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Physics @ Future Linear + e e Collider

A. Raspereza, DESY QFTHEP 2004 Conference, 18/06/2004


Synergy Between Hadron & Lepton Machines


Hadron colliders : higher energy reach - higher discovery potential, high backgrounds moderate precision measurements machines of "scientific breakthrough" (SPS, Tevatron) Lepton colliders : lower energy reach - lower discovery potential, clean experimental environment high precision measurements machines of "model validation and indirect prediction" (LEP, SLAC)



Historical retrospective : establishment of SM


CERN SPS : discovery of weak bosons Z and W (early 80s) LEP experiments, SLD : validation of the SM through high precision measurements, indirect prediction of top mass Tevatron : discovery of top quark LEP, SLD, Tevatron : indirect constraints on Higgs mass and new physics through precise measurements in EW sector and direct mea surements


Anticipated Nearest Future of HEP


One of the possible scenarios :
EWSB is realized in nature through Higgs mechanism Low energy s upers y mmetry is "true model"




LHC :
discovers Higgs and supersymmetric particles performs moderate prec is ion meas urements of H iggs bos on(s ) properties a n d p r o p e r t i e s o f S U S Y p a rt i c l e s




Linear collider :
p e p p L


erforms high precision measurements in the Higgs sector - complete stablishment of EWSB mechanism erforms precise measurements in SUSY sector ossible discoveries in those regions of model parameters space where HC is "blind"



LHC + Linear collider :


J o in t r e c o n s t r u c t io n o f S U S Y L a g r a n g ia n Indirect constraints through the precise measurements in the EW, Higgs and S U S Y s e c t o r s o n n e w p h y s ic s a t G U T a n d P la n c k s c a le s

But... Nature may be much reacher than our imagination!


Features of Linear e e Collider
Linear Collider = precision tool
CMS energy 500..1000 GeV = scale of EWSB High luminosity (~3-5 з 1034 cm2s1) Clear path to "phase 2" (multiTeV) exists (CLIC)


+

Well defined initial state Complete kinematic reconstruction Threshold scans (disentangle complicated new physics)

Clean environment
Experimental systematics small O(%) level measurements possible (= challenge for theory!)


Running options ( , e, ee, GigaZ)
Redundancy of measurements = cross - checks Complementarity of measurements Specific physics for specific option


Beam polarization (crucial for studying SUSY processes)


Important to pin down model parameters Disentangle various states, suppress some of backgrounds


Machine Technology Options



C o n v e n ti o n a l w a r m te c h n o l o g y (N L C ) 500 - 1000 GeV C MS energy 1.4 ns (40 cm !) bunch separation 11 . 4 G H z R F f r eq ue nc y 1 9 2 b u n c h e s in t r a in 200 - 300 MW AC power x / y = 220250/23 nm z = 110 Еm Ne / bunch at IP = 0.8 з 10 Lumi : 2-3 з 1034 cm2s1
10





z = 300 Еm

S u p e r c o n d u ct i n g C o l s T e ch n o l o g y (T E S L A ) 500 - 800 GeV CMS energy 180-340 ns bunch s eparation 1. 3 G H z R F f r eq u en c y 2820-4886 bunches in train 100-160 MW AC power x / y = 400550/35 nm
10

Ne / bunch at IP = 1.4 2 з 10 Lumi : 3.4-5.8 з 1034 cm2s1


Unpleasant Features of LC
"well define" initial state?





Beams are extremely collimated with large bunch charge electrons of one b u n c h r a d i a t e a g a i n s t c o h e re n t f i e l d o f ot her bu n c h Av erage energy loss 1.5% for e/e+ @ 500GeV

"clean environment"?


N / bunch ~ Ne / bunch ~ 10

10

Beambeam interactions (e.g. ~105 e+e / bx, few hadrons / 10 bx) Pileup : ex c es s iv e energy @ low c os H igh t imes t amp c apabilit y f or N LC det ec t or (1 . 4 n s b u n c h s e p a ra t i o n ) i s n e e d e d t o reduce hadronic background


Detector Concep t
EXAMPLE : TESLA Detector


Silicon VTX heavy flavour tagging Large volume tracker (TPC + SIT) precise reconstruction of charged par ticle momenta Finely segmented ECAL and HCAL efficient separation of showers within jet Tracking + calorimeter inside magnet coil (4T) Forward calorimetry (LCAL+LAT) hermeticity down to very small angles, luminosity measurements with bhabha



p/p = 10 p IP = 5Еm 10Еm/sin3/2 Eem/Eem= 11%/ E

4







Ejet/Ejet= 30%/ E


Vertexing
Pixelbased vertex detector
Options: CCD, APS, CMOS 3 - 5 layers Inner layer @ R ~ 10mm Flav our tag b/c separation Measurements of hadronic branching fractions of Higgs



