1. Prospects for New Physics in CP Violation and Rare Decays at LHCb
10 November 2008
Prospects for New Physics in CP Violation and Rare Decays at LHCb
Pascal Perret
LPC Clermont
On behalf of the LHCb Collaboration

2. Pascal Perret - LPC Clermont
b Production in LHCb
bb pair production correlated and sharply peaked forward-backward
Single-arm forward spectrometer : θ~ mrad (rapidity range: 4.9>η>1.9)
Cross section of bb production in LHCb acceptance: σbb ~ 230 µb
B+ (40%), B0 (40%), Bs (10%), b-baryons (10%), Bc (< 0.1%)
LHCb limits luminosity to few 1032 cm-2s-1 instead of 1034 cm-2s-1 by not focusing the beam as much as ATLAS and CMS
maximizes probability of a single interaction per crossing
design luminosity soon after start-up
pp interactions/crossing
LHCb
n=0
n=1
collect 2fb-1 per nominal year
~ bb pairs produced per year
1 LHCb day = 100 B-factory day
10/11/2008
Pascal Perret - LPC Clermont

3. LHCb overview and performance
10/11/2008
Pascal Perret - LPC Clermont

4. Pascal Perret - LPC Clermont
LHCb: vertex locator
VELO
Vertex Locator (Velo)
Silicon strip detector
8 mm from beam with
~ 5 mm hit resolution
30 mm IP resolution
Decay time resolution ~ 40 fs
10/11/2008
Pascal Perret - LPC Clermont

5. LHCb: momentum & mass measurement
Track reconstruction efficiency:
95% for tracks with p>5 GeV
Magnet OT IT TT
Drift time tube
Momentum measurement (s(p)/p ~ ( p/TeV)%) and Mass resolution s ~14 MeV
10/11/2008
Pascal Perret - LPC Clermont

6. LHCb: particle identification
HPD
RICH2:
100 m3 CF4 n=1.0005
16-~100 GeV
RICH1:
5 cm aerogel n=1.03 : 2-~10 GeV
4 m3 C4F10 n= : 10-~60 GeV
RICH: K/p identification (KK: ~96.8%, pK: ~3.9%) ; eg. distinguish Dsp and DsK events.
10/11/2008
Pascal Perret - LPC Clermont

7. Pascal Perret - LPC Clermont
LHCb: calorimeter
ECAL
HCAL
Inner Outer Middle
region
ECAL (inner modules): σ(E)/E ~ 8.2% /√E + 0.9% PS
SPD
Calorimeter system :
Detection of electrons, π0, γ, hadrons
Level 0 trigger: high ET electron and hadron, photon
10/11/2008
Pascal Perret - LPC Clermont

8. Pascal Perret - LPC Clermont
LHCb: muon system
Muon system:
Level 0 trigger: High Pt muons
Muon ID: ~ 95% for 5% hadron misID
Muons
Multi Wire Proportional Chamber
Triple-GEM for M1-R1
M1 under installation …
10/11/2008
Pascal Perret - LPC Clermont

9. Pascal Perret - LPC Clermont
LHCb: beam pipe
Magnet TT
Beam pipe:
Under vacuum June – Oct.
Detector closed
SPD Pb M2
HCAL
ECAL PS Be
inox
RICH2
10/11/2008
Pascal Perret - LPC Clermont

10. LHCb trigger system Two levels: High pT : m, e, h, g 4 µs
1st level: hardware 4 ms latency
“moderate” pT m, e, g & hadrons, e.g. pT m >1.3 GeV/c : full custom made
HLT: software ~2000 CPU
HLT rate
Event type
Physics
200 Hz
Exclusive B candidates
B (core program)
600 Hz
High mass di-muons
J/, bJ/X (unbiased)
300 Hz
D* candidates
Charm (mixing & CPV)
900 Hz
Inclusive b (e.g. bm)
B (data mining)
(Interaction rate ~ 10 MHz
b hadron inside LHCb ~50 kHz)
40 MHz
Pile-up
Calorimeter
Muon
+ L0DU
Level 0:
High pT :
m, e, h, g
4 µs
1 MHz
HLT:
L0 confirmation m, e, h, g alleys inclusive/exclusive Selection
Full reconstruction
of event
2 kHz
Storage(event size ~ 35 kB)
10/11/2008
Pascal Perret - LPC Clermont

