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10 November 2008. Prospects for New Physics in CP Violation and Rare Decays at LHCb. Pascal Perret LPC Clermont On behalf of the LHCb Collaboration. b Production in LHCb. bb pair production correlated and sharply peaked forward-backward. - PowerPoint PPT Presentation
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Prospects for New Physics in CP Violation and Rare Decays
at LHCbPascal Perret LPC Clermont
On behalf of the LHCb Collaboration
10 November 2008
2
b Production in LHCb bb pair production correlated and sharply peaked forward-backward
Pascal Perret - LPC Clermont10/11/2008
collect 2fb-1 per nominal year ~ 1012 bb pairs produced per year 1 LHCb day = 100 B-factory day
Single-arm forward spectrometer : θ~15-300 mrad (rapidity range: 4.9>η>1.9)
Cross section of bb production in LHCb acceptance: σbb ~ 230 µb
B+ (40%), B0 (40%), Bs (10%), b-baryons (10%), Bc (< 0.1%)
LHCb limits luminosity to few 1032 cm-2s-1 instead of 1034 cm-2s-1 by not focusing the beam as much as ATLAS and CMS
maximizes probability of a single interaction per crossing
design luminosity soon after start-up
pp interactions/crossing
LHC
b
n=0
n=1
3
LHCb overview and performance
Pascal Perret - LPC Clermont10/11/2008
4
LHCb: vertex locator
Pascal Perret - LPC Clermont10/11/2008
VELO
Vertex Locator (Velo)Silicon strip detector 8 mm from beam with ~ 5 mm hit resolution30 mm IP resolutionDecay time resolution ~ 40 fs
5
LHCb: momentum & mass measurement
Pascal Perret - LPC Clermont10/11/2008Momentum measurement (s(p)/p ~ (0.4 + 1.5 p/TeV)%) and Mass resolution s ~14 MeV
Track reconstruction efficiency:95% for tracks with p>5 GeV
TTITOT
Magnet
Drift time tube
6
LHCb: particle identification
Pascal Perret - LPC Clermont10/11/2008
RICH: K/p identification (KK: ~96.8%, pK: ~3.9%) ; eg. distinguish Dsp and DsK events.
HPD
RICH1: 5 cm aerogel n=1.03 : 2-~10 GeV4 m3 C4F10 n=1.0014 : 10-~60 GeV
RICH2: 100 m3 CF4 n=1.0005 16-~100 GeV
7
LHCb: calorimeter
Pascal Perret - LPC Clermont10/11/2008
PS SPD
ECALHCAL
Inner Outer Middleregion
ECAL (inner modules): σ(E)/E ~ 8.2% /√E + 0.9%
Calorimeter system : • Detection of electrons, π0, γ, hadrons• Level 0 trigger: high ET electron and hadron,
photon
8
LHCb: muon system
Pascal Perret - LPC Clermont10/11/2008
Muon system: • Level 0 trigger: High Pt
muons• Muon ID: ~ 95% for 5%
hadron misID
• Multi Wire Proportional Chamber
• Triple-GEM for M1-R1
• M1 under installation …
Muons
9
LHCb: beam pipe
Pascal Perret - LPC Clermont10/11/2008
Magnet
TTSPD
Pb
M2
HCAL
ECAL
PS
Beinox
Beam pipe:Under vacuum June – Oct.Detector closed
RICH2
10
LHCb trigger system Two levels:
1st level: hardware 4 ms latency“moderate” pT m, e, g & hadrons, e.g. pT m >1.3 GeV/c : full custom made
HLT: software ~2000 CPU
Pascal Perret - LPC Clermont10/11/2008
40 MHz
1 MHz
Pile-upCalorimeter
Muon + L0DU
Level 0:High pT : m, e, h, g
4 µs
HLT:L0 confirmation m, e, h, g alleys
inclusive/exclusive Selection
Full reconstruction of event
2 kHz Storage(event size ~ 35 kB)
(Interaction rate ~ 10 MHzb hadron inside LHCb ~50 kHz)
HLT rate Event type Physics
200 Hz
Exclusive B candidates
B (core program)
600 Hz
High mass di-muons
J/, bJ/X (unbiased)
300 Hz
D* candidates Charm (mixing & CPV)
900 Hz
Inclusive b (e.g. bm)
B (data mining)
11
Status of LHCb LHCb detector fully installed and commissioned, including L0
trigger All sub-detectors have undergone the first readout synchronisation
and alignment with cosmics & LHC beam induced particles
Pascal Perret - LPC Clermont10/11/2008
OT Calo MuonTop view
Events with LHC beam induced particles
OT
Calo
Muon
Side view
Splashy event from lost particles (not all tracks reconstructed...)
