Beauty Experiments at the LHC

Transcription

1 Beauty Experiments at the LHC Historical perspective. Why propose fixed target experiments? Gajet: beautiful beauty trigger LHB: 800 Tesla magnet and life-target. Proposed collider experiments What does Pythia say on Barrel vs Forward P238/Cobex LHCb appears on the scene: design/re-design/re-optimize Pick the running luminosity radiation environment. LHCb detector systems and their challenges: Silicon detectors: VErtexLOcator + SiTracker Gas detectors: OuterTracker + Muon system Light detectors: RingImagingCHerenkov + Calorimetry Data reduction: Trigger and DAQ. How will it probably perform? Already thinking about how to do better: UPGRADE! - 1 -

2 Look for b b-factory Machine s σ(b b) σ(inelastic) σ(b b) [TeV] [µb] ee Υ(4S) HERA fixed target LHC fixed target SPS Tevatron LHC SSC LHC fixed target Hence: hadron colliders are truly b b-factories. In addition: time-dependent analysis of all B-species. Several LOIs to exploit this: Experiment Machine year P238 SPS-Collider 1988 Gajet LHC fixed target 1993 LHB LHC fixed target 1993 Cobex LHC-Collider 1993 HERA-B HERA fixed target 1994 LHCb LHC-Collider 1995 BTeV Tevatron

3 Why consider s = 115 GeV? Higher B-momentum in lab-frame: Longer B-flight path. Larger p decay-products: less MS Choose your own target size: mm compared to 20 cm in collider. allows for better trigger/background rejection. Hadronic p T trigger: p T of B-decay products similar. If ɛ B ππ = 0.8 minimum bias rejection 100 better. HERA-B: internal target Wire targets Gajet: internal target Use H: low multiplicity events. high p-flux thin target LHB: external target Put vertex detector in target

4 The first level trigger was based on an idea published in NIM: A trigger for beauty: Charpak, G.; Giomataris, Y.; Lederman, L. NIM in Physics Research Section A, Volume 306, Issue 3, p (1991) (a) Lederman: Nobelprize 1988 (b) Charpak: Nobelprize

5 Appropriate choice of refractive indexes n 1 and n 2 will trap Cherenkov light for large impact parameter tracks. Two requirements for it to work: B needs large flight path Optical Trigger for Beauty B-production spot very small compared to flight path Both fulfilled by the design of the Gajet experiment. Test performed: Very low light yield multiple layers Good MC description of results thought to get 60% B-eff for factor 10 minimum bias rejection

6 Extract 7 TeV beam from LHC: Construct vertex detector right behind (in?) target. WA92 did this before. Advantages: Allows small impact parameter trigger. Electronic Bubble chamber quality: background rejection. But: LHC will not waist beam on fixed target area. Need to extract halo from collider slowly, without interfering. LHB: LHC extracted beam - 6 -

7 Beam extraction by Crystal Channeling Particles captured in crystal if transverse energy smaller than depth potential well of the crystal. 1,6 No channeling 2 Channeling 3 De-channeling 4 Volume reflection 5 Volume capture - 7 -

8 First question to answer: Central or Forward? What about collider? - 8 -

9 Or how to lie with a plot... Central vs Forward continued NOTE: essential that both B s are in acceptance! Before deciding: make sure Pythia makes sense

10 Pythia and b b Production And compare with experiments: Gives reasonable comparison with exp. But only data for central region. Rely on Pythia

11 Look at B µx Trigger/reconstruct the muon. Typical µ-shield: 20 λ I p µ > 7 GeV to penetrate. Require p T > 1 GeV for trigger. ɛ Central ɛ Forward Central vs Forward cont

12 Some Forward arguments: Longer B-flight path. Larger p decay-products: less MS Central vs Forward cont

13 3 Beauty LOIs to LHCC LHCb

14 The (forced) Birth of LHCb

15 LHCb Considerations (LOI) LOI arguments: b b correlation within 3 η units: single forward for B + tagging B. cτ B =0.46 mm, decay-length 7 mm with < p B > 80 GeV. Momentum distribution well suited for RICH PID. Forward spectrometer facilitates small p T triggers, especially µ triggers. Planar: better/easier/cheap detector geometry. Aperture: 0, 10, 20 mrad beam-pipe. a) all decay tracks in acceptance. b) + µ opposite B in acceptance, c) + all p > 0.5 GeV, p µ > 10 GeV. Hence: θ max < 400 mrad is OK. Later (SF ) θ(x y) = mrad

