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980 GeV/c2 p
Precision measurements of CP violation and
D0-D0bar mixing at CDF
Mark MattsonWayne State University
ICHEP 23 Jul 2010
CDF
Fermilab, IL, USA
980 GeV/c2 p
Overview
• Why is charm mixing and CPV interesting?
• Quick overview of the CDF II detector
• Charm mixing with D0 -> K+π- or π+K-
• Previous result, and prospects with current data
• CP violation measurements with D0 -> h+h-
• Previous result, and prospects with current data
2
Charm Mixing• Neutral K/D/B mesons
can oscillate between matter to anti-matter
• For no CPV,
• Charm mixing is small
• x, y ~ O(1 %)
• kaon mixing seen 1962
• beauty mixing seen 1987
• first evidence of charm mixing was in 2007
3
|D1,2(t)� = |D1,2� e−�
Γ1,22 +iM1,2
�t
x ≡ M2 −M1
Γ
y ≡ Γ2 − Γ1
2Γ
xy
Bs 0 Bd 0 K 0 D 0
|D1,2� = p��D0
�± q
��D̄0�
|q/p| = 1
• No mixing point (0,0)
• excluded at 10.2σ
• Many results combined; no single measurement has reached 5σ significance
• No CPV (|q/p|, φ) = (1,0)
• Experiments are currently consistent with CP conservation
• Experiment and theory need more precision to test for new physics
4
World Average
CDF II Detector
• Located at point B0 on the Fermilab Tevatron
• Looking at fully reconstructed D0 decaying to charged K and π
• silicon vertex detector surrounded by wire drift chamber (COT) in 1.4T solenoid (central tracking)
• These analyses do not use the (EM, hadronic, muon) calorimeters
• Particle identification using energy loss (dE/dX) in the COT
5
Displaced Track Trigger• Using events from trigger
that selects two oppositely charged tracks that are consistent with a detached vertex• Track momentum transverse to
the beam pT > 2.0 GeV
• Track impact parameter > 100 µm
• Initially optimized for B decays, but also good acceptance for charm
6
D0→K+π-
D0→π+π-
D0→K+K-
Untagged D0N(D0→π+π-) ≈ 1.7×106 N(D0→K+K-) ≈ 4.7×106 N(D0→K-π+) ≈ 47×106 D* tagged
Note on Charm Yield & Luminosity
• Number of D* does not scale linearly with integrated luminosity
• Charm trigger is prescaled at higher beam luminosites
• Earlier data had higher yield of charm per 1/fb
7
Jan 2007 1.5/fb good for hadronic charm analysisJun 2009 5 / fb good for hadronic charm analysis
Charm Mixing with Kπ• Use D* to tag initial production of meson
• “right-sign” (RS) - Cabibbo favored decay
• “wrong-sign” (WS) - doubly Cabibbo suppressed decay, or mixing followed by a CF decay
• In the limit of |x|, |y| << 1 and no CPV, ratio of WS to RS versus decay time is
• Cannot measure mixing parameters directly, but still put limits on amplitude
8
r(t) ∝ e−Γt
[
RD +√
RD y′(Γt) +x′2 + y′2
4(Γt)2
]
D∗+→ D0π+ , D0
→ K−π+
D∗+→ D0π+ , D0
→ K+π− D∗+→ D0π+ , D0
↔ D̄0→ K+π−
δKπ is the strong phase differencebetween the DCS and CF amplitudes
y� = y cos δKπ − x sin δKπx� = x cos δKπ + y sin δKπ
!t/0 2 4 6 8 10
R
0.002
0.004
0.006
0.008
0.01
Previous CDF Result
• PRL 100, 121802 (2008)
• “Evidence for D0-D0bar mixing using the CDF II Detector”
• Difference in chi2 between mixing fit (red dashed) and the no-mixing fit (blue bots) is 17.6• Equivalent to 3.8σ significance
• Results were competitive with the best experimental results at the time
9
)-3 (102x'-0.5 0 0.5
)-3
y' (1
0
-10
0
10
20
No mixing point (x’2,y’=0)Best fit point Best fit point with x’2=0
10
1.5/fb: 3.03 million RS D*5.2/fb: ~6.3 million RS D*
1.5/fb: 12.8 thousand WS D*5.2/fb: ~26 thousand WS D*
Work in Progress
• Time-integrated D*• Light green is the published result with 1.5/fb• Blue is current, with 5.2/fb
• Peak at 5.9 MeV/c2 is D*• Rest of the distribution is D0 + random track
from the primary vertex
• Working to improve systematic uncertainties on the analysis (ex. removing D* from B decays, dE/dX variation over time, etc.)
