Presentation is loading. Please wait.

Presentation is loading. Please wait.

21 26 Aug 2005, Rio de Janeiro, Brazil The PANDA project at GSI.

Similar presentations

Presentation on theme: "21 26 Aug 2005, Rio de Janeiro, Brazil The PANDA project at GSI."— Presentation transcript:

1 21 26 Aug 2005, Rio de Janeiro, Brazil The PANDA project at GSI

2 PANDA antiProton ANnihilation at DArmstadt

3 PANDA PANDA is an experiment that will use a very high intensity p beam with momentum from 1.5 GeV/c up to 15 GeV/c on a fixed proton target : s from 2.25 up to 5.47 GeV It will continue and extend the successful physics program initiated at facilities like LEAR at CERN and FERMILAB

4 Physics topics covered in PANDA Charmonium Exotics : hybrids, glueballs and other exotics Mesons in nuclear matter Charmonium absorption in nuclear matter Hypernuclear physics Open charm factory : CP violation, and D physics Crossed-channel Compton scattering and related exclusive processes Electromagnetic form factors of the proton in the time-like region

5 The PANDA collaboration

6 PANDA Collaboration At present a group of 340 physicists from 47 institutions of 16 countries Basel, Beijing, Bochum, Bonn, IFIN Bucharest, Catania, Cracow, Dresden, Edinburg, Erlangen, Ferrara, Frankfurt, Genova, Giessen, Glasgow, KVI Groningen, GSI, Inst. of Physics Helsinki, FZ Jülich, JINR, Katowice, Lanzhou, LNF, Mainz, Milano, Minsk, TU München, Münster, Northwestern, BINP Novosibirsk, Pavia, Piemonte Orientale, IPN Orsay, IHEP Protvino, PNPI St. Petersburg, Stockholm, Dep. A. Avogadro Torino, Dep. Fis. Sperimentale Torino, Torino Politecnico,Trieste, TSL Uppsala, Tübingen, Uppsala, Valencia, SINS Warsaw, TU Warsaw, AAS Wien Spokesperson: Ulrich Wiedner – Uppsala deputy Paola Gianotti, INFN-LNF Austria – Belaruz - China - Finland - France - Germany – Holland - Italy – Poland – Romania-Russia – Spain - Sweden – Switzerland – U.K. – U.S.A..

7 The PANDA experimental site at the Gesellschaft für Schwer Ionenforschung (GSI) facility in Darmstadt - Germany

8 High Intensity Mode: Luminosity 2x10 32 cm -2 s -1 (2x10 7 Hz) p/p (st. cooling) ~10 -4 High Resolution Mode: Luminosity 2x10 31 cm s p/p (electron cooling) ~10 -5 For a detailed description of the FAIR facility project at GSI see talk by K. Peters on Monday morning plenary session The PANDA experiment site within FAIR

9 The PANDA detector

10 Detector requirements full angular acceptance and angular resolution for charged particles and particle identification (, K, e, ) in the range up to ~ 8 GeV/c high momentum resolution in a wide energy range high rate capabilities, especially in interaction point region and forward detector : expected interaction rate ~ 10 7

11 The PANDA detector beam of p of momentum from 1.5 up to 15 GeV/c proton pellet target (or gas jet target) Micro Vertex Detector Inner Time of Flight detector (still under discussion) Tracking detector : Straw Tubes Tracker or TPC DIRC Electromagnetic Calorimeter 2 Tesla solenoid scintillation muon counters 2 stations of Multiwire Drift Chambers Target region Spectrometer also wire targets or foil targets for nuclear target physics carbon target interleaved with silicon detector for hypernuclear physics

12 The PANDA detector 6 stations of Multiwire Drift Chambers analysing dipole : 2 Tesla·meter Forward DIRC and RICH Forward Electromagnetic Calorimeters Time of Flight counters Hadron Calorimeter Forward Spectrometer Top View

13 The PANDA detector

14 The pellet target To achieve design luminosity required effective target thickness of 3.8x10 15 atoms/cm 2 Frozen droplets of hydrogen (pallets) successfully operating at CELSIUS/WASA facility very close now to requirements (2.8x10 15 atoms/cm 2 ), still working to reach goal pellet beam pipe 6 mm diameter

