: status and prospects

Transcription

1 Charm at : status and prospects Gagan Mohanty Tata Institute, Mumbai DHEP Seminar February 2, 2012 Outline of the talk 1) Introduction and motivation 2) KEKB SuperKEKB 3) Enter Belle II detector 4) Status of the project 5) Conclusions and prospects

2 With a Higgs boson being discovered at the LHC, the standard model (SM) is on the verge of completion What is the fuss about? (r,h) However, there are many compelling reasons to believe that the SM cannot be the full story 1) About ten orders of magnitude difference a,f between 2 the matter-antimatter asymmetry in universe and CP violation content of the SM 2) What is the nature of dark (0,0) matter? (1,0) 3) and, the list goes on Energy (ATLAS, CMS) Three complementary ways to probe the new physics (NP) beyond the SM Luminosity (LHCb, Belle II) Cosmic (neutrino, ray) 2

3 Why a flavor factory in the LHC era? NP reach in terms of mass Illustration purpose only (r,h) NP flavor-violatinga,f coupling 2 A flavor factory (FF) studies processes that occur at one-loop level in the SM but may be of O(1) in NP: FCNC, (0,0) neutral meson mixing, (1,0) CP violation. These loops probe energy scales that cannot be directly accessed at the LHC. For instance, if SUSY is found at the LHC, the next question will be: how is it broken. By studying various flavor-violating couplings the FF can address that. 3

4 What s so special about Belle II? Thanks to its pristine e + e environment: Low background, high trigger efficiency, excellent photon & 0 reconstruction capability, high flavor-tagging efficiency with low dilution factor Good kinematic resolution Dalitz-plot analyses are straightforward Absolute branching fraction can be measured Ideal for measuring decay channels with large missing energy (r,h) A sample of measurements at Belle II a,f 2 (0,0) (1,0) Belle II TDR, arxiv:

5 Now, all these sound good. But why charm? Charm provides an interesting test bed for NP as SM footprints in this sector are tiny owing to a) large GIM/CKM suppression, and b) the lack of a large hierarchy in the down-type quark masses CP violation is expected (in the SM) to be the order of 10 3 an excellent NP probe [most promising candidate: singly Cabibbo-suppressed decays] (r,h) While talking about percentage effect, one a,f needs a good control on SM 2 predictions, something that is in general lacking in this sector because of long-distance effects (0,0) An example of short vs. long PRD 75, (2007) (1,0) 5

6 Direct CP violation: probe# 1 for Belle II Mode L int [fb 1 ] A CP [%] Belle II with 50ab 1 [%] D 0! KS¼ :28 0:19 0:10 0:05 D 0! ¼ 0 ¼ ±A CP ¼ 0:6% D 0! KS :54 0:51 0:16 0:10 D 0! KS :98 0:67 0:14 0:10 D 0! ¼ + ¼ :55 0:36 0:09 0:07 D 0! K + K 976 0:32 0:21 0:09 0:05 D 0! ¼ + ¼ ¼ :43 1:30 (r,h) D 0! K + ¼ ¼ :6 5:3 D 0! K + ¼ ¼ + ¼ 281 1:8 4:4 D +! Á¼ :51 0:28 0:05 a,f 2 0:05 D +! ¼ :74 1:13 0:19 0:20 D +! 0¼ (0,0) 0:12 1:12 0:17 (1,0) 0:20 D +! KS¼ :363 0:094 0:067 0:05 D +! K 0 S K :08 0:28 0:14 0:10 D s +! KS¼ :45 2:50 0:33 0:30 D s +! K0 S K :12 0:36 0:22 0:10 Luminosities (results) shown on the second (third) column are from Belle Looking ahead, Belle II has a big advantage over LHCb for the final states with neutral mesons ( 0, and ) 6

