View
225
Download
1
Tags:
Embed Size (px)
Citation preview
LHCb - The Future of LHCb - The Future of Heavy Flavour ExperimentsHeavy Flavour Experiments
LHCb - The Future of LHCb - The Future of Heavy Flavour ExperimentsHeavy Flavour Experiments
Franz MuheimUniversity of Edinburgh
Beauty and Charm Decays: A Window on New Physics
In honor of Sheldon Stone's 60th birthday
May 20-21, 2006, Syracuse, NY
Syracuse, 20 May 2006 F. Muheim 2
OutlineOutline Physics Motivation
– UT triangles– NP sensitivity
LHCb experiment at LHC– B physics at Hadron Colliders– LHCb detector– Vertexing– RICH– Trigger– Status
Physics Programme– Bs oscillations and CP violation– CKM angle gamma– Rare decays– Sensitivities
LHCb Upgrade– Luminosity, Detector– Physics motivation
Conclusions
Syracuse, 20 May 2006 F. Muheim 3
Standard Model rho-eta fitsStandard Model rho-eta fits
New Status including CDF Bs oscillation measurement - ms
Standard Model is very successful 1.7 discrepancy between Sin2 and Vub inclusive
Syracuse, 20 May 2006 F. Muheim 4
b
B0
t
s
s
W
ss
s
s
Motivation for Flavour PhysicsMotivation for Flavour Physics
Standard Model
W
W
b
Bs0
s
b
s
B s
0
t
t
–Bs-Bs oscillations
Supersymmetry New Physics
?
Bs penguin decay
Standard Model (SM) is a low-energy effective theory– Based on more fundamental theory manifest at a higher energy scale– Expect new particles and/or symmetries likely in the TeV region
How to probe New Physics (NP) ? – Discovery of new particles at energy frontier (LHC)– NP appears as virtual particles in loop processes leading to observable
deviations from SM expectations in flavour physics and CP violation ( )
?
Syracuse, 20 May 2006 F. Muheim 6
B-Physics at the LHC vs B-B-Physics at the LHC vs B-Factories Factories
ee (4S) BBPEPII, KEKB
ppbbX (√s = 14 TeV, tbunch=25
ns)LHC - LHCb, ATLAS/CMS
Production bb 1 nb ~500 b Typical bb rate 10 Hz 100–1000 kHz
bb purity ~1/4 bb/inel = 0.6%Trigger is a major issue !
Pileup 0 0.5–5
b-hadron types B+B– (50%)B0B0 (50%)
B+ (40%), B0 (40%), Bs (10%)Bc (< 0.1%), b-baryons (10%)
b-hadron boost Small Large (decay vertexes well separated)
Production vertex Not reconstructed Reconstructed (many tracks)
Neutral B mixing
Coherent B0B0 pair mixing
Incoherent B0 and Bs mixing(extra flavour-tagging dilution) Event
structure BB pair alone Many particles not associated with the two b hadrons
Syracuse, 20 May 2006 F. Muheim 7
Large Hadron Collider --- LHCLarge Hadron Collider --- LHC
with a B-physics programme LHCb
dedicated for precision measurements of CP violation and rare decays in B hadrons
ATLAS/CMS optimized for high-pT discovery physics competitive for channels with leptons
Mont Blanc
Lake GenevaChâteau Farges
ATLAS
Syracuse, 20 May 2006 F. Muheim 8
LHC interaction points– 40 MHz pp interaction rate, bunch crossing every 25 ns
– cross section inel = 80 mb Luminosity
– Starting luminosity L = to cms
– Design luminosity L = cms
ATLAS/CMS – run at highest available luminosity– expect L<21033 cm–2s–1
n < 5 for first 3 years– n = 25 at L=1034 cm–2s–1
LHCb– Luminosity tuneable by adjusting beam focus– run at L ~ 21032 cm–2s–1
(max. 51032 cm–2s–1)– little pile-up (n = 0.5)– less radiation damage – Luminosity will be available for 1st physics run
