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DISCRETE '08, 11–16 December 2008, València. Rare B decays at LHCb. Hugo Ruiz On behalf of the LHCb Collaboration. Institut de Ciències del Cosmos. Introduction. In the SM, b s only through loops (FCNC) which implies: Processes are rare - PowerPoint PPT Presentation
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Rare B decays at LHCb
Hugo RuizOn behalf of the LHCb
Collaboration
Institut de Ciències del Cosmos
1
DISCRETE '08, 11–16 December 2008, València
Introduction• In the SM, b s only through loops (FCNC) which
implies:– Processes are rare– Powerful to find/constrain NP!
• Operator Product Expansion allows parametrizing effect of new physics throughout different b s observables :
• Observables are functions of C’s. – Branching ratios (BR)– Polarizations– Angular distributions
• Three examples for LHCb:
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Bs KKB0 K*K+-
Bs +-
Three interesting rare decays
Bs
BR(SM) BR exp @ LHCb
polarization
Bs+- (3.35±0.32)·10-9
helicity suppressed
TeVatron @ 90% CL (2 fb-1) < 4510-9
BR
Large theory
errors on exclusive
BRs
(57+18-12
+12-11) 10-6
Belle’08
3
Z, Z,
t
NP? in
B0K*+- (1.22+0.38-0.32)·10-6 B
factories
angular distributions
LHCb overview
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L = 2(5)·1032 , 2fb-1/year10 MHz visible interaction10 KHz bb (1012 bb / year)
VELO:(IP) ~ 14mm + 35mm/pT
() ~ 40-100 fs
Tracking: = 95% p>5 GeV, 1.9<h<4.9(p)/p ~ (0.4 + 1.5 p/TeV)%(m[Bs →]) ~ 20 MeV(m[K*+-]) ~ 15 MeV
ECAL:(E)/E ~ (9.4/√E 0.83)%⊕(m[Bs → ]): 90 MeV
Muon, RICH:k-ID: 88% for 3% misID-ID: 95% for 5% /k misID
MC:Full sim, pile-up & spilloverPhotos for FSR in signal
Bs
5
polarization in Bs • SM @ LO: O7 B0XsR, B0XsL, tan AR/AL~ ms/mb ~ 0– NLO (gluon interchange, etc..) tan ~ 0.1 [1]– SM extensions (left-right-symmetric [2] , unconstrained MSSM [3]) predict
large tan while no change on inclusive BR (bs)• Interference mixing-decay gives access to polarization:
• In the SM: C=0, S=sin 2 sin AΔ=sin 2 cos cos (mix + CP odd weak phases)
• B-factories: ACP @ BdK*(Ksπ0): C=-0.03±0.14, S=-0.19±0.23 [HFAG]
• LHCb can study Bs : s≠0, it probes AΔ as well as C and S !!
6[1] B. Grinstein et al, Phys. Rev. D 71,011504 (2005), Phys. Rev. D 73, 014013 (2006)[2] R. N. Mohapatra et al, Phys. Rev. D 11 (1975) 566; (1979) 334.[3] H. E. Haber et al, Phys. Rept. 117 (1985) 75.
no flavour tagging required
flavour tagging required
B0 XsR(L)
B0_
XsL(R)
Bs→ at LHCb• Acceptance function: ()
– because of IP, vertex displacement cuts @ trigger and selection
– Bd→K*(K+-)useful x-check
• Selection: 0.3%– L0 85% , HLT 80%
– ET>2.7 GeV
• Main background: BX + 0
– Bs → < 4% CALO
– B → K*0< 0.3% RICH
()
#/2fb-1 rate B/SBs 11k 5/hour <0.55
BdK* 68k 30/hour ~0.60
Belle: O(1 Bs→)/day at (5S)
Yields and purities:
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Bs→ at LHCb• Other analysis issues:
a) depends on Bs
• Precision on ACP parameters:– Fix ms, s, s, acceptance, tagging, background “lifetime”
Tagging 0.5fb-1 2fb-1
(A) No 0.3 0.22
(S, C) Yes 0.2 0.11
(n
s)
cos Bs
Left mass side-band
Right mass side-band
b) Background “lifetime” vs mass:
checked that parameter resolutions are robust under bkg lifetime, B/S,
event-by-event errors used in fit
0.1
B0 K*+-
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Angular distributions in B0 K*+-
• Decay described by l, , K and q2 m2
• Some observables have low theoretical error• Ex: AFB of l vs q2 in 1 < q2 <6 GeV2 low systs.– For 0 x-ing point s0, cancellation of form factors,
– s0SM
= 4.36+0.33-0.31 GeV2 [1]
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q2(GeV2)
CDF ~20 K* events (0.9fb-1)
BELLE ~230 K*ll evts (657M BB) BaBar ~60 K*ll evts (384 M BB)compatible with BR(bs
right handed weak currents
[1] M Beneke et al, Eur Phys J C 41 173-188, 2005
B0 K*+- at LHCb• Selection:
• Background:
• Developed 4 methods, with increasing:– Sensitivity to NP, model independence– Requirements in terms of statistics, control of acceptance functions
S/2fb-1 B/2fb-1 (%) B/S S/√S+B Cuts 4 k 1 k 0.7 0.3 60
Fisher 8 k 3 k 1.4 0.3 80
L0 90%HLT 75%
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fractionbμ, bμ 60%bμc(μ) 40%BsBd,usmissid
negligible
effect on asymmetry, ex:
but can be modeled from mass side-bands
~230@BELLE
B0 K*+- at LHCb1. Counting AFB in bins of q2
– Precision from linear fit, incl. bkg:
– @ 0.07 fb-1 competitive with B-facts
2. Unbinned AFB vs q2
– No need to assume linearity– Remove dependence on bin-size, fit range
An example 0.1fb-1 experimentA FBforward backward
q2(GeV2)
A FB
q2(GeV2)
0.5fb-1 2fb-1 10fb-1
σ(s0) 0.8 GeV2 0.5 GeV2 0.3 GeV2 s0SM
)
12
13
Bd→K* at LHCb3. Fitting projections on l, , K*:
– FL, AT, AFB model-indep. functions of C7, C9, C10.
