1. in rappresentanza di LHCb Italia
Vincenzo Vagnoni
in rappresentanza di LHCb Italia
Riunione CSN1
Napoli, 22 Settembre 2005

2. Current status of ms and s
Despite the “heroic” efforts at LEP, SLD and CDF Run-I (now also CDF/D0 Run-II), ms is still unmeasured although there is an interesting feature in the amplitude plot at ~18 ps-1
Differently, first measurements of s from BsJ/ exist
CDF:
D0:
Theory
Constraint from semileptonic lifetime
Direct measurement
Combined result: ~2 above expectations
disfavours low ms value!
ms > 14.5 ps-1 at 95% CL
Sensitivity at 18.5 ps-1

3. Unitarity Triangle Fits
Collaboration
M. Bona, M. Ciuchini, E. Franco, V. Lubicz, G. Martinelli, F. Parodi,
M. Pierini, P. Roudeau, C. Schiavi, L. Silvestrini, A. Stocchi, V. Vagnoni

4. Prediction of ms from Unitarity Triangle fits
p.d.f. for ms in SM without using its current experimental limit
ms > 31 3 σ > 38 5 σ
“Compatibility plot” for an
hypotetical future measurement
ms = 22.2 ± 3.1 ps-1

5. Relevance of LQCD for exploiting precise md,s measurements in Unitarity Triangle fits
md,s enter the UT fits through the constraints
It is crucial to improve the precision on the Lattice quantities (now at 10-15%) in order to fully exploit the current and future measurements of md and ms
where the long distance hadronic quantities are calculated in the framework of LQCD:

6. New Physics model independent parametrization in |F|=2 transitions
The mixing processes being characterized by a single amplitude, they can be parametrized in a general way by means of two parameters
HSMeff includes only SM box diagrams while Hfulleff includes New Physics contributions as well
See e.g. M. Bona et al., hep-ph/ and refs. therein
Four “independent” observables (C=1, =0 in SM)
CBd, Bd, CBs, Bs
For the neutral kaon mixing case, it is convenient to introduce only one parameter
mK is not considered since the long distance effects are not well controlled

7. Exercise already done for the K0 and B0 mixing
CK = 0.95 ± 0.22
[0.64,
Macroscopic effects from New Physics in K0 and B0 mixing are absent
Exercise already done for the K0 and B0 mixing
Still 50% room for New Physics in md amplitude
But the New Physics mixing phase must be close to zero
CBd = 1.21 ± 0.46
[0.45,
fBd = -4.5 ± 2.6
[-9.4,

8. What to say then?
New Physics in the bd sector starts to be quite constrained and
most probably will not come as an alternative to
the CKM picture, but rather as a «correction»
Basically two scenarios
Minimal Flavour Violation:
the only source of flavour violation is in the SM Yukawa couplings (implies =0)
New Physics couplings between third and second families (bs sector) are stronger with respect to the bd ones
Flavour physics needs to improve existing measurements in the Bd sector and perform precise measurement in the Bs sector: Physics case for SuperB and LHCb

9. bb production and detection at LHCb
all b-hadron species are produced:
~40%
~10% p
Parton 1 x1
Parton 2 x2 p 

10. Partial readout: Vertex Locator
Trigger System
1 MHz
Calorimeter
Muon system
Pile-up system
Hard. Level-0
pT of
m, e, h, g
40 MHz
40 kHz
Soft. Level-1
Impact parameter
Rough pT ~ 20%
Partial readout: Vertex Locator
Trigger Tracker
Level 0 objects
2 kHz output
Soft. HLT
Final state
reconstruction
Full detector
information
1 MHz readout is the new baseline solution as decided these days (see Umberto’s)

11. Trigger output bandwidths (2 kHz total)
Original baseline stream
200 Hz: exclusive trigger
Exclusive reconstruction of B decays
“Real life” streams
600 Hz: di-muon trigger
No bias from impact parameter cuts, this stream is particularly relevant to study the proper time resolution from data itself (very important for ms)
Reconstruction of exclusive b-hadron  J/ X decay, for spectroscopy and lifetime measurements (Bc and various b-baryons)
900 Hz: single muon trigger
Mainly triggers on semi-leptonic B decays, no bias on the other B; allows to collect unbiased B decay samples, useful to understand various systematics
Data mining: reconstruction of accompanying b-hadron in modes not included in the exclusive HLT algorithms, not foreseen at the start of the experiment, or “untriggerable modes”
For hadronic modes, good tagging (eff  15%) due to already detected b on other side
300 Hz: D* trigger
D0K, but also D0KK,  modes
Large K and  samples for RICH PID calibration
Charm physics, including D0 mixing (x and yCP), CP violation in D0KK, 

