Jet physics at the EIC and medium modifications

Transcription

1 Jet physics at the EIC and medium modifications Kyle Lee Stony Brook University INT 2018 week 7 11/12/18-11/16/18 1

2 Introduction Jets at the LHC Jets are produced copiously at the LHC At the LHC, % of ATLAS & CMS papers use jets in their analysis! 2

3 Introduction Jets at the EIC p SEIC p S LHC, p p TJ,EIC p p TJ,LHC Lower p T,J for EIC N J,EIC N J,LHC Smaller jet multiplicity for EIC Less contamination from underlying events and pileups Different circumstances compared with the LHC and New opportunities 3

4 Introduction Jets at the EIC p SEIC p S LHC, p p TJ,EIC p p TJ,LHC Lower p T,J for EIC N J,EIC N J,LHC Smaller jet multiplicity for EIC Less contamination from underlying events and pileups Role of higher power corrections? Different circumstances compared with the LHC and New opportunities 4

5 Introduction Application of jet studies at the LHC Precision probe of QCD Inclusive jets - perturbative probe 5

6 Introduction Application of jet studies at the LHC Precision probe of QCD What is the role of jet as a perturbative probe at the EIC? Inclusive jets - perturbative probe 6

7 Introduction Application of jet studies at the LHC Precision probe of QCD What is the role of jet as a perturbative probe at the EIC? Constrain BSM Models Fat jet from BSM signal Probe of quark gluon plasma 7

8 Introduction Application of jet studies at the LHC Precision probe of QCD What is the role of jet as a perturbative probe at the EIC? Constrain BSM Models Classification of different type of jets? Cold Nuclear Modification in e+a Fat jet from BSM signal Probe of quark gluon plasma 8

9 Introduction Application of jet studies at the LHC LHC HERA Typical event at the LHC and HERA 9

10 Introduction Application of jet studies at the LHC LHC HERA Typical event at the LHC and HERA What is the role of NP physics at the EIC? 10

11 Plans of this talk Inclusive jets Jet substructure measurements at the LHC Subtracted moments Conclusions 11

12 Inclusive Jets Inclusive Jets ep! jet + X, final lepton unobserved, high p T Boughezal, Petriello, Xing `18, Hinderer, Schlegel, Vogelsang `18, Uebler, Schfer, Vogelsang `17, Abelof, Boughezal, Liu, Petriello, `16 ep! e + jet + X p T Q 2, DIS, high and ep! e + jet + X, photoproduction, high p T and Q 2 < 1GeV 2 12

13 Inclusive Jets Inclusive Jets ep! jet + X, final lepton unobserved, high p T Boughezal, Petriello, Xing `18, Hinderer, Schlegel, Vogelsang `18, Uebler, Schfer, Vogelsang `17, Abelof, Boughezal, Liu, Petriello, `16 ep! e + jet + X p T Q 2, DIS, high and ep! e + jet + X, photoproduction, high p T and Q 2 < 1GeV 2 We focus on the photoproduction 13

14 Inclusive Jets Relevant Subprocesses LO DIS Resolved Direct 14

15 Inclusive Jets Relevant Subprocesses LO DIS does not contribute to high pt jet production LO DIS for the photoproduction. Resolved Direct 15

16 Inclusive Jets Photoproduction at the EIC f a/ H c ab H c ab direct resolved hadron d ep!ehx dp T d f b/p = X f a/l f b/p Hab c Dc h a,b,c d f b/p ep!ehx dp T d For polarized case, = X f a/l f b/p Hab c Dc h a,b,c Observe outgoing lepton to tag Q 2 Weizsäcker-Williams spectrum f a/l = P l f a/ For the direct process, f a/ = (1 x ). Require high and (near on-shell photon) p T Q 2 < 1GeV 2 See Jäger, Stratmann, Vogelsang `03 16

17 Inclusive Jets Polarized Gluon and Photon PDF Study in 2003, Jäger, Stratmann, Vogelsang `03 p s =100GeV A LL = d d = d ++ d + d ++ + d + f max = f f min =0 Sensitivity to polarized gluon pdf at low lab Sensitivity to polarized photon pdf at high lab Assumptions: D 0 c has been well-determined. Use inclusive jets as a perturbative probe! Study of polarized pdfs d ep!e 0 X dp T d = X a,b,c f a/l f b/p H c ab D 0 c 17

18 Inclusive Jets HERA PDF fit with and without jets Important for constraining gluon PDF Without jets With jets Role as a perturbative probe 18

19 Inclusive Jets Photoproduction at the EIC J c or G c f a/ J c or G c H c ab H c ab direct resolved hadron d ep!ehx dp T d f b/p = X a,b,c f a/l f b/p H c ab D h c d f b/p ep!ehx dp T d For polarized case, = X f a/l f b/p Hab c Dc h a,b,c Inclusive Jet d ep!ejetx dp T d = X a,b,c f a/l f b/p H c ab J c + O(R 2 ) +O( QCD p T R ) Power corrections relevant for EIC Replacement of the fragmentation function with the perturbative jet function. Sensitivity to the photon pdfs. Can be done for polarized and unpolarized case. Role of power corrections? Role as a perturbative probe 19 Jäger, Stratmann, Vogelsang `03 Chu, Aschenauer, Lee, Zheng `17 In collaboration with Elke Aschenauer and Brian Page

20 Inclusive Jets Unpolarized inclusive jets for photoproduction dσ /dηlab p jet T > 10 GeV res GRS, NLO+NLL dir, NLO+NLL res, Pythia dir, Pythia [pb], anti-k T, R =0.8 s =141GeV,Ep =250GeV,E e =20GeV 0.2 <y<0.8, Q 2 max < 1GeV2 At p T > 10 GeV, we see a good agreement. p T R ) power corrections must be studied. +O( QCD Power corrections 200 H c ab(p T ) J c (p T R) η lab 20 In collaboration with Elke Aschenauer and Brian Page

21 Angularity Jet angularity A generalized class of IR safe observables, angularity (applied to jet): a e+ e a = 1 E J X i2j pp a = 1 p T X i2j E i 2 ij a p T,i ( R ij ) 2 a = 2EJ p T Medium modifications a =1 g(girth) = 1 p T X i2j More relevant for the EIC 2 a e+ e a pp 0 = m2 J p 2 T p T,i ( R ij ) + O(( pp a ) 2 ) + O(( pp 0 )2 ) a =0 Power corrections Sterman et al. `03, `08, m/p T Hornig, C. Lee, Ovanesyan `09, Ellis, Vermilion, Walsh, Hornig, C.Lee `10, Chien, Hornig, C. Lee `15, Hornig, Makris, Mehen `16, Kang, KL, Ringer `18

22 Angularity Factorization for jet angularity Replace J c (z,p T R, µ)! G c (z,p T R, a,µ) When a R 2, Refactorize G c as G c (z,p T R, a,µ)= X i Z H c!i (z,p T R, µ) d C i a d S i a ( a C i a S i a )C i ( C i a,p T 1 a 2 a,µ)s i ( S i a, p T a R 1 a,µ) Power corrections m 2 +O p 2 T R2 Each pieces describe physics at different scales. Resums ( s ln R) n and ( s ln 2 R ) n 1/(2 a) a µ C p T ( a ) 1 2 a µ S p T a R 1 a 22 Kang, KL, Ringer `18

23 Non-perturbative Effects Non-perturbative Effects Non-perturbative effects: Figs from P. Bartalini et al. `11 Multi-Parton Interactions (MPI) (Underlying Events (UE)) Multiple secondary scatterings of partons within the protons may enter and contaminate jet. soft soft 23

24 Non-perturbative Effects Non-perturbative Effects Non-perturbative effects: soft soft Figs from P. Bartalini et al. `11 Multi-Parton Interactions (MPI) (Underlying Events (UE)) Multiple secondary scatterings of partons within the protons may enter and contaminate jet. Pileups Secondary proton collisions in a bunch may enter and contaminate jet. soft soft 24

25 Non-perturbative Effects Non-perturbative Effects Non-perturbative effects: Hadrons Hadronization Partons forming the jet eventually hadronizes. 25

