Transcript Rare B decays at the LHC

Rare B decays (at the LHC)
as a probe of b → s transitions
Gerhard Raven
NIKHEF & Vrije Universiteit, Amsterdam
•Framework
•LHC & experiments
•b → s g
•b → s l +l •B(s) → m+m-
•LHC Schedule
ITEP Meeting on
The Future of Heavy Flavour Physics
Future of Heavy Flavour Physics
•Summary
24 & 25 July 2006
1
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…
Future of Heavy Flavour Physics
24 & 25 July 2006
2
b→s transitions & OPE…
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)
From G. Hiller [hep-ph/0308180]
Future of Heavy Flavour Physics
24 & 25 July 2006
3
Operators & Observables
From G. Hiller [hep-ph/0308180]
Future of Heavy Flavour Physics
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4
e+e- @Y(4S) vs. pp @ LHC…
For Rare Decay analysis, having access to large samples
produced is an obvious starting requirement…
e+e-  (4S)  BB
PEPII, KEKB
ppbbX (√s = 14 TeV, tbunch=25 ns)
LHC (LHCb–ATLAS/CMS)
Production bb
1 nb
~500 mb
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




Next step is collecting the data…
Future of Heavy Flavour Physics
24 & 25 July 2006
5
The LHC Experiments
(that have a B physics program)
• LHCb:
dedicated B physics experiment
LHCb
• ATLAS/CMS:
general purpose experiments,
optimized for high-pT discovery
physics at 1034 cm–2s–1
ATLAS
Future of Heavy Flavour Physics
CMS
24 & 25 July 2006
6
Detector Acceptance
• ATLAS/CMS:
– central detectors, ||<2.5
– will do B physics using
high-pT muon triggers, mostly
with modes involving dimuons
100 mb
• purely hadronic modes
triggered by tagging muon
230 mb
• 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
Future of Heavy Flavour Physics
24 & 25 July 2006
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Luminosity & Pile-up
ATLAS/CMS (f = 32 MHz)
– Will run at highest luminosity available
– Expect L < 2  1033 cm–2s–1 10 fb–1 / year
(n < 5) for first 3 years
30 fb–1 total at low L
34
–2
–1
– At L = 10 cm s (n = 25),
expect only Bsmm still possible
LHCb (f = 30 MHz)
– L tuneable by defocusing the beams
– Choose to run at <L> ~ 21032 cm–2s–1
(max. 51032 cm–2s–1)
pp interactions/crossing
n=0
ATLAS/CMS
– number of inelastic pp interactions in a bunch
crossing is Poisson-distributed with mean
n = Linel/f
L = instantaneous Luminosity
inel= 80 mb
f=non-empty crossing rate
LHCb
Pileup:
n=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 run
2 fb–1 / year 1012 bb events
10 fb–1 in first 5 years
Future of Heavy Flavour Physics
(nominal year = 107 s)
24 & 25 July 2006
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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
Future of Heavy Flavour Physics
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CMS Trigger
• Triggers for B-physics
40 MHz
– Level1:
• Single muon, pt>14GeV/c
• Dimuon, pt>3 GeV/c
– HLT:
~100 kHz
• Inclusive b,c trigger
– L1: high ET jet,
 5 Hz
• Exclusive B decays
~100 Hz (total!)
– Partial reconstruction of detector in the region
around the muons
O(1Hz) per decay
From T. Speer [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
Future of Heavy Flavour Physics
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LHCb Trigger
10 MHz (visible bunch crossings)
Hardware trigger
custom
electronics  Fully synchronized (40 MHz), 4 ms fixed latency
boards  “High pT” m, mm, e, g and hadron + pileup info
(e.g. pT(m) > 1.3 GeV/c)
L0
1 MHz (full detector readout)
Software trigger
farm of
~ 2000
CPUs
 Full detector info available, only limit is CPU time
1st 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)
Future of Heavy Flavour Physics
Main changes since
original design:
2003: track pT at 1 MHz
2005: increased output rate
2005: full readout at 1 MHz
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Trigger Summary
Atlas
CMS
LHCb
Trigger level
Total
output rate
Output rate
B physics
LVL1
75 kHz
10–15 kHz
LVL2
2 kHz
1–1.5 kHz
EF
200 Hz
10–15 Hz
Trigger level
Total
output rate
(at startup)
Output rate
B physics
LV 1
50 kHz
14 kHz (1m)
0.9 kHz (2m)
HLT
100 Hz
~ 5 Hz of incl. b,cm+jet
+ O(1 Hz) for each excl. B
mode
Trigger level
Total
output rate
L0
1000 kHz
HLT
2000 Hz
Future of Heavy Flavour Physics
24 & 25 July 2006
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Expected Performance
ATLAS CMS LHCb
Mass resolutions
in
MeV/c2
Bs  mm
80
46
18
Bs Ds 
46
?
14
Bs  J/ 
38
32
16
Bs  J/ 
17
13
8
without J/ mass constraint
with
J/ mass constraint
Good mass resolution important for
background rejection !
