LHCb results

Bolek Pietrzyk

LAPP, Annecy, IN2P3, CNRS

SUSY 2011August 28 – September 02, Fermilab

(New Physics Search at LHCb)

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Flavour Physics is Important

Many of open questions in Standard Model (SM) found in flavour sector

- Why are there 3 generations - What determines the extreme hierarchy of fermion masses? - What determines the elements of the CKM matrix? - What is the origin of CP violation (CPV)?

Progress in flavour physics may help understand open questions in cosmology - SM CPV insufficient to explain matter/antimatter asymmetry

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Flavour Physics is Important

Flavour physics is a proven tool of discovery:

- Kaon mixing, BR(K0L→μμ) & GIM→ prediction of charm

- CP violation → need for a third generation - B mixing → mass of top is very heavy - SUSY parameter space already severely constrained by e.g. b→sγ

Precise studies of flavour observables are an excellent way to look for New Physics!

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LHCb Essentials

CMS and LHCb are complementary

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LHCb EssentialsLHCb is optimised for flavour physics.

# Dedicated heavy flavour trigger- L0: hardware trigger firing on high pt hadrons and muons(~few GeV/c)- HLT: software trigger exploiting, in particular, tracking and vertexing, outputs at 3 kHz → Efficient for hadronic B and D decays, as well as leptonic channels

#Very precise vertexing - VELO (planes of forward silicon) approach to within 8mm of beam

#Hadron identification - Two RICHes provide good π/K separation over 2 < p < 100 GeV/c

#LHCb design luminosity << maximum design luminosity of machine - LHCb already operating at (above!) design luminosity (2x1032cm-2 s-1)

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LHCb data takingLHCb collected 37 pb-1 in 2010, and so far 690 pb-1 in 2011,expect about 1 fb-1 by the end of 2011. 2011 analyses presented today use ~330 pb-1

Luminosity levelling delivers ~constant operation at 3-3.5x1032cm-2s-1

ATLAS & CMS lumi falls . off exponentially

Lumi of LHCb ‘levelled’ continually

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The golden mode: Bs→μμ

BR(Bs→μμ)SM = (3.2 ± 0.2) x 10-9 [A.J.Buras, arXiv:1012.1447]

- Very high sensitivity to NP, eg. MSSM: - One example [O. Buchmuller et al, arXiv:0907.5568; F. Mahmoudi, arXiv: 08083144; B.C. Allanach, Comput. Phys. Commun. 143 (2002) 305-331]

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Bs→μμ : experimental context

# BR Upper Limit 95% CL as of Spring 2011: - CDF (3.7 fb-1): < 4.3 x 10-8

- D0 (6.1 fb-1): < 5.1 x 10-8 - LHCb (37 pb-1): < 5.6 x 10-8 (2010 data)

# Recent exciting hint from CDF (7 fb-1): - BR = 1.8+1.1 -0.9 x 10-8

[arXiv:1107.2304]

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2011 Bs→μ+μ- search with LHCb

# Strategy very similar to 2010 analysis [PLB 699 (2011) 330] After di-μ preselection: -Build Boosted Decision Tree out of 9 kinematical and topological variables

-Train BDT on MC, but calibrate on data:

& signal response: use B → hh decays triggered on ‘other B’ (avoid biases!)

& background response: use sidebands

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2011 Bs→μ+μ- search with LHCb

- Invariant mass of expected signal parameterised as crystal ball, with scale & resolution (~25 MeV) calibrated from data (dimuon resonances & B → hh) - Now look in a 6 x 4 grid of μ+μ- invariant mass vs BDT output

-To obtain relative BR for signal use three normalisation channels:B+ → J/ΨK+, Bs → J/Ψφ and B0 → Kπ – all give consistent results

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2011 Bs→μ+μ- search with LHCb Combinatorial

background

B → hhmisid background

0.1±0.1 events in each of 4 BDT bins

Data

Signalwith SM BR

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2011 Bs→μ+μ- search with LHCb

M=5.357 GeV, B mom. 58.16 GeV, transverse mom. 3.5 GeV, lifetime 3.52 ps, flighting pass 1.15 cm

