Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://nuclphys.sinp.msu.ru/conf/lpp14/240809/Sigamani.pdf Äàòà èçìåíåíèÿ: Wed Sep 16 16:32:48 2009 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 00:41:33 2012 Êîäèðîâêà:

Semileptonic B decays at BaBar!
On behalf of the BaBar collaboration

Michael Sigamani!

14th Lomonosov Conference on Elementary Particle physics! ! ! August 19th-25th, 2009!

!


!"#$%&'(
·! Introduction! ·! Inclusive semileptonic B decays!
­! Measurements of moments of the hadronic mass, and combined hadronic mass and energy distribution from B ! Xc l ! ! ­! Measurements of moments of the unfolded hadronic mass distribution from B ! Xu l ! ! ­! Inclusive results!

·! Exclusive semileptonic B decays!
­! |Vcb| and For m Factors from B ! D l ! (tagged measurement) ! ­! |Vcb| and For m Factors from B ! D(*) l ! (untagged measurement) ! ­! Exclusive results!

·! Conclusion!

,%

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!"#$%&'(')#%!**+%


)&#*+,"-#%+&(
! ! ! Semileptonic B ! Xc(u) l ! decays provide a clean environment for ! !! ! studies on the b quark inside the B meson. ! As well as a method for measuring CKM elements |Vub|,|Vcb|% Can be split into two distinct g roups!
·! Inclusive decays! ­! Sum over all possible final state hadrons.! ­! Use Operator Product Expansion (OPE) and Heavy Quark Expansion (HQE) to calculate decay rates.! ·! Exclusive decays! ­! Specifically reconstruct Xc(u) ! ­! Better background rejection! ­! Less statistics! ­! Use Heavy Quark Effective Theory (HQET) and For m Factors (FF) to describe hadronization!
!%
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)&-$".%/'(.'0%$'1#+&%-(
HQE calculates the relation between the total rate# and |Vc(u)b|!
pert

c(u)

"( B # X

c( u )

G 2F l$ ) = m 3 192%

5 B

| Vc

( u )b

|2 (1 + Aew ) A

A

nonpert

!

·! Non perturbative parameters need to be measured precisely in order to extract |Vub| and |Vcb| precisely.! ­! Kinetic energy of b quark, !"2; ! ­! Chromomagnetic moment, !G2; ! ­! Higher order ter ms: "LS3 , "D3. !

·! Moments have a sensitivity to these quark masses and same non-perturbative parameters!
­! Use moments for hadronic mass , lepton energy , and mixed moments !

=%

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!"#$%&'(')#%%!**+%


)&-$".%/'(.'0%$'1#+&%-(
·! Lepton moments! ·! Hadronic mass moments!
! E
n l

$ d# ' = N * ( E l " E l ) n & c( u ) )dE % dE l ( m
n X

l

# n d" = N ) mX % c( u $ dmX
2

)

& ( dm '

X

·! Mixed moments

Give a more precise deter mination of higher order non-perturbative parameters!

n
!

X

= mX " 2 #E X + #2 # = 0.65GeV

2

! ·! Translations from moments to non-perturbative parameters available in kinetic and 1S schemes!
­! All results in this presentation are calculated in the kinetic scheme!

"%

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!"#$%&'(')#%%!**+%


2+0'&#.(3*+0(!"! Xc l "(

4546789:4(;<'1='>?( @."A0%##',(#+(BCDE(

!=*%/011034%99%.>.4#)%

·! Tagged side! ­! Fully reconstruct one B meson! ·! Recoil side! ­! Select lepton with p*l > 0.8 GeV/c (l = e, !) ! ­! Missing mass consistent with neutrino! ­! Remaining particles for m Xc system! ­! Improve resolution with kinematic fit! ·! Residual backg round! ­! B ! Xu l ! decays ! ­! Secondary semileptonic D decays! ­! Semileptonic ! decays! ­! Leptons from J/$! l l ! ·! Combinatorial backg round ! ·! BB backg round! ­! e+e- ! c c or l l !
?%

%

&"

'% #

"

$"

Moments measured as lower limits ! ! ! on pl* (0.8 - 1.9 GeV)!

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!"#$%&'(')#%%!**+%


2+0'&#.(3*+0(!"! Xc l "(

Apply correction factors (calculated from MC) to ! mX and nX2 spectrum to correct for ! unmeasured/missing particles!