– (s0) factor ~2 better
4. Full angular analysis:– Requires 2fb-1, full acceptance correction– Can form any observable– Eg [2]:
A T(2)
SUSY [1]
LHCb, 2fb-1
q2(GeV2)
SUSY, large-gluino +positive mass insertion
1, 2 LHCb
LHCb 10fb-1
SM with theory error
bandsA T(4
)
q2(GeV2)[1] Kruger et al, Phys.Rev.D71:094009, 2500[2] Egede et al, arXiv:hep-ph/0807.2589
vs
SM
Bs +-
14
Bs +-
• SM: BR = (3.35±0.32)·10-9 [1]
• TeVatron– @ 90% CL (~2 fb-1) < 45·10-9
– final (8 fb-1): < 20·10-9 6x BR!
• MSSM:
• Ex: Non-Universal Higgs Masses framework (generalization of CMSSM) [2]– bs , Mh>114.4 GeV, (g-2) @ 3.4
from SM, WMAP dark matter density BR(Bs+-)~20x10-9
15
40
622 tan)(
A
lbMSSM
M
mmllBqBr
[1] arXiv:hep-ph/0604057 (2006)[2] arXiv:0709.0098
20·10
-9
10-7
5·10-9
NUHM
68%
95%
Excluded @ 95% if BR (Bs +- ) <
Bs +- analysis1. Selection 6%
2. Categorization of signal likelihood:– Geometry: combination of IPS, B lifetime,
isolation, B IP, DOCA– Invariant mass– identification
3. Exclude/observe BR from distrib. in 3D bins, use CLs method [1]– BR reach 20% better than in simple cut
analysis
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Geometry likelihood
[1] A. L. Read, http://doc.cern.ch/yellowrep/2000/2000-005/p81.pdf
Arbitrary normalization
Bs +-
Bkg, L ~ 0.05 fb-1
#/2fb-1 for GL>0.5Signal 21*
bμbμ 172*Bhh 7.8*
BcJ+missid
0
L0 95% , HLT 90%)
(*) In many bins!
Bs +-: calibration
• For normalization of BR, use control channels instead of MC
• Bs BRs measured with large errors (>20%) use Bd, B+
– Then the largest syst. (13%) comes from additional factor:
• Useful channels:
17
nTRIGSELREC
TRIGn
SELn
RECnn
N
NBRBR
[HFAG]
Geometry likelihood
Bs +-
B(s) h+h-
TRIGGERED ON OTHER B
Ex: Calibration of geometry likelihood
< 6% per bin for 0.5fb-1 (bkg incl.)
#/2fb-1 BR/BRB+ J/ (+-) K+ 1.6 M 3%
B J/ (+-) K* (K+-) 1.3 M 5%B(s) h+h-(Bd K+-) 440 k ( 4%)
Bs +-: performance
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BR (x
10–9
)
Expected final CDF+D0 limit
Discovery (@ SM BR):3 fb–1 3 evidence10 fb–1 5 observation
90%CL limit (only bkg observed)
SM prediction
SM prediction
Discovery
5 observation
3 evidence
BR (x
10–9
) L dt (fb–1) L dt (fb–1)
Exclusion0.25 fb–1 BR < 10-8
2 fb–1 BR < SM
Uncertainty from MC stats on bkg
Conclusions• LHCb ready to exploit the B factory known as LHC
• With 2fb-1 integrated luminosity:– Bs→μμ: BR exclusion down to SM value
• 5 observation at SM value with 10 fb-1
– Bd→K*μμ: σ(s0) ~ 0.5GeV2
• Start having sensitivity to other observables with more complex fits
– Bs → from CP asymmetry, / 10%
• Rare B decays in LHCb will constrain extensions of SM or find NP
19
Back-up
20
More rare decays• Radiative :
– Polarization through ancular distributions:• b → γ, b → *γ for tan@ 3 >20-25% each with 10fb-1
• B±→ K±for cos2
– B → 0, B → for b d
• Other bsll observables: – B+ → K+ll direct CP asymmetry in B K*+-B+ K++-
• small in SM <~0.01, statistical error with 10/fb: ~0.01
– B+ → K+ll for ratio e+e- / +- (RK)• SM prediction 0.1% theoretical uncertainty, 4% @ LHCb after 10fb-1
– Bs → +- , Bs/Bd, ¼, flavour tagging 1/15
– b → +- not yet studied
• b dll:– Bs → K*+- Bs/Bd, ¼, |Vtd/Vts|2=0.2082 ~ 1/25
• Lepton Flavour Violation : Bq → ll’
21
(B K+-)/(B Ke+e-)
22