Transcript LHCb: status and perspectives Yu. Guz, IHEP, Protvino

LHCb:
status and perspectives
Yu. Guz, IHEP, Protvino
on behalf of the LHCb collaboration
1.
LHCb detector status
2.
Key measurements
3.
LHCb upgrade issues
4.
Conclusions
1
LHCb: A Large Hadron Collider experiment for Precision
Measurements of CP Violation and Rare Decays
>700 physicists, 50 institutes, 15 countries
ATLAS
CMS
ALICE
2
LHCb experiment
-
LHC: √s=14 TeV, σinelastic~80mb, σ(bb)~0.5mb
The bb production is sharply peaked forwardbackward.
b
b
b
PT of B-hadron
LHCb is a single arm detector 1.9<|η|<4.9
B hadron signature: particles with high PT
(few GeV); displaced vertex (~1cm from
primary vertex)
Reconstruction of B decays is based on:
• good mass resolution
• excellent particle id to reject background
• good proper time resolution to resolve B0S
oscillations
b
bb angular
distribution
100μb
230μb
Pythia
η of B-hadron
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The LHCb detector
Main components:
• silicon strip vertex
detector
• magnet
• tracker stations (inner
area: silicon; outer:
straw tubes)
• two RICH detectors
• EM calorimeter with
preshower
• muon system
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ready to take
data !
The LHCb detector : is
installation
is complete
Muon det
Calo’s
RICH-2
OT+IT
Magnet
RICH-1
VELO
a beam-gas event 10/09/08
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LHCb detector performance
Detailed Geant4 simulation
• proper time resolution ~ 40 fs
BsDs(KKπ)K
• effective mass resolution ~ 20 MeV
• good K/π separation up to ~60 GeV
proper time resolution ~ 40 fs
ε(KK) : 97%
ε(πK) : 5%
Eff. mass resolution ~ 20 MeV
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LHCb operation at LHC
Inelastic pp interactions σ ~ 80 mb
Bunch crossing frequency: 40 MHz
Design LHC luminosity 1034 cm-2s-1
Nominal LHCb luminosity:
2∙1032 cm-2s-1
(appropriate focusing of the beam)
Expect ≥2 fb-1 / year
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LHCb trigger
L0, HLT and L0×HLT efficiency
L0 Trigger: hardware, 4 μsec latency
High ET (h>3.5 GeV; e, γ>2.5 GeV;
μ, μμ>1GeV)
Pileup VETO
Output rate ~1 MHz
High Level Trigger: software, two
stages: HLT1 and HLT2
HLT1: confirm L0 objects, with
T, VELO, optionally IP cuts …
output ~ 30 kHz
HLT2: full reconstruction,
exclusive and inclusive candidates
Output 2 kHz  storage, event size
~35 kB
HLT
rate
Event type
Physics
200 Hz
Exclusive B decay
candidates
B (core programme)
600 Hz
High mass dimuons
J/, bJ/X
(lifetime unbiased)
300 Hz
D* candidates
Charm (mixing &
CPV)
900 Hz
Inclusive b (e.g.
bm)
B (data mining)
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Flavour tagging
e-mB0opposite
PV
Bs0signal
K+
D
Qvertex ,QJet
K-
K
K
Same side
– Fragmentation K± accompanying Bs
– π± from B** → B(*) π±
Effective tagging efficiency:
εD2= ε(1-2ω)2
ε : tagging efficiency
ω: wrong tag fraction
Opposite side
– High Pt leptons
– K± from b → c →
s
– Vertex charge
– Jet charge
Tag
Bd %
Bs %
Muon
1.1
1.5
Electron
0.4
0.7
Kaon opp.side
2.1
2.3
Jet/ Vertex Charge
1.0
1.0
Same side p/p/K
0.7 (pp)
3.5(K)
Combined (Neural Net)
~ 5.1
~9.5
LHCb key measurements
► CP-violation
►charm physics
✔ φS
✔Mixing
✔ γ in trees
✔ CP violation
✔ γ in loops
► rare B decays
✔ BS μμ
✔B
K*
μμ
►other
✔ τ  3μ (analysis
is ongoing)
✔ ...
✔ photon polarization in
radiative penguin decays
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Physics program
2008 (beginning of 2009?): Lumi ~1031 cm-2s-1 10 TeV
~108 sample of minimum bias; L0+proto-HLT trigger, collect ~ 5 pb-1
Calibration, alignment, minimum bias physics, charmonium production
2009: Lumi 2 1032 cm-2s-1 14 TeV
L0 + HLT , collect ~ 0.5..1 fb-1
B Physics: calibration CP (sin2β, Δms ); key measurements (βs, Bsμμ, …)
2010-2013: Luminosity 2-5 1032 cm-2s-1
collect total of ~10 fb-1
Full physics program Phase I
2013+: Upgrade proposed to run at 2 1033 cm-2s-1.
Collect ~ 100 fb-1
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CP violation
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φS measurement
Key measurement for 2009
φS is small in SM: φS =-2βS =-2λ2η ≈ -0.036
sensitive probe for New Physics: φS = φSSM + φSNP
Tevatron results:
D0
2bs=  0.57 + 0.24-0.30 with with 2.8 fb-1
CDF 2bs = [0.32,2.82] @ 68%CL with 1.35 fb-1
Measure from time dependent CP asymmetry in bccs
(BS  J/ψ φ, BS  J/ψ η(η’), BS  ηCφ, BS  DSDS, …)
“golden mode” BS  J/ψ φ : high BR (~130k per 2 fb-1)
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φS measurement
J/ψ φ is not a pure CP eigenstate:
angular analysis is necessary to
separate CP-odd and CP-even
Other bccs processes (J/ψ η, ηCφ,
DSDS) can be added: angular analysis
not needed, but smaller statistics
The BSM effect in φS can be
discovered or excluded with
2008/2009 LHCb data
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angle γ
Measured values
90% CL
Fit results
90% CL
α
87.5 +31.1-10.2
90.7 + 16.8 - 5.4
β
21.5 +2.0-1.9
21.7 + 2.0 - 1.8
γ
76.8 +52.7-50.4
67.6 + 5.3 - 15.9
Least constrained by
direct measurements
Key measurement of LHCb
Comparison of γ measurement in trees with fitted values, as well as
with measurement in loops, is a sensitive probe of New Physics
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angle γ
From tree amplitudes : BS  DSK
Time dependent CP asymmetry
1
1
2 From tree amplitudes: B±DK±, B0DK*
comparison of counting rates:
ADS - use doubly Cabibbo-suppressed
D0 decays, e.g. D0  K+πGLW: Use CP eigenstates of D(*)0 decay,
e.g. D0  K+K- / π+π–, Ksπ0
Dalitz: Use Dalitz plot analysis of 3-body
D0 decays, e.g. Ks π+ π-
2
3
From penguins : B  h h
Sensitive to New Physics  compare
“effective” γ with tree measurements
3
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γ from BSDSK
• interference between tree level decays
via mixing
• insensitive to New Physics
• Measures  + 2bs (bs from Bs  J/)
• Bs  Dsp
• 10 times higher branching ratio
• suppressed using PID by RICH
• used for determination of Δms, ΔΓs and
mistag rate
Channel
Yield 2 fb-1
B/S (90% C.L.)

