hard-soft correlations in pa collisions

Transcription

1 hard-soft correlations in A collisions José Guilherme Milhano CENRA-IS (Lisbon) & CERN PH-H guilherme.milhano@cern.ch Correlations and fluctuations, IN, 3rd July 05

2 b-deendent npdfs :: imact arameter /centrality

3 A dijets and npdfs :: how successful? - S Pb 35 nb s NN,, = 5.0 ev > 0 GeV/c > 30 GeV/c φ > π/3, 4< η <5. All E dn dijet dη dijet dijet N C C + EPS09 Pb (a) nuclear effects are small within the robed kinematics but essential to describe data 0. R Pb R Pb.6 +. < y* < +.8 Pb R +. < y* < (b) (c) 0.4 ALAS Preliminary +Pb, 0-90% EPS09 calculation R Pb < y* < +. Pb R [GeV] +0.3 < y* < +0.8 [GeV] Data-NLO C C Unc. Ex. Unc. C+EPS09 C+EPS09 Unc. Ex. Unc. R Pb < y* < +0.3 Pb R [GeV] -0.8 < y* < -0.3 [GeV] η dijet η dijet R Pb < y* < -0.8 Pb R [GeV] -. < y* < -. [GeV].0 +Pb s NN = 5.0 ev 0.4 anti-k t, R =0.4 - L Pb dt = 7.8 nb - L dt = 4.0 b [GeV] [GeV] [GeV]

4 A dijets and npdfs :: how successful? arxiv: v [he-h] 0 Aug 04 s he gluon arton distribution functions (PDFs) in heavy nuclei are not articularly well constrained [, ]. Before the nuclear collisions at the LHC, one of the very few available data directly sensitive to the nuclear gluons at erturbative scales were from inclusive ion roduction in deuteron+gold collisions at RHIC [3, 4]. hese data were included into the EPS09 [5] global fit of nuclear PDFs (npdfs) and gave rise to the antishadowing and EMC-e ect for gluons shown in Figure (similar results have been recently obtained by the nceq collaboration [6]). However, one can interret the nuclear modifications seen in the RHIC ion data also as being due to nuclear e ects in the arton-to-ion Paukkunen, fragmentation Eskola, Salgado functions :: [7] and hence [he-h] reroduce the RHIC ion data ractically without any nuclear modifications EPS09 successful, others not [note anti-shadowing in EPS] Figure. Comarison of nuclear modifications for gluon

5 imact arameter deendence of npdfs - S Pb 35 nb = 5.0 ev s NN dn dijet dη dijet dijet N < η <5. E classes (GeV): < > 40,, φ > 0 GeV/c > 30 GeV/c, > π/3 (a) Pb η dijet imact arameter deendence of npdfs [ ] cannot account for large centrality deendence of dijet η distributions

6 centrality is not imact arameter N art 30 0 Glauber-MC -Pb s NN = 5.0 ev N art Glauber-MC Pb-Pb s NN =.76 ev Event fraction - - S Simulation HIJING Pb s NN = 5.0 ev 4< η <5. E (GeV): All < > b (fm) b (fm) -6-3 Multilicity 600 Glauber-MC -Pb s NN = 5.0 ev - -3 Multilicity Glauber-MC Pb-Pb s NN =.76 ev N art S :: [nucl-ex] N art N art -6 ALICE :: [nucl-ex] unlike in AA, multilicity [or activity] not tightly correlated to N art and N art not tightly correlated to imact arameter Fig. 7: o: Scatter lot of number of articiating nucleons versusimactarameter; Bottom: Scatter lot of multilicity versus the number of articiating nucleons from the Glauber fit for V0A. he quantities are calculated with a Glauber Monte Carlo of Pb (left) and Pb Pb (right) collisions. interaction: dσ inel = πdb NN[ e (σ soft+σ hard ) NN (b centrality classes necessarily mix NN )) ], wide range of (6) imact arameters where σ soft is the geometrical soft cross-section of 57 mb [8] related to therotonsizeand σ hard the energy deendent QCD cross-section for artonscatterings.further,asinthe clan model, there is a Poissonian robability both RHIC and LHC data show hallmarks of centrality fuzziness

