Transcript Scopi principali di LHCb

LHCb Physics reach
Marco Musy
Università di Milano Bicocca
and INFN Milano
LHC2003 International Symposium
Fermilab, 3th May 2003
Marco Musy
Fermilab 3th May 2003
(1)
Ambitious physics goals of LHCb
 Overconstrain the unitarity triangles
 Search for New Physics beyond SM
 Precision CPV measurements, using also
pure hadronic and multi-body final states
(Bd pp, Bd D*p, . . .)
 Exploit CPV in new decay channels as in Bs
(BsKK, BsDsK, BsJ/yf , . . .)
 Rare b-decays
(BdK* g, BdK*mm, Bsmm . . .)
 New particles may show up in loop diagrams,
overconstrain will allow to disentangle SM
components from the new-physics ones
b
t
b
d
t
d
Marco Musy
NP?
Fermilab 3th May 2003
High statistics
is a requirement
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r
2007
|Vtd/Vts|
sin 2b
g and dg
CPV from LHCb
in one year
not well known
|Vub/lVcs|
h
BdJ/yKS
Bd D*p
BdJ/yKS
Bdpp
BsJ/yf
Bs DsK
Bs mixing
h
fNR
|Vub/lVcs|
r
• If New Physics is there
LHCb experiment can spot it in 2008 !
Marco Musy
Fermilab 3th May 2003
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Experimental challenge
HIGH
STATISTICS
Bd K*g
BdJ/y r 0
• LHCb has to deal with a large variety of final states with different topologies
• Hot pp environment needs a robust trigger sbb / sinel.~ 0.01 (sbb~ 500 mb),
many particles are not associated to b-hadrons
• b-hadrons do not evolve coherently
• High bb yield, 1012/year of Bd, Bs , baryons, Bc with bgct ~ 7mm
Marco Musy
Fermilab 3th May 2003
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LHCb detector
 Detector has undergone a reduction of material in front of RICH2
(60%  40% for X0, 20%  12% for lI)
Less interactions in detector, Level-1 Trigger includes momentum measurement
 Technologies have not changed
 September 2003: “Detector Reoptimization TDR” and “Trigger TDR”
 Construction phase is in good shape
( T. Nakada talk)
Marco Musy
Fermilab 3th May 2003
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Fully simulated bb event in Geant3
•
•
MC Pythia 6.2 tuned on CDF and UA5 data
Multiple pp interactions and spill-over effects included
•
•
Complete description of material from TDRs
Individual detector responses tuned on test beam results
•
Complete pattern recognition in reconstruction:
MC true information is never used
•
•
•
1M inclusive bb events produced in Summer 2002
New “Spring” production ready: 10M events for September TDRs
Sensitivities quoted here are obtained by rescaling earlier
studies to the new yields
Marco Musy
Fermilab 3th May 2003
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Main performances
VELO
PV: s ~ 47 mm
SV: s ~170 mm
VELO
Bs mixing
Measure Dms
RICH-1
at 5s
up to 48 ps-1
RICH
2<p<100 GeV/c
<e(KK)>= 88%
Tracking
<e(pK )>=2.7%
• <Ntracks>= 27 “physics” tracks
e, m PID
etrack ~ 95% p>5 GeV/c
<e(mm)>= 86%
“ghost” rate ~ 8% @pT>0.5GeV
<e(ee )>= 78%
 see dedicated talks!
<e(p e,m)>=1%
Marco Musy
Fermilab 3th May 2003
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Event
yield
yield 
untagged
 L(t)dt  s
 2  Prob(b  b-hadron)  BRi  etot
i
year
bb
eacc* e2track* ecut* eL0* eL1= 13% * (96%)2 * 22% * 61% * 51%
Channel
1 year = 2 fb
L=
2x1032
-1
cm–2s-1
Efficiency includes:
 Geometrical acceptance, eacc
including detection efficiency, material
 Trigger efficiency: Level-0 && Level-1, eL0,1
e tot
Yield
B0  p+p-
0.78 %
27 k
B0  K+ p-
0.85 %
115 k
B s  K+ K-
0.94 %
35 k
Bs Ds-p+
0.26 %
72 k
Bs Ds-K+
0.34 %
8k
Bs J/y (m-m+ )f
1.66 %
109 k
Bs J/y (e-e+ )f
0.29 %
19 k
B0 J/y(m-m+) KS
0.76 %
119 k
B0K0* g
0.09 %
20 k
including expected Pile-up rate veto
 Reconstruction efficiency (tracking, calorimeters, PID), etrack
norm. to 4p
 Selection cuts efficiency to reconstruct the final state and reject background, ecut
Marco Musy
Fermilab 3th May 2003
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Flavour tagging

p+
B0
Knowledge of flavour at birth is essential
for the majority of CPV measurements
B0
D
l)

