1 Physics at a Future Linear Collider Tobias Haas, DESY-F1 DIS04/WG E7 16 April, 2004

2/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider This Talk Collider: Collider: Linear Collider Basics Linear Collider Basics Rates and Backgrounds Rates and Backgrounds Polarisation Polarisation Additional Collider Options Additional Collider Options Detector Considerations Detector Considerations VXD, Tracking and Calorimetry VXD, Tracking and Calorimetry Physics Physics Higgs Higgs Supersymmetry Supersymmetry Precision parameter determinations Precision parameter determinations Summary and conclusions Summary and conclusions

3/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Acknowledgments Material used here is based on work done for Material used here is based on work done for TESLA TDR TESLA TDR US and Japanese LC studies US and Japanese LC studies ECFA/DESY study ECFA/DESY study Ongoing ECFA LC study Ongoing ECFA LC study In particular, I have used material from In particular, I have used material from K. Desch, E. Gross, H. Nowak, D. Miller, P. Grannis, G. Moortgat-Pick K. Desch, E. Gross, H. Nowak, D. Miller, P. Grannis, G. Moortgat-Pick

4/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Linear Collider Basics LEP gave ~ 1 fb -1 /expt. in 11 years, with 10 7 Z 0 LEP1 LEP gave ~ 1 fb -1 /expt. in 11 years, with 10 7 Z 0 LEP1 At √s = 500 GeV one needs 500 fb -1 to get: At √s = 500 GeV one needs 500 fb -1 to get: ~ 30,000 Zh 120 ~ 50,000 h 120 νν 10 6 W + W - At √s = 1000 GeV one needs 1000 fb -1 to get: At √s = 1000 GeV one needs 1000 fb -1 to get: ~ 6,000 HA (300GeV) ~ 3,000 h 500 νν ~ 2,000 WWνν (if no Higgs) Need lots of luminosity to scan multiple thresholds, vary polarisation, go to γγ, e - γ, e - e - Need lots of luminosity to scan multiple thresholds, vary polarisation, go to γγ, e - γ, e - e -

5/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Linear Collider Basics A decade of R&D at SLAC, DESY and KEK has given: ~ x100: More bunches with more charge. ~ 1/100 reduction in σ y to 5 nm: Lower emittance, demagnify more New problems, including: Wakefields “Accelerator” Emittance growth Disruption “Experiment” Beamstrahlung Pair production

6/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Linear Collider Basics Big E and B fields Beamstrahlung: Synchrotron radiation in the field of the opposing bunch gives a smeared spectrum electrons/bunch, with  ~ 10 6 dimensions ~ nanometers Disruption: e + e - beams focus each other inward (L enhanced), then fly apart after collision: e - e - defocus immediately (L reduced). Pair Production: Incoming beam particles scatter from the beamstrahlung photons:

7/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Rates and Backgrounds NLC bunch structure different but average flux the same Much gentler than LHC: Record everything and sort out offline: trigger-less Hard virtual photons from beam particles make h.e.  collisions. Cross section is dominated by resolved photon-photon (0.02/bx, c.f. LHC) HERA input important for rate calculations.

8/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Polarisation SLC has shown that e - can be polarised to ~80%; hope for more in 10 years. e-e- Much harder: Have to make polarised  ’s, then pair produce e + e - Needs e - with >160 GeV, so use incoming beam: TESLA e + source: If acceptances are restricted, should be possible to get ~ 50% e + polarization, maybe more with reduced L. e+e+ Uses: Turn off SM bg processes (Anything that couples to W ± ) Measure polarisation dependence of signal, e. g. asymmetries like A LR. Sensitivity to CP.

9/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Additional Collider Options Easiest: Add a second e - gun at the e + end. Especially useful if SUSY sector complicated. (Needed for  and  e) e-e-e-e- Use Compton backscattering of near-visible laser light: 2 nd IR Right choice of e - and laser polarisations gives “monochromatic” peak with ~ 80% of full energy and ~ 50% of L ee.   e Include bypass in linac to get good L at M Z and 2M W ; Polarisation is important; Hope for L = 5· GigaZ

10/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Detector Considerations Vertexing: Vertexing: Flavour tagging with high purity and efficiency Flavour tagging with high purity and efficiency Tracking: Tracking: Momentum resolution to measure recoil masses Momentum resolution to measure recoil masses Calorimetry: Calorimetry: Good segmentation and excellent EM energy resolution Good segmentation and excellent EM energy resolution

11/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider VXD for Heavy Flavour Identification Flavour couplings of Higgs are basic to test SUSY scenarios: Many have different +2/3 vs. - 1/3 couplings. b vs. c best hope. Flavour couplings of Higgs are basic to test SUSY scenarios: Many have different +2/3 vs. - 1/3 couplings. b vs. c best hope. 5 layers with 800 Mio pixels. Innermost layer at 1.5 cm 5 layers with 800 Mio pixels. Innermost layer at 1.5 cm 0.03% X 0 /layer 0.03% X 0 /layer

12/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Overall Tracking Higgs dictates: Whatever its decays, if coupled to Z 0 (and light enough), will see its recoil against Z 0 → e + e - or μ + μ -. Need momentum resolution: TESLA TDR: Silicon tracking inside a big TPC, B = 4T; Good dE/dx; Tesla TDR

13/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Calorimetry/Energy Flow In e + e - → VV νν: Separate WW → 4 jets from ZZ → 4 jets EWSB has to appear if nowhere else In e + e - → tt → bbWW → 6 jets Measure all the interesting features!