16 Benchmark Channels Select a few benchmark channels, to check if the detector capability covers all needs: CKM: B s D s h, B d J/ψ(µµ)K S, B s J/ψ(µµ)φ, B hh, B d D 0 K 0, B s φφ, B d D π, B d π + π π 0, B + D 0 (K S ππ)k +, B s D ( ) s Rare decays: B d µµk, B s µµ, B s φγ, B u eek + Charm: D D 0 (h + h )π Requirements not a big surprise... Good tracking and particle identification performance. Excellent proper-time resolution. Ability to select and trigger on many different B decays: fully hadronic (also with one neutral like K 0 S, π0 or η), decays with muons, electrons, and radiative decays. acceptable background rejection, i.e. dp/p, vertexing. Adequate flavour tagging performance. D ( ) s

17 LHC-B (1995) mrad aperture 3 RICHes 12 tracking stations 86 MCHF Some Detector Incarnations.. LHCb (1998) 330 mrad aperture 2 RICHes + B-shielding wall 11 tracking stations (9 tracking stations in 2001) Added M1 86 MCHF LHCb

18 LHCb-Light (2003) θ(x y) = mrad. B-shielding wall shielding boxes 9 4 tracking stations: λ I 20% 12%: but tracking? 75 MCHF next slide

19 LHCb-Light and electrons Reduced X % Only air in magnet. Bremsstrahlung material removed from magnetic field area. e Magnet p γ γ ECAL E 1 E 0 E

20 Tracking Up/Downstream Track reconstruction Upstream: start at last station.. Needs to cope with complicated events

21 Downstream tracking Start at the Vertex Detector: sub-divided in 8 octants. One octant looks like: 910 mm r 34 mm Hence: rather clean. Combine every track with hit behind magnet p=fixed for combination small search window. loop over all reasonable combinations. z

22 Downstream tracking Manage to get same efficiency as upstream, even in events like: Performance: reconstruct 94% of µ s in B 0 J/ψ(µµ)K 0 S

23 Luminosity Considerations: LHC machine LHC: MHz, 2622/ MHz of possible pp interactions:

24 Luminosity and nr-interactions L peak LHC 1034 cm 2 s 1, 201n Assume σ visible = 63 mb 32 : 10 MHz xings with 1 33 : 26 MHz xings with 1 int. nr-xings with 1 pp max at σ z (beam) 5 cm. a Pythia: σ inelastic = 80 mb, of which 80% has at least 2 charged tracks in LHCb acceptance

25 Level-0: Implemented in hardware. Latency 4µs. Largest E T hadron, e(γ) and µ. Multiplex max 32 channels. Hence: 1 MHz max-output rate High Level Trigger: Access to all detector info. LHCb Trigger for pedestrians Limitation: CPU (brain?) power. Will improve with Moore s law automatically : plan to replace CPU boxes every 3 years. M5 M4 M3 M2 Pile Up System # interactions per crossing HCAL Calorimeter Triggers PS SPD ECAL Highest E T clusters: hadron, e, γ, π 0 SPD multiplicity M1 RICH2 T3 T2 T1 Magnet RICH1 TT VELO All DATA HLT Event Filter Farm VELO Pile Up Muon Trigger Two highest p muons T L0 Decision Unit defines L0 trigger To FE 40 MHz Readout Supervisor timing & fast control Level 0 1 MHz HLT 2 khz Storage

26 LHCb and Luminosity Trigger: L0 limiting yield for larger L peak > : L0-retention > : L0-retention = pp/xing. Result: E T threshold M B. L peak no hadron-trigger gain. hadronic-channels: yield (time ) µ-channels: yield L Conclusion-1: h-trigger plateaus at L = Conclusion-2: µ-trigger linear with L. Mbias B s φφ

27 Radiation for few design for L 20 fb 1 radiation damage. Affects mainly large η. Run Fluka (and Mars/GCalor/Geant): Follow n down to MeV MeV n equivalent/cm 2 /10 years at VELO MeV n equivalent/cm 2 /10 years at TT ECAL: 1.3 Mrad/10 years. Note: just beam-beam pp interactions. neutrons hadrons ±

