Recent results from Recent results from LHCbLHCb

Alessia SattaAlessia SattaRoma Tor VergataRoma Tor Vergata

On behalf of LHCb CollaborationOn behalf of LHCb Collaboration

BORMIO 2011 BORMIO 2011 XLIX International winter meeting on nuclear physicsXLIX International winter meeting on nuclear physics

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OutlookOutlook

• The LHCb experiment in a nutshellThe LHCb experiment in a nutshell• Detector and performanceDetector and performance• First resultsFirst results

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The LHCb experiment at CERNThe LHCb experiment at CERN

730 authors

54 institutes

15 countries

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LHCb physic goals LHCb physic goals • Main LHCb objective is the indirect search for New

Physics performing precision measurements of CP violation and Rare decays in the b quark sector

• In indirect search NP enters through contributions from virtual heavy particles in loop-mediated processes modifying the SM prediction

• Higher scale can be accessed wrt direct search• Mass scale, couplings and phase of NP can be

accessed• “Indirect discoveries” in the past

• suppression of FCNC → prediction of 2nd quark family • CP violation → prediction of 3rd quark family

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CP violation measurementsCP violation measurements• CPV sensitive to NP phases• Within uncertainties, flavor changing

data described by SM: Consistency is at 2 level. There are several 2…3 tensions

• Improve measurements on CKM elements and challenge the Standard Model by overconstraining the unitarity triangle

• Compare two measurements of the same quantity sensitive and not to the NP (tree vs loop)

• γ: B(s) → D(s) K, B(s) →hh

• Measure with high precision the Bs J/ CPV phase which is predicted small on SM sensitive to NP contribution

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Rare decaysRare decays• FCNC process, mediated by

electroweak box and penguin diagrams in SM.

• New Physics enters at same (i.e. loop) order and can give rise to comparably large deviations from SM predictions in:

• Branching ratios.• Angular distributions.• CP asymmetries.

• AFB BK*• BR Bs• CP of BK*

bt s

W

,Z l+l-

?

b s

l+l-

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LHCb design overviewLHCb design overviewLHCb Physics goal requires high statistics Exploit large bb production cross section at LHC @ √s=14 TeV 500-600b 80mb for bb or inelasticLHCb covers forward region: 1.9 < < 4.9● optimized for the strongly forward peaked heavy quark production at the LHC● only ~4% of solid angle but keep ~40% of heavy-quark production cross section•LHCb designed to operate at an instantaneous luminosity of 2x1032cm-2s-1 factor 50 lower than LHC maximum to maximize single interaction per crossing. Disregard very busy events

Unique coverage

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LHCb detectorLHCb detector

Vertex Locator

RICH Detectors

Tracking system Calorimeters

Muon system

Interaction point

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TriggerTrigger• bb cross section is less than 1

% of the total inelastic cross section

• interesting B decay channels have typical branching fractions of 10-5

• exploit generic B decay signature: decay products with large pT (“large” = few GeV) and high impact-parameter, well separated B decay vertex

• L0 (Hardware) detect high PT lepton and hadron in muon and Calo

• HLT Software uses all detector info

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Data takingData taking

• In 2009 LHC makes the pilot run. The first LHC collisions at √ s = 900GeV

• On such data the velo was not closed

• In 2010 LHC increases the energy reaching the √s = 7 TeV

o Also a 0.31nb-1 at 900Gev• Impressive increases of the

luminosity during the year• recorded 37.7 pb-1 at √s = 7 TeV• LHCb performs very well: data

taking efficiency > 90%

Last month

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2010 running conditions and trigger 2010 running conditions and trigger • peak instantaneous luminosity almost 2

x 1032cm-2s-1 (LHCb design luminosity) but: with only 344 colliding bunches instead of 2622 at beginning of fill: up to more than 2.5 interactions per crossing on average significantly harsher conditions than design

• multiple primary vertices• high occupancies, track multiplicities

• detector & reconstruction cope better with these conditions than expected

- main limitation found: HLT reconstruction time for very busy events

- Despite that exploiting the trigger flexibility and adapt continuously to changing running condition high efficiency were reached.

