Transcript OT-Installation at CERN

Prospects for new physics in rare
decays, mixing and related CP
violation at LHCb
Sebastian Bachmann on behalf of LHCb
University of Heidelberg/CERN
Symposium on hadron collider physics
Isola d’Elba, 21-25 May 2007
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Motivation
A lot of precise measurements are
available from B-factories and Tevatron
to test the CKM picture of flavour
structure and CP violation.
(from
CKM-fitter)
However it is expected that New
Physics is accessible from box and/or
loop diagrams.
LHCb aims to find New Physics
contributions in these processes.
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What do we get from LHC?
 bb cross section: 500µb +
LHCb luminosity ~ 2-5 • 1032 cm-2 s-1
Inelastic pp collisions/crossing:
For LHCb mainly single
interactions
(avoid Pile-Up!)
LHCb
b-production rate ~100kHz
One year of nominal data taking
corresponds to 2fb-1
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A signal event: Bs→Ds-(K+K-π-)K+
Signal side
~100 charged
particles in
LHCb acceptance
• Excellent tracking, vertex finding
and proper time resolution
• Particle identifiation
• Excellent mass resolution
• Trigger including
low cuts on pt
fully hadronic trigger
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Flavour tagging
Opposite side
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LHCb detector
4Tm
Dipole
Vertex
Locator
(Silicon)
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RICH counters
Tracking
p/K/p Identification
Calorimeters
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Muon
System
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LHCb detector in place
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LHCb performance:
Proper time resolution:
LHCb:
Momentum resolution:
~ 40 fs for (Bs  Ds-p+)
CDF:
87fs for fully reconstructed
decays.
PRL 242003 (2006)
π-K separation:
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Bs-mixing
and
related CP-asymmetries
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NP from mixing and CP-asymmetries
CDF: Δms = (17.77 ± 0.1stat ±0.07syst) ps-1
Bs→Ds-π+:
Precise measurement of Δms  LHCb: Observation expected after few month
using Bs→ Ds+π-.
data taking at nominal luminosity
Bs→J/ψΦ:
Extract Φs and ΔГs in golden
mode Bs→ J/ψΦ.
? ?
?
(NP → contribution to box diagram)
Bs→ΦΦ:
Measure hadronic
penguin Bs→ ΦΦ.
+
(NP → contribution to
decay mode?)
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ΦNP?
W-
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CP-violation in the Bs-system
Decay into a final state f
with CP f → ηf f
(assume only one amplitude
contributes to decay)
|A| e+iω
Bs
f
e2iΦs
Bs
CP-asymmetry:
 ( Bs0 ( t ) f CP ) -  ( Bs0 ( t ) f CP )
ACP (t )  ( B0 ( t ) f
s
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0
CP ) +  ( Bs ( t ) f CP )
 f sin( s -2 ) sin( ms t )
|A| e-iω
For Bs→J/ψ:
≈0
 t
 t
cosh s  - f coss sinh  s 
 2 
 2 
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Φs and ΔГs
In the SM:
s  2 arg[Vtb*Vts ]  -0.04rad
s
 0.12  0.06
s
Phys.Rev.D63 114015(2001)
If new physics contributes to
Bs mixing:
s  s + NP
Any sizeable CP violation in
Bs→J/ψΦ or Bs→ΦΦ is a
clear sign for NP!
s  s cos(s )
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Bs→J/ψ(µ+µ-) (K+K-)
Advantages:
b
Bs
s
High branching ratio
Good experimental signature
c
c J/ψ
s
Φ
s
JPC=1-JPC=1--
CP(J/ψ) = CP(J/ψ) CP() (-1)L
L=0, 2: CP even
L=1: CP odd
}
Final state is
a mixture of
CP even/odd
Angular analysis needed to identify CP even and CP odd states!
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also valid for Bs→
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Bs→J/ψ(µ+µ-) (K+K-)
Use angle θtr between µ+ and normal of
 decay plane:


d
2
2 3

 A0 (t ) + A2 (t )
1 + cos 2 tr 
d cos tr
8
3 2
+ A1 (t ) sin tr
4
2

A0, 2 (t )  A0, 2 (0) e Lt - e t sin( s ) sin( ms t )
┴
2
2
A1 (t )  A1 (0) e Lt + e t sin( s ) sin( ms t )
2
2



