Tevatron Physics Results – the Springboard to the LHC

1. Tevatron Physics Results – the Springboard to the LHC The Large Hadron collider will start operations at 7 – 10 TeV late this year. The program there will rest on the physics legacy from the 2 TeV Tevatron Paul Grannis Univ. Michigan 9/16/09

2. Tevatron Physics Results – the Springboard to the LHC The Large Hadron collider will start operations at 7 – 10 TeV late this year. The program there will rest on the physics legacy from the 2 TeV Tevatron Wolverine exchange boson M Paul Grannis Univ. Michigan 9/16/09

3. + the other 2 color sets u c t d s b ne nm nt e m t g + the other color gluon states g f2 f1 W± coupling ‘const.’ B f3 f4 Z The Standard Model Fermion (‘charge’ carrying) matter particles 3 quark ‘flavor’ isospin doublets (generations). The weak int’n quark states ≠ strong states: Mixing matrix VQ connects. 3 lepton flavor isospin doublets (generations). Mass eigenstates are rotated from flavor states: transformation matrix VW. (3 generations is minimum needed for CP violation as seen in nature) Interactions/force carriers: Strong (QCD) Electroweak SU(3) x SU(2) x U(1) 26 arbitrary parameters: 12 fermion masses 8 mixing matrix parameters 3 force couplings 2 EW boson masses 34 + 1 strong CP phase

4. ( ) b0 w- w0 w+ EWSB in SM The unified EW force broken to EM and Weak by spontaneous symmetry breaking. Introduce ad hoc complex doublet scalar Higgs fields – two neutral degrees of freedom and two charged. The vacuum symmetry point is not the minimum of the potential: Massless gauge bosons in symmetry limit (2 helicity states each) massless g W- W+ Z0 ( ) EWSB massive f+f0 Higgs field doublet (4 real d.o.f) ( )  • In the symmetry breaking induced by the Higgs fields, 3 Higgs d.o.f. go to provide the missing helicity 0 states needed by massive (W+ W- Z). • Before symmetry breaking: 12 d.o.f (4x2 gauge boson plus 4 Higgs) • After EWSB, 12 d.o.f. (3x3 for W±/Z, 2 for g and 1 Higgs). We are left with an observable Higgs boson whose mass is not predicted by the theory. 33

5. In SM context, the ~100 precision measurements of the properties of Z, W, top quark indicate MH=87± GeV. Direct searches say MH>114.4 GeV. 35 26 SM Higgs boson V(F) =l(F2 – ½ v2) (v ~ 246 GeV) MH = 4 l v2 . All parameters of the EW interaction are fixed by experiment, except MH (lis not known). Higgs gives mass to W and Z – and quarks & leptons too Higgs Without incredible fine tuning of parameters, loops like these drive the W, Z, H masses to the Planck scale – the Hierarchy Problem e.g. W boson W boson l l Higgs Yukawa coupling also generate the quark masses. The more massive the quark, the larger its Yukawa coupling l. Many observables of the Z and W bosons are dependent upon the mass of the Higgs boson. Of course, Nature may choose some other way, so need to continue to look outside this window. 32

6. The SM Higgs boson – in analogy From D. J. Miller Before the arrival of the star physicist Prof. Higgs, the room is filled with quietly chattering students (i.e. the vacuum) Prof. Higgs arrives and starts to move across the room. The students cluster around him, slowing his progress. Reduced speed is equivalent to adding to his mass (momentum is conserved). Higgs mechanism is the Giver of Mass, responsible for the Higgs boson’s mass, as well as that for the other particles like W/Z bosons and quarks. 31

7. The SM Defects • The 26 arbitrary parameters put in ‘by hand’ are embarrassing. A real understanding should explain these. • The SM does not unify the strong force and electroweak force. Einstein’s dream is not fulfilled. • The Higgs boson that breaks the EW symmetry is precarious. It seems to have a mass of ~100 GeV but higher order corrections would try to push its mass up to a value 15 orders of magnitude to the Planck scale !! • We observe only matter, no anti-matter, in the universe. To get this from an initial condition of equal matter and anti-matter requires a violation of CP symmetry. Violation of the size needed cannot be obtained in the SM. • The dark matter seen in galaxies dominates the ordinary matter made from quarks and leptons by a factor of five. The SM has no dark matter candidate. • Gravity is a fundamental force but does not even enter into the SM. Why the 100’s of measurements to date agree so well with the SM is a big puzzle!! 30

