Transcript Hot Topics at D0 David Buchholz (Northwestern Univ) On behalf of the DØ

Hot Topics at D0
David Buchholz
(Northwestern Univ)
On behalf of the DØ
Collaboration
D0 Results
D0 Talks at this conference b physics
 B mixing and lifetimes- Piedra
 Bs decays and B leptonic decays- Van Kooten
 t physics
 Top Physics – Clement
Many new b and t physics results
 Watch for these in other talks
Hot Topics at D0
 Bs and Bd mixing
 CP violation result in B decays
 Flavor Changing Neutral Current results (D±→ π±μ+μ- )
4/9/2006
D. Buchholz
2
Excellent Tevatron Performance
Run II Integrated Luminosity
19 April 2002 - 22 February 2006
2.0
1.9
1.8
1.7
1.41
1.6
Luminosity (fb-1)
1.5
1.4
1.19
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
Delivered
0.3
0.2
Recorded
0.1
0.0
Apr-02
Jul-02
Oct-02
Jan-03
Apr-03
Jul-03
Oct-03
Jan-04
Apr-04
Jul-04
Oct-04
Jan-05
Apr-05
Jul-05
Oct-05
Jan-06
Apr-06
Jul-06
 Data sample corresponding to over 1 fb-1 of the
integrated luminosity used for the Bs mixing analysis
 Results are being reported on this 1 fb-1 sample
4/9/2006
D. Buchholz
3
D0 Detector
B Physics Program based on excellent performance of
1) muon system, |η|<2.0, pT > 3,4,5 GeV
2) silicon microstrip tracker
3)Good single and dimuon triggers
4/9/2006
D. Buchholz
4
Unitarity Triangle- B Mixing Contribution
(,)
VudVub*
VcdVcb*

 V V* 
arg   td tb* 
 VudVub 
*
tb
*
cb
B
VtdV
VcdV
B
0
d
0
s
b
W
u, c, t W 
d , s Vtd*

(0,0)
Vtd
Vts
d, s
u,c,t
Bd0
Bs0
b
Vts*

(0,1)
 VudVub* 
 VcdVcb* 
arg  
arg  
* 
* 
V
V
 cd cb 
 VtdVtb 
Measurement of Δms
contributes to better
determination of Vtd
Dmd ~ (lots of QCD)x|Vtd|
Dms ~ (lots of QCD)x|Vts|
Dms/Dmd ~ (much less QCD)x|Vts|/|Vtd|
4/9/2006
D. Buchholz
5
B  B Mixing and Oscillations
A  cosDms t 
4/9/2006
D. Buchholz
6
Analysis Outline
Opposite Side
Ds
Bs0  Bs0     K  K 

Reconstructed Side
X
μ(e)
B
μ+
B B
0
s
0
s
LT
D-S
πφ
ν
K+
 Select Bs candidate
K-
 Concentrate on the most clean decay mode BsνμDs(φπ)
 For each Bs candidate




BS flavor at decay time from muon sign at the reconstructed side
Transverse length LT and its error
Transverse momentum PT(Bs) (use PT(Dsμ))
B-hadron flavor at the opposite side (indicates BS flavor at production time)
4/9/2006
D. Buchholz
7
Proper Decay Length
ct Bs  x K
M
 Proper Decay Length is
determined from the
Visible Proper Decay
Length
 K-factor takes into
account the escaping
neutrino and other missing
particles
Ds 
T
p
K
Bs
T
p
 From MC for each decay
mode- different excited
states
4/9/2006
D. Buchholz
8
Resolution Calibration Using Data
 Use J/ψ→μμ sample
 Fit pull distribution for J/ψ Proper Decay Length with 2 Gaussians
 Resolution Scale Factor is 1.0 for 72% of the events and 1.8 for the rest
 Confirmed by Impact Parameter tuning procedure in MC
DØ Run II Preliminary
μ
resolution
resolution
plus decays
J/ψ vertex
PV
μ
4/9/2006
D. Buchholz
L±σL
9
Efficiency Dependence on VPDL
 From MC
 Cross-checked and tuned using data
 Note that efficiency at VPDL=0 is not 0
4/9/2006
D. Buchholz
10
Opposite Side Tagging
,e