26 Non-perturbative Effects Non-perturbative Model As gets smaller, (smallest scale) can approach a non-perturbative scale. µ S p T R We shift our perturbative results by convolving with non-perturbative shape function to smear Z Single parameter NP soft function : F apple (k) = 4k 2 apple exp Stewart, Tackmann, Waalewijn `15 Both hadronization and MPI effects in jet mass is well-represented by just shifting first-moments. The parameter apple is related to shift in the distribution: = pert + NP = pert + R apple = pert + R ( hadro. + MPI ) p T p T corresponds to non-perturbative effects coming primarily from the hadronization alone. apple had 1GeV d d dp T d = dkf apple (k) d pert d dp T d 2k apple R p T k 26

27 Angularity Phenomenology NLL ATLAS 200 < p T < 300 GeV single inclusive ungroomed jet s=7tev, anti-kt, R=1, η < < p T < 400 GeV dσ dmj 1 σ < p T < 500 GeV 500 < p T < 600 GeV dσ dmj 1 σ m J (GeV) m J (GeV) 27 Kang, KL, Liu, Ringer `18

28 Angularity Phenomenology NLL ATLAS 200 < p T < 300 GeV single inclusive ungroomed jet s=7tev, anti-kt, R=1, η < < p T < 400 GeV dσ dmj 1 σ < p T < 500 GeV Perturbative result 500 < p T < 600 GeV dσ dmj 1 σ m J (GeV) m J (GeV) 28 Kang, KL, Liu, Ringer `18

29 Angularity Phenomenology NLL NLL + NP(Ω =8) ATLAS 200 < p T < 300 GeV single inclusive ungroomed jet s=7tev, anti-kt, R=1, η < < p T < 400 GeV dσ dmj 1 σ < p T < 500 GeV 500 < p T < 600 GeV dσ dmj 1 σ m J (GeV) m J (GeV) 29 Kang, KL, Liu, Ringer `18

30 Angularity Phenomenology NLL NLL + NP(Ω =8) ATLAS 200 < p T < 300 GeV single inclusive ungroomed jet s=7tev, anti-kt, R=1, η < < p T < 400 GeV dσ dmj 1 σ < p T < 500 GeV Perturbative result NP shape function 500 < p T < 600 GeV dσ dmj 1 σ m J (GeV) m J (GeV) 30 Kang, KL, Liu, Ringer `18

31 Angularity Soft Drop Grooming Underlying Events (UE) are difficult to understand. How do we get a better hold of these soft uncorrelated contaminations (SUEs) in the jet? Hint : contamination generally from soft radiations. Groom jets to reduce sensitivity to wide-angle soft radiation. Hadrons 31

32 Angularity Phenomenology (groomed jet mass) 1 dσ/dlog σresum 10(m 2 J,gr /p2 T ) NLL NLL + NP(Ω =1) ATLAS s=13tev, anti-kt, R=0.8 p T > 600 GeV, η < 1.5 soft drop, z cut =0.1, β =0 Groomed inclusive di-jet β =1 β = log 10 (m 2 J,gr /p2 T ) log 10 (m 2 J,gr /p2 T ) log 10(m 2 J,gr /p2 T ) Developed the formalism for single inclusive groomed jet mass cross-section. Shows very good agreement with the data. k =1GeV =) Reduced contamination as expected. NP effects mostly from hadronization. See also ATLAS, arxiv: Larkoski, Marzani, Soyez, Thaler `14 Frye, Larkoski, Schwartz, Yan `16 32 Kang, KL, Liu, Ringer `18

33 Angularity EIC results NLL (R =0.4) NLL (R =0.8) s=141gev, 2 < ηlab < 4 Pythia(R=0.4) Pythia(R=0.8) 1 σ dσ/dlog 10(τa) p T > 10 GeV, anti-k T a =0.5 a =0 a = 0.5 a = 1 a = log 10 (τ a ) log 10 (τ a ) log 10 (τ a ) log 10 (τ a ) log 10 (τ a ) Perturbative results show good agreement without a need for a large shift. Small contamination from UE compared to the LHC. Non-perturbative effects 33 In collaboration with Elke Aschenauer and Brian Page

34 Angularity Shift from hadronization effects NLL NLL + NP(Ω a =0.5 GeV) Pythia 1 σ dσ/dlog 10(τa) s=141gev, anti-kt p T > 10 GeV, η < 2.5 R =0.8, a =0 Even without grooming, EIC results only require a small shift to agree with the Pythia result. ( ) QCD NP effects mostly from hadronization log 10 (τ a ) 34 Non-perturbative effects In collaboration with Elke Aschenauer and Brian Page