2 fb–1 / year10 fb–1 in 5 years1 year = 107 s
10 fb–1 / year at low L30 fb–1 total at low L
Luminosities at LHCLuminosities at LHC
n = # of pp interactions/crossingn = # of pp interactions/crossing
LH
Cb
n=0
n=1
AT
LA
S/C
MS
Syracuse, 20 May 2006 F. Muheim 9
VELO
collision point
~1 cm
B
Dipolemagnet
Crucial for B physics:• optimised geometry and choice of luminosity• Trigger efficient in hadronic & leptonic modes • excellent tracking and Vertexing (m, )• excellent particle ID - RICH
LHCb ExperimentLHCb Experiment
Syracuse, 20 May 2006 F. Muheim 10
LHCb TriggerLHCb Trigger
Level-0 (Hardware)High pT - , , e, , hadron + pileup synchronized (40 MHz), 4 s latency
10 MHz (visible bunch crossings)
1 MHz (full detector readout)
≤ 2 kHz (storage media)
Output rate
Event type Physics
200 Hz Exclusive B candidates
Specific B final states
600 Hz High mass di-muons
J/, bJ/X (unbiased)
300 Hz D* candidates CharmCalibrations
900 Hz Inclusive b (e.g. b)
B (data mining)
HLT (PC farm ~2000 CPUs)Confirm Level-0Associate tracks with minimum impact parameter and pT , e, h, alleysInclusive/exclusive selections
L0 efficiency
Syracuse, 20 May 2006 F. Muheim 11
VELO – Vertex Locator – laid out as a series of R and Φ silicon detector stations– 0.8 cm to the beam line, situated inside beam vacuum
vessel
Detached Vertex Trigger– Allows to select B-meson vertices
High efficiency for all decay modes– Gives excellent proper time resolution
Vital for resolving Bs oscillations
VELO – Silicon Vertex DetectorVELO – Silicon Vertex Detector
BsDs proper time resolution
t ~ 40 fs
VELO – Silicon Vertex DetectorVELO – Silicon Vertex Detector
Syracuse, 20 May 2006 F. Muheim 12
Charged particle Identification– LHCb has 2 RICH detectors with 3 radiators– Allows clean separation of different Bh+h modes– Not possible elsewhere at hadron colliders.
CDF data
Bd signalBd
signal
BsKK signal
Tevatron
Ring Imaging Cherenkov Ring Imaging Cherenkov DetectorsDetectors
Syracuse, 20 May 2006 F. Muheim 13
Installation StatusInstallation Status
RICH2Muon system
CalorimeterECAL, HCAL
DipoleMagnet
RICH1
Syracuse, 20 May 2006 F. Muheim 15
LHC StatusLHC Status
LHC start– July 2007 – 1st beam in late 2007– Physics operation in 2008
Cryogenic services
line
LHC dipole
LHC tunnel
Syracuse, 20 May 2006 F. Muheim 16
LHCb Physics ProgrammeLHCb Physics Programme
~Vub* ~Vtd
~Vcb
~Vub* ~Vtd
~Vts
S0s
s
DB
m
)('0s ΨJ,ΦΨJB
0S
0d KΨJB
πππB 00d
KDB s0s
000d
0d
KDBKDB
KKBandB 0s
0d
and
B production , Bc , b-baryon physics Charm decays Tau Lepton flavour violation
Rare decays - very sensitive to NP– Radiative penguin e.g. Bd K* , Bs Φ
– Electroweak penguin e.g. Bd K*0
– Gluonic penguin e.g. Bs ΦΦ, Bd ΦKs
– Rare box diagram e.g. Bs
Syracuse, 20 May 2006 F. Muheim 17
BBss Oscillations Oscillations Precision measurement of ms
– is one of the first goals of LHCb physics programme– Expect 80k Bs Ds
+ events per year (2 fb–1) with t ~ 40 fs– S/B ~ 3 derived from 107 fully simulated inclusive bb events
5 observation for ms < 68 ps–1 with 1 year/ 2 fb–1 ms < 40 ps–1 in ~1 month /0.25fb–1Distribution of unmixed
sample after 1 year (2 fb–1) assuming ms = 20 ps-1
CDF measurement
Syracuse, 20 May 2006 F. Muheim 18
CP Violation in Bs mesons– Interference between Bs mixing and decay– Bs J/ is the Bs counterpart of B0J/ KS