@%

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!"#$%&'(')#%%!**+%


2+0'&#.(3*+0(!"! Xc l "(
·! Perform combined"2 fit in kinetic scheme: !
·! Hadronic mass moments/mixed moments; ! ·! Lepton energy moments in B ! Xc l !;! ·! Photon energy moments in B ! Xs #;!

·! Fit on subsets of measurements to reduce correlation! ·! Uneven mass/mixed moments not used to provide an unbiased comparison with fitted HQE prediction ! ·! 8 fit parameters: ·! |Vcb|, mb , mc , BF(B ! Xc l ! ),!"2 , !
Additionally:( ·! !B = (1.585 ± 0.007) # 10-12 s ! ! ·! !G2 = (0.35 ± 0.07) GeV2! ·! #LS3 = (-0.15 ± 0.10) GeV3! !
A%
!

G

2

! ,#

3 LS

,#

D

3

!

(B lifetime) Input parameter! Constraint! ! Constraint!
!"#$%&'(')#%%!**+%

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2+0'&#.(3*+0(!"! Xc l "(

Mass moments!

Mixed moments!

B%

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!"#$%&'(')#%%!**+%


2+0'&#.(3*+0(!"! Xu l "(
·! Tagged side!
­! Fully reconstruct one B meson!

=B=%/011034%99%.>.4#)%

·! Recoil side!
­ ­ ­ ­ ! ! ! ! Select lepton with p*l > 1.0 GeV/c (l = e, !)! Remaining particles for m Xu system ! Missing mass consistent with neutrino! Veto K±, KS and partially reconstructed D*!

·! Large !"! Xc l " backg round!
­! Subtract using a "2 fit to the hadronic mass spectrum (a)! Unfold background subtracted spectrum (a) ! for detector acceptance, resolution and efficiency to get unfolded spectrum (b). ! Then extract moments from (b) for m2X < 6.4 GeV2!

,*!A%C%,A@% D)0(471%.>.4#)E%

Statistical error (inner bar)! Experimental (outer bar) ! +%
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F"00G*H(+3(%&-$".%/'(*'."$#.(

*FPCP(

Results from !"! Xc l ! and !"! Xu l ! moments analyses(

·! Good agreement of results from mixed and mass moments! ·! Good agreement of results with the HFAG world average! ·! Good agreement for !"! Xc l " and !"! Xu l " results!
,*%
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I>-$".%/'(.'0%$'1#+&%-"
HQET calculates the relation between the total rate$ and |Vcb|G2(w)!

d" G 2F 3 ( D) = ( mB + mD )2 mD ( w 2 $ 1) dw 48# 3

3/2

| Vcb | G 2 ( w )

­! G2(w) is the only relevant for m factor (FF) in null lepton mass limit.!

!

w = VB " VD =

(M

2

B

+ M 2D # q2 ) 2 MB MD

­! (D meson produced at rest) 1.0 < w < 1.6 (D momentum opposite to W)

!

!

·! HQET expansion of FF!

"""()*+,-.-"/%"*%0"+*,*1/2/,-3*2-4.5"67$%089:;0!<=>"(?@@ABC?<=B"

G( w ) = G(1)[1 " 8 # 2 z + (51# 2 " 10) z " (252 # 2 " 84 ) z 3 ] z =
·! Slope of G(w) at w=1, #2 is extracted with fit along with G(1)|Vcb|!
!
,,%
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w +1 " 2 w +1 + 2

!

!"#$%&'(')#%%!**+%


JGKK',(!"! D l "(

·! Tagged side! ­! Fully reconstruct one B meson! ·! Recoil side! ­! Select lepton with p*l > (l = e, !) ! ­! Reconstruct D0 (9 final ­! Reconstruct D+ (7 final ­! Identify semileptonic B missing mass squared!

454L7L49M(;<'1='>?(( @."A0%##',(#+(BCNE(

"@*%/011034%99%.>.4#)%

0.6 GeV/c states)! states)! decays from the
2

m

2

miss

= [ p("( 4 S )) # p(Btag ) # p(D) # p(!)]

!

·! Extract B ! D l ! for each bin of w using a binned maximum likelihood fit to m2miss! ­! 10 bins of w ! ­! 1.0 < w < 1.6 !
,!%
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JGKK',(!"! D l "(
Background subtracted spectrum (~3250 signal events)!
Use %2 fit to w spectrum to ! calculate G(1)|Vcb| and #2 !