35 Angularity Power corrections Smaller power corrections for smaller R due to soft scales. Power corrections µ C p T ( a ) 1 2 a µ S p T a R 1 a 35 In collaboration with Elke Aschenauer and Brian Page

36 Moments Subtracted moments Heavy ion collisions produce large number of uncorrelated soft particles in the background contaminating the jet. 1. Develop a background subtraction techniques to identify true compositions of the jets. or 2. Define an observable insensitive to the uncorrelated background. a. Grooming (recursive algorithm) b. Subtracted moments 36 Kang, Makris, Mehen `17 Chien, Kang, KL, Makris, In Preparation

37 Moments Subtracted moments An observable that studies the correlation between p and a linearly additive substructure v T. Linear additivity : v = X i2signal v i signal + X j2sues Soft Uncorrelated Emissions (SUEs) v j SUEs i.e. jet mass ( 0 ) p J,signal + p J,SUEs p J,signal p J =2p T (only signal is correlated with the p T of the jet) 0 = m2 J p 2 T = p J p+ J p 2 T =2 1 p T (p + J,signal + p+ J,SUEs )=m2 J,signal p 2 T + 2 p T p + J,SUEs such separation gives the form of d dp T d 0 = Z dp + signal 2 J,SUEs f(p+ J,SUEs )d ( 0 p + J,SUEs dp T d 0 p ) T 37 Chien, Kang, KL, Makris, In Preparation

38 Moments d dp T d 0 = Z Subtracted moments dp + signal 2 J,SUEs f(p+ J,SUEs )d ( 0 p + J,SUEs dp T d 0 p ) T Moments of the distribution can be separated into contribution from signal and background: h 0 i = 1 Z d 0 0 Experiments often done with several bins of The binned version would give: d = h 0,corr i + 2 signal f d dp T p T p T range. h 0 i [n] = h 0,signal i [n] +2 f hp 1 T i[n] f = Z dk k f(k) Subtracted moments (independent of contribution from SUEs) : jk 0 = h 0 i [j] h 0 i 1 [k] hpt i[j] hp 1 T i[k] = h 0,signali [j] h 0,signal i 1 [k] hpt i[j] hp 1 T i[k] 38 Chien, Kang, KL, Makris, In Preparation

39 Moments Subtracted jet mass moments Independent of model, i.e. shape function. Useful to test modifications by medium with reduced sensitivity to uncorrelated radiations. 39 Chien, Kang, KL, Makris, In Preparation

40 Moments Testing limit of SUE independence Even at 50 pile ups, the subtracted moments of 0 gives same subtracted moments! 40 Chien, Kang, KL, Makris, In Preparation

41 Moments Testing limit of SUE independence p J,signal + p J,SUEs p J,signal p J =2p T At higher PU events, additivity starts failing since change in due to SUEs starts to become signficant. p T 41 Chien, Kang, KL, Makris, In Preparation

42 Moments 200 PU events Subtracted moments of is insensitive to 200 PU events. Useful for studying jets in high-luminosity LHC (HL-LHC) and in the heavy ion collisions! ˆ ˆ = m2 J p T = p J p+ J p T =2(p + J,signal + p+ J,SUEs ) 42 Chien, Kang, KL, Makris, In Preparation

43 Moments Quark and gluon fraction changes h i [n] = f g [n] h i [n] g + (1 f g [n] )h i [n] q Medium modifications Subtracted moments have discriminating power on models that predict changes in quark and gluon jet fractions due to the interaction with the medium. 43 Chien, Kang, KL, Makris, In Preparation

44 Conclusions Conclusions Formalisms for studying semi-inclusive jet production with and without a substructure measurement were introduced. Discussed phenomenology of angularities, which are useful substructure observables to test medium modifications. Going from pp to ep, contamination from non-perturbative soft radiations was shown to be reduced. (can expect similar reduction from pa to ea?) Going from pp to ep, size of power corrections for inclusive and substructure observables for the EIC were discussed. (can expect similar effects from pa to ea?) Subtracted moments are shown to be independent of soft uncorrelated emissions and can be useful to study jets in HL-LHC and heavy ion collisions. 44