1. Flavour physics at the LHC
Marie-Hélène Schune
LAL-Orsay IN2P3
Introduction
(Very) rare B decays
Precise measurements of UT angles
And also Bc and D physics
I will not discuss b production physics
Many thanks to Maria Smizanska (ATLAS), Urs langenegger (CMS) and my LHCb colleagues
Vth SuperB workshop, Paris May 9-11

2. ATLAS, CMS, LHCb and the LHC
The LHC : proton-proton collisions at √s = 14 TeV in a 27km ring
Design luminosity from L=1033cm-2s-1 (2008) to 1034cm-2s-1 for ATLAS and CMS
Two general purpose detectors : ATLAS and CMS
One experiment dedicated to flavour physics : LHCb
LHCb
ATLAS
pT of B hadron
CMS
Rapidity of B hadron
Vth SuperB workshop, Paris May 9-11

3. ATLAS and CMS main features
Both detectors are designed for high pT (=discovery) physics
Charm and B events are mostly low pT events  triggering is challenging  use mostly decay modes with µ
High trigger efficiency for µ
Dedicated B trigger for both experiments
Good tracking and calorimetry (but no K/p separation)
CMS : PWO crystals for the calorimeter
ATLAS : pixel detector
 CP violation
rare B decays (search for new physics)
Bs oscillation
Vth SuperB workshop, Paris May 9-11

4. Vth SuperB workshop, Paris May 9-11
LHCb main features
Forward one-arm spectrometer (10 to 300 mrad)
Very precise vertex reconstruction and powerful PID
Experiment dedicated to B physics  wider trigger
VELO
Collision point
Very high trigger efficiency on  channels
High trigger efficiency on γ, e and hadron channels
40 MHz  1MHz (hardware)  2 kHz (software)
Output rate
Trigger Type
Physics Use
200 Hz
Exclusive B candidates
Specific final states
600 Hz
High Mass di-muons
J/, bJ/X
300 Hz
D* Candidates
Charm, calibrations
900 Hz
Inclusive b (e.g. bµ)
B data mining
2 kHz
Vth SuperB workshop, Paris May 9-11

5. (Integrated) luminosities
LHC machine, pp collisions at s = 14 TeV (bunch crossing : 40 MHz)
design luminosity : L = 1034 cm–2s–1
average non-empty bunch crossing rate : f = 30 MHz (in LHCb)
Pileup:
n = number of inelastic pp interactions occurring in the same bunch crossing
Poisson distribution with mean <n> = Linel/f, with inel = 80 mb for LHCb
<n> = 25 at 1034 cm–2s–1  problematic for B physics
At LHCb:
L tuneable by adjusting final beam focusing
Run at <L> ~ 21032 cm–2s–1 (max. 51032 cm–2s–1)
Clean environment: <n> = 0.5
Less radiation damage
2 fb–1 of data in 107 s (= nominal year)
ATLAS or CMS : a nominal year is 10 fb-1
pp interactions/crossing
LHCb
n=0
n=1
Vth SuperB workshop, Paris May 9-11

6. Vth SuperB workshop, Paris May 9-11
A scenario
Hopefully in 2008 :
∫Ldt = 0.5 fb-1 for LHCb
∫Ldt = 2.5 fb-1 each for ATLAS and CMS :
∫Ldt = 30 fb-1 each for ATLAS and CMS
Progressive end of the “low” luminosity running.
end of B physics era (except Bsμμ) and move to 1034 regime
In ~2013 LHCb should have collected ~10 fb-1 (= 5 nominal years)
For B physics (except Bsμμ) consider :
30 fb-1 for ATLAS and CMS
10 fb-1 for LHCb
Vth SuperB workshop, Paris May 9-11

7. Flavour physics framework
Today : the SM is in reasonably good shape
Good agreement between sides and angles measurements
 New physics should appear as a correction
The Bs sector is less tested
A second UT has to be considered c
η0  CP violation through the CKM mechanism
(ρ,η)SM given by tree processes   measurement should be improved
Vth SuperB workshop, Paris May 9-11

8. Vth SuperB workshop, Paris May 9-11
New Physics
Penguin diagram ?
Box diagram
d vs Cd
Model independent NP parameterization in mixing : SM
s vs Cs
5 new free parameters
Cs,s Bs mixing
Cd, d Bd mixing
CeK K mixing SM
Vth SuperB workshop, Paris May 9-11

