Ulrich UwerUniversity of Heidelberg

On behalf of the LHCb collaboration

Beauty 2003, Carnegie Mellon University, Pittsburgh, PA, USA

Physics Performance

Physics Goals

• pure hadronic and multi-body final states.

• new decay channels in particular Bs decays

Study rare and loop-suppressed decays

CPV measurements in many decay channels:

precise determination of CKM elements: measurement of bu+W (tree) phase

overconstraining the Unitarity Triangles: disentangle the tree phases from phases of oscillations (loops) and penguins

2 B0 →J/()K

2 + B0 →D*_ +

B0 →D0 K*0

and B0 + Bs K+ K

Bs→ DS K

Bs→ J/()

= B0→ + ,

W

New Physics

WNew

Physics

Search and filter-out effects of New Physics

At 2x1032 cm-2s-1 1012 bb pairs produced / yr

Example: New Physics in B mixing

Φd = 2 + ΦdNP

Φs = 2 + ΦsNP

CPV in B0 J/ Ks sin(2+ΦdNP)

B0 D* sin(2+ΦdNP+)

Bs J/ sin(2+ ΦsNP)

Bs DsK sin(2+ ΦsNP+)

Rate of B0 D0 K*0, D0K*0, D0CP

K*0

Redundant measurements necessary to disentangle CKM phases from New Physics

WNew

Physics

B(s)B(s) mixing phase:

Observation of new phase:

Discovery Potential

In 1 year: e.g. (B DK*): 70

sind(B0J/Ks): 0.022

“reference channel”

2007 BABAR+BELLE

Monte Carlo Simulation

Full Geant 3.2 simulation:

• PYTHIA 6.2 tuned on SPS(UA5) and Tevatron (CDF) data

• Multiple pp interactions and spill-over effects included

• Size of beam spot (z=5cm)

• Complete description of material from TDRs

• Individual detector responses tuned on test beam results

Trigger simulation and full reconstruction:

• Full simulation of L0 and L1 triggers: cuts tuned for max. efficiency at limited output rate (1 MHz L0, 40 KHz L1)

• Full reconstruction including pattern recognition

Simulated samples:

• Signal samples

• Background samples: 10 M incl. bb events 4 min30 M min. bias events 2 sec

T1 T2 T3

Detector Performance

Bs K

K

, K

Ds

Dsmass (GeV)

BsDs+(K+)

Bs vtx z resolution (mm)

Proper time resolution (fs) Ds vtx z resolution (mm)

core=5.1 MeV

BsDs / BsDsK Separation

Bs Ds is a physics background for Bs Ds

K

– BR(Bs Ds) / BR(Bs Ds

K) ~ 12

(Bs Ds ) / (Bs Ds

K) = 1% after PID and mass cuts

BsDsKBsDs

BsDsK

BsDs

Event Yield (untagged)

Channel Trig (L0+L1) tot Yield B/S

B0 34 % 0.69 % 26 k < 0.7

B0 K 33 % 0.94 % 135 k 0.16

Bs K-+ 37 % 0.55 % 5.3 k < 1.3

Bs KK 31 % 0.99 % 37 k 0.3

Bs Ds 31 % 0.34 % 80 k 0.3

Bs Ds-+K+- 30 % 0.27 % 5.4 k < 1.0

B0 J/KS 61 % 1.39 % 216 k 0.8

B0 J/e-eKS 27 % 0.16 % 26 k 1.0

Bs J/ 64 % 1.67 % 100 k < 0.3

Bs J/e-e 28 % 0.32 % 20 k 0.7

B0 36 % 0.03 % 4.4 k < 7

B0 K 38 % 0.16 % 35 k < 0.7

s 34 % 0.22 % 9.3 k < 2.4

1 year (107s) at L = 2x1032 cm-2 s-1

tot det* rec/det* sel/rec* Tri g = 0.120.920.180.34norm. to 4 ( for B0

Flavour Tagging

Tag Tag (%) w (%)

eff (%)

Muon 11 35 1.0

Electron 5 36 0.4

Kaon 17 31 2.4

Vertex Charge 24 40 1.0

Frag. kaon (Bs) 18 33 2.1

Combined B0 (decay dependent:

Combined Bs trigger + select.)

~4

~6

l

B0

B0D

K-

b

b

s

u

s

u

Bs

+

• Lepton • Kaon other B• Vertex charge• Fragmentation kaon near Bs

Tagging tracks: large impact par.

Kaon tag

Physics Sensitivity

– Generate many fast MC samples

• Signal efficiencies (including tagging) as well as background levels and shapes taken from full simulation studies

– extract physics parameter from each sample

• for CP asymmetries, fit together a second fast MC sample of flavour-specific decays to extract the mistag “from the data”

Reference measurements: sin(2) from B0J/Ks

ms from BsDs

CPV measurements: sin(2) and s from BsJ/

BsDsK

from B0 and BsKK

B0D0K*0

Radiative decays: bs penguins

CP reach evaluation: all numbers for 1 yr

sind in BJ/Ks

sinΦd = sin(2) Adir 0 New Physics beyond SM

Annual B0J/()Ks yield: 216k

Background: B/S 0.8

Tagging probability: 45 %

Mistag probability w: 37 %

MC simulation of many experiments:

(sin(d)) = 0.022

(“measurement” of mistag rate w through simulated B0J/()K* evts)

ms with BsDs+(KK)-

Expected unmixed Bs Ds sample

in one year of data taking (fast MC)