– Bs weak mixing phase s is very small in SM
s = –arg(Vts2) = -2 ≈ –22 ≈ –0.04
sensitive probe for New Physics– J/ final state contains two vectors
Angular analysis needed to separate CP-even and CP-odd amplitudesFit for sin s, s and CP-odd fraction (using external ms value)
s Sensitivity – at ms = 20 ps–1
– Expect 125k Bs J/ signal events per 2 fb–1 (1 year) with S/Bbb > 3– Expected precision (sin s) ~ 0.031
– Small improvement s by adding pure CP modes, e.g. J/, J/’, c (sin s) ~ 0.013 for 10 fb-1 (first 5 years)
~3 evidence for s ≈ –0.04 (SM) Bs Lifetime difference s/s
– Expected sensitivity (s/s) ~ 0.011 using Bs J/ events
– Similar sensitivity in untagged semileptonic Bs Ds-l+ eventsExpect 700k events per 2 fb–1
ss and and ss from B from BssJ/J/
Syracuse, 20 May 2006 F. Muheim 19
from Bfrom Bss D DssKK
Two tree decays (bc and bu) of O(3)– Interference via Bs mixing
– Weak phase of Vub = e-i for bu diagram
– Theoretically clean
– Insensitive to New Physics Large background ~20
– from Cabibbo allowed decay
– need RICH, residual background ~10% Expect 5.4 k events in 1 year
– S/Bbb > 1 at 90% CL
ss DB0
With RICH
Vub
Vcb
Syracuse, 20 May 2006 F. Muheim 20
Fit the 4 tagged time-dependent rates:– Extract + s, strong phase
difference , amplitude ratio
– Bs Ds events used in fit
to constrain other parameters (mistag rate, ms, s …)
Sensitivity for – () ~ 14 in 2 fb-1 or 1 year
for ms = 20 ps–1
– Precision statistically limited– 8-fold ambiguity can
be resolved ( 2-fold) if s large enough, or using B0 D together with U-spin symmetry (Fleischer)
Both DsK asymmetries (after 5 years, ms = 20 ps–1)
Ds–K+: info on + ( + s)
Ds+K–: info on – ( + s)
from Bfrom Bss D DssKK
Syracuse, 20 May 2006 F. Muheim 21
()
dBs KK (95% CL)
B
(95% CL)
from Bfrom B and B and BssKKKK
Measure time-dependent CP asymmetry
– Adir and Amix depend onCKM angle , mixing phases d and s, and ratio of penguin-to-tree amplitudes (d ei)
U-spin symmetry (d s)– Assume d=dKK and =KK
– 4 measurements and 3 unknowns (, d and )using d from Bd-> J/KS and s from Bs-> J/
– Extract angle LHCb sensitivities
– Event yields - 1 year data set, 2fb-1
26k B and 37k BsKK
– Precision - () ~ 5
)sin()cos()( tmAtmAtA mixdirCP
R. Fleischer, PLB 459 (1999) 306 Bd/s
Bd/s
/K
/K
/K
/K
– Sensitive to New Physics in penguins– Uncertainty from U-spin assumption
Syracuse, 20 May 2006 F. Muheim 22
Dunietz variant of Gronau-London-Wyler method (GLW)– Two colour-suppressed diagrams with
|A2|/|A1| ~ 0.4 interfering via D0 mixing
Measure 6 decay rates (self-tagged + time-integrated):– LHCb expectations for 2 fb–1 (=65, =0)
from Bfrom B00 D D00KK**00
Mode (+ cc) Yield S/Bbb (90%CL)
B0 D0 (K) K*0 3.4k > 2
B0 D0 (K) K*0 0.5k > 0.3
B0 D0CP (KK) K*0 0.6k > 0.3
Sensitivity () ~ 8 in 2 fb-1
A1 = A(B0 D0K*0): bc transition, phase 0
A2 = A(B0 D0K*0): bu transition, phase +
A3 = 2 A(B0 DCPK*0) = A1+A2, because DCP=(D0+D0)/2
d
b
d
s
u
c
B0
D 0
K*0
D0
d
b
d
s
c
u
B0
K*0
Syracuse, 20 May 2006 F. Muheim 23
Two interfering tree processes in charged B decay
Decays common to D0 and D0
– Interference effects depend on 3 parameters – b→u , b→c interferencerB – the amplitude ratio betweend two diagrams (0.1 – 0.2)δB – a CP conserving strong phase difference
