ulrich uwer university of heidelberg on behalf of the lhcb collaboration beauty 2003, carnegie...
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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
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