Physics Opportunities and Experimental Techniques for the Next Large Scale Facility in Accelerator Particle Physics The International Linear Collider Marco Battaglia UC Berkeley and LBNL TASI, Boulder, June 2006

International e + e - Linear Collider ILC highest priority for future major facility in HEP needed to extend and complement LHC discoveries with accuracy which is crucial to understand nature of New Physics, test fundamental properties at high energy scale and establish their relation to Cosmology; Technology decision promotes ILC towards next stage in accelerator design definition, R&D and cost optimization: Matching program of Physics studies and Detector R&D needed develop new accurate and cost effective detector techniques from proof of concepts to a state of engineering readiness to be adopted in the ILC experiments.

Synergy of Hadron and Lepton Colliders

Mass scale sensitivity vs. centre of mass energy

ILC Energy Physics to define next thresholds beyond 100 GeV: Top Quark pair production threshold: Strong prejudice (supported by data) on Higgs and New Physics thresholds between EW scale and ~ 1 TeV:

ILC Energy in Perspective Cosmotron (3.3 GeV), BNL Bevatron (6.2 GeV), LBNL

Centre-of-Mass Energy vs. Year as of 1992as of 2000 ? we have fallen off the scaling predicted by Stanley Livingston’s curve.

Why Linear ? ? Particles undergoing centripetal acceleration a=v 2 /R radiate at rate: if R constant, energy loss is above rate x time spent in bending=2  R/v R R for e - (E in GeV, R in km) for p (E in TeV, R in km) Since energy transferred to beam per turn is constant: G x 2  R x F at each R there is a maximum energy E max beyond which energy loss exceeds energy transferred, real limit set by dumped power; Example: LEP ring (R=4.3 km) E e =250 GeV  W = 80 GeV/turn Synchrotron Radiation

ILC Energy Technology to define reachable energy:

Cold SC cavity technology chosen; Global Design Effort to produce costed Technical Proposal by end 2006 CLIC technology being demonstrated by R&D CTF3 facility at CERN. Major step towards construction of new HEP facility in August 2004: Accelerator R&D reached maturity to assess technical feasibility and informed choice of most advantageous technology. ILC potential in future of scientific research praised by OECD. DOE Office of Science ranked ILC as top mid-term project.

ILC Baseline Design 9-cell 1.3GHz TESLA Niobium Cavity 35 MV/m baseline gradient

ILC Baseline Design Cavity GradientCavity Cost vs. Gradient 32 km 44 km 51 km Optimisation for 500 GeV ILC Cost vs. Gradient

SC Cavity Gradient TESLA Cavities 2005 LEP-2 Cavities

ILC Luminosity Since cross section for s-channel processes scales as 1/s, luminosity must scale to preserve data statistics;

ILC Luminosity Luminosity functional dependence on collider parameters: Compared to circular colliders (LEP) f rep  and must be compensated by increasing the nb. of bunches (N b ) and reducing the transverse beam sizes (  x,  y ); Small beam size induces beam-beam interactions: self focusing and increase of beamstrahlung resulting in energy spread and degraded luminosity spectrum: N = L x 

ILC Luminosity Optimization High Efficiency High Beam Power Parameter0.5 TeV 1.0 TeV NbNb 2820  y (nm)  BS HDHD P BS (W) Large Beamstrahlung Small vertical emittance and short bunch length Parameter0.5 TeV 1.0 TeV G (MV/m)30 L (10 34 cm -2 s -1 )    2.0 t b (ns)307 nyny

Global Design Effort Projec t Baseline configuration Reference Design ILC R&D Program Technical Design Bids to Host; Site Selection; International Mgmt LHC Physics from B. Barish ILC GDE : Plan and Schedule CLIC feasibility

Three Main Physics Themes Solving the Mysteries of Matter at the TeraScale (= Higgs/SUSY/BSM); Determining what Dark Matter particles can be produced in the laboratories and discovering their identities (=SUSY/ED); Connecting the Laws of the Large to the Laws of the Small (=EW/SUSY/ED) ILC Physics Objectives

The Higgs Boson Profile at the ILC

Higgs Boson Production at ILC M H (GeV)  (e + e -  H) (fb)

Model Independent Higgs Reconstruction Associate H 0 Z 0 production, with Z 0  ll, allows to extract Higgs signal from recoil mass distribution, independent on H decay; Analysis flavour blind and sensitive to non-standard decay modes, such as H  invisible

Model Independent Higgs Reconstruction H Z

The Recoil Mass Technique e + e -  HZ E cm = E Z + E H 0 = p Z + p H M H 2 = E H 2 – p H 2 = = (E cm -E Z ) 2 – p Z 2 = = E cm 2 + E Z 2 – E cm E Z – p Z = = E cm 2 – 2E cm E Z + M Z 2 Resolution on MH depends on knowledge of colliding beam energy and on lepton momentum resolution.