– i) Cabbibo favoured self-conjugate D decays e.g. D0 Ks, KsKK, KKππ Dalitz
analysisSensitivity () ~ 5 in 2 fb-1
– ii) Cabbibo favoured/doubly Cabbibo suppressed D decayse.g. D0 K, K ADS method
u
bB 0D
u
c
K
u
s
u
b
B
K
u
s
0Dc
u
from Bfrom B± ± DK DK±±
Colour allowed Colour suppressed
Syracuse, 20 May 2006 F. Muheim 24
from Bfrom B±± DK DK±± ADS method ADS method based on Atwood-Dunietz-Soni [Phys. Rev. Lett. 78, 3257
(1997)] Measure relative rates of B– DK– and B+ DK
– Two interfering tree B-diagrams, one colour-suppressed (rB ~0.15)
– Two interfering tree D-diagrams, one Doubly Cabibbo-suppressed (rD
K ~0.06)
– Self-tagging – advantageous for LHCb– No proper time measurement required
– 3 observables, 4 rates, but only 3 ratios 5 parameters (D
KrB, rDKrD
K known Sensitivity
() ~ 5 in 2 fb-1
30k
1k
30k
1k
Events per 2 fb-1
Syracuse, 20 May 2006 F. Muheim 25
BBs,ds,d→μ→μ++μμ- - at LHCat LHC
Very rare FCNC decay – in SM low uncertainty
– BR(Bs→μ+μ-) = (3.5 ± 0.9) 10–9
– BR(Bd→μ+μ-) = (1.0 ± 0.5) 10–10
Very sensitive to New Physics:
– Large enhancement in Higgs mediated SUSY processes
– Decay is one of the most sensitive SUSY probes– Complementary to direct SUSY searches at LHC
s, s,
Syracuse, 20 May 2006 F. Muheim 26
BBs,ds,d→μ→μ++μμ- - at LHCat LHC
< 1
< 20
< 100
b, bbackground
48 MeV/c2
75 MeV/c2
18 MeV/c2
Mass resolution
10 fb–1
10 fb–1
2 fb–1
1 year
< 750017LHCb
7
7
Bs + – signal (SM)
Inclusive bb background
CMS (1999)
ATLAS
New Physics Sensitivity– For BR at SM value
M0, M½ > 1500 GeV– Competitive with direct searches
Current Results – dominated by Tevatron– New limit from CDF&D0 at FPCP 2006
BR(Bs→μ+μ-) < 8 10-8 @ 90% CL
LHC expectations– Will observe decay
down to SM level– LHCb will face competition from ATLAS/CMS
Excluded!
M0 [
GeV
]
Syracuse, 20 May 2006 F. Muheim 27
Rare FCNC decay– Inclusive branching fraction
well known in SM– BR(B→Xsμ+μ-) = (1.59 ± 0.11) 10–6
– Exclusive decays better at LHCb
– Di-lepton invariant mass s– BR - well controlled in region
outside resonances -J/ and ’
Forward-backward asymmetry AFB(s)– Asymmetry angle - B flight direction
wrt + direction in +- rest-frame
Sensitive probe of New Physics– Deviations from SM by SUSY,
graviton exchanges, extra dimensions
– AFB(s0) = 0 - predicted at LO without hadronic uncertainties
– Zero point s0 and integral at high s sensitive to Wilson coefficients
BBdd→→K*K*00μμ++μμ--
BR(s) for B0AFB(s) for B0
Syracuse, 20 May 2006 F. Muheim 28
AAFBFB in B in Bdd→→K*K*00μμ++μμ--
Expected Signal Yield– 4400 events in 1 year/2fb-1
Background/Signal– Full simulation, 11 M b-bbar
MC– B/S ~ 0.2 – 2.6
AFB zero point sensitivity
– s0 = 4.0±1.2 GeV2 in 1 year
– s0 = 4.0±0.5 GeV2 in 5 years
– 13% error on C7eff/C9
eff
AFB after 1 year AFB after 5 years
Syracuse, 20 May 2006 F. Muheim 29
Sensitivity SummarySensitivity Summary Based on 10 fb-1
Bs mesons– Precision measurements– Oscillations
(ms,) < 0.01 ps-1 – CP violation
(s) ~ 0.013– Lifetime difference stat(s/s) < 0.01
CKM angle – Reduce error on by factor 5
( ) ~ 30 in best mode– Bs→Ds
+K-
– B0→D0K*0
– B+→D0K+ ADS, Dalitz Rare Decays
– AFB in Bd→K*μ+μ-
– Bs→μ+μ-
– B→K*, Bs→ Charm Physics
– CP violation– D0 oscillations – Under study