15 The microvertex detector Baseline requirements : 1.vertex spatial resolution ~100 m (charm vertices) 2.low material thickness to avoid MCS and conversions 3.forward angular coverage since PANDA is fixed target 4.radiation hardness technology

16 pellet target pipe : 6 mm beam forward disk barrel present design : barrel geometry with 5 layers. First 3 layers: pixel 400x50 m 2, 2 outer layers : double sided strips are forseen to reduce material 5 forward wheels, pixel dimensions : 150x50 m 2, 2 outer layers : double sided strips to reduce material barrel innermost 3 layers, pixels 50x400 m 2 mm ~ 7.2 million pixels in barrel ~ 2 million pixel forward disks The microvertex detector

17 Pixel technology Hybrid technology used in LHC, pixel total thickness : 250 m (sensor)+200 m(frontend)= 450 m digitization performed locally with time over threshold method (as in Atlas) Forseen 0.13 m technology for readout chip probably standard of the near future: smaller chips and lower power consumption than 0.25 m technology Pixel technology Hybrid technology used in LHC, pixel total thickness : 250 m (sensor)+200 m(frontend)= 450 m digitization performed locally with time over threshold method (as in Atlas) Forseen 0.13 m technology for readout chip probably standard of the near future: smaller chips and lower power consumption than 0.25 m technology Under investigation option 100x100 m 2 pixel detector

18 The PANDA detector : central tracker, straw tube option 11 double-layers of 150 cm long straw drift tubes. First and last double-layers parallel to beam axis, remaining arranget at skew angles from 2° to 3° allowing z position measurement at 1cm precision. Left-right ambiguity resolution thanks to double and staggered layers. beam Straw diameter : from 4mm innermost to 8 mm outermost wire diameter : 20 m, wall thickness : 30 m ~ 9000 straws Also charge division for measuring position along beam axis. Prototype straws typical momentum resolution for particles between 2 and 8 GeV/c in relevant physics channels : 1% Expected x and y resolution : 150 m Ar-CO 2 mixture with gas gain ~ 10 5 for long operation time outer radius 42 cm inner radius 15 cm

19 The PANDA detector : central tracker, TPC option Gas Electron Multiplier detectors for charge readout at the end caps : new solution from CERN inner radius : 15 cm outer radius : 42 cm length : 150 cm gas volume : 700 liters typical momentum resolution for particles between 2 and 8 GeV/c in relevant physics channels : (0.5 – 2 )% more challenging : collection of charge in ungated mode and tracks of different events E field along beam axis

20 The PANDA detector : multiwire drift chambers Dc1 and Dc2 option under study: cathod foil drift chambers 2 stations inside solenoid to track particles below 22° placed 1.4 and 2. m downstram target. Octagonal frames high flux rates expected near beam pipe : 3x10 4 cm s needed detector resistent to ageing minimal detector material : X 0 ~ 1% 6 stations forward, 2 before dipole 2 inside dipole, 2 downstream dipole detector planes arranged in staggered pairs to resolve left/right ambiguity forward MDC inside dipole or downstream it, is made of 3 pairs of detection planes vertical, +45°, 45° rectangular shape to match dipole symmetry forward MDC before dipole is made of 4 pairs of detection planes vertical, +45°, 45°, horizontal octagonal shape to match solenoid azimuthal symmetry Coverage of very high forward momentum tracks and low momentum spiralizing expected resolution of MDC system for 3 GeV/c protons : p/p = 0.2 %

21 Charged particle identification for angles > 22° : the Dirc Charged particle ID essential in PANDA. Achieved with DIRC, RICH, dE/dx, ToF The DIRC for angles > 22° Measure Cerenkov cone calculate angle of emission of Cerenkov light measure of the particle Fused silica with n= 1.47 will allow K identification starting at 460 MeV/c PMT option : read out by 7000 PMT located outside magnetic field, with ultrapurified water as optical coupling APD option : read out by APDs (Geiger mode) just outside the quartz bars R&D in progress for self-quenching Geiger mode APDs Alternative option : measure precisely time of arrival of light instead of Cerenkov cone reduce PMTs down to 120 They should be placed in contact with silica bars work in high B field use microchannel PMTs already available (25 m microchannel) ACTIVE R&D in progress quartz bar cross section : 17 mm x 30 mm