Proper time resolution:
–
–
–
–
CDF:
ATLAS:
CMS:
LHCb:
t ~ 100 fs
t ~ 100 fs (was 70 fs)
t ~ 100 fs
t ~ 40 fs
BsDs
proper time
resolution
t ~ 40 fs
Good proper time resolution essential
for time-dependent Bs measurements !
Future of Heavy Flavour Physics
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Back to the physics…
Future of Heavy Flavour Physics
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b→sg
From G. Hiller [hep-ph/0308180]
Future of Heavy Flavour Physics
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b→sg
•
•
•
•
•
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…
Future of Heavy Flavour Physics
24 & 25 July 2006
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LHCb: B → K*g, Bs → g
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]
Future of Heavy Flavour Physics
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LHCb: B → K*g, Bs → g
• Require B to point back to
the Primary Vertex
• Mass resolution: 65 MeV
• Lifetime resolution: 62 fs
Future of Heavy Flavour Physics
24 & 25 July 2006
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b → s g : photon polarization
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]
Photon Polarization is not well known
•(New) Right-handed operators could
increase this!
•But gluons could also contribute
O(10%)
• B→ gK** (K)
Gronau & Pirjol, [PRD66 054008, 2002],
Gronau et al., [PRL88 051802, 2002]
• Time Dependent ACP(K*g)
•
Lb baryons
Hiller & Kagan , [PRD65 074038, 2002]
Grinstein et al., [PRD71:011504, 2005]
Future of Heavy Flavour Physics
24 & 25 July 2006
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LB → Lg polarisation
[Hiller, Kagan, PRD 65, 074038 (2002)]
Expect Lb to be polarized
• Can be measured with L b  L J/ at 1%
level
• Assume 20% for now…
[E. Leader] [Hrivnac et al, hep-ph/9405231]
But
• Lg does not have a distinctive secondary
vertex
• Most L decay after escaping the vertex
detector
Future of Heavy Flavour Physics
From F.Legger, T.Schietinger
[hep-ph/0605245]
24 & 25 July 2006
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LB → Lg
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
Future of Heavy Flavour Physics
24 & 25 July 2006
21
b→sl
+l -
From G. Hiller [hep-ph/0308180]
Future of Heavy Flavour Physics
24 & 25 July 2006
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Radiative decays & b
→sl
+l -
Supressed by aEM
• 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
Future of Heavy Flavour Physics
24 & 25 July 2006
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b→sl
+l Supressed by aEM
• 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
Sensitive to
• Susy
• Graviton exchange
• …
Future of Heavy Flavour Physics
24 & 25 July 2006
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b→sl
+l -: inclusive vs. exclusive
Inclusive 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)]
Future of Heavy Flavour Physics
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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 m+m-
From Goto et al. [PRD55 4273 (1997)]
Future of Heavy Flavour Physics
24 & 25 July 2006
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Reminder: current B-factory results
Belle [hepex/060318]
Belle [PRL93
061803 (2004) ]
BaBar [hepex/0507001]
b → sg : C7g
C10/C7
b → s l +l - : C9 and C10
Again: any deviation likely
to be small…
Likely need high precision
measurement to
recognize deviations from
SM…
C9/C7
Future of Heavy Flavour Physics
24 & 25 July 2006
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Exclusive B0→m+m-K*0
• Expected signal and
background for 2 fb-1 (one
nominal year)
– Assuming Br = 12 . 10-7
Future of Heavy Flavour Physics
24 & 25 July 2006
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AFB(B0→m+m-K*0)
• Toy MC, based on full simulation results
• Generate several experiments
2 fb-1: s0 = 4.0 ± 1.2 GeV2
10 fb-1: s0 = 4.0 ± 0.5 GeV2 13% error on C7/C9
Future of Heavy Flavour Physics
24 & 25 July 2006
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Atlas: AFB(B0→m+m-K*0)
From N. Nikitine [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]
Future of Heavy Flavour Physics
24 & 25 July 2006
30
Atlas: Lb→m+m-L
• Very similar to B0→m+m-K*
• Select L with
– t > 0.5 ps
– 1 < RL < 45 cm
• M(Lb): 75 MeV resolution
• After 3 years: ~1500 events
From P. Reznicek [Flavour at the LHC]
Future of Heavy Flavour Physics
24 & 25 July 2006
31
RK in B+→ l +l -K+
•Can get O(10%) corrections due to Higgs
boson exchanges…
•RX is related to Br(Bs→mm)
Hiller & Krueger [PRD69 (2004) 074020]
Future of Heavy Flavour Physics
24 & 25 July 2006
32
RK in B+→ l +l -K+
Currently Allowed…
Current Status:
Future of Heavy Flavour Physics
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RK at LHCb…
• 2 fb-1: signal yield from fit:
• Addition of dedicated inclusive dielectron 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 ]
Future of Heavy Flavour Physics
24 & 25 July 2006
34
RK & Br(Bs m+m-) with 10 fb-1
Broken lepton universality…
Minimal Flavour Violation
SM, or MSSM with small tanb
[ Patrick Koppenburg Beach, Physics at LHC ]
Future of Heavy Flavour Physics
24 & 25 July 2006
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Bd,s → m+m-
From G. Hiller [hep-ph/0308180]
Future of Heavy Flavour Physics
24 & 25 July 2006
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+m–
+
–
B

m
Bs s m m
Very rare decay, sensitive to new physics:
Tevatron: BR <1.5 10-7
– BR ~ 3.5  10–9 in SM, can be strongly
enhanced in SUSY: Br  tan6b/MH2
– Current limit from Tevatron (CDF+D0):
 10–7 at 95% CL
1.5
– CDF+D0 could exclude upto
few times 10-8 with 10 fb-1
Future of Heavy Flavour Physics
24 & 25 July 2006
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+m–
+
–
B

m
Bs s m m
Very rare decay, sensitive to new physics:
Tevatron: BR <1.5 10-7
– BR ~ 3.5  10–9 in SM, can be strongly
enhanced in SUSY: Br  tan6b/MH2
– Current limit from Tevatron (CDF+D0):
 10–7 at 95% CL
1.5
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!