Clean event from halo muonsVelo
F. Dett
ori
poste
r
12 Pascal Perret - LPC Clermont10/11/2008
t,c,u
t,c,u
W W
s,d
b s,d
b
0B 0B
Box diagram
0B,K0
s
b
s,ds
s,d
ss
Penguin diagram
stsSMstd
SMd
tstdSM
VV
Vm
2arg,2arg 22
2,
New Physics in CPV Unitarity Triangles
Overconstrain the unitarity triangles (consistency checks)
Bs
Bd0 p p
Bd0 r p
BS0 DS p
Bd0 J/ KS
0
Bd
a
g
VudVub VtdVtb
VcdVcb
* *
*Bd0 DK*0
BS0 DSK
Bd0 D* p,3p
BS0 J/
s
VtsVtb
VcsVcb
*
VusVub*
*
13 Pascal Perret - LPC Clermont10/11/2008
t,c,u
t,c,u
W W
s,d
b s,d
b
0B 0B
Box diagram
0B,K0
s
b
s,ds
s,d
ss
Penguin diagram
stsSMstd
SMd
tstdSM
VV
Vm
2arg,2arg 22
2,
New Physics
?
?
d
m
s
New Physics in CPV
b-physics measurements probe New Physics and are complementary to direct searches
New particles may show up in loop process
Unitarity Triangles
Overconstrain the unitarity triangles (consistency checks)
will allow to understand the nature and flavour structure of possible New Physics ones
Bs
Bd0 p p
Bd0 r p
BS0 DS p
Bd0 J/ KS
0
Bd
a
g
VudVub VtdVtb
VcdVcb
* *
*Bd0 DK*0
BS0 DSK
Bd0 D* p,3p
BS0 J/
s
VtsVtb
VcsVcb
*
VusVub*
*
14
g Measurements from Bs Ds K+
Interference between 2 tree diagrams via Bs mixing: BsDs
K (b c) and BsDsK (b u) (+ CP conjugates)
Pascal Perret - LPC Clermont10/11/2008
Measure g + s in a clean way (no theoretical uncertainty) from time dependent rates
Use s from Bs J/
Include Bs Dsp (20x Br) to determine Δms ΔΓs and tagging dilution
Simultaneous fit to Bs→Dsp and Bs→DsK decay time distributions (tagged and untagged) 10 fb-1 data:
Bs→ Ds-p
Bs→ Ds-K+
(ms = 20)
Mode Sig. yield
B/S
Bs→DsK 6.2k 0.7
Bs→Dsp 140k 0.2
Sensitivity
2 fb-1 10 fb-1
s stat(g)° 10.3 4.6
15
g Measurements Different ways to measure g at LHCb:
Pascal Perret - LPC Clermont10/11/2008
Compare angle g measured from interfering tree decays (which should always take the value from the CKM matrix) to angle measured from penguin diagrams:
Any difference is a sign of New Physics
B mode D mode Method s(g) 2fb-1
Bs→DsK KKp Tagged, A(t) 10º
B+→D K+ Kp+ K3p +KK/pp counting, ADS+GLW 5º - 13º
B+→D K+ Kspp Dalitz, GGSZ 7-12º
B+→D K+ KKpp 4 body Dalitz 18º
B0→D K*0 Kp + KK + pp counting, ADS+GLW 9º
B→pp,KK - Tagged, A(t) 10º
2 amplitudes, b→c (dominant) & b→u (color suppressed), interfere in decays to a common D0 and D0 modes state:
Global fit of all the channels: σ(g) = 4.3-6.2° with 2fb-1Tr
ee d
ecay
s on
ly
Penguin amplitudes:Interference of b→u tree & b→d(s) penguin diagrams
Other modes under study: B+→D*(D → Kp/KK/pp) K+, B+→D(→ Kppp)K+, …
16
s measurements from Bs J/
Pascal Perret - LPC Clermont10/11/2008
t,c,u
t,c,u
W W
s,d
b s,d
b
0B 0B+NP?
e(1-2w)2
Muon 0.8Electron 0.4
K (OS) 1.5
K (SS) 2.1
Q vertex 1.1
Invariant mass ofBsJ/(mm)
The measure of Bs-Bs mixing phase s in BsJ/(µµ) is sensitive to New Physics effects in mixing: s = s(SM) + s(NP) in SM: s = – 2βs = arg(Vts
2) ~ –0.04 Tevatron: s ~2.2s away from SM
(central experimental value -0.77) It is not a pure CP eigenstate (VV decay).