BSDSK
6.2 k
[0.08-0.4]
BSDSp
140 k
[0.08-0.3]
Sensitivity at 2 fb-1: σ(γ+φs) = 9o–12o
Bs0 ( t )
0
s
f e
i s 
Ds K 
B ( 0)
 f ei
e 2 i
s 
Bs0 (t )

s
u K

c
s D s
B0s bs




B0s bs
Ds K 




s D 
s
c
u K –
s




Bs→ Dsp
Bs→ DsK+
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γ from BDK
Measure rates of different BDK modes, where D decays into:
KŦπ±; CP eigenstates h+h-(h=K,π) (combined ADS+GLW method)
Colour favoured
Double Cabbibo
suppressed
rDe
i DKp
Colour suppressed
rB ei ( B  )
Cabbibo favoured
rD=0.0611 known to ~1% from
elsewhere
Nhh/NKπ measurable to ~3%
6 equations, 5 unknowns
Decays into KŦ(3π)± can also be included: add 4 equations 2 unknowns
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γ from BDK
Channel
Yield (2 fb-1)
B/S
B → D(hh) K
7.8 k
1.8
B → D(Kp) K
favoured
56 k
0.6
B → D(Kp) K
suppressed
0.71k
2
B → D(K3p) K favoured
62k
0.7
B → D(K3p) K suppressed
0.8k
2
σ(γ) = 8o–10o in 2 fb-1 (depending on strong phases)
Other methods :
B± → DK± with D → Ksππ
B± → DK± with D → KKππ
(Dalitz analysis)
(Dalitz analysis)
B0 → DK*0 with D → KK, Kπ, ππ
B± → D*K± with D*Dπ, γ; D → KK, Kπ, ππ
All methods combined: σ(γ) ~ 5o from BDK with 2 fb-1 of data
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γ from Bhh
time-dependent CP asymmetries in Bπ+πand BSK+K- :
ACP (t ) 
C cos( m t )  S sin( m t )
  