Design value

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Vertex and Impact parameter Vertex and Impact parameter resolutionresolution

• Good primary vertex and Impact parameter resolution crucial Good primary vertex and Impact parameter resolution crucial for most of the analyses and triggerfor most of the analyses and trigger

• From data single hit resolution in Velo 4 From data single hit resolution in Velo 4 m m • Good primary vertex resolutionGood primary vertex resolution• IP 15 IP 15 m for high Pt tracksm for high Pt tracks

• For low Pt tracks worse than MC work on material description For low Pt tracks worse than MC work on material description ongoingongoing

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TrackingTracking• Excellent momentum Excellent momentum

resolution crucial for good resolution crucial for good invariant mass and invariant mass and background reductionbackground reduction

• High tracking efficiency High tracking efficiency crucial for multibody decays crucial for multibody decays reconstruction reconstruction

• Tracking efficiency Tracking efficiency estimated with tag and estimated with tag and probe: > 90% for tracks probe: > 90% for tracks above few GeVabove few GeV

TT OT

Hit resolution agrees well with current simulation

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Tracking: excellent momentum Tracking: excellent momentum resolution demonstratedresolution demonstrated

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RICH Particle identificationRICH Particle identification

• crucial for flavour tagging and for separation of B decays with identical topology, e.g.B0 → - ↔ B0 → K+ ↔ Bs→ K+K-

• efficiencies and mis-ID determined from data using tag-and-probe methods on → K+K-, Ks→ → p

• performance found to be close to simulation over full momentum range

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Calorimeter PIDCalorimeter PID

• trigger on hadronic decay channels• reconstruction of final states with e,

D0.Kp0

J/seeY(ns)ee c1,2J/

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Muon IdentificationMuon Identification

• efficiency determined from data using tag-and-probe method on J/found to be > 90 % for p > 10 GeV

• mis-ID probabilities K→, , p→determined from data using tag-and-probe method on spall found to be < 2 % for p > 10 GeV

• good agreement between data and simulation

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First LHCb resultsFirst LHCb results

With the present integrated luminosity the LHCb With the present integrated luminosity the LHCb physics core measurements not possible. Waiting physics core measurements not possible. Waiting for larger integrating luminosity several interesting for larger integrating luminosity several interesting analyses :analyses :

• Particle productionParticle production• Open Charm cross sectionOpen Charm cross section• Hidden charm cross sectionHidden charm cross section• bb cross sectionbb cross section• Electroweak physicsElectroweak physics

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Ks production cross sectionKs production cross section• First measurement for LHCb with 2009 pilot run data √s

=0.9TeV• Ks→π-π+ selection based on tracking and impact parameters• First test for detector calibration• New method to estimate luminosity using beam profiles

estimated from vertices made by VELO tracks in beam-gas and beam-beam collisionsComparison with PYTHIA

Comparison with other experiment

Good consistency with PYTHIA Expectation slightly harder PT

Unique measurement at high rapidity and low Pt

Published Phys Lett B 693 (2010) 69-80

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Hadron production ratiosHadron production ratios

• Motivation:: Baryon number transport and Hadronisation MC tuning

• 2 analyses: V0 ratios (tracking &vertexing only) and p/p (+ RICH PID)

• Use minimum bias data• No need to know absolute luminosity

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andandKs ratiosKs ratios

• Ks-+ andp• Ks and Λ selection based on impact parameter of decay

products and Ks and wrt primary vertex• Systematics partially cancel• Data sample at 0.9TeV and 7TeV

Yields asymmetry clearly visible in raw mass plot

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Preliminary Preliminary andandKsKs

Baryon transport higher than predicted at √s 0.9 TeV

/Ks

Baryon/Meson suppression lower than predicted

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Prompt p/p production ratioPrompt p/p production ratio

• Pure samples of protons selected with RICH particle ID

• Calibration of efficiency and purity of RICH PID extracted from data

• Different interaction cross-sections in the material between p and p, particularly at low momentum Therefore limit analysis to tracks with P > 5 GeV

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Preliminary results Preliminary results √s =0.9TeV0.9TeV

Baryon transport higherthan predictions andconsistent with Λ/Λ

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Prompt p/p production Prompt p/p production √s =7TeV7TeV