K,
Ds
B
Bs
Primary Vertex
Tagging side
K
K
P
a
Secondary Vertex

,e
Reconstructed B-meson
Q 
 ( p  q)
p
t
 Muon (electron) jet charge defined as:
t
 Sum is taken over all tracks in the cone ΔR<0.5 around muon;
 SV Charge:
 p||0.6  q
QSV 
p
0.6
||
Qev 
 ( p  q)
p
t
 Event charge:
 all tracks with ΔR < 1.5 w.r.t. reconstructed B direction are used
t
4/9/2006
D. Buchholz
11
Increasing dilution
Increasing dilution
Calibration of Dilution Using BdD*±μνX
ΔmHFAG = 0.507 ± 0.004 ps-1
4/9/2006
D. Buchholz
12
Final Signal Selection
Use likelihood ratio method
 Set of discriminating variables xi
constructed for each event
 Helicity Angle (Ds,K1)
 Ds Isolation
 pT(K1K2)
 m(Ds)
 2 of Ds Vertex Fit
 m(K1K2 or K1)
 Construct likelihood ratio for each
variable
bgrd from m(Ds) sidebands
signal from bgrd-sub peak
 Use for final selection
n
Y   yi
f i S ( xi )
yi  B
f i ( xi )
4/9/2006
Combine into single
variable
i
D. Buchholz
13
μ sample @ D0 (~1 fb-1)
Opposite-side flavor
tagging
μD±: 7,422±281
μDs: 26,710±560
μD±: 1,519±96
Tagging efficiency ~20%
4/9/2006
μDs: 5,601±102
D. Buchholz
14
Cross-check Using BdXμD±()
Amplitude Scan
DØ Run II Preliminary
 The Amplitude Scan reveals the Bd oscillations
 at correct place  no lifetime bias
 with correct amplitude  correct dilution calibration
4/9/2006
D. Buchholz
15
Event-by-Event Fit
Minimize the Likelihood function
Probability Density Functions (PDF) for each source





Proper Decay Length
Dilution
Proper Decay Length Error
Mass
Signal Selection Variable
4/9/2006
D. Buchholz
16
Vertex Resolution
DØ Run II Preliminary
e.g. Period of oscillations @ 19ps-1
Limit of sensitivity to mixing at 22ps-1
 Determined by vertex fitting procedure
4/9/2006
D. Buchholz
17
Results of the Lifetime Fit
Most important region
 Different background models are used for cross-check and systematic errors
 Trigger biases have been studied
 Different efficiency models
 Central values for cτBs= 404 − 416 μm
 Statistical error ~10 μm
 HFAG value cτBs = 438 ± 12 μm
4/9/2006
D. Buchholz
18
Amplitude Scan For Bs
 Deviation of the amplitude at 19 ps-1
 2.5σ from 0
 1.6σ from 1
4/9/2006
D. Buchholz
19
Log Likelihood Scan
In agreement with the amplitude scan
Systematic
 Resolution
 K-factor variation
 BR (BsDsX)
 VPDL model
 BR (BsDsDs)
Have no sensitivity
above 22 ps-1
17 < Dms < 21 ps-1 @ 90% CL assuming Gaussian errors
Most probable value of Dms = 19 ps-1
4/9/2006
D. Buchholz
20
World Average
With current D0 result
HFAG Preliminary
Correlated systematics
not yet included
@19ps-1: 1.5σ  2.3σ
4/9/2006
D. Buchholz
21
Ensemble Tests
 Using data
 Simulate Δms=∞ by
randomizing the sign
of flavor tagging
 Probability to observe
Δlog(L)>1.9
(as deep as ours)
in the range 16 < Δms < 22 ps-1 is 3.8%
 5% using lower edge of syst. uncertainties band
 Region below 16 ps-1 is experimentally excluded
 No sensitivity above 22 ps-1
Using MC
 Probability to observe Δlog(L)>1.9 for the true
Δms=19 ps-1 in the range 17 < Δms < 21 ps-1 is 15%
4/9/2006
D. Buchholz
22
Impact on the Unitarity Triangle
4/9/2006
D. Buchholz
23
Impact on the Unitarity Triangle
4/9/2006
D. Buchholz
24
CP Violation in Mixing
MCP   p M
0
q M
0
Three phenomenological signatures
First in K
CPV in Mixing
eK: KL   
eB: ll  ll ?
Last in B
4/9/2006
| q | | A f | i

e
| p | | Af |
Mixing vs Decay
: KL  0 ?
/1: J/y Ks

CPV in Decay
e//e: KL  00 ,  
ACP: K, K

D. Buchholz
25
Analysis Strategy
Goal is to measure eB with part per mil precision by looking for
asymmetry in like-sign dimuons
N (bb      X )  N (bb      X )
ASL 
N (bb      X )  N (bb      X )
Toroid
How?
Using independent
spectrometers and
reversing the polarities
Solenoid
Toroid








4/9/2006
Solenoid
D. Buchholz
26
Raw Results
Tor*Sol
polarity
-1
+1
N++
177,950
156,183
N--
176,939
156,148
N+-
1,175,547
1,029,604
After removing detector based asymmetries:
A  0.0013  0.0012( stat )  0.0008( syst )
Now need the fraction of  from B
ASL  fB  A
4/9/2006
D. Buchholz
27
Sample Composition
signal
b ; b  b  
b ; b  c  
Backgrounds with false
asymmetries:
Backgrounds that
dilute the
asymmetry
4/9/2006
Reaction KNYπ (Y=Λ,Σ...)
has no K+N analog
D. Buchholz
28
Sample Composition
signal
b ; b  b  
b ; b  c  
Backgrounds with false
asymmetries:
Backgrounds that
dilute the Cross-check:
asymmetry
Reaction KNYπ (Y=Λ,Σ...)
has no K+N analog
 ( D0)  0.136  0.001  0.024
 ( PDG )  0.1281  0.0076
4/9/2006
D. Buchholz
29
Results
Raw Asymmetry:
A  0.0013  0.0012(stat )  0.0008(syst )
Asymmetry from Mixing:
ASL  0.0044  0.0040(stat )  0.0028(syst )
Re(e B 0 )
CP Violation Parameter:
Re( ε B0 )
1  ε B0
4/9/2006
2
1  e B0
2
ASL

