CMS Physics Overview

1. CMSPhysics Overview

2. f Open Questions in Particle Physics Origin and hierarchy of particle masses Is there a Higgs particle and what is its mass? How must the Standard Model be extended? Supersymmetry, Grand Unified Theories, … Is there a substructure of quarks and leptons? Are there more than three light generations? Are there heavy neutrinos? Asymmetry between matter and antimatter Stability of the proton What is the cosmological dark matter made of? Origin of QCD Confinement Quark Gluon Plasma How can gravity be included?

3. CERN’s accelerator complex LHC/LEP SPS

4. Parameters of the Large Hadron Collider Proton- Proton Circumference: 27 km Bunches: 3564 + 3564 Protons / bunch: 1011 Beam energy: 2 x 7 TeV Peak luminosity: 1034 cm-2s-1 Bunch crossing interval: 25 ns Collision rate: 107 … 109 Hz Dipole field: 8.4 T Number of dipoles: 1104 Heavy Ions (Pb-Pb, S-S, etc.) Beam energy: up to 5.5 TeV/nucleon pair Peak luminosities: 1027 cm-2s-1 for Pb-Pb 3.1031 cm-2s-1 for O-O Bunch crossing interval: 125 ns Bunches Parton

5. CMS Detector

6. Physics Goals of CMS Standard Model physics QCD, electroweak theory (Higgs, W, Z, Top, Jets, …) Supersymmetry SUSY Higgses, sparticles, ... Other extensions of the Standard Model Compositeness, technicolor, leptoquarks, new heavy vector bosons, extra dimensions, ... B-physics CP violation, B0-B0 oscillations, rare B-decays, ... Heavy Ion physics Quark-Gluon Plasma Soft physics stotal, elastic scattering, diffraction New phenomena

7. Cross sections and production rates for various processes vary by many orders of magnitude • inelastic: 109 Hz • W ->ln: 100 Hz • tt: 10 Hz • Higgs (100 GeV): 0.1 Hz • Higgs (600 GeV): 0.01 Hz • Required selectivity • 1 : 10 10- 11 Cross sections -

8. Experimental Challenges Pile-up stot @ 80 mb, high luminosity -> up to 25 p-p collisions per bunch crossing, 1000 charged particles in |h| < 2.5 Consequences for detectors: Short response times (typically 25 to 50 ns) High granularity (> 108 channels) Radiation resistance (1017 neutrons/cm2 flux, integrated radiation dose up to 107 Gy after 10 years’ operation close to beam) QCD background Rate dominated by jet production (qq -> qq, gg -> qq etc.), therefore in practice generally only decays with leptons and photons are usable leading to small event rates.

9. Where is the Higgs? 18 superimposed p-p collisions in the inner part of the CMS tracker, including 4 muon tracks from a Higgs decay

10. Here! Transverse momentum cut of pT > 2 GeV after track reconstruction

11. Standard Model Higgs Branching ratios Total decay width

12. Discovery Strategy for the Standard Model Higgs At LHC the SM Higgs is accessible in the entire mass range from the present LEP limit of ~ 115 GeV up to 1 TeV. Depending on mass different decay channels are traditionally used: - 100 GeV < mH < 150 GeV H -> gg in incl. prod.,WH, ttH 90 GeV < mH < 120 GeV H -> bb in WH, ttH 130 GeV < mH < 200 GeV H -> ZZ* -> 4l (leptons) 140 GeV < mH < 180 GeV H -> WW-> ln ln 200 GeV < mH < 750 GeV H -> ZZ-> 4l 500 GeV < mH < 1000 GeV H -> ZZ -> 2l + 2n mH ~ 1 TeV H -> WW -> ln + 2 Jets mH ~ 1 TeV H -> ZZ-> 2l + 2 Jets Recently the following channels have been investigated: H -> Zg mH ~ 130 GeV qq -> qqH with H -> tt - -

13. H -> gg The crystal electromagnetic calorimeter has been optimized for this channel. Mass resolution DmH/mH < 1% needed. Irreducible backgrounds at mgg = 100 GeV: qq -> gg gg -> gg Isolated bremsstrahlung Main reducible background: g + jet with “jet” = p0 -> gg less than 15% of irreducible background

14. H -> gg

15. _ Event selection: 1 isolated e or m, 6 jets of which 4 must have a b-tag. Reconstruction of both t’s by kinematic fit necessary to suppress combinatorial bb background. - H -> bb Only associated production is feasible! Problems with background and trigger! This channel and H -> gg are only way to explore the 115 GeV mass region! NB: WH production perhaps accessible for very high luminosities (300 fb-1).

16. H -> ZZ* -> 4l Need good tracker, ECAL and muon system as Higgs width is small (DmH < 1 GeV) for mH < 2mZ. In this mass range the main backgrounds are tt, Zbb (reducible) and ZZ*/Zg continuum production (irreducible). Lepton isolation, dilepton mass cuts and impact parameter cuts are used for background suppression. - - 100 fb-1

17. H -> WW -> ln + ln for mH ~ 2mW For mH = 170 GeV the BR is about 100 times larger than in H->ZZ*->4l. Can make use of W+W- spin correlations to suppress “irreducible” background. Look for l+l- - pair with small opening angle.