7 imact arameter deendence of npdfs - S Pb 35 nb = 5.0 ev s NN dn dijet dη dijet dijet N < η <5. E classes (GeV): < > 40,, φ > 0 GeV/c > 30 GeV/c, > π/3 (a) Pb η dijet S :: [nucl-ex] imact arameter deendence of npdfs [ ] cannot account for large centrality deendence of dijet η distributions dijet =, = 0 GeV =) x 0.3(E. ev)

8 what is going on? Physics scenarios Presence of high-x jet is correlated with downward shift in Pb-going ΣE more jets in eriheral bins, fewer jets in central bins Alvioli et al, arxiv: : Reduction in size of roton configuration for events when a high-x arton is available for scattering - reduces N coll and multilicity Armesto et al, arxiv: Reduction in energy of roton, due to removal of high-x arton - reduces multilicity and shifts raidity Bathe et al, arxiv: Reduction in gluon content of rojectile roton undergoing a high-x arton-arton scattering - reduces multilicity Kordell & Majumder - revious talk Each of these can exlain asects of existing data: how do we exlore this exerimentally? 3 P. Steinberg [ALAS] :: HP05

9 simle roof of rincile Armesto, Gulhan, Milhano:: [he-h] Event by event matching PYHIA Jets η dijet x s NN = E E Pb ( x ) η = log E ( x ) E Pb HIJING Underlying event E, E Pb he energy that goes in hard scattering from one roton in PYHIA taken away from roton in HIJING x Pb is not taken into account in HIJING Good aroximation when N coll is large and x Pb is small

10 simle roof of rincile Armesto, Gulhan, Milhano:: [he-h] Event by event matching PYHIA Jets η dijet x s NN = E E Pb ( x ) η = log E ( x ) E Pb HIJING Underlying event E, E Pb he energy that goes in hard scattering from one roton in PYHIA taken away from roton in HIJING x Pb is not taken into account in HIJING E truth : Sum of of articles at large η from HIJING MB events Searate in centrality classes by slicing E truth in same fractions as in data Scale the E truth values with a constant so that the lower bound of highest centrality class in data and MC match (e.g. Scale factor ~ 0.7 for S dijet measurement) Good aroximation when N coll is large and x Pb is small Obtain E raw comarable to what is measured by exeriment

11 MB vs dijet events Bias towards small imact arameter collisions with higher E on both sides. PYHIA+ HIJING MB N coll scaled DAA MB Dijet events Doga Gulhan HI Jet Worksho 9 th July 04

12 dijet η shift [S] large dijet energy requirement shifts E down for low E [eriheral] events model fails as Pb energy deletion becomes imortant to calculate activity

13 η dijet distributions PYHIA+HIJING % % x matched S ) All dijet )/(dn/dη dijet (dn/dη % η dijet Pb % η dijet ) All dijet )/(dn/dη dijet (dn/dη % η dijet

14 R Pb [ALAS] :: η inclusive PYHIA+HIJING x matched R Pb η -η <3 jet 0-% -0% R Pb % R Pb R Pb % 40-60% % (GeV/c) (GeV/c) (GeV/c) NOE: centrality determination from only Pb side

15 R Pb [ALAS] :: η inclusive R Pb PYHIA+HIJING η -η <3 jet 0-% x matched -0% R Pb % N coll from ALAS [model deendent] :: don t add to unity R Pb R Pb % 40-60% % (GeV/c) (GeV/c) (GeV/c) NOE: centrality determination from only Pb side

16 R Pb [ALAS] :: η inclusive N coll from ALAS [model deendent] :: don t add to unity self-consistent determination of N coll [events that ass the cuts in in the model]adds to unity NOE: centrality determination from only Pb side

