the babar experiment: status and plans - mcgill physics40 layer drift chamber (de/dx) 1.5 t solenoid...

The BABAR Experiment: The BABAR Experiment: Status and PlansStatus and Plans

Steven RobertsonInstitute of Particle Physics

Canadian Association of Physicists Congress 2008

Québec City, Québec June 10, 2008

Sep 3, 2008 2Steven Robertson, Institute of Particle PhysicsThe BABAR Experiment

OutlineOutline

● Flavour physics overview● The BABAR experiment and B factory operations● Run 7 and ongoing analysis activities● Some recent Canadian highlights


Why Flavour?Why Flavour?Flavour sector contains 20 (22) of 25 (27) parameters of the SM, which

are intrinsically connected to EW physics and symmetry breaking ● Tantalizing structure (similarly for lepton sector) which is not predicted

by the SM:

● All known CP violation phenomenology arises from a single complex phase in VCKM

● B sector provides access to a substantial fraction of the CKM matrix either at tree level or via one-loop processes

● Indirect probes of New Physics from “redundant” determinations of CKM parameters or from rare decay searches D0

π

Β+

u

ud

b c

u

Vcb

V*ud

Vud Vus Vub

V = Vcd Vcs Vcb

Vtd Vts Vtb


Effective theory approachEffective theory approach

In explicit models:● Λ ~ mass of virtual particles

(e.g. Fermi theory.: mW)

● C ~ (loop coupling) x (flavour coupling)

(e.g. SM/MFV: αw x CKM)

New Physics scaleEffective flavour-violating couplings

Increasing luminosity

Precision flavour measurements provide bounds on ratio C / Λ i.e. they constrain coupling strengths at any given mass scale

● Loop-level flavour processes (FCNCs) can act as probes of mass scales far beyond the CM energies of accelerator-based experiments


Unitarity Triangle constraintsUnitarity Triangle constraints● Unitarity of CKM matrix implies relationships between CKM

elements which can be tested experimentally

● Bd meson Unitarity Triangle (UT):

● “Tree-level” determination of UT parameters permits the SM mechanism for CP violation to be tested

B → ψKS

B → φKS

B0 → D*π B+ → D0

CP K+

α

γ β

Vtd V

tb *

VcdVcb*

V udV ub

*

B0 → π+π−

B0 → ρ+ρ−b → ulν

b → clν

B0B0 mixing


Trees vs penguinsTrees vs penguinsUnitarity of CKM matrix implies relationships between CKM elements

which can be tested experimentally

● Bd meson Unitarity Triangle (UT):

B → ψKS

B → φKS

B0 → D*π B+ → D0

CP K+

α

γ β

Vtd V

tb *

VcdVcb*

V udV ub

*

B0 → π+π−

B0 → ρ+ρ−b → ulν

b → clν

B0B0 mixing

● “Redundant” determinations of UT parameters in modes which proceed via different mechanisms (i.e. tree vs loop) can yield information about possible New Physics contributions

B0

K0

J/ψb→ccs

New Physicss

ds/

dd

g

b

ds/

s~b~

g~

K0

ϕB0

b ss

sd

dg

, ,u c t

W+

K0

B0ϕ

b→sss


Trees vs penguinsTrees vs penguins● Determination of sin2β from

b→ccs modes consistent with overall CKM fit (both including and excluding kaon constraints):

● Determination of sin2β from penguin-dominated modes not as clearly consistent with SM expectation:


Rare decaysRare decaysSearches for “rare” decay processes can provide additional NP

sensitivity since the NP contribution may be comparable or larger than the (suppressed) SM rate● Leptonic B, Ds or D decays:

iq jqiq jq2q 23(13)(m )

● Flavor-changing neutral currents (FCNCs)

● Lepton flavour violation (e.g. in τ decays):


The BABAR experimentThe BABAR experiment

● Currently ~350 physicists from eleven nations


ϒϒ(4S) (4S)

B0B0 pair is produced in a coherent L=1 state

The ϒ(4S) is a bb resonance which lies just above the mass threshold for production of BB meson pairs.

