Hadron Production in Photon-Photon Processes at the International Linear Collider Swathi Sasikumar 29th Feb, DPG 2016 Introduction > The International Linear Collider (ILC) - a proposed e+e- collider Tunable at centre-of-mass energies between 200 GeV to above 500 GeV (will be upgraded to 1 TeV) Luminosity of about 500 fb-1 in first four years at 500 GeV > γγ background an important issue Every e+e- event is accompanied by one or two photon collisions Overlay of low Pt hadrons over the important physics events Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 2 Impact of Hadron Overlay > Overlay of soft hadrons affects a few 0.1 ZHH (llbbbb) γγ processes specific but important cases e.g. : M(H1)= 125GeV not included 0.08 included s=500GeV Measurement of Higgs self coupling from normalised 0.06 double-Higgs production - rare process 0.04 Overlay degrades the mass resolution 0.02 Signals of new particles with small mass 0 differences (dark matter candidates) 50 100 150 200 M(H1) [GeV] Ref:Claude Duerig Visible decay products very soft and thus similar to hadron overlay Need more differential methods to remove gamma-gamma background • Identify gamma-gamma collision products by explicit reconstruction Very important to have detailed simulation hep-ph/1307.3566 (2013) Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 3 e+ e- beams are accompanied by : > γγ Luminosity as a function of psγγ Real photons fr(x): 10 > real-real real-virtual ‣ Beamstrahlung - emission of real ] virtual-virtual -2 1 photons in high electrical field of cm 33 oncoming bunch 0.1 /GeV) [10 CM 0.01 /d log(E γγ 0.001 > Virtual photons fv(x): dL ‣ Weizsaecker-Williams process - emission 0.0001 0.01 0.1 1 10 100 of virtual photons which can interact with p sγγ E CM [GeV] an oncoming photon or an electron Ref:hep-ph/0406010v1(2004) Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 4 Vector Meson Dominance > Photon is a hadron 1/400 of the time > Vector meson dominance the most dominating subprocess in photon-photon processes > A photon fluctuates into a vector meson (⍴,⍵,ϕ, j/⍦, ⌥ ) ( same quantum properties) > The highest probability for the photon to fluctuate is into a rho meson. > Production of number of low momentum soft hadrons Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 5 Cross sections at different psγγ > Comparison of γγ cross section ×10-3 predictions from Pythia 6,PDG and 0.7 MD-1 PLUTO Amaldi et al (hep-ph/9305247) with (mb) OPAL σ 0.6 L3 data from LEP,PETRA and VEPP Pythia standard function(PDG) p Amaldi Parametrization > s γγ > 10 GeV: Good description of 0.5 LEP data with Pythia-6 0.4 p > s γγ < 10 GeV: Measurements have large uncertainties and widespread Cross sections 0.3 > Cross section from Pythia 6 possibly 0.2 too low? 10 102 103 sγγ (GeV) Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 6 A Dedicated Event generator for γγ processes > For p s γγ > 2 GeV Pythia 6 could be 10 real-real used to simulate γγ low Pt hadron real-virtual ! ] virtual-virtual processes -2 1 cm 33 > Below 2 ⇡ threshold, pure QED beam- 0.1 beam interaction is modeled by /GeV) [10 CM Pythia-6 dedicated programs, e.g. Guinea Pig 0.01 Guinea Pig ? /d log(E > Need to evaluate impact of uncovered γγ 0.001 region - how can it be modeled? dL 0.0001 > Dedicated generator have been 0.01 0.1 1 10 100 p E [GeV] developed in ILC community to study sγγ CM the low energy areas by Tim Barklow > To study the events : p s γγ > 2 GeV Pythia-6 is used p s γγ < 2 GeV Barklow generator is used Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 7 Event Properties of Barklow generator > Barklow generator takes cross section from Amaldi parametrization thus folding it into the luminosity spectrum giving all combinations of hadrons at given p sγγ > The Barklow generator produces ⇡⇡ - at pion threshold energy (300 MeV) ⇢⇡ - at rho threshold energy (1.5 GeV) 0 ⇢± ⇡±⇡ ! 0 + ⇢ ⇡ ⇡− ! 0 > The cross sections for producing ⇢ is greater than ⇢± > Until recently a much simpler version of Barklow generator was used which produced 0 ⇢ ± without width and produced no ⇢ s > A better version of the generator was thus developed correcting the flaws in older version - big progress Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 8 Investigating Pion threshold energy range > To study impact on detector, simulated collisions of two real photons in the range 2 ⇡ < p s γγ < 0.5 GeV > The particles produced here have very low Pt > Significance of particles produced in these range with respect to ILC condition > The polar angles of all reconstructed Theta of reconstructed particles (0.1-0.5GeV) particles