Opposite side lepton tag ( b 

Opposite side kaon tag ( b  c  s )
- unique to LHCb, BTeV
- correlated to hadron trigger

Same side pion and kaon tag
(with p coming either from B** or fragm.
successfully used by CDF already)

p-
K-
l
b
d
b
d
u
Vertex charge tagging
u
•Only single particle tagging (e, m, K) from opposite side B decay used
in this presentation
e = 0.40, D = 0.40  e D2 = 6.4%
•The new MC data give similar results
Marco Musy
Fermilab 3th May 2003
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B0
p+
eeff
Flavour tagging
Bs Opposite Side
K-tag
 Typical tagging efficiencies:
in Bs  K p, KK, Dsp channels
(after L0*L1 trigger, any nr of collisions)
tag
 tag
eff
m
12.4
35.5
1.0 ±0.1
e
7.7
43.3
0.14 ±0.07
K (OS)
26.3
36.2
2.1 ±0.3
K (SS)
17.3
29.7
2.9 ±0.3
Vtx Charge
23.9
40.0
0.9 ±0.2
TOTAL
65.8
34.8
6.1 ±0.4
Method
IP/s
Bs Same Side
K-tag
 Work is in progress to update
and improve the efficiencies
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Fermilab 3th May 2003
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B(s)  p p, K p, K K
max pT
min IP/s
Proper time s = 41 fs
 Selection cuts on
Signal charged tracks, PID
Reconstructed B
incl. bb
signal
92% purity
s=18 MeV/c2
pT(B)
L/sL
 Combinatorial bb bckgr, can be
fully rejected even relaxing mass cut
S/B ~ 1
Marco Musy
Fermilab 3th May 2003
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g from B
(s)
 p p, K K
(proposed by R. Fleischer )
• Relies on “U-spin” symmetry assumption (ds) which is the
only source of theoretical uncertainty
• Clean measurement of
g
assuming dg from Bs  J/y f and b from B  J/y Ks
• Sensitive to New Physics contribution which can be pointed out
by comparing with g obtained from DsK
Marco Musy
Fermilab 3th May 2003
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g from B
(s)
 p p, K K
input values
B0  p+ p- BS  K+ K-
yield
27k
35k
mix
sensitivity
CP
B/S
0.8
0.55
xq
0.755
20
from time-dependent measured asymmetry
eD2
0.064
0.064
-0.30
0.16
0.58
-0.17
0.0
0.0
 Evaluation of
dir
CP and
A
A
dir
ACP
mix
ACP
A  cos(x  t ) + A  sin(x  t )
A (t ) 
 DG 
 DG 
cosh
 t  - AD G  sinh
t 
 2

 2
 D G 0
th
CP
dir
CP
B0  p+ p-
Marco Musy
mix
CP
DG
BS  K+ K-
Fermilab 3th May 2003
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g from B
(s)
 p p, K K
BS  K+ K-
In one year:
B0  p+ pdir
mix
s (DACP
)  s ( ACP
)  0.054
dir
mix
Corr ( ACP
, ACP
)  - 0.53
tagging efficiency

BS  K+ K-
dir
mix
s ( ACP
)  s ( ACP
)  0.043
BS  K+ K-
dir
mix
Corr ( ACP
, ACP
)0
@ D Gs  0
x s  20
CP asymmetry can be measured in Bs  K+K- up
to xs=40 with an error increase of a factor 1.6
For xs=20
Marco Musy
s(g) ~ 3o
Fermilab 3th May 2003
increasing xs
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
a from B  p p
0
 RICH PID and hadron trigger are fundamental
 Decay is polluted by penguin diagrams
Penguin/Tree might be as high as 0.2
 If |P/T| will be known to ±0.1 then
5°< s(a) < 10° (depending on parameter value)
Marco Musy
Fermilab 3th May 2003
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Bs  Dsp, DsK
Bs
K+
Kp-
Ds
72k Ds- p+
8k Ds- K+
s ~ 6.5 MeV/c2
Ds mass (GeV)
p+, K+
s = 168 mm
s = 418 mm
Bs vtx resolution (mm)
Ds vtx resolution (mm)
When selecting Bs  Ds- K+
BR(Ds- K+)/BR(Ds- p+) = 1/15 while
e(Ds- K+)/ e(Ds- p+) = 70 thanks to the RICH PID
Marco Musy
Fermilab 3th May 2003
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g from B
s