● Cross section of ~1.1nb

~1.1 million BB pairs per fb-1

OffOn

PEP-II BABAR

BB

thre

shol

d

ECM -M Υ(4S) (MeV)

The two B mesons evolve in phase until one decays

(EPR situation)

⇒ Enables studies of time-dependence of decays of “flavour-tagged” neutral B mesons


PEP-II Asymmetric B FactoryPEP-II Asymmetric B FactoryFirst collisions: 1998Final collisions: April 2008Collide 9.0 GeV electrons with3.1 GeV positrons for ϒ(4S)

CM Energy = 10.58 GeVDesign luminosity 3.0 x 1033 cm-2 s-1

Record luminosity 12.07 x 1033 cm-2 s-1

Number of bunches: 1720

Beam current: (HER) 1.875 A (LER) 2.9 A


The The BBAABBARAR detectordetector

e-

(9.0 GeV)

e+ (3.1 GeV)

EM calorimeter6580 CsI(Tl) crystals

σpT/pT = (0.13 · pT /[GeV/c] + 0.45)% 40 layer drift chamber (dE/dx)

1.5 T solenoid

5-layer silicon vertex detector

DIRC – RICH utilizing total internal reflection

BABARK-π separation

pLAB (GeV/c)

K-π

sepa

ratio

n(σ)

Magnet flux return instrumented with RPCs (→ LSTs)

B factory operations at SLAC since 1999:● Centre of mass energy of 10.58 GeV

for ϒ(4S) → BB● Asymmetric beam energies produce

boost of βγ=0.56 in lab frame


BABAR/PEP-II OperationsBABAR/PEP-II Operations

● Final BABAR ϒ(4S) “onpeak” data sample corresponding to an integrated luminosity of 430 fb-1 ~0.5x109 BB pairs● substantial samples of

continuum tau and charm● also ~45fb-1 of ϒ “narrow

resonance” data (surprise!)...●


Interesting times...Interesting times...Run plan for Run 7 approved until Oct 2008 with luminosity target of

~2x1034 with anticipation of an additional ~50% new data ● substantial upgrades to accelerator during 3-month shutdown in fall 2007● BABAR IFR (barrel muon system) upgrade completed prior to 2007 run

Dec 21st – Congressional budget cuts (targetted at ILC) result in termination of BABAR run effective Jan 1st 2008● BABAR successfully argues

that physics case for ϒ(3S) & ϒ(2S) justifies a 3-month extension of the run

● PEP-II/BABAR retool accelerator, detector and trigger system within a 3-day period over the holiday break

Continuesto Oct 2008

End of ϒ(4S) Run

ϒ(3S) Run ϒ(2S) Run

Scan


Final OperationsFinal Operations● Monday April 7th 2008 (12:43PM)


30.2/fb@ Y(3S)

4.2 0.2( ) nb ( 5% syst.)~120M (3S) (x10 Belle, 25x CLEO)

stat ϒ

7.3 0.3( ) nb ( 7% syst.)~100M (2S) (~12x CLEO)

stat ϒ

14.5/fb@ Y(2S)

Narrow Upsilon PhysicsNarrow Upsilon Physics● New element of BABAR physics

program: Upsilon spectroscopy!● Search for elusive singlet states

(ηb and hb)

● Hadronic transitions, etc.● New Physics searches● Invisible width of ϒ(1S), etc.

● World largest samples by one order of magnitude

●

●


Direct Higgs/DM searches (?!)Direct Higgs/DM searches (?!)

Can have either completely invisible final states, or (invisible + γ), depending on spin of the mediator● Require a “tag” to identify that the event has occurred

● Expected sensitivity with BABAR ϒ(3S) data sample Br(ϒ(1S) → invisible) ~few x 10-4 (prelim results “soon”)

●

● Light (pseudoscalar) Higgs and/or light dark matter candidates can be directly produced in decays of heavy quarkonium states:*

● ϒ → χχ via U (new gauge boson or scalar)

● ϒ → A1 γ where A1 → χχ or τ+τ-

Models manage to evade existing Higgs & SUSY LSP limits from e.g. LEP, while predicting quite large branching fractions

*B. McElrath, Light Higgses and Dark matter at Bottom and Charm Factories, arXiv:0712.00116v2 [hep-ph]J. Gunion, D. Hooper and B. McElrath, Light Neutralino Dark Matter in the NMSSM, hep-ph/0509024.


High Energy ScanHigh Energy Scan● Last ~two weeks of Run 7 were dedicated to an energy scan of

the region above the ϒ(4S)

● 25 MeV steps, 25pb-1 per point (previous scans by CLEO and CUSB in 1984 based on ~100pb-1)

● Motivation: study properties of ϒ(5S) and ϒ(6S) resonances, search for exotic bb states (analogous to “unexpected” Y(4260),Y(4350),Y(4660) charmonium-like states)

● Clear evidence of ϒ(5S) and ϒ(6S) resonances, but not a simple resonance structure● interference contribution?

● ⇒ Results “soon”...


