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24 & 25 July 2006 Future of Heavy Flavour Physics 1
Rare B decays (at the LHC) as a probe of b → s transitions
Gerhard Raven NIKHEF & Vrije Universiteit, Amsterdam
ITEP Meeting on
The Future of Heavy Flavour Physics
•Framework
•LHC & experiments
•b → s
•b → s l l •B(s) →
•LHC Schedule
•Summary
24 & 25 July 2006 Future of Heavy Flavour Physics 2
Disclaimers• This talk heavily borrows from:
– Patrick Koppenburg: Beach, Physics at LHC – Pavel Reznicek: Beach– Olivier Schneider: Flavour at the LHC– Thomas Speer: Beach, Capri workshop– Nikolay Nikitine: Capri workshop– And others…
• Little new news, a lot of the attention right now is on installation, commisioning, calibrations, alignment, preparations for data-taking…
24 & 25 July 2006 Future of Heavy Flavour Physics 3
Describe b→s transitions by an effective Hamiltonian
• Long Distance:– Operators Oi
• Short Distance: – Wilson coef. Ci
New physics shows up as modified Ci,(or as new operators)
b→s transitions & OPE…
From G. Hiller [hep-ph/0308180]
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Operators & Observables
From G. Hiller [hep-ph/0308180]
24 & 25 July 2006 Future of Heavy Flavour Physics 5
e+e- @Y(4S) vs. pp @ LHC…
Next step is collecting the data…
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 (L=1034cm-2s-1) 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 (well separated vertices)
Production vertex Not reconstructed (Not needed) Reconstructed (many tracks)
Neutral B mixing Coherent B0B0 mixing Incoherent B0 and Bs mixing(extra flavour-tagging dilution)
Event structure BB pair alone Many particles not associated with the two b hadrons
For Rare Decay analysis, having access to large samples produced is an obvious starting requirement…
24 & 25 July 2006 Future of Heavy Flavour Physics 6
The LHC ExperimentsLHCb
ATLAS CMS
(that have a B physics program)
• LHCb:dedicated B physics experiment
• ATLAS/CMS: general purpose experiments, optimized for high-pT discovery physics at 1034 cm–2s–1
24 & 25 July 2006 Future of Heavy Flavour Physics 7
Detector Acceptance• ATLAS/CMS:
– central detectors, ||<2.5
– will do B physics using high-pT muon triggers, mostly with modes involving dimuons
• purely hadronic modes triggered by tagging muon
• LHCb:– designed to maximize B acceptance
(within cost and space constraints) – forward spectrometer, 1.9 < < 4.9
• more b hadrons produced at low angles • single arm OK since bb pairs produced correlated in
space
– rely on much softer, lower pT triggers, efficient also for purely hadronic B decays
100 b
230 b
24 & 25 July 2006 Future of Heavy Flavour Physics 8
Luminosity & Pile-up• Pileup:
– number of inelastic pp interactions in a bunch crossing is Poisson-distributed with mean n = Linel/f
• ATLAS/CMS (f = 32 MHz)– Will run at highest luminosity available– Expect L < 2 1033 cm–2s–1
(n < 5) for first 3 years– At L = 1034 cm–2s–1 (n = 25),
expect only Bs still possible
• LHCb (f = 30 MHz)– L tuneable by defocusing the beams– Choose to run at <L> ~ 21032 cm–2s–1
(max. 51032 cm–2s–1)• Clean environment (n = 0.5)• Less radiation damage
– LHCb 8mm from beam, ATLAS 5 cm, CMS 4 cm• Will be available from 1st physics run2 fb–1 / year 1012 bb events
10 fb–1 in first 5 years
10 fb–1 / year30 fb–1 total at low L
(nominal year = 107 s)
pp interactions/crossing
LHC
b
n=0
n=1
AT
LAS
/CM
S
L = instantaneous Luminosity
inel= 80 mb f=non-empty crossing rate
24 & 25 July 2006 Future of Heavy Flavour Physics 9
Atlas (di)muon Trigger– LVL1:
• Pt(1)>6 GeV/c, Pt(2) > 4 GeV/c• L<1033: single mu• L~1033: dimuon
– LVL2• Confirm LVL1, refine pt
– LVL2&EF• vertex constraints + mass
24 & 25 July 2006 Future of Heavy Flavour Physics 10
CMS Trigger
From T. Speer [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
40 MHz
~100 kHz
~100 Hz (total!)