8. Physics beyond the SM • The SM defects become critical at the TeV scale, so experiments there should reveal some kind of new physics. • There are many suggested model classes (each with many variant subclasses): • Supersymmetry: New anti-commuting space time degrees of freedom leading to a new boson for every fermion (and vice versa) with all quantum numbers the same apart from spin. • Large extra spatial dimensions with various SM (or Susy) particles propagating in the new dimensions, or different metrics in the ‘bulk’. • New strong coupling models patterned on QCD, yielding new particles and forces. • New sectors of particles that couple only weakly to SM particles. etc. Only experiment can decide if any of these are correct, and the energy scale for the experiments is now accessible. 29

9. Scattering Garbage Cans : Jets Two protons containing “partons” (quarks and gluons) approach each other, each with 7 TeV of energy 2 partons within the protons scatter The partons fragment into ‘jets’ of observed particles Each parton carries only a fraction of the proton energy characterized by the “parton distribution function” (PDF) 28

10. 22 The Tevatron CDF DØ Counter-rotating p and p, colliding at 1.96 TeV. Protons are bags of quarks and gluons, so in effect the Tevatron is a quark-antiquark collider ( 15% of collisions are gg/ gq) with qq energy up to ≈ 1 TeV. Two experiments CDF and DØ will operate until the LHC program is producing physics results (run through 2011 (2012?) ) 2 km Expect 12 fb-1 delivered; 10 fb-1 to physics Collision rate = luminosity x s Peak luminosity is ~300 mb-1 s-1 Expect ∫L dt ~10 fb-1 by the end of the program, so for Higgs production with s≈100 fb, will produce ~1000 events. now Summer ’09 results up to 5.8 fb-1, typically ~ 4fb-1 27

11. 20 The LHC The Large Hadron Collider (LHC) at CERN will collide protons with protons starting at 7 TeV, rising to 14 TeV. This will provide collisions of the constituent quarks and gluons to about 5 TeV (dominantly gg collisions). General purpose experiments ATLAS and CMS. LHCb will focus on b-quark physics; ALICE on heavy ions; TOTEM on small angle scattering. After the magnet splice accident in 2008, first collisions are now expected in late 2009; first physics results in 2011?? Mt. Blanc Lake Geneva ATLAS 8.6 km CMS Luminosity should reach 10,000mb-1 s-1 (~30x Tevatron) The LHC will reach the energy scale where current experiments tell us that new physics should surely exist – LHC is the primary discovery vessel. 26

12. Compilation of many experiments aS √Q2 Couplings change with Q2 Viewed at low magnification (low momentum transfer Q2 at a vertex), interactions look simple. Viewed at higher Q2 (high magnification, shorter distance) the situation is more complex and the couplings change. QCD coupling aS decreases with Q2 (asymptotic freedom) The Electroweak couplings increase with Q2 (slowly) 25

13. The Tevatron sets the stage for the LHC Although the energy and luminosity of the LHC will make it primary discovery machine, the Tevatron will point the way to new discoveries. The Tevatron has some unique advantages (lower backgrounds, qq collisions rather than gg). The Tevatron will leave its own unique legacy. • I will not give an exhaustive summary of Tevatron physics (>600 publications to date), but will focus on those bearing on EW symmetry breaking: • Top quark properties • W/Z boson properties • Higgs boson search • And a few of the measurements that will provide critical understanding needed for LHC expts: • Jet studies • Heavy quark states 24

14. The Voyage of Discovery Grand Unification Gondwandaland EWSB- land Bay of SUSY Cliffs of Dark Matter Planck Dragon Oceanus LHC Beagle n Oscillations Dark Energy Maelstrom Quark mixing Mare Tevatorum nCP B≠B e→m Muon g-2 The Flavor Archipeligo GZK Atolls Gravitational Waves Quark-gluon plasma perfect liquid 23

