First Results from the LHCb Experiment

First Results from the LHCb First Results from the LHCb

ExperimentExperiment

First Results from the LHCb First Results from the LHCb

ExperimentExperimentAntonio Pellegrino on behalf of the LHCb

Collaboration, HESI 2010, Kyoto, 12-08-2010

Outline:

introduction (our goal)

LHCb mission and key measurements

first data (where we are, LHC start-up)

LHCb performance

first results

prospects for future measurements (where we are going)

LHCb MissionLHCb Mission

The LHCb mission is to search for New Physics (NP)

arXiv:0912.4179v2 [hep-ex]

• Mainly search of possible corrections to the Standard Model (SM) picture of flavor

LHCb key measurements described in detail in

o typical LHCb physicists “expert” of standard electro-weak model

• QCD mainly perceived as a “theoretical” uncertainty to overcome to get to the new physics!?

Actually a hugely successful part of the electroweak (EW) sector of the SM!

2008 Nobel prize to Kobayashi and Maskawa!

http://arxiv.org/abs/0912.4179v2

LHCb Key MeasurementsLHCb Key Measurements CKM angle

improve tree-level determination compare with virtual-loop-level determination

CP violation in Bs decays Rare decay B0

s µµ Lorentz structure

• Scattering angular distribution B0 K0 µµ• Time evolution of B0

s

new particles contributions (strength, phase, Lorentz structure) to loop diagrams in Flavor-Changing Neutral

Currents (FCNC)

Potentia et ActusPotentia et Actus• LHCb key measurements require ~1,00010,000 pb-1

not yet results on key measurements

Days since Jan 1st 2010

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LHC still “ramping up”• ~0.1 pb-1 per fill (~15 hours)• expect O(103 pb-1) by 2011

2011 “annus mirabilis” for B0s µµ and B0

s J/

Last update: August 9

First resultsFirst results

First results on particle production

I will focus on:

o J/ cross section(s)o (pp bbX) cross sections

• extrapolation from inclusive J/• extrapolation from b D0 X

o open-charm cross sectionso Ks cross sectiono /, p/p, /Ks production

ratios first fully reconstructed B decays and prospects for 2010-2011 o CP violation studies with charm (D+K+K-+)

o CP violation in Bs J/ o rare decay B0

s µµo angular distribution B0 K0 µµ

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6

The LHCb DetectorThe LHCb DetectorLHCb is a forward spectrometer

b-hadrons predominantly produced in the forward

cone

Where it isWhere it is

The LHCb CavernThe LHCb Cavern

Shielding wall(against radiation)

Electronics + CPU farm

Offset interaction point (to make best use of

existing cavern)

Detectors can be moved away from beam-line

for access

Cavern ~100m below

surface

Proton beam

Proton beam

April 21, 2023 Antonio Pellegrino 9

B-Physics Experiment in a B-Physics Experiment in a nutshellnutshell

~1 cm

1. vertex resolution identify B and D hadrons resolve fast oscillations

2. momentum resolution separate topologically

similar final states

3. K/ separation separate topologically

similar final states tag B flavor

K-4. muon, electron and photon ID for various other interesting final states to tag B flavor

5. highly selective trigger to reduce rate to acceptable level based on muons, electrons,

high pT hadrons, large IP tracks Example: Bs Ds K

Btag


LHCb Detector (Overview)LHCb Detector (Overview)

VELO

proton beam

collision point

~1 cm

B

Dipolemagnet

Crucial for B physics:– polyvalent trigger (incl. hadrons) – excellent particle ID– excellent tracking/vertexing (m, )

proton beam

VELO: Vertex Locator (around IP) ; TT, T1, T2, T3: Tracking stations RICH 1-2: Ring Imaging Cherenkov (PID) ; M1–M5: Muon stationsECAL, HCAL: Calorimeters

Detector Performance Detector Performance IntermezzoIntermezzo

follow a few slides on sub-components of the LHCb detector

o main focus will be on performance

o main message will be• things work largely as expected• even if we may not always have the “ultimate” performance no limitation for any measurement


LHCb Detector Slide Show (1)LHCb Detector Slide Show (1)o contains the pp-collision pointo precise determination of primary and secondary vertices (B lifetime)

~1 cm

B

21 silicon -strip stations

• r-φ geometry• pitch= 40-100 μm

21 silicon -strip stations

• r-φ geometry• pitch= 40-100 μm

e.g. with 25 tracks ~15m in X,Y and

~90m in Z

VertexingVertexingo excellent hit resolutiono cluster finding efficiency 99.7%o module and sensor alignment better than 5 mo VELO is opened during injection !

• Fill-to-fill variation of alignment < 5 m

X resolution

Y resolution

pp vertex resolution

~20m IP resolution at high

pTexpected to improve with

better material description


LHCb Detector Slide Show (2)LHCb Detector Slide Show (2)o charged particle momentum determinationo TT before magnet, Inner and Outer Tracker after magnet

TrackingTracking

Residual (mm)

LHCb Preliminary

Residual (mm)

LHCb Preliminary

LHCb Preliminary

TT IT

OT

Hit resolutions close to expected IT : 54 m TT : 55 m OT : 250 m

expected to improve with better alignment

Invariant Mass ResolutionInvariant Mass Resolution

Ks →

(data) = 3.3 MeV

(MC) = 2.6 MeV

D0 → K(data) = 9 MeV(MC) = 7 MeV

→ (data) = 52 MeV

L~100 nb-1

J/ →

(data) = 16 MeV

(MC) = 12 MeV

At present already good mass resolution (will be improved)


LHCb Detector Slide Show (3)LHCb Detector Slide Show (3)o Particle IDentification; kaon-pion separation

Particle IdentificationParticle Identification

RICH1 RICH2

C4F10 gas

n=1.0014

Up to ~70 GeV/c

CF4 gas

n=1.0005

Beyond ~100 GeV/c

Silica Aerogel

n=1.03

1-10 GeV/c

LHCb Data (Preliminary)

Kaon Ring

lnL(K-)>0

p/K/p separation in 2–100 GeV/c range• two gaseous and one aerogel radiator


LHCb Detector Slide Show (4)LHCb Detector Slide Show (4)o muon trackingo trigger (at 40MHz)

Muon IdentificationMuon Identification

Tracking system

Muon system

J/µ probe

µ tag

J/

(2S)

High -ID efficiency• P() = (2.350.04)% [Ks]• P(p) = (0.210.05)% [p]• P(K) = (1.670.06)% [KK]


LHCb Detector Slide Show (5)LHCb Detector Slide Show (5)o particle identification; electron, photon, hadrono trigger (at 40MHz)

The LHCb TriggerThe LHCb Trigger

40 MHz

LHC clock

~30 MHz

crossings

~10 MHz visible

inelastic in LHCb

L0 trigger

max. 1 MHz

L0 trigger

max. 2 kHz

[hardware] [CPU farm]

LHCb has a trigger system “dedicated” to B Physics “efficiently” select decays with various final states (, e, , K, , …) triggering is a challenge

~1/100 events with bb B decays of interest branching fractions ~10-3 (or lower)

Meeting this challenge is one of the main objectives of LHCb operation!

_

Present Trigger StrategyPresent Trigger StrategyFor bulk of running foreseen this year, with luminosities up to ~1030 cm-2 s-1,we can relax many of our trigger cuts

Apply very low pt cuts – main purpose ofL0 is now to seed HLT1 regions of interest

Reduce requirements on track impactparameter w.r.t. nominal settings

Not needed at all initially, then introducewith rather loose suppression requirements

2010 approach

Boost trigger efficiencies for hadronic decays of promptly produced D’s Golden opportunity for charm physics studies!

Total efficiencies for hadronic B decays ~70% and for leptonic decay modes >90%.

Trigger PerformanceTrigger Performance

nominal running conditions

The LHCb trigger concept works!• full trigger operational• efficiencies as expected

• at low lumi, running with relaxed thresholds and quickly adapting to conditions more challenging than nominal

trig = [NMC(J/) triggered] / [NMC(J/) reconstructed]

Day 1 at Day 1 at s = 7 TeVs = 7 TeV

Event display, top view

pp collision at 3.5+3.5 TeV, March 30, 2010

LHCb OperationLHCb OperationLHCb operation proceeds very reliably and efficiently ~92% data taking efficiency

Days since Jan 1st 2010

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I will focus on:







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J/J/ Production Production

o intrinsically interesting (J/ production mechanisms)o b J/ X of crucial importance in the LHCb core program

measured J/’s through their J/ µ+µ- decay modeo N(J/) = N(J/ µ+µ-) / BR(J/ µ+µ-)

separate contribution from b-decays from the “prompt” one (directly in a pp collision or from decay of heavier (2S), c,etc.)

o use pseudo proper time

Measurement strategy:

measured total cross section and d/dpT

present measurement coverage (limited by statistics)

o yJ/ψ (2.5,4.0) and pT

J/ψ < 10 GeV

BR(J/ µ+µ-) = (5.930.06)%

J/J/ Selection Selection

o select events through µ+µ- invariant-mass window• N(J/ µ+µ-) = 287273

Fit to data/background

yielded: S/B = 1.3 Mean = (3088 ± 0.4) MeV/c2

σ = (15.0 ± 0.4) MeV/c2

o Trigger• L0 : MUON with pT > 0.48 GeV• HLT : (pT)single-µ>1.3 GeV M(µ+µ-)>2700 MeV/c2

o Offline• 2 µ’s with good vertex• pT > 0.7 GeV

Separate b-Decays Separate b-Decays ContributionContribution

PV

µ+

µ-

displacement of the di-µ vertex along the beam linezz

tz = [z / pz(J/)] M(J/)Pseudo-proper time

o Prompt J/’s zero pseudo-proper timeo J/’s from b-decays exponentially decaying tz distribution

• due to the lifetime of the parent B-hadrons

maximum-likelihood fit to the (unbinned) tz distribution J/’s from b-decays

J/J/’s from b Decays’s from b Decays

max.-likelihood fit to tz

N(prompt) = 252774 N(from b decays) = 31624

fJ/(from b) = (11.10.8)%

Acceptance and EfficiencyAcceptance and Efficiency

to complete cross section extraction )/(1 JN

dt

L

= ACCEPTANCE TRIGGER RECONSTRUCTION

[NMC(J/) with both µ’s in LHCb] / [NMC(J/) generated]

[NMC(J/) triggered] / [NMC(J/) reconstructed]

[NMC(J/) reconstructed] / [NMC(J/) in acceptance]

In the analysis phase space : TOT 4070%

Limited by statistics

J/J/ Cross Section(s) Cross Section(s)o For yJ/ψ (2.5,4) and pT

J/ψ < 10 GeV/c• σ(J/ inclusive) = (7.65 ± 0.19 ± 1.10 )

μb• σ(J/ from b decays) = (0.81 ± 0.06 ± 0.13)

μb

+0.87

-1.27

o For yJ/ψ (2.5,4)• dσ/dpT(J/

inclusive) Dominant systematic errors trig. and tracking eff. (~9%) luminosity meas. (~10%)

However, measurement still dominated by statistics now increasing ~0.1 pb-1 / fill bin in y and extend pT range full angular analysis

Prospects for J/Prospects for J/ Cross Cross Section(s)Section(s)

Measurement still dominated by statistics

o now increasing ~0.1 pb-1 / fillo bin in y and extend pT range

• e.g with ~50pb-1, 5 bins in y and 10 in pT up to 12 GeV/c with ~10% accuracy

o extend analysis to (2S)effects of J/ spin configuration not discussed here

o with increasing statistics, angular analysis polarization

Extrapolation to bb Cross Extrapolation to bb Cross SectionSection

if one extrapolates (J/ from b decays) (Hb X)

For Hb(2,6), ½ (pp Hb X) = (84.5 6.3 15.6)

b

any b- or b-hadron in LHCb acceptance

2<<6

_

Extrapolation with PYTHIA 6.4 assume LEP b-hadrons production fractions

with further extrapolation to full angular acceptance

(pp bbX) = (319 24 59) b

_

compare with extrapolation from B D0 X …



I will focus on:







_ _

Extrapolation to bb Cross Extrapolation to bb Cross SectionSection

From PDG b in B/B0/Bs

0/b-baryon admixture D0 l+ l X• BR = 6.82% 0.35%• (production fractions from Heavy Flavor Averaging Group)

… extrapolation to (pp bbX) from to B D0 X …

_

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Measurement strategyo measure right-sign D0 - pair originating at a common vertex different from the pp interaction vertex

o separate D0’s from b-decays from “prompt” ones (directly in a pp collision or from decay of heavier states)

• use impact parameter of D0’s wrt pp vertex

DD00 Selection Selection

Measured D0’s through their K- + decay modeo N(D0) = N(D0 K- +) / BR(D0 K- +)

• BR(D0 K- +) = (3.91 0.05)%

Reject background and mass combinationso require minimum pT

• pT and pK

T > 0.3 GeV• K- and + from same vertex• K-,+ vertex not the same as pp

~3 nb-1

DD00‘s from b-Decays‘s from b-Decays

If D0 comes from a b-decay, then K-

+ has a large impact parameter (IP) with respect to the pp vertex

PV

K-

+

X

D0

bIP

Use IP to separate D0‘s from a b-decay from “prompt” ones (produced in pp collision directly or from decay of

heavier states)

From b-decay

Prompt

~3 nb-1

DD00 from b-Decays from b-Decayso require in final stateo require common D0 vertexo require right sign combination D0- and D0+

o combine M(K) window with large IP(D0) requirement• yield from unbinned log-likelihood fit simultaneously to M(K) and ln(IP)

