Monday: Quarks and QCD. Quarks and gluons: QCD, another gauge theory! Basic physics of QCD Quarks and their properties The strong interaction: mesons and

  • View
    215

  • Download
    3

Embed Size (px)

Text of Monday: Quarks and QCD. Quarks and gluons: QCD, another gauge theory! Basic physics of QCD Quarks...

  • Slide 1

Monday: Quarks and QCD. Quarks and gluons: QCD, another gauge theory! Basic physics of QCD Quarks and their properties The strong interaction: mesons and baryons Slide 2 Today: (mainly) mesons + recent discoveries. QCD reminder Conventional qq mesons (cc) Making new hadrons (hit things together) Glueballs and hybrids (gluonic excitations) MOST RECENT ARE: Trouble in charmed mesons Molecules, multiquarks and pentaquarks Slide 3 The Theory of the Strong Interaction QCD: The Theory of the Strong Interaction QCD = quantum chromodynamics, ca. 1973 Theory of the strong nuclear force. Its due to the exchange of gluonsg spin-1 particles gluons g between spin-1/2 matter particles, quarks q and antiquarks q. photons Similar to QED (quantum electrodynamics), spin-1 photons are exchanged between spin-1/2 electrons e - and positrons e +. The basic rules of interaction Feynman vertices in this non-Abelian quantum field theory are that quarks and antiquarks can emit/absorb gluons, gluons interact with gluons and [novel] gluons interact with gluons. Slide 4 Comparing QED and QCD. (lagrangians) Its dj vu all over again. -Y.Berra Slide 5 Small qq separation Large qq separation basic physics of QCD Slide 6 The QCD flux tube (LGT, G.Bali et al; hep-ph/010032 ) LGT simulation showing the QCD flux tube Q Q R = 1.2 [fm] funnel-shaped V QQ (R) Coul. (OGE) linear conft. (str. tens. = 16 T) Slide 7 Quarks Minimal solution for quarks needed to explain the known light hadrons: (1964, Gell-Mann, Zweig; Neeman): All J P = + (fermions) u Q = 2/3 e (u,d very similar in mass) d Q = 1/3 e s Q = 1/3 e (somewhat heavier) Thus p = uud, n = udd, = uuu, = uds, + = ud, K + = us, etc. Slide 8 qqq baryons The lightest qqq baryon octet. (SU(3) symmetry.) 3 x 3 x 3 = 10 + 8 + 8 + 1 Slide 9 qq meson The lightest qq meson octet. (SU(3) symmetry.) 3 x 3 = 8 + 1 Slide 10 The six types or flavors of quarks. Gens. I,II,III. Label Name Q/|e| I I z ca. mass habitat u up +2/3 + 5 MeV p(938)=uud, n(940)=udd, d down -1/3 - 10 MeV + (135)=ud - (135)=du, s strange -1/3 0 (etc) 150 MeV strange hadrons; =uds,K + =us, c charm +2/3 1500 MeV family (cc); open charm hadrons; D o =cu, D + =cd; D s + =cs c + =udc, b bottom -1/3 5 GeV U family (bb); open b hadrons t top +2/3 175 GeV t decays too quickly to hadronize Slide 11 Nave physically allowed hadrons (color singlets) qq q3q3 Conventional quark model mesons and baryons. q 2 q 2, q 4 q, multiquarks g 2, g 3, glueballs maybe 1 e.g. qqg, q 3 g, hybrids maybe 1-3 e.g.s 100s of e.g.s exotica : _ Slide 12 qq mesons states The quark model treats conventional mesons as qq bound states. Since each quark has spin-1/2, the total spin is S qq tot = x = 1 + 0 Combining this with orbital angular momentum L qq gives states of total J qq = L qq spin singlets J qq = L qq +1, L qq, L qq -1 spin triplets First, some conventional hadrons (qq mesons) to illustrate forces. Slide 13 Parity P qq = (-1) (L+1) C-parity C qq = (-1) (L+S) qq mesons quantum numbers 1S: 3 S 1 1 ; 1 S 0 0 2S: 2 3 S 1 1 ; 2 1 S 0 0 1P: 3 P 2 2 ; 3 P 1 1 ; 3 P 0 0 ; 1 P 1 1 2P 1D: 3 D 3 3 ; 3 D 2 2 ; 3 D 1 1 ; 1 D 2 2 2D J PC forbidden to qq are called J PC -exotic quantum numbers : 0 ; 0 ; 1 ; 2 ; 3 Plausible J PC -exotic candidates = hybrids, glueballs (high mass), maybe multiquarks (fall-apart decays). The resulting qq NL states N 2S+1 L J have J PC = Slide 14 How to make new hadrons (strongly int. particles): Hit things together. A + B -> final state You may see evidence for a new resonance in the decay products. Some reactions are clean, like e + e - -> hadrons. e.g.s SLAC, DESY 1970s Now: CLEO-c, BES cc B-factories bb (SLAC, KEK) W,Z machines (LEP@CERN) J/y and other 1 -- cc Slide 15 Charmonium (cc) A nice example of a QQ spectrum. Expt. states (blue) are shown with the usual L classification. Above 3.73 GeV: Open charm strong decays (DD, DD* ): broader states except 1D 2 2 2 3.73 GeV Below 3.73 GeV: Annihilation and EM decays. , KK*, cc, , l l ..): narrow states. Slide 16 s = 0.5538 b = 0.1422 [GeV 2 ] m c = 1.4834 [GeV] = 1.0222 [GeV] Fitted and predicted cc spectrum Coulomb (OGE) + linear scalar conft. potential model blue = expt, red = theory. S*S OGE L*S OGE L*S conft, T OGE Slide 17 cc from LGT exotic cc-H at 4.4 GeV oops cc has been withdrawn. Small L=2 hfs. What about LGT??? An e.g.: X.Liao and T.Manke, hep-lat/0210030 (quenched no decay loops) Broadly consistent with the cc potential model spectrum. No radiative or strong decay predictions yet. Slide 18 SP Sector of the 1 st shocking new discovery: cscs Slide 19 PS LGT 0 + : 2.44 - 2.47 GeV. Slide 20 Where it all started. BABAR: D * sJ (2317) + in D s + 0 D.Aubert et al. (BABAR Collab.), PRL90, 242001 (2003). M = 2317 MeV (2 D s channels), < 9 MeV (expt. resolution) (Theorists expected L=1 cs states, e.g. J P =0 +, but with a LARGE width and at a much higher mass.) Who ordered that !? I.I.Rabi (about the - ) Since confirmed by CLEO, Belle and FOCUS. Slide 21 And another! CLEO: D * sJ (2463) + in D s * + 0 Since confirmed by BABAR and Belle. M = 2457 MeV. D.Besson et al. (CLEO Collab.), PRD68, 032002 (2003). M = 2463 MeV, < 7 MeV (expt. resolution) A J P =1 + partner of the possibly 0 + D * sJ (2317) + cs ? Slide 22 (Godfrey and Isgur potential model.) Prev. (narrow) expt. states in gray. DK threshold Slide 23 Theorists responses to the BaBar states Approx. 100 theoretical papers have been published since the discovery. There are two general schools of thought: 1) They are cs quark model mesons, albeit at a much lower mass than expected by the usual NRQPMs. [Fermilab] 2) They are multiquark states. (DK molecules) [UT,Oxon,Weiz.] 3) They are somewhere between 1) and 2). [reality] Slide 24 Slide 25 2. They are multiquark states (DK molecules) [UT,Oxon,Weiz.] T.Barnes, F.E.Close, H.J.Lipkin, hep-ph/0305025, PRD68, 054006 (2003). 3. reality Recall Weinstein and Isgurs KKbar molecules. Slide 26 X(3872 ) Belle Collab. K.Abe et al, hep-ex/0308029; S.