1. 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, May 2007
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

2. Motivation
(from
CKM-fitter)
A lot of precise measurements are available from B-factories and Tevatron to test the CKM picture of flavour structure and CP violation.
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.
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

3. What do we get from LHC? bb cross section: 500µb +
LHCb luminosity ~ 2-5 • 1032 cm-2 s-1
b-production rate ~100kHz
Inelastic pp collisions/crossing: For LHCb mainly single interactions
LHCb
One year of nominal data taking
corresponds to 2fb-1
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

4. 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
Flavour tagging
Opposite side
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

5. LHCb detector 4Tm Dipole Vertex Locator Muon RICH counters Tracking
(Silicon)
RICH counters
p/K/p Identification
Muon
System
Tracking
Calorimeters
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

6. LHCb detector in place 11/18/2018 Sebastian Bachmann
HCP’07/Isola d’Elba

7. LHCb performance: Momentum resolution: π-K separation:
Proper time resolution:
LHCb:
~ 40 fs for (Bs  Ds-p+)
CDF:
87fs for fully reconstructed decays.
PRL (2006)
Momentum resolution:
π-K separation:
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

8. related CP-asymmetries
Bs-mixing
and
related CP-asymmetries
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

9. NP from mixing and CP-asymmetries
CDF: Δms = (17.77 ± 0.1stat ±0.07syst) ps-1
LHCb: Observation expected after few month
data taking at nominal luminosity
Bs→Ds-π+:
Precise measurement of Δms
using Bs→ Ds+π-. ?
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?) +
ΦNP? W-
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

10. CP-violation in the Bs-system
Decay into a final state f with CP f → ηf f
(assume only one amplitude contributes to decay) Bs f
|A| e+iω
|A| e-iω
e2iΦs
CP-asymmetry:
For Bs→J/ψf:
 ≈ 0
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

11. Φs and ΔГs Any sizeable CP violation in Bs→J/ψΦ or Bs→ΦΦ is a
In the SM:
Phys.Rev.D (2001)
If new physics contributes to
Bs mixing:
Any sizeable CP violation in
Bs→J/ψΦ or Bs→ΦΦ is a
clear sign for NP!
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

12. } Bs→J/ψ(µ+µ-) f(K+K-) Advantages: High branching ratio
Good experimental signature b c
J/ψ
JPC=1-- c Bs s Φ
JPC=1-- s s
CP(J/ψf) = CP(J/ψ) CP(f) (-1)L }
Final state is
a mixture of
CP even/odd
L=0, 2: CP even
L=1: CP odd
Angular analysis needed to identify CP even and CP odd states!
also valid for Bs→ff
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

13. Bs→J/ψ(µ+µ-) f(K+K-)
Use angle θtr between µ+ and normal of f decay plane: ┴
Total
CP even
bkgnd
CP odd
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

14. Selection and signal decay rate
Yield: k events per 2fb-1
B/S:
<δt>: fs
σMass: Mev/c2
wtag: %
εtag: %
Tagged Bs
fs = 5 x SM
Signal decay rates including:
Trigger and selection bias on τ
Background parametrization
Mass resolution
Proper time resolution
Tagging efficiency and dilution
Transversity angle distribution
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

15. Projection for Φs and ΔГs with 2fb-1
Parameter
Exp. error
Channel fs
0.023 rad
Bs→J/ψ(µ+µ-) Φ(K+K-)
ΔГ/Г
0.0092
Δms
0.007 ps-1
Bs→ Ds-(K+K- π-)π+
wtag
0.0036
Control
channel
only
Sensitivity can be improved by adding more channels.
Using Bs→J/ψη, Bs→ηCf, Bs→DsDs gives σΦ=0.021 rad.
CP-Eigenstates
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

16. Bs→ ff: Sensitvity to fs
LHCb profits from excellent
PID and hadronic trigger!
Distribution from 500 MC experiments:
Expected yield: events per 2fb-1
BG estimate limited by MC statistics:
0.4<B/S<2.1 at 90%CL
Sensitivity to fs is 0.1rad at 2 fb-1.
No significant variation as a
function of input fs, Rt and
proper time resolution.
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

17. Rare decays Decay Sensitivity to Example for model
1. Bd,s→µ+µ large tanβ CMSSM
2. Bd→K*0µµ small tanβ non-MFV MSSM
- right handed currents MIA MSSM
SUGRA
3. Bu→K+ll no right handed MFV
(in combination currents
with 1.) (pseudo-)scalar
couplings
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

18. 1. Bd,s→µ+µ- SM 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
In Supersymmetry:
Large contributions e.g. by
Higgs penguins ~tan6β, i.e.
BR(Bd,s→µ+µ-) is very
sensitive to high values
of tan β.
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

19. Sensitivity by LHCb SM 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
BR(Bs→µ+µ-) in CMSSM as a
Function of gaugino mass SM
D0 limit
10-9
10-7
10-8
10-6 1
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

20. 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) )
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

