eps 2003 aachendaniele pedrini - focus results1 focus mixing and cpv results recent results on charm...
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EPS 2003 Aachen Daniele Pedrini - Focus results 1
FOCUS mixing and CPV resultsRecent results on charm
from E831-FOCUS
Daniele Pedrini (INFN-Milano)
on behalf of the FOCUS collaboration
EPS 2003 Aachen Daniele Pedrini - Focus results 2
Outline• Charm lifetimes
• Semileptonic decays
• Hadronic decays
• Conclusions
EPS 2003 Aachen Daniele Pedrini - Focus results 3
PWC
Over 1 million reconstructed!
Vertexing
Cerenkov
spectrometer
Muon id
Successor to E687. Designed to study charm particles produced by ~200 GeV photons using a fixed target spectrometer with updated Vertexing, Cerenkov, EM Calorimeters, and Muon id capabilities. Member groups from USA, Italy, Brazil, Mexico, Korea.
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Charm lifetimes
• lifetime determination allows conversion of relative BRs to partial decay rates • FOCUS is the only experiment to have measured the lifetimes of all the charm particles• most of the systematic errors cancel out in the ratio of lifetimes• increasingly precise measurements of the heavy quarks lifetimes have stimulated the development of theoretical models able to predict this rich pattern ( more than one order of magnitude from D+ to Ωc)• charm lifetime hierarchy established • crucial for meaningful measurements of lifetime difference
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Charm lifetimes, technique
• proper time resolution ~ 35 ps
• use of reduced proper time t’ = (L-nσL)/βγc
• f(t’) from Monte Carlo
• binned maximum likelihood
• this technique allows direct use of sidebands for the background (no background parametrization)
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Charm lifetimes
FOCUS (*) produced new lifetimes results with precision better than the previous world average (○), PDG 2002
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21,370events
D+ Kevents from FOCUS
Right SignWrong Sign
DataFit
charm bkg
Our K spectrum looks like everyone else’s, 100% K*(890), with much more data.
This has been so for last 20 years.
But strange things happen when we tried to measure form factors.
M(K (GeV/c2)
even
ts
RS
-WS
backgrounds are pretty small
WS Subtracted Plots
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An unexpected asymmetry in the K* decay
dataMC
Yield 31,254
We noticed a forward-backward asymmetry in cosV below the K* pole, but almost none above the pole. QM interference?
HUGEasymmetry!
Vd
d 2cos1
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Simplest approach
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Studies of the acoplanarity-averaged interference
20*
2 )Re(sincos8 HBeA Ki
lV
Extract this interference term by weighting data by cosV,
Since all other -averaged terms in the decay intensity are constant or cos2v.
We begin with the mass dependence:
090
00
045
Our weighted mass distribution..
A=0
0.36 exp(i)
..looks just like the calculation..
Efficiency correction is small
A constant 450 phase works great...
…other options also possible.
m0- m0 m0+
Re(e-iδB K* )
FOCUS, PLB535 (2002) 43
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But surely an effect this large must have been observed before?
Although the interference significantly distorts the decay intensity....
...the interference is nearly invisible in the K mass plot.
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K
*l
/
K
E691
E653
Focus
Argus
Omega
Cleo 1
Cleo 2
Cleo 2
E687
0.3
0.4
0.5
0.6
0.7
0.8
0.9
muons electrons
The FOCUS result on BR(D+ KK2
New W. A. 0.620.02
Our number, the only one to consider an s-wave contribution explicitly, is 1.6 below CLEO and 2.1 above E691.
With the correction factor applied,
All muon results multiplied by 1.05 to be compared to electron results
65,421 events
11,698 eventsFOCUS, PLB 541 (2002) 243
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BR(Ds+
br stat sys stat+syscleo 0.49 0.1 0.12 0.156argus 0.57 0.15 0.15 0.212e687 0.58 0.17 0.07 0.184cleo2 0.54 0.05 0.04 0.064focus 0.540 0.033 0.048 0.058
This branching ratio is traditionally used to set the scale for Ds
+ branching fractionsby assumptions such as:
*8 0
focus
cleo2
cleo
argus e687
0
0.2
0.4
0.6
0.8
1
New WA: 0.540 0.040
Consistent results between experiments.
FOCUS, PLB 541 (2002) 243
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E6
91
E6
53
E7
91
FO
CU
S
BE
AT
E6
87
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
E68
7E79
1
FO
CU
S
BE
AT
E69
1
E65
3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Form Factor Measurements, D+ K
1.66 0.060
0.827 0.055
The experimental RV value is getting smaller with the passing years. The new Focus value is 2.9 below E791. We were consistent before charm background correction.
Apart from E691 the R2 values have been pretty consistent.
