Overview of the LHCb Experiment

Overview of the LHCb Experiment
5th FOUR SEAS CONFERENCE IASI, ROMANIA , 29 May - 3 June 2007 Physics motivation Overview and expected performance of detector Prospects for physics performance on selected channels Outlook and conclusion presented by Andreas Schopper (CERN) on behalf of the Collaboration

CP violation and the CKM matrix
In Standard Model (SM), CP violation arises from quark mixing The Cabbibo-Kobayashi-Maskawa matrix VCKM describes rotation between the weak (flavour) eigenstates and quark mass eigenstates For anti-quarks, the complex conjugate matrix V*CKM describes the rotation Vij proportional to transition amplitude from quark j to quark i Weak states CKM matrix Mass states quarks anti-quarks d u π D, Ds Tree diagram The two matrices are not identical (complex elements) This introduces a phase responsible for CP violation Iasi, 29 May 2007 5th Four Seas Conference

CKM matrix and the unitarity triangles
The CKM matrix is complex and unitary: V†CKM VCKM = 1 Unitarity gives relationship between rows and columns: S Vij Vik* = 0 (j  k) The 6 relations can be represented as 6 unitarity triangles in the complex plane The area of each triangle corresponds to the amount of CP violation From the 6 triangles only 2 have sides of similar length (un-squashed) Re a +c -c Im Re a   Im Rescale the unitarity triangles by Iasi, 29 May 2007 5th Four Seas Conference

Parameters of the Unitarity Triangles
Im Bd mixing phase: d = 2β = –arg(Vtd2) Bs mixing phase: s = – 2χ = –arg(Vts2) Weak decay phase: γ = –arg(Vub)    1 Re Im c is small in Standard Model  +   Re Iasi, 29 May 2007 5th Four Seas Conference

Current status of CKM parameters
B-factories (BABAR&BELLE) are extremely successful in constraining the unitary triangle within the SM and Tevatron (CDF&D0) has demonstrated its Bs physics capability! Accuracy of angles is limited by experiment: α ~ ± 12° β ~ ± 1° γ ~ ± (20°-30°) χ not yet measured Need to improve measurements of angles to further improve CKM consistency check Search for New Physics by looking at influence of possible new particles in loop diagrams Iasi, 29 May 2007 5th Four Seas Conference

5th Four Seas Conference
Search for New Physics New Physics models introduce new particles, dynamics and/or symmetries at a higher energy scale (expected in the TeV region) with virtual particles that appear e.g. in loop processes ? New Physics Box diagram Penguin diagram B Physics measurements are complementary to direct searches and will allow to understand the nature and flavour structure of possible New Physics LHC will act as a b-factory with large b-quark production rate including Bs, allowing to improve the precision of CKM parameters look for New Physics via precision study of loop processes Iasi, 29 May 2007 5th Four Seas Conference

Completing the program on B Physics…
Precise measurement of B0s-B0s mixing: mixing phase fs and Dms, DGs BsDsp, … BsJ/yf, BsJ/yh(’) B(s)0Xg, B0K*0l+l-, bsl+l-, Bsm+m-... Search for effects of NP appearing in suppressed and rare exclusive and inclusive B decays Precise γ determinations including processes only at tree-level, in order to disentangle possible NP contributions Other measurements of CP phases in different channels to over-constrain the Unitarity Triangles and to search for NP contributions in loop decays BsDsK, B0D0K*0, B±DK±, B0pp & BsKK, … B0fKs, Bsff, ... B0rp, B0rr, … Iasi, 29 May 2007 5th Four Seas Conference

B-factories vs. b-factory
ee  (4S)  BB PEPII, KEKB ppbbX (√s = 14 TeV, tbunch=25 ns) LHC (LHCb–ATLAS/CMS) Production bb 1 nb ~500 b  Typical bb rate 10 Hz 100–1000 kHz bb purity ~1/4 bb/inel = 0.6% Trigger is a major issue !  Pileup 0.5–5 b-hadron types B+B– (50%) B0B0 (50%) B+ (40%), B0 (40%), Bs (10%) Bc (< 0.1%), b-baryons (10%) b-hadron boost Small Large (decay vertexes well separated) Production vertex Not reconstructed Reconstructed (many tracks) Neutral B mixing Coherent B0B0 pair mixing Incoherent B0 and Bs mixing (extra flavour-tagging dilution) Event structure BB pair alone Many particles not associated with the two b hadrons Iasi, 29 May 2007 5th Four Seas Conference

