Rare Decays and their sensitivity to New Physics.
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Rare Decays
sB
sB
00 KB
and their sensitivity to New Physics
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320
22/1
422/1
66 )(GeVtan10
)(
MMM
BB s
Klassiker: sB
hep-ph/0108037
-9100.4)3.4(BR :SM mSUGRA Parameter:
sign,tan,)(,, 002/1 AMMM A
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Light chargino bounds from LEP, Radiative EWSB
LSP not neutral hep-ph/0108037
320
22/1
422/1
66 )(GeVtan10)( MMMBB s
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< 5.8·10-8 95% CL
2 fb
-1arXiv:0712.1708 to PRL
< 9.3·10-8 95% CL
D0 Note 5344-Conf (2007)
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Problem:
Untergrundunterdrückung
0B
B
Invariante Masse keine ausreichende Diskriminate
Multivariate Analyse
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Lifetime of B
Muon Impact Parameter Sign.
Bs Impact Parameter
DOCA between muons
Isolation
Geometry Likelihood
Muon Pion Likelihood (LL)
Muon Kaon Likelihood (LL)
PID Likelihood
signalbb inclusiveb b BcJ/
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M
signalbb inclusive
3-dim. Binning:
• 4 Bins in Geometry LL
• 3 Bins in PID LL
• 5 Bin in invarianter MasseMeV18
Untergrund Ereignisse/Bin
Signalereignisse/Bin (BR)
Sensitivität
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BR excluded at 90 % CL, i.e. only background is observed BR observed or discovered.
Exclude the interesting region between 10-8 and SM with little Lumi (~0.5 fb-1)
Observe (discover) SM BR with 3 (5) after ~2 (~6) fb-1
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Events after preselection cuts in 600 (60) MeV mass window
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Radiative bs decays
Standard Model bs (bs):
• LH s-quark (RH s-quark)
• LH (RH) photons
BSM physics (SUSY, LR Models) could lead to appreciable RH component photon helicity probes BSM physics
Probing photon helicity:
• (Photon conversion)
• Time dependent ACP:
• Parity-odd triple correlations between photon and 2 out of 3 hadrons in B (K++) decays
b(X)
sB
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B0s
[1] hep-ph/0607258 [2] arXiv:hep-ex/0607071v1
Erste Beobachtung von Bs
10)7.5()( 52.17.1
8.15.1
sBBR
510)19.194.3(:SM (Ball et al.)
5.5
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sensitive to NPSM NP
polarization predominantly left handed
right handed components
CPV in decay < 1 % 10%-40%
Inclusive decays : theory experimentExclusive decays theory experiment
CPV in interference mixingdecay
B0 (B0bar)X0 very small
B0 (B0bar)X0 Could be large
Why this decay ?
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Expected for one year of measurement ( 2 fb-1 )
• have to fight background
• very good PID necessary, 0 rejection
• proper time resolution (Time dependent CPV polarization)
• high trigger efficiency
• good offline selection
What do we expect at LHCb ?
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• two body kinematics
• geometrical cuts on pp-interaction PV and B-decay SV
Selection mainly based on
Selection criteria maximize with
=
S: signal evts
B: background evts
SS+B
K-
K+
PV
SV
Reconstruction and Selection
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Photon selection
• 2 body kinematics hard ET()
spectrum
• from numerous 0 decay soft
Require ET() > 2.8 GeV
On the way to the
• Charged tracks must NOT
come from PV ( of B)
• K+K- should come from SV
Some selection criteria…
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On the way to the B
• pB = ppshould point to PV
• use B ( allow rather large B as the SV resolution is not good because of K’s !)
PV
SV B
reconstructed p
flight path
Some selection criteria…
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• large background from B0s und BK*0
use vector meson polarization helicity of for B0
s
for B0s
• define helicity angle H
• sin2H distribution for signals
cos2H distribution for
correlated bkg
flat for combinatorial bkg
K+
K-
B H
Background…
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Expect 68k signal events for 2 fb-1 with B/S < 0.6
• red: true events
• blue : comb. bkg.
min13
And finally one gets…
B0 B0
Expect 11.5k signal events for 2 fb-1 with B/S < 0.6
Bs
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• from bspredominantly left-handed (SM: V-A
coupling of W boson)
• e.g. in MSSM can be largely right-handed
( doesn’t effect incl. radiative decay rate predicted by
SM)
• helicity measurement via time-dependent CP asymmetry, …
Polarization
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Polarization
0)( MtB
R
L
R
L
iL
iR
iR
iL
eAMBA
eAMBA
eAMBA
eAMBA
sin)(
cos)(
sin)(
cos)(
0
0
0
0amplitudes
)(
)(tan
L
R
MBA
MBA
Relative amount of „wrong photon polarization“
LR , Weak phases (CP odd)
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Time dependent decay rate
)sin()cos(
2sinh
2cosh))(( 0
tmStmC
tA
teMBB
qqtqq
q
0cos2sinsin2sin CAS
LRM
Standard Model:
12sinA
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The CP asymmetry
From the time dependent decay rate one gets
CP Asymmetry
The measurement of Adetermines the fraction of ‘different-polarized’ photons !
LHCb Toy study: 2.0 A for 2 fb-1
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B
bb
B m
mm
m
ss ˆ,ˆ
2
00 KB
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Asymmetrie:
2M
Interesting observable: Muon forward-backward Asymmetry
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„Zero crossing point:“
2ˆ
Bm
ss
hep-ph/9910221
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Generator Studie: 6.5 M Ereignisse.
Change in order to which Wilson coefficients are calculated.
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A. Ali et al. hep-ph/9910221
SMSUGRA MIA SUSY
(lower lines = pure short distance components)
M2 mass distributiuon Forward backward asymmetry
SMSUGRA MIA SUSYMIA SUSY C10 >0
Upper/lower lines C7 < 0 / C7 > 0
MIA = Flavor violating SUSY, mass insertion approx.
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0B
K
0K
B
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0B
K
0K
B
mRMS 33
mRMS 97
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%89%95%9310Trigger LL
%3.1%6.20%1.6sel recselrec
totKKBRKBBRS )()(398.0210 00012
61022.1 67.0
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Non-resonant background: KB
Upper limit: BR < 4 10-7 173075 events / 2 fb-1
irreducible
Asymmetry
In kinematischer Region II erwartet man gleiche Afb wie für K*ll
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Q2 Verteilung für Daten-Set von 2 fb-1:
signal
Untergrund (fluktuiert), flach in M
Bemerkung: Nicht-resonanter Untergrund wird vernachlässigt.
Signal Ereignisse: 37001200
Untergund: 1100 250222 GeV94 qm
(non-res ignoriert)
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Statistische Signifikanz des Zero-Crossing Punktes:
Kein Untergrund: 0.41 GeV2
Mit Untergrund (kein non-res): 0.46 GeV2 / 0.27 GeV2
Standardmodell: s02 = 4.2 0.6 GeV2
1fb)10(2
Systematische Effekte sind bisher noch nicht untersucht !!
(aus 10000 toy Experimenten)
AF
B
s=m2 [GeV2]
2 fb-1
(s0) = 0.46
(s0) = 0.27 (10 fb-1)