Latest form factor calculation Damir Becirevic (ICHEP02) RV = 1.55 0.11which is remarkably close to RV = 1.504 0.087(FOCUS)
time
RV
R2
New WA
New WA
New FOCUS Results:
RV = 1.504 0.057 0.039 R2 = 0.875 0.049 0.064
FOCUS, PLB 544 (2002) 89
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Summary on semileptonic
(1) S-wave interference in D+ Kof the form2
2 v 00 2
0
cos m0.36exp
)o
H im m im
The new amplitude is small: 7% of BW peak amplitude in the H0 part. 6% of all Kover the full K range
(2) New results on BR D+ K*/K2• CLEO value 0.74 0.04 0.05 (is higher than previous data)
• FOCUS value is 0.60 0.01 0.02 (1.6 lower than CLEO)
(3) New measurements of BR Ds+
• Data from all experiments remarkably consistent one another.
4New measurements of D+ K*form factors• Charm backgrounds artificially raise RV significantly (~3• Our RV measurement is 3 lower than E791 but very much in line with most recent Lattice Gauge Calculation by Rome group.• (S-wave helps fit but we have a V(q2) problem for q2 < 0.2 GeV2 )
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Summary on semileptonic
(5) Will there be similar effects (interference) in other charm semileptonic or beauty semileptonic channels?
Good question.
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Hadronic decays
• the correct interpretation of the hadronic decays is complicated
• FSI play a central role ( in the B decays they are supposed to be small, is it true? )
• amplitude analysis (Dalitz plot) is the correct tool to determine the resonant substructure
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FSI, an example the BR(D0K- K +)/(D0-
+)
Summing over Isospin rotated channels, SU(3) breaking is reduced.
The effect of elastic FSI on BR (K- K +) /(- +) is significant, but is unable to explain the discrepancy between experimental results and theoretical predictions ((K- K + )/(- +) ≤ 1.4)
Conclusions:
Most reasonable explanation : inelastic FSI
- + 0 0
DKKD
0
0
2.81 0.12
0000
0000
DD
KKDKKD2.06 0.24
Not affected by elastic FSI
Large SU(3) breaking SU(3) breaking is reduced
Elastic Elastic FSI FSI
Elastic FSI - rotation in Isospin space
K- K+ K0 K0
FOCUS, PLB555 (2003) 167
(BR and Isospin analysis)
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D0 K+ K- K-+
• D0K+K-K-+ is Cabibbo favored but it is strongly suppressed by phase space
• This decay mode requires the production of a couple ss either from the vacuum or via FSI
Preliminary
EPS 2003 Aachen
D0 K+ K- K-+ Preliminary
Experiment (D0K+K-K-+) / (D0K--++) Events
E687 0.0028±0.0007±0.0001 20 ± 5
E791 0.0054±0.0016±0.0008 18.4 ± 5.3
FOCUS
(this result)
0.00257±0.00034±0.00023 143 ± 19
Mode phase(deg) magnitude fraction(%)
K*0(890) 0 1. 48±6±1
K-+ 194±24 0.60±0.12 18±6±3
K*0(890)K+K- 255±15 0.65±0.13 20±7±2
Non-resonant 278±16 0.55±0.14 15±6±2
Amplitude analysis
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Can we get a pure s CP odd from D0 Ks K+K- ? s is a CP odd state: Ks and are CP even
s is in a relative p-wave with parity -1
s f0(980) is a CP even state: Ks and f0are CP even
s f0(980) is relative s-wave with parity +1
Two states interfere in same region in Dalitz plot:
Is there a pure CP odd eigenstate near the ?
No. A CP even eigenstate will be present with a non-negligible fraction.
Tagged sample
K+K-
Ks K
asymmetry in lobes indicates interference
Suggests
But is 50% CP odd + 50 CP even oD K
Fraction of events in the region due to Ks is: *
62 3%tota
region
regio
l to al
n
t
A A
A A
0 62% CP odd and 3" " 8% CP even is sD K
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Ks CP odd purity can be improved with a tighter cut
The contaminating f0 fraction rapidly reduces as we narrow the phi region from 50 MeV to 4 MeV
Tagged sample
K+K-
Ks K
Fraction of events in the region due to Ks is:
*
*93 2 1%region
regi
tot
on
al total
A A
A A
Now 0 93% CP odd and " " 7% CP even is sD K
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Conclusions
• At 30 years from the discovery of the c quark the physics analysis of the first heavy quark has reached a complete maturity
• With the large statistics now available in the charm sector, we start to see strange effects which complicate the explanation of the decay processes
• FSI play a crucial role• Light hadron physics is important in charm decays
• Lessons for the b sector?