12. Simulation and Reconstruction
Full GEANT 4 simulation
Complete description from TDRs
Detector response
Based on test-beam data (resolution, efficiency, noise, cross-talk)
Spill-over effects included (25 ns bunch spacing)
Trigger simulation
thresholds tuned to get maximal signal efficiencies at limited output rates of 1 MHz (L0) and 40 kHz (L1)
HLT simulation almost ready
Offline reconstruction
Full pattern recognition (track finding, RICH reconstruction, …)
RICH2
RICH1
VELO TT
T1 T2 T3
Geant event display
No true MC info
used anywhere!

13. Monte Carlo samples
During last year many hundreds of million events were produced on the LCG GRID (see Domenico’s)
Mostly minimum bias events (for fixing trigger bandwidths) bb events with inclusive decays (for assessing backgrounds in physics analyses) signal events (of course...)
Still far from a complete understanding of the backgrounds (eventually will need real data...)
Recently inclusive Ds events started to be produced (cc cross section 7 times larger than bb... dangerous?)

14. Trigger simulation
Typical L0xL1 efficiencies (for offline selected events)
hadronic channels: ~40%
di-muons: ~70%
EM channels: ~30%
Exclusive HLT simulation in progress
Typical efficiency ~90%
Timing:
L0: 3.5 s (synchronous)
L1: 3 ms (max. 58 ms)
L0 efficiency
L1 efficiency
L0L1 efficiency

15. Measurement of ms
Need a flavour specific Bs decay to measure mixed/unmixed decays
The best channel (if not limited by statistics) is BsD-s+
“Large” visible branching ratio ~ 1.2 x 10-4
BR(BsD-s+) ~ 2.8 x 10-3
BR(D-sK+K--) ~ 4.4 x 10-2
Fully exclusive reconstruction
Limited background
Optimal proper decay time resolution
Ingredients for the measurement
Good trigger efficiency for fully hadronic channels
Good hadron particle ID, particularly relevant for same and opposite side kaon tagging
Good tagging efficiency
Good mass resolution for limiting background impact
Good proper time resolution for resolving the fast Bs oscillations

16. Importance of RICH for K/ separation
BsK+K- without RICH PID
/K separation for
BsDs / BsDsK
RICH Particle ID extremely important for tagging using kaons
BsK+K- with RICH PID
BsDsK
BsDs

17. Flavour tagging e-, m- Qvertex ,QJet Opposite side
High Pt leptons
K± from b → c → s
Vertex charge
Jet charge
B0opposite K- D PV
Bs0signal K+
Same side
Fragmentation K± accompanying Bs
± from B** → B(*)± K-
K +
D2=(1-2)2: tagging power
: tagging efficiency
: mistag probability
~7.5
3.1 (K)
0.8
2.4
0.6
1.4 Bs
~ 4.4
0.7 (p)
0.7
2.1
1.2 Bd
Same side p / K
Combined
Jet/ Vertex Charge
Kaon opp.side
Electron
Muon
Tag
Tagging power in %
(Same opposite side performance for Bd and Bs within errors)

18. Bs  Dsp event yield and resolutions
80k reconstructed signal/year with DsKK mode
Combinatorial background from beauty events: B/S~0.3
Excellent resolutions from full GEANT simulation
Proper time resolution ~40 fs
Mass resolution ~14 MeV
Decay length resolution ~200 mm
Proper time resolution
Bs invariant mass
Bs decay vertex resolution
Bs mass [GeV/c2]

19. Sensitivity on oscillation amplitude A as a function of ms
Sensitivity to ms
Resolution for Standard Model ms in one nominal year of data taking L=2 fb-1 (statistical only)
(ms=20 ps-1) ~ 0.01 ps-1
Reconstructed Bs Ds unmixed decay rate (1 year) simulated for Dms = 25 ps-1
Bs mixing can be clearly
observed
10% better t/t
1 year sensitivity much larger than SM expectations (ms~20 ps-1)
Statistical significance on oscillation amplitude A above 5 for ms up to 68 ps-1 (at L=2 fb-1)
Sensitivity on oscillation amplitude A as a function of ms
10% worse t/t