B production in LHCb b and b quarks are produced in pairs bb production is correlated and sharply peaked forward-backward LHCb single-arm forward spectrometer : θ~ mrad (rapidity range: 4.9>η>1.9) Cross section of bb production in LHCb acceptance: σbb ~ 230 µb LHCb limits luminosity to few 1032cm-2s-1 instead of 1034cm-2s by not focusing the beam as much as ATLAS and CMS Maximizes probability of a single interaction per crossing Design luminosity from start-up of LHC ~ bb pairs produced/year in LHCb acceptance boost pp interactions/crossing LHCb n=0 n=1 ATLAS/CMS Iasi, 29 May 2007 5th Four Seas Conference

Detection of B decays Triggering & selecting B’s B’s have a typical decay length of L~1cm in LHCb B decay products have large transverse momentum (because of their high mass) Select particles with high pt that come from displaced vertex Reconstructing B decays good mass resolution particle identification Efficient background reduction good decay time resolution Time resolved measurements for Bs decays Tagging flavour of the B at production Opposite side tagging (companion B) Charge of the kaon in the b→ c→ s chain. Charge of the lepton in semi-leptonic decays. Charge of accompanying b jet Same side tagging Charge of the K accompanying Bs Charge of the π from B** → B*π± Tagging power: εD2 = 4-5% for B0d and 7-9% for B0s Qvertex Bs B0 D l- K– K+ primary vertex displaced vertex L~1cm b s u Bs0 K+ Iasi, 29 May 2007 5th Four Seas Conference

a dedicated B-Physics Experiment at the LHC Mont Blanc 565 scientists 47 universities and laboratories 15 countries Geneva airport lake LHCb CERN ATLAS CMS ALICE LHC Tunnel Iasi, 29 May 2007 5th Four Seas Conference

LHCb in its cavern Shielding wall (against radiation) Cavern ~100m below surface Electronics + CPU farm Detectors can be moved away from beam-line for access Offset interaction point (to make best use of existing cavern) 7 TeV Proton beam Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector ~ 300 mrad p p 10 mrad  Forward spectrometer (running in pp collider mode) Outer acceptance of ~300 mrad and inner acceptance 10 mrad from conical beryllium beam pipe Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector Beam   Vertex locator around the interaction region Silicon strip detector with ~ 30 mm impact-parameter resolution at pT ~2GeV/c Approaches 8mm from beam in complex secondary vacuum system Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector  Tracking system and dipole magnet to measure angles and momenta Momentum resolution: Dp/p ~ 0.5 % Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector  Two Ring-Imaging-CHerenkov detectors for charged hadron identification Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector e h  Calorimeter system to identify electrons, hadrons and neutrals Important for the first level of the trigger Iasi, 29 May 2007 5th Four Seas Conference

LHCb detector m  Muon system to identify muons, also used in first level of trigger Iasi, 29 May 2007 5th Four Seas Conference

LHCb trigger Efficient and selective trigger crucial for LHCb:
Fraction of B’s is <1% of inelastic cross-section Branching fraction of interesting B decays <10-4 Software trigger (HLT) Full detector info available, only limit is CPU time Use more tracking info to re-confirm L0 decision + high IP Full event reconstruction: exclusive and inclusive streams tuned for specific final states Hardware trigger (L0) Fully synchronized (40 MHz), 4 s fixed latency High pT tracks: , , e,  and hadron (typical pT ~1-4 GeV/c) 10 MHz (visible bunch crossings) 1 MHz (full detector readout) ≤ 2 kHz (storage: event size ~35kB) Custom electronics boards PC farm of ~2000 CPUs L0, HLT and L0×HLT efficiency Iasi, 29 May 2007 5th Four Seas Conference

Reconstruction performance
Mass resolution MeV/c2 Bs   18 Bs Ds  14 Bs  J/  16 8 Good mass resolution essential for background suppression Good proper time resolution essential for time-dependent Bs measurements without/ with J/ mass constraint Proper time resolution BsDs st ~ 40 fs BsDsK BsDs ~15x larger BR than DsK reduced by PID! Iasi, 29 May 2007 5th Four Seas Conference

Particle Identification performance
Requirements: Background suppression => high momentum hadrons in two-body B decays B flavour tagging (identify K from b→c→s) => low momentum hadrons π π hypothesis No RICH Kaon ID: ~88% Pion mis-ID: 3% Fully simulated pattern recognition in two LHCb RICHes: Reconstruct rings around tracks found in tracking Good K- separation achievable in 2–100 GeV/c range Iasi, 29 May 2007 5th Four Seas Conference

