Transcript Document

07/07/15
1
In this talk we report
On
D** mesons
Observed by D0 detector
and
Searches of
Flavor Changing Neutral Current Charm Decays
01/03/2006
Valentin Kuzmin
PhiPsi 2006
2
Tevatron pp-collider
 Run I (1992 – 1995) √s = 1.8 TeV
•delivered ~ 260 pb-1
 Run II (2002 -–
) √s = 1.96 TeV
•collisions every 396 ns
•rate to tape 50 Hz
•delivers ~ 15 pb-1/week (January 2006)
•max luminosity 1.58·1032 (January 2006)
detector
commissioning
Jul 2002
Feb 2002
April 2001
More than 1.4 fb-1 delivered &1.2 fb-1 recorded
data for physics
first
data for
analyses
 So far reconstructed
~1 fb-1
~10x the total Run I data
01/03/2006
Valentin Kuzmin
PhiPsi 2006
3
The DZero Experiment
 Beam line shielding
•Reduces accelerator background
 Silicon tracker
•Coverage up to |η| <2
 Fiber tracker
•Coverage up to | η | <2
•8 double layers
 Solenoid (2 Tesla)
 Forward + central muon system
•Coverage up to | η | <2
 Three level trigger system
•Outputs 50 Hz
01/03/2006
Valentin Kuzmin
PhiPsi 2006
4
D** mesons
Four orbitally excited D-meson states, collectively known as D**
Previous studies by various experiments
Theoretical interest of
Heavy Quark Effective Theory (HQET)
• hyperfine splitting between states
with different jq
• semileptonic branching fractions
(B  D**) are among least
model-dependent predictions
D0 has studies on the narrow (jq=3/2)
resonances D1(2420),D2*(2460)
decaying  D*+π
Four (L=1) resonant states decaying thru
S-waves expected to be wide (~100MeV)
(jq=1/2)
D-waves expected to be narrow (~20MeV)
(jq=3/2) seen by various experiments
01/03/2006
Valentin Kuzmin
PhiPsi 2006
5
D**, signal selection
• Data: 460 pb-1
• Search for : BD1,2* + µνX
in chain: D1,2* D*- +
_
_
_
π+ , D*- D0 + π- , D0 K+ + π-
• selection all events with D0 and
µ, (216870±1280 events)
_
• combine with_π- and select D* (55450±280 events)
• suppression cc by cuts on significance and proper decay length of the B meson (31160±230 D*- events)
• in such events combine D*- and π• Fit found signal with two relativistic Breit-Wigner’s functions convoluted with the detector
resolution and 2nd order polynom(bkgnd). Fixed [PDG] M(D2*)-M(D1) and widths
Ν
Ν
01/03/2006
Valentin Kuzmin
PhiPsi 2006
D
1
D*
2
 467  39
 176 37
6
D** mesons properties
Semileptonic (B→D**) branching fractions and their ratio
Br(b  B) Br(B  μν(D 0 D* 0 ) X)  Br((D 0 , D* 0 )  D*  π  )  Br(b  B) Br(B  μν D* X) 
1 2
1 2
PDG
Ndata
1
1
D* * 

Ndata Br(D*  Do π  ) ε D**
D*
PDG
MC
Br(b  B) Br(B  μν(D 0 D* 0 ) X)  Br((D 0 , D* 0 )  D*  π  )  (0.122 0.007( st )  0.015( sys))%
1 2
1 2
Br(b  B) Br(B  μν D 0 X)  Br(D 0  D*  π  )
 (0.087  0.007( st )  0.014( sys))%
1
1
Br(b  B) Br(B  μν D* 0 X)  Br(D* 0  D*  π  )
 (0.035 0.007( st )  0.008( sys))%
2
2
Br(B  μν D* 0 X)  Br(D* 0  D*  π  )
2
2
 0.39 0.09(st) 0.12(sys)
0
0
*