17 R Pb [ALAS] :: central R Pb.5.<η-η <.8 ALAS 0-% PYHIA+HIJING 0-% x matched.<η-η <. 0.8<η-η <. 0.3<η-η < <η-η < <η-η < <η-η < <η-η <-. R Pb R Pb (GeV/c) (GeV/c) (GeV/c) (GeV/c) excellent overall descrition [N coll from ALAS] deviations on Pb side :: same model limitation as before Pb

18 R Pb [ALAS] :: mid-central.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η <0.8.5 R Pb.5-0.3<η-η < <η-η < <η-η < <η-η <-. R Pb R Pb ALAS 0-30% PYHIA+HIJING 0-30% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) deviations due to neglecting of npdf effects [anti-shadowing] roton PDFs used for both roton and nucleon from Pb Pb

19 R Pb [ALAS] :: eriheral.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η <0.8.5 R Pb.5-0.3<η-η < <η-η < <η-η < <η-η <-. R Pb R Pb ALAS 60-90% PYHIA+HIJING 60-90% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) not good outside model alicability [N coll eaks at, x Pb becomes imortant] Pb

20 hysics scenarios and imlementation high-x arton in roton

21 hysics scenarios and imlementation high-x arton in roton Bzdak, Skokov,Bathe fewer other artons [gluons] Alvioli, Cole, Frankfurt, Pereelitsa, Strikman smaller roton Armesto, Gulhan, Milhano Kordell, Majumder deleted roton energy for UE

22 hysics scenarios and imlementation high-x arton in roton fewer other artons [gluons] smaller roton deleted roton energy for UE

23 hysics scenarios and imlementation high-x arton in roton fewer other artons [gluons] smaller roton deleted roton energy for UE alternative hrasings of same hysics

24 hysics scenarios and imlementation high-x arton in roton fewer other artons [gluons] smaller roton deleted roton energy for UE alternative hrasings of same hysics imlementations [and hysical effects] are not indeendent, rather they should be equivalent even if hrased rather orthogonally

25 hysics scenarios and imlementation high-x arton in roton fewer other artons [gluons] smaller roton deleted roton energy for UE alternative hrasings of same hysics imlementations [and hysical effects] are not indeendent, rather they should be equivalent even if hrased rather orthogonally formal equivalence not straightforward to show [ossibly a surious exercise] imlementations SHOULD NO, CANNO be combined :: results should be comared

