Cross sections and di raction in PYTHIA 8. Christine O. Rasmussen

Transcription

1 det. of astronomy and theoretical hysics Cross sections and di raction in PYTHIA 8 Christine O. Rasmussen Goals Regge theory intro Total and elastic cross sections Di raction cross sections Conclusion and outlook Aril 2016 Slide 1/19

2 det. of astronomy and theoretical hysics Goals Better descrition of the total and elastic cross sections at LHC energies (Pythia currently is too low) Better descrition of elastic di erential cross section (Pythia currently only exonential) Better descrition of di ractive (di erential) cross sections (none of the models available in Pythia currently describes all asects of data) Include ossibility for roducing truly hard QCD and electroweak articles in di ractive events (only soft with small tail of hard QCD available in Pythia before). See arxiv: [he-h]. Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 2/19

3 det. of astronomy and theoretical hysics Regge theory intro Old-school scattering theory describing article collisions, eg. elastic scattering. Can be described in a diagrammatic way, similar to Feynman diagrams in QFT., R, P We can construct roagators for X and vertex rules for X, XXX etc. (X = R, P). Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 3/19

4 det. of astronomy and theoretical hysics Regge theory intro Neglecting Couloumb scattering, amlitude for elastic scattering at lowest order is A el = X F 2 (t) G X ( s s 0, t) And the cross section t el X X F 4 (t) G X ( s s 0, t) 2 Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 4/19

5 det. of astronomy and theoretical hysics Regge theory intro The amlitude for!anything is A(! X )= X tot X F 2 (0)G X ( s s 0, 0) Amlitudes and cross sections for various rocesses, eg. elastic, total and di ractive rocesses, can be constructed with these form factors, roagators and vertices from Regge theory, to various degrees of comlexity. Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 5/19

6 det. of astronomy and theoretical hysics Total and elastic cross sections Old Donnachie-Landsho arametrization does not describe measured cross sections at the LHC. DL, old tot = Xs P(0) 1 + Ys R(0) 1 Pythia currently only includes simle exonential fallof in d el dt, and do not fully describe LHC data. d el = 2 tot 16 ex(b elt) dt Various arametrizations of di erential elastic cross section available from di erent authors. Two chosen: COMPETE arametrization from PDGs Review of article hysics 2014 (RPP), DL-based arametrization from Aleby et.al. (ABMST). Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 6/19

7 det. of astronomy and theoretical hysics Total and elastic cross sections A ABMST = 4X A i (s, t)+a ggg i=1 A RPP = 6X F+ i + F i i=1 Hard P. Soft P. f 2, a 2 trajectory.,! trajectory. Trile-gluon. Froissaron (F H + ). Maximal O (F MO ). P, O oles (F P +, F O + ). f 2, a 2 and,! trajectories (F R +, F R ). PP, RP, OP cuts (F+ PP, F± RP, F OP ). Trile-gluon exchanges (N +, N ). Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 7/19

8 det. of astronomy and theoretical hysics Total and elastic cross sections 200 RPP ABMST DL PDG data 150 tot (mb) s (GeV) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 8/19

9 det. of astronomy and theoretical hysics Total and elastic cross sections 50 RPP ABMST SaS PDG data 40 el (mb) s (GeV) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 9/19

10 det. of astronomy and theoretical hysics Total and elastic cross sections s = 23.5 GeV RPP ABMST SaS data 10 1 d el/dt (mb/gev 2 ) t (GeV 2 ) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 10/19

11 det. of astronomy and theoretical hysics Total and elastic cross sections s = 13 TeV RPP ABMST SaS 10 1 d el/dt (mb/gev 2 ) t (GeV 2 ) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 11/19

12 det. of astronomy and theoretical hysics Di ractive cross sections The single di ractive amlitude can be constucted similarly A SD = X t X SD X X X and obtain SD F 2 (0) G X ( M2 X, 0) 2 gxxx 2 s F 4 (t) G X ( s 0 MX 2, t) 4 The fractional momentum loss of the roton is = M2 X s. Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 12/19

13 det. of astronomy and theoretical hysics Di ractive cross sections Default in Pythia: Schuler-Sjöstrand arametrization (SaS) d SD 2 dtd =g PPP 16 where 3 P ex(b SDt)F SD 2 P =X s P ref B SD (s) =2b 2 P 0 ln( ) F SD =(1 )(1 + c resm 2 res M 2 res + s ) and s ref = 20 GeV, g PPP ' mb 1/2, b =2.3, c res =2andM res =2GeV. Additional otions available. Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 13/19

14 det. of astronomy and theoretical hysics Di ractive cross sections ) [mb] σ(ξ cut σ(ξ ) cut ATLAS (+TOTEM) Monash Monash DL Monash CR QCD 4C A14 NNPDF 7000 GeV χ2 /N 5% bins 2.1 ± ± ± ± ± Theory/Data 50 Data from EPJC72(2012)1926, NatComm2(2011)463, EPL101(2013)21003 Pythia log (xi ) 10 cut V I N C I A R O O T Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 14/19

15 det. of astronomy and theoretical hysics Di ractive cross sections Raidity ga size in h starting from h = ±4.9, T > 200 MeV ds/ddh F [mb] Data SaS DL MBR H1 Fit B 1 MC/Data Dh F Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 14/19

16 det. of astronomy and theoretical hysics Di ractive cross sections New imlementation: ABMST arametrization M X > M cut M X < M cut d 2 SD dtd =g PPPs P P(0) 2 P (t) +g PPR s R R(0) 2 P (t) +g RRP s P P(0) 2 R (t) +g RRR s R R(0) 2 R (t) + g 2 t 16 2 (t m ) 2 2 F 2 (t) 1 (t) 0 (s ) d 2 SD dtd =a(t, s)( t) 2 +b(s, t)( t ) d HM 2 ( c, t, s) t dtd c t ex(13.5(t +0.05)) + 4X c l m l l (s ml 2)2 +(m l l ) 2 l=1 Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 15/19

17 det. of astronomy and theoretical hysics Di ractive cross sections s =7TeV Total Low mass High mass Resonances d SD/d (mb) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 16/19

18 det. of astronomy and theoretical hysics Di ractive cross sections s =7TeV Total PPP PPR RRP RRR Pion d SD/d (mb) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 17/19

19 det. of astronomy and theoretical hysics Di ractive cross sections SD integrated cross section for <0.05 ABMST SaS 10 1 SD (mb) s (GeV) Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 18/19

20 det. of astronomy and theoretical hysics Conclusion and outlook Imlemented two new arametrizations of the total and elastic cross sections in Pythia 8. Imlemented new arametrization of SD cross sections. Comare the new SD arametrization to LHC data. Invent descrition for double- and central di raction close to ABMST descrition. Imlement alternative scenario, keeing ABMST good oints, but with di erent high-energy behavior. Christine O. Rasmussen Cross sections and di raction in PYTHIA 8 Aril 2016 Slide 19/19