Combined results( G(1)|Vcb|! =! (43.0 ± 1.9 ± 1.4) # 10-3 (5.5% error) ­ Mainly statistics! "2 ! ! ! =! 1.20 ± 0.09 ± 0.04! BR(B0 ! D l !) =! (2.17 ± 0.06 ± 0.09) %!
,=%
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!


O&#GKK',(!"! D(*) l "(

BCD:5P(4Q8448(@8445E(

!=*%/011034%99%.>.4#)%

Select !DE>"! D0/+ l " ! from D0 l or D+l pairs ! select lepton with p*l > 1.2 GeV/c (l = e, !) ! F Analysis has ! sensitivity to! $D2, $D*2 ! and|Vcb|! F
K% *%

!

Extract B ! D(*) l ! from binned 3D fit to: p*l (momentum of lepton)! pD (momentum of D) ! cos#B ­ D l!

!

FG%FHG%FHH%G%3#$.:%99%I75J(:3'46%

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O&#GKK',(!"! D(*) l "(
·! Result from combined fit from electron and muon samples.! ·! BR(B0) obtained from BR(B-) results using lifetime ratio.!

D :! ! G(1)|Vcb|! ! =! ! (43.1 ± 0.8 ± 2.3) # 10-3! ! (5.5% error) ­ Mainly systematics! D* :! ! F(1)|Vcb|! ! =! ! (35.9 ± 0.2 ± 1.2) # 10-3! !

! !

·! Consistent with existing measurements.! Theory Validation( ·! ·!
,?%

G(1)/F(1) = 1.20 ± 0.09 agrees well with lattice computation (1.17 ± 0.04).! Slope difference "D2 ­ "D*2 = 0. Consistent with prediction.!
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F"00G*H(+3('>-$".%/'(*'."$#.(
Combine tagged and untagged ! measurements for B ! D l ! !
G(1) ! |V cb| [10 ]
-3
# "2 = 1

CLEO ALEPH

50
BELLE BABAR global fit

40

AVERAGE BABAR tagged

G(1)|Vcb|! ! "2! ! ! ! BR(B0 ! D l !)!
! !

=! =! =!

(42.4 ± 0.7 ± 1.6) # 10-3! 1.18 ± 0.04 ± 0.04! (2.16 ± 0.08)% !

Using Okamoto et al. (FNAL05) LQCD: ! G(1) ! ! = 1.074 ± 0.018 ± 0.016!

30

|Vcb|!

=!

(39.2 ± 1.6 ± 0.9G) # 10-3 !

HFAG
20
WINTER 2009 "2/dof = 1.3/ 8

Consistent with existing measurements!
1 2

0

|Vcb| (B ! D* l ! )! =! ! |Vcb| (inclusive)! =!
2

(38.1 ± 0.5 ± 1.0F) # 10-3 (41.5 ± 0.7) # 10-3 !
!"#$%&'(')#%%!**+%

!

,@%

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R+&-$".%+&( ·! Presented are inclusive measurements of:!
­ ­ ­ ­ ! ! ! ! The first six moments of hadronic mass spectrum for B ! Xc l !! The first measurements of mixed hadronic moments k = 2, 4, 6! Moments from the unfolded mass spectrum in B ! Xu l !! Good consistency between measured parameters from both moments analyses!

·! Presented are exclusive measurements of:!
­! G(1)|Vcb| from !"! D l " using tagged and untagged sample.! ­! Combined measurements of |Vcb| are compatible with existing measurements! ­! Recent BaBar results have improved total error on world average of G(1)|Vcb| (4%)! ­! Inclusive |Vcb| is at currently at 2%!

,A%

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! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! END !


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As of 2008/04/11 00:00

Integrated Luminosity [fb -1]

BaBar Run 1-7
500
PEP II Delivered Luminosity: 553.48/fb BaBar Recorded Luminosity: 531.43/fb BaBar Recorded Y(4s): 432.89/fb BaBar Recorded Y(3s): 30.23/fb BaBar Recorded Y(2s): 14.45/fb Off Peak Luminosity: 53.85/fb

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! ! To extract moments additional corrections are applied ! !! ! which distort mX spectrum!

·! Correct fitted by:! ·! Using the observed relationship (from MC) between : ! to !! and ! to ! ·! Then apply correction factors on an event by event basis!


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