search for lfv decays involving ’ at belle y. enari, belle collaboration nagoya university
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9/15/2004 Search for LFV tau decay involving neutral meson at Belle 2
Motivation
• In MSSM at large tanmay have alarge branching ratio by Higgs mediated process.
• Comparison other mode.Mslepton > weak scale, Br( is not large.
M. Sher, Phys.Rev.D66 05731(2002)K.S.Babu PRL,89,241802 (2002)A. Dedes, et.al. PLB 549,2442 (2002)
is important process!!
Br() : Br(3) : Br() =
a. (ms/m)2
b. color factor c. phase space
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 3
110-7
Status of LFV decay search
Belle 3l
CLEO result (PDG2004)
Today’s report.
1/L @ ~ 9%
1/L @ ~3%
In MSSM, Br of LFV decay may have O(10-7~10-9).
Babar 3l1/ L @ ~3%
Efficiency BG level
l 3l.
l
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 4
KEKB & Belle detector
Lpeak = 13.91033/cm2/sec
Ldt = 287.85 fb-1
Cross section @ s =10.58GeV
: 0.9 nb
BB : 1.0 nb
KEKB is Factory!!!.
-ID eff. = 87.5% fake = 1.4 %
e-ID eff. = 92.4% fake = 0.25 %
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 5
Analysis.
• Modes
– e
– e•
– e ’, ’• ’
• Blind analysis
Blind region
±10
±5
±10
Invariant mass : M= E2
- p2
Energy difference : E = E – Ebeam
*
Blind region: -0.5< E < 0.5(GeV),
-5 < M < 5
Evaluation # of signal event
- Low BG level Counting signal candidates
using elliptical region
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 6
’
Selection criteria (l l l ’)
• Signal event reconstruction signal side ( e’) + tag side (1 trk + n+ missing.)
• BG suppression For QED BG.
– NOT (e) (for 1-1prong)– 5 < ECM
< 10.GeV
For qq and BG– 0 veto for ’s – 0.5 < cos < 0.95
– Mtag < 1.777 GeV/c2
– missing momentum towards tag side.– pmiss vs. mmiss
2 2-D cut.
total
Br(1 prong) = 84 %
(1prong or 3 prong)
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 7
Background suppression (1)Bhabha, , 2photon process
Total energy
not-(e or in tag side.
(Only 1-1 prong modes)
Hadronic process (u,d,s,c)
generic process
Opening angle
signal : 5% loss : 80% reject.
sig : 2% loss : 67% rej.uds: 65% rej.
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 8
Background suppression(2)
• missing particle : pmiss towards detectable regions.
signal event : is in only tag side costhrust-miss< -0.55 BG event : are in both sides
Effective missing mass
black: signal MC Blue: generic
After all kinematical cut applied: (except e/ ID for signal side)
eff.( = 3.8 10-6.
eff.(uds) = 3.0 10-7.
eff.( = 3.4 10-8.
eff.(ee) = 3.0 10-7.
signal : 17% loss : 95% reject
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 9
Mass distribution
• ’ mass peak.
(ID; 1.3<M<2.1; with Blind)
~5.2 MeV/c2 ~ 14 MeV/c2
m’ region
m– m
~12 MeV/c2
m– m
data:57ev. MC:48.1±4.0 data: 77ev. MC:81.6 ± 8.4data:109ev. MC:100±5.9
BG: Fake /K (80%) l 0 : true 0
others : mis-combination
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 10
E vs Minv. : l 0, l , l ’
BG estimation Nexp is calculated from the side band events
with assuming a flat distribution.Open blind.
Nexp=3.1±1.0
Nexp=0.15±0.15
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 11
E vs Minv. : l 0, l , l ’
BG estimation Nexp is calculated from the side band events
with assuming a flat distribution.Open blind.
Nexp=3.1±1.0
Nexp=0.15±0.15
Systematic uncertainties - eID:1%, ID: 2%, track: 2%, 0 veto 5.5%
Beam BG:2.3% Trigger:1.4% 4.5~8.7% - BG estimation: If Nexp<1, assume Nexp=0.
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 12
Result
Br is obtained from
• Upper limit evaluation (POisson Limit Estimator program)– Feldman-Cousins method
s02( BX N)
B =s0: signal events : efficiencyN: # of pairs
BX : B of sub-decay
Systematic uncertainty: using the Gaussian error.
First search!!
J. Conrad et al., PRD 012002 (2003)
Preliminary
10-70 timestighter limitfrom PDG2004
140M
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 13
Discussion - - (1)
• Statistics 4.7fb-1 154fb-1
• Signal efficiency
7.2%B 8.0%B
not use 7.2%B
• Observed events 0 1
CLEO Belle 33
1.7
Keeping BG level low.
Comparison with CLEO result
B () < 1.310-7@ 90% C.L.