15. secondary vertex secondary vertex primary vertex Top Quark CDF and DØ discovered the top quark in 1995 at ~35 times bottom quark mass (≈MAu). At Tevatron, produce tt pairs through qq interactions (LHC is mainly gg interactions). • In SM, t →W+b 100% of time. W decays to qq’ or ln, so final states are • a)dilepton (2 leptons +2b quarks) • b) lepton+jets (one lepton, missing energy, 2b quarks and two light quarks); • c) all jets (6 jets, no leptons). • Dilepton channel has low background but small branching ratio (7%) • Lepton+ jets has moderate background but higher BR (34%) • All jets has highest BR (44%) but large backgrounds. Identify b-quark jets by seeing their displacement from vertex In 10 fb-1, we analyze ~1000 dilepton events and ~4000 lepton+jet events per experiment, so rather precise measurements become possible. LHC XS ≈ 100xTevatron and L ≈30xTevatron, so LHC is a top quark factory. Even with larger backgrounds, LHC will ultimately improve top quark studies over the Tevatron. 22

16. ? u c t d s b Tevatron Top Quark Profile First question is if it is really the SM object expected. Is it the isospin partner to the b-quark with Q=+2/3e & J=1/2? Since it decays before the Strong Interaction can make it ‘hadronize’ to ordinary particles, we can probe decays to W bosons and see if the spins are as predicted in QCD. Does QCD predict its production cross section properly? 1. tt XS agrees with QCD NNLO prediction with uncertainty 6%/expt. Close to systematics limited. 2. Charge Q=4/3e ruled out at 92% C.L. (so t is SM partner to b) 3. top-antitop masses equal to 3.7% (CPT symmetry confirmed) 4. Decay W boson has L-handed spin projection expected in V-A weak interaction (but some hint of discrepency – more data will tell) 5. Top spin correlations at production revealed in decay particle momenta; again agree with QCD prediction, but small hint of something new. * 6. Small preference (2s) for top aligned with p beam, not expected in SM * 7. No evidence for excited top (but there is a hint from CDF?) 8. No tt resonances seen up to mass of 820 GeV. Angle, pT distributions as in QCD * LHC won’t do It walks like a quark, looks like a quark, quacks like a quark, so … 21

17. Single Top Quark Production Top quarks produced in pairs by the strong interaction (preserve flavor symmetry). Single top quarks can be produced by EW interaction via s-channel or t-channel W exchange). SM predicts s ≈ 3.2 pb. (Exercise for student: why is this weak process so large as half the strong int. pair production?) It’s a small signal with large backgrounds! Pull out all the stops and use neural networks, boosted decision trees, matrix element analyses. Both CDF and DØ recently published observation at 5s level at SM expected level. Increased background will make this truly challenging at LHC. The payoff is large; see the recent DØ measurement of t-channel process separately. The comparison of s- and t-channel XS is sensitive to many models of new physics. More data can reveal non-SM physics. Also can measure the tbWcoupling directly (a fundamental parameter of the quark mixing matrix) to be |Vtb|=0.91±0.08 consistent with SM (=1) SM 20

18. top top l Higgs l Top Quark Mass The large top quark mass means its coupling to Higgs is large. The top mass depends on MH through loop diagrams (DMt ~ logMH). Thus a precise top mass measurement is a primary indicator of Higgs mass in SM framework. Many mass measurements have been made in dilepton, lepton+jets, all jets channels with a variety of techniques by both CDF and DØ. They are in agreement: Tevatron average in Mar. 2009: Mt=173.1±1.2 GeV (0.7%) This will improve with summer results. Have now exceeded the Tevatron goal; expect the final average mass to be below 1 GeV. Are now reaching the systematic limit (heavy flavor jet energy scale, signal model, jet resolution). Reaching this precision will take LHC experiments some time ! 19