22 Charged particle identification for angles < 22° : the forward Dirc and the Rich forward Dirc : fused silica disk (or proximity imaging RICH) angle coverage between 10° and 22° RICH, located downstream of dipole angle coverage < 10° Forward DIRC present design ideas : fused silica (n= 1.47) read out by 2304 pixels 10mm x 5° + 864 pixels 10mm x 10° lower momentum /K separation ~ 1 GeV/c upper momentum /K separation : 10 GeV/c at =0, 5 GeV/c at = 25° RICH present design ideas : 3rd generation aerogel, hydrophobic, > 80% transmittance and no Hermes meniscus difect read out : new type of multipixel hybrid photocatode GaAsP photocatode (60% q.e. in 300-700 nm range) multipixel avalanche diode, 64 pixels 2mm x 2mm, with < 100 ps time resolution in 1.5 T field

23 Gianluigi Boca, Rio de Janeiro, Brazil, 21-26 Aug 2005 Charged particle identification : dE/dx, ToF A cylindrical Time of Flight scintillation counter is placed around the DIRC 96 strips of fast scintillator like BC404 : decay constant 1.8 ns thickness 0.5 cm mechanically mounted together with DIRC phototubes : channel plate photomultipliers, can work up to 2.2 Tesla field /K separation at 3 level up to 430 MeV/c at = 90° and up to 760 MeV/c at = 22° dE/dx measurements to separate /K/p typically below 800 MeV/c If TPC will be implemented, it will be ideal device but also Straw Tubes since working in proportional mode and the MicroVertex Detecor pixels can measure dE/dx Time of Flight in the Target Region

24 Gianluigi Boca, Rio de Janeiro, Brazil, 21-26 Aug 2005 the ToF wall in the forward region particle identification with momentum < 5 GeV/c distance ToF wall from target : 7 m; 5.6 m wide, 1.4 m tall 60 vertical strips of scintillator 5-10 cm wide side ToF wall inside dipole 5 vertical strips 10 cm wide, 1 m long Simulations show that with the help of the tracking system, a time resolution of 50 ps can be achieved for this ToF system

25 The PANDA detector : identification system The PANDA detector : identification system muon system only for pattern recognition momentum measured in MVD Coverage up to 60° Scintillator counters : 96 strips 10 cm wide 200 cm long, 1 cm thick Mini Drift Tube counters : stations of double layer of 4 or 6 drift tube planes scintillator counters MDT

26 Required fast, high resolution, radiation hard scintillator for between 20 MeV - 4 GeV Presently favored solution : PbWO 4 (PWO) crystals 2 2 cm 2 22 X 0 read out by APDs used for the presence of strong magnetic field. Expected resolutions of < 2%/E + 1% The PANDA detector : the EM calorimeters EM calorimeter located in three positions : central barrel end caps forward upstream end cap : 0.34 m radius, 816 crystals, segmentation in 16 slices Central Barrel Barrel : 2.5 m long, 0.54 m radius, 11360 crystals downstream end cap : 1 m radius, 6864 crystals

27 The PANDA detector : the EM calorimeters the end caps Forward : Shashlyk modules composed of lead absorbers and scintillators (E) E (1.96 0.1)% (2.74 0.05)% EGeV

28 The forward hadronic calorimeter Detect neutrons, K L and to trigger on forward hadronic showers Filter for muon counters. Located 8 m downstream the target Plan to refurbish and use the calorimeter MIRAC from WA80 20 + 20 modules arranged in 2 rows Each module contains 100 layers steel-scintillator, 1.12 m long for a total 4.8 absorption lengths. Including phototubes and light guides is 170 cm long. Read out with WLS fibers into phototubes MIRAC calorimeter PANDA arrangment beam direction Geant 4 simulation shows resolution /E = 0.40/E

29 Physics topics in more detail

30 Charmonium physics 1 Charmonium masses and widths below and above the open charm threshold are predicted by non-relativistic potential models + relativistic corrections 2 In a p p experiment like PANDA ALL c c states can be formed and not just (as in e + e experiments) 3Excellent resolution of mass and width of all states driven by resolution on p beam momentum and not by detector performances E 835 ev./pb 35003520 MeV3510 CBall ev./2 MeV 100 E CM 1000 c1 CBall E835

