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27/September./2008 Satellite Meeting on Super Tau-Charm Factory
1
Search for -> /e at the Super--charm Factory
[Comments from Belle experience]
This talk is based on a study done for Super-B factory by T. Iijima, K. Hayasaka
(Nagoya U.)
H. Hayashii (Nara)
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
2
Introduction Lepton flavor violation (LFV) in charged lepton⇒negligibly small probability in the Standard Model (SM) even including neutrino oscillation
- Br(→ℓ) <O(10-54)
Why SM + mprediction is so small ?
(or e)
W-
γ
(or e)22* 54
21,2
3( ) 10
32li
i ii w
mBr U U
m
U2 2 2ij i jm m m
: PMNS neutrino mixing matrix
:Neutrino mass square difference
-Lepton Flavor is conserved accidentally.
-If O(1TeV) particles exit, Br is enhanced significantly, Theory needs some suppression mechanism.
-Almost all Beyond Standard Model predict LFV
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
3
Status of LFV Decay Searches (Tau08)(based on data)
B-f
acto
ryC
LEO
ℓf0(980)
ℓℓℓℓhh’ ℓV0
ℓℓ//0
ℓKs10-7
10-8
10-6
10-5
Upp
er li
mits
for
LF
V
dec
ay
Improve by factor ~100 from CLEO
update from TAU06
500/ fb
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
4
→e(PLB666,16(2008)) Data: 535fb-1 Br(→)<4.5x10-8 at 90%C.L. Br(→e)<1.2x10-7 at 90%C.L.
Results from Belle (1) signaldata
→
→(→)→e/+(’) (PLB648, 341 (2007))
Data: 401fb-1
Expected BG : (0.0-0.6) events
Nobs : 1 event Br(→,’,0)<(6.5-13)x10-8 Br(→e,e’,e0)<(8.0-16)x10-8
signal region
Final state: 1-prong decays and others
Remaining many BG from e+e-→+-sensitivity is limits by the background
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
5
Super-B and Super -c Factory
B-factory ( nb, root(s)=10.6 GeV)
• L =1036 cm-1s-1 /year Super-B at Roma =3x1035 cm-1s-1 Super KEKB
-c factory ( nb, root(s)=4.25 GeV)
L= 1035 cm-1s-1 3.5x109/year -Final reach depends on , efficiency, background -Typical efficiency in B-factory exp.: 5-10%. -Background
Ldt
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Super B-factory
Expected sensitivity→ℓ Br~O(10-8~9) →ℓℓℓ, l+meson Br~O(10-9~10) ▲
Super (KEK)B-factory:(10~50) ab-1
Br(→)<3x10-10@50ab-1
Current UL@BelleBr(→) <3.2x10-8@543fb-1
Super (KEK) B GOAL:
Improve the sensitivity by additional factor of 100 and achieve 10-10
and >e
Background dominated
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Some detail of search • e+e+
ee
generic decay
signal event
(signal side)
1 prong + missing ( tag side)
)( 22 pEM CMbeam
CM EEE
0~,~ EmM
for signal event
signal MC
3 ellipse: blinded regionsignal extraction: ME plane
•blind analysis
-Tag side is not muon.
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Analysis of search II• Main BGs:
– +ISR ()– +ISR
• Requirement on missing mass useful to reduce BG (signal: 1or2; :>2)• signal extraction:
– Unbinned Extended Maximum Likelihood fit likelihood function:
e
e
ISR
BG: +ISR
e
e
ISR
BG: +ISR
generic decay
signaldata
N
iBGsig
bs
bPDFsPDFN
e
1
)(
)(!
L
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Result of search• Lum:535fb-1(Belle)
•more tight requirements to reduce BG
than the previous 86 fb-1.
•remaining events: 94ev./535fb-1
•signal detection eff.: 11% 6.7%
•signal region: 5box 2ellipse
•signal extraction: UEML fit
result:s=3.9, b=13.9 (allow negative s and its prob. 25%)
Br<4.5x10-8 at 90%C.L.
signaldata
2D fit on ME plane
blinded region
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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BG events in analysis
If we can remove BG events caused by ISR completely…
When we run an accelerator with lower energy than (4s),Can we reduce these ISR BG events?
1.5 ab-1 generic MC sample
removed by MC generator info.
90% events removed!
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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ISR Spectrum• At near threshold
– E for ee background cannot be as high as E for .– Background from ee will become more important.
good MUID is essential.
s =10.58GeV s =5.0GeV
s =4.25GeV s =4.0GeV
E (CMS) from and ISR()
(4s)
maximum
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Summary
• Background source: 1) ISR ee-> 2) ee-> where tag-side muon is miss identified as
pion.• Achievable sensitivity in Super (KEK) B-factory sensitivity
will be limited by ISR BG although there is a room to optimize selection criteria.
• High intensityc factory running at root (s)= 4.25 GeV is ideal place for as well as->e searches.• Very good separation is essential to suppress ee-
> background.
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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Backup Slide
27/September./2008 Satellite Meeting on Super Tau-Charm Factory
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pair production cross section
• Threshold at 3.55GeV• Maximum at 4.25GeV ( ((4s))x 4)
2 30 4 (3 )
3 2s
: velocity of B-factory