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The XXth International Workshop High Energy physics and Quantum Field Theory. First Results from LHCb. 2 4 September – 01 October 2011, Sochi, Russia. Yu. Guz (IHEP Protvino), on behalf of the LHCb collaboration. LHCb detector Selected physics results LHCb upgrade issues Conclusions. - PowerPoint PPT Presentation
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First Results from LHCbYu. Guz (IHEP Protvino),
on behalf of the LHCb collaboration
24 September – 01 October 2011, Sochi, Russia
The XXth International Workshop High Energy physics and Quantum Field Theory
LHCb detector
Selected physics results
LHCb upgrade issues
Conclusions
2
LHC is a pp collider with ECM = 14 (or 7) TeV and luminosity up to 1034 cm-2s-1
The LHCb experiment at LHC
3
bb
bb
LHC is good as a B factory: the bb cross section σ(ppbbX) is large, ~300 μb
• The bb production is sharply peaked forward-backward.
LHCb choice: a single arm detector 1.9<|η|<4.9σ(bb)~75 μb in the acceptance
‒ to be selected out of ~60 mb of all visible pp interactions very selective trigger is required!
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb is dedicated to study processes with heavy quarks (b, c): flavor oscillations , CP violation, rare decays etc. Main physics objective: indirect search for New Physics phenomena, mainly in loop-mediated processes‒ can access much higher mass, not limited by √s‒ complementary to direct searches: provides information
about magnitudes and phases of NP couplings
The LHCb experiment at LHC
4
B hadron signature: particle(s) with high pT and displaced vertex.
Typical B hadron flight distance is ~ few mm.
To be able to reconstruct complex decay chain, it is important to have: good (vertex) coordinate resolution; magnet and tracking detectors for momentum measurement; particle identification:
π/K/p separation in wide momentum range; muon identification;
calorimetry: for γ/π0 reconstruction; electron identification;
trigger for high pT particle
Yu. Guz QFTHEP-2011 First Results from LHCb
PV
K-
π+
BD0 X
D0K-π+
p p
IP
K+
μ+
μ-B1 cm
The LHCb experiment at LHC
5
• tracker stations (inner area: silicon; outer: straw tubes)
• two RICH detectors• EM calorimeter with preshower
• hadron calorimeter, to trigger high pT hadrons
• muon identification system
Muon System
Calorimeters Tracking System
RICH detectors Vertex Locator(VELO)
Magnet
Yu. Guz QFTHEP-2011 First Results from LHCb
Main components:• Vertex Locator (VeLo): a silicon strip
detector surrounding the IP ‒ sensitive area starts at 8 mm from the beam!
• warm magnet, ~4 Tm; reversible field polarity to cancel out possible biases in measurements
LHCb Collaboration: 55 institutes of 15 countries, 755 participants
Search for New Physics in CP violation and Rare Decays
7
Tracking system
Yu. Guz QFTHEP-2011 First Results from LHCb
Vertex detector (VeLo): primary vertex of pp interaction and B decay vertices with few μm accuracy;
tracking stations (silicon strip and straw tubes) upstream and downstream the magnet measure the momentum
Accurate magnetic field map and good alignment are necessary prerequisites PV resolution (for 25 tracks): ~16 μm in X&Y,
~76 μm in Z IP resolution: ~13 μm in X, Y (~12 μm in MC) effective mass resolution: as an example,
~15 MeV on J/ψμμ
VeLo: two retractable halves, 21 station, Rφ silicon sensors
8
Particle ID
Particle ID with RICH detectors K ID efficiency ≈ 96%, πK misID ≈ 7%
Yu. Guz QFTHEP-2011 First Results from LHCb
Muon IDefficiency: 97.3±1.2% at p(μ)>4 GeV/c misID πμ ≈ 2.4%, p μ ≈ 0.18%
BR(ημμ)=5.8±0.8·10-6
9
Trigger Hardware Level-0 trigger followed by two-stage software High Level Trigger, HLT1 and HLT2
● L0 requires presence of a high pT object (h, μ, μμ, γ, e±) in CALO and Muon system
● HLT1 performs partial reconstruction, confirms L0 objects: associates them with reconstructed tracks, especially with those displaced from the PV
● HLT2: full reconstruction; uses reconstructed objects for exclusive selections with clear signature
Depending on luminosity, the L0 and HLT thresholds can be tuned such that not to exceed maximal throughput of the systems.
First data of 2010 with low LHC luminosity: loose trigger conditions, data suitable for production studies.
