Rare B decays (at the LHC) as a probe of b → s transitions

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


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…


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]


Operators & Observables



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…


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


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


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


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


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


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


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


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 !


Back to the physics…


b → s



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…


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]


LHCb: B → K*, Bs → • Require B to point back to

the Primary Vertex• Mass resolution: 65 MeV• Lifetime resolution: 62 fs


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]


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)]


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


b → s l l



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


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


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)]


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)]


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


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…


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


Atlas: AFB(B0→K*0)

From N. Nikitine [Capri workshop on Theory, Phenomenology and Experiment in Heavy Flavour Physics]


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]


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→)


RK in B+→ l l K+

Current Status:

Cur

rent

ly A

llow

ed…


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 ]


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 ]


Bd,s →



– 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 +–


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 +–


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)


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


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


(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…


LHCb Installation Status

RICH2Muon system

CalorimeterHCAL, ECAL

Magnet RICH1VertexLocator

TriggerTracker

TrackingStations

May 2006March 2005


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


BACKUP


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)


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)


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%


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



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

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Rare B decays (at the LHC) as a probe of b → s transitions

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