18. H -> WW -> ln + ln The mass can only be determined indirectly from rates and shapes. - - The tt and Wtb backgrounds can be reduced by a jet veto.

19. H -> WW -> ln + ln 5s discovery can be made with 30 fb-1 in the mass range 130 to 190 GeV.

20. H -> llnn,lljj, lnjj As Higgs width increases and production rates fall with higher masses one must use channels with larger branching ratios. Need to select leptons, jets and missing energy.

21. Summary of Standard Model Higgs in CMS CMS 5s Significance for 100 fb-1 5 s - Contours

22. Supersymmetry SUSY Particle Production

23. The Higgs Sector in the MSSM The MSSM has 5 Higgs bosons: h0, H0, A0 and H±. 2 parameters needed to fix properties: mA, tanb. In the limit of large mA the couplings of h0 are similar to SM. Couplings of A and H to quarks of 1/3 charge and leptons enhanced at large tanb. A does not couple to WW, ZZ. Couplings of H to WW and ZZ for large mA and tanb are suppressed. The following decay channels can be used as for the SM Higgs: h, A -> gg (for mA < 2 mt due to branching ratio) H -> ZZ* (no H -> ZZ at large mass since BR too low) The following decay channels open up: H, A -> tt, mm (t-channels enhanced over SM for large tanb) H, A -> hh A -> Zh A -> N.B. Decays into sparticles will be discussed later.

24. H/A -> tt Due to high rates this channel can be observed over a large region of parameter space. Useable final states: t (-> enent) t (-> mnmnt) t (-> h± p0’s nt) t (-> lnlnt) t (-> h± p0’snt) t (-> hmp0’snt) Main backgrounds: Z, g* bb, tt, W + jets, Z + jets, QCD lepton + jet misidentified as t (for lepton + hadron final state) - -

25. Mass Determination for H/A -> tt Mass reconstructed assuming n directions parallel to lepton and t-jet.

26. H/A -> mm BR smaller than that for tt-channel by (mm/mt)2. This is somewhat compensated by better resolution for m’s. Useful for large tanb.

27. H -> hh Dominant decay to . Problem is triggering: need soft muons in jets. Sensitivity for tanb < 3 and 250 GeV < mA < 2 mt. Easier to trigger is the channel H -> hh -> t+t-. In MSSM most of the accessible region is excluded by LEP, but in more general models this channel might be relevant. H -> hh -> gg can be triggered on, but rates are low. Background is small, however, and there is a convincing sharp peak in the gg mass distribution.

28. - A, H -> tt This is the dominant decay channel for large masses. Background comes from QCD tt production. It is large, but significant signal can be extracted if background can be correctly estimated. The search is based on the WWbb final state, with one W decaying leptonically. The trigger requires an isolated lepton. In the analysis 2 b-jets are required in addition. Determination of mass will be difficult as there is no observable mass peak. The mode is likely to be used as a comfirmation of a signal seen in other channels. - -

29. A -> Zh Can use the leptonic decay of the Z in the trigger. In the analysis 2 electrons (muons) with ET > 20 GeV (pT > 5 GeV) of invariant mass within ± 6 GeV of the Z peak and 2 jets with ET > 40 GeV are required. One or two b-tags are also required. Background comes mainly from tt and Zbb events (for smaller mA). Signal to background ratio is quite good for moderate mA and small tanb, but this region is already excluded in MSSM by LEP. - -

30. Charged Higgs In the MSSM the decay t -> bH± may compete with the Standard Model t -> bW± if kinematically allowed. H± decays to tn or cs depending on tanb. Over most of the range 1 < tanb < 50 the mode H± -> tn dominates. The signal for H± production is therefore an excess of t’s in tt events. If mass of H± is larger than mt it cannot be produced in t-decays. It can be produced by gb -> H-t. Again the search focusses on the decay H± -> tn. One can use the decay t -> bqq so that ETmiss gets contribution only from H±  decay resulting in a Jacobian peak. The t polarization leads to harder pions from t -> pn than from W decays. - -

31. Charged Higgs tanb = 30 Transverse mass reconstructed from t-jet and ETmiss for pp -> tH± with m(H±) = 400 GeV Events for 3x104 pb-1 / 40 GeV H± -> tn, t -> qqb 100 200 300 400 500 mT (t-jet, ETmiss) / GeV tanb = 20 Transverse mass reconstructed from t-jet and ETmiss for pp -> tH± with m(H±) = 200 GeV Events for 3x104 pb-1 / 40 GeV 50 100 150 200 250 300 350 mT (t-jet, ETmiss) / GeV