14/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Summary of Assumptions Machine: Machine: √s = 500 … 1000 GeV √s = 500 … 1000 GeV L = 2 … 3 x cm -2 s -1 → several 100 fb -1 /year L = 2 … 3 x cm -2 s -1 → several 100 fb -1 /year Polarisation: P(e - )  80%, P(e + )  60% Polarisation: P(e - )  80%, P(e + )  60% Detector: Detector: Hermetic ( H → invisible) Hermetic ( H → invisible) Excellent EM calorimeter ( H →  ) Excellent EM calorimeter ( H →  ) Excellent momentum resolution ( ZH → l + l - X, recoil mass ) Excellent momentum resolution ( ZH → l + l - X, recoil mass ) Small beamspot ( 500x5 nm ), small beampipe radius and VXD allow b/c separation and τ- ID Small beamspot ( 500x5 nm ), small beampipe radius and VXD allow b/c separation and τ- ID

15/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Higgs Physics Several 10 4 Higgs bosons produced / year for “light” Higgs; Several 10 4 Higgs bosons produced / year for “light” Higgs; Detection with high efficiency; Detection with high efficiency; Nearly background free. Nearly background free. ECFA/DESY Higgs LC working group, M. Battaglia, K. Desch, A. Djouadi, E. Gross, B. Kniehl, et al.

16/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider LC is a Higgs Analyzer Measure Higgs properties: Measure Higgs properties: Production rate, Production rate, Mass, Mass, Lifetime, Lifetime, Spin and parity. Spin and parity. Higgs Branching Fractions: Higgs Branching Fractions: Matter couplings (g hff ) Matter couplings (g hff ) Gauge bosons (g hZZ ) Gauge bosons (g hZZ ) Establish the Higgs Mechanism as EWSB by measuring the Higgs coupling to itself (λ) Establish the Higgs Mechanism as EWSB by measuring the Higgs coupling to itself (λ)

17/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Cross Section: HZ, Hνν Higgs Strahlung: Recoil mass in e + e - → μ + μ - X WW-Fusion: Missing mass in e + e - → ννbb N. Meyer, K. Desch (2000) P. Garcia-Abia, W. Lohmann (2000) Very low bg; Model independent; Δσ ZH  3% μ + μ -, e + e - combined Δσ Hνν  3 – 8 %

18/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider ee → HZ → ZZZ, ZWW ee → HZ → ZZZ, ZWW H → ZZ, WW with hadronic decay, so no missing energy H → ZZ, WW with hadronic decay, so no missing energy Use 4C kin fit Use 4C kin fit Δm H  400 MeV (0.2%) Δm H  400 MeV (0.2%) ΔΓ H  800 MeV (25%) ΔΓ H  800 MeV (25%) Higgs Mass ee → HZ → bbqq ee → HZ → bbqq Use 5C fit to signal on top of bg Use 5C fit to signal on top of bg Δm H = 40 … 70 MeV Δm H = 40 … 70 MeV m H < 130 GeVm H > 2 m Z m H (GeV)

19/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Spin and Parity For √s~ For √s~m H +m Z (Threshold) For J=0 σ~β J=1 σ~β 3 J=2 σ~β 5 Threshold scan with 20 fb -1 /pt P: Angular Distribution: P: Angular Distribution:

20/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Higgs Branching Fractions Battaglia, Borissov, Richard (1999) Disentangle bb, cc and gg using simultaneous fit to lifetime-sensitive variables: Disentangle bb, cc and gg using simultaneous fit to lifetime-sensitive variables: 500 fb - 1

21/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Higgs Selfcoupling and Higgs Potential σ(HHZ) is very small: σ(HHZ) is very small: < 0.1 fb Signature: Signature: 4 b-tagged jets + Z Unfold coupling from total cross section Unfold coupling from total cross section Need very high lumi: Need very high lumi: (1000 fb 500 GeV)

22/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Summary on Higgs The LC will do an excellent job on profiling the Higgs: The LC will do an excellent job on profiling the Higgs: Determine J PC unambiguously, Determine J PC unambiguously, Accurate mass and width, Accurate mass and width, Measure the branching fractions for all dominant decays; distinguish SM from SUSY Higgs; verify the coupling to mass, Measure the branching fractions for all dominant decays; distinguish SM from SUSY Higgs; verify the coupling to mass, Measure the Higgs self couplings; determine the potential. Measure the Higgs self couplings; determine the potential.