Tracking
Benc

hmark for momentum resolution : e+e HZ X(e+e,Е+Е) try to reconstruct mZ better than Z


Imaging Calorimetry @ LC
Requirements












Ability to separate closeby WSi EC AL (1x1 cm2 cells, 24X0 depth) showers to improve jet energy Analog T ile H C AL (5x 5 c m2 cells , 46 depth) resolution and enable realization of Particleflow (Pflow) concept Digital (RPC, Tile or GEMbased) HCAL (1x1 cm2 cells, 46 depth) Good containment of shower F ine segmentation = ability to s ee intrins ic Ability to reconstruct objects non structure of the shower : imaging device pointing to IP (crucial for some SUSY signatures) ID of low momentum Е, not reach HCAL ECAL ing muon system High ECAL resolution mea surements of photons Moderate HCAL resolution mea surements of neutral hadrons Good time resolution for both calorimeters to avoid pilup

Solution : highly granulated calorimeters


ParticleFlow Concept Ideology of event reconstruction @ LC




Reconstruction of every particle Superiority of tracker w.r.t. c alorimeters use tracker to measure charged objects As sign calo hits to tracks, perform clustering on remaining hits neutral objects Us e ECAL to measure photons Us e ECAL+HCAL to meas ure neutral h a d ro n s

R econs truc tion of complex topology tt 6jet s F ull Geant3 s imulation of T ESLA detec tor F ull reconstruction based on Pflow concept N o kinematic fits

PFlow @ work


Long awaited by you Physics Topics


Picture of Modern HEP


K e y q u e s ti o n : m e c h a n i s m o f E W S B
Conventional Higgs mechanism? Structure of the Higgs sector (single doublet, 2HDM, CP violation in the Higgs sector)? Alternatives (dynamical EWSB, composite models, strong EWSB)





Hierarchy problem, unification of forces, gravity as QFT new physics C a s tl e o f Ne w P h y s i c s
The two towers : Supersymmetry and Extra Dimensions The ancient (renewed?) tower : new strong interactions Extended Gauge Theories GUT' s




Higgs Mechanism of EWSB (LHC corner)


LHC : detection of Higgs via vari



ous production mechanisms and decay channels, discovery poten tial over the whole mass range At least one Higgs (light SMlike) will be detected First measurements of Higgs boson properties (mass, couplings) Extended Higgs sector (MSSM) - more than one Higgs particle Regions in parameter space where additional Higgs particles may es cape detection


Higgs at LC
Detection of Higgs independent of its decay mode in HZ X(ee+ЕЕ) : model independent extraction of HZZ coupling

Exploration of extended Higgs sectors, detection of heavy Higgs bosons in a wedge region of LHC

Mass, width, branch ing measurements in variety of chan nels with high preci sion


Higgs at LC (Continued)
Higgs quantum numbers & reconstructed Higgs potential complete establishment EWSB mechanism
H i g g s s p i n t h r o u g h t h re s h o l d s c a n

Higgs parity from HZ xsec and angular spectrum Higgs selfcoupling from e+e HHZ


Supersymmetry

Low energy SUSY gold plated

candidate for new physics Hierarc hy problem s olved Clear path to grand unification Planc k scale models naturally supersymmetric Most of the spectrum of SUSY particles is within reach of sub TeV LC Excellent c hanc e to obs erv e SUSY particles at early stage of LC operation (500GeV) Clean signatures, low bac k grounds precision measure ments of physics observables in SUSY sector From observ ables to SUSY La grangian (joint LHC LC effort)


Sleptons
(Production in @ LC and Decays)

Main signatures : 1) two leptons + missing E 2) two narrow jets ( ') + missing E s


Sleptons at Linear Collider

Masses from threshold scans (10 fb1 / point)


Gaugino Production and Decays
Gaugino' = mixture of wino' , zino, photino and higgsino' s s s in total 6 physical states : 2 charginos, 4 neutralinos

1 2 3 4

) ) ) )



4 3 2 1



Variety of signatures: observable fermions + missing E observable fermions + missing E observable fermions + missing E lepton + missing E


Gaugino Mass Determination
Exploit sensitivity of dijet and dilepton energy & mass spectra to gaugino masses


Gaugino Masses
Or use traditional threshold scan technique


Chargino Properties

P{}=80% P{+}=60%


Neutralino Properties


Stop Particles


Large mixing in stop sector large mass splitting is possible ~~ + Process e e t1t1 most likely within reach of subTeV LC Decays : t1 Exploited topologies : 2 cjets + Em 2 bjets + 2 jets + Em
is