31 PDG 2005 : M ( c ) MeV MeV Discovery of c by Belle in B c ( KK ) confirmed by BaBar, Cleo Belle Charmonium physics below the DD threshold : the c issue Disagreement of experiments on the mass and with early findings by Crystal Ball. Only marginal consistency with most theoretical predictions. Width measured only at 50 % precision. New high statistic measurement needed to settle the question

32 Poor agreement among experiments on the mass and the width of the state. Width measured only at 10 % precision New high statistic measurement needed to settle the matter Charmonium physics below the DD threshold : the c issue The radiative decays of the cJ Radiative decays like cJ J/ and cJ are described by a dominating dipole term and multipoles arising from relativistic treatment of interaction between charmonium and electromagnetic field.This can be checked measuring the angular distributions of the c0 c1 and c2 radiative decays

33 Charmonium physics below the DD threshold : the h c issue pp h c c E835 M ±0.2 MeV/c 2 C. Patrignani, BEACH04 presentation e + e 0 h c h c c h c c c hadrons M(h c ) MeV/c 2 Cleo A. Tomaradze, QWG04 presentation This singlet P resonance is very important in determining the spin dependent components of the the qq confinement potential. Two recent results presented at conferences and an early E760 result. Agreement on the mass at the 8.5 % level. New high statistic measurement needed ! E760 : M(h c ) ±0.19 MeV/c 2 In h c J/ 0 (1992)

34 What is the X(3872) ? Charmonium 1 3 D 2 or 1 3 D 3. D 0 D 0 * molecule. Charmonium hybrid (c cg). PDG 2005 M= 3871.7 0.6 MeV/c 2 2.3 MeV (90% C.L. ) Good agreement on X mass of the 4 experiments Charmonium physics above the DD threshold : the X discovery Discovery of X(3872) by Belle (2003) B K X(3872) (and X J/ confirmed by CDF(2004), D0(2004), BaBar (2005) Belle

35 Charmonium physics above the DD threshold Structures at 4040, 4160 and 4415 need confirmation relatively narrow states expected by potential model Above DD threshold charmonium spectrum poorly know with measures of R in large steps

36 What PANDA can do for charmonium physics At 2 10 32 cm -2 s -1 accumulate 8 pb -1 /day (assuming 50 % overall efficiency) 10 4 10 7 (c c) states/day. Total integrated luminosity 1.5 fb -1 /year (at 2 10 32 cm -2 s -1, assuming 6 months/year data taking). Improvements with respect to Fermilab E760/E835: –Up to ten times higher instantaneous luminosity. –Better beam momentum resolution p/p = 10 -5 (GSI) vs 2 10 -4 (FNAL) –Better detector (higher angular coverage, magnetic field, ability to detect hadronic decay modes).

37 Gluonic excitations (hybrids, glueballs) and other exotics QCD allows for richer spectrum than quark model because gluons can became principal components of new hadrons : glueballs and hybrids. Additional gluons allow to have an exotic J pc forbidden for regular hadrons. Their properties are determined by the long distance features of QCD studying them is fundamental !! Also hadrons with more than qq or 3 quarks are expected to exist. Hybryds : qqg Glueballs : states of pure glue Oddballs : states of pure glue with exotic quantum numbers: ( etc.) Other exotics : tetraquarks, pentaquarks. Exotic J PC will be a powerful signature for experimental detection. LQCD calculations improved precision along the years in prediction of masses and widths of these states. _

38 Gluonic excitations charmonium hybrids non-charmonium hybrids potential and wavefunctions energy levels 1-g exchange excited glue K. Juge, J. Kuti, C. Morningstar PRL 90 (2003) 161601 overlap with many broad states overlap with few narrow states see also K.Juge talk at this conference, parallel session on Thursday

39 Gluonic excitations : glueballs and oddballs Morningstar,Peardon, PRD60(1999)34509 Morningstar,Peardon, PRD56(1997)4043 0 +- 2 +- Investigation of glueballs is essential to understand long-distance QCD. LQCD predicts 15 glueball states with mass accessible to PANDA, some with exotic quantum numbers (oddballs). Glueballs can mix with normal hadronic resonances in same mass range while oddballs, due to exotic J PC are predicted to be narrower and easier to find in partial wave analysis Predicted width ~ 100 MeV Glueball color blindness : can dacay in uu, dd, ss and cc First oddball 2 predicted at 4.3 GeV/c 2 very well in the reach of PANDA in formation or production. Glueballs decays most favourable to PANDA are or if mass < 3.6 GeV/c 2 or to J/ or J/ above 3.6 GeV/c 2 PANDA can form and produce glueballs (oddbals) : pp statistics 2 orders of magnitude better than Jetset at LEAR also measure pp KK * study of (1475) KK seen by Obelix at LEAR exotic