Total
CP even
bkgnd
CP odd
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Selection and signal decay rate
•Yield:
• B/S:
• <δt>:
• σMass:
• wtag:
• εtag:
130k events per 2fb-1
0.12
36 fs
14 Mev/c2
33%
57%
Signal decay rates including:
• Trigger and selection bias on τ
Bs→J/ψΦ:
Tagged Bs
Tagged Bs
s = 5 x SM
• Background parametrization
• Mass resolution
• Proper time resolution
• Tagging efficiency and dilution
• Transversity angle distribution
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Projection for Φs and ΔГs with 2fb-1
Parameter
Exp. error
Channel
s
0.023 rad
Bs→J/ψ(µ+µ-) Φ(K+K-)
ΔГ/Г
0.0092
Bs→J/ψ(µ+µ-) Φ(K+K-)
Δms
0.007 ps-1
Bs→ Ds-(K+K- π-)π+
wtag
0.0036
Bs→ Ds-(K+K- π-)π+
Control
channel
only
Sensitivity can be improved by adding more channels.
Using Bs→J/ψη, Bs→ηC, Bs→DsDs gives σΦ=0.021 rad.
CP-Eigenstates
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Bs→ : Sensitvity to s
LHCb profits from excellent
PID and hadronic trigger!
Distribution from 500 MC experiments:
Expected yield: 4000 events per 2fb-1
BG estimate limited by MC statistics:
0.4<B/S<2.1 at 90%CL
 Sensitivity to s is 0.1rad at 2 fb-1.
 No significant variation as a
function of input s, Rt and
proper time resolution.
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NP by Tree↔Penguin comparison
Bd-system:
Bs-system:
d
Vcb W
b

b
Vtb
d

–

W –
t 
Vcs
d
*
s
c J/y
c
Vts
*

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b
s
s
s
d

Ks
Vcb W
–
Vcs
*
Tree



Φd(tree)-Φd(penguin)
 = dΦdNP)
B-factories:
Currently: db  8o 2.6s
s
Ks
b
Penguin

Vtb

W –
t 
Vts*
s

s
c
J/y
c
s
s
s
s


s


 (penguin) = dΦ NP)
Φs(tree)-Φ

s
s

And:
Φs(SM) small!
LHCb-projection (2fb-1): σs) = 6°
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Rare decays
Decay
1. Bd,s→µ+µ-
Sensitivity to
- large tanβ
Example for model
CMSSM
2. Bd→K*0µµ
- small tanβ
- right handed currents
3. Bu→K+ll
- (pseudo)-scalar
couplings
non-MFV MSSM
MIA MSSM
SUGRA
MFV
(in combination
with 1.)
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1. Bd,s→µ+µSM expectation:
BR(Bs→µ+µ-) = (3.4±0.4) x 10-9
BR(Bd→µ+µ-) = (1.0±0.5) x 10-10
World best limit by D0:
BR(Bs→µ+µ-) < 7.5 x 10-8@90%CL
In Supersymmetry:
Large contributions e.g. by
Higgs penguins ~tan6β, i.e.
BR(Bd,s→µ+µ-) is very
sensitive to high values
Sebastian Bachmann
of
tan
β.
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Sensitivity by LHCb
Main background:
 Combinatoric b→µ, b→µ
Bc± → J/ψ(µ+µ-)µ±ν
 Bd,s→ h+h-
Adressed by excellent
mass resolution (18MeV),
vertex resolution and
particle ID
10-6
D0 limit
BR(Bs→µ+µ-) in CMSSM as a
Function of gaugino mass
10-7
10-8
1 year@LHCb
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SM
10-9
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3.) Bu+→K+ll
H0/A0?
SM prediction can get
corrections of ~10%
by neutral Higgs boson
exchange due to couplings
~ ml
Use the ratio
Hiller & Krüger, PRD69 (2004) 074020)
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Bu+→K+ll with 2fb-1
Takes into account an
inclusive di-lepton
trigger
 applies Bremsstrahlung corrections
eeK
µµK
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Signal
Mean
Sigma
349±34
1550±50
5245 MeV
5279 MeV
74 MeV
15 MeV
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σRk(2fb-1)≈ 10%
σRk(10fb-1)≈ 4-6%
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Rk in a MFV model
Assume
o Right handed currents are
negligible.
o (Pseudo-)scalar couplings
lepton masses
o No CP-phases beyond the
SM
Predicted by MFV model
Predicted by MFV model
Rk-1 ~ BR(Bs→µµ)
Hiller & Krüger, PRD69 (2004) 074020)
LHCb projection
if SM is holds
But we hope for
something else…
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Conclusion
 LHCb is on a good track to take first data soon.
 It has a wide potential to search for New Physics
complementary to new particle searches.
 Searches allow to
 find New Physics in model independent analysis,
e.g. by measuring Bs-mixing and related CP-asymmetries.
 pin-down the nature of New Physics e.g. by the study of rare
decays.
 The challenge is to achieve that performance with
real data!
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Backup slides
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Physics motivation
 A copious number of B-mesons is produced at LHC (105Hz @ 2x1032cm-2s-1).
 SM contributions to mixing and many decay processes are well understood.
 New Physics may alter SM predictions
LHCb aims to search for New Physics contributions
to loop processes, e.g.
Bs-mixing:
+
?
b → sγ:
+
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?
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Performance: Vertex locator
Proper time resolution:
LHCb:
~ 40 fs for (Bs  Ds-p+)
CDF:
87fs for fully reconstructed
decays.
PRL 242003 (2006)
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Tracking
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Performance: Particle Identification
p–K separation
Unique feature of LHCb
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Performance of VeLo
Impact parameter resolution:
δIP = 14µm + 35µm/pt
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Proper time resolution:
~ 40 fs (Bs  Ds-p+)
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Calorimeter
Calorimeter system to
identify electrons, hadrons
and neutrals
Important for the first level
of the trigger
o Scintillating Pad Detector /
PreShower
o Electromagnetic calorimeter
o Hadron Calorimeter
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Muon identification
Muon ID efficiency (%) vs -π DLL cut
94%
Pion mis ID efficiency (%) vs -π DLL cut
1.1%
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Trigger
HLT rate Event type
Calibration
Physics
200 Hz
Exclusive B candidates
Tagging
B (core program)
600 Hz
High mass di-muons
Tracking
J/y, bJ/yX (unbiased)
300 Hz
D* candidates
PID
Charm (mixing & CPV)
900 Hz
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Inclusive b (e.g. b)
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Trigger
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d’Elba
B (data mining)
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Flavor tagging
 Opposite side
 Charge of the kaon in the b→ c→ s chain
 Charge of the lepton in semi-leptonic
decays
 Charge of accompanying b jet
 Same side
 Charge of the K accompanying Bs
 Charge of the p from B** → B*p±
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Δms from Bs→ Ds-(K+K- π-)K+
0
Bs