32. SUSY Higgs to Sparticles If neutralinos/charginos are light the branching ratios of H and A into these sparticles is sizeable. Most promising with respect to background are channels with leptonic decays of the sparticles: c20 -> c10l+ l- and c1+ -> c10l+n. Signal: A, H -> c20 c20 -> 4l + X Backgrounds: SM: ZZ, Zbb, Zcc, tt, Wtb SUSY: q/g, ll, nn, qc, cc In the following only the case m(l) > m(c20) will be considered. ~ ~ ~ ~ ~ ~ - - - - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

33. SUSY Higgs to Sparticles 100 fb-1 tanb = 5 mA = 350 GeV Signal Background (mainly SUSY)

34. 5s significance contours MSSM parameters: M(c10) = 60 GeV, M(c20) = 120 GeV, m = - 500 GeV, m(l) = 250 GeV, m(q,g) = 1000 GeV ~ ~ ~ tanb 30 fb-1 100 fb-1 ~ ~ A, H -> c20 c20 -> 4l + X Excluded by LEP mA (GeV) SUSY Higgs to Sparticles ~ ~

35. SUSY Higgses in CMS 5s significance contours

36. Sparticles If SUSY is relevant to electroweak symmetry breaking then gluino and squark masses should be of order 1 TeV. As in general many SUSY particles are produced simultaneously, a model with a consistent set of masses and branching ratios must be used in the simulations. Traditionally CMS uses the Supergravity (SUGRA) model, which assumes that gravity is responsible for the mediation of SUSY breaking. Another possible model is the Gauge Mediated SUSY Breaking Model (GMSB) which assumes that Standard Model gauge interactions are responsible for the breaking -> see J. Krolikowski’s talk at this workshop.

37. Sparticles Supersymmetric particles may have striking signatures due to cascade decays, leading to final states with leptons, jets and missing energy. ~ ~ Shown here is a qq event: q -> c20q q -> c1±q ~ ~ ~ m m ~ c10 m ~ ~ ~ e n ~ c10e

38. Squarks and Gluinos They dominate the SUSY production cross section and contribute about 10 pb for masses around 1 TeV. In minimal SUGRA they give rise to ETmiss from c10’s plus multiple jets and a variable number of leptons from the gauginos. The charges of the leptons can be used to extract signals, even in the CMS level-1 trigger. The figure shows results for the channels n leptons + ETmiss + > 2 jets ~

39. Squarks and Gluinos ~ ~ The figure shows the q, g mass reach for various luminosities in the inclusive ETmiss + jets channel. 1 year at 1034 cm-2s-1 1 year at 1033 cm-2s-1 1 month at 1033 cm-2s-1 1 week at 1033 cm-2s-1

40. Charginos, Neutralinos, Sleptons ~ ~ Example for Drell-Yan production of c1±c20: qq -> W* -> c1±c20 -> c10 ln + c10 l+l- Search in 3l and no jets channels, possibly also with ETmiss. Backgrounds: tt, WZ, ZZ, Zbb, bb, other SUSY channels In SUGRA the decay products of SUSY particles always contain c10’s. Kinematic endpoints for combinations of visible particles can be used to identify particular decay chains. Examples: l+l- mass distribution from c20 -> c10l+l- has endpoint which measures m(c20 ) - m(c10 ); c20 -> l±lm -> c10l+l- has different shape with a sharp edge at the endpoint which measures the square root of: [m2(c20 ) - m2 (l)] [m2(l) - m2 (c10)] m2(l) ~ ~ ~ ~ - - - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

41. Neutralino Mass Determination Final state with: 3l, no jets, ETmiss

42. Overview of physics not discussed • If electroweak symmetry breaking proceeds via new strong interactions many resonances and new exotic particles will certainly be seen • New gauge bosons with masses less than a few TeV can be discovered • Signals for extra dimensions will be revealed if the relevant scale is in the TeV range • Standard Model physics involving the top quark will be explored in detail (e.g. top mass measurement, rare top decays) • A Beauty physics programme is foreseen provided that adequate financial resources can be found! Precise determination of sin2b, study of Bs-Bs oscillations and rare B-decays (e.g. B -> mm) can be performed. • Quark-Gluon-Plasma signatures can be studied within the Heavy Ion programme -

43. Conclusions • The Standard Model Higgs can be discovered over the entire expected mass range up to about 1 TeV with 100 fb-1. The most plausible part below 200 GeV mass can be explored with several channels. • Most of the MSSM Higgs boson parameter space can be explored with 100 fb-1, all of it can be covered with 300 fb-1. • The mass reach for squarks and gluinos is in excess of 2 to 2.5 TeV • (m0 < 2 to 3 TeV, m1/2 < 1 TeV) for all tanb within mSUGRA • Sleptons can be detected up to 400 GeV mass in direct searches and probed indirectly up to 700 GeV • c10 canbe found up to 600 GeV mass. The dark matter hypothesis will be systematically tested and should be within reach for tanb < 20. ~

44. Conclusions The CMS experiment at the LHC accelerator will enable us to explore physics in the TeV region. We are eagerly awaiting the first data!