What next?What next?● 3-month transition period to prepare detector for “Minimum

Maintenance State” (MMS) ● Detector could (with difficulty) be brought back into service from MMS● Requires continuous monitoring (e..g gases, fluids) but no expert shifters

● “Decommissioning and Disposal” (D&D) to begin in late 2008 or 2009● Planning underway – requires

agreement between BABAR member countries

● Important to preserve valuable/unique hardware assets

● BABAR collaboration retains ownership of the detector until the end of MMS phase● The lab will assume ownership at

the end of MMS and the responsibility for the D&D


Detector reuse for SuperBDetector reuse for SuperB

Super-conducting solenoid

CsI(Tl) barrel calorimeter and support structure

DIRC quartz bars

Muon system iron/flux return (?)

● SuperB project (see talk in Monday morning session) assumes reuse of significant portions of the existing BABAR detector

⇒ Complicates D&D phase (issues of ownership, disposal and transportation costs etc)


Post data-taking periodPost data-taking period

Post data-taking “intense analysis period” had been anticipated to begin in Oct 2008 following completion of ϒ(4S) run with total data set expected to be >700fb-1 of onpeak data

● Final “onpeak” ϒ(4S) data sample of ~430fb-1 ● Over 100 “core” analyses expected to be performed/updated with full

data sample● Many, many other analyses also currently in progress on topics

ranging from new states, τ and charm physics, ISR physics, rare decay searches, B decays etc.

● New narrow-resonance studies well underway

No evidence so far of any slowdown of analysis activities...● 130 BABAR abstracts submitted to ICHEP08, 20(+2) talks!

⇒ SLAC has commited to providing computing resources through the intense analysis period – currently no obvious resource issues


Published 320 PRL 165 PRD 66 PRD(RC) 114

Total Submitted 345

Publication statisticsPublication statistics


Publication statisticsPublication statisticsSustained publication rate of over 1 paper/week over the past

four years! ● Very rich physics program: only ~half of all papers relate directly

to primary BABAR program of CKM / CP violation


Publication statisticsPublication statistics● Asymmetric B factories still have only a very short history:

CP violation in B decays proves CKM mechanism

Current BABAR grad students are born


Leptonic and LFV B decaysLeptonic and LFV B decays● Use hadronic tag reconstruction method to

search for leptonic and lepton flavor violating B decay modes ● Two-body decays yield clean signature in

signal B rest frame

B+ B-ϒ(4S)µ+ K-

π+

π-ν

PRD-RC 77, 091104 (2008)

Mode Data Sample 90% CL limit


VVusus from inclusive from inclusive ττ→K→K decays decays● New precise BABAR measurements of τ decays to final states with charged kaons ● branching fractions consistent with, but

lower than, previous measurements


VVusus from inclusive from inclusive ττ→K→K decays decays

Currently a 3.4σ discrepancy with CKM unitarity!

● Will be interesting (and important) to see results from other modes

● Bfactories each have O(103) more data than LEP

K. M

altman, C

.E. Wolfe, S. B

anerjee, M.R

oney, I. Nugent


BABAR SymposiumBABAR Symposium

● One-day symposium planned for Monday October 27, 2008 at SLAC to celebrate the achievements of BABAR/PEP-II

● Announcement/invitations anticipated to be sent out around mid-June


ConclusionConclusion● BABAR is still going strong, in spite of the untimely termination of the

data taking phase● Interesting (and unexpected) expansion of the physics program to

include ϓ(3S) and ϓ(2S) bottomonium runs and a cross section scan above the ϓ(4S)

⇒ First results anticipated for ICHEP08

“Intense Analysis Period” is well underway (and living up to its name...)● Full ϓ(4S) data set is in hand, many analysts freed from operational

responsibilities● Expected to be a record year for BABAR publications

Canadian groups very active and productive, with interesting physics results spanning the spectrum of the BABAR program

(B semileptonic and rare decays, charmonium and exotica, Upsilon physics, tau decays etc)


Backup slidesBackup slides


The Flavour ProblemThe Flavour ProblemLoosely stated, generic New Physics would imply observable effects

which are are inconsistent with experiment unless either the New Physics scale is high (e.g. 1-0-100TeV) or the (loop x flavour) couplings are small

● F=2 processes occur at the loop level, thus could receive O(1) NP corrections but effects > ~20% are excluded

NP < 1 TeV● suppression of flavour violating couplings required in all sectors

possibly pointing to MFV. SUSY can stabilize the Fermi scale with mild fine-tuning

If 1< NP < 10-100 TeV● suppression of flavour violating couplings needed in sector 1-2 only.