7 Rare and forbidden decays: probe# 2 for Belle II (r,h) (top) FCNC decays and (bottom) lepton flavor (LF), lepton number (L) & baryon-lepton number (BL) violating decays Shaded regions indicate the decays with a or 0, where Belle II will have an edge (0,0) a,f 2 (1,0) 7

8 Is it all about more data? Any innovation? Charm tagging at B factory (r,h) arxiv: a,f 2 (0,0) (1,0) Already have some good working examples from Belle and BaBar See the talk of A. Zupanc Great prospects for Belle II especially for channels with missing neutrinos viz. D (s) l l and D 0 K/ l l 8

9 (r,h) The list can go on, let s move to the project a,f 2 (0,0) (1,0)

10 Need 50 more data Enter SuperKEKB SuperKEKB (cm 2 s 1 ) 40 times higher luminosity 10

11 How to increase the luminosity? - - (1) Smaller y* (2) Increase beam currents (3) Increase y Nano-Beam scheme Collision with very small spot-size beams Invented by P. Raimondi at Frascati 11

12 Machine design parameters of two machines KEKB parameters SuperKEKB LER HER LER HER units Beam energy Eb Half crossing angle φ Horizontal emittance εx nm Emittance ratio κ % Beta functions at IP βx*/βy* 32/ /0.30 mm Beam currents Ib A Beam-beam parameter ξy Luminosity L / x 1034 GeV mrad 8 x 1035 cm-2s-1 Nano-beams and a factor of two more beam current to increase L Large crossing angle Change beam energies to solve the problem of short lifetime for the LER 12

13 KEKB to SuperKEKB Belle II New IR e 2.6 A New beam pipe & bellows Colliding bunches e+ 3.6 A New superconducting /permanent final focusing quads near the IP Replace short dipoles with longer ones (LER) Add / modify RF systems for higher beam current Low emittance positrons to inject Redesign the lattices of HER & LER to squeeze the emittance TiN-coated beam pipe with antechambers Damping ring Positron source New positron target / capture section Low emittance gun Low emittance electrons to inject To obtain 40 higher luminosity 13

14 Need to build a new detector Critical issues at L= cm 2s 1 4 Higher background ( 10-20) - radiation damage and occupancy - fake hits and pile-up noise in the EM 4 Higher event rate ( 10) - higher rate trigger, DAQ and computing 4 Require special features - low p m identification f smm efficiency - hermeticity f n reconstruction Belle II Have to employ and develop new technologies to make such an apparatus work! Belle II TDR, arxiv:

15 Enter Belle II KL and muon detector: Resistive Plate Counter (barrel outer layers) Scintillator + WLS Fiber + SiPM (end-caps, inner 2 barrel layers) EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI + waveform sampling (end-caps) Particle Identification electrons (7 GeV) Time-of-Propagation counter (barrel) Prox. focusing Aerogel RICH (forward) Beryllium beam pipe 2 cm diameter Vertex Detector 2 layers DEPFET + 4 layers DSSD positrons (4 GeV) Central Drift Chamber He(50%):C2H6(50%), small cells, long lever arm, fast electronics 15

16 Belle II compared with Belle SVD: 4 DSSD layers g 2 DEPFET + 4 DSSD layers CDC: small cell, long lever arm PID: ACC+TOF g TOP+A-RICH ECL: waveform sampling (+pure CsI for endcaps) KLM: RPC g Scintillator+SiPM (endcaps, barrel inner 2 lyrs) 16 16

17 A close-up view of the vertex region SVD Beryllium beam pipe 2cm diameter Vertex Detector (PXD+SVD) 2 layers DEPFET + 4 layers DSSD PXD Beam Pipe r = 10mm PXD (2 layers DEPFET) Layer 1 r = 14mm Layer 2 r = 22mm SVD (4 layers DSSD) Layer 3 r = 38mm Layer 4 r = 80mm Layer 5 r = 104mm Layer 6 r = 135mm 17