11. Events with LHC beam induced particles
Status of LHCb
LHCb detector fully installed and commissioned, including L0 trigger
All sub-detectors have undergone the first readout synchronisation and alignment with cosmics & LHC beam induced particles
Events with LHC beam induced particles
F. Dettori
poster
Top view
Splashy event from lost particles (not all tracks reconstructed...)
Muon
Calo OT
Calo OT
Muon
Velo
Side view
Clean event from halo muons
10/11/2008
Pascal Perret - LPC Clermont

12. Pascal Perret - LPC Clermont
New Physics in CPV
Unitarity Triangles Bs
Bd0  p+ p-
Bd0  r p
BS0  DS p
Bd0  J/y KS0 Bd a b g
VudVub
VtdVtb
VcdVcb *
Bd0  DK*0
BS0  DSK
Bd0  D* p,3p
BS0  J/y f bs
VtsVtb
VcsVcb
VusVub
Box diagram
Penguin diagram
Overconstrain the unitarity triangles (consistency checks)
10/11/2008
Pascal Perret - LPC Clermont

13. Pascal Perret - LPC Clermont
New Physics in CPV
Unitarity Triangles
New particles may show up in loop process Bs
Bd0  p+ p-
Bd0  r p
BS0  DS p
Bd0  J/y KS0 Bd a b g
VudVub
VtdVtb
VcdVcb *
Bd0  DK*0
BS0  DSK
Bd0  D* p,3p
BS0  J/y f bs
VtsVtb
VcsVcb
VusVub
Box diagram
New
Physics ?
Penguin diagram
Overconstrain the unitarity triangles (consistency checks)
will allow to understand the nature and flavour structure of possible New Physics ones
b-physics measurements probe New Physics and are complementary to direct searches
10/11/2008
Pascal Perret - LPC Clermont

14.  Measurements from Bs  Ds K+
Interference between 2 tree diagrams via Bs mixing:
BsDs K (b  c) and BsDsK (b  u) (+ CP conjugates)
Measure  + s in a clean way (no theoretical uncertainty) from time dependent rates
Use s from Bs  J/y f
Include Bs Ds (20x Br) to determine Δms ΔΓs and tagging dilution
Simultaneous fit to Bs→Ds and Bs→DsK decay time distributions (tagged and untagged)
10 fb-1 data:
Bs→ Ds-p+
Bs→ Ds-K+
(Dms = 20)
Mode
Sig. yield
B/S
Bs→DsK
6.2k
0.7
Bs→Ds
140k
0.2
Sensitivity
2 fb-1
10 fb-1
 stat()°
10.3
4.6
10/11/2008
Pascal Perret - LPC Clermont

15. Pascal Perret - LPC Clermont
 Measurements
Different ways to measure  at LHCb:
2 amplitudes, b→c (dominant) & b→u (color suppressed), interfere in decays to a common D0 and D0 modes state:
B mode
D mode
Method
s(g) 2fb-1
Bs→DsK
KKp
Tagged, A(t)
10º
B+→D K+
Kp+ K3p +KK/pp
counting, ADS+GLW
5º - 13º
Kspp
Dalitz, GGSZ
7-12º
KKpp
4 body Dalitz
18º
B0→D K*0
Kp + KK + pp 9º
B→pp,KK -
Tagged, A(t)
Tree decays only
Global fit of all the channels: σ(g) = ° with 2fb-1
Penguin amplitudes:
Interference of b→u tree & b→d(s) penguin diagrams
Other modes under study: B+→D*(D → Kp/KK/pp) K+, B+→D(→ Kppp)K+, …
Compare angle  measured from interfering tree decays (which should always take the value from the CKM matrix) to angle measured from penguin diagrams:
Any difference is a sign of New Physics
10/11/2008
Pascal Perret - LPC Clermont

16. fs measurements from Bs  J/y f
The measure of Bs-Bs mixing phase s in BsJ/(µµ) is sensitive to New Physics effects in mixing:
s = s(SM) + s(NP)
in SM: s = – 2βs = arg(Vts2) ~ –0.04
Tevatron: s ~2.2 away from SM
(central experimental value -0.77)
It is not a pure CP eigenstate (VV decay).
2 CP even, 1 CP odd amplitude
need to fit angular distributions of decay
final states as function of proper time
Good proper-time resolution is essential: ~39fs
Good tagging of initial Bs flavour :
Combined = 6.2%
Good mass resolution: 13 MeV
Good particle identification
e(KK)~80% e (pK)~ 3%
+NP?
e(1-2w)2
Muon
0.8
Electron
0.4
K (OS)
1.5
K (SS)
2.1
Q vertex
1.1
Invariant mass of
BsJ/()
10/11/2008
Pascal Perret - LPC Clermont