Yukawa couplings vs. fermion mass Determining the Higgs Couplings After discovery of a new boson at LHC, essential to verify that this new particle does indeed its job of providing gauge bosons and fermions with their masses; ILC can perform fundamental test of scaling of Yukawa couplings with masses for Gauge bosons, quarks and leptons with accuracy matching theoretical predictions; Recent improvements in m b and m c determinations at B factories make ILC measurements even more compelling.

Higgs Decay Branching Fractions vs. Higgs Mass Determining the Higgs Couplings Extract Higgs couplings from decay branching fractions into fermions and gauge bosons and from production cross sections (controlled by g HZZ, and g HWW ); Strong dependence on (unknown) Higgs Boson mass. Excluded by LEP-2

Generation of Mass: the Gauge Sector E cm TeV M H 120 M H 140 M H 150  g HZZ /g HZZ  g HWW /g HWW Determine HZZ coupling from Higgstrahlung cross section and HWW coupling from double-WW fusion and H  WW branching ratio;   H also possible at  collider considered as ILC option;

The Jet Flavour Tagging Technique Tag H hadronic decay products to separate b, c and g yields; Jet flavour identification relies on distinctive topology and kinematics of heavy flavour decays; H  bb

The Jet Flavour Tagging Technique Short lived particle with proper time  has a decay distance l =  c  B from H decay at 0.5 TeV m B = 5.2 GeV, c  = 500  m E B = 0.7 x E jet = 0.7 x 500/4 = 100 GeV  ~ 3.5 mm bcg (mm) ~ ~ 0. D from H decay at 0.5 TeV m D = 1.9 GeV, c  ~ ( )/2  m  ~ 1.3 mm

Generation of Mass: the Quark Sector Extract individual branching fractions from 3-parameter simultaneous fit:  g Hbb /g Hbb  g Hcc /g Hcc  g Hgg /g Hgg c-tag b-tag cc gg bb Coupling Accuracy for M H =120 GeV

Generation of Mass: the Lepton Sector E cm TeV M H  g H  /g H   g H  /g H   g H  /g H  Higgs decays into  pairs identified by topology, multiplicity; H   as rare decay allows test of Yukawa coupling scaling with mass in leptonic sector;

Higgs Quantum Numbers J PC numbers can be determined in model-independent way: Threshold cross section rise and angular dependence of the Z boson production from longitudinal polarization at high energies allows to determine and to distinguish SM H 0 boson from a CP-odd A 0 boson and the ZZ background as well as from a CP-violating mixture: Observation of H   or   H sets  and ;

Determining the Higgs Potential Fundamental test of Higgs potential shape through independent Determination of g HHH in double Higgs production Opportunity unique to the ILC, LHC cannot access double H Production and SLHC may have only marginal accuracy;

Determining the Higgs Potential Experimental challenge: not only cross sections are tiny (< 1 fb), but need to discard HH production not sensitive to HHH vertex.

Double Higgstrahlung at 0.5 TeVDouble WW Fusion at 1 TeV HH Mass Decay Angle

 p t /p t 2 = 4 x  p t /p t 2 = 8 x  p t /p t 2 = 6 x  p t /p t 2 = 2 x Reconstructing the Higgs profile sets challenging requirements on vertexing, tracking and calorimetry:  E/E BR(H  WW) MHMH ee  HHZ  E/E ee  HZ  X  Higgs Physics and Detector Response

The Higgs Profile and Physics beyond In models with extended Higgs sector, such as SUSY, Higgs couplings get shifted w.r.t. SM predictions: Precise BRs measurements determine the scale of extended sector:

The Higgs Profile and Physics beyond Higgs/Radion mixing In models with new particles mixing with the Higgs boson, branching fractions are modified, generally through the introduction of an additional (invisible) decay width; Models of extra dimensions stabilised by the Radion are characterised by potentially large changes to Higgs decay Branching fractions: