH)for low multiple
in data (●)40 µm
First Year of BaBar/PEP-II Masahiro Morii
0
0.005
0.01
0.015
0.02
0.025
-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1
BABAR
Signed distance from wire (cm)
Res
olut
ion
(cm
)
Design Goal = 140 µm
◆ He-iC4H10 (80/20) scattering
◆ Single hit resolutionreached design: <1
Tracks with p>1GeV/c
◆ dE/dx resolution ~7.5% forBhabhas (design 7%)
◆ K/π separation >2σ up to700 MeV/c → DIRC coversp > 500 MeV/c
SLAC
DIRC: the PID Device
0
500
1000
1500
2000
2500
1.6 1.8 2
C
GeV)
D0 → K- π+
With DIRC
K- π+ Mass (GeV)
Num
ber
of e
vent
s/10
MeV
BABAR
2
ov light in quartzmitted by inter-
ectioncted by PMTs resolutiond (target 2 mrad)aration atc is 6.5 mrad
First Year of BaBar/PEP-II Masahiro Morii
Without DIR
K- π+ Mass (
Num
ber
of e
vent
s/10
MeV
D0 → K- π+
0
2000
4000
6000
8000
1.6 1.8
◆ Cerenk→ transnal refl→ dete
◆ 3 mradachieve
◆ K/π sep4 GeV/
◆ K efficiency ~80% for D0 → K+π-
inside the acceptance◆ Background rejection factor ~5
(NB: background contains kaons)
SLAC
Electromagnetic Calorimeter (EMC)
d / E expected deposited9 1 1.1 1.2 1.3
lusters
BaBar
)
100%
abhasonversions
3π→ 2π
First Year of BaBar/PEP-II Masahiro Morii
mγγ (GeV)0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24
En
trie
s
0
200
400
600
800
1000
1200
1400
1600
1800
π0 Mass E γγ > 500 MeV
BaBar
π0-mass = 134.9 MeV
π0-width = 7.2 MeV
E measure0.6 0.7 0.8 0.
Entri
es/B
in
0
200
400
600
800
1000
1200
1400
1600
1800Constant = 1674
Mean = 1.016
Sigma = 0.02214
EMC Bhabha C
Forward Barrel
Constant = 1674
Mean = 1.016
Sigma = 0.02214
◆ CsI(Tl) with photodiode readout◆ E(Bhabha) and m(π0) resolutions
close to Monte Carloσ = 2.2%(MC 2.0%
Electron ID (p > 0.5 GeV)
Electrons >90%
Pions 1–2%
Bhγ c
τ →KS
σ = 5.3%(MC 5.0%)
SLAC
Instrumented Flux Return (IFR)
GeV)
5%
%
First Year of BaBar/PEP-II Masahiro Morii
BABAR
p (GeV/c)
eff.
muons from eeµµpions from τ-3prong and Ks
IFR Barrel
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4
◆ Bakelite-based RPCs sand-wiched between iron plates
◆ Muons above p = 0.5 GeV/cidentified
◆ Neutral hadrons (KL) detected
Muon ID (p > 0.5
Muons >7
Pions ~3
e+e− → e+e−µ+µ−
τ → 3πKS → 2π
SLAC
Are We Ready to Measure sin2β?
ration!)
te
mer
s I speak
First Year of BaBar/PEP-II Masahiro MoriiPEP-II had a terrific startup!◆ Collected 3.2 fb-1 on tape → But we need more
BABAR works beautifully◆ Initial problems have been solved◆ Performance very promising → Still much to do (calib
Physics analysis has started◆ Signals are seen in key channels → Limited statistics
→ We don’t have a CP measurement just yet
What can I show you today?