)2) (MeV/c! - M!K - M!!K
WS (M0 10 20 30
2 p
er 0
.5 M
eV/c
0W
S D
0
5000
10000
15000
20000
)2) (MeV/c! - M!K - M!!K
WS (M0 10 20 30
2 p
er 0
.5 M
eV/c
0W
S D
0
5000
10000
15000
20000
)-1CDF II Preliminary (5.2 fb
)2) (MeV/c! - M!K - M!!K
RS (M0 10 20 30
2 p
er 0
.5 M
eV/c
0R
S D
0
500
1000
1500
310"
)2) (MeV/c! - M!K - M!!K
RS (M0 10 20 30
2 p
er 0
.5 M
eV/c
0R
S D
0
500
1000
1500
310" )-1CDF II Preliminary (5.2 fb
• In addition to direct CP violation, D0 oscillations can generate time dependent CP asymmetries that survive integrating over time
• To make precision measurement, need to correct for detector systematics that can bias the asymmetry
CP Violation with
€
ACPππ =
Γ(D0 →π−π +) −Γ(D 0 →π +π−)Γ(D0 →π−π +) + Γ(D 0 →π +π−)
€
Γ(D*− → D 0π s− → [h+h−]π s
−)Γ(D*+ → D0π s
+ → [h+h−]π s+)
=Nh + h −π s
−
Nh + h −π s+
⋅εh + h −
εh + h −
⋅επ s
+
επ −
€
Γ(D 0 →K +π−)Γ(D0 →K−π +)
=NK +π −
NK −π +
⋅εK −π +
εK +π −
D0 → h+h−
Previous CDF Result• PRL 94, 122001 (2005)
• “Relative Branching Fractions and Search for CP Asymmetry for D0 -> Kπ/KK/ππ
• L = 0.123 / fb• (first 15 months of data taking)• D0 -> KK 8.2 thousand• D0 -> ππ 3.7 thousand• D0 -> Kπ 88.3 thousand
12]2KK Mass [GeV/c1.75 1.8 1.85 1.9 1.95
2En
trie
s/3
MeV
/c
0
1000
2000
3000
4000
5000
+]+K-[K+0D*+D+ charge conjugate
CDF II
]2 Mass [GeV/c1.78 1.8 1.82 1.84 1.86 1.88 1.9
2En
trie
s/4
MeV
/c
0
1000
2000
3000
4000
5000
+]+-[+0 D*+D+ charge conjugate
CDF II
]2) [GeV/c+-) - M(K++-M(K0.14 0.145 0.15 0.155 0.16
2En
trie
s/0.
2 M
eV/c
0
2000
4000
6000
8000
10000
12000
+]+-[K+0D*+D+ charge conjugate
CDF II
]2 Mass [GeV/cK1.82 1.84 1.86 1.88 1.9
2En
trie
s/1
MeV
/c
0
1000
2000
3000
4000
5000
6000
7000
8000+]+-[K+0D*+D
CDF II
+ charge conjugate
• These plots are to get an estimate for current signal size
• a lot more than previous published result)
• Different method
• data-driven technique to measure detector efficiencies
• previous used MC
13
133k D*+→D0π+→[π-π+]π+ 140k D*-→antiD0π−→[π+π−]π−D*+→D0π+ →[h−h+] π+ (now)
380k D*+→D0π+→[K−K+]π+ 401k D*−→antiD0π−→[K+K−]π−
Work in Progress
14
Assuming:
€
σN ≅σN ≅1/ N ⇒σACP=1/ N + N
Systematic uncertainty is expected to be O(0.1%), comparable to statistical uncertainty.
Experiment N (D0→π+π-) ACP(D0→π+π-) (%)CDF(0.123/fb) 7.3K 1.0 ± 1.3(stat) ± 0.6 (syst)CDF(4.8/fb) 273K xxx ± 0.19(stat) ± xxx (syst)
Babar (386/fb) 64K −0.24 ± 0.52(stat) ± 0.22(syst) Belle(540/fb) 51K +0.43 ± 0.52(stat) ± 0.12 (syst)
Experiment N (D0→K+K-) ACP(D0→K+K-) (%)CDF(0.123/fb) 7.3K 1.0 ± 1.3(stat) ± 0.6 (syst)CDF(4.8/fb) 781K xxx ± 0.11(stat) ± xxx (syst)
Babar (386/fb) 129K 0. ± 0.34(stat) ± 0.13(syst)Belle(540/fb) 120K -0.43 ± 0.30(stat) ± 0.11 (syst)
Conclusion
15
• Working to update two previous results (charm mixing, charm direct CPV) with more data
• Substantial charm samples
• Mature detector, understood systematic effects
• Working to improve precision of the syst. errors
• Stay tuned!
Displaced Track Trigger
18
07/15/10
M.J. Morello
Run I collected O(1) Bs--> Dsπ (all Ds modes)
Run II collected ~2000 Bs--> Dsπ (Ds--> φ[-->K+K-] π)
Compare with only 10x integrated luminosity!
The trigger had a much bigger impact than Tevatron upgrade!!!
Without SVT With SVT
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