D-
s
K+
,
D+
s
Needed:
K-
 Hadronic trigger
 From the measurement of 4 time-dependent
asymmetries one gets g-2dg (with 2dg from BsJ/yf)
 2 same order tree level amplitudes (l3) :
large asymmetries, NP contributes unlikely
 K/p separation
 Good proper time
resolution
Sensitivity depends upon
• relative amplitudes
• strong phase difference
• values of g, Dms , DGs /Gs
For Dms=20 ps–1:
s(g) ~ 10o
In one year: 8k BsDsK reconstructed events
For Dms=30 ps–1:
s(g) ~ 12o
 Same principle holds for B0  D*p, (study at the time of TP
gives similar precision on g, a new evaluation is under way)
Marco Musy
Fermilab 3th May 2003
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dg from B
s
 J/y f
 In SM fS  -2dg  -2l2h ~10-2
 Sensitive to New Physics effects
in the Bs-Bs system
In one year:
109 k events Bs J/y (m+m-) f
J/y f is not CP eigenstate:
needs fit to angular distributions of
decay final states as a function of
proper time
19 k events Bs J/y (e+e-) f
s 36±1 fs
Assuming Dms=20 ps–1:
s (2dg) ~ 2o
Determination of DGs
s( DGs/ Gs) ~ 0.03
for DGs/Gs = 0.15
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Fermilab 3th May 2003
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b from B
0
 J/y Ks
 The ‘gold plated’ channel at B-factories
 Precision measurement of this parameter
is very important:
=0 in SM
=sin 2b
 LHCb will bring a lot of statistics to this channel, which can be
used to look into higher order effects, and fit Adir
In one year with 119k events: s (sin 2b ) ~ 0.02
 Comparing with other channels may indicate NP in penguin diagrams
Marco Musy
Fermilab 3th May 2003
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Rare decays: B0  K0* g
 BR( B0  K0* g ) = (4.30.4) 10-5
 Direct CP violation in SM <2%
g
 Sensitive to New Physics effects
W
b
u,c,t
s
Mass resolution ~ 72 MeV
Background from B0K*p0 can be
rejected using K* helicity
In one year:
20k events B0  K0* (K+p-) g
triggered and reconstructed
Marco Musy
Fermilab 3th May 2003
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Bc mesons
 Possible CPV with Bc J/y
D ,
Bc  DsD,
DD,
...
LHCb acceptance ~30%
 Precision measurement of mass, life-time
CDF: mBc= 6.4  0.4 GeV,
tBc ~
0.5 ps
p (GeV)
LHCb preliminary study
s(ppBc) ~300 nb  109 Bc/ year
Bc  J/y p (BR ~10-2)
e ~ 2%
12k events/year
Background from B  J/y X and prompt J/y
reduced cutting on the distance between
primary vertex and Bc vertex
M( J/y(mm) p) GeV/c2
Marco Musy
Fermilab 3th May 2003
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Current status of LHCb Physics Reach in 1 year (2fb–1)
Channel
b
Bd  J/y Ks
g
Bs  Ds K
Bd  pp, Bs  KK
Yield
Precision*
119 k
s(b)  0.6o
8k
27 k, 35 k
s(g) 10o
s(g)  3o
a
2dg
Bd  p+p-
27 k
s(a)  5o- 10o
Bs  J/y f
128 k
s(2dg)  2o
|Vtd/Vts|
Bs  Ds p
72 k
Dms up to 58 ps-1
rare decays Bd  K* g
20 k
*Precisions obtained by scaling old results with the new yields
All numbers will be updated together with more channels
in the re-optimization TDR (September 2003)
Marco Musy
Fermilab 3th May 2003
(22)
Systematics in CPV measurements
Possible sources of systematic uncertainty:
• Asymmetry of b vs b production
• Detector efficiencies which depend on charge
can bias tagging efficiencies
can fake CP asymmetries
• CP asymmetry also in background processes
 Alternate runs, swapping the orientation of magnetic field
 Use control samples available with high statistics:
Bs  Ds p
72k events/year
B0  J/y K*
600k events/year
(from Technical Proposal)


B  J/y K
600k events/year
 Study CP asymmetries in the B mass side bands
Marco Musy
Fermilab 3th May 2003
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Conclusion
 LHCb is a dedicated detector for B physics measurements in
many channels from the beginning of LHC
 A very precise determination of CKM unitarity triangle will
be possible
 Detector performances are being evaluated with a realistic
and complete Monte Carlo simulation
 LHCb offers an excellent opportunity to spot New Physics
signals beyond Standard Model very soon at LHC
Marco Musy
Fermilab 3th May 2003
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back-up slides
Marco Musy
Fermilab 3th May 2003
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p0 reconstruction
•PreShower (scintillator+Pb+scintillator) 2X0
•ECAL (Pb+ “shashlik” scintillator) 25X0
•HCAL (Fe+scintillator) 5.6 lI
s(E)/E=10% /E 1.5%
s(E)/E=80% /E 10%
pT>200 MeV
Purity ~20% in range
0.1<m <0.17 GeV/c2
Marco Musy
Fermilab 3th May 2003
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