21. Bu+→K+ll with 2fb-1 σRk(2fb-1)≈ 10% σRk(10fb-1)≈ 4-6%
Takes into account an
inclusive di-lepton
trigger
applies Brems-
strahlung corrections
Signal Mean Sigma
eeK 349± MeV 74 MeV
µµK 1550± MeV 15 MeV
σRk(2fb-1)≈ 10%
σRk(10fb-1)≈ 4-6%
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

22. Rk in a MFV model Rk-1 ~ BR(Bs→µµ) LHCb projection if SM is holds
Assume
Hiller & Krüger, PRD69 (2004) )
Right handed currents are
negligible.
(Pseudo-)scalar couplings
lepton masses
No CP-phases beyond the SM
Babar & Belle (Rk)
CDF & D0 (BR(Bs→µµ))
Excluded by
Rk-1 ~ BR(Bs→µµ)
Predicted by MFV model
Predicted by MFV model
LHCb projection
if SM is holds
But we hope for
something else…
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

23. 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!
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

24. Backup slides
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

25. Physics motivation
A copious number of B-mesons is produced at LHC 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:
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

26. Performance: Vertex locator
Proper time resolution:
LHCb:
~ 40 fs for (Bs  Ds-p+)
CDF:
87fs for fully reconstructed decays.
PRL (2006)
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

27. Tracking
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

28. Performance: Particle Identification
p–K separation
Unique feature of LHCb
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

29. Performance of VeLo Impact parameter resolution: δIP = 14µm + 35µm/pt
Proper time resolution: ~ 40 fs (Bs  Ds-p+)
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

30. Calorimeter
Calorimeter system to identify electrons, hadrons and neutrals
Important for the first level of the trigger
Scintillating Pad Detector /
PreShower
Electromagnetic calorimeter
Hadron Calorimeter
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

31. Muon identification 94% 1.1% Muon ID efficiency (%) vs -π DLL cut
Pion mis ID efficiency (%) vs -π DLL cut
1.1%
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

32. Trigger HLT rate Event type Calibration Physics 200 Hz
Exclusive B candidates
Tagging
B (core program)
600 Hz
High mass di-muons
Tracking
J/, bJ/X (unbiased)
300 Hz
D* candidates
PID
Charm (mixing & CPV)
900 Hz
Inclusive b (e.g. bm)
Trigger
B (data mining)
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

33. Flavor tagging Opposite side Same 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±
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

34. Δms from Bs→ Ds-(K+K- π-)K+
has a large branching fraction
of (3.4±0.7)x10-3.
is flavor specific.
Total efficiency: εtot=0.39%
Signal yield: 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)
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

35. Sensitivity to Δms CDF: Δms = (17.8 ± 0.1) ps-1
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
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

36. Sensitivity for New Physics
In april 2006, including
first CDF measurement
of Δms
Model independent parametrization
for New Physics:
CL>0.32
from hep-ph/
CL>0.05
This results in:
In 2010, with one year
of LHCb data (2fb-1)
from hep-ph/
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

37. NP by Tree↔Penguin comparison
Bd-system:
Bs-system: d d s s Ks
J/y
Vcb
Vcs*
Vcb
Vcs* f
J/y
Tree
Vtb
Vts*
Vtb
Vts* f f Ks
Penguin s d d s
Φd(tree)-Φd(penguin) = dΦd(NP)
B-factories:
Currently: db = 8o (2.6s)
Φs(tree)-Φs(penguin) = dΦs(NP)
And:
Φs(SM) small!
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

38. 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/ψf a full angular analysis to extract CP-asymmetry is needed.
Experimentally demanding, as full hadronic trigger is needed.
Remark:
In SM Bs→J/ψf and Bs→ ff measure both arg[Vtb* Vts].
Deviations point to physics beyond the SM.
Belle/Babar have 2.7σ deviation when comparing tree and penguin decays
of Bd to CP-Eigenstate.
Tree
Penguin
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

39. Event selection and sensitivity studies
Reconstruct only f→K+K-.
Full detector simulation including
trigger bias.
Reconstruction based on:
RICH K± ID
pt and impact parameter of K±
and f candidates.
Bs and f invariant mass.
Bs and f vertex quality.
Sensitivity to fs 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
for BG
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

40. From G. Hiller [hep-ph/0308180]
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

41. 2.) B0→K*0µ+µ- SM 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.
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

42. Observables in B0→K*0µ+µ-
Two 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*)
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

43. AFB and AT(2) tan(β) = 5 AFB(s) in SM and different SUSY models:
SUSY I = SUGRA
SUSY II = MIA MSSM
(from Phys.Rev.D61 (2000) )
Non-MFV MSSM with
tan(β) = 5
from HEP-ph/
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

44. Selection of events: B0→K*0µ+µ-
Expected yield for 2fb-1:
7200 ± 180(stat.) ± 2200 (BR)
Estimate for Background:
MC sample No. of events per 2fb-1
Bd,u→sµµ (no K*) ± 3
b→µ, b→µ 1050±250
b→µ, c→µ 690±180
Total ±310
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba

45. 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:
11/18/2018
Sebastian Bachmann
HCP’07/Isola d’Elba