20. Road map to Dms in real life
Proper time calibration with lifetime measurements from B J/y X
Triggered by di-muon trigger (no displaced vertex trigger bias)
Can measure acceptance: did displaced vertex trigger also fire?
Establish resolution model
Can measure resolution from negative side of proper time distribution
Tagging calibration measuring mixing in B0J/y K*(K+p-)
Establish tagging performance for opposite side taggers
For same side kaon tagger no trivial calibration exists unfortunately, since one has to have measured Bs mixing before…
Need to rely on Monte Carlo
Lifetime with hadronic decays
Learn to live with displaced vertex trigger
Mixing with BsDsp
All the hell together…

21. A comparison with CDF: Bs mixing in Bs Ds
Channel
Yield
S/B
Bs®Dsp (Ds®fp)
526±33
1.80
Bs®Dsp (Ds®K*K)
254±21
1.69
Bs®Dsp (Ds®3p)
116±18
1.01
Opposite side flavour tags (e, , jet charge): D2=(1.12±0.18)%
Very low sensitivity for hadronic only
Sensitivity: 0.4 ps-1

22. A comparison with CDF: Bs mixing in semi-leptonics
Channel
Yield
S/B
Bs®Dsln (Ds®f p)
4355±94
3.12
Bs®Dsln (Ds®K*K)
1750±83
0.42
Bs®Dsln (Ds®3p)
1573±88
0.32
Note: new D0 results with semileptonic decays
and more data than CDF 610 pb-1 (D0) vs 355 pb-1 (CDF)
Limit: ms>7.3 ps-1 @95% CL (current WA ms>14.5 CL)
Opposite side flavour tags (e, , jet charge) D2=(1.43±0.09)%
Limit: ms>7.7 ps-1 @95%CL

23. An exercise: a possible scenario in 2010
Assumptions
B Factories will collect L=2 ab-1
two good years of data taking at LHCb (L=4 fb-1)
improvements in LQCD quantities
Observable
Sensitivity in 2010
sin2
0.010  5o 
|Vcb| 1%
|Vub| 4% BK 5%  3%
ms
0.3 ps-1 (syst.)
sin2
0.045

24. 2010 sensitivity to New Physics observables in |F|=2 transitions from UT fits (assuming Standard Model)
  0.1 (now ~0.2)
K0 sector
  1.3° (now ~3°)
Bd sector
  0.12 (now ~0.5)
  1o
Bs sector
  0.1
Only using the measurements from a few key LHCb Bs channels (in particular ms and sin2), the precision on NP observables for bs FCNC transitions in 2010 will be at the same level as the bd transitions!
Furthermore, LHCb will provide the same measurements as the beauty factories, thus improving the precision in the Bd sector

25. Concluding remarks
Key numbers for BsDs selection at LHCb according to full GEANT 4 simulations:
Annual signal yield: 80k
Background to signal ratio: 0.3
Tagging efficiency: 7.5%
Proper time resolution: 40 fs
LHCb resolution for ms around Standard Model prediction (ms=20 ps-1) in one nominal year of data taking (L=2 fb-1):
(ms) ~ 0.01 ps-1 (statistical only)
1-year statistical significance on oscillation amplitude A above 5 for ms up to 68 ps-1
Far away from Standard Model expectations…
Beauty factories are not finding clear evidence of New Physics in bd |F|=2 transitions
still an important physics case is to understand whether the same happens in bs transitions (hints from bs penguins at B-factories)
What prospects for New Physics discovery from |F|=2 at LHCb?
In 2010, knowledge from bs transitions will be at the same level as bd !!

26. Backups!

27. Wolfenstein parametrization
CKM matrix
Wolfenstein parametrization
, A, , 

28. Unitarity Triangle(s)
2: Bd mixing phase
-2: Bs mixing phase
: weak decay phase Im 
key measurements from Bs   1 Re Im 
 Re

29. Bs mixing in SM Bs CKM factors Perturbative: NLO QCD correctionW
u, c, t Bs
CKM factors
Perturbative: NLO QCD correction
Complementarity s: the larger  the easier ms: the larger  the harder
Non perturbative: decay constant and bag factor from LQCD

30. Long track efficiency vs p
Tracking
Long track efficiency vs p
Ghost rate vs p
Momentum resolution
p/p ~ 0.37%
Ghost rate = 3%
(for pT > 0.5 GeV)
 = 94%
(p > 10 GeV)
T track
Upstream track
A typical reconstructed event
VELO track
Long track
26 long tracks
11 upstream tracks
4 downstream tracks
5 T tracks
26 VELO tracks
Downstream track