• 2 CP even, 1 CP odd amplitude • need to fit angular distributions of decay
final states as function of proper time• Good proper-time resolution is essential: ~39fs• Good tagging of initial Bs flavour :
• Combined = 6.2%• Good mass resolution: 13 MeV• Good particle identification
• e(KK)~80% e (pK)~ 3%
17
BRvis[BsJ/(µµ)(K+K-)]= (3.1±1.1)x10-5
With 2 fb-1 (1 nominal year): 114k reconstructed events (before
tagging)S/B ~2s stat(s) ~0.03
• 5σ NP discovery, if s >0.1! Low systematic uncertainties:
• Proper time acceptance: no bias from selection• Angular resolution: very good & negligible• Mistag and proper time are crucial…
Already at the start-up with 0.5 fb-1:28.5k reconstructed eventss stat(s) ~0.06LHCb should rapidly pin down whether really sign of new physics …
s measurements from Bs J/
Pascal Perret - LPC Clermont10/11/2008
ηf = +, - 1 CP eigenstates
18
New Physics in rare decays
Pascal Perret - LPC Clermont10/11/2008
19 s = (mmm)2 [GeV2]
AFB(s), theory Forward-backward asymmetry AFB(s) in the mm rest-frame is sensitive NP probe Uncertainties from Bd→K* transition form-
factors cancel zero of AFB(s) depends on Wilson
coefficients C7eff/C9eff
New Physics in BdK*0mm
Pascal Perret - LPC Clermont10/11/2008
gluino, chargino,neutralino, ?
Higgs, ?
Flavour Changing Neutral Current Decay in SM: b s electroweak penguin NP diagrams could contribute at same level
Sensitive to magnetic and vector and axial semi-leptonic penguin operators
Decay described by three angles (θl, φ, θK) and di-μ invariant mass q2
20
New Physics in BdK*0mm
Current Measurements: BR measured at B-factories, in
agreement with SM: 1.1 ±0.3x10-6
AFB also: Belle has ~230 K*ll events LHCb sensitivity:
Expected yields: 7.2k events/2fb–1 Background:
• dominated by b→ m, b→ m, symmetric distribution in θl observed
• b→ m, b→ c → m significant contribution, asymmetric θl distribution …
• B/S ~0.2Acceptance correction …
Simple linear fit suggests precision:
Pascal Perret - LPC Clermont10/11/2008
NB: Opposite sign convention w.r.t. LHCb657 MBB
0.5 fb-1 2 fb-1 6 fb-1
s(s0) 0.8 GeV2 0.5 GeV2 0.3 GeV2 More complex fit methods being evaluated
q2(GeV2)
An example 0.5fb-1 experiment
AFB
21
New Physics in Bsmm
Pascal Perret - LPC Clermont10/11/2008
SM SM MSSM
W
W
b
s
m
t
m
? ?
~ tan6/MH2
Helicity suppressed and in SM: BR(Bs → mm) = (3.4 ± 0.5) 10-9 sensitive to New Physics; could be strongly enhanced in SUSY Current limit from CDF: BR(Bs → mm) < 4.7 10-8
Event selection Main issue is background rejection:
dominated by B → mX, B → m X decays good mass resolution and PID essential SM Yield (2 fb-1): Signal: 23 – Bkg: 150 Statistical method applied to separate signal from background using PID, vertexing, mass
CDF Sensitivity with 8fb-1?
Sensitivity
0.1 fb-1 0.5 fb-1 2 fb-1 6 fb-1
BR SM BR < 10-8
(CDF limit)Excluded <SM
3 s evidence
5 s observation
22
Summary Few hints of deviation from SM in b-physics are observed …
Flavour physics at the LHC will play a central role in the understanding of any new physics signals
LHCb offers exciting prospects for precision measurement and search for new physics in CP violation & rare decays: with 10fb-1
g measurements:with trees: a combined sensitivity of sg~2-3o is expectedwith loops: g with a sensitivity of sg~5o is expected
s measurements: s (s) ~0.01 Rare decays:
BdK*0mm : s(s0) =0.3 GeV2
Bsmm :5 s observation of SM value Ready and waiting for the first collisions!
With fraction of a 1 year nominal data set LHCb can already perform important key measurements probing New Physics
Pascal Perret - LPC Clermont10/11/2008
Many topics not addressed in this talk: a, measurements, charm physics, radiative decays … (Many channels still to be investigated …) F. Dettori
poster