Ratios become flatter aspredicted by models

Better agreement with MC

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Inclusive Inclusive production production

• Unique way to study strangeness production• Discrepancies from MC seen by all major LHC experiments• Test QCD fragmentation models in pp interactions in LHCb's

kinematic region• Φ→K+K- candidates selection requires RICHPID information• Cross section measurement is performed in bins of PT and

Both tunings underestimate Φ production in the measured kinematic range

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Open Charm cross-sectionOpen Charm cross-section• Same aspects of LHCb that makes us good for b -physics also Same aspects of LHCb that makes us good for b -physics also

aids charm physicsaids charm physics• Charm cross section ~20x larger than beautyCharm cross section ~20x larger than beauty• First measurement at First measurement at √s =7TeV7TeV• Measurements down to very low PtMeasurements down to very low Pt• Current results:Current results:

• Cross section for D0,D+, D+*,Ds with 1.8nbCross section for D0,D+, D+*,Ds with 1.8nb-1-1

• Measurement in 2D (Pt and Measurement in 2D (Pt and ))• Efficiency extracted both from data (PID) and from MCEfficiency extracted both from data (PID) and from MC• Removal of secondary charm ( from beauty decays) using IPRemoval of secondary charm ( from beauty decays) using IP• Work in progress to add Work in progress to add c and to increase data sample c and to increase data sample

statisticsstatistics

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D* , D0 cross section resultsD* , D0 cross section results

σ(D0;pT<8GeV/c,2<y<4.5)=1488±182 μbPYTHIA prediction: σ(D0;pT<8GeV,2<y<4.5)=1402±2 μb

σ(D*+;pT<8GeV/c,2<y<4.5)=676±137 μbPYTHIA prediction: σ(D*+;pT<8GeV,2<y<4.5)=653±1 μb

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DD+,+, Ds cross section results Ds cross section results

σ(D+;pT<8GeV/c,2<y<4.5)=717±109μbPYTHIA prediction: 509±1 μb

σ(Ds+;pT<8GeV/c,2<y<4.5)=194±38μbPYTHIA prediction: 255±1 μb

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Open charm resultsOpen charm results

• Various cross-sections results are in agreement with Various cross-sections results are in agreement with MC predictionsMC predictions

• Using published fragmentation fractions Using published fragmentation fractions – σ(pp→HcX,2<y<4.5,pT<8GeV/c)=1.23±0.19mbσ(pp→HcX,2<y<4.5,pT<8GeV/c)=1.23±0.19mb

• Using PYTHIA to extrapolate to 4π, we obtain the Using PYTHIA to extrapolate to 4π, we obtain the following (preliminary) total open charm cross-following (preliminary) total open charm cross-section:section:– σ(pp→cc)=6.10±0.93mbσ(pp→cc)=6.10±0.93mb• Result for total cross-section in 4π consistent with expectations ( Result for total cross-section in 4π consistent with expectations (

σ(pp→cc) ≈ 20×σ(pp→bb) ) seen next for σ(pp→bb)σ(pp→cc) ≈ 20×σ(pp→bb) ) seen next for σ(pp→bb)

• Work ongoing to measure cross-sections with more Work ongoing to measure cross-sections with more datadata

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J/J/ production production

• Very important measurement:Very important measurement:– J/ψ production mechanism not well understood, the color-octet J/ψ production mechanism not well understood, the color-octet

model used to fit the CDF data doesn't describe the J/ψ model used to fit the CDF data doesn't describe the J/ψ polarizationpolarization

– BBJ/ψ X decays fundamental for the LHCb core physics J/ψ X decays fundamental for the LHCb core physics programprogram

• Large signal yield:Large signal yield:– Differential cross section d2σ/dptdy Differential cross section d2σ/dptdy

as a function of transverse as a function of transverse momentum pT and rapidity ymomentum pT and rapidity y

– 14 bins in pt: 0 < pT < 14 GeV/c , 14 bins in pt: 0 < pT < 14 GeV/c , X 5 bins in y: 2 < y < 4.5 X 5 bins in y: 2 < y < 4.5

• Excellent mass resolution Excellent mass resolution (~ 15 MeV/c2 depending on bin)(~ 15 MeV/c2 depending on bin)

