1. B Physics prospects at LHC
Rencontres de Moriond “Electroweak Interactions and Unified Theories”
5-12 March 2005
B Physics prospects at LHC
Marta Calvi
Università di Milano Bicocca and INFN
Electroweak Interactions and Unified Theories, 2005

2. B Physics in the LHC era
At LHC start-up several precise measurements will be available from B-Factories and Tevatron to test the CKM paradigm of flavour structure and CP violation.
(from CKM-fitter )
However New Physics could still be hidden in mixing, in box and in penguin diagrams, realm of indirect discoveries.
If NP will be found at LHC in direct searches, B Physics measurements will allow to understand its nature and flavour structure.
Electroweak Interactions and Unified Theories, 2005

3. A complete program on B Physics would include:
Precise measurement of B0s-B0s mixing: Dms, DGs and phase fs.
BsDsp, … BsJ/yf, BsJ/yh(’)
Precise g determinations including from processes only at tree-level, in order to disentangle possible NP contributions
Several other measurements of CP phases in different channels for over-constraining the Unitarity Triangles
BsDsK, B0D0K*0, B0pp&BsKK, …
B0fKs, Bsff, ... B0rp, B0rr, …
Search for effects of NP appearing in rare exclusive and inclusive B decays
B0K*g, B0K*0l+l-, bsl+l-, Bsm+m-...
Electroweak Interactions and Unified Theories, 2005

4. Advantages of hadron colliders
Huge bb cross section: sbb~500 TeV (~1nb @Y(4S) )
Access to all b-hadrons: Bd,Bu, Bs, b-baryons and Bc
The challenge
Presence of underlying event. High particle multiplicity.
High rate of background events (sinel~80 mb).
Experimental requirements
Trigger (also on fully hadronic decays)
Excellent tracking and vertexing (mass resolution, proper time resol.)
Excellent PID
Other B physics topics at LHC:
b production, bb correlation
b-baryon physics, polarization
Bc physics
Electroweak Interactions and Unified Theories, 2005

5. LHC: pp at s =14 TeV, nbco=40 MHz
ATLAS/CMS: for discovery Physics
central detectors: |h| < run at maximum available luminosity
ℒ (cm–2s-1)= 21033 / ~ 1013 bb produced per year (1yr=107s)
Npp/bc ~ 4 / 23
B-physics program will depend on trigger strategy
LHCb: dedicated to B Physics
forward spectrometer: 1.9 < |h| < 4.9
run at lower luminosity (locally defocusing) ℒ (cm–2s-1) = 2 bb produced per year Npp/bc ~ 0.4
bb correlation qb qb
Electroweak Interactions and Unified Theories, 2005

6. LHCb trigger
40 MHz
Level-0: high pT (m,e,g,h) + pile-up system Hardware trigger [4 ms]
L0 efficiency
L1 efficiency L0*L1 eff.
1 MHz
Level-1: high IP, high pT tracks Software trigger [1 ms]
40 kHz
HLT: software trigger on complete event [10 ms]
200 Hz kHz
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)
Systematics from data
Electroweak Interactions and Unified Theories, 2005

7. CMS trigger
50kHz at start up in 2007
Level-1 Trigger designed to cover widest possible range of discovery Physics (Higgs, SUSY ...)
B Physics events triggered by single m or 2m triggers Only a small fraction of HLT output accounted for inclusive b,c (~5Hz 1m)
100 Hz
Exclusive B events selected at HLT exploiting online tracking
To stay within time budget (~40 ms/evt) restrict Bs reconstruction to Region of Interest around the m, or use reduced # hits/track (Dsp )
s(pT)
e.g. BsJ/yf
Lvl-1 e
HLT e
events 10 fb-1
Trigger rate
16.5%
11.9%
84 k
<1.7 Hz
full tracker
Electroweak Interactions and Unified Theories, 2005

8. ATLAS trigger Three level Trigger:
40 MHz  Level-1(75 kHz)  Level-2 (2 kHz)  Event Filter(200 Hz)
B-physics ‘classical’ scenario: LVL1 muon with pT>6 GeV/c, ||<2.4, LVL2 muon confirmation, ID track ‘full scan’
Flexible trigger strategy to maximize B-physics capabilities at ℒ =2 1033 cm-2s-1 and with reduced detector at start-up:
Start with a di-muon trigger
Add further triggers in the beam-coast and for low-luminosity fills.
Additional triggers will require a single m at LVL1 and a Jet or em. cluster LVL1 will guide reconstruction at LVL2 and LVL2 will seed EF.
Electroweak Interactions and Unified Theories, 2005

9. B0s-B0s mixing with Bs0  Dsp
Bs0Ds-p+ (Ds-fp-, fK+K- )
Expected unmixed Bs Ds sample in one year of LHCb data taking
LHCb: 80k events/yr B/S=0.32
st~ 40 fs
5 observation of B0s-B0s oscillation up to Dms=68 ps-1 1 yr
Once observed, precision to measure Dms is ~0.01ps-1
proper time resolution (fs)
ATLAS/CMS
Events triggered by m from opposite b decay Performance strongly dependent on the allocated bandwidth.
ATLAS: (LVL1 pTm > 6 GeV/c) in 10 fb-1 expect. sensitivity up to Dms=36 ps-1
CMS: (restricting to 5 Hz at HLT) in 20 fb-1 expect. sensitivity up to Dms=20 ps-1
Electroweak Interactions and Unified Theories, 2005