Lepton Flavour Violation– B and D, e.g. B,D→μe, μ – Tau decays, e.g. + →μ+μ-μ+
Sensitivity Comparison ~2013LHCb 10 fb-1 vs Super-B factory 5 ab-1
LHCb and B-factories are complementary
Bs
No IP
Neutrals,
Com
mon
Syracuse, 20 May 2006 F. Muheim 30
LHCb Upgrade LHCb Upgrade LHCb Operation
– Increase luminosity adjabatically to ℒ ~ 5 x1032 cm-2s-1
– LHCb detector can cope, could/should be done anyway Upgrade LHCb to run at 10 times nominal Luminosity
– ℒ ~ 2 x1033 cm-2s-1
– Multiple interactions per beam crossing increases to n ~ 4– Does not require LHC luminosity upgrade (SLHC)
Detector Considerations – to operate LHCb above 5 x1032 cm-2s-1
– Vertex detector (VELO) requires replacing after 6 to 8 fb-1
– Existing Front-End electronics limits L0 Trigger output to 1.1 MHz – Muon (Hadron) L0 trigger does (does not) scale with luminosity
LHCb Upgrade Ideas – Replace VELO with a radiation tolerant vertex detector
Strips and/or pixels, remove RF foil (closer to beam 5mm)– Improve trigger by adding first level displaced trigger
Implementation in FPGAs– Replace inner most region of RICH photo detectors– Increase/decrease size of Inner/Outer Tracker – Replace inner most region of ECAL with crystal calorimeter– Replace all Front-End electronics with 40 MHz read-out– Initial studies to operate LHCb at 2 x1033 cm-2s-1 after 2011 have started
Syracuse, 20 May 2006 F. Muheim 31
Physics Case for LHCb UpgradePhysics Case for LHCb UpgradeSensitivity Comparison ~2020
LHCb 100 fb-1 vs Super-B factory 50 ab-1
LHCb and Super-B factory are complementary
Bs
No IP
Neutrals,
Com
mon
100 fb-1 data sample– run 5 yrs at ℒ ~ 2 x1033 cm-2s-1
– Estimates scaled with luminosity– trigger improvements not included
CP Violation in Bs Mesons – SM prediction s = -0.040 s precision statistically limited – to 3 evidence with 10 fb-1
– ~10 measuement with 100 fb-1
b->s transitions– Very sensitive to New Physics– 2.6 discrepancy in average of
S(b->s) = sind -sin2 Best b->s penguin mode for LHCb
– Bs→ – Expected yield 1.2 k events per 2
fb-1– If you measure S() ≠ s (SM)
clear signal for New Physics S() precision statistically limited– With 100 fb-1 estimate
S() = 0.040– Similar precision for Bd→ KS
Syracuse, 20 May 2006 F. Muheim 32
ConclusionsConclusions Heavy Flavour Physics in 2006
– The CKM mechanism is very successful in describing the data – New Physics will manifest itself as corrections to the SM– Require precision measurements to over-constrain UT
triangles LHCb experiment
– Will exploit the large rates of B-mesons at the LHC– Construction of LHCb detector and accelerator well underway – Will be ready for physics in 2007
LHCb physics programme– Exploit the Bs system
Precision measurements of Bs mass and lifetime difference Measure CP violation in Bs mesons
– Reduce error on CKM angle by a factor 5 – Probe New Physics in rare B meson decays
with electroweak, radiative and hadronic penguin modes– Hopefully find the unexpected
Syracuse, 20 May 2006 F. Muheim 34
Table from
G. Isidori
Heavy Quark Flavour Structure Heavy Quark Flavour Structure
Syracuse, 20 May 2006 F. Muheim 35
LHC ExperimentsLHC ExperimentsLHCb
ATLASCMS
with a B-physics programme LHCb