Annual event yield: 80k

Background B/S: 0.32

Tagging probability: 55 %

Mistag probability w: 33 %

Proper time res. 33 fs (core)

ms (ps-1) 15 20 25 30

(ms) 0.009 0.011 0.013 0.016

Statistical precision / yr

5 observation of Bs oscillation: 68 ps-1 / yr

error A of oscillation amplitude

Φs and and ΓΓss with B with BssJ/J/ΦΦThe “gold plated decay” of Bs:

SU(3) analogue of Bd J/Ks

ACP in SM Φs = -2 = -22 ~ -0.04

Problem: PS VV

3 contributing amplitudes 2 CP even, 1 CP odd

fit angular distribution of decay states (transversity angle tr) as function of proper time.

event yield () / yr: 100k

background B/S: <0.3

tagging efficiency 50%

Mis-tag rate: 33%

proper time resolution 38 fs

If Γ/Γ is ~0.1, can do a 5 discovery in one year

() ~ 2 O

from BsDs+K+

Time dependent BsBs asymmetries

5 yrs of data, ms=20 ps-1

Interference between 2 tree diagrams due to Bs mixing

Measure s from time-dependent rates: BsDs

K and BsDsK

(+ CP-conjugates) Use s from BBssJ/J/

After 1 year, if s/s = 0.1, 55 < < 105O 20 < T1/T2 < 20O

ms 20 25 30

(+Φs) 14 0 16 0 18 0

event yield () / yr: 5.4k

background B/S: <1.0

tagging efficiency 54%

Mistag rate w: 33% (extract from BsDs)

No theoretical uncertainty;insensitive to new physics in B mixing

from B and BsKK

2sinh

2cosh

)sin()cos()(

A

mAmAA

mix

CP

dir

CPth

CP

Measurement of time-dependent CPasymmetry for both decays Adir and Amix w/ strong phase contribution of unknown magnitude

Adir (B0 +-) = f1(d, , ) Amix(B0 +-) = f2(d, , , d)Adir (BsK+K ) = f3(d’, ’, ) Amix(BsK+K ) = f4(d’, ’, , s)

U-spin symmetry:d = d’ and = ’

In both decays large b d(s) penguin contributions to b u:

Method proposed by R. Fleischer:

• use B and BsKK together

• exploit U-spin flavour symmetry for P/T ratio described by d and

4 measurements (CP asymmetries) and 3 unknown (, d and ) can solve for

Φs (BsJ/) Φd (B0J/Ks)

d d

from B and BsKK

68% and 95% CL regions(for input = 65 deg)

“fake” solution

d vs

Adir

, Amix

, AdirKK , Amix

KK and w (mistag), AK ,,, AK,,, Γ, m, Γ, m and resolutions (17 par.) from fit to:

B (26k / yr)

BsKK (37k / yr)

BK+ (135k / yr)

BsK+ (5.3k / yr)

p.d.f. F(d, , )

B (95%CL)

BsKK (95%CL)

() = 46 deg

If ms= 20 ps1, s/s=0.1, d =0.3, = 160 deg, 55 < < 105 deg:

U-spin symmetry assumed;sensitive to new physics in penguins

from Bfrom B D DKK** and B and B D DKK**

A1 = A1

√2 A3 √2 A3

A2

A2

2

Variant of the Gronau-Wyler method proposed by I.Dunietz:

A ( B DCPK* ) = A3 =

1/2 ( A(B D0K*) + A(B D0 K* ) )

1/2 ( A1 + |A2| ei (+) )

together with CC decays two triangle relations for amplitudes

Measure 6 decay rates: yield/yr B/S

B D0 (K+) K*(K+) 0.5k 1.8

B D0 (K+) K*(K+) 3.4k 0.3

B DCP (KK) K* (K+) 0.6k 1.4

55 < < 105 deg20 < < 20 deg

() = 78 deg

sensitive to new phase in DCP

+ cc

=65o, =0

B0K*0 and Bs

W

b u,c,t s

In SM:

loop-suppressed bs transitions

BR( B0 K*0 ) = (4.30.4) 10-5

expected direct CP violation <1% for B0K*0 expected CP violation in mixing ~0 for Bs

1 yr B/S

B0 K*0 (K+-) 35k <0.7

Bs (K+K-) 9.3k <2.4

(ACP) ~ 0.01 (1year)

~64MeV ~65MeV

B0K*0 +-

SM:

BR(B0K*0 +-) = (1.2 0.4) x 10-6

Measurement determines |Vts|

Variables sensitive to New Physics:

+- invariant mass distribution

+- forward-backward asymmetry FBA = (+, B direction in +- CMS)

Annual yield (SM): 4.4kEfficiency: 0.7%Background (B/S) <2

(BR) ~ 3%(ACP) ~ 3%

Conclusion

LHCb can study many different B-meson decay modes with high precision excellent particle identification capability excellent mass and decay-time resolution

LHCb can fully exploit the large B-meson yields at LHC from the start-up flexible, robust and efficient trigger design luminosity of 2x1032 is lower than typical LHC luminosity

LHCb detector will be ready for data taking in 2007 at LHC start-up detector production is on schedule installation of detectors will start end of next year

LHCb will offer soon an excellent opportunity to determine precisely the CKM parameters through phase meas. spot New Physics by overconstraining the Unitarity Triangles