10. fs and Gs with BsJ/f (h)
The “gold plated” decay of Bs, sensitive to the weak phase of Vts
SM: fs =-22 ~  High sensitivity to NP in Bsmixing
BsJ/f is a complicated analysis: 2 CP even, 1 CP odd contributing amplitudes  fit angular distribution of decay states as function of proper time.
Derive also DGs=G(BsL)-G(BsH) ( DGs/GsSM ~0.1 )
BsJ/f
s(sinfs) s(DGs/Gs ) ℒ
LHCb ~ fb-1 ATLAS ~ fb-1 CMS ~ fb-1
If Dms~20 ps-1
Similar sensitivity reached in LHCb also using BsJ/y()h, Bshc(4h)f with 7k+3k events/yr, under study.
Electroweak Interactions and Unified Theories, 2005

11. Time dependent BsBs asymmetries
 from BsDsK
Measure   fs from 4 time-dependent rates: BsDsK and BsDsK (+CP conjugates)
Use fs from BsJ/ f
Only tree diagrams  g insensitive to NP in mixing
BsDsK
BsDs
Time dependent BsBs asymmetries
Need excellent PID for K/p separ.
5400 events/ yr B/S<1.0 at 90% CL
() =14º (1 year)
5 yrs of data, ms= 20 ps -1
20<<20
New analysis underway: combination of BsDs(*)K and B0D(*)p using U-spin symmetry. Expected sensitivity ~5º in 5 year.
Electroweak Interactions and Unified Theories, 2005

12.  from B DK*, DCPK*
(—–)
Theoretically clean determination of g. Measure 6 time-integrated decay rates with B0D0K*0 self-tagged through K*0K+p- and DCPK+K-(or p+p-)
A1 = A1 A3 A4 A2 2
  
Dunietz variant of the Gronau-Wyler method:
A(BDCPK*)=1/2 (A(BD0K*) + A(BD0K*))
A3 /2 = 1/2 ( |A1| + |A2| ei (+) )
Similar to B± D0K± but here two colour suppressed diagrams and |A2|/|A1|~0.4
Variant of the Gronau-Wyler method as proposed bt I.Dunietz:
Amplitude triangles are not as squashed as in case of B+/- -> DK+/-
Difficulty: also detect the D0 CP eignestate Dcp
LHCb 1 year
yield
B/S
B0 D0 (K+) K*0(K+)
3000
<0.6
B0 DCP(K+K-)K*0(K+)
540
<2.9
()=7º8º (1 year)
for 55 <  < 105 deg
20 <  < 20 deg
Electroweak Interactions and Unified Theories, 2005

13.  from B and BsKK
Bd/s
/K
/K
Bd/s
Large penguins contributions in both decays
Measure time-dependent CP asymmetry for B and BsKK and exploit U-spin flavour symmetry for P/T ratio (R. Fleischer).
Use RICH detectors for K/p separ.
without RICH
Bd+-
Take fs, fd from J/,J/Ks  can solve for g
B (95%CL) d
sM=17 MeV
BsKK (95%CL)
events/yr B/S B k <0.7 BK+ k BsKK k
() = 4º6º (1 year)
g (º)
+(theory)
Electroweak Interactions and Unified Theories, 2005

14. r+- a from B r-+  +p- r00
Quinn & Snyder: time dependent analysis of Dalitz distribution allows a clean determination of a independently from penguin contributions
M(p0p-)
M(p0p+)
po reconstr. eff.
11-par. fit including resonant and non-res. background
sa vs B/S
Merged po
sright
Resolved po
sleft
LHCb: evts/yr B/S<3
sa < 10o (1 year)
Electroweak Interactions and Unified Theories, 2005

15. B0  K*0 +- BR(B0K*+-)SM=(1.20.4)x10-6 ACPSM < 0.05%
BR(s)
AFB(s)
BR(B0K*+-)SM=(1.20.4)x10-6
ACPSM < 0.05%
Zero of AFB(s) known in SM at 5%
Sensitivity to NP via non-standard values of Wilson coeff. C7,C9,C10
s=M(+-)2 [GeV2]
(s)/s(%)
(AFB)
LHCb: evts/yr B/S<2.6
(BR) ~ 2% (ACP) ~ 2%
Sensitivity to AFB need careful study of background shape.
In 5 years: (AFB )~ 0.12, fitting the intersection at zero: (s0 ) ~ 0.02
ATLAS ~2000 events, B/S=0.14 (30 fb-1)
Electroweak Interactions and Unified Theories, 2005

16. Bs0  +-
BR(Bs0+-)SM = (3.50.1)x Good sensitivity to NP
BR(Bs0+-) ~(tanb)6, ACP ~(tanb) for large tanb
Bs  m+m-
CMSHLT
CMS
Lvl-1 e
HLT e
events
Bs+-
Trigger rate
offline evts
offline
backgr
15.2%
33.5% 47
<1.7 Hz 7
<1
10 fb-1
s=74 MeV
Bs0+-
Bd0+-
backgr.
1 year 1033cm–2s-1 9 1 31
1 year 1034cm–2s-1 92 14
660
ATLAS
CMS Full tracking
LHCb: 1 year events Bs0+ Backgr. study requires additional MC statistics, present limit from bmX+cc. B/S< (MBs)=18 MeV/c2
s=46 MeV
Bs mass resolution
SM signal in the first year !
Electroweak Interactions and Unified Theories, 2005

17. Conclusions
Future experiments at LHC will offer a great opportunity to pursue an extensive program on B Physics
Access to B0 and Bs decays with high statistics will allow precise determination of:
B0s-B0s mixing parameters Dms, DGs and fs
a,b,g measurements in several channels
access to rare decays
over-constrain the Unitarity Triangles and look for signals of NP
The program will also include studies with b-baryons and Bc mesons.
The goal will be reached thanks to:
dedicated triggers
excellent mass and decay-time resolution
excellent particle identification capability
Electroweak Interactions and Unified Theories, 2005