• Triggers for B-physics– Level1:
• Single muon, pt>14GeV/c• Dimuon, pt>3 GeV/c
– HLT:• Inclusive b,c trigger
– L1: high ET jet,
5 Hz
• Exclusive B decays– Partial reconstruction of detector in the region
around the muons
O(1Hz) per decay
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LHCb Trigger
customelectronics
boards
Hardware trigger Fully synchronized (40 MHz), 4 s fixed latency “High pT” , , e, and hadron + pileup info (e.g. pT() > 1.3 GeV/c)
10 MHz (visible bunch crossings)
1 MHz (full detector readout)
farm of~ 2000 CPUs
Software trigger Full detector info available, only limit is CPU time1st stage: ~1 ms 40 kHz (could change)
Tracks with min. impact param. and pT
(di)muon High-Level trigger: ~ 10 ms
Full event reconstr.: excl. and incl. streams
≤ 2 kHz (storage)
Main changes since original design:
2003: track pT at 1 MHz2005: increased output rate2005: full readout at 1 MHz
L0
24 & 25 July 2006 Future of Heavy Flavour Physics 12
Trigger Summary
Trigger levelTotal
output rate(at startup)
Output rate B physics
LV 1 50 kHz14 kHz (1)
0.9 kHz (2)
HLT 100 Hz ~ 5 Hz of incl. b,c+jet
+ O(1 Hz) for each excl. B mode
CMS
Trigger levelTotal
output rateOutput rate B physics
LVL1 75 kHz 10–15 kHz
LVL2 2 kHz 1–1.5 kHz
EF 200 Hz 10–15 HzAtlas
Trigger levelTotal
output rate
L0 1000 kHz
HLT 2000 HzLHCb
24 & 25 July 2006 Future of Heavy Flavour Physics 13
Expected Performance
Proper time resolution:– CDF: t ~ 100 fs
– ATLAS: t ~ 100 fs (was 70 fs)– CMS: t ~ 100 fs– LHCb: t ~ 40 fs
BsDs proper time resolution t ~ 40 fs
Mass resolutionsin MeV/c2
ATLAS CMS
80 46
?
32
13
46
38
17
Bs
Bs Ds 14
Bs J/ 16
Bs J/ 8
LHCb
18
Good proper time resolution essential for time-dependent Bs measurements !
without J/ mass constraint
with J/ mass constraint
Good mass resolution important for background rejection !
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Back to the physics…
24 & 25 July 2006 Future of Heavy Flavour Physics 15
b → s
From G. Hiller [hep-ph/0308180]
24 & 25 July 2006 Future of Heavy Flavour Physics 16
b → s
• Amplitude Vts|C7|• First evidence for penguins (’93)• WA: Br = (3.55 ±0.26) 10-4
• SM: Br = (3.7 ± 0.3) 10-4
• Sets strong constraints on charged Higgs, New Physics…
24 & 25 July 2006 Future of Heavy Flavour Physics 17
LHCb: B → K*, Bs → Charged Tracks:• Consistent with req. PID• Inconsistent with primary
vertex• Good secondary vertex• Consistent K*, mass
Photons:
• Et > 2.8 GeV
• Remove B→K*0, Bs→0 using K*, polarisation
From I. Belyaev, G. Pakhlova [LHCb-2003-090]
24 & 25 July 2006 Future of Heavy Flavour Physics 18
LHCb: B → K*, Bs → • Require B to point back to
the Primary Vertex• Mass resolution: 65 MeV• Lifetime resolution: 62 fs
24 & 25 July 2006 Future of Heavy Flavour Physics 19
b → s : photon polarization
Photon Polarization is not well known
•(New) Right-handed operators could increase this!
