Two Photon Physics at a Linear Collider. Richard Nisius, CERN Lund, 13 September 1998

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1 Two Photon Physics at a Linear Collider Richard Nisius, CERN Lund, 3 September 998 Introduction. The instruments 2. The physics Conclusions VLEPP

2 Photon;photon scattering ( ) ( ) Interaction of two quasi-real photons! X e.g. X(s ) = `+`;, qq, QQ, Z 0 Z 0, W + W ;, H Q 2 i = 2E i E 0 i ( ; cos i) 0 X! 2 W 2 = s = E h ; h X h ~p h! 2

3 Electron-Photon Scattering e tag (E tag,θ tag ) e γ Q 2 Λ 2 e γ f q,γ (x,q 2 ) W e untag (P 2 Λ 2 ) d 2 e!ex dxdq 2 2 = 22 xq 4 4 ( + ( ; y)2 ) F 2 (x Q 2 ) ; y 2 F L (x Q 2 ) {z }!0 Q 2 = 2 E b E tag ( ; cos tag ) P 2 x = y Q 2 Q 2 + W 2 + P 2 = ; E tag E b cos 2 ( tag 2 ) 3 5

4 The general layout of a future Linear Collider e + -e - Beam Dump Advanced Power Source for TeV Final Focus Main Linac Main Linac γ-γ Compressor Pre-Accelerator Compressor Compressor Pre-Accelerator Compressor Damping Ring Electron Source Positron Source Damping Ring A506

2-96 8047A365 Positron Beam Dump Electron Beam Transport 0.

5 A365 Positron Beam Dump Electron Beam Transport 0.2 GeV Accelerator Positron Production Target 33 GeV Electron Beam Transport Electron Damping Ring Interaction Point Final Focus Electron Beam Dump Positron Beam Transport 50 GeV Accelerator 0.2 GeV Positron Beam Transport Positron Damping Ring.0 GeV Accelerator 0.2 GeV Accelerator Electron Source From LEP/ SLC to TESLA ; ; LEP TESLA SLC LEP SLC TESLA radius [km] 8.5 length [km] gradient [MV/m] x = y [m/m] 0 / 5.4 / /0.09 energy [GeV] luminosity [0 3 cm ;2 s] L int [/pb y]

6 The expected cross sections L int = 20fb ; =y ) Events/y (a) σ[pb] qq μμ ee Zγ γγ e + e e + e e + e μ + μ e + e qq e + e tt e + e WW e + e ZZ e + e γγ e + e Zγ WW ZZ tt (b) σ[pb] e γ e γ e γ e Z e γ νw μμ qq eγ e γ e qq e γ e μ + μ γγ W + W γγ μ + μ γγ qq ez 0 eqq eμμ νw WW s [GeV] 0 < i < 70 deg, M +; qq > 50 GeV = s ee e

7 Some advantages of photon colliders f(x) = M 2 W 2 = s ee s dl dw = 4 0 ;2 / fb GeV Larger cross sections than e + e ; for several final states, e.g. W + W ; pairs. Good prospect for two photon production of Higgs bosons. Replace the Weizsäcker Williams Photons in collisions by high energy compton scattered photons ) larger W. Single production of Leptoquarks, Higgs bosons, etc. gives access to larger masses.

8 The creation of the Photon beam Spent electrons deflected in a magnetic field Spot size for hard γ Polarized e-beam Spot size for soft γ Polarized laser beam A M M2 e QUAD IP M M2 e e QUAD

9 Critical parameters for collisions beam energy spread helicities conversion point Remaining e and e + e ; luminosities dl dz L geom γγ γe.0 dl dz L geom γγ ee 0.8 γe A566 z = W/2E 0 no deflection of e A57 z = W/2E 0 deflection of e

From LEP to TESLA the detector Hadron calorimeters and return yoke Electromagnetic calorimeters Muon detectors Jet chamber Vertex chamber

10 From LEP to TESLA the detector Hadron calorimeters and return yoke Electromagnetic calorimeters Muon detectors Jet chamber Vertex chamber Microvertex detector y z θ ϕ x Forward detector Solenoid and pressure vessel Presampler Time of flight detector Silicon tungsten luminometer Z chambers

11 The general detector concept Central tracker Mask 200 mm Calorimeter 3000 mm Additional Mask Quadrupole Kryostat Vertex detector Graphite Beam pipe Tungsten Calorimeter

12 Some features of the background beamstrahlung initial state radiation transverse momentum [GeV/c] theta [rad] N e + e ; BX = 05 E tot = :5 0 5 GeV N had (W had >5GeV ) BX he vis i = 0 GeV = 0:3