9.  Measurements to be done
“Control” measurements
Bs oscillations
sin(2β) from Bd J/ΨKs
Measure processes very suppressed in SM
CP in Bs mixing ( in SM) from BsJ/f
Radiative and very rare B decays
BdK*g, Bs f g, Bd K*mm, Bs mm
Precision measurements of UT angles
Compare pure tree level processes with processes sensitive to NP : bsss penguin decays
Compare angles and sides measurements
And also … Bc, D measurements
Any inconsistency will be evidence for NP
Requires clean and improved theory predictions
Vth SuperB workshop, Paris May 9-11

10. “Control” measurements
Vth SuperB workshop, Paris May 9-11

11. Vth SuperB workshop, Paris May 9-11
Tagging principle
Luis Fernández
What is different from B factories ?
+ information from Brec side (“same-side”)  better Bs tagging than Bd tagging
- b b correlation instead of B B correlation  intrinsic dilution (wtag = 50% in case of Bs production in the opposite side …)
Effective tagging efficiency eff=(1-2)2 = 6 to 10 % (~30% at B factories)
and also correlation between tagging category and trigger
Vth SuperB workshop, Paris May 9-11

12. Vth SuperB workshop, Paris May 9-11
sin(2β) from BdJ/Ks
Current measurement (B-factories) : sin(2β) = ± 0.026
Expected uncertainty at the end of BABAR+BELLE data taking: ~ 0.018
Expected to be one of the first CP measurements:
Validation channel for CP analyses (in particular tagging control) : can be used from 0.5 fb-1
ATLAS
LHCb
s(sin(2β))
0.01 (30fb-1)
0.02 (2fb-1)
2fb-1
Expect 0.01 for 10fb-1
Vth SuperB workshop, Paris May 9-11

13. Vth SuperB workshop, Paris May 9-11
Bs mixing frequency
Measurement of ms:
CDF observed Bs oscillations in 2006 : ms=17.77 ± 0.10 ± 0.07 ps–1 compatible with the SM expectation
ATLAS (10fb-1)
LHCb (2 fb-1)
s(t)[fs]
~110 40
s(M(Bs))[MeV] 43 14
N(Dsp)
2.7k
120k
B/S
<1
0.4
stat(ms) = ± ps1, i.e. 0.04%
will be completely dominated by ssyst on proper time scale (~ 0.5% ? using tB ?)
interesting physics result AND a proof that
- the tagging of the B production state can be controlled
- a precise proper time measurement can be performed
in the LHC environment
Vth SuperB workshop, Paris May 9-11

14. Vth SuperB workshop, Paris May 9-11
(Very) Rare B decays
Vth SuperB workshop, Paris May 9-11

15. Vth SuperB workshop, Paris May 9-11
fs and DGs from BsJ/
Tagging and decay time reconstruction necessary
Good mass resolution and good proper time reconstruction  low background
J/ final state contains two vectors :
Mixture of CP-even and CP-odd components CP=+1 for L =0,2 and CP=-1 for L=1
Angular analysis needed to separate them
Total
CP=+1
Bkgd (to be checked on data (SB))
CP=-1
cos qtr
Vth SuperB workshop, Paris May 9-11

16. Vth SuperB workshop, Paris May 9-11
ATLAS
CMS
LHCb
s(t)[fs] 83 77 36
s(M(Bs))[MeV]
16.5 14
N(evts)
106k
109k
131k
B/S
0.30
0.33
0.12
s(DGs/Gs)
0.03
0.015
0.0092
s(fs)
0.08
0.072
0.023
~0.04 (30fb-1)
~0.01 (10fb-1)
Untagged fit : if ΔΓs0 still sensitive to fs (+ no need to resolve for Dms)
Results for one nominal year at low luminosity
Adding pure CP states: J/yh, hcf, DsDs  s(fs)= 0.021
With the full B physics ∫Ldt (10fb-1 for LHCb and 30fb-1 for ATLAS and CMS) :
test up to 4-5s
fs well known from indirect UT fits: ±0.002
After one year of nominal data taking : test up to 2s
Vth SuperB workshop, Paris May 9-11