Since summer 2010 – trigger optimized for B-physics
Yu. Guz QFTHEP-2011 First Results from LHCb
Average event size ~35 kB
10 MHz
850 KHz
3 KHz
10
LHCb running in 2011
Yu. Guz QFTHEP-2011 First Results from LHCb
The luminosity is limited, in particular, by requirement from reconstruction of not too many visible pp interactions in one event (μ).
LHC does luminosity leveling for LHCb by varying the bunch overlap
Currently, at LHC energy of 2x3.5 TeV, LHCb is running at L≈ 3.5·1032 cm-2s-1 . With ~1400 bunches in LHC, this corresponds to μ≈1.3 (the original design parameters for 2x7 TeV running with ~2800 bunches were L≈ 2·1032 cm-2s-1 and μ≈0.4 ).
11
LHCb luminosity
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb is running smoothly since the LHC startup, no major hardware problems, the detector is > 99% operational.
2010 2011
1 fb-1 expected by the end of 2011, same (or more) in 2012
Selected physics results
13
Mass measurements
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-027
LHCb, MeV/c2
5279.17 ± 0.295279.50 ± 0.305279.50 ± 0.305366.30 ± 0.605620.2 ± 1.66277 ± 6
PDG
Performed with 2010 data, 37 pb-1.
More precise than PDG values!
14
Lifetime measurements
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-001Performed with 2010 data, 37 pb-1.
1.638 ± 0.0111.525 ± 0.0091.525 ± 0.0091.477 ± 0.0461.391 ± 0.038
PDGLHCb, ps
BsJ/ψ φ, t > 0.3 ps
15
bb production
Yu. Guz QFTHEP-2011 First Results from LHCb
The ppbb cross section was measured in two ways: deduced from J/ψ-from-b production cross-section using the
LEP average bJ/ψ branching fraction and extrapolating into 4π (see talk of K. Belous):
σ(ppbbX)=288± 4±48 μb measured using b D0Xμ-ν (+cc) inclusive yields gives a compatible result:
σ(ppbbX)=284±20±49 μb
In this analysis the b decay candidates were selected as D0 (K-π+) and μ- having common vertex; the right sign combinations has significant nonzero impact parameter (IP) of D0 (K-
π+), which is a signature of a true b decay.
PL B694 (2010) 209
EPJ C71 (2011) 1645
wrong sign (D0μ+) combinationright sign (D0μ-) combinationall D0K-π+ candidates
16
B+ production
Yu. Guz QFTHEP-2011 First Results from LHCb
The B+ production total and differential cross-section were measured in the LHCb acceptance in B+J/ψK+ :
σ(B+, 2<y<4.5)=37.1±1.9(stat)±5.3(syst) μb
B+
LHCb-CONF-2011-033
17
b fragmentation, fs/fd
Yu. Guz QFTHEP-2011 First Results from LHCb
Important input for absolute branching measurements, like Bsμμ.
Average obtained using independent measurements by LHCb:
• ratio of yields of exclusive hadronic modes BsDs-(K+K-π-)π+
and BdD-(K+π-π-)π+:
• fs/fd=0.256±0.014(stat)±0.019(syst)±0.026(theor);
• ratio of BsDs-π+ to BdD-K+:
• fs/fd=0.250±0.024(stat)±0.017(syst)±0.017(theor);
• ratio of yields of inclusive semileptonic modes, D0Xμν, D-Xμν and DsXμν:
• fs/fd=0.268±0.008(stat) (syst)
The combined result is:
fs/fd=0.267
+0.022- 0.020
+0.021- 0.020
LHCb-CONF-2011-034
LHCb-CONF-2011-028
LHCb-PAPER-2011-006
18
flavor tagging
Yu. Guz QFTHEP-2011 First Results from LHCb
Necessary for the B time-dependent studies!
The flavor tagging was optimized on 2010 data using the B+J/ψK+, B0J/ψK*0 and B0D*-μ+νμ decays. Typically, εeff≈2% for OS taggers only, 2.8% for OS+SS combination; different but close numbers for other B decays; is carefully calibrated for each particular study.
The algorithm is designed to provide a per-event estimate of the mis-tag probability.
LHCb-CONF-2011-003
Effective tagging efficiency:εeff=εtagD2=εtag(1-2ω)2, where:εtag – tagging efficiencyω – mis-tag fractionD – dilution factor
19
Δms
Yu. Guz QFTHEP-2011 First Results from LHCb
The Bs mixing frequency, Δms, measured on 341 pb-1 LHCb data in the decay BsD π+, with D K+K–π–, using all three KKπ modes: φπ, K*K and non-resonant KKπ.