17. fs measurements from Bs  J/y f
BRvis[BsJ/(µµ)(K+K-)]= (3.1±1.1)x10-5
With 2 fb-1 (1 nominal year):
114k reconstructed events (before
tagging)
S/B ~2
 stat(s) ~0.03
5σ NP discovery, if s >0.1!
Low systematic uncertainties:
Proper time acceptance: no bias from selection
Angular resolution: very good & negligible
Mistag and proper time are crucial…
Already at the start-up with 0.5 fb-1:
28.5k reconstructed events
 stat(s) ~0.06
LHCb should rapidly pin down whether really sign of new physics …
ηf = +, - 1 CP eigenstates
10/11/2008
Pascal Perret - LPC Clermont

18. New Physics in rare decays
10/11/2008
Pascal Perret - LPC Clermont

19. New Physics in BdK*0m+m-
Flavour Changing Neutral Current Decay
in SM: b  s electroweak penguin
NP diagrams could contribute at same level
Sensitive to magnetic and vector and axial semi-leptonic penguin operators
Decay described by three angles (θl, φ, θK) and di-μ invariant mass q2
gluino, chargino,
neutralino, ?
Higgs, ?
s = (m)2 [GeV2]
AFB(s), theory
Forward-backward asymmetry AFB(s)
in the mm rest-frame is sensitive NP probe
Uncertainties from Bd→K* transition form-factors cancel
zero of AFB(s) depends on Wilson coefficients C7eff/C9eff
10/11/2008
Pascal Perret - LPC Clermont

20. New Physics in BdK*0m+m-
NB: Opposite sign convention w.r.t. LHCb
Current Measurements:
BR measured at B-factories, in agreement with SM: 1.1 ±0.3x10-6
AFB also: Belle has ~230 K*ll events
LHCb sensitivity:
Expected yields: 7.2k events/2fb–1
Background:
dominated by b→ m, b→ m, symmetric distribution in θl observed
b→ m, b→ c → m significant contribution, asymmetric θl distribution …
B/S ~0.2
Acceptance correction …
Simple linear fit suggests precision:
657 MBB
q2(GeV2)
An example 0.5fb-1 experiment
AFB
0.5 fb-1
2 fb-1
6 fb-1
(s0)
0.8 GeV2
0.5 GeV2
0.3 GeV2
More complex fit methods being evaluated
10/11/2008
Pascal Perret - LPC Clermont

21. Pascal Perret - LPC Clermont
New Physics in Bsm+m- SM SM
MSSM ? ?
~ tan6/MH2
Helicity suppressed and in SM: BR(Bs → m+m-) = (3.4 ± 0.5) 10-9
sensitive to New Physics; could be strongly enhanced in SUSY
Current limit from CDF: BR(Bs → m+m-) < 4.7 10-8
Event selection
Main issue is background rejection:
dominated by B → m+X, B → m- X decays
good mass resolution and PID essential
SM Yield (2 fb-1): Signal: 23 – Bkg: 150
Statistical method applied to separate signal
from background using PID, vertexing, mass
CDF Sensitivity with 8fb-1?
Sensitivity
0.1 fb-1
0.5 fb-1
2 fb-1
6 fb-1
BR SM
BR < 10-8 (CDF limit)
Excluded <SM
3  evidence
5  observation
10/11/2008
Pascal Perret - LPC Clermont

22. Pascal Perret - LPC Clermont
Summary
Few hints of deviation from SM in b-physics are observed …
Flavour physics at the LHC will play a central role in the understanding of any new physics signals
LHCb offers exciting prospects for precision measurement and search for new physics in CP violation & rare decays: with 10fb-1
g measurements:
with trees: a combined sensitivity of sg~2-3o is expected
with loops: g with a sensitivity of sg~5o is expected
s measurements:  (s) ~0.01
Rare decays:
BdK*0m+m- : (s0) =0.3 GeV2
Bsm+m- :5  observation of SM value
Ready and waiting for the first collisions!
With fraction of a 1 year nominal data set LHCb can already perform important key measurements probing New Physics
Many topics not addressed in this talk: ,  measurements, charm physics, radiative decays …
(Many channels still to be investigated …)
F. Dettori
poster
10/11/2008
Pascal Perret - LPC Clermont