17. Example of the impact of fs from BsJ/
End of LHC σ(s)~0.6° ?
Present knowledge on fs
Expected precision at the end of Tevatron σ(s)~5.6°
! the x scales are different !
Vth SuperB workshop, Paris May 9-11

18. Vth SuperB workshop, Paris May 9-11
BK* and Bs ?
A priori sensitive to New Physics
But measured BR (BK* ) in agreement with SM with a precision better than few %
However Bs not seen and still room for improvement in ACP
ATLAS (30fb-1)
LHCb (2fb-1)
s(MB)
65 MeV
s(Proper time)
62 fs
Yield K*g
14.1k
35k
B/S (90%CL) K*g
<100
<0.7
Yield fg
4.7k 9k
B/S (90%CL) fg
<400
<2.4
End of B factories (2 ab-1) N(K*g) ~13k
Fully dominated by MC stats. Should be better.
Vth SuperB workshop, Paris May 9-11

19. Vth SuperB workshop, Paris May 9-11
BK*ℓℓ
Second order diagram  sensitive to New Physics
Well known SM inclusive branching fraction : ~10-6
Sensitive probe to NP : Forward-backward asymmetry AFB
Goto et al hep-ph/
AFB
ℓℓ CM frame ℓ+ ℓ- q B
s0 value sensitive to NP
End of BABAR+ BELLE data taking : s0 known to ~25%
Vth SuperB workshop, Paris May 9-11
s = (m)2 [GeV2]

20. Vth SuperB workshop, Paris May 9-11
AFB(s), fast MC, 2 fb–1
s = (m)2 [GeV2]
ATLAS
LHCb
s(M(Bd)) [MeV] 39 14
N(signal)
2500
7700
B/S
<4
0.4  0.1
NB : non resonant contribution below the K* peak is ignored
30 fb-1
2 fb-1
LHCb with 10 fb-1 zero of AFB(s) located to ±0.28 GeV (~7%)
Vth SuperB workshop, Paris May 9-11

21. Vth SuperB workshop, Paris May 9-11
Bs  +–
Very rare loop decay, sensitive to new physics:
BR ~3.510–9 in SM can be strongly enhanced in SUSY (up to x100)
Current 90% CL limit from CDF+D0 with 1 fb–1 is ~20 times SM
+ : pure leptonic channel (trigger very effective)
+ : no need for tagging
+ : no need for decay time measurement
- : very tough background (dominated by b, b) but size of MC samples limited
 Impact parameter cuts, PID ...
ATLAS
CMS
LHCb
s(M(Bs)) MeV 70 36 18
N(Background)
20 20
N(Signal) for the SM BR 7
6.10.1
Use of the shapes of discriminating variables for signal and background
10 fb-1
Vth SuperB workshop, Paris May 9-11

22. Vth SuperB workshop, Paris May 9-11
Bs  +–
LHCb limit on BR at 90% CL
BR (x10–9)
Uncertainty in bkg prediction
Expected final CDF+D0 limit
SM prediction
Integrated luminosity (fb–1)
Excluded BR(Bs  +–) in 10-9
ATLAS
6.6 (30 fb-1)
CMS
14 (10 fb-1)
LHCb
3.5 (0.5 fb-1)
LHCb with 2 fb–1 : 3 evidence of SM signal
LHCb with 10 fb–1 : 5 evidence of SM signal
ATLAS and CMS running at 1034 cm-2s-1 4 evidence of SM signal in one year
Vth SuperB workshop, Paris May 9-11

23. Precise measurements of UT angles
Vth SuperB workshop, Paris May 9-11

24. Vth SuperB workshop, Paris May 9-11
g measurements
Unique to LHC u s c s
BsDsK decay mode : interference via Bs mixing
Similar to B factories
D0 Kp, K3p (ADS)
D0 KK, pp (GLW)
D0 Kspp (GGSZ)
A(B-D0 K-) = AB
A(B-D0 K-) = ABrB e i(d-g)
Need LHC data
 from B and BsKK
Time dependent CP asymmetries + U-spin symmetry
Sensitive to NP
Crucial ingredients : L0 hadron pT trigger, K/p separation
Vth SuperB workshop, Paris May 9-11