•But gluons could also contribute O(10%)
Grinstein et al., [PRD71:011504, 2005]
How to measure?
• Virtual photons (eg. b → s l l )Melinkov et al., [PLB442 381-389, 1998]
• Converted photons
Grossman et al., [JHEP06 29, 2000]
• B→ K** (K)
Gronau & Pirjol, [PRD66 054008, 2002], Gronau et al., [PRL88 051802, 2002]
• Time Dependent ACP(K*)
• b baryons
Hiller & Kagan , [PRD65 074038, 2002]
24 & 25 July 2006 Future of Heavy Flavour Physics 20
B → polarisation
Expect b to be polarized• Can be measured with b J/ at 1%
level• Assume 20% for now… [E. Leader] [Hrivnac et al, hep-ph/9405231]But• does not have a distinctive secondary
vertex• Most decay after escaping the vertex
detector
From F.Legger, T.Schietinger [hep-ph/0605245]
[Hiller, Kagan, PRD 65, 074038 (2002)]
24 & 25 July 2006 Future of Heavy Flavour Physics 21
B → Annual yields (2fb-1) @ LHCb:
Approx 20% resolution on r = C7’/C7
after one year• Far from SM, but already interesting for
some NP models
24 & 25 July 2006 Future of Heavy Flavour Physics 22
b → s l l
From G. Hiller [hep-ph/0308180]
24 & 25 July 2006 Future of Heavy Flavour Physics 23
Radiative decays & b → s l l Supressed by EM
• Br(b → s l l ) = (4.5±1.0) 10-6
• Br(B+ → K+l l )= (0.5 ± 0.1) 10-6
Currently rarest observed B decay
24 & 25 July 2006 Future of Heavy Flavour Physics 24
b → s l l
Sensitive to• Susy• Graviton exchange• …
Supressed by EM
• Br(b → s l l ) = (4.5±1.0) 10-6
• Br(B+ → K+l l )= (0.5 ± 0.1) 10-6
Currently rarest observed B decay
24 & 25 July 2006 Future of Heavy Flavour Physics 25
b → s l l : inclusive vs. exclusiveInclusive decays well described by theory• Shape of dilepton mass distribution
sensitive to NP• SM branching ratio (1.36±0.08) 10-6
(NNLL) for s = q2/mb2 < 0.25
… but hard to analyze experimentally (impossible at hadron colliders?)
Exclusive decays much easier for experiment
… but what about hadronic uncertainties?
From Goto et al. [PRD55 4273 (1997)]
24 & 25 July 2006 Future of Heavy Flavour Physics 26
b → s l l : exclusive
Use ratios to cancel hadronic uncertainties
• Forward-Backward asymmetry (AFB)
• Zero of AFB: s0 = 2C7/C9(s0)• CP asymmetry• CP asymmetry in AFB
• Ratio of e+e- to
From Goto et al. [PRD55 4273 (1997)]
24 & 25 July 2006 Future of Heavy Flavour Physics 27
Reminder: current B-factory results
b → s l l : C9 and C10b → s : C7
Again: any deviation likely to be small…
Likely need high precision measurement to recognize deviations from SM…
Belle [hep-ex/060318]
BaBar [hep-ex/0507001]
Belle [PRL93 061803 (2004) ]
C9/C7
C1
0/C
7
24 & 25 July 2006 Future of Heavy Flavour Physics 28
Exclusive B0→K*0
• Expected signal and background for 2 fb-1 (one nominal year)– Assuming Br = 12 . 10-7
New: updated analysis expects 7.7K/year, at
similar background levels…
24 & 25 July 2006 Future of Heavy Flavour Physics 29
AFB(B0→K*0)
2 fb-1: s0 = 4.0 ± 1.2 GeV2
