First Results from LHCb

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


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


PV

K-

π+

BD0 X

D0K-π+

p p

IP

K+

μ+

μ-B1 cm


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


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


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%


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


Average event size ~35 kB

10 MHz

850 KHz

3 KHz

10

LHCb running in 2011


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


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


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


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


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


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


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


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


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


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


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


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


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


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


From http://lhcb-public.web.cern.ch/lhcb-public

26

φs from BsJ/ψ f0(980)


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


+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


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


)()()()()(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.


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


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


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


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


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


• 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.


Thank you!

Backup

41

Luminosity measurement in 2010


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


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


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


LHCb-CONF-2011-055First step: measure BR.

Next step: measure AD (or effective lifetime)

Bd → K*g Bs → fg

Documents

First Results from LHCb