dedicated for precision measurements of CP violation and rare decays in B hadronsmay be the only B-physics experiment running after the B factories unless new projects (Super-B, LHCb upgrade) are approved
ATLAS/CMS optimized for high-pT discovery physics competitive for channels with leptons
Syracuse, 20 May 2006 F. Muheim 36
b Production at the LHCb Production at the LHC
Momentum pB and decay length L – larger in forward region– <pB> ~ 100 GeV/c – Mean B meson flight path <L> ~10 mm
230b
100bB
b-b angular correlation
PT vs pseudo-rapidity
Syracuse, 20 May 2006 F. Muheim 37
Flavour TaggingFlavour Tagging
LHCb– Most powerful tags - opposite kaon, bcs, (Bd) and same side kaon (Bs)
– Combined D2 ~ 7.5% (Bs) or ~ 4.5% (B0)
– Neural network approach leads to ~9% and 5% Comparison
– CDF/D0 achieved ~1.5%/2.5% (Bd) and ~4% (Bs )
– B factories achieved ~ 30%
D2 = (1–2w)2 in %
Tag Bd Bs
Muon 1.2 1.4
Electron 0.6 0.6
Kaon 2.1 2.4
Jet/vertex 0.7 0.8
Same side 0.7() 3.1 (K)
Total 4.4 7.5
Syracuse, 20 May 2006 F. Muheim 38
sin(2sin(2) with B) with B00J/J/ K KSS
CPV in interference of mixing and decay– Measure time dependent CP asymmetry
1st Analysis for LHCb– Test proper time reconstruction– Test tagging performance
• Using control channelse.g B+ J/K+ and B0 J/K*0
• Dependent on how event is triggered - on signal or on rest of the event
Sensitivity – Expect ~240k signal events/year
stat(sin(2)) ~ 0.02– Can also push further the search for
direct CP violation in term cos(mdt)
Syracuse, 20 May 2006 F. Muheim 39
AngleAngle from B from Bdd 00––++ decays decays–Dalitz plot analysis (Quinn Snyder method)
•Bd0–+ selection based on multivariate analysis•Use resolved and merged 0
•Expect 14k events per year, B(bb)/S < 1
– Toy MC study:• 11-parameter likelihood fits
performed in time-dependent Dalitz space
• B/S = 0.8 (flat and resonant bkg)
00
–+
+–
m2(0+)
m2 (0–
)
Combined discriminant variable1 year () ~10°
gen=106°
Syracuse, 20 May 2006 F. Muheim 40
Additional ObservablesAdditional Observables
Angular correlations– 3 angles l, K* and
– 4-dim decay amplitude
Transversity amplitudes – A┴,A║,A0 for full description
– Sensitive to left and right-handed currents
– Expect large effects for New Physics
Kruger&Matias hep-ph/0502060
Syracuse, 20 May 2006 F. Muheim 41
from Bfrom B±± DK DK±± ADS method ADS method based on Atwood-Dunietz-Soni [Phys. Rev. Lett. 78, 3257
(1997)] Measure relative rates of B– DK– and B+ DK
– Two interfering tree B-diagrams, one colour-suppressed (rB ~0.15)– Two interfering tree D-diagrams, one Doubly Cabibbo-suppressed
(rDK ~0.06)
– Self-tagging, i.e. good for LHCb– No proper time measurement required
– Event yields 30k, 1k, 30k, 1k in 2 fb-1
– 3 observables, 4 rates, but only 3 ratios 5 parameters (D
KrB, rDKrD
K known Sensitivity
() ~ 5 in 2 fb-1
Syracuse, 20 May 2006 F. Muheim 42
B → XB → Xss μ μ++μμ--
FCNC diagrams– Well known SM BR
BR(B→Xsμ+μ-) = (1.59 ± 0.11) 10–6
Observables – Branching fraction BR– Forward-backward asymmetry AFB
Sensitive to New Physics – Deviations from SM by SUSY,
graviton exchanges, extra dimensions ... At hadron colliders
– Inclusive decays are difficult to access preferred by theory– Exclusive decays affected
by hadronic uncertainties– Channels under study
• Bd→K*0μ+μ-
• B+→K+μ+μ-
• Λb→Λμ+μ-
• Bs→μ+μ-