normalized to particles per 0.5 photon-photon event is plotted 0.4 > Reconstruction of charged particles as normalized 0.3 neutral above 7 degrees due to tracker acceptance 0.2 > Particles at pion threshold can be seen in 0.1 the detector 0 0 50 100 150 θ[°] Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 9 Conclusions > Although ILC environment is much cleaner than LHC, the overlay from γγ backgrounds is still an issue > The impact of this overlay is observed on a very few but important physics events > The existing generators can cover the impact partially (data in insufficient) , we need better methods to cover the impact completely > Recently significant progress was made in modeling the low energy region (Barklow generator) > Currently evaluating impact of these processes on Physics studies and detector design for ILC Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 10 Back up Swathi Sasikumar | Hadron production in gamma-gamma processes | 05-11-2015 | Page 11 Hadron Interactions in VMD A photon is a hadron a fraction 1/400 of the time Rise in gamma-gamma cross sections much similar to hadronic cross sections All event classes known for ordinary hadron-hadron interactions are found to occur here Behaves more like a Hadron collider than a lepton collider Reference : Particle Data Group 2014 Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 12 Current γγ => low pt hadron simulation The γγ => low pt hadron processes simulated by methods provided by T.Barklow Based on a blend of Pythia events at p s γγ > 10 GeV Paper by Chen, Barklow and Peskin for 0.3 GeV< p s γγ <10GeV Integrated into Whizard which provides the γγ => Hadron processes Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 13 Outline ‣ Introduction ‣ Total Cross Sections ‣ Event Properties ‣ Towards an improved description ‣ Summary and Outlook Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 14 Total Cross Sections from Chen, Barklow and Peskin Determination of photon-photon hadronic cross sections essential for computing hadronic backgrounds Photon-photon total cross section proportional to ⍴-⍴ total cross section The parametrization of Amaldi et al. give cross sections as 3 2.1 0.37 σ(γγ >hadrons)=σ (1 + (630 10− )[ln(s) +(1.96)s− ) − 0 ⇤ (Ref: Peskin et al, PRD, 49(3209) 1994) Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 15 γγ - Processes in Pythia 6.4 Direct Interactions(DIR) - Real photons interacts directly Vector Meson Dominance(VMD) - Photon fluctuates into a vector meson Anomalous Interactions(GVMD) - Photon fluctuates into a q q¯ pair of larger virtuality Deep inelastic Scattering(DIS) - A process of probing the Hadrons with very high energy leptons. Subprocesses Cross-sections (nb) VMD * VMD 239.2 DIR * VMD 87.52 GVMD * DIR 9.77 GVMD * GVMD 12.05 Usage of Gamma - gamma beams with varying energy is preferred - more realistic results Missing of Deep Inelastic scattering process - trying to include by changing some parameters Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 16 Update: Total cross section from PDG The standard theory for calculating hadronic cross sections as per PDG: γγ 2 2 S γγ γγ S ⌘1 σ = δ [H ln ( γγ )+P ]+R1 ( γγ )− SM SM (Ref: Particle data group 2014) R: Regge term defines the cross section Cross sections for different energies at low energies where the interactions are ×10-3 0.7 (mb) explained using meson exchange σ 0.6 P : Pomeronchuk term defines the cross section at higher energies where the 0.5 Cross section interactions are explained using pomeron 0.4 exchange. 2 ~c 0.3 H: H = ⇡ ( ) The Heisenberg term M 2 defines the rise in cross section with 0.2 2 3 energy 10 10 Energy (GeV)10 Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 17 Total Cross Sections Cross sections for different energies ×10-3 0.7 The results from Pythia very MD-1 (mb) PLUTO much in accordance with the σ OPAL L3 Pythia standard function and the 0.6 standard function(PDG) measured data. Amaldi Parametrization 0.5 Data for gamma-gamma cross cross section sections at very high energies not available 0.4 Pythia seems to be quiet okay for evaluating gamma- 0.3 gamma backgrounds 0.2 2 3 10 10 Energy(GeV)10 Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 18 Outline ‣ Introduction ‣ Total Cross Sections ‣ Event Properties ‣ Towards an improved description ‣ Summary and Outlook Swathi Sasikumar | Hadron Production in photon-photon processes | 29-02-16 | Page 19 Event Properties Taking a look at the individual events from γγ => low pT hadrons m ⇢ = 770 MeV and Γ ⇢= 145 MeV Barklow generator produces Rho mesons of same mass and no width at all.