40 Other exotics : tetraquarks, pentaquarks Recent hints of pentaquarks qqqqq discoveries have been claimed The (1540) decaying into pK s or nK + has been seen by 10 experiments. The weighted average of the mass is 1533.6 ± 1.2 MeV/c 2 but unfortunately compatibility of 10 measurements is only 1.6x10 5 Pentaquark with strange content decaying into with Mass = 1862±2 MeV/c 2 and < 18 MeV/c 2 claimed by NA49 in 2004 Pentaquarks with charm content decaying into D* p with Mass = 3099±3±5 MeV/c 2 and =12 ±3 MeV/c 2 claimed by H in 2004 PANDA can access to pentaquarks and tetraquarks (qqqq) up to ~ 2700 MeV/c 2 The p p reaction could be studied near threshold PANDA can access to pentaquarks and tetraquarks (qqqq) up to ~ 2700 MeV/c 2 The p p reaction could be studied near threshold

41 : substantial shifts predicted. Experimental goal of HADES at GSI Hadrons in nuclear matter D Mesons: theoretical predictions on size of mass splitting depending on the model. Important to measure experimentally Hayaski, PLB 487 (2000) 96 Morath, Lee, Weise, priv. Comm. D 50 MeV D D+D+ vacuum nuclear medium K 100 MeV K+K+ K 25 MeV cc mesons sensitive only to gluon condensate in nuclei due to heavy c mass predicted only 5 10 MeV mass reduction for J/ and c but 40 MeV for cJ, 100 MeV for and 140 MeV for (3770) Mass shifts caused by potential in nuclear matter Calculation: A. Sibirtsev et al., Eur. Phys. J A6 (1999) 351 high intensity p beam up to 15 GeV/c opens up the possibility of : study of nuclear bound states with slow K or produced inside nuclei study of mass shifts of charmonium states, produced in nuclei and decaying into leptons or study of production yield of DD pairs produced below threshold in nuclei. Increase of cross section due to increased phase space dependence of all above on nucleus size study of the possible effect of the opening, in nuclei, of the DD decay channel to states normally below threshold like (3770),, c2

42 c J/ c 0,1,2 (3686) (3770) Expected Mass shift -5 MeV to -8 MeV -7 MeV to -10 MeV -40 MeV to -60 MeV -100 MeV to -130 MeV -120 MeV to -140 MeV Observation through e + e - / + - J/ e + e - / + - Predicted rates at L = 10 32 cm -2 s -1 : few 10 … few 100 events/day S.H. Lee, nucl-th/0310080 p _ ~ 1 fm final state = e + e - / + - / / J/ t ~ 10…20 fm/c 10 fm/c (collisional broadening) Hadrons in nuclear matter, physics reach in PANDA

43 J/ absorption in nuclear matter p + A J/ + (A-1) ; detect J/ + - (e + e - ) J/ absorption cross section in nuclear matter, scarce experimental data can be used later by experiments that study J/ suppression as signal for Quark Gluon Plasma _

44 Hypernuclear physics In hypenuclei one (or more) substitute one (or more) nucleon. A whole new set of states can exist containing an extra degree of freedom : strangeness. The lighter single strangeness ( hypernuclei ) energy levels are predicted in the frame of the shell model, where the particle is subject to an effective single particle potential. Heavier hypernuclei and hypernuclei are described by more complicated models. Experimental situation : ~35 hypernuclei established since 50 years ago Only 6 hypernuclei

45 produce at threshold in pp use a secondary target where is captured in a hyperatom and then interacts in nucleus + A Z A+1 (Z )* A+1 (Z 1) + s) detected in apparatus A+1 (Z+1) + detect with high resolution germanium detector in coincidence with tag. A+1 (Z-1) subequently decays via pionic cascade into normal nucleus. -hypernuclei production and detection in PANDA - (dss) p(uud) (uds) (uds) - 2.6 GeV/c Tag _ secondary target p X ray excited hyp.nucl. ground state hyp.nucl. s) detected in apparatus normal nucleus hypernucleus pionic decay detected