25. Vth SuperB workshop, Paris May 9-11
g from Bs  DsK
Depends on s + 
Similar to 2+ extraction with B0  D*, but the two decay amplitudes are similar (~3)  their ratio can be extracted from data
m = 14 MeV/c2
Expect 6200 signal events/year
B/S <0.5 at 90% CL
Bs  Ds–+ background (with ~ 12  larger BR)
suppressed using PID:
 residual contamination estimated to 155%
Vth SuperB workshop, Paris May 9-11

26. Vth SuperB workshop, Paris May 9-11
Fit the 4 tagged time-dependent rates:
Extract s + , strong phase difference , amplitude ratio
Bs Ds also used in the fit to constrain other parameters (mistag rate, ms, s …)
Both DsK asymmetries 10 fb–1, ms = 20 ps–1)
Ds–K+: info on  + ( + s)
Ds+K–: info on  – ( + s)
s(g) ~ 13 with 2 fb–1
expected to be statistically limited
Vth SuperB workshop, Paris May 9-11

27. Vth SuperB workshop, Paris May 9-11
 from B±  DK±
Interference between
the two diagrams
if same final state
A(B-D0 K-) = AB
A(B-D0 K-) = ABrB e i(d-g)
D0  K or K3 (“ADS”) strategy depends on : rB, g , d the relative magnitudes (known) and strong phases between the D0 Cabbibo-allowed and Cabbibo-suppressed decays
D0  KK or  (“GLW”) strategy depends on : rB, g , d
 common ADS +GLW fit can solve for all unknowns, including 
Decay
2 fb–1 yield
Bbb/S
B–  (K–+)D K–
28k
~0.6
B+  (K+–)D K+
B–  (K+–)D K–
180
4.3
B+  (K–+)D K+
530
1.5
rB=0.077
Sensitivity with 2 fb-1
σ(γ) ~ 5°-15°
(depends on strong phase δD)
Vth SuperB workshop, Paris May 9-11

28. Vth SuperB workshop, Paris May 9-11
 from B0  DK*0 ds
colour-suppressed
colour-suppressed
Despite the presence of a B0 : self-tagging mode
Magnitude ratio = rB ~ 0.4
Treat with same “ADS+GLW” method
Modes : D0  Kp, KK, pp
Decay mode (+cc)
2 fb–1 yield
Bbb/S
B0  (K+–)D K*0
3400
<0.3
B0  (K–+)D K*0
500
<1.7
B0  (K+K–, +–)D K*0
600
<1.4
rB=0.4
Sensitivity with 2 fb-1
σ(γ) ~ 7°-10°
(depends on strong phase δD)
Vth SuperB workshop, Paris May 9-11

29.  from B and BsKK
Measure CP asymmetry in each mode:
Adir and Amix depend on mixing phase, angle , and ratio of penguin to tree amplitudes = d ei
Exploit U-spin symmetry (Fleischer):
Assume d=dKK and =KK
4 measurements and 3 unknowns (taking mixing phases from other modes)  can solve for 
With 2 fb–1:
36k B, B/S ~ k BsKK, B/S < 0.14
Sensitivity to Adir and Amix ~ twice better than current world average
With PID
KK invariant mass
 invariant mass
With PID
stat() = 4
If perfect U-spin symmetry assumed
stat() = 7-10 + fake solution
If 20% violation of U-spin symmetry
For 2 fb–1 :
Vth SuperB workshop, Paris May 9-11

30. Vth SuperB workshop, Paris May 9-11
g measurement summary
B mode
D mode
Method
s(g), 2 fb–1
B+ DK+
Kp + KK/pp + K3p
ADS+GLW
5º–15º
B+  DK+
KSpp
Dalitz
8º(*)
KKpp
4-body “Dalitz”
15º(*)
B0  DK*0
Kp + KK + pp
7º–10º
Bs  DsK
KKp
tagged, A(t)
13º
Bd  + Bs KK
A(t) + U-spin
4º (perfect U-spin)
7º–10º (20% U-spin viol.)
(*) Signal only, no accept. effect
Could be affected by NP
s(g) with 2fb-1
Under study :
B+  D*K+ ADS+GLW
B+  DK+ Kppp 4-body “Dalitz”
B0  DK*0 GGSZ
B  DK + Bs  DsK
Bd  + Bs KK
4-5º
4º (perfect U-spin)
7º–10º (20% U-spin viol.)
With 10 fb-1 obtained from DK and DsK channels s(g) should be ~ 2-3º
Vth SuperB workshop, Paris May 9-11