LHCb is (almost) built-up, commissioning started…
2007: commissioning phase LHCb is confident that the experiment will be ready for data-taking in spring 2008 2008: early phase Complete commissioning of detector and trigger at s=14 TeV Calibrate momentum, energy and particle ID Start first physics data taking, assume ~ 0.5 fb–1 Look asap for New Physics with measurements competitive at low luminosity 2009–20xx: stable running Stable running, assume ~ 2 fb–1/year Develop full physics program, exploit statistics, work on systematics Iasi, 29 May 2007 5th Four Seas Conference

Expected physics performance (from selected channels)
Bs oscillations Dms with Bs0  Dsp Bs mixing phase fs (=-2) from Bs J/f (h) from Bs  Rare decays Bs0  +- Weak decay phase g from Bs DsK from B DK* (and B±  DK±) from B and BsKK Iasi, 29 May 2007 5th Four Seas Conference

Bs oscillations: Δms Bs oscillations observed by CDF in 2006: Δms = 17.8 ± 0.10 ps-1 ms is an example of early physics measurement at LHCb Expect ~80k Bs  Ds-π+ events per 1year/2fb–1, average t~40 fs B/S <0.05 at 90% CL (derived from fully simulated inclusive bb events) LHCb Need to take care of flavour tagging, proper-time resolution, background rejection and acceptance correction Distribution of unmixed sample after 1year /2fb–1 (with ms = 20 ps-1) with 0.5 fb-1 in 2008 expect: stat(ms) = ± ps1, i.e. 0.07% Iasi, 29 May 2007 5th Four Seas Conference

fs from BsJ/ (η,η’…) SU(3) analogue of B→J/Ks, measuring the Bs- Bs mixing phase in SM: s = – 2χ = –arg(Vts2) ~ –0.035 Sensitive to New Physics effects in mixing  S = S(SM) + S(NP) Box diagram +NP? ηf = +, - 1 CP eigenstates J/ is not a pure CP eigenstate: 2 CP even, 1 CP odd amplitudes contributing need to fit angular distributions of decay final states as function of proper time (needs external ms) requires very good proper time resolution Expected sensitivity: 130k BsJ/(µµ) signal events/year (before tagging)  stat(s)~0.023 with 1year/2fb–1  stat(s)~0.01 after 5 years/10fb–1, also adding pure CP modes like J/η, J/η’ (small improvement) Θtr= angle between l+ and normal to  decay plane Iasi, 29 May 2007 5th Four Seas Conference

Penguin diagram +NP? Penguin decays: Bs  Penguin dominated decays such as B Ks and Bs involve loop diagrams where new particles might contribute Comparing those to the corresponding tree dominated decays B→J/Ks and BsJ/ allows to reveal possible New Physics Some indication from the B factory experiments that their results for penguin decays do not agree with expectations hint of new physics? β(tree)-β(penguin)=8º~2.6σ(exp.only), >2.1σ(theo.corr.) LHCb can best contribute with Bs CP violation in SM expected <1% (Vts enters in both mixing and decay amplitudes) significant CP-violating phase would be due to NP Decay to two vector particles requires angular analysis Expect 4K signal events in 1year/2fb-1 if BR=1.4x10-5, with 0.4 < B/S < 2.1 at 90% CL  Expected precision of σstat (NP) ~6º from time dependent analysis with 5 years/10fb-1 Iasi, 29 May 2007 5th Four Seas Conference

(signal+bkg is observed)
Rare decays: Bs  +– Very rare loop decay, sensitive to New Physics BR ~ 3.510–9 in SM, can be strongly enhanced in SUSY Main issue is background rejection: dominated by B+X, B-X decays Good mass resolution (18 Mev/c2) and PID essential Expected performance:  with 0.5 fb–1: exclude BR values down to SM value  with 2 fb–1: 3 evidence of SM signal  with 10 fb–1: > 5 observation of SM signal ? Integrated luminosity (fb–1) 5 observation 3 evidence SM prediction BR (x10–9) LHCb sensitivity (signal+bkg is observed) MSSM Iasi, 29 May 2007 5th Four Seas Conference