4
 0.0011  0.0010(stat )  0.0007(syst )
D. Buchholz
30
Results
(0.4±1.4±0.9)
Re( ε B0 )
1  ε B0
4/9/2006
2
 0.0011  0.0010(stat )  0.0007(syst )
D. Buchholz
31
Flavor Changing Neutral Currents
(1/G)(dG/dm2) GeV-2)
Strict limits from b s and s d
Possible to have effects in up sector and not down sector
D+    
10-4
10-6
10-8
c  u  
RPV in the up sector and not the
down sector
Burdman et al. hep-ph/0112235
10-10
0.5
Little Higgs models with new up
sector vector quark
Fajfer et al. hep-ph/0511048
1.0
1.5


m(    GeV)
factors of >1000 over SM not ruled
out. Similar in magnitude to Bs  
but orthogonal parameter space
4/9/2006
D. Buchholz
32
c  u   Analysis Strategy
DØ Preliminary
 First find Ds  
 BF(Ds     / 09%
 BF   (2.85 +/- 0.19) x 10-4
 Product ~ 1 x 10-5
1 fb-1
~55k w
~51k 
 Then search for excess in the
continuum region
 D    with m( ! 
 Start with low mass dimuon candidate,
add track to form D candidate
?, 
 Reduce background with lifetime and
topological cuts
Dimuon invariant mass
4/9/2006
D. Buchholz
33
Results for D      
DØ Preliminary
Optimized cuts
1 fb-1
n(Ds) = 65 ± 11
n(D+) = 26 ± 9
m( GeV/c2 for candidates with 0.96 < m() < 1.06 GeV/c2
DØ: BF( D        (1.75 +/- 0.70 +/- 0.50) x 10-6
CLEO-c: (2.7 +3.6 -1.8 +/- 0.2) x 10-6 Expected: 1.77 x 10-6
4/9/2006
D. Buchholz
34
Results for D 
DØ Preliminary
DØ Preliminary
1 fb-1
1 fb-1
n(D) = 6
n(Ds) = 3
n(S+B) =
5.3 +/- 1.5
n(S+B) =
4.6 +/- 0.7
0.96 < m() < 1.06 GeV/c2
0.2 < m() < 0.96 GeV/c2
1.06 < m() < 1.76 GeV/c2
Good agreement with expectations
4/9/2006
n(bkg) =
20.9 +/- 3.4
D. Buchholz
35
Results for D 
DØ Preliminary
Branching fraction limit
D+   :
1 fb-1
DØ: < 4.7 x 10-6 (at 90%)
n = 17
n(bkg) =
20.9 +/- 3.4
CLEO-c(e+e-): 7.4x 10-6 at 90%
FOCUS: 8.8 x 10-6 at 90%
New limit on second generation
RPV couplings
 22k  21k < 0.002
4/9/2006
D. Buchholz
0.2 < m() < 0.96 GeV/c2
1.06 < m() < 1.76 GeV/c2
36
Check of SM with Lifetimes and BR
In SM ( with CP conserved) eigenstates are CP
specific- check decay portion of matrix
Measure of decay rates and widths
in Bs0-Bs0 system
Γs measures lifetime average
1/ΔΓs measures off diagonal decay matrix element
Measure
 Flavor specific, e.g.
 Branching ratios
 Lifetimes Differences
4/9/2006


Bs  Ds    Bs  Ds  
0
Bs  Ds Ds
0
(*)
0
(*)
Bs  J /y
0
D. Buchholz
37
1 Sigma Contours on ΔΓs and 1/Γs
4/9/2006
D. Buchholz
38
Conclusions
 Tevatron’s first fb-1 opening up several new opportunities in flavor physics
 Today, 3 world’s best results
 Rare FCNC charm decays
 CP Violation in B mixing
 First double sided bound on Dms
19 years after the observation of Bd mixing and 12 years after
the first lower limit on Dms, we now have first direct double
sided bound on the Bs oscillation frequency.
17 < Dms < 21 ps-1 @ 90% CL
 More improvements this summer extend analysis and new hardware = layer 0
4/9/2006
D. Buchholz
39
Backup Slides
4/9/2006
D. Buchholz
40
Initial State Tagging
Get best estimate for reconstructed B meson to
contain b(b) at origin
Definitions:
N tagged
Efficiency:
e 
N total
N RS  NW S
D
Dilution:
N RS  NW S
Tagging power:
e D
use to compare the performance of taggers
2
4/9/2006
D. Buchholz
41
Dilution
 Determine dilution
on event-by-event
basis from
BdD*±μνX events
D
Use opposite side
events
dpr
4/9/2006
Plot dpr ( predicted)
versus D measured
D. Buchholz
42