-K.Choi et al, hep-ex/0309032, PRL91 (2003) 262001. J MeV = 3 D 1 cc. If the X(3872) is 1D cc, an L-multiplet is split much more than expected assuming scalar conft. MeV Another recent shock to the system: (From e + e - collisions at KEK.) cc sector Slide 27 Fitted and predicted cc spectrum Coulomb (OGE) + linear scalar conft. potential model blue = expt, red = theory. X(3872) not cc ??? Slide 28 X(3872) confirmation (from Fermilab) G.Bauer, QWG presentation, 20 Sept. 2003. n.b. most recent CDF II: M = 3871.3 pm 0.7 pm 0.4 MeV CDF II Collab. D.Acosta et al, hep-ex/0312021, PRL to appear OK, its real X(3872) also confirmed by D0 Collab. at Fermilab. Perhaps also seen by BaBar Slide 29 X(3872 ) n.b. D D* MeV D D* MeV Accidental agreement? If not cc 2 or 2 or , a molecular (DD*) state? MeV Charm in nuclear physics??? Slide 30 The glueball spectrum from an anisotropic lattice study Colin Morningstar, Mike Peardon Phys. Rev. D60 (1999) 034509 The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is investigated using Monte Carlo simulations of gluons on several anisotropic lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Glueballs: Theor. masses (LGT) Slide 31 How to make new hadrons (strongly int. particles) (II): Hit more things together. A + B -> final state You may see evidence for a new resonance in the decay products. Reactions between hadrons (traditional approach) are rich but usually poorly understood. e.g.s BNL p -> mesons + baryon LEAR (CERN) pp annih. All light-q and g mesons, incl. qq, glueballs, hybrids, multiquarks. Slide 32 Slide 33 Glueball discovery? Crystal Barrel expt. (LEAR@CERN, ca. 1995) pp -> p 0 p 0 p 0 Evidence for a scalar resonance, f 0 (1500) -> p 0 p 0 n.b. Some prefer a different scalar, f 0 (1710) - > hh, KK. PROBLEM: Neither f 0 decays in a nave glueball flavor-symmetric way to pp, hh, KK. qq G mixing? Slide 34 Hybrid meson? J PC = 1 -+ exotic. (Cant be qq.) E852@BNL, ca. 1996 p - p -> (p - h) p p 1 (1600) a 2 (1320)q (Current best of several reactions and claimed exotics.) Follow up expts planned at a new meson facility at CEBAF; HallD or GlueX. exotic Slide 35 (Too?) exciting news: the pentaquark at CLAS (CEBAF). nK + = (udd)(us) = u 2 d 2 s. Cant be a 3 quark baryon! A flavor exotic multiquark (if it exists). ( > 200 papers) Slide 36 An experiment expressly designed to detect pentaquarks confirms the existence of these exotic physics particles, researchers reported Sunday. [] Physicists are cautious about leaping onto the pentaquark bandwagon because of past bad experiences [] USA Today 3 May 2004 Slide 37 The multiquark fiasco These are very serious charges youre making, and all the more painful to us, your elders, because we still have nightmares from five times before. - village elder, Young Frankenstein Slide 38 The dangerous 1970s multiquark logic: (which led to the multiquark fiasco) The known hadron resonances, qq and qqq (and qqq) exist because they are color singlets. Therefore all higher Fock space multiquark color singlet sectors will also possess hadron resonances. q 2 q 2 baryonia q 6 dibaryons q 4 q Z* for q = s now pentaquarks MANY theoretical predictions of a very rich spectrum of multiquark resonances followed in the 1970s/early 1980s. (Bag model, potential models, QCD_SRs, color chemistry,) Slide 39 M pp [GeV] I=2 pp S-wave d 0 I=2 [deg] No I=2 q 2 q 2 resonance at 1.2 GeV. (Bag model prediction, would give Dd = + 180 [deg] there.) Expt sees only repulsive pp scat. The simplest e.g. of had-had scat: I=2 (A flavor-exotic 27 channel, no s-channel qq resonances, so no qq annihilation. Similar to the NN and BB problems.) Q = +2 channel No qq states. u 2 d 2 ? Slide 40 Why are there no multiquark resonances? Fall-Apart Decay (actually not a decay at all: no H I ) Most multiquark models found t

Related documents