19. W and Z bosons W and Z bosons are copiously produced at Tevatron. Expect samples ~10M W’s and ~500K Z’s. Production and decay properties are now well measured: • Production cross sections agree with QCD (and are becoming the standard candle for measuring luminosity). The pT dependence measures non-perturbative QCD corrections. • Forward/backward charge asymmetry in W production/decay improves knowledge of proton’s quark content (needed as input for all Tevatron/LHC studies). Expt errors now smaller than existing theory uncertainty. Pseudorapidity h=-ln tanq is the natural polar angle variable • Lepton forward-backward asymmetry for ll production measures Z-g interference as fn. of M(ll) and gives EW mixing angle in new regime (high Q2, light quarks). (LEP left us with puzzling discrepancy.) 18

20. Diboson Production Diboson production (Wg, Zg, WW, WZ, ZZ) processes have low XS. All have now been observed at Tevatron and are consistent with the SM. Diboson, tt, t, Higgs XS’s • The rates and angular distributions allow search for non-SM anomalous couplings: VVV coupling No anomalous couplings are observed. Can translate into anomalous magnetic dipole/electric quadrupole moments of W. (LHC will do much better at this). • First observation of WW/WZ production in the challenging jet jet l n channel. The W/Z mass peak is observed. Allows validation of methods for Higgs search in ‘known’ processes. 17

21. data/MC bknds <MW> fit range W boson Mass W mass depends on Higgs mass. For W→lncan measure pTl, pTn (missing energy) or MT=√[pTl pTn(1-cosfln)]. Compare templates from MC with data to get the best MW. These are exquisitely difficult measurements, requiring control of systematics to 10-4 level. • Recent world best measurement of MT in electron channel. Data (red) compared to best MC template (blue) gives MW=80.401±0.043 GeV. c vs. MT at bottom shows excellent agreement over full range. • Combining all measurements from Tevatron and LEP gives new world average MW=80.399±0.023 GeV (<0.03%). Tevatron is now better than LEP. • W width also measured from high mass Breit Wignertail: GW=2.092±0.072 GeV, in agreement with SM. World avg error ≈ 42 MeV. It will be a long time before LHC does this ! 16

22. q’ q W+ H q W/Z g t H W/Z W- g q q H q’ gluon-gluon fusion (gg) associated VH production (V=W/Z) vector boson fusion (VBF) Search for the SM Higgs Boson The Higgs boson is produced in 3 main ways. The relative sizes depend on energy and on the initial particles (quark-antiquark at Tevatron; gluon-gluon at LHC). Tevatron s(pb) (VH) gg (VBF) • Cross sections at LHC are ~50X those at Tevatron. • gg fusion is largest at both machines, but VBF rivals gg at large Higgs mass for LHC. At Tevatron, associated VH production is closer to gg fusion (due to valence antiquarks in antiprotons). • Backgrounds also vary from Tevatron to LHC: For example the QCD production of W+2 b-quark jets is a dominant background for the WH process, and this cross section grows rapidly with √s . 15

23. SM Higgs Boson Decay Channels Higgs couples to mass, so decays mainly into heaviest pair of particles kinematically accessible. At low mass (<135 GeV) mainly bb (and some tt). At high mass (>140 GeV) H→WW* dominates. A final state with just 2 b quark jets (gluon gluon fusion) has huge QCD backgrounds, so typically seek W/Z H where W/Z decay to leptons suppresses background. At high mass, the HWW gives lepton final states and the ggf process can be accessed. WH: e/mn bb t n bb qq’ tt e/m n W(e/m)W(e/m) jj bb ZH: ee/mm bb nn bb tt bb qq tt ttH: lnb qq’b bb gg→H:W(e/m)W(e/m) gg tt (+ 2 jets) WW →H: tt (+ 2 jets) The XS’s and acceptances are very small, so to gain sensitivity, many different processes are used, and for each there are various sub-processes (e, m, t decays, different numbers of tagged b jets…). Table shows the channels now used (ones in green are most sensitive) 14