CKM angle g Experimental status: From the SM fit using only indirect measurements: γ=(63.1±4.6)° (UTFit) From direct measurements with B→DK decays: γ=(83±19)° (BaBar and Belle  UTFit) LHCb can measure angle γ using various methods Tree-level processes allow clean extraction of γ Access interference effects involving the phase between Vub and Vcb Bs  DsK B, Bd D(*)K(*), with D0 decaying to: 2 bodies: πK , KK, ππ 3 bodies: KS ππ, KS KK, KS Kπ 4 bodies: K πππ, KK ππ Processes involving large Penguin contributions are sensitive to New Physics Bd  +– & Bs  K+K– U-spin approach expect combined precision σ(γ) ~ 4.5o per 1year/2fb-1 expect σ(γ) ~ 4o per 1year/2fb-1 (7-10o with 20% U-spin violation) Iasi, 29 May 2007 5th Four Seas Conference

g from Bs  DsK b u transition, phase + b c transition, phase 0 Vub 2 time dependent asymmetries from 4 decay rates: Bs (Bs)  D-s K+ , D+s K- 2 tree decays (b→c) and (b→u) of same magnitude interfere via Bs mixing:  large interference effects expected  insensitive to new physics Vcb N(Bs! D+s K−) − N(Bs! D+s K−) N(Bs! D+s K−) + N(Bs! D+s K−) Bs D-sK+ Fs + Vub Vcb mixing Fit the 4 tagged, time-dependent rates: phase of D-s K+ = D + (g + fs) phase of D+s K- = D - (g + fs) extract both D and (g + fs) with fs being determined using Bs → J/y f Expect 5400 signal events with B/S<1 at 90% CL  s(g) ~ 10° in 1year/2fb-1 Iasi, 29 May 2007 5th Four Seas Conference

g from B0  D0K*0 Two colour-suppressed diagrams with |A2|/|A1| ~ 0.4 interfering via D0 mixing [Atwood-Dunietz-Soni variant of Gronau-London-Wyler method, Phys. Lett. B270, 75 (1991)] 6 decay rates, self-tagged and time-integrated B tagged by charge of K in K* decay D tagged by charge of K in D decay Vub Vcb A1 = A(B0  D0K*0): b c transition, phase 0 A2 = A(B0  D0K*0): b u transition, phase + A3 = 2 A(B0  DCPK*0) = A1+A2, because DCP=(D0+D0)/2 Expected signal rates and background: 1year/2fb-1, γ=65°, Δ=0 Mode (+ CP conjugates) Yield Bbb/S (90%CL) B0  D0 (K+p-) K*0 (K+p-) 3350 [0.3,2.0] B0  D0 (K-p+) K*0 (K+p-) 536 [2,13] B0  D0CP (K+K-) K*0 (K+p-) 474 [0,4] Expected sensitivity (for amplitude ratio rb=0.4):  s(g) ~ 6-12° in 1year/2fb-1 (depending on strong phase Δ) Iasi, 29 May 2007 5th Four Seas Conference

Outlook: Effect of LHCb on UT
Summer 2006 LHCb after 5 years/10fb-1 (sin(2)) = 0.01 ; () = 2.4º ; () = 4.5º (incl. Lattice QCD improvements, σ(ξ)/ξ=1.5%) Iasi, 29 May 2007 5th Four Seas Conference

Outlook: New Physics in loops?
Will γ measured with tree processes be compatible with loop measurements ? At present large uncertainties on γ from tree processes only LHCb precision on γ from B→DK (tree process only) after 5years/10fb-1 32 loops (2006)  loops (2006) γ |Vub | | Vcb| Trees agree with loops → No evidence for NP Or……!!! Either: Iasi, 29 May 2007 5th Four Seas Conference

Conclusion LHCb will be ready to collect data with its full detector at LHC start-up in 2008 to exploit the large B-meson yields at LHC with access to Bs decays with excellent mass and decay-time resolution, and particle ID with a flexible and robust trigger dedicated to B-physics After 5 years/10fb-1:  SM expectation s(Bs→ ccss) ~  Br(Bs→ ) ~0.7 ~ DsK, DK) ~2-3 ~60 (tree only) ) ~2-3 ~60 (tree + penguin) LHCb is also in the process of studying a possible upgrade of the detector (SuperLHCb) to run at 10 times its design luminosity with a more selective trigger (displaced vertex trigger at first level and 40MHz R/O) LHCb will contribute significantly to the search for NP via precise and complementary measurements of CKM angles and the study of loop decays  Iasi, 29 May 2007 5th Four Seas Conference

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