B-physics reach of the LHCb Experiment B-physics reach of the LHCb Experiment RAL-Southampton Seminar 26 April Paul Soler University of Glasgow and Rutherford Appleton Laboratory

2 RAL-Southampton Seminar, 26 April 2002 Physics aims (I) To test the consistency of the Standard Model interpretation of CP violations and to search for new physics. o LHCb is a 2nd generation experiment that will determine CP violations in a variety of decays of B d and B s mesons to test consistency of Unitarity Triangles. It will follow on from Babar, BELLE that have already established CP violations for B d mesons (in the decay B d -> J/ K) and will constrain unitarity triangles to unprecedented accuracy.

3 RAL-Southampton Seminar, 26 April 2002 Physics aims (II) _ B d -B d Mixing Phase _ B s -B s Mixing Phase Weak Decay Phase Standard Model: CKM Matrix

4 RAL-Southampton Seminar, 26 April 2002 Physics aims (III) Possible unitarity triangle measurements in LHCb

5 RAL-Southampton Seminar, 26 April 2002 Physics aims (IV) Possible situation in 2005 Babar, BELLE have established CP violations for B mesons with B d -> J/ K: –sin 2 = (Babar, 56 fb -1 ) –sin 2 = (BELLE, 42 fb -1 ) o Consistent with Kobayashi-Maskawa mechanism Standard Model fit (0.5< sin 2 <0.8)

6 RAL-Southampton Seminar, 26 April 2002 Physics aims (V) Aims for LHCb in 2008 (after 1 year data taking)

7 RAL-Southampton Seminar, 26 April 2002 Physics aims (V) … or maybe not consistent with SM fits

8 RAL-Southampton Seminar, 26 April 2002 B-meson Production (I) LHC is the most intense source of B mesons (B d, B u, B s, B c ) with bb = 500 mb o Modest LHC luminosity LHCb = 2 x10 32 cm -2 s -1 Ô10 12 bb / 10 7 s o Range of channels available in LHCb:

9 RAL-Southampton Seminar, 26 April 2002 B-meson Production (II) o LHCb Detector –forward single arm spectrometer o Experimental challenges –Trigger: leptonic and hadronic final states (eg B d -> ) amongst minimum bias background –Particle Identification: -K separation 1 GeV < p < 150 GeV –Vertexing: proper time resolution 43 fs B s -> D s (K) 30 fs B s -> J/ –Experimental signature: time dependent asymmetry bb angular production

10 RAL-Southampton Seminar, 26 April 2002 LHCb-classic Experiment o LHCb Detector: forward single arm spectrometer Acceptance: mrad bending mrad non-bending VELO RICH2 RICH1

11 RAL-Southampton Seminar, 26 April 2002 Vertex Detector (VELO) o Si strip detectors p-n, n-n, single sided, double metal read-out 220 m thick, wedges o Level 1 trigger (L1) Alternate r and strip detectors varying strip pitch m in r o Detector halves retracted by 30 mm in y during injection Ô8 mm from beam during physics o Radiation damage Ômay have to replace detectors after a few years Liverpool, Glasgow participation VErtex LOcator Design Si Strip Layout radial Si detectors

12 RAL-Southampton Seminar, 26 April 2002 Vertexing B s D s K

13 RAL-Southampton Seminar, 26 April 2002 Particle Identification Excellent Particle Identification ( -K separation) required from GeV/c o RICH system divided into 2 detectors and 3 radiators: aerogel, C 4 F 10, CF 4 Momentum vs polar angle Momentum

14 RAL-Southampton Seminar, 26 April 2002 RICH1 RICH2 RICH System Overview o Acceptance –300 mrad RICH 1 –120 mrad RICH 2 o Radiators: thickness L, refractive index n, angle c, /K threshold Aerogel C4F10 CF4 L cm n c mrad GeV K GeV Photo detectors

15 RAL-Southampton Seminar, 26 April 2002 Photon Detectors Photon Detectors o Photo detector area: 2.6 m 2 o Single photon sensitivity: nm, quantum efficiency > 20% o Good granularity: ~ 2.5 x 2.5 mm 2 o Large active area fraction: 73% o LHC speed read-out electronics: 40 MHz o LHCb environment: magnetic fields, charged particles Hybrid Photodiodes (HPD) baseline CF 4 Aerogel large rings C 4 F 10 small rings

16 RAL-Southampton Seminar, 26 April 2002 RICH Performance o Simulation –based on measured test beam HPD data –global pattern recognition –background photons included o # of detected photons – 7 Aerogel 33C4F10 18CF4 o Angular resolution [mrad] –2.00 Aerogel 1.45C4F CF4 3 -K separation 3-80 GeV/c ( GeV/c

17 RAL-Southampton Seminar, 26 April 2002 Triggering (I) 5 kHz 200 Hz

18 RAL-Southampton Seminar, 26 April 2002 Triggering (II)

19 RAL-Southampton Seminar, 26 April 2002 Re-optimisation (I) Problems LHCb design: o Material budget too high: After Outer Tracker (OT) and Vertex Locator (VELO) Technical Design Reports (TDR), the material upstream of RICH-2 has increased by 70% with respect to Technical Proposal. Material up to RICH-2: ~ 0.6 X 0, 0.2λ I => Increased secondaries, reduced track finding & reconstruction efficiency, increased fake tracks => B + - ~ 15% loss; B S D S K ~ factor 3 loss ! o Desirable to reduce trigger rate (or increase trigger efficiency) at levels 0 & 1: Trigger rate after level 1 trigger 40 kHz with a B + - efficiency of 30%. Solution: include magnetic field in VELO + RICH1 region allows 25% resolution in VELO Pt measurement doubles B + - efficiency or reduces trigger rate depending on need.