Br(B  μν D X)  Br(D  D π )
1
1
• Assuming that the D1 meson decays
only into D*π
• Assuming that the D2* meson decays
into D*π in (30±6)% of the cases [PDG]
• Ratio
(first direct measurement)
Br(B  D 0l  νX)
1
 (0.33  0.06)%
Different from PDG value (0.74 ±0.16)% by 2.5σ
Br(B  D *0l  νX)  (0.44  0.16)%
2
In agreement with [PDG] 95% CL upper limit 0.65%
R  1.31 0.29(stat)  0.47(syst )
HQET = 1.6│mc= ∞
01/03/2006
Valentin Kuzmin
PhiPsi 2006
7
DS1 meson search
Ds** are orbitally excited states of Ds meson
We will look for narrow (L=1,jq=3/2,JP=1+)
b  BS0  Ds1 ( 2536)  X
Ds1 (2536)in
K S0    
Ds1 ( 2536)  D* K S0
0
Data: 485pb-1
0
D*  D   ,
D  K  
Muon plus 5-Track final state
52670±330
D* candidates
In 0.142-0.149GeV
mass difference window
5900±100
0.47 candidates 0.52
01/03/2006
Valentin Kuzmin
PhiPsi 2006
8
Evidence of DS1(2536) meson
D±s1(2536) signal
Gaussian for the signal plus an exponential with a threshold cutoff
0
at M(D*) +M(KS)
• 18.5±5.5
D±s1(2536) candidates
• 2536±1 MeV/c2
• 3.4σ
position
significance
Towards investigation of
D±s1(2536) properties
— there are no experimental measurements
of Br(BS→DS**)
01/03/2006
Valentin Kuzmin
PhiPsi 2006
9
FCNC searches
Motivation
D± → +- 
For every rare SM process there is a
“beyond the SM” theory in which it is enhanced.
• RPV SUSY can enhance SM suppressed
FCNC processes.
FCNC processes with down type quarks
• s->d type studied with kaons (K±,K0)
• b->s type studied with B mesons.
FCNC processes with up type quarks
• Still lot of room for new results
• In this talk we focus on c→u transitions
01/03/2006
Valentin Kuzmin
PhiPsi 2006
PRD66 (2002) 014009
f
RPV SUSY
ω
SM
c→u
m(+-) (GeV/c2)
10
FCNC c -> u transitions with D± & Ds±
D± → μ+μ- π 
Ds± → μ+μ- π 
Non-resonant decays
 Non-resonant decays
(GIM suppressed, Br~10-8)
Penguin
(Penguin & Box diagrams absent)
Resonant decay
Box
(Analogous to b->sl+l- studies after
B+->K+J/ψ->K+μ+μ- observation)
Br(Ds± → φπ ) Br(φ → μ+μ- )
(3.6±0.9)x10-2 (2.85±0.19)x10-4
 Resonant decay
• Observation = essential step to study c->ul+l- FCNC transitions
(dominant, Br~10-6)
–
–
–
In pp collisions at √s = 1.96 TeV σ(pp → cc) ~ microbarns
Ds± production mechanisms at the Tevatron:
–
–
• Prompt production: pp -> cc -> Ds± +X
–
– ->bb
• Secondary production: pp
->B+X -> Ds±+Y+X
Ds± and D± decay products tend to be within a narrow jet
01/03/2006
Valentin Kuzmin
PhiPsi 2006
–
11
FCNC, data selection
Data: 508pb-1

ω
Μ = χ2πμμ-vtx + (1/pT(π))2 + (ΔRπ)2
•χ2πμμ-vtx - three particle vertex
•ΔRπ – transverse distance between
MC
f
π and (μμ) system
Sum
Prompt
min(M)
secondary
Sideband data for background studies
0.96 < m(μ+μ-) < 1.06 GeV/c2
π  track selection
•Track in the same jet as μ+μ- pair.
•Track from the same vertex as the μ+μ- pair.
Ds±
and
D±
Ds± and D±
signal
region
selection
•μ+μ- & π  track form a good vertex
•1.3 < m(μ+μ- π  ) < 2.5 GeV/c2
•p(μ+μ- π) in the PV→SV direction
3.3 candidate/event
01/03/2006
Valentin Kuzmin
Do you see the Ds± or D± ?
PhiPsi 2006
12
FCNC, background suppression variables
To minimize background, we employ 4 variables:
 ID: tracking isolation of Ds±
ID=p(D)/Σp(cone), cone ΔR < 1
 SD: transverse flight length significance of Ds±
SD = Lxy/σ(Lxy)
 RS: ratio of π  impact parameter significance
to SD
• RS= (IPπ/σ(IPπ))/SD
 θD: collinearity angle
Angle between direction PV→SV and p(Ds±)
we use likelihood function of these variables to extract Ds± and D±
01/03/2006
Valentin Kuzmin
PhiPsi 2006
13
Combined likelihood variable
θD vs SD
 Isolation ID is independent of SD,θD & RS
Correlated
Independent
 SD,θD & RS are independent if SV well
separated from PV
 Combined likelihood “L” reflecting
correlations:
L=L(ID)xL(SD,θD,RS)
if SD <20
L=L(ID)xL(SD)xL(θD)xL(RS) if SD >20
Likelihood Ratio “d”
Plot likelihood ratio “d” :
d=L(Signal)/(L(Signal)+L(Background))
01/03/2006
Valentin Kuzmin
PhiPsi 2006
14
FCNC, signal extraction
The red histogram is after selection d>0.9
In the Ds± region 1.91 <m(μ+μ- π ) <2.03 GeV/c2
• 51 events found
• 18±4 background events expected
31±7 Ds± events observed
(corresponds to >7σ significance)
 Relax cut on likelihood ratio to 0.75 and Fit 2
Gaussians (signal) & exponential (background)
• Free Number(Ds±),mean(Ds±), σ(Ds±), Number(D±)
• Fix mean(Ds±)-mean(D±) to 1.969-1.869 GeV
• Fix σ(D±) to m(D±)/m(Ds±) x σ(Ds±)
Use the above found mean(Ds±), σ(Ds±) and fit
the d>0.9 distribution
13.2+5.6-4.9 D± events observed
(corresponds to >2.7σ significance)
01/03/2006
Valentin Kuzmin
need more data
for observation,
we will set the
upper limit on
D± -> μ+μ-π decays
PhiPsi 2006
UL
 drL( r)
0