10 fb-1: s0 = 4.0 ± 0.5 GeV2 13% error on C7/C9
• Toy MC, based on full simulation results• Generate several experiments
24 & 25 July 2006 Future of Heavy Flavour Physics 30
Atlas: AFB(B0→K*0)
From N. Nikitine [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
24 & 25 July 2006 Future of Heavy Flavour Physics 31
Atlas: b→ • Very similar to B0→K*• Select with
– t > 0.5 ps– 1 < R< 45 cm
• M(b): 75 MeV resolution• After 3 years: ~1500 events
From P. Reznicek [Flavour at the LHC]
24 & 25 July 2006 Future of Heavy Flavour Physics 32
RK in B+→ l l K+
Hiller & Krueger [PRD69 (2004) 074020]
•Can get O(10%) corrections due to Higgs boson exchanges…•RX is related to Br(Bs→)
24 & 25 July 2006 Future of Heavy Flavour Physics 33
RK in B+→ l l K+
Current Status:
Cur
rent
ly A
llow
ed…
24 & 25 July 2006 Future of Heavy Flavour Physics 34
RK at LHCb…
• 2 fb-1: signal yield from fit:
• Addition of dedicated inclusive di-electron trigger should gain O(40%) in eeK (not included here)
• Note: llK* background not yet considered…– Could complicate eeK, so maybe just do
RK* instead ;-)
• 10% error on RK
[ Patrick Koppenburg Beach, Physics at LHC ]
24 & 25 July 2006 Future of Heavy Flavour Physics 35
RK & Br(Bs ) with 10 fb-1
SM, or MSSM with small tan
Minimal Flavour Violation
Broken lepton universality…
[ Patrick Koppenburg Beach, Physics at LHC ]
24 & 25 July 2006 Future of Heavy Flavour Physics 36
Bd,s →
From G. Hiller [hep-ph/0308180]
24 & 25 July 2006 Future of Heavy Flavour Physics 37
– CDF+D0 could exclude upto few times 10-8 with 10 fb-1
Bs +–
• Very rare decay, sensitive to new physics:– BR ~ 3.5 10–9 in SM, can be strongly
enhanced in SUSY: Br tan6/MH2
– Current limit from Tevatron (CDF+D0): 1.5 10–7 at 95% CL
Tevatron: BR <1.5 10-7
Bs +–
24 & 25 July 2006 Future of Heavy Flavour Physics 38
Bs +–
• Very rare decay, sensitive to new physics:– BR ~ 3.5 10–9 in SM, can be strongly
enhanced in SUSY: Br tan6/MH2
– Current limit from Tevatron (CDF+D0): 1.5 10–7 at 95% CL
• Expect CMS and Atlas to do very well– Higher luminosity, sufficiently easy to
trigger on
more signal
• But LHCb has also some advantages– Better invariant mass resolution, better
propertime resolution
easier background rejection!
Tevatron: BR <1.5 10-7
Mass Resolution (MeV/c2)
ATLAS CMS
Bs 80 46 18
LHCb
Bs +–
24 & 25 July 2006 Future of Heavy Flavour Physics 39
Bs,d →: & K misidentification• Two body modes:
– Eg. Br(B0K) = 2 10-5
Misid rate: need better than O(1%)– Fake rate: 2 10-5 (1%)2=2 10-9
LHCb:• 1 event/fb-1 in a 2 mass
window
Does not seem to be a major problem…
(but: eg. Atlas has a ~4x worse mass resolution than LHCb)
24 & 25 July 2006 Future of Heavy Flavour Physics 40
Bs,d →: LHCb selection• Tracks with
– Pt > 1 GeV– IP/ > 3
• B candidate– Vertex < 9 (momentum, decay direction) < 5 mrad
yields 2 fb–1
b+, b- background < 100
Inclusive bb background < 7500
All backgrounds ???