31. a sensitivity with B00
00
–+
+–
Challenging analysis in the LHC environment :
Need for 0 reconstruction ep0 =53 % for B0p+p-p0.
Time dependent Dalitz plot analysis.
average
gen
70 expts superimposed (2fb–1)
2 vs 
2fb-1 : 14k signal events 90%CL. (time resolution : 50 fs, tagging power : 6%)
Use B/S=1 for sensitivity studies
15% fake solutions (< 1% with 10 fb–1)
stat() < 10º in 90% of the cases (2 fb–1)
Vth SuperB workshop, Paris May 9-11

32. bsss hadronic penguin decays
Bd / Bs
Tree
Bd / Bs
Penguin f
Ks / f
Vtb
Vts*
d/ s ?
d/ s
d/ s
Vcb
Vcs*
Ks / f
J/y
Same s-penguin diagram contributes to Bd and Bs
sin(2β) from J/ΨKs
Using bsss naïve average
Currently: DS=sin(2β)Tree-sin(2β)Peng is 2.6s away from 0
2 fb–1 yield
B/S
Bd  Ks
0.8k
90%CL
Bs    (BR=1.410–5) 4k
0.4 < B/S < 90%CL
Vth SuperB workshop, Paris May 9-11

33. Vth SuperB workshop, Paris May 9-11
The Bs decays are PVV decays  full angular, time-dependent CP analysis
M(ff) GeV
34M bb events …
Bs mass resolution : 12 MeV
Proper time resolution : 42 fs
Bs    CP violation <1% in SM
 significant CP-violating phase NP would be due to New Physics
2fb-1
10fb-1
Bd  Ks s(sin2beff)
0.32
0.14
Bs   
s(fNP) rad
0.10
0.042
Vth SuperB workshop, Paris May 9-11

34. Vth SuperB workshop, Paris May 9-11
Bc and D physics
Vth SuperB workshop, Paris May 9-11

35. Vth SuperB workshop, Paris May 9-11
Bc meson properties
Studying Bc can help understanding heavy quark dynamics
• Different theoretical descriptions give Bc properties with large uncertainties
Bc  J/ψp 1 fb-1
The mass and lifetime measurements could be done with a small data sample.
1 fb-1
2 fb-1
CMS
LHCb
Bc mass resolution [MeV]
22.0 (stat) 14.9 (syst)
~14
N(signal)
120
14000
s(ct)/ct
~10%
~ 6%
PDG 2006 :
J/y ℓ n s(ct)/ct ~ 37 %
Vth SuperB workshop, Paris May 9-11

36. Vth SuperB workshop, Paris May 9-11
Charm physics
Dedicated D* trigger  huge sample of D0h+h– decays (100M / 2fb-1)
Useful for PID calibration
CP violation and mixing in D0 decays (tag D0 or anti-D0 flavour with charge of pion from D*D0)
Use BD*hX to find the D* vertex
2fb-1
D0
K-p+
K+K-
p+ p-
K+p- N
50M 5M 2M
0.2M
D* from B decays
Interesting (sensitive to NP) & promising searches/measurements:
Time-dependent D0 mixing with wrong-sign D0K+– decays
Direct CP violation in D0K+K–
ACP  10–3 in SM, up to 1% (~current limit) with New Physics
Expect stat(ACP) ~ O(10–3) with 2 fb–1
LHCb (10fb-1)
s(x’2)~
s(y’)~
End of B factories (2ab-1)
s(x’2)~
s (y’)~
Performances studies just started : not as detailed as in B physics case
Vth SuperB workshop, Paris May 9-11

37. Impact on Unitarity Triangle
Taken from V. Vagnoni at CKM06-Nagoya
Without LHCb
With LHCb at 10 fb-1
But hopefully some NP will show up …
Vth SuperB workshop, Paris May 9-11