  
cosh 
t   A sinh 
t
 2 
 2 
Extract C and S :
C(Bππ) = f1(d, θ, γ)
S(Bππ) = f2(d, θ, γ, φd)
C(BSKK) = f3(d’, θ, γ)
S(BSKK) = f4(d’, θ, γ, φS)
deiθ = ratio of penguin and tree
amplitudes in Bπ+πd’eiθ’ = ratio of penguin and tree
amplitudes in BSK+K-
U-spin symmetry (d  s) : d=d’ and θ=θ’
φd and φs known from BdJ/ψ Ks and BSJ/ψ φ
4 observables , 3 unknowns
Expected sensitivity:
σ(γ) ~ 10o with 2 fb-1
σ(γ) ~ 10o with 2 fb-1
Channel
Yield
(2 fb-1)
B/S
Bpp
36k
0.5
BsKK
36k
0.15
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Rare B decays
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BSμμ
Strongly suppressed in SM by helicity: Br= (3.35 ± 0.32) x 10-9
Sensitive to NP models with S or P coupling
MSSM: Br ~ tan6β/MA4 .
• Current limits from Tevatron:
• CDF BR < 4.7 10-8 90 % CL
• D0 BR < 7.5 10-8 90 % CL
LHCb sensitivity
(SM branching ratio) :
• 0.1 fb-1 BR < 10-8
• 0.5 fb-1 BR < SM expectation
• 2 fb–1: 3 evidence
• 10 fb–1: 5 observation
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Bsφγ
In SM photon from bsγ is left-handed,
from bsγ right-handed
 φγ final states in B and B do not interfere
 CP asymmetry in mixing cannot occur
Measuring time-dependent CP asymmetry is a
probe for NP
ACP (t ) 
b   (L) + (ms/mb)  (R)
( BS   )  ( BS   )
A cos mt  Amix sin mt
 dir
( BS   )  ( BS   )
 t 
 t 
cosh 
  A sinh 

2
2




In SM:
Adir  0, Amix  sin 2ψ sin 2β
Channel
Yield
B/S
AΔ  sin 2ψ cos 2β
(2 fb-1)
tan ψ = |b→sγR| / | b→sγL|
11k
<0.55
Bs→
cos 2β  1
Statistical precision after 1 year (2 fb-1)
(Adir ) = 0.11 , (Amix ) = 0.11 (requires tagging)
(A) = 0.22
(no tagging required)
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Afb(s) 
BdK*μμ
● Zero crossing point of forward-backward
asymmetry AFB in θl angle, as a function of mμμ
precisely computed in SM:
s0SM(C7,C9)=4.39(+0.38-0.35) GeV2
● sensitive to NP contribution
2 fb-1
s0
(s0) = 0.5 GeV2
s = (mmm)2 [GeV2] 
(resonances excluded)
Channel
Yield (2 fb-1)
BG (2 fb-1)
Bs→K*m+ m–
7200+-2200 (BR)
1770+-310
B factories total ~ 1000 events by now
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Charm & tau
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Dedicated D* trigger
2 charged tracks from a detached vertex with -700<(mππ-mD0)< 50 MeV;
+ another charged track matching the hypothesis of D*D0π decay
(vertex, Δm)
D0s are flavor tagged with π from D* decay
Two sources of D0s in LHCb:
 from B decays
 favoured by LHCb triggers
 prompt production in primary interaction
Estimated annual yields (per 2 fb-1) from B decays:
D0K-π+ (right sign) 12.4 M
D0K+π- (wrong sign) 46.5 k
D0K+K1.6 M
D0π+π0.5 M
Similar amounts expected from prompt production
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LHCb prospects for Charm physics studies
D0 mixing
x
M1  M 2

y
1  2
2
 Time-dependent D0 mixing with wrongsign D0K+π- decays
 Strong phase δ between DCS and CF
amplitudes: (x,y)(x’,y’)
 Lifetime ratio: mean lifetime (DK- π+)
The mixing has been
and CP even decay DK+K-(π+π-)
2
0
 