31. Particle ID RICH 2 RICH 1 e (KK) = 88% e (pK) = 3%
3 radiators to cover
full momentum range:
Aerogel
C4F10
CF4
RICH PID
2<p<100 GeV/c
<(KK)> = 88%
<(K)> = 3%
Muon PID p>5 GeV
<()> = 94%
<()> = 2%
Electron PID
<(ee )> = 81%
<(e)> = 1%

32. Trigger Rates Overview (just with exclusive HLT)
L1-confirmation
HLT
Full reconstruction
Level-0
Level-1
simulation in progress...
200 Hz

33. Breakdown of trigger and selection efficiencies for some benchmark channels

34.  and DGs from Bs  J/y f
“El Dorado” Bs counterpart of the “Golden” mode B0  J/y KS
CP asymmetry arises from interference of Bs  J/y f and Bs  Bs  J/y f
measures the phase of Bs mixing
Reconstruct J/y  m+m- or e+e-, f  K+K-
120,000 signal events/year with B/S~0.3
Final state is admixture of CP-even and odd contributions
angular analysis of decay products required
Need of angular analysis to separate the two components
Likelihood is sum of CP-odd and CP-even terms L(t) = R- L-(t) (1+cos2qtr)/2 + (1-R-) L+(t) (1-cos2qtr)
Fit for sin 2c, R- and DGs/Gs
s(sin 2c) ~ 0.06
s(DGs/Gs) ~ 0.02
L=2 fb-1 ms=20 ps-1 @

35.  from Bs  DsK Ds+ K+ W+ W+ K- Bs Bs Ds-
CP asymmetry arises from interference between two tree diagrams via Bs mixing: Bs  Ds+K- and Bs  Ds-K+
measures g - 2c
Decay diagrams insensitive to New Physics
assuming NP contributions from loops only
Reconstruction using just Ds-  K-K+p-
5400 signal events/year
B/S~1
1-year sensitivity on g - 2c
(g - 2c) = 14o @ L=2 fb-1 and ms=20 ps-1 s
Ds+ s K+ c u W+ W+ b u K- Bs Bs b c
Ds- s s s s
Not outstanding due to limited statistics but will enrich NP-free tree level  measurements from Bd decays 4

36.  from Bd+- and BsK+K-
Bd/s
/K
/K
Bd/s
Bd (95%CL)
BsKK (95%CL)
Measure time dependent asymmetries for Bd→ and Bs→KK to determine Adir and Amix
ACP(t) = Adir cos(mt) + Amix sin(mt)
Adir and Amix depend on
decay phase 
mixing phases  or 
Penguin/Tree ratio = dei
Use  and  from J/Ks and J/
U-spin symmetry: d=dKK, =KK
4 observables, 3 unknowns: solve for 
26k Bdpp events/year, B/S<0.7
37k BsKK events/year, B/S~0.3
s(g) ~ 5+ uncertainty from U-spin
symmetry breaking
Sensitive to New Physics in penguin

37. An exercise: a possible scenario in 2010
Observable
Projection to 2010
Comment
sin2
0.695 ± 0.015
B-factories at 2 ab-1 
(104 ± 7)o 
(54 ± 5)o
B-factories at 2 ab-1 + LHCb BDK at 4 fb-1
|Vcb| (incl. + excl.) (10-3)
41.7 ± 0.4
|Vub| (incl. + excl.) (10-4)
36.4 ± 1.6
md
0.503 ± 0.003 mt
171 ± 3
CDF/D0 K ±
Current value  ±
e.g. NA48/3 BK
0.846 ± 0.047
Lattice QCD
(0.276 ± 0.014) MeV 
1.200 ± 0.037
ms
(20.5 ± 0.3) ps-1
LHCb BsDs at 4 fb-1 (cons. syst. added)
sin2
0.031 ± 0.045
LHCb BsJ/ at 4 fb-1
-2
(52 ± 10)o
LHCb BsDsK at 4 fb-1

38. Knowledge of CKM parameters in 2010 Scenario from UT fits allowing New Physics in |F|=2 transitions
  0.02
  3.5o
  3o
  0.02
 = 0.05o
  1o

39. How far is the Tevatron? Will CDF be able to add same-side kaon?
Will D0 catch up to CDF?