Compute limits using frequentist CLs method and LHCb combined result for fs/fd = 3.745 +-0.295 LHCb-CONF-2011-034

Backgd only Backgd + SM signalExpected limit at 95% (90%) C.L. 1.0 (0.8) x 10-8 1.5 (1.2) x 10-8

Observed limit at 95% (90%) C.L. 1.6 (1.3) x 10-8

p-value of bckgd only hypothesis 14%Observed limit at 95% (90%) C.L. 1.5 (1.2) x 10-8 (5 – 4 x SM)when combined with 2010 result , Bolek Pietrzyk

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Bs→μ+μ- LHCb preliminary limit

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B0→K*l+l-

Many observables exist in B0→K*l+l- to probe helicity structure of any New Physics...

...in particular, forward-backward asymmetry (AFB) of lepton system as a function of lepton invariant mass (q2).

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B0→K*l+l- : experimental context

Results from CDF & B-factories show intriguing behaviour at low q2 :

C7=‐C7SM

SM

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B0→K*μ+μ- : event selection Select events using Boosted Decision Tree from sample of 309 pb-1

Veto decays in J/Ψ and Ψ(2S) resonance regions

Measure in 6 q2 bins: •differential branching

fraction, dΓ/dq2

•longitudinal polarisation, FL

•AFB

303 signal eventsafter mass cut

Simultaneous fit of 1D projections of helicity angles of kaon & lepton

Performance of fit validated on MC and B0→J/ΨK* decays }

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AFB in B0→K*μ+μ- Systematic uncertainties are small, and generally statistics limited.

Data are consistent with the SM predictions at present sensitivity and indicate for the first time that the asymmetry is changing sign as predicted by the SM.

LHCb-CONF-2011-039

C. Bobeth et al. [arXiv:1105.0376v2]

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AFB in B0→K*μ+μ-

arXiv:1108.0695

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CP-violation in Bs mixing Interference between mixing and decay gives rise to CP violating phase 𝜙𝑠=𝜙𝑀 −2 𝜙𝐷 final state is mixture of CP even and CP odd eigenstates (P—VV decay)

Described by three polarization amplitudes: (CP-odd) 0 , (CP-even)𝐴⊥ 𝐴 𝐴∥Final states described by three angles: Ω={ , , } 𝜑 𝜃 𝜓

𝐽/Ψ Φ 𝐵𝑠

𝐵𝑠

𝜙𝐷

−𝜙𝐷 𝜙𝑀

[SM −0.0363 ± 0.0017 rad]

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𝜙𝑠 : experimental context 𝜙𝑠=𝜙𝑀 −2 𝜙𝐷 SM prediction: −0.0363 ± 0.0017 rad [CKMfitter, Eur. Phys. J. C41 (2005)]

LHCb measurement with 2010 data:

757 ± 28 signal candidates

D0 / EPS 2011 Conference / S.Burdin CDF Public Note 10206

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Bs→ J/

L = 337 pb-1

8276 ± 94 signal candidates(10x more than in 2010)

S/B ~ 11 in 3 mass window 𝜎Perform unbinned maximum likelihood fit in mass, proper time, transversity angles

OS tagger optimized and calibrated on 2011 data using 𝐵+ → /𝐽 Ψ 𝐾+, 𝐵0 → /𝐽 Ψ 𝐾∗ and 𝐵0 → 𝐷 -∗ 𝜇+𝜈𝜇 𝜖𝐷𝑒𝑓𝑓2 = 2.08 ± 0.17 ± 0.37%

Bs

K

K

J/

-

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Bs→ J/

Systematic uncertainties are small, and generally statistics limited.

