early flavor physics at the lhc - cern€¦ · atlas and cms Ælimited bandwidth for b trigger...

Early flavor physics at the LHCWalter M. Bonivento

sezione di Cagliari

on behalf of the ATLAS, CMS and LHCb collaborations

Thanks to: M.Smizanska (ATLAS), Urs Langenegger (CMS) and LHCb colleagues

Walter M. Bonivento - INFN Cagliari 2

Near future of B physics

understanding of the CKM paradigm (SM)

search for physicsBeyond the Standard Model (BSM)

appearing in loops.

The goal of heavy flavor physics is now shifting from

tree levelno NP

loops:can be affected by NP

Future goals of (collider) b physics:1) precise measurement of γ2) study loop processes in b s transitions where NP can sneak in

a) hadronic penguinsb) FCNC decays b sll, b sγc) mixing related observables: ΦS, ∆Γs, ACH,indirect CP in As

SL

Bs ΦΦB K*µµ, Bs ΦγBs J/ψΦ


LHC experimentsExperiments being prepared now at LHC

• ALICE heavy ion and soft-pp experiment• ATLAS general purpose pp and heavy ion experiment• CMS general purpose pp and heavy ion experiment• LHCb dedicated heavy flavour experiment• LHCf forward π0 and γ production• MOEDAL magnetic monopole search• TOTEM logs and diffraction physics

ATLAS, CMS and LHCb are relevant forthe flavor physics considered here, andI do not cover production and spectroscopy See JP Revol’s talk


LHCb

VELO

VELO: Vertex Locator (around interaction poinTT, T1, T2, T3: Tracking stations RICH1-2: Ring Imaging Cherenkov detectorsECAL, HCAL: CalorimetersM1–M5: Muon stations

proton

beam

proton

beam

Dipolemagnet

1.9 < η < 4.9 or15 < θ < 300 mrad


Tracking performance

VELO

TT

T1 T2 T3 RICH2

RICH1

Magnet

PYTHIA+GEANT full simulationHigh multiplicity environment:In a bb event, ~30 charged particles traverse the whole spectrometer

Track finding:efficiency > 95% for long tracks from B decays(~ 4% ghosts for pT > 0.5 GeV/c)KS→π+π– reconstruction 75% efficient for decay in the VELO, lower otherwise

Average B-decay track resolutions:Impact parameter: ~30 µmMomentum: ~0.4%


Particle ID performanceAverage efficiency:

K id = 88%π mis-id = 3%

Good K/π separation in 2–100 GeV/c range

Low momentum kaon tagging

High momentumclean separation of the different Bd,s→hh modeswill be the best performance ever achieved at a hadron collider

2GeV/c5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5

Co

un

ts

0

50

100

150

200

250

300 -π +π → dB-π + K→ dB- K+ K→ sB- K+π → sB

- p K→ bΛ-π p → bΛ

2GeV/c5.2 5.25 5.3 5.35 5.4 5.45 5.5 5.55 5.6

Co

un

ts0

50

100

150

200

250

-π +π → dB-π + K→ dB- K+ K→ sB- K+π → sB


ππ invariant mass Kπ invariant mass

With PID With PID

2MeV/c5100 5150 5200 5250 5300 5350 5400 5450 5500

Co

un

ts

0

200

400

600

800

1000

1200 -π +π → dB-π + K→ dB- K+ K→ sB- K+π → sB


ππ invariant mass

No PID


Schedule (sliding…)April 2008(?): Old “commissioning run”very low luminosity 1029 @ √s = 900 GeVdetector commissioning, alignment and calibration

Middle of 2008: Start of run @ √s = 14 TeVcalibration and trigger commissioning,increasing luminosity toward 1033 for ATLAS/CMS (?)and ~2·1032 for LHCb for physics

From 2009: Stable physics run @ √s = 14 TeVATLAS and CMS: clear interest to increaseluminosities towards 1034 as quick as possible.B physics will become increasingly difficult.LHCb: collecting data with <1033 for some years


Luminosity/energy steps considered in this talk

Independently of the schedule changes I investigated which physics can be studied in these scenarios:

a) √s = 900 GeVb) √s = 14 TeV

i. one hundreth of the nominal one year intergrated luminosityii. one fourth of the nominal one year integrated luminosity

<L>=1033 for ATLAS and CMS (optimistic?)<L>=2·1032 for LHCb (should be possible…)∫Ldt = 2.5 fb-1 each for ATLAS and CMS(if <L> is lower, trigger could be adjusted to have a similar number of b’s)∫Ldt = 0.5 fb-1 for LHCb

then everybody can scale the numbers…


Cross sectionsbb cross section large at both √s =900 GeVand 14 TeV, but at √s = 900 GeV thebb fraction of total inelastic events is ~10 xsmaller than at 14 TeV.