28 Radiation Environment Simulation only gives flux and particle type+momentum, which then needs to be converted to possible degradation per detector or electronics. Accumulation of space charge at insulator interfaces discharge. Damage of crystal (Si) lattice due to Non Ionizing Energy Loss (NIEL). Probability of Single Event Upset or Single Event Latch-up due to single large local ionization dose

29 Sub-systems Overview Next few slides: quick overview of all sub-systems VELO: Si-vertex detector. Two RICH detectors to separate π/k/p Dipole magnet: 4 Tm. Trigger Tracker: Si-planes for tracking. T1-T3: Tracking stations, Straws/Si. M1-M5: MWP Muon Chambers. Calorimetry: Scintillating Pad detector (SPD), Pre-Shower (PS), ECAL and HCAL. Trigger and DAQ Then: treat each detector system in more detail, emphasis on LHCb-specials, i.e. Si, HPDs, Trigger

30 VErtex LOcator VELO tasks : Provide precise tracking close to the B-vertex. Stand-alone tracking capability. Contribute HLT triggers. VELO: µm thick Si, µm pitch, 170k channels, 0.23 m 2 of Si, Each station is a sandwich of a R and Φ-sensor. Φ-sensors have a stereo angle. Sensitive Si-area: 8 mm from LHC beams But: during LHC injection 3 cm away from beam. Critical issues: Roman-pot mounting, radiation damage

31 VELO mounting 3 cm retracted during LHC injection. Re-positoned within few µm. VELO on XY-table to center on beam-line. Al foil between sensors and LHC vacuum

32 Tracking Stations Beryllium conical beam-pipe to avoid too many secondaries. Outer Tracker: 3 8 layers of 5 mm, 5 m long, straws, 0, 5 stereo. Si-Trackers (TT and IT): 200 µm pitch Silicon, 0, 5 stereo. 14 m 2 of Si

33 Magnet Warm magnet: 4.2 MW 4 Tm over 10 m ton

34 RICH Systems What is the relevant momentum range? High p: distinguish between B 0 ππ, πk, B s πk, KK, Λ b pk, pπ Low p: tagging kaons. Photon detection: Hybrid Photon Detectors (Si-pixel detectors encapsulated in photo-tube) cover 2.6 m 2 with segmented photon detectors Typical resolution required corresponds to pads of mm 2 Number of tracks 300 (a) (b) B ππ decay tagging kaons Momentum (GeV/c) 300 RICH-1 θ [mrad] RICH Momentum [GeV/c ]

35 RICH1 RICH2 Photon Detectors 300 mrad CF 4 gas Aerogel C 4 F mrad Spherical Mirror Beam pipe 120 mrad Beam pipe VELO exit window Track Flat mirror Spherical mirror Plane Mirror Photodetector housing z (cm) m

36 Calorimetry Scintillating Pad Detector: 5984 cells Distinguish e/γ in Level-0 Trigger. Preshower: scintillator, 5984 cells, 2.5 X 0 Electromagnetic-Cal.: shashlik, 5984 cells, 25 X 0 σ EE = 9.5% E 1% Hadron-Cal.: iron/scintillating tiles, 1468 cells, 5.6λ I Level-0 hadron Trigger. σ EE = 80% E 10% Cell-sizes: cm 2 ECAL HCAL

37 Muon System Technology: Multi-Wire-Proportional-Chamber, projective in Y for L0-trigger. Triple Gas-Electron-Multiplier in inner part M1 120k pads and strips. Eff> 99% by.or. 2 layers per station. Covers 435 m 2 Combine strips 26k pads for the L0-trigger Pad sizes: cm 2 (M1-inner) to cm 2 (M5-outer)

38 40 MHz, but 30 MHz of x-ings with p p LHCb runs at L= cm 2 s 1. L0 highest E T µ,e,γ,π 0 and h: 1 MHz Trigger Overview HLT 2 khz using all info

39 Control and DAQ Overview

40 Muon MWPC RICH2 HPDs OT: straws 5 mm 4 Tm Magnet VELO Si IT DAQ HCAL & ECAL Be beam-pipe Si Trigger Tracker RICH1: mirrors

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42 End of introduction part. Next, look at three special systems in more detail: VELO-sensors, Trigger and HPDs