Ds
p
+
-has a large branching fraction
of (3.4±0.7)x10-3.
- is flavor specific.
Total efficiency: εtot=0.39%
Signal yield:
140 k ± 0.67 k (stat.) ± 40 k (syst.)
(assuming 1 year of nominal running,
i.e. 2 fb-1)
B/S at 90% CL: [0.014, 0.05] (bb combinatorial)
[0.08, 0.4] (bb specific)
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Sensitivity to Δms
 Plot made for 1 year of data
(80k selected events, LHCb)
for Δms =20 ps-1
 Control of mistag rate,
resolution, background
and acceptance important
 Expected sensitivity for 2 fb-1
(i.e. year of data)
σ(Δms) = ±0.007 ps-1
CDF: Δms = (17.8 ± 0.1) ps-1
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Sensitivity for New Physics
In april 2006, including
first CDF measurement
of Δms
Model independent parametrization
for New Physics:
M 12  1 + hs exp( 2is s ) M 12SM
CL>0.32
from hep-ph/0604112
CL>0.05
This results in:
ms  msSM 1 + hs exp( 2i )s s
s  sSM + arg 1 + hs exp 2is s 
In 2010, with one year
of LHCb data (2fb-1)
s  sSM cos 2 arg 1 + hs exp 2is s 
from hep-ph/0604112
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Bs→ Φ(K+K-) Φ(K+K-)
 FCNC (b→sss)with SM prediction for CP-asymmetry < 1%.
see e.g. M.Raidal, PRL 89,231803(2002)
 Sizeable CP asymmetry is an unambiguous sign for NP.
 Like in Bs→J/ψ a full angular analysis to extract CPasymmetry is needed.
 Experimentally demanding, as full hadronic trigger is needed.
Remark:
• In SM Bs→J/ψ and Bs→  measure both arg[Vtb* Vts].
Tree
Penguin
• Deviations point to physics beyond the SM.
• Belle/Babar have 2.7σ deviation when comparing tree and penguin decays
of Bd to CP-Eigenstate.
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Event selection and sensitivity studies
Selection:
Reconstruct only →K+K-.
 Full detector simulation including
trigger bias.
 Reconstruction based on:
o RICH K± ID
o pt and impact parameter of K±
and  candidates.
o Bs and  invariant mass.
o Bs and  vertex quality.
Sensitivity to s studied by toy MC:
- proper time resolution of 42fs.
- proper time acceptance function.
- flat BG in mB and transversity
angle.
- mistag dilution: ε(1-2ω) = 9.6%
- exponential lifetime distribution Sebastian Bachmann
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for BG
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From G. Hiller [hep-ph/0308180]
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2.) B0→K*0µ+µSM processes contributing to decay:
BR(B0→lls) = 4.5x10-6
BR(B0→llK) = 0.5x10-6
Decay is very sensitive to extensions of SM, especially to models with
right handed currents:
Analysis of angular distributions allow to extract this
information about new Physics.
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Observables in B0→K*0µ+µTwo observables are of
special interest, as they
have small theoretical errors
and are very sensitive to NP:
Forward-Backward Asymmetry in θl:
Transverse Asymmetry:
(asymmetry in the spin amplitude of the K*)
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AFB and AT(2)
AFB(s) in SM and different
SUSY models:
Non-MFV MSSM with
tan(β) = 5
SUSY I = SUGRA
SUSY II = MIA MSSM
from HEP-ph/0612166
(from Phys.Rev.D61 (2000) 074024)
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Selection of events: B0→K*0µ+µExpected yield for 2fb-1:
7200 ± 180(stat.) ± 2200 (BR)
Estimate for Background:
MC sample
Bd,u→sµµ (no K*)
b→µ, b→µ
b→µ, c→µ
Total
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No. of events per 2fb-1
9±3
1050±250
690±180
1770±310
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AFB and AT(2) from B0→K*0µµ
1 year of data taking,
errors expected to be
limited by statistics
AT(2)
Zero crossing point
is a probe for NP:
s A( 0 ) ( 2fb -1 )  1.2GeV 2
FB
s A( 0 ) (10fb -1 )  0.5GeV 2
FB
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