Process σ @900GeV σ@14TeV

Visible σ@14TeV ATLAS+CMS

Visible σ@14TeV LHCb

0.1mbtotal bb cross section 0.025mb 0.5mb 0.23mb

total inelastic cross section 40mb 70mb


B triggers at LHC in one slideATLAS and CMS limited bandwidth for b trigger (5-10% at low L)ATLAS: L1 ( 100kHz) µ pairs or single µ (pT>6GeV) with R.O.I. em+jetsinfo

HLT ( 100Hz) with r.o.i. or full scan inside inner detector: jets for hadronic channels, em for channels with e or γ, muons if a second muonis missed by L1; reconstruct intermediate resonancesCMS: similar + partial track reco in r.o.i. and B inv mass LHCb: L1( 1MHz) is called L0(!)

µ, e,γ and h in HCAL+ pile-up system HLT ( 2kHz) based on alleys with partial reco

Event type Physics

Exclusive B candidates B (core program)

High mass di-muons J/ψ, b→J/ψX (unbiased)

D* candidates Charm

Inclusive b (e.g. b→µ) B (data mining)

pT,ET

hadrons 3.8electrons 2.8muon 1.12muon 1.3

G.V. +


Triggers for the commissioning runATLAS 40mb 4kHz interaction rate

Data analysis with loose level-1 (LVL1) muon triggers or minimum bias (MB) triggers

HLT pass through

possibly large background from muon decays in flight from PV hadrons due to low bb/MB ratio

LHCb: only L0 with loose cuts; HLT pass through

decay cross section rate ev/day

150bb µ5µ3X 2nb 2·10-4Hz 5.2

bb J/ψ(µ5µ3)X 0.1nb 0.1·10-4Hz 0.3pp J/ψ(µ5µ3)X 1nb 1·10-4Hz 3

4.4

bb µ5X 60nb 60·10-4Hz

bb Υ(µ5µ3) 1.7nb 1.7·10-4Hz

first tests of mass reconstruction


Physics with the first 14TeV data Assume 100pb-1 ATLAS+CMS (1/100 of the nominal 1 year luminosity)

20pb-1 LHCbUnderstanding of detector, trigger, calibration, alignment, material, field,

reconstruction, particle ID

Beauty production cross sections and bb correlations, productionasymmetries covered in Revol’s talkJ/ψ production both prompt and from beauty: measurement of proper time distribution and reconstruction of exclusive channelsReconstruction of background or control channels for most important measurements Measurement of branching fractionsLifetimes


J/ψ µµ reconstruction

Mode LHCb # ev20pb-1

ATLAS # ev 100pb-1

Total 107 106

ATLAS LHCb

after trigger cuts


Yields of some channels (10-2y) Decay LHCb # ev

20pb-1 LHCb B/S ATLAS B/S

0.4

0.043

B0 J/ψK0* 9320 0.155 8700 flavor tagging, lifetime

BS J/ψφ `1320 0.12 900 0.15 ΦS

Λb J/ψΛ 260 Λb lifetime

<5

B0 J/ψKS 2280 0.9 1300 sin(2β), lifetime

0.5

0.4

0.36

17000

72

1200

B0 ππ 260

B0 Kπ 1350

BS KK 370

10000

ATLAS # ev100pb-1

BS DSπ 25

hadronic triggerin LHCb!!

B+ J/ψK+ 17000flavor taggingreference for rare declifetime

B0 µµ K0* 25 new physics

BS Dsµν ASL, tagging


Lifetime sensitivity (10-2y)

Decayσ(τ)/τstat

ATLASσ(τ)/τstat+systW.A. today

B+ J/ψK+ 1.5% 0.4%

B0 J/ψK0* 2.2% 0.5%

BS J/ψφ 6% 2%

Λb J/ψΛ 8% 5%

better with semileptonic


CKM physics with 2008 data (¼y)Some of the very first measurements with 0.5fb-1 will be most probably the

reproduction/refinement of the main results from the B factories and the Tevatron:Bd mixing phase: βd from Bd J/ψKs