No indication of MFV. SUSY can still stabilize the Fermi scale with moderate fine-tuning


New Physics Bounds from New Physics Bounds from τ→µγτ→µγ


CP violation in interferenceCP violation in interference

0B

0B

CPfCP

mixing

decay

t=0

tCPfA

CPfA

~e-2iβ

● Combination of two decay amplitudes to the same final state manifests as an “interference pattern” in the measured decay rate as a function of decay time

λfCP ~ e-2iβ (AfCP /AfCP )

● Measure CP violation in the interference between the decays of mixed and unmixed B0 decays


Sensitivity (MFV) ~200GeV

Present Flavour ContraintsPresent Flavour Contraints

2 2 2

2

d

NP

q

SMi B B

SMB

C Q QeQ

φ Δ Δ

Δ

1034 luminosity gives measureable effects if NP is at the EW scale

BABAR/Belle purpose: “test SM mechanism for CP violation”

E.g. Model independent parameterization of New Physics contributions to B mixing amplitudes:


ΔF=2 parameterizationΔF=2 parameterization


FCNC decaysFCNC decays● Flavour changing neutral current (FCNC)

processes do not occur in SM at tree level● Loop-mediated processes can have large

contributions from non-SM diagrams of same order as leading SM contributions:

●

●

Products of field operators(nonperturbative hadronic matrix elements; HQE in inverse powers of mb)

Wilson coefficients (calculated perterbatively; encode short-distance physics)

● Low-energy effective Hamiltonian for b →s (or d) transitions:●

● New Physics can enter via non-SM values of Wilson coefficients

cc

ss

tt

bb

uu

dd

SM dominated by t-quark contribution


Electroweak FCNCsElectroweak FCNCsB → Xs/d γ

C7 (Photon penguin) only

Observables: branching fractions Eγ (or mhad) spectrum, ACP

B0s/d → l+l-

C10 (Axial vector EW) only

Observables: branching fractions

B → Xs/d l+l-

C7 ,C9 (Vector EW) and C10

Observables: (partial) branching fractions, dilepton AFB, ACP

New physics could result in a distinctive pattern of deviations in observables across a variety of related FCNC modes


Trees and PenguinsTrees and Penguins● Time-dependent CP asymmetries in b→ccs, b→sss, b→qqs

(q=u,d)● b→ccs is tree decay clean sin2β measurement● b→sss purely penguin decay: sin2β in Standard Model

● (0.05 hadronic), sensitive to heavy particles in loops● “New Physics” potentially contributes at same order as Standard Model

● b→qqs proceeds via penguin diagrams and b→u tree diagrams

b ss

sd

dg

, ,u c t

W+

K0

sds /

dd

g

b

ds /

s~b~

g~

b sd

dd

d

W+

g

, ,u c t

B0K0B0

b→ccs

b→sss b→dds

New Physics

π0


Beyond Tree Level...Beyond Tree Level...

● Uncertainties from Vub and fB cancel in ratio of modes!

● ⇛ Can we get there???●

● Tree-level charged Higgs (Type-II 2HDM or MSSM) contribution has the same effect on all leptonic modes:

● B(B+→l+ν)MSSM = B(B+→l+ν)SM x [ 1 – (m2B/m2

H+) tan2β/(1+ϵ0 tan2β) ]2 ● “Universality” preserved at tree level

● At one-loop level, potentially large Lepton Flavour Violation (LFV) effects entering from e.g. SUSY in grand unification scenarios:

i.e. B+ → l+ νl' where l' ≠ l via effective l H+ ν coupling

Observable effects in ratios, Rbl/τ, of B leptonic branching ratios:

●

G. Isidori and P. Paradisi hep-ph/0605012A. Masiero, P. Paradisi and R. Petronzio hep-ph/0511289


Lepton Flavour ViolationLepton Flavour Violation● In Standard Model, lepton flavour conservation is not associated

with any underlying symmetry principle● LFV generally permitted in New Physics models containing more

than one Higgs doublet● In SUSY seesaw models, flavour changing insertions arise from Yukawa

couplings in the slepton mass RGEs:

● ⇛ New Physics effects in τ → l γ (l = e,µ) can saturate experimental bounds in natural and well-motivated models

● MSSM with heavy right-handed neutrinos and seesaw mechanism: Br~10-7 ● heavy Dirac neutrinos, RPV SUSY models, flavour changing Z' models...


Higgs mediated LFVHiggs mediated LFV● Higgs mediated LFV present in MSSM at loop level given that

there is a source of LFV among sleptons:

From A. Dedes, Super B Factory proceedings: hep-ph/0503261

Effective SUSY

● Predicts LFV effects in a variety of τ and B decay modes (with preference for 3rd generation couplings):


More Charmless ResultsMore Charmless Results• Observation of B → ηρ+

● Tree dominated decay

● BR in good agreement with prediction

• Searches for B → η’ η, η’ π0, η π0, ωπ0 and B → ηK0, ηη, η’η’, η(’)φ, η(’)ω

● Input to ΔS from SU(3)-based theoretical predictions

● No signal observed● All limits around ~10-6

6( ) (9.9 1.2 0.8) 100.13 0.11 0.02CP

BR BA

ηρ

9σ signif.