 Rm  1 recently observed
 (D  K p )
yCP 

1

y
cos


x
sin



 ( D 0  K  K  , p p _ )
 2  (Belle, BaBar, CDF)
yCP=y in absence of CP violation (φ=0)
0.26
LHCb sensitivities with 10 fb-1:
σstat(x’2) ~ 6.4·10-5, σstat(y’) ~ 8.7·10-4;
σstat(yCP)~ 4.9·10-4
x = 0.89±
0.27
%
0.17
y = 0.75±0.18 %
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LHCb prospects for Charm physics studies
 Direct CP violation can be measured in D0KK lifetime
asymmetry
 ACP<10-3 in SM, up to 1% with New Physics
 current HFAG average Belle, BaBar, CDF): ACP = -0.16 ± 0.23
LHCb sensitivity with 10 fb-1: σstat(ACP) ~ 4.8·10-4
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τ3μ (preliminary)
Present upper limit:
Br(τ3μ) < 3.2·10-8 @90%CL (Belle)
Br(τ3μ) < 5.3·10-8 @90%CL (BaBar)
Preliminary analysis shows that at 2fb-1 LHCb can obtain upper limit
of ~6·10-8
The result is not final: background estimate may change, event
selection refined.
background
τ3μ
σ=8.6 MeV
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Upgrade issues
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10 fb-1 will be collected by 2013
Sensitivities for 100 fb-1
• φS measured to 0.023
• γ to 2 - 5o
• BS μμ observed at 5σ level
• many more excellent physics
results
next step – collect 100fb-1
Probe/measure NP at % level
• have to work at > 1033cm-2s-1
• upgrade is necessary
Also studying Lepton Flavour Violation in mmm
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LHCb at higher luminosity
• The L0 hadron trigger saturates the bandwidth (1 MHz) at
2·1032 cm-2s-1
• typical L0 efficiency for purely hadronic final states ~ 50%
will drop with luminosity
• apart from the trigger, the LHCb performance does not
deteriorate significantly up to 1033 cm-2s-1
• A 40 MHz readout of all the detectors is the only way to
achieve 1033. Introduce first level trigger on detached vertex
on a CPU farm
LHC schedule
• Phase 1: IR upgrade. Install new triplets β*=0.25m in IP1 and
5. Requires 8 month shutdown in 2012-2013
• Phase 2: inner detectors of ATLAS and CMS need to be
replaced. 18 month shutdown in ~2017
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LHCb upgrade strategy
the main effort is to upgrade by 2014 all Frontend
Electronics to 40 MHz readout.
• perform also necessary upgrade of subdetectors
• replace readout chips in the vertex detector (VELO)
• RICHs: the readout chips are encapsulated inside
photodetectors  replace all photodetectors !
• Tracking system: replace all Si sensors, as readout chips
are bonded on hybrids
• run from 2014 at 1033 cm-2s-1 until the Phase 2 shutdown.
Reach 20 fb-1.
in 2017 upgrade the subdetectors for >2·1033 cm-2s-1
• fully rebuild vertex detector (pixels or 3D)
• rebuild Outer Tracker, replace central part of EM
calorimeter, …
• run at highest possible luminosity for 5 years.
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Conclusions
• The LHCb detector at LHC is commissioned and ready to take data
• key measurements with 2009 data:
• φ S:
precision ~0.023
• BSμμ : sensitivity ~ SM expectations
• Full physics program in 2010-2013 at 10 fb-1:
• angle γ (precision of ~5o with 2 fb-1 )
• search for New Physics in photon polarization in bsγ
• precision measurement of AFB in BK*μμ
• Charm physics: D0 mixing, direct CP violation in D0KK(ππ)
• and much more…
• 2013+: upgrade of the detector, aiming to reach 100 fb-1 at operating
luminosity of 1033cm-2s-1 (and >2·1033 cm-2s-1 in 2017+)
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Backup
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τ3μ (preliminary)
τ3μ Event selection
cuts per track:
❚ PT
> 0.4 GeV
❚ IP(m)/IP > 3.0
❚ dLLm
> -3
Main source of τ: DS decays
cuts per 3m vertex:
❚ 2
< 9
❚ |V3m-Vprim|/  > 3
❚ Z3m-Zprim
> 0 cm
❚ IP()/IP
< 3
Background rejection: 4.9·10-9
2 fb-1: 5.6·1010 τ produced
Per 2 fb-1 ~2200 bg evts expected
Signal selection efficiency: 2.3%
 upper limit 78.5 ev
Corresponds to Br limit 6.1 ·10-8
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