38. Vth SuperB workshop, Paris May 9-11
Conclusion
Data taking for physics will start in 2008 at √s = 14 TeV and experiments are getting ready
Search for New Physics will be possible through several observables : Bs  +–, BsJ/, radiative decays …
With the full B dataset
CKM matrix elements will be very well measured
B and D physics exploration will continue after B factories and Tevatron
But in order to translate very precise measurements of experimental quantities to very precise SM parameters determination one needs improved theoretical computation of hadronic parameters (form factors, decay constants …)
What I have shown is based on (very detailed) MC simulations ; reality will be different (higher backgrounds, worse resolution …) and it will take some time to understand the detectors.
Vth SuperB workshop, Paris May 9-11

39. Vth SuperB workshop, Paris May 9-11

40. Vth SuperB workshop, Paris May 9-11

41. Vth SuperB workshop, Paris May 9-11
Backup slides
Vth SuperB workshop, Paris May 9-11

42. Framework : the CKM matrix
Mass eigenstates  weak interaction eigenstates  mixing matrix : the Cabbibo-Kobayashi-Maskawa matrix
Weak interaction eigenstates
Mass eigenstates
CKM matrix
Transition amplitude between the quarks i and j : Vij
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb d’ s’ b’ = d s b W b u
Vub
Vij complex  CP violation
Wolfenstein parametrisation
1-  A 3(-i)
- 2/ A 2
A3(1- -i) A 
+ O(4)
Vth SuperB workshop, Paris May 9-11

43. Vth SuperB workshop, Paris May 9-11
LHCb trigger
Vth SuperB workshop, Paris May 9-11

44. Tagging is needed for many CPV measurements
We need to know the flavour of the B at a reference t=0 (at the primary vertex)
Tag (give best estimate of) the flavour by examining the rest of the event
Dz/bgc = Dt
Bs0
rec
t =0 b s u K+
Dt picoseconds after leaving the primary vertex, the reconstructed B decays. PV
b-hadron
l + (e+, m+)
l - (e-, m-)
K -
Uses flavour conservation in the hadronization around the Brec
eD2  1% (B0) , 3% (Bs)
Same-side tag
Assume:
Opposite side tag
eD2  5%
Vth SuperB workshop, Paris May 9-11

45. Tagging performances for ATLAS, CMS and LHCb
eD2=e(1–2w)2
Tag
LHCb
ATLAS
CMS
Opposite 
0.7%
Opposite e
0.5%
0.3%
Opposite K
1.6% -
Opposite Qvtx
1.0%
3.6%
Same side  (B0)
0.8%
Same side K (Bs)
2.7%
Combined (B0)
4%–5%
4.6%
Combined (Bs)
7%–9%
Vth SuperB workshop, Paris May 9-11

46. Vth SuperB workshop, Paris May 9-11
Bs-> Psi Phi
L(t, qtr) = (1-RT) Leven(t) (1+cos2qtr) / 2 + RT Lodd(t) (1-cos2qtr)
Vth SuperB workshop, Paris May 9-11

47.  from B and BsKK
Measure CP asymmetry in each mode:
Adir and Amix depend on mixing phase, angle , and ratio of penguin to tree amplitudes = d ei
Exploit U-spin symmetry (Fleischer):
Assume d=dKK and =KK
4 measurements and 3 unknowns (taking mixing phases from other modes)  can solve for  
2 fb–1
stat() = 4
If perfect U-spin symmetry assumed
2 fb–1
If 0.8<dKK/d<1.2 assumed
stat() = 7–10 + fake solution
Vth SuperB workshop, Paris May 9-11

48. a sensitivity with B00
sM ~ 10 MeV/c2
sM ~ 15 MeV/c2
2fb-1 : 14k signal events 90%CL.
Use B/S=1 for sensitivity studies
merged
resolved
<>=53%
Distribution of fit error
15% (< 1%) fake solutions with 2 (10) fb–1
Vth SuperB workshop, Paris May 9-11
stat() < 10º in 90% of the cases (2 fb–1)

49. SU(2) analysis of B0  +–, ±0,00
Larger branching fraction than pp
Small BF(B0r0r0) (= 1.20.4 )
Low penguin contamination  good limit on a-aeff
VV final state  3 polarization amplitudes
In principle: dilution due to mixed CP
In practice: dominated by longitudinal polarization  pure CP-even state
B0  +–, ±0 measurements are not competitive with B-factories
Main LHCb contribution could be B0  00 (time dependent analysis) :
with 2fb-1 1k events reconstructed
Vth SuperB workshop, Paris May 9-11