2.6σ signif.

FPCP 466M BB

0SB Kη

Submitted on full data set (arXiv:0804.2422)!


CP Asymmetries in B CP Asymmetries in B → J/→ J/ψψ ππ00

● Cabibbo-suppressed mode with respect to B → J/ψ KS and opposite CP● Expect S = -sin2β and C = 0

if tree dominated● Penguin diagram or New Physics could

modify CP asymmetries

FPCP 466M BB

0 0 5( / ) (1.69 0.14 0.07) 101.23 0.21 0.040.20 0.19 0.03

BR B JSC

ψπ

184 15signal events

4σ evidence for CP violation,consistent with tree-dominated decay


0-tagB

0-tagB


CP Asymmetries in B CP Asymmetries in B → K → K ηη γγ● Radiative penguin decay

● Photon polarization different for B and B in SM, expect no interference and thus no CPV

● New Physics could contribute with different polarization amplitudes

FPCP 465M BB

5

0 0 5

( ) (7.7 1.0 0.4) 100.09 0.10 0.01

( ) (7.1 2.1 0.4) 100.2 0.5 0.10.3 0.4 0.1

CP

BR B KA

BR B KSC

ηγ

ηγ

8 signif.σ


0-tagB

0-tagB0B

B

3.9 signif.σ

No significant CP violation,consistent with SM


0tagB

0recB

B-Flavour Tagging

ExclusiveB Meson

Reconstruction0SK

J/Ψ π+

π-

µ-

µ+

e- e+

ϒ(4S)

Δ zl-

K-

Time dependent CP measurementTime dependent CP measurement

Reconstruct decay vertex positions

Exploit correlationbetween B0 flavour and lepton charge,K charge etc


Charmless B Decays to bCharmless B Decays to b11

• Observation of B+ → b1 K0

● 6.2 σ significance

● consistent with QCD factorization• Search for B0 → b1

+ ρ

● VA modes may shed light on polarization puzzle in VV modes

● QCD factorization predicts:

– No B0 → b1+ ρ observed !

0 61( ) (9.6 1.7 0.9) 100.03 0.15 0.02CP

BR B b KA

0 12 61 5( ) (33 17 ) 10BR B b ρ

∓

0 61( ) 1.7 10 (90% CL)BR B b ρ ∓

466M BBFPCP



Semileptonic and Leptonic Decays (w/ SL tag)Semileptonic and Leptonic Decays (w/ SL tag)

● Exclusive B → Xu l ν branching fractions

● Search for B → K* νν ● SM BR prediction ~10-5, but could be

significantly enhanced by New Physics

0 4

0 4

4

4

0.7 30.5

( ) (1.38 0.21 0.07) 10( ) (0.96 0.15 0.07) 10

( ) (0.64 0.20 0.30) 10

( ' ) 0.47 10 @ 90% CL

| | (4.0 0.5 0.2 ) 10

l

l

l

l

ub

BR B lBR B lBR B lBR B l

V

π ν

π ν

η ν

η ν

0lB lπ ν 0

lB lπ ν

lB lη ν ' lB lη ν 3.2 signif.σ

0 *0 5

* 5

( ) 21 10( ) 9 10

BR B KBR B K

νν

νν

454M BB

383M BB

FPCPSubmitted on full data set (arXiv:0805.2408)!


● Rare EW penguin decays BRs

● Rate asymmetries (CP, isospin, e/µ) expected to be very small● Measured separately in ll-mass region

above and below J/ψ● All rate asymmetries compatible with

zero, except isospin asymmetry in low mass region for ee sample

FPCP

6

* 4

( ) (0.39 0.07 0.02) 10( ) (1.11 0.19 0.07) 10

BR B Kl lBR B K l l

0.18,low s 0.160.83 (4.2 )ee

IA σ

384M BBB B → K→ K(*)(*) l lll


Run 7Run 7

● Data taken between December 16, 2007 and April 7, 2008

● 30.2 fb-1 at ϒ(3S)

● 14.5 fb-1 at ϒ(2S)

● ~5 fb-1 above ϒ(4S) scan● Several ϒ(3S) analyses and

above ϒ(4S) scan targeting ICHEP 2008

the babar experiment: status and plans - mcgill physics40 layer drift chamber (de/dx) 1.5 t solenoid...

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