Bs + – signal (SM) 17
24 & 25 July 2006 Future of Heavy Flavour Physics 41
Bs +–
• LHC should have prospect for significant measurement, but difficult to get reliable estimate of expected background:– LHCb: Full simulation: 10M inclusive bb events + 10M b, b events
(all rejected for M(+–)>4 GeV/c2)
– ATLAS: 80k bb +– events with generator cuts, efficiency assuming cut factorization
– CMS: 10k b, b events with generator cuts, trigger simulated at generator level, efficiency assuming cut factorization
1 yearBs + –
signal (SM)
b, bbackground
Inclusive bb background
All backgrounds
LHCb 2 fb–1 17 < 100 < 7500
ATLAS 10 fb–1 7 < 20
CMS (1999) 10 fb–1 7 < 1
24 & 25 July 2006 Future of Heavy Flavour Physics 42
(current) LHC Startup Schedule
• End of Summer 2007– Closure of beam vacuum in August– Closure of interaction regions
• “November-December” 2007– Pilot run at injection energy (450 GeV)
• Jan—April 2008– Shutdown
• Summer 2008– Run at Full Energy…
24 & 25 July 2006 Future of Heavy Flavour Physics 43
LHCb Installation Status
RICH2Muon system
CalorimeterHCAL, ECAL
Magnet RICH1VertexLocator
TriggerTracker
TrackingStations
May 2006March 2005
24 & 25 July 2006 Future of Heavy Flavour Physics 44
Summary & Conclusions• The hadronic flavour sector will surely contribute
significantly to the overall LHC effort to find and study physics beyond the SM:– New physics will be chased at LHC in b→s transitions
• A few superb (highly-sensitive) bs observables are accessible:Bs mixing magnitude and phase, exclusive bs, B(s)
• Large phase space can already be covered with the first good year of data
– LHCb will improve precision on CKM angles • Several measurements from tree decays only: stat() ~2.5 in 5
years• May reveal inconsistencies with other/indirect measurements after
several years
– Looking forward to end of LHC machineinstallation and first collisions in 2007
• LHCb aiming for complete detector at end of 2006, ready to exploit nominal luminosity from day 1
24 & 25 July 2006 Future of Heavy Flavour Physics 45
BACKUP
24 & 25 July 2006 Future of Heavy Flavour Physics 46
Bs →: Atlas & CMS…
From N. Nikitine [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
From T. Speer [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
4 observatio
n with
30fb-1
(3 year low-lu
mi)
24 & 25 July 2006 Future of Heavy Flavour Physics 47
Trigger output rates and physics
• Output rates:– Rough guess at present
(split between streams still to be determined)
– Large inclusive streams to be used to control calibration and systematics (trigger, tracking, PID, tagging)
• Charm physics possibilities (to be explored):– Could trigger on 500M signal D*D0(h+h–) per year, 50M D0
K+K–
– D0 mixing (x and yCP) and CP violation in D0 K+K–
• could reach SM levels or close• systematics ?
Output 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
900 Hz Inclusive b (e.g. b)
B (data mining)
24 & 25 July 2006 Future of Heavy Flavour Physics 48
Particle ID: K/ separation• Fully simulated pattern recognition in two LHCb RICHes:
– Reconstruct rings around reconstructed tracks– Good K- separation achievable in 2–100 GeV/c range
Kaon ID: ~88%
Pion mis-ID: 3%
24 & 25 July 2006 Future of Heavy Flavour Physics 49
Flavour tagging• LHCb:
– Most powerful tag is opposite kaon (from bcs)
– Combined D2 ~ 7% (Bs) or ~ 4% (B0)
– Recent neural network approach leads to ~9% for Bs
• Compare with:– CDF achieved 4% (SS) +1.5% (OS) – B factories achieved ~ 30% (Coherent Production!)
Qvtx
BsB0
D
l-K–
K+PVSV
24 & 25 July 2006 Future of Heavy Flavour Physics 50
24 & 25 July 2006 Future of Heavy Flavour Physics 51
VELO
TT
T1 T2 T3 RICH2
RICH1
Magnet
PYTHIA+GEANT full simulation
Expected LHCb tracking performance
10 mm
MC truth
100 m
• High multiplicity environment:– In a bb event, ~30 charged
particles traverse the whole spectrometer
MC truthReconstructed
• Full pattern recognition implemented:– Track finding efficiency > 95%
for long tracks from B decays(only 4% ghosts for pT > 0.5 GeV/c)
– KS+– reconstruction 75% efficient for decay in the VELO, lower otherwise