–

564603 +/- 924

5.2pb-1

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J/J/ production cross section production cross section

• Two measurements (pseudo proper time Two measurements (pseudo proper time separation):separation):– prompt J/ψ: direct production in pp collisions or seed down from prompt J/ψ: direct production in pp collisions or seed down from

other charmonium states ( ψ(2S), χc ...)other charmonium states ( ψ(2S), χc ...)– J/ψ from B decayJ/ψ from B decay

• Efficiencies are computed from Monte Carlo and are Efficiencies are computed from Monte Carlo and are extensively checked on data with control samplesextensively checked on data with control samples

• Polarization affects a lot the detection efficienciesPolarization affects a lot the detection efficiencies– Quote results in three extreme cases Quote results in three extreme cases

for for prompt production prompt production – Polarization measure ongoingPolarization measure ongoing

• Luminosity 5.2 pbLuminosity 5.2 pb-1-1

Prompt From b

Tails

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J/J/ cross section results cross section resultsPrompt J/Prompt J/ J/J/ from b from b

Extrapolation to bb cross section in 4π via Pythia 6.4 with LEP branching ratio: Br(b→J/ψ+X) = (1.16±0.1)%

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J/J/ comparison with theory comparison with theory

• A comparison with three different models is proposed.o LO and NLO NRQCD (Non Relativistic QCD summing color

Singlet and color Octet)o NLO CEM (Color Evaporation Model)

• The NLO NRQCD model seems to fit data reasonably well in the high Pt region, though the uncertainty is much large and there is a clear problem at low Pt.

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bb Cross Section: b → Dbb Cross Section: b → D00XX• reconstruct D0 in K- reconstruct D0 in K- + decay mode+ decay mode

• reconstruct D0reconstruct D0- pairs from a common vertex- pairs from a common vertex

• select “D from B” by large impact parameterselect “D from B” by large impact parameter

• use wrong-sign D0use wrong-sign D0 pairs to estimate pairs to estimate backgroundsbackgrounds

PromptFake

Signal

Right sign Wrong sign

L=

3pb-1

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bb cross sectionbb cross section

• 2 samples: 3nb2 samples: 3nb-1-1 data taken with open trigger and data taken with open trigger and 11nb11nb-1-1 with muon trigger : results in agreement with muon trigger : results in agreement

• b quark fragmentation fraction from LEPb quark fragmentation fraction from LEP

• 17% systematic dominated by uncertainties in 17% systematic dominated by uncertainties in luminosity and Monte Carlo representation of the luminosity and Monte Carlo representation of the tracking efficiencytracking efficiency

•

within LHCb acceptance( 2 < η(Hb) < 6)σ (pp → HbX) = (75 ± 5.4 ± 13) μb

using Pythia to extrapolate to full phase spaceσ (pp bbX) = (284 ± 20 ± 49) μb

Published Phys Lett B 694 (2010) 209

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Electroweak physicsElectroweak physics

• At LHCb unique possibility to measure Z, W in forward region

• Such measurement probe PDF the low-x, high Q2 region inaccessible to other experiments o At the LHC unprecedented Q2 due to the

higher beam energy

• Reconstruction of ZReconstruction of Z and W and W

• PID tracking and trigger efficiency PID tracking and trigger efficiency extracted from dataextracted from data

• preliminary results from 16.5 pbpreliminary results from 16.5 pb-1-1

o All results in agreement with theoryAll results in agreement with theory

o Provide new constraint on proton PDFProvide new constraint on proton PDF

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ConclusionsConclusions

• LHCb data taking started successfully LHCb data taking started successfully

• Very good detector performance despite of harder condition Very good detector performance despite of harder condition than designthan design

• Several analysis on going:Several analysis on going:o Particle productionParticle productiono Open and hidden charmOpen and hidden charmo bb cross sectionbb cross sectiono ElectroweakElectroweak

• In 2011 expected luminosity ~1fbIn 2011 expected luminosity ~1fb: core LHCb physics results : core LHCb physics results expectedexpectedo Eg. BsEg. Bs(actually first result expected for winter conference)(actually first result expected for winter conference)o Bs mixing CPBs mixing CP from tree and loop from tree and loop o AAFBFB B BK*K*