18 Few words on PXD DEPFET: Mechanical mockup of the pixel detector DEPFET pixel sensor DEPFET sensor: very good S/N 18

19 SVD: high-point and current status Origami chip-on-sensor Gearing up for ladder production! Mechanical mockup 19

20 Performance comparison Pixel detector close to the beam pipe a b p sin Less Coulomb scattering + KS B vertex IP profile B decay point reconstruction using the KS trajectory Larger radial coverage of SVD 20

21 CDC: Main tracking device Much bigger than in Belle Wire stringing in a clean room Exceeding the expectation 21

22 PID devices Endcap PID: Aerogel RICH (ARICH) 200mm Barrel PID: Time of Propagation Counter (TOP) Quartz radiator Focusing mirror Small expansion block Hamamatsu MCP-PMT (measure t, x and y) Aerogel radiator n~1.05 Hamamatsu HAPD + new ASIC Aerogel radiator Hamamatsu HAPD + readout

23 Barrel PID: TOP counter Cherenkov ring imaging with precise time measurement Device uses the internal reflection of Cerenkov ring images from quartz similar to the BaBar DIRC Reconstruct Cherenkov angle from two hit coordinates and the time of propagation of the photon Quartz radiator (2cm) Photon detector (MCP-PMT) Excellent time resolution ~40 ps Single photon sensitivity in 1.5 T Fast read-out electronics Hamamatsu SL10 MCP PMT 8 PMTs with read-out electronics quartz bar 23

24 TOP performance time Likelihood Functions: p K B0gK+p- full simulation results: Ng (signal) = 22 Ng (bkg) = 15 ep = 92 % (Belle: 89%) ek = 7.4 % (Belle: 12%) 24

25 Endcap PID: Aerogel RICH Test Beam setup Aerogel Clear Cherenkov image observed Cherenkov angle distribution Hamamatsu HAPD RICH with a novel focusing radiator a two-layer radiator Employ multiple layers with different refractive indices Cherenkov images from the individual layers overlap on the photon detector. 6.6 σ p/k at 4GeV/c! 25

26 Event size and rate: Belle II vs. LHC expts (r,h) a,f2 (0,0) (1,0) 26

27 A snapshot of the Belle II computing model (r,h) a,f2 (0,0) (1,0) 27

28 Belle II: a truly global collaboration A very strong group of over 500 highly motivated scientists! Recently several new additions from Italy and USA 28

29 SuperKEKB and Belle II Schedule Commissioning in three phases: Phase 1: w/o final quads and Belle II basic machine tuning low emittance beam tuning vacuum scrubbing (at least a month at beam currents of A) Damping ring commissioning Phase 2: with final quads and Belle II, but no vertex detector low * beam tuning small x-y coupling tuning collision tuning study beam background (carefully check the beam background before VXD installation) Phase 3: with QCS and full Belle II physics run luminosity increase 29

30 Peak luminosity (cm-2s-1) Integrated luminosity (ab 1) SuperKEKB luminosity projection Goal of Belle II/SuperKEKB Same size data as Belle 9 months/year 20 days/month Commissioning starts in early 2015 Shutdown for upgrade Calendar Year Aim to reach 50 ab 1 by the end of

31 Conclusions and future prospect e+e B factories have proven to be an excellent tool for flavor physics, producing a wealth of physics results, the most celebrated one being the confirmation of the Kobayashi-Maskawa mechanism for CP violation in the SM 2008 Major upgrade of KEKB factory to SuperKEKB ( 50 data) will take this legacy forward by providing a suitable probe for NP complementary to LHC Belle II at SuperKEKB should resolve current flavor puzzles from the present generation B factory, e.g., difference in the UT angle 1 between b c tree and b s loop diagrams, possible enhanced loop contribution in B K decays It will also have a prolific charm physics program: should greatly improve the precision of mixing/cpv parameters (together with LHCb) and should probe NP by diligently searching for direct CP asymmetries and rare and forbidden decays Thanks for your kind attention 31