13 From LEP to TESLA the physics. Total cross section 2. Jet production in,? and?? collisions 3. QED and QCD Structure Functions of the photon 4. Heavy Quark production 5. BFKL signatures in?? collisions 6. Production of W pairs 7. Higgs Production using! H 8. Resonances 9. Searches for new particles 0. Diffraction. Production of Z pairs and photon pairs... and much more

14 The total - cross section σ γγ [nb] pre LEPII Schuler and Sjöstrand Engel and Ranft (PHOJET) 2 2σ γp /(σ pp +σ _ pp ) MD- 99 TPC/2γ 990 PEP/2γ 985 PLUTO 984 σ γγ [nb] LEPII data OPAL Preliminary L3 Preliminary DL without hard Pomeron (σ γp 2 /σ pp ) DL with hard Pomeron term from γp fit Schuler and Sjöstrand Engel and Ranft (PHOJET) Minijet, p T min=2 GeV (Godbole and Panchieri) 400? W [GeV] W [GeV]..202????? pre LEPII LEP II LC data

15 Leading order diagrams Direct: Single-Resolved: AK VDM direct resolved Hj hard interaction anomalous Double-Resolved:

16 The inclusive jet cross-sections dσ/de jet T [pb/gev] 0 2 OPAL η jet, η jet2 < 2 data (hadrons) NLO QCD (partons) 0 direct single-resolved double-resolved 0 - LEP II E jet T [GeV] d de jet T d NLO Calculation LC

17 The sensitivity to parton densities OPAL (LEP II) dσ/d η jet [pb] (a) E jet T > 5, Ejet2 T > 3 GeV PYT. LAC p mi =2.5 GeV/c t PYT. GRV p mi =2.0 GeV/c t PHOJET GRV PYTHIA SaS-D PHOJET SaS-D dσ/d η jet [pb] η jet 20 (b) E jet T > 5, Ejet2 T > 3 GeV 8 6 (c) E jet T > 5, Ejet2 T > 3 GeV x ± γ < x ± γ > η jet dσ/d η jet [pb] η jet The gluon density f g= in the photon can be constrained. The simulation of hadronic final states has be be improved.

18 The contributions to F 2 (x Q2 ) γ F 2 (x Q 2 ) = x P c f e2 q f q (x Q 2 ) q q hadronic, p T = small non perturbative VDM (! γ q q pointlike, p T = large perturbative F γ 2(x) / α F γ 2Box (x)/α (n f =3,Q2 =20.GeV 2, m q =0.3GeV) F γ 2,VDM (x)/α = 0.2 x0.4 (-x) x

19 The LEP data on F 2 GRV (HO) F 2 γ (x,q 2 ) / α Q 2 =.86 GeV 2 Q 2 =.9 GeV 2 Q 2 = 3.76 GeV 2 Q 2 = 5.0 GeV 2 Q 2 = 2. GeV F γ 2 (x,q 2 ) / α a) L3 OPAL Q 2 = 7.5 GeV 2 Q 2 = 6.3 GeV 2 b) L3 OPAL Q 2 = 9.0 GeV 2 Q 2 = 8.9 GeV 2 c) DELPHI x GRV (HO) Q 2 =.0 GeV 2 Q 2 = 2.0 GeV 2 Q 2 = 3.0 GeV OPAL d) DELPHI prel. Q 2 = 4.5 GeV 2 Q 2 = 9. GeV 2 OPAL e) ALEPH prel. Q 2 = 4.7 GeV 2 Q 2 = 22.0 GeV 2 OPAL f) DELPHI prel. Q 2 = 30. GeV OPAL g) ALEPH prel. Q 2 = 4. GeV 2 OPAL h) DELPHI prel. Q 2 = 59. GeV 2 i) OPAL Q 2 = 35. GeV 2 Q 2 = 279. GeV j) OPAL k) OPAL l) OPAL ALEPH prel. x

20 F 2 prospects for a LC F 2 γ 0 LEP 2 LC 500 θ 0 = 75 mr LEP II > 75 mrad x ( 4.0) ( 2.8) ( 2.0) LEP II LC x 0.8 ( 4.0) 0.6 ( 2.8) 0.4 ( 2.0) (.5) 0.25 (.5) LC F 2 γ LC Q 2 (GeV 2 ) tag > 40 mrad x ( 4.0) LC 500 θ 0 = 40 mr LC x 0.8 ( 4.0) ( 2.8) 0.6 ( 2.8) ( 2.0) 0.4 ( 2.0) (.5) (.5) Q 2 (GeV 2 )

21 The Q 2 evolution of F 2 F γ 2 (Q 2,udsc) / α OPAL (0. < x < 0.6) TOPAZ (0.3 < x < 0.8) AMY (0.3 < x < 0.8) ALEPH prel. (0.3 < x < 0.8) JADE (0. < x <.0) L3 prel. (0.3 < x < 0.8) DELPHI prel. (0.3 < x < 0.8) TPC (0.3 < x < 0.6) GRV LO (0. < x < 0.6) GRV LO (0.2 < x < 0.9) GRV LO (0.3 < x < 0.8) SaSD (0. < x < 0.6) HO (0. < x < 0.6) ASYM (0. < x < 0.6) Q 2 [GeV 2 ] E tag E b > 0:5 tag > 75 mrad LC - E tag E b > 0:5 tag > 40 mrad LC - To achieve overlap with LEP II data the mask has to be instrumented.