Bs mixing frequency: ∆ms from Bs DsπΦS and ∆ΓS from untagged time-dependent measurements of Bs J/ψφdecays (CMS study – see afterwards) ∆ΓS from lifetime measurement of decays to pure CP+ or CP- states such as Bs K+K- (CP + measures ΓL) and Bs Dsµν decay (flavor specific measures <Γ> ) sensitivity under studyindirect CP in As

SL with Bs Dsµν sensitivity under study

Bc physics: ex. Bc J/ψπ


CKM physics with 2008 data (ii)Other measurements will be a peculiarity of the LHC experiments due to

the- high statistics- high energy- good particle ID- good vertexingA couple of golden measurements from Bs physics- Search for Bs µµ decays- Φs measurement from tagged time-dependent measurements of

Bs J/ψΦ decayswhere large, >O(1), BSM contribution not yet excludedTevatron will run till 2009:CDF and D0, well understood detectorsLHC can get b statistics fast


Search for the Bs µ+µ- decay

Very rare loop decay, sensitive to new physics:BR ~3.5×10–9 in SM, can be strongly enhanced in SUSYCurrent 90% CL limit from CDF+D0 with 1 fb–1 is ~20 times SM

Main issue is background rejectionwith limited MC statistics, indication that main background is b→µ, b→µassume background is dominated by b→µ, b→µ

(in LHCb we have generated an LHC morningof events)


Search for Bs µ+µ- decayFinal states with leptons: lepton trigger very effective for ATLAS, CMS and

LHCbFlavor tag not necessary, tough backgroundPID: B ππ, Kπ, etc.vertex resolution: b µ-X + b µ+Xmass resolution: B µX, etc.+ isolation, pT, etc.Bs mass resolutions Bs µ+µ-

ATLAS CMS LHCbσm(MeV/c2) 77 36 18


SensitivityATLAS CMS

Nsignal 2 2

Nbackground 5 4

assuming the SM Br = ~3.5·10-9

upper limit<~5·10-8 (90%CL)

LHCb

1

10

10 2

0 0.1 0.2 0.3 0.4 0.5

Integrated luminosity (fb–1)

BR

(x10

–9)

Uncertainty in bkgprediction

Expected final CDF+D0 limit

SM prediction

LHCb: BSM contribution down to the level of SM can be excluded


Bs mixing phase φs with b→ccsφs=2βs is the strange counterpart of φd=2β:

φs very small in SMφs

SM = –arg(Vts2) =–2λη2 = –0.036 ± 0.003

(CKMfitter) Could be much larger if New Physics runs in the box

Measured with the time-dependent tagged CP asymmetry (CP in the interference between mixing and decay)Golden b→ccs mode is Bs→ J/ψφ:

Angular analysis needed to separate CP-even and CP-odd contributions

Add also pure CP modes such as J/ψη(’), ηcφ, DsDs

No angular analysis needed, but smaller statisticsTevatron expect σ(ΦS)=0.2 at the end of the run (6fb-1)

W Wb

Bs0

⎧ ⎨ ⎪

⎩ ⎪ s b

s ⎫ ⎬ ⎪

⎭ ⎪ B s

0t

t

} ψ/J

⎩⎨⎧

sB0

s

b

sscc

}φ

sb unitarity triangle


Ingredient 1: Flavor taggingNumber of selected signal events = N(sel)Number of useful tagged events for ACP measurement =N(sel)* εtag

Probability of wrong tag = wtag; Probability of giving a correct tag is D= (1-2 wtag) dilution

ACP= ACP(true)*DA figure of merit for ACP measurement is √εtag *D

opposite side: lepton, jet-charge and kaonsame side: “slow” kaon from the fragmentation

O.S. S.S. combined

e µ K Qvtx

ATLAS 0.25 0.7 X 3.63 ∑=4.6CMS Only untaggged analysis so far availableLHCb 0.5 0.7 1.6 1.0 2.7 7.1 (NN)

Qvtx

Bs

B–

D

l- K–

K+

PV

εtag*D2[10-2]


Flavor tagging (ii) - LHCbMistag rate (wtag) will be measured in data using several high-statistics control channels:

σ(wOS)/wOS ~ 0.3% σ(wSS)/wSS ~ 2%

ChannelYield

in 0.5 fb–1 Bbb/S

B+ → D0π+ 250k 0.1

0.3

0.7

Bs → Ds(*) µ+ ν 0.5 M 0.4

Bs → Ds+ π- 30 k 0.4

2.2 M

0.6 M

B0 → D* - µ+ ν

B+ → D0 (*) µ+ ν

Clean B+ → D0π+

signal

B mass (GeV/c2)