LHCb-CONF-2011-050
Average proper time resolution calibrated on prompt Ds: σt≈45 fs (cf ~350 fs oscillation period of Bs).
Flavor tagger performance, εeff=εtag(1-2ω)2 : OST: (3.2±0.8)% ; SST: (1.3±0.4)%
–s
–s
(preliminary) result: Δms = 17.725±0.041±0.026 ps-1.
Earlier results:
LHCb, 37 pb-1 : 17.63±0.11±0.03 ps-1;
CDF (2006) : 17.77±0.10±0.07 ps-1.
New WA: Δms = 17.731±0.045 ps-1.
LHCb-CONF-2011-005
PRL97, 242003 (2006)
- world’s best measurement !
20
φs
Yu. Guz QFTHEP-2011 First Results from LHCb
Search of New Physics effects in the Bs mixing.
The mixing phase φs in SM is small and has little theoretical uncertainty: φs (SM) = -2arg[-(VtsVtb*)/(VcsVcb*)] = 0.0363 0.0016Good sensitivity to New Physics effects.
Via time-dependent analysis of Bs decay into CP eigenstates. The most suitable final states are J/ψφ, J/ψf0(980) : the decay amplitude is tree-dominated and not sensitive to NP.
BR(BsJ/ψφ) · BR(J/ψμμ) · BR(φK+K-) ≈ 4·10-5
however with V+V final state both CP parities are present, angular analysis is necessary.
BR(BsJ/ψf0(980)) · BR(J/ψμμ) · BR(f0π+π-) ≈ 0.8·10-5 ,
angular analysis is not needed.
21
φs from BsJ/ψ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
Apart from 3 KK P-waves for φ, the KK S-wave is included. Total of 10 physics parameters: 3 independent magnitudes out of four (|A ┴|, |A║|, |A0|, |As|) at t=0; 3 relative phases (δ┴, δ║, δs) w.r.t. δ0; φs, Γs, ΔΓs, Δms (the latter was fixed to its LHCb measured value, 17.725±0.11 ps-1).
A two-fold ambiguity is present: φs↔π-φs, ΔΓs↔-ΔΓs, δ║↔-δ║, δ┴↔π-δ┴.
Unbinned maximum likelihood fit, the event variables being candidate mass, decay time, decay angles and initial flavor. Required accurate description of background, efficiencies, resolutions, flavor tagging.
LHC
b-CO
NF-2011-049
22
φs from BsJ/ψ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
8276±94
The lifetime cut t>0.3 ps removes most of the background, resulting in total of 8276±94 signal events.
Only OS flavor tagging used for the J/ψφ analysis, calibrated on J/ψK* :
D=0.277±0.011±0.025, εtag = (2.08±0.41)%
LHC
b-CO
NF-2011-049
Proper time resolution was calibrated on prompt J/ψ: σt~50 fs .
per-event mistag probabilities
23
φs from BsJ/ψ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
Goodness of fit was checked using the “point-to-point dissimilarity test” (arXiv:1006.3019).
LHCb-CONF-2011-049
δ║ [3.01, 3.36] @ 68% CL
The 4% KK S-wave contribution.
The systematic errors mainly come from uncertainties in the description of angular and decay time acceptance and background angular distribution.
24
φs from BsJ/ψ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-049
SM
To date, world’s most precise result:
φs = 0.13 ± 0.18(stat) ±0.07(syst)
Γs = 0.656 ± 0.009(stat) ±0.008(syst)
ΔΓs = 0.123 ± 0.029(stat) ±0.008(syst)
- first 4σ evidence of ΔΓs > 0 !
Expectations for 2 fb-1 of 2011+2012• φs statistical uncertainty of ~0.07 – from
simple scaling• further improvement of statistical uncertainty
from including same side tagging• reduction of systematic errors from better
understanding of acceptance and background
25
φs from BsJ/ψ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
From http://lhcb-public.web.cern.ch/lhcb-public
26
φs from BsJ/ψ f0(980)
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-051
CP-odd final state, cannot determine Γs and ΔΓs simultaneously.
CL contours obtained using Γs from J/ψφ.