Rig

ht

Sig

nW

ron

g S

ign

0.1 pb-1

0.1 pb-1 0.1 pb-1

0.1 pb-1

from B

prompt1540 ± 45 events with D0 from b-

decay

_

Extrapolation to bb Cross Extrapolation to bb Cross Section Section

cross section defined as

2

)(1 00

DDN

dtLefficiency (acceptance, trigger, reconstruction)

d/d in 4 bins of pseudo-rapidity in the LHCb acceptance 2<<6 = -ln(/2), with determined from the pp and D0 vertices dominating systematic uncertainties from luminosity and tracking extrapolate to (pp Hb X) (PYTHIA 6.4, LEP b-hadrons production fractions)

½(ppHb X) = (74.95.312.8) b

Total in 2<<6 :

½(ppHb X) = (2822048) b

Further extrapolation to full :

From J/ incl. : (3192459) b

Theory MCFM : 332 bTheory NFMR : 254 b



I will focus on:







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Open CharmOpen Charmo forward D-meson production intrinsically interesting

• mixing and CP violation (e.g. lifetime difference between D0KK and D0K)• rare decays D0+-

measurements of D*, D0, D, Ds production cross sections ongoing

D+

Ds

• impact parameter key tool to separate “prompt” D,Ds production

Prompt

From secondar

y

(D+)/(Ds) = 2.32 ± 0.27 ± 0.26

PDG 2008: f(cD+)/f(cDs) = 3.08±0.70

L~124 nb-1

Huge yield of D0KK with O(100 pb-1)

o necessary step for the understanding of B-meson decays

L~2 nb-1



I will focus on:







B-meson DecaysB-meson Decays

Nsignal = 22.9±5.3

= 12.0±2.5 MeV

L~13 nb-1

B

D

B

KFirst signal in charmed B decays combining:

B0D+- and B+D0+

Expect soon Bs Ds- and Cabibbo-suppressed BDK

analysis of fully reconstructed B-decays advancing by the day• integrated luminosity growing “exponentially”• event yields in line with MC expectations• good mass resolution

Bs

KK

Nsignal = 36.6 5.5

= (36.56.3) MeVL~230 nb-1

Nsignal = 9.5 1.4

= (33.78.6) MeVL~230 nb-1

BB++ J/ J/ K K++ Event Display Event Display

Y (mm)

X (mm)

M(J/ψK) = 5326.7±10.9 MeV/c2

p(J/ψK) = 62.7 GeV/c pT (J/ψK) = 10.48 GeV/c L = 2.03 mm cos() = 0.9999

B B J/ J/ K Analysis K Analysis

analysis of BJ/K+ and BJ/K*0 rapidly advancing• good momentum resolution

• event yields in line with MC expectations

B

J/K

+

B

J/K

*0

L~230 nb-1 L~230 nb-1

t>0.3 ps t>0.3 ps

• proper-time resolution not yet final, but good enough to extract signal• unbinned log-likelihood fit to (M,t | t)



I will focus on:







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BBss J/ J/ Event Display Event Display

• M(μμ) = 3072 MeV/c2

• M(KK) = 1020 MeV/c2

• M(μμKK) = 5343 MeV/c2

• 2vtx / nDOF = 0.8

• t/σ(t) = 78 (L = 20 mm!)• cos() = 0.9999998

First reconstructed Bs J/ decays:

main lines of analysis analogous to BJ/K t>0.3 ps

L~230 nb-1

in line with expected yield

Prospects for BProspects for Bss J/ J/ BsJ/ one of the key measurements that will be pursued in 2010/2011

sJ/ψ = -2S is very small and precisely predicted in the

standard model Very sensitive to NP !!!

Based on the fact that:o ~50k events / fb-1 consistent with

number of BsJ/ seen in datao proper-time resolution <st> = 0.038

ps• at present is ~1.6 worse in data

o Tagging performance eD2 = 6.2%• to be tested with more data

2010/2011 run promises exciting results on the sJ/ measurement!!

Prospects for BProspects for Bss ++--

Bs +- another of the key measurements that will be pursued in 2010/2011

Branching ratio is hyper-small and precisely predicted in the standard model : (3.20.2)10-9

Very sensitive to NP !!!

LHCb exclusion limit @ 90% C.L.

Current limit can already be improved with 100 pb-1

Exclusion of “enhancements” up to ~7×10-9 should be possible with 1 fb-

1

2010/2011 run promises exciting results on the BR(Bs+-) measurement!!

Summary and OutlookSummary and Outlook

First data are being used for calibration, first of all of detector and trigger

o LHCb trigger concept has been proven with datao Charm resonances and B mesons have been

reconstructed• (even Z & W candidates)

o First measurements of production cross-sections at √s = 7 TeV for open charm, J/ and bb

high class measurements in the charm sector possible with 50 pb-1

Bs mm and Bs J/ will reach new sensitivity with ~100 pb-1

exciting prospects of discovery with full 1 fb-1 sample LHCb upgrade to collect data at 5-10 times higher luminosity in preparation

_

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First Results from the LHCb Experiment

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