~ c ~ + 0 , 1




1

b
is

; bjet + cjet + jet + Em

is

;



Extraction of mass and mixing angle through simultaneous measure ments of R (P{},P{+}) & L (P{},P{+}), P{}=80%, P{+}=60%


Rparity violating SUSY @ LC


R=(1)L+3B+2S, 1 for SM particles, 1 for sparticles R conservation prevents proton from fast decay Consequences З Sparticles produced in pairs ~ З LSP (presumably 0) is stable
1


Specific SUSY Signatures & Detector Universality Issues


Extrapolating SUSY Parameters to Higher Scales



Key steps towards revealing SUSY breaking mechanism and understanding more fundamental theories
Reconstruction of SUSY Lagrangian from physics observables Extrapolating SUSY parameters to higher (GUT) scales



Joint effort of LHC and LC : combination of higher mass reach and high production rates of strongly interacting sparti ~~ cles (g, q) @ LHC with high precision measurements in slep ton and gaugino sectors @ LC


Extra Dimensions
Alternative solution of hierarchy problem

SM fields live in "3+1" space, but gravity feels 4+n dimensions Additional compactified dimensions of size R 2 Large M is artifact : M = M 2 nR n + Pl D Pl D M ~ O(T eV) for particular choice of R and n Two scenarios Many (n 2) XD' s One XD with specific properties (RandallSundrum model) Signals at LC :



Production of KK Graviton
Real graviton emission: e+e Gn


Gn KK tower of states with

tiny mass splitting : ~ 103...107 keV (2 n 6) Determine number of XD' with s running at two different energies

Sensitivity to MD (in TeV) @ 800GeV with 1 ab
1


XD' via Virtual Effects s


Virtual graviton exchange in 2 2 scattering e.g. e+e bb


modified angular distribution modified leftright asymmetry : beam polarization!


RandallSundrum Model
5

dimensional space hierarchy via exponential function of compactification radius R C

KK states may have largely splitted masses:


Nonzero states (n > 0) couple to SM fields (e.g. fermions)



Extended Gauge Theories
GUT : all forces are described by single group GGUT at high scales


G


GUT

contains SU(3)з SU(2)з U(1) as subgroup
'

But GUT gauge group may be broken in steps
E6 SU(3)з SU(2)з U(1)з U(1)Y




SO(10) SU(3)з SU(2)Rз SU(2)Lз U(1)


new light gauge boson Z' TeV scale @
+

Three additional gauge bosons (W ,W )R , Z



R



Extended fermion representations : new fermion s ta te s These scenarios can be verified both at LHC (di rect observation) and LC (virtual effects)


Probing Extended Gauge Theories Example : Accessing Z' roperties p
Assume new state is outside experimental reach From the analys is of propagator effects on v arious observables in the process Z' ass and couplings to fermions can be constrained m



Renewed OldFashioned EW Physics






Measurements in EW sector as they are done @ LEP but with higher statistics (high er precision), higher energy reach (extended kinematic domain) access to new physics Novel measurements which were not done @ L E P Example : measuring anomalous TGC' and s QGC' & probing Strong EWSB s


Anomalous Gauge Couplings & Strong EWSB


Triple Gauge Couplings


Quartic Gauge Couplings


Quantum Chromodynamics


High precision measurement of S @ Z pole (GigaZ) and higher energies "chasing" running strong coupling

analysis of event shape variables




constraints on the GUT scale improving prediction power of perturbative QCD


Uncovered (partially covered) Topics
L i ttl e H i g g s m o d e l s C o m p o s i te m o d e l s Strong EW Symmetry Breaking QCD & top quark physics CKM matrix & CPviolation in all sectors (EW, S US Y , H i g g s ) Lepton flavour violation ......... Many topics still need to be scrutinized Any interesting topic for you? Expertise is needed, volunteers are searched



Summary


Linear e+e collider - next large experimental facility after LHC (possible concurrent running) Fascinating physics anticipated

Elucidating mechanism of EWSB Exploration of SUSY models Access to higher scales via RGE and high precision

studies of virtual effects @ subTeV and TeV scales Probing alternative models, new physics & "physics beyond new physics"


Will complement knowledge we' obtain with ll L H C Yet not just "complementary" machine but has v a l u e o n i ts o w n


Summary (Continued)






Universality of detector (from hardware side) and universality of thinking (from human side) is mandatory to grasp all expected and even unexpected and surprising physics signatures Should be global (not national or regional) project : enhanced chances of success Current LC detector R&D and LHC project are nice examples of global efforts in HEP - Encouraging sign! Interested, intrigued? Join us!