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Antonio Pellegrino on behalf of the LHCb Collaboration, HESI 2010, Kyoto, 12-08-2010. First Results from the LHCb Experiment. Outline: introduction (our goal) LHCb mission and key measurements first data (where we are, LHC start-up) LHCb performance first results - PowerPoint PPT Presentation
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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!
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
Inte
gra
ted
lu
mi (n
b-1)
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
_ _
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
April 21, 2023 Antonio Pellegrino 10
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
April 21, 2023 Antonio Pellegrino 12
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
April 21, 2023 Antonio Pellegrino 14
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)
April 21, 2023 Antonio Pellegrino 17
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
April 21, 2023 Antonio Pellegrino 19
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]
April 21, 2023 Antonio Pellegrino 21
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
Inte
gra
ted
lu
mi (n
b-1)
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
_ _
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 …
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
_ _
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 …
_
__
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
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
_ _
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
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
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)
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
_ _
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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