24. W/Z W/Z H t t H t W W b Constraints on the SM Higgs Boson We have seen that top, W (and Z) masses and other observables are modified by Higgs loops. Measurement of many observables for W/Z/t thus indirectly constrain allowed SM Higgs masses. Example: Measured MW vs. Mtop (blue ellipse), constraints from precision observables for Z (orange ellipse) compared with lines of different SM Higgs masses. (improved dMW is needed !) A direct search at LEP e+e- collider gave limit MH > 114.4 GeV. As of a year ago, these constrained fits gave a c2 vs. MH in the blue band. The yellow region is ruled out by LEP. The data were already strongly favoring low MH (< 160 GeV) and there was tension between LEP limits and the constrained prediction. 13

25. secondary vertex secondary vertex primary vertex Higgs Boson Search Methods • Searches now include between 1 and 5 fb-1, so more data will help • Choose events with desired objects (e.g. Wmn,Hbb search requires isolated m, missing ET (n), 2 or 3 jets above some pT cut and no electrons or additional muons. • Many analyses require evidence that jets are from b-quarks by requiring tracks that do not point to primary vertex. This substantially reduces background. • No single kinematic variable distinguishes signal from background effectively, so introduce multivariate techniques (neural networks, boosted decision trees etc.) that use the correlations among variables. • Present a final variable (e.g. NN output) to a limit setting program that uses the data and MC background distributions to obtain the maximum allowed Higgs XS using a frequentist method where many MC pseudoexperiments are performed (DØ) or a Bayesian calculation using known prior information (CDF). • Combine limits from all channels for both experiments 12

26. Higgs Boson Limits Plot the ratio of the resulting 95% C.L. limit cross section to the SM XS. Thus for Higgs masses where the ratio < 1, we exclude the SM Higgs. In this combination (Mar. 2009), Tevatron excludes 160<MH<170 GeV. A sanity check: Search for the previously unmeasured diboson process, WW/WZ→ln +2jets using all the same multivariate and limit setting machinery as for Higgs. (b-tagging algorithms are extensively tested in top quark studies). Red portion shows expected signal on top of W+jets or Z+jets background. Bottom shows signal after background subtraction. Measure s = 20.2±4.5 pb, in good agreement with the SM, and previous measurements in the much cleaner four lepton final state. 11

27. 10 fb-1 Higgs prospects at Tevatron CDF+D0 If no improvements are made, we would expect the limit to scale as √L. In fact, the limits have improved faster than this – using refined analysis techniques, more production and decay channels, etc. Tevatron will run through 2010 and will likely run in 2011 (10 fb-1in analyses). Red line shows the luminosity needed for 95% CL exclusion as a function of MH. With 10 fb-1 (purple line), can exclude SM Higgs up to 190 GeV. The black line shows luminosity needed for 3s evidence of Higgs as a function of MH. Can find evidence for MH≈115 GeV and 150<MH<180 GeV. 10

28. Higgs prospects at LHC The LHC will turn on later this year. For low mass Higgs (now indicated by Tevatron), the favored Hbb decay is swamped by background at the LHC, so must resort to the rare Hgg decay. At higher (disfavored in SM) Higgs mass, the LHC can more readily discover the Higgs through its decays to WW or ZZ. To discover 115 GeV Higgs, LHC needs ~5 fb-1 of data at 14 TeV (will start at 7–10 TeV with 0.6X of full Higgs XS.) This will take a few years to acquire and a couple more to analyze. Luminosity required for 5s discovery (red) and 95% exclusion (blue) in both LHC experiments. The LHC detectors will ultimately find (or rule out) the SM (or more complex) Higgs if it exists at any mass below 1000 GeV. But the favored low mass region is the most difficult at LHC, so if Higgs is ≈115 GeV, a combination of Tevatron and LHC may be needed. 9

29. QCD studies with jets CDF and DØ have accurately calibrated the jet energy scale using g+jet and Z+jet samples. The inclusive jet cross section extends to pT(jet)≈ 60% of the beam momentum and agree well with perturbative QCD. These results are also important in constraining the PDFs, needed for making predictions at LHC. Relative to existing PDFs, they favor larger gluon content at high momentum fraction. These data allow extraction of the running of the QCD coupling aS which extend and improve those from e–p scattering (HERA) 8

30. QCD studies with jets The angular distributions of dijets can be plotted in a variable c = e , where rapidity, y=log(E+pz)/(E-pz). In this variable, the Rutherford 1/sin4q/2 distribution is flat. For QCD dijets, the running of aS modifies the distributions. The distributions, particularly at high dijet mass, are sensitive to many types of new physics, such as quark compositeness and extra spatial dimensions and allow new best limits on these models. |y1-y2| DØ data Distributions as a function of dijet invariant mass and rapidity offer yet another constraint on PDFs, and will modify the next generation of fits. 7

31. W/Z + jets The differential cross sections f(pT, y) for W/Z+jets production are not well calculated or simulated in MC event generators. Tevatron and LHC need to understand these dominant backgrounds for Higgs production very well. Recent DØmeasurements, with jet pTs unfolded, give the needed information (and show discrepancies with existing generators). Meas vs true pT migration matrix Ratios of Data, SHERPA, PYTHIA and NLO QCD to ALPGEN. ALPGEN gets shape right, normalization wrong. CDF has extended this kind of study to Z+b jets, even more needed for modeling Higgs backgrounds. 6

32. CKM matrix relates quark eigenstates of specific flavor to weak int’n eigenstates (quark mixing matrix). This enables transitions of neutral mesons Bd (bd), BS(bs) or K0 (sd) to their antiparticles. 2nd order weak process in which BS0 meson evolves (mixes) to BS0 meson. (BS at t=0) BS(t) and BS(t) BS – BS Mixing Weak eigenstates (decays) flavor eigenstates B meson time evolution is governed by Hamiltonian. Decompose the flavor eigenstates to mass eigenstates which propagate with different eimj(and different lifetimes), so get oscillations in time when transforming back to the flavor eigenstates. Oscillation frequency=Dm (difference between mass eigenstates). Dm large for BS requiring superb time (decay distance) resolution. BS mixing first observed by CDF/DØ in 2006. 5

33. CP violation in BS Mixing In the SM, CP violation occurs due to a phase in the CKM matrix relating quark flavor eigenstates to weak eigenstates. This phase is consistent for the CP violation seen in the K0 and Bd0 systems. Now studies are being done in the Bs0 (bs) and Bs0 systems that are inaccessible in the B factories. LHC will develop these studies further. Both can decay to same final state, e.g. BSJ/yf . CP violation can occur in the mixing, or in the decays to some common final state. In SM, it depends on the CKM matrix phase and is small. CKM unitarity gives ‘triangle’ relation with angle bS In SM, bS =0.002; If new CP violation source, bS can be large. 4

34. CP violation in BS Mixing Final state J/yf is a mixture of CP even and odd states which can be disentangled at Tevatron using decay angular correlations, lifetime measurement and flavor state at production. In SM, DGS= GL – GH ≈ 2cos 2b Both CDF and DØ observe DG consistent with SM, but angle bS to be large (~0.5 rad) and disagreeing with SM by 2.3s. New data will help determine if this is a breakdown of the SM. Further measurements BS → J/yf, BS → DSm± charge asymmetry; dimuon charge asymmetry (m+m+ vs. m-m-); time dependent BS → DS-m+X will all provide further constraints on bS. 3

35. Hidden valley of new particles, weakly coupled to SM Supersymmetry neutralino/ chargino search in trileptons Extra spatial dimensions; RS graviton  ZZ Next to minimal SUSY: Ordinary Higgs decays to new light Higgs/ LHC But the LHC is coming! Vast new territory for searches. Supersymmetry squark/ gluino search in jets+MET Searches for New Phenomena CDF/DØ have searched for a wide variety of new particles, interactions predicted in models of Beyond the SM physics. No evidence has been found. 2

36. Summary The LHC will soon take over from the Tevatron in exploring the energy frontier. The Tevatron results set the stage for the LHC, and will give their own lasting legacy.