23/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Supersymmetry Aim: Precise mass and cross section measurements of all kinematically accessible sparticles: Precise mass and cross section measurements of all kinematically accessible sparticles: Explore SUSY breaking mechanism, Unification at High Energy?

24/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider

25/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider SUSY Scenarios and Examples Only scenario with squarks in reach of LC500

26/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider mSUGRA Scenario SPS5

27/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Example 1: Light stop If m stop < 250 GeV, may not be detected at LHC If m stop < 250 GeV, may not be detected at LHC Assumptions: Assumptions: m stop = 180 GeV m stop = 180 GeV cosθ t = 0.57 cosθ t = 0.57 Δm < m W Δm < m W   topology:  2c jets + E miss  2b jets + E miss

28/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Example 1: Light stop Procedure: Procedure: Use 9 event variables (E vis,N 0 jets, thrust, N 0 clusters, E ║ miss, E ┴ miss, jets, acoplanarity, M(jets)) Use 9 event variables (E vis,N 0 jets, thrust, N 0 clusters, E ║ miss, E ┴ miss, jets, acoplanarity, M(jets)) Charm tag (ZVTOP) Charm tag (ZVTOP) Feed into NN or Iterative Discriminant analysis Feed into NN or Iterative Discriminant analysis Polarization! Polarization!

29/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Example II: Scalar Muons Topology: Topology: 2 acoplanar muons + E miss 2 acoplanar muons + E miss Require good muon detection efficiency of the detector Require good muon detection efficiency of the detector Small backgrounds: Small backgrounds: SM: 2f, 2γ, 4f processes SM: 2f, 2γ, 4f processes SUSY: like χ 2 0 χ 1 + SUSY: like χ 2 0 χ 1 + Use the “Endpoint” method Use the “Endpoint” method

30/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Example II: Scalar Muons smuons decay isotropically: smuons decay isotropically: decay spectrum is flat except for radiation effects: decay spectrum is flat except for radiation effects: Relate the two kinematic endpoints to the masses of smuon and neutralino Relate the two kinematic endpoints to the masses of smuon and neutralino ΔM=200MeV ΔM=200MeV E1E1 E2E2

31/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Example III: Threshold Scans Good choice if mass range already known (e. g. top, or something found at LHC) Good choice if mass range already known (e. g. top, or something found at LHC) Precision: Precision: Limited by the beam spread (1%) Limited by the beam spread (1%) Statistics Statistics Remember “beamstrahlung”, ISR and FSR Remember “beamstrahlung”, ISR and FSR Gives also info about the nature of a sparticle: Gives also info about the nature of a sparticle: σ ~ β 3 (Boson) σ ~ β 3 (Boson) σ ~ β (Fermion) σ ~ β (Fermion)

32/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Threshold Scan: top is the classic is the classic is very clean is very clean Fit m t from the excitation curve Fit m t from the excitation curve 10 fb -1 /point 10 fb -1 /point δ(m t ) ~ 100 MeV δ(m t ) ~ 100 MeV αSαS mtmt

33/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Threshold Scan: smuon Σ(lumi)=100 fb -1 Σ(lumi)=100 fb fb -1 /point 10 fb -1 /point a few months of running a few months of running δ(m μ ) < 100 MeV δ(m μ ) < 100 MeV ~

34/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Threshold Scan: neutralino Same procedure Same procedure δ(m μ ) ~ 50MeV δ(m μ ) ~ 50MeV possibly also squarks if light enough! possibly also squarks if light enough! ~

35/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Mass Accuracy

36/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider What is the Mechanism of SUSY Breaking? Extrapolate to High Energies! From the physical observables From the physical observables Reconstruct the mass parameters at the EW scale according to Evolve the parameters to high scale through the RGE’s Evolve the parameters to high scale through the RGE’s e. g. mSUGRA gives a very different pattern than GMSB e. g. mSUGRA gives a very different pattern than GMSB mSUGRA GMSB

37/37 16 April, 2004Tobias Haas: Physics at a Future Linear Collider Summary and Conclusions An e + e - collider with 500 … 1000 GeV has a very rich program or new physics An e + e - collider with 500 … 1000 GeV has a very rich program or new physics It is an essential complement to the LHC It is an essential complement to the LHC Precise exploration of Higgs boson properties Precise exploration of Higgs boson properties Establish essential elements of the Higgs mechanism Establish essential elements of the Higgs mechanism Very precise measurement of SUSY parameters Very precise measurement of SUSY parameters Extrapolate to the GUT scale Extrapolate to the GUT scale Studies are being performed at a very detailed level all around the world Studies are being performed at a very detailed level all around the world The next ECFA LC workshop is next week in Paris The next ECFA LC workshop is next week in Paris I hope we will manage to start building it within the foreseeable future. I hope we will manage to start building it within the foreseeable future.