Flavor tagging (iv)

Validation channel for OS tagging: Bd0→J/ψKS

to be compared with σstat(sin(2β))=0.017 from final BaBar+Belle statistics

AC

P(t)

( ) ( )( ) ( ) )2sin()sin(

////)( 00

00

βψψψψ tm

KJBNKJBNKJBNKJBNtA d

SS

SSCP ∆=

→+→→−→

=

}K} ψ/J

⎩⎨⎧

dB0

d

b

dscc

ATLAS LHCb

# events 62k 59k

B/S 0.043 0.9σstat(sin(2β)) 0.035 0.04

2fb-1


Bs-Bs oscillation has to be well resolved: good στ needed-good that ∆ms is not too big-resolution function must be well understood

measuring lifetimes, oscillation plot with Dsπ etc.Proper time resolutions

N B: worse resolution =more dilution in the CP

asymmetries

ATLAS CMS LHCb

στ(fs) 83 77 36

Ingredient 2: Proper time


Proper time issues (LHCb)

Proper-time dependence of trigger+selection efficiency:Proper-time resolution

dilutes cos(∆mst) and sin(∆mst) terms, like mistag does → knowledge of resolution essential

for Bs time-dependent physicsObtain information from unbiased data (J/ψ trigger without biasing cuts):

Prompt J/ψ→µµ, B+→J/ψK+, B0→J/ψK*0

Resolution modelling

proper time error distributions

τ(fs)


Calibration channel: Bs→Ds-π+

Bs→Ds−π+: important control channel for time-dependent Bs analyses

Flavour-specific decay:→ can use to measure dilution of Bs oscillations

→ once mistag known (from other channels) can isolate resolution effectExpect 35k events in 0.5 fb–1 (LHCb only)iwith Bbb/S < 0.05 at 90% CL

Other uses of Bs→Ds−π+:

Measurement of ∆ms (with 0.5 fb–1)σstat(∆ms) = ± 0.012 ps−1, i.e. 0.07%will be completely dominated by systematics on proper time scale, i.e. σ(τ(Bs))/τ(Bs)

end of Tevatron run (6fb-1) σ(∆ms)~0.5%, i.eσ(∆ms)~0.08ps-1

Normalization channel for all Bs branching fraction measurements

~10% absolute measurement of BR(Bs→Ds−π+) expected from Belle’s current data

Reconstructed proper time [ps – 1]

Entri

es p

er 0

.02 ps

Full simulation 0.5 fb–1(signal only, ∆ms = 20 ps –1)

s sb c

ud

Bs0{ }Ds

−} +π


Ingredient 3: mass resolutionGood mass and vertex resolutions to reduce backgroundBs mass resolutions and Background/Signal ratios

(*)with J/ψ mass constraint(**)without mass constraint

ATLAS CMS LHCb

σm(MeV/c2)16.5(*) 14(*) 14(**)

B/S 0.25 0.33 0.12


Event yieldsEvent yields from the “2008” runNumbers of reconstructed J/ψφ

Full decay topology analysis is needed to determineJ/ψφ(CP = +1) / J/ψφ (CP = -1) (LJ/ψφ = 0, 2 vs LJ/ψφ = 1)

ATLAS CMS LHCbNsel 23k 27k 33k


SensitivityBs-Bs oscillation phase and decay width differencewith 2008 data

(*) if ∆Γs/Γs~ 10%(**) from untagged analysisStandard model expectation: φs = -0.04LHCb: BSM effect down to the level of SM can beexcluded with the 2008 dataLHCb: J/ψ η, ηc φ, Ds

+Ds- can be added

ATLAS CMS LHCbσ(φs) 0.158 ? 0.044

0.15σ(∆Γs)/∆Γs 0.45(*) 0.30(**)


Bc physicsExample: Bc J/ψπ

•Can help undertsanding heavy quark dynamics

•Expected resolution (CMS):

•mass 22Mev/c2 (stat) 14.5Mev (syst)

Yield CMS B/S CMS Yield LHCb B/S LHCb

σ(τ)/τstat+syst

CMS

300 0.2 3500 0.8 6%

early flavor physics at the lhc - cern€¦ · atlas and cms Ælimited bandwidth for b trigger...

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