46 Hypernuclei physics : detector requirements Solid state detector (diamond or silicon) compact : thickness ~ 3 cm high rate capability high resolution capillar (2D) or pixel (3D) position sensitive Germanium detector (like Vega or Agata) Current state of the art detection resolution : 2 KeV (KEK E419) Current state of the art p detection resolution : E = 1.29 MeV Finuda Collaboration, PLB622: 35 44, 2005

47 Hypernuclei physics : expected rates in PANDA using a 12 C wire as primary target at L = 2 x10 32 cm -2 s PANDA will produce ~ 7x10 2 / sec pp ( ) = 2 b @ 3 GeV/c pA ( ) = A 2/3 pp ( ) joint escape probability : 5x10 (trigger on and 100 < P < 500 MeV/c) reconstruction efficiency : ~ 50 % stopping and capture probability : ~ 20 % ~ 3x10 3 captured /day p conversion probability : 5%~ 150 -hypernuclei /day emission probability: 50% Ge photopeak efficiency : 10% ~ 7 golden events/day K + K + trigger~ 700 events /day

48 PANDA as an open charm factory Running at full luminosity of 2x10 7, above the 3.73 GeV open charm threshold or at the (3770), assuming (ppDD ) ~ 1 b, with 50 % reconstruction efficiency in the D golden modes from MC calculations, and 10 7 s running time in a year, PANDA will detect ~ 10 9 /year DD golden mode pairs per year in a SUPER CLEAN almost backgroundless type of event. PANDA will be the mecca for all those who want to do the D mesons charm physics. The only forseeable next generation charm factory, with possibly 10 3 times todays BaBar charm yields. It will continue the very successful program in charm physics of experiments like Cleo, Focus, BaBar, Belle.

49 PANDA as an open charm factory Possibility of studying a large part of the physics issues concerning charm physics : direct CP violation T-violation mixing in the D 0 D 0 system rare and forbidden decays D + l + semileptonic decay and form factors Dalitz plots relative and ABSOLUTE branching ratios singly and doubly Cabibbo forbidden decays multihadronic decays new D decays

50 Crossed-channel Compton scattering and related exclusive processes Recently shown this reaction can be described in terms of Generalized Parton Distributions p Using a hand bag diagram the process separates into a soft part parametrized by GPDs and a hard part described by a quasi-free qq scattering into Lately a new approach applied the same formalism to pp e + e pp pp + vector meson ( ) The production of a hard di-lepton pair is a hard subprocess that is assumed to factorize from the lower part that is described by a hadron to transition amplitude

51 Crossed-channel Compton scattering and related exclusive processes Expected rates at PANDA at L = 2x10 32 cm s and 3.2 GeV Conservative : 10 3 events/month Optimistic : 5x10 4 events/month PANDA has a great potential for and e detection

52 Electromagnetic form factors of the proton in the time-like region Electromagnetic form factors in timelike region can be studied in pp e e to first order QCD (E,P energy, momentum p in cms) : data at high Q 2 are crucial : check Q 2 behaviour check spacelike timelike equality for corresponding Q 2

53 Electromagnetic form factors of the proton in the time-like region Proton timelike f.f. measured by several experiments at low Q 2 at high Q 2 only E760 and E835 up to Q 2 ~15 GeV 2 but due to low statistics measured only |G E | and |G M | under assumption |G E | = |G M |

54 Electromagnetic form factors of the proton in the time-like region possibility of measuring form factors from threshold up to 29 GeV 2 ! in PANDA : much wider angular acceptance and higher statistics possibility of measuring |G E | and |G M | separately 29 GeV 2

55 Time schedule of the project

56 2005 (Jan 15)Technical Proposal (TP) with milestones. Evaluation and green light for construction. 2005 (May)Project starts (mainly civil infrastructure). 2005-2008Technical Design Report (TDR) according to milestones set in TP. 2006High-intensity running at SIS18. 2009SIS100 tunnel ready for installation. 2010SIS100 commissioning followed by Physics. 2011-2013Step-by-step commissioning of the full facility. Time schedule of the project

Download ppt "21 26 Aug 2005, Rio de Janeiro, Brazil The PANDA project at GSI."

Similar presentations

Ads by Google