Future of Heavy Flavour Physics
Mass Resolution
(MeV/c2)
ATLAS
CMS
LHCb
Bs  mm
80
46
18
24 & 25 July 2006
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Bs,d →m+m-:  & K misidentification
• Two body modes:
– Eg. Br(B0K) = 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)
Future of Heavy Flavour Physics
24 & 25 July 2006
39
Bs,d →m+m-: LHCb selection
Tracks with
– Pt > 1 GeV
– IP/ > 3
B candidate
– Vertex c2 < 9
– (momentum, decay direction) < 5 mrad
yields
Bs  m+ m– signal (SM)
2 fb–1
17
bm+, bm- background
< 100
Inclusive bb background
< 7500
All backgrounds
Future of Heavy Flavour Physics
???
24 & 25 July 2006
40
Bs  m+m–
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m, bm events
(all rejected for M(m+m–)>4 GeV/c2)
– ATLAS: 80k bb m+m– events with generator cuts, efficiency assuming cut
factorization
– CMS:
10k bm, bm events with generator cuts, trigger simulated at generator
level, efficiency assuming cut factorization
1 year
Bs  m+ m–
bm, bm
signal
background
(SM)
LHCb
2 fb–1
17
< 100
ATLAS
10 fb–1
7
< 20
CMS (1999)
10 fb–1
7
<1
Future of Heavy Flavour Physics
Inclusive bb
background
All
backgrounds
< 7500
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(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…
Future of Heavy Flavour Physics
24 & 25 July 2006
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LHCb Installation Status
March
May 2006
2005
Muon system
Calorimeter
HCAL, ECAL
Future of Heavy Flavour Physics
RICH2
Magnet
RICH1
Trigger Vertex
Tracking
Tracker Locator
Stations
24 & 25 July 2006
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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) bs observables are accessible:
Bs mixing magnitude and phase, exclusive bsmm, B(s)mm
• Large phase space can already be covered with the first good year of
data
– LHCb will improve precision on CKM angles
• Several g measurements from tree decays only: stat(g) ~2.5 in 5
years
• May reveal inconsistencies with other/indirect measurements after
several years
– Looking forward to end of LHC machine
installation and first collisions in 2007
• LHCb aiming for complete detector at end of 2006,
ready to exploit nominal luminosity from day 1
Future of Heavy Flavour Physics
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44
BACKUP
Future of Heavy Flavour Physics
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45
Bs →m+m-: 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]
Future of Heavy Flavour Physics
24 & 25 July 2006
46
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
tracking, PID, tagging)
Output
rate
Event type
Physics
200 Hz
Exclusive B
candidates
B (core program)
600 Hz
High mass
di-muons
J/, bJ/X (unbiased)
300 Hz
D* candidates
900 Hz
Inclusive b (e.g.
bm)
(trigger,
Charm
B (data mining)
• 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 ?
Future of Heavy Flavour Physics
24 & 25 July 2006
47
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%
Future of Heavy Flavour Physics
24 & 25 July 2006
48
Flavour tagging
l-
LHCb:
– Most powerful tag is opposite kaon (from bcs)
– Combined D2 ~ 7% (Bs) or ~ 4% (B0)
– Recent neural network approach leads to ~9% for
Bs
Qvtx
K–
D
B0 B
s
PV
SV
K+
Compare with:
– CDF achieved 4% (SS) +1.5% (OS)
– B factories achieved ~ 30% (Coherent Production!)
Future of Heavy Flavour Physics
24 & 25 July 2006
49
Future of Heavy Flavour Physics
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50
Expected LHCb tracking performance
PYTHIA+GEANT full simulation
• High multiplicity environment:
– In a bb event, ~30 charged
particles traverse the whole RICH1
VELO
spectrometer
TT
MC truth
Reconstructed
Magnet
T1 T2 T3
RICH2
100 mm
• Full pattern recognition implemented:
10 mm
Future of Heavy Flavour Physics
– 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
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