Using both Γs and ΔΓs from BsJ/ψφ:
φs =-0.44±0.44(stat)±0.02(syst)
When combining BsJ/ψφ and BsJ/ψf0(980):
φs =-0.03 ± 0.16(stat) ±0.07(syst)
LHCb-CONF-2011-056
The decay BsJ/ψf0(980) first observed by LHCb,CERN-PH-EP-2011-011
27
Bsφ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
+NP
BR much lower than BsJ/ψ φ. As a first stage - measurement of time-integrated triple product asymmetry
In SM both AU/V =0. Non-zero measurement means weak phase difference between CP even and odd eigenstates, clear sign of NP [M. Gronau and J. L. Rosner, arXiv:1107.1232]
)()()()(
0000
UNUNUNUNAU
)()()()(
0000
VNVNVNVNAV
, U=sin(2Φ)
, V=sin(±Φ), sign from cos(θ1)*cos(θ2)
Proceeds via bs FCNC penguin, possible New Physics contribution can be revealed e.g. through comparison of CPV phase with the one obtained from BsJ/ψφ
28
Bsφ φ
Yu. Guz QFTHEP-2011 First Results from LHCb
Studied with 340 pb-1 of data.Very clean mass peak.
No flavour tagging needed for triple product asymmetry
Consistent with zeroNext step : time-dependent CP
asymmetry measurements (needs more statistics)
LHCb-CONF-2011-052
AU=-0.064±0.057±0.014 AV=-0.070±0.057±0.014
29
direct CP asymmetry in Bd,sKπ
Yu. Guz QFTHEP-2011 First Results from LHCb
)()()()()(CP
πππππ
KBKBKBKBKBA
ΓΓΓΓ
δAAAAAA CPprodCPRAW det
LHCb-CONF-2011-042
Acp(Bd→Kπ) = -0.088±0.011(stat) ±0.008(syst) – World Average = -0.098
Acp(Bs→Kπ) = 0.27±0.08(stat) ±0.02(syst) - first evidence
+0.012 -0.011
Non-physical asymmetries Aδ were evaluated:
Aδ(BdKπ) = -0.007±0.006Aδ(BsKπ) = -0.010±0.002
30
Bs,dμμVery rare in SM (FCNC & helicity suppressed):
BR(Bsμμ)SM=(3.2±0.2)·10-9;
BR(Bdμμ)SM=(1.1±0.1)·10-10.
Yu. Guz QFTHEP-2011 First Results from LHCb
Previous measurements:
D0: BR(Bsμμ) < 5.1·10-8 (95%) (6.1 fb-1) PL B693, 539 (2010)
CDF: BR(Bsμμ) = (1.8 )·10-8 (hint !) (7 fb-1) arXiv:1107.2304
LHCb: BR(Bsμμ) < 5.6·10-8 (95%) (6.1 fb-1) PL B699, 330 (2011)
Recent CMS measurement: BR(Bsμμ) < 1.9·10-8 (95%) (1.1 fb-1) arXiv:1107.5834
+1.1- 0.9
A.J.Buras, arXiv:1012.1447
see talk by Yu. Shcheglov
May be significantly enhanced in models with S or P coupling; e.g. in MSSM
BR(Bs.dμμ) ~ tan6β / MA4 ,
a good probe for New Physics!
World best limits obtained by LHCb with 300 pb-1 of 2011 (+37 pb-1 of 2010)
BR(Bsμμ) < 1.5 (1.2) ·10-8 at 95% (90%) CL
BR(Bdμμ) < 5.2 (4.2) ·10-9 at 95% (90%) CL
31
Bsμμ
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-047CMS PAS BPH-11-019
Combined with recent CMS result:
BR(Bsμμ) < 1.08 (0.90) ·10-8 at 95% (90%) CL
Prospects for LHCb taken from arXiv:1108.3018
see talk by Yu. Shcheglov
32
Other LHCb results
Yu. Guz QFTHEP-2011 First Results from LHCb
Physics results not covered here:
• studies of radiative decays Bsφγ and BdK*γ.
• FB asymmetries in BK*μμ;
• CPV in charm, measurement of AΓ and ΔACP: results of 2010 available, 2011 expected soon
• LFV search in BK(π)μμ;
• CP asymmetry in B+DK+;
• Bc production and decays;
• b baryons;
• and more …
LHCb-CONF-2011-042
LHCb-CONF-2011-046LHCb-CONF-2011-023
LHCb-PAPER-2011-009
LHCb-CONF-2011-023
LHCb-CONF-2011-038
LHCb Upgrade
LHCb long term plans
34Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb Upgrade LoI: CERN-LHCC-2011-001
By 2017, LHCb is expected to take 5-10 fb-1 of data.