22 [pb] Charm cross section in Direct and -res (NLO), 2-res (LO) calculation, all based on the EPA = p 2m c, m c = :6 GeV W min = 3:8 GeV 0 7 cc events/year Direct process is pure QCD prediction = f(m c s )

23 Charm production in 0 total massless massive d 2 dydp 2 T (d) pb GeV 2 massless massive total (d) 0 ; 0 ; 0 ;2 0 ;2 0 ;3 0 ;4 e + e - e + e - c/c _ + X Ös = 500 GeV y = 0 Beamstrahlung + WWA e + e - e + e - c/c _ + X e + e ; Ös = 500 GeV e + e ; p = 0 GeV Beamstrahlung + WWA 0 ;3 0 ; total massless massive (d) massless massive total (d) ; 0 ;2 0 ;3 e + e - e + e - c/c _ + X Ös = 500 GeV y = 0 Laser Spectrum PLC e + e - e + e - c/c _ + X Ös = 500 GeV p = 0 GeV Laser Spectrum PLC ;2 ; 0 2 p T =GeV NLO calculation, EPA integrated up to tag = 75 mrad, m c =.5 GeV y 0 ; 0 ;2

24 Charm production? hadronic ) f g = LO Q 2 = 0 GeV 2 pointlike? NLO.06 NLO LO x EPA a BS b pl LO ---NLO had E tag E b > 0:5, tag > 40 mrad, m c = :5 GeV, = Q

25 BFKL signature in?? y = q k 2 k k 2 Q 2 Q2 2 no AP evolution Q 2 = ;q2 s = (k + k 2 ) 2 ^s = sy y 2 s 0 = p Q 2 Q 2 2 y y 2 ^s Q 2 i LC500 LEP I BFKL gluon - E tag > 20 GeV log( s s 0 ) > 2 2:5 < Q 2 i < 200 ) O(6000) events/y

26 Some and e cross sections 8pb 43pb s e, s

27 W - pair production in Cross sections for WW and WW final states, Born + O() corrections. = 6 pb, ee = 6:6 pb within cuts using the PLC photon energy spectrum. The radiative corrections are moderate but do strongly depend on W. O(0 6 ) W + W ; pairs per year are produced. A sample well suited to study the anomalous couplings of the W.

28 Higgs search in! H! b b PLC luminosity distributions event rates L int = 0fb ;. The Higgs is produced as an s-channel resonance. 2. To suppress the continuum production of bb and cc one needs to select J z = 0, good b tagging ( b > 90%) and c suppression ( c!b < 5%). 3. With a mass resolution of 0% M H (FWHM) a signal with larger than 0 significance can be established in the range 80 < M H < 40 GeV for L int = 0fb ;.

29 Determination of ;(H! ) PLC luminosity distributions event rates L int =0fb ;. A measurement of ;(H! ) is very fundamental as it is sensitive to all new particles in the loop which couple to the Higgs. 2. The expected event rates are calculated for j cos j < 0:7 and a resolution of MH = 0:M H. 3. ;(H! ) can be determined with an O(0%) error for L int = 0fb ;.

30 ZZ final states The cross sections are based on the PLC photon energy spectrum. The cross section strongly depend on the helicities of the Z bosons. Higgs signals up to M H = 350 GeV can be observed, for higher masses the background from the continuum Z T Z T production is too high.

31 Conclusions. The LC is an unique tool to investigate two photon physics at the highest energies. 2. Due to the high centre-of-mass energy, especially in the PLC mode new channels (Higgs, W, Z, LQ,...) are open to be copiously produced in the two photon mode. 3. The tagging of electrons down to the lowest possible angles is a challenging task, but it is mandatory in order to achieve overlap with the two photon physics results from LEP II in several areas, i.e structure function measurements. 4. In all physics channels a careful determination of the, e and e + e ; luminosity distribution is essential. Lots of work is in front of us to bring a LC to life, but it should be fun and the physics potential is certainly worth the effort. slides:

Measurement of the photon structure function (x,q 2 ) with the LUMI detector at L3. Gyongyi Baksay

Measurement of the photon structure function F (x,q ) with the LUMI detector at L3 Gyongyi Baksay Florida Institute of Technology Melbourne, Florida, USA Advisor: Dr. Marcus Hohlmann Orlando, March -3,