𝜙 𝑠 = 0.13 ± 0.18 ( ) ± 0.07 ( ) rad𝑠𝑡𝑎 𝑠𝑦𝑠ΔΓ 𝑠 = 0.123 ± 0.029 ( ) ± 0.008 ( ) 𝑠𝑡𝑎𝑡 𝑠𝑦𝑠𝑝𝑠-1

Γ𝑠 = 0.656 ± 0.009 ( ) ± 0.008 ( ) 𝑠𝑡𝑎 𝑠𝑦𝑠 𝑝𝑠-1

Standard Model

[ CKMfitter, Eur. Phys. J. C41 (2005)]𝜙𝑠

(ΔΓ Lenz, Nierste, JHEP 0706 (2007) 072)𝑠

LHCb-CONF-2011-049

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Bs→ J/

This is NOT an official accurate overlay!! – only an “artist’s view”

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Bs→ J/f0(980)

Feb. 1, 2011 – LHCb: “1st observation ofBs→ J/ψ f0(980) decays“[arXiv:1102.0206]

f0 is a scalarwith an sscomponentbut decayspredominatlyinto π+π-

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Bs→ J/f0(980)

Bs→J/ψππ

B0→J/ψKπ

B0→J/ψππBs→J/ψ η’,φ B+→J/ψπ

2011 dataNsig = 1428 ± 47 events365 ± 22 after taggingεD2 = 2.13%

The f0(980) signal region looks pure scalarpurely CP odd no angular analysisrequired

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Bs→ J/f0(980)

ϕs = -0.44 ± 0.44(stat.) ± 0.02(syst.)

LHCb-CONF-2011-051

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J/and J/f0(980) combination

ϕs = -0.44 ± 0.44(stat.) ± 0.02(syst.) 𝜙 𝑠 = 0.13 ± 0.18 ( ) ± 0.07 ( ) rad𝑠𝑡𝑎 𝑠𝑦𝑠pleriminary simple combination

Φs = 0.03 ± 0.16(stat) ± 0.07(syst) radSM Φs = −0.036 ± 0.002

LHCb-CONF-2011-056

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Δms : experimental context

# CDF (2006): - Δ𝑚 𝑠 = 17.77 ± 0.10 ( ) ± 0.07 ( ) 𝑠𝑡𝑎𝑡 𝑠𝑦𝑠𝑡-5,600 fully and 3,100 partially reconstructed hadronic 𝐵𝑠0, 61,500 semileptonic 𝐵𝑠0

- 𝑡 = 87 fs (fully rec. hadr.) - 𝜀𝐷2 = 3.7 % (hadr., OST+SST)

# LHCb (2010): - Δ𝑚 𝑠 = 17.63 ± 0.11 ( ) ± 0.03 ( ) 𝑠𝑡𝑎𝑡 𝑠𝑦𝑠𝑡- 1381 signal candidates - 𝑡 = 44 fs - 𝜀𝐷2 = (3.8 ± 2.8) % (OST only)

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Δms : LHCb 2011 data

# LHCb, 2011 data 341 pb-1

Δ𝑚 𝑠 = 17.725 ± 0.041 ( ) ± 0.025 𝑠𝑡𝑎𝑡( )𝑠𝑦𝑠𝑡

- 9189 signal candidates - 𝜀𝐷2 = (3.2 ± 08) % (OST) - 𝜀𝐷2 = (1.2 ± 04) % (SST)

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CP violation … is easy

B0 B0

B0S

B0S

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Summary - LHCb at LHC is making precise measurements- Hints for strong signs of NP from other experiments are not confirmed- LHCb results presented here are in agreement with the SM prediction, but …-There is still a lot of room for NP- At the end of 2011 we should have about 3 times more data and improved analyses

Excellent prospects for excellent resultsat Moriond 2012

Backup slides

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Bs→μ+μ- CMS search (1.14 fb-1 )

# No significant excess seen

Barrel Endcap

B→hh

# Compute limits using frequentist CLs method and PDG fs/fd = 0.282 ±0.037

Expected limit at 95% (90%) C.L. 1.8 x 10-8 (including SM signal)

Observed limit at 95% (90%) C.L. 1.9 (1.6) x 10-8

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Bs→μ+μ- combination

A preliminary CMS-LHCb combination on BR(Bs→μ+μ-) has been performed, using the CLs approach, & taking LHCb value of fs/fd as common input

CMS + LHCb preliminary

Observed limit at 95% (90%) C.L.

1.1 (0.9) x 10-8

3.4 times the expected SM value

CDF hint is not confirmed

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Like-sign di-muon asymmetry

D0 observes 3 deviation from the SM

LHC is a pp-collider, not a ppbar-collider

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LHCb detector