There is strong physics motivation to continue the present programme. Next step is to collect other ~50 fb-1 probe / measure NP effects at % level.
For this, LHCb should be able to run at higher luminosities: (1-2)·1033 @√s = 14 TeV.Upgrade is necessary
LHCb upgrade plan
35Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb Upgrade LoI: CERN-LHCC-2011-001LHCb at higher luminosity• typical L0 efficiency for purely hadronic
final states ~ 50% and will drop with luminosity. The acquisition rate for purely hadronic channels (like Bsφφ) does not increase with increasing luminosity!
• apart from the trigger, the LHCb performance will not deteriorate significantly up to 1033 cm-2s-1
The only way out is to replace the present hardware L0 trigger by a flexible software one which is able to digest the full input bandwidth, up to 40 MHz.
This implies replacement of almost all the frontend electronics.
LHCb upgrade plan
36Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb Upgrade LoI: CERN-LHCC-2011-001
Presently: • hardware L0 • software HLT1 with max 1 MHz input • HLT2 with up to 2 (3) kHz output• run now at 3.5 1032 cm-2s-1 @ √s=7 TeV
Upgrade: • fl;exible software LLT• up to 40 MHz input• up to 20 kHz HLT output • run at 5 times higher luminosity • big gain for hadronic modes
Detector issues
37Yu. Guz QFTHEP-2011 First Results from LHCb
• VELO: replace the whole detector (rad damage). New readout chips. Choice between strip and pixel options.
• other tracking detectors: leave present OT straw tubes at the periphery. Middle part: the options are silicon strips or scintillating fibers.
• RICHes: replace all the photodetectors, as present HPDs include readout electronics. MAPMTs is baseline. Remove aerogel in RICH1 (material budget).
• additional PID detector: Time of Internally Reflected Cherenkov Light (TORCH). Quartz plate radiator, 10-15 ps resolution. Installed between RICH2 and calorimeters.
• CALO: reduce PMT gain. Possible replace few modules in hottest areas. Removing part of the preshower is discussed.
• MUON: present frontend electronics can be kept and read out at 40 MHz. remove the M1 station before calorimeters.
Conclusions
38
● LHCb is running successfully at its design luminosity (and beyond!), demonstrating very good detector performance, and collected by now ~800 pb-
1 of physics data● already now, LHCb obtained physics results competitive with B-factories and
Tevatron experiments: most precise direct CP violation measurements in Bd,sKπ most precise measurement of Δms, most precise measurement of φs and ΔΓs in Bs J/ψφ, J/ψf0(980), best upper limits on rare decay Bsμμ
● by now, no significant deviation from SM observed, in particular the hints observed by Tevatron in Bsμμ and φs not confirmed
● 1 fb-1 expected by the end 2011, more in 2012. Many important physics results expected!
● high luminosity upgrade is foreseen.
Yu. Guz QFTHEP-2011 First Results from LHCb
Thank you!
Backup
41
Luminosity measurement in 2010
Yu. Guz QFTHEP-2011 First Results from LHCb
N
i YiXi
iinnfL1
21
4
N – number of bunchesf – collision frequencyn1i, n2i -- # of protons in bunchesσXi, σYi – transverse bunch sizes
LHCb preliminary 2009, ECM=0.9 TeV
In 2010, luminosity will be estimated from beam properties
Determined with ~15% accuracy in 2009 (dominated by the bunch current measurement uncertainty). In 2010 5-10% precision is expected.
42
Lepton flavor violation
Yu. Guz QFTHEP-2011 First Results from LHCb
Looking for DL=2 processes B+→K-μ+μ+and B+→μ+μ+ (allowed in NP models with a Majorana neutrino)
No signal observed in 36 pb-1
Improved present best limits by a factor of 40 (30).Publication in preparation.
LHCB-PAPER-2011-009
43
Bsφγ
Yu. Guz QFTHEP-2011 First Results from LHCb
Experimental probe: AD (or effective lifetime) [F. Muheim, Y. Xie, R. Zwicky, PLB 664:174, 2008]
2/sinh2/cosh tAtetR ssts DD D
AD sensitive to fraction of right-handed photons (even for small fs)
AD ~ 0 in SM, can be enhanced by NP with large RH currents.
Dominating SM quark level diagram has left handed photons
An example MSSM diagram with right-handed photons
44
Bsφγ
Yu. Guz QFTHEP-2011 First Results from LHCb
LHCb-CONF-2011-055First step: measure BR.
Next step: measure AD (or effective lifetime)
Bd → K*g Bs → fg
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