Upper limit : B () < 9.6 10-6
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 14
Discussion - - (2)
Constraint on tan vs mA
Preliminary
• CDF result : measurement (ppA/bbbbbb)• LEP result : LEP Higgs Working Group,
PRL 86,4472 (2002)
http://lephiggs.web.cern/LEPHIGGS/paper/Note2001-04
B () < 1.310-7@ 90% C.L.
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 15
• Search for l l l ’ meson mode using 154fb-1.
• No indication of signal events.
B(l l l ’) < 1.3 ~ 1010–7 @ 90%C.L.. 10-70 times tighter bounds. First searches in e’, ’.
Summary
1/L @ ~ 9%
1/L @ ~3%
1/ L @ ~3%l 3l.
l
Preliminary
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 17
Signal efficiency and BG - muon mode -
side bandMC : data : b0
12.5±2.7 132.7 ± 0.7
0.8 ± 0.32
0.6 ± 0.4
9.2 ± 2.39
3.1 ± 1.0
5.5 ± 1.95
1.4 ± 0.6
(153.8, 428, 232, 160 fb-1)
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 18
Signal efficiency and BG - electron modes -
side bandMC : data : b0
0.7±0.7 0 0 – 0.0
0.0 ± 0.71
0.23 ± 0.23
0.0 ± 0.71
0.15 ± 0.15
0.8 ± 0.31
0.16 ± 0.16+0.4
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 19
Result: l 0, l , l ’
5ev./2.7±0.7
1ev./0.2±0.2
1ev./3.1±1.0
0ev./0.0+0.4 0ev./0.2±0.2 0ev./0.2±0.2
0ev./0.6±0.4 0ev./1.4±0.6
Preliminary
= 4.7% = 6.8% = 5.7% = 8.5%
= 6.4% = 7.2% = 8.0% = 8.4%
-0.0
Nobs/Nexp
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 20
History of integrated luminosity
Continuous injection
2003 Summer: SVD/CDC inner partreplacement
Ldt = 154fb-1
Ldt = 288fb-1
Ldt = 244fb-1
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 21
KEKB
HER: 8.0 GeV e–
LER: 3.5 GeV e+
Lpeak = 13.9×1033/cm2/sec
Ldt = 287.85 fb-1
Cross section @ s =10.58GeV
: 0.9 nb
BB : 1.0 nb
performance snap shot (2004.3.1)Continuous injection mode
LER 1.6A
HER 1.1A
L ~ 1.1×1034/cm2/sec
KEKB is Factory!!!.
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 22
Belle detector
/ KL detection 14/15 lyr. RPC+Fe
Central Drift Chamber small cell +He/C2H5
CsI(Tl) 16X0
Aerogel Cherenkov cnt. n=1.015~1.030
Si vtx. det. 3 lyr. DSSD
TOF conter Scinti + FM-PMT
SC solenoid 1.5T
8 GeV e
3.5 GeV e
-ID eff. = 87.5% fake = 1.4 %
e-ID eff. = 92.4% fake = 0.25 %
proton ID eff. ~ 70 % fake ~ 1 %
E resol.E /E = 1.8% @E=1GeV
Trk. resol. pt/pt ~ 0.19pt 0.30/ %
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 23
Status of LFV search in Belle
New result of this summer.CLEOBabar
Belle Published Preliminary
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 24
Summary table of LFV search in Belle
Preliminary result
Published resultsNew result in this summer.
First search result.
B < O(10-7) are obtained
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 25
Systematic uncertainty
• Related sensitivity
• Related BG– Using statistical error as systematic error. (30~45%)
– If b0 < 1, we set b0=0 in order to obtain conservative limit.
In Total : 4.5 ~ 8.7 %
POLE program
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 26
2.1 Selection criteria ( 1-3 prong + ’)
– 1-3 prong + n2
E > 0.1 GeV , barrel and endcap
ptrk>0.06GeV/c barrel.
ptrk >0.1GeV/c endcap. net charge=0.
dzrms < 1cm, drrms < 1cm to reject junk track.
signal side: eID > 0.9 + 2trk(+,–).
– Missing momentum towards tag side.– pmiss vs. mmiss
2 2-D cut.– 0.5 < cos’ < 0.92– -3 < M < 3
using thrust axis, divide 2 hemisphere
for tag side, mtag < 1.777 GeV/c2
’
e/
9/15/2004 Search for LFV tau decay involving neutral meson at Belle 27
2.2 Selection criteria (1-1 prong + )
– 1-1 prong + n 2
signal side:
eID > 0.9 + 2 .
Pe>0.7GeV/c, E > 0.22GeV
– 0 veto for ’s
tag side:– NOT (e)
– Mtag < 1.777 GeV/c2
Kinematical cut.
– Missing momentum towards tag side.
– pmiss vs. mmiss2 2-D cut.
– 0.5 < cos’ < 0.92
– -5 < M < 3
e/
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