 drL( r)
N ( D )
 0.9 , r 
N ( DS )
0
15
FCNC, branching ratios
Br(D± →φπ →μ+μ- π)
Br(Ds± →φπ →μ+μ- π)
To determine
Br(Ds± →φπ →μ+μ- π)
=
x
Literature
ε(Ds±)
ε(D±)
From MC
Br(D± →φπ →μ+μ- π)
= 0.17 ±0.07±0.07
PDG:
f(Ds±)
f(D±)
N(Ds±)
±0.08±0.06
Br(D± →φπ →μ+μ- π) = (1.70
x
Measured or
Limit Setting
PDG
Br(D± →φπ →μ+μ- π)
N(D±)
Br(Ds± →φπ →μ+μ- π)
< 0.28 (90% C.L)
Br(Ds± →φπ)· Br(φ→μ+μ-)
+0.79+0.76
-0.73 -0.82
)x10-6
Br(D± →φπ →μ+μ- π) <3.14x10-6 (90% C.L)
In agreement with expected [PDG]: Br(D± →φπ)· Br(φ→μ+μ-) =1.75 x10-6
+3.6
and the CLEO measurement: (2.7 -1.8 ±0.2) x10-6
01/03/2006
Valentin Kuzmin
PhiPsi 2006
16
Conclusion
Using 460pb-1 of DØ’s data sample we observe semileptonic
decays of B in D10(2420), D2*0(2460). The narrow D** mesons
branching fractions were separately measured for such decays.
The ratio between semileptonic fractions of the two modes is
R=1.31±0.29(stat)±0.47(syst) in agreement with HQET
The D0 Collaboration also observes the Ds1(2536) resonance and
the measurement of its properties is in progress.
 We see final state of the decay Ds± →φπ →μ+μ- π with a
significance of 7 standard deviations. DØ has nice sensitivity to
study FCNC in charm decays and we now continue to search the
non-resonant continuum for signs of physics going beyond the
Standard Model.
 Tevatron is doubling the luminosity each year  MORE GREAT
PHYSICS RESULTS are coming soon
01/03/2006
Valentin Kuzmin
PhiPsi 2006
17
01/03/2006
Valentin Kuzmin
PhiPsi 2006
19
Result: Br ( D± → π± μ+μ- ) limit
Br(D± →fπ →μ+μ- π)
Br(Ds±
→fπ →μ+μ- π)
=
N(D±;>0.9)
N(Ds±;>0.75)
x
f(Ds±)
f(D±)
To determine PDG From Limit Setting
ε(Ds±;d>0.75)
x
ε(D±;d>0.9)
Literature
From MC
UL
 90% C.L. upper limit on
Br(D± →fπ →μ+μ- π) found by:
∫drL (r)
0
∞
∫drL (r)
= 0.9, where r=
0
Br(D± →fπ →μ+μ- π)
Br(Ds±
→fπ →μ+μ- π)
Br ( D± → π± μ+μ01/03/2006
< 0.28 (at 90% C.L.)
) < 3.14 x 10-6 (at 90% C.L.)
Valentin Kuzmin
PhiPsi 2006
N(D±;>0.9)
N(Ds±;>0.75)
Uncertainties summary
Statistical
+47,-43 %
Fitting
+14%,-24%
f(Ds±)
26%
f(D±)
8%
ε(Ds±)/ε(D±)
19%
Br(Ds± →fπ)
25%
Br(f→μ+μ-)
7%
20