Examples of what we have done to demonstra➤How well we understand the detector
➤How well the data agree with our expectation
➤How realistic is our plan to measure sin2β by Sum
Everything is PRELIMINARY and improving a
SLAC
J/ψ → l+l- Signal
(µ+µ-) GeV/c2
(µ+µ-)(µ+µ-)
BABAR
3.2 3.4
- (~380 pb-1)
V
e to muon ID
First Year of BaBar/PEP-II Masahiro Morii
m(e+e-) GeV/c2
Can
dida
tes
/ 10
MeV
/c2
m(e+e-)
J/ψ → e+e-
m(e+e-)
BABAR
0
20
40
60
2.6 2.8 3 3.2 3.4
J/ψ → e+e- (~540 pb-1)
σ = 16 MeV
m
Can
dida
tes
/ 10
MeV
/c2
m
J/ψ → µ+µ-
m
0
25
50
75
100
2.6 2.8 3
J/ψ → µ+µ
σ = 15 Me
◆ Efficiency consistent with expectation
→ Already reasonable, but can be improved
Background duTail due to Bremsstrahlung
SLAC
K → π+π- Signal
First Year of BaBar/PEP-II Masahiro Morii
S
M(π+π-) (GeV)
N(π
+π- )
can
did
ate
s/1
.7 M
eV
BABAR
0
100
200
300
0.45 0.475 0.5 0.525 0.55
◆ Mass resolution OK
Mass 498.94 ± 0.12 MeV
σnarrow 2.8 MeV (69%)
σwide 11 MeV (31%)
SLAC
B0 → J/ψ K Signal
BABAR
.25 5.275 5.3
12 events
1.4 ± 0.2
9.8 ± 1.1
First Year of BaBar/PEP-II Masahiro Morii
S
-0.1
-0.05
0
0.05
0.1
5.2 5.225 5
BABAR
0
1
2
3
4
5.2 5.225 5.25 5.275 5.3
◆
◆
∆E EBCMS
EbeamCMS
–=
mB EbeamCMS( )
2pB
CMS( )2
–=
Data ~620 pb-1
Signal
Background
Expected signal
SLAC
B+ → J/ψ K+ Signal
Mb(GeV)5.25 5.275 5.3
s under control expectations
(calibration, PID)
First Year of BaBar/PEP-II Masahiro Morii
B A B A R
∆E(G
eV)
-0.1
-0.05
0
0.05
0.1
5.2 5.225
Bchmass(GeV)
Nev
/2.5
MeV
BABAR
0
2.5
5
7.5
10
5.2 5.225 5.25 5.275 5.3
Data ~620 pb-1
Signal 41 events
Background 5.0 ± 0.6
Expected signal 39.0 ± 3.4
→ J/ψ K signal◆ Yields agree with◆ Resolution OK◆ Bkg will improve
SLAC
D* Signal and Vertexingroves with beam
0 1 2 3
π proper decay time (ps)
BABAR
ial ⊗ gaussian fitpectednt with PDG
First Year of BaBar/PEP-II Masahiro Morii
0
100
200
0.14 0.145 0.15 0.155
0
100
200
300
0.14 0.145 0.15 0.155
GeV
N e
ven
ts/2
00
ke
V
m(Kππ) - m(Kπ)
BABAR
Before refitσ1=354 keV (27%)σ2=908 keV (73%)
GeV
N e
ven
ts/2
00
ke
V
m(Kππ) - m(Kπ)
BABAR
After refitσ1=280 keV (47%)σ2=679 keV (53%)
◆ ∆m resolution impprofile constraint
0
20
40
60
-3 -2 -1
Candidate D0 → kE
ntrie
s/0.
1 ps
~220 pb-1
◆ Simple exponent◆ Resolution as ex◆ Lifetime consiste
SLAC
B0 → D*−e+ν Signal
0.15 0.16 0.17
m(D*)-m(D0), GeV
BABAR
-2 0 2 4
MM2, GeV2
BABAR
asurement
First Year of BaBar/PEP-II Masahiro Morii
0.14
0.15
0.16
0.17
-4 -2 0 2 4
BABAR
MM2, GeV2
∆m, G
eVBABAR
0
20
40
60
80
0.14
even
ts/1
MeV
0
20
40
60
-4
even
ts/0
.4 G
eV2
~390 pb-1
◆ ∆m = m(D*−)−m(D0), MM = missing mass◆ ~120 signal events
→ Will be used for a mixing measurement→ Tagging efficiency and purity → CP me
SLAC
Summary and Outlook
ugust
ion OK
D*l ν
ing ready
2 β) ≤ 0.3
First Year of BaBar/PEP-II Masahiro Morii
PEP-II had a terrific first year◆ Record luminosity: 1.7 x 1033 cm-2s-1. 80 pb-1/day◆ BABAR recorded 3.2 fb-1 → 10 fb-1 by the end of A
BABAR is working great◆ Performance approaching the design goals
Analyses are progressing rapidly◆ Signals seen in key channels. Efficiency & resolut◆ Vertexing resolution OK. More tests will follow◆ Tagging being studied using real data, e.g. B0 →
→ All ingredients for the CP measurement gett
More data is coming!!!◆ With 10 fb-1: Expect ~160 J/ ψ KS events → σ(sin