20 RAL-Southampton Seminar, 26 April 2002 Re-optimisation (II) B J/ ( )K s is saturated using L0( ). B + - is improved by a factor >2 due to the VELO Pt information. 10 kHz

21 RAL-Southampton Seminar, 26 April 2002 Re-optimisation (III) Material reduction: Beam pipe: Al to Be-Al alloy VELO: 0.19 X 0, 0.04 I Possibilities are being investigated for Be RF shield, thinner Si , less stations, etc X X 0 RICH-1: 0.14 X 0, 0.05 I Possibilities are being investigated for composite mirror, light mirror supports X X 0 Outer Tracker: 0.03 X 0 9 stations=0.27 X 0, 0.11 I Reduce to 4 stations 0.27 X X 0 Preliminary indications show that tracking efficiency very similar to classic design. Full re-optimisation studies to appear in a TDR at end of 2002.

22 RAL-Southampton Seminar, 26 April 2002 Re-optimisation (IV) remove magnet tracking stations LHCb-light LHCb-classic

23 RAL-Southampton Seminar, 26 April 2002 Re-optimisation (V) Complete redesign of RICH-1: magnetic field (~500 G) imposes two mirror system with magnetic shielding like RICH-2, but rotated in vertical direction Large effort at Imperial College, Bristol and RAL to modify design.

24 RAL-Southampton Seminar, 26 April 2002 from B J/ K s from B J/ K s (sin 2 ) ~ 0.03 in (sin 2 ) ~ 0.02 after 1 year Theoretically clean High statistics to fit A dir : > 10 5 events/year B mass resolution = 7 MeV B time resolution = 36 fs

25 RAL-Southampton Seminar, 26 April 2002 o Sensitive to CKM angle o ~ in 1 year –depends on |P/T| and strong phase o Backgrounds also have 4900 B events/year B events/year for |P/T| from B 0 from B 0 Tree TPenguin P

26 RAL-Southampton Seminar, 26 April 2002 o Dalitz plot analysis o Fit tree and penguin parameters (angle + 8 parameters) o ~ – in 1 year o B mass resolution: 42 MeV (35 MeV when 0 mass constrained) from B 0 from B B 0 events/year 200 B 0 events/year 100 B 0 events/year

27 RAL-Southampton Seminar, 26 April 2002 o Theoretically clean o Small CP asymmetry o Hadron trigger o B mass resolution: 13.6 MeV (excl) 220 MeV (incl) o Time resolution: 60 fs (excl) 170 fs (incl) from B 0 D from B 0 D 73k B 0 D*(D( events/year (S/B=5.6) 460k B 0 D*(D(incl events/year (S/B=4.4) 360k B 0 D*(D(incl a events/year (S/B=4.0) ( mix + ) versus mix + ~ in 1 year Fit mix + and strong phase strong Get using mix from B 0 J/ K s

28 RAL-Southampton Seminar, 26 April 2002 from B s -> D s K from B s -> D s K Rate asymmetries measure angle o Time: 43 fs, B mass: 11 MeV Expect 2100 B s D s - (KK K events/year Expect 320 B s D s + (KK K events/year depends x s,, strong phase) Get using from B s J/ (next slide)

29 RAL-Southampton Seminar, 26 April 2002 from B s -> J/ from B s -> J/ o Expect 80K (32k tagged) events o Negligible background J/ mass resolution: 9 MeV o B mass resolution: 12 MeV o Time resolution: 32 fs sin 1 year, depending on x s ) Standard Model: sin CP eigenstate

30 RAL-Southampton Seminar, 26 April 2002 |V td /V ts | from m s Maximum x s = m s / s = 75

31 RAL-Southampton Seminar, 26 April 2002 Rare Decays B s -> + - –Standard Model branching ratio: 3.7 x ideal to search for new physics - FCNC – Combine with B d -> + - to obtain |V td /V ts | 2 –Expected signal (bkgd) :11 (3.3) 1 year B d -> K* + - –Standard Model branching ratio: 1.5 x dimuon mass spectrum, forward-backward asymmetry –combine with B d -> + - |V td /V ts | 2 =11% 1 year –Expected signal (bkgd) :22400(1400) 1 year B d -> K* –Standard Model branching ratio: 5 x search for new physics in asymmetry CP ~1% in SM –Expected signal: year

32 RAL-Southampton Seminar, 26 April 2002 LHCb Physics summary ParameterChannels Evts/year (1 year)LHCb feature 2( + ) B d 4900 |P/T| = PID, hadron trigger B d PID, hadron trigger 2 + B d D 460k~10 PID, hadron trigger B d J/ K s 100k B s D s K PID, hadron trigger, t B d DK PID, hadron trigger B s J/ t B s oscillations x s B s D s up to 75 hadron trigger, t Rare Decays BRB s < t B d K 22400PID

33 RAL-Southampton Seminar, 26 April 2002 Conclusions o LHCb is undergoing re-optimisation to acquire efficiencies as stated in Technical proposal. o Critical sub-detectors: Vertex Detector, RICH and Trigger all have UK involvement. o VELO can achieve 43 fs proper time resolution RICH design with two detectors and three radiators provides 3 -K separation from 3-80 GeV/c o LHCb can measure all angles of unitarity triangles and test models of CP violation. o LHCb in time to take data when LHC becomes operational in 2007