26 jet R A / hadron R A / jet FFs

27 jet R A / hadron R A / jet FFs

28 what is going on? Hard robes access the artonic structure of the nucleus. +Pb rocesses are comared to by: Pb. Hard Probes in +Pb collisions 0.8, R Pb R* S Pb - = 5.0 ev, L = 35 nb s NN NLO (npdf=eps09, FF=fDSS), y=0 S η < ALICE η <0.3 Fully correlated syst. uncert. 0.4 otal syst. uncert. 0. < Pb > uncertainty 3 ard robes access the artonic structure of the nucleus. 0 +Pb rocesses are comared to by: - < Pb > = mb [GeV/c] harged-article nuclear modification factors measured by S in h < (filled by ALICE in h < 0.3 (oen squares), are comared to the NLO QCD reef. [53]. he theoretical uncertainty is based on the EPS09 error sets. For the S nt, the shaded band at unity and 0.6 reresents the uncertainty in the Glauber endence of charged-article roduction in Pb collisions ALICE Collaboration of h Pb i, the smaller uncertainty band around the data oints shows the fully corertainties and the total systematic uncertainty is shown by the larger band (see athe ALICE measurement, the total systematic uncertainties, excluding the normalertainty of 6%, are shown ± with oen hboxes. ±, -Pb s NN = 5.0 ev, NSD (ALICE) h, Pb-Pb (ALICE).8 ± γ, Pb-Pb =.76 ev, 0-% (S).6 in the charged-article roduction at Z 0, high Pb-Pb s = beyond.76 ev, 0-% NLO(S) NN exectations, without ding increase.4 the jet R Pb [5, 6]. We note that the gluon-to-hadron fragmenions are not well constrained in collisions at LHC energies [7], although such. s should largely cancel in ratios of cross sections. mary, R Pb R PbPb 0.8, Pb-Pb (S) s arxiv: h NN ± s =.76 ev, 0-5% W, Pb-Pb s NN NN =.76 ev, 0-% (S) 0.6 rticle sectra have been measured in Pb collisions at s NN = 5.0 ev in the transentum range of < < 0 GeV/c for seudoraidities u to h =.8. he ckward yield asymmetry 0. has been measured as a function of for three bins in h. GeV/c, the charged-article roduction is enhanced in the direction of the Pb beam, 0 e agreement with 0 nuclear 0 shadowing exectations he 80 nuclear 90 0 modification factor dity, relative to a reference sectrum (GeV/c) interolated or mass from(gev/c measurements ) at lower collision energies, rises above unity at high reaching an RPb value of.3.4 at V/c. he observed enhancement is larger than exected from NLO QCD redicnclude ransverse antishadowing momentum deendence effects of the in nuclear the nuclear modification PDFs factor in Rthis kinematic range. Future Pb of charged articles (h ± )meaminimum-bias of the (NSD) sectra Pb collisions of jetsat and s NN urement charged = 5.0 ev articles in comarison in to data collisions on the nuclear at a modifica- R PbPb center-ofytorof 5.0 in ev central ispb Pb necessary collisions toat better s NN = constrain.76 ev. he thepb Pb fragmentation data are for charged functions article and [9, 6], also 0 ± nhancement of charged sectra at high. uggestive of modification of jet internal structure. Inclusive jet rate in +Pb collisions is only slightly enhanced with resect to. Consistent with npdf exectations. Figure 8: he inclusive jet nuclear modification factor R Pb as a function of jet in s NN = 5.0 ev Pb collisions using the extraolated reference. he error bars on the data oints are the statistical uncertainties and the oen boxes reresent the systematic uncertainties. he shaded boxes are the systematic uncertainties due to the reference extraolation. he shaded area around R Pb = reresents the luminosity uncertainty in the Pb measurement. Charged jets in Pb ch jets R Pb ALICE -Pb s NN = 5.0 ev Charged jets, anti-k, η < lab Reference: Scaled jets 7 ev Global normalization uncertainty Resolution arameter R = (GeV/c), ch jet Resolution arameter R = 0.4 ALICE Collaboration (GeV/c), ch jet Fig. 5: (Color online) Nuclear modification factors R Pb of charged jets for R = 0. (left)andr = 0.4 (right). he combined global normalization uncertainty from Pb,thecorrectiontoNSDevents,themeasuredcross section, and the reference scaling is deicted by the box around unity.

29 what is going on? Charged hadron RPb 3 Pb, R Pb, R R* Pb R* Pb S Pb S Pb - = 5.0 ev, L = 35 nb s NN NLO (npdf=eps09, FF=fDSS), y=0 s NN S η < NLO (npdf=eps09, FF=fDSS), y=0 ALICE η <0.3 S η < ALICE η <0.3 [GeV/c] - < Pb > = mb Fully correlated < syst. uncert. Pb > = mb otal syst. uncert. Fully < correlated Pb > uncertainty syst. uncert. otal syst. uncert. Low (< GeV/c) article roduction dominated by softer scattering Mid (-5 GeV/c) range RPb is = 5.0 ev, L = 35 nb < Pb > uncertainty [GeV/c] High rise beyond theoretical exlanation M. B. onjes (UMD) Nuclear modification of jet and hadron sectra with S, HP S EPJC 7 (0) 945 Paukkunen arxiv.org: ALICE EurPhysJ C74 (04) 3054 ALICE-S differences rimarily from reference

30 what is going on? Charged hadron RPb 3 Pb, R Pb, R R* Pb R* Pb S Pb S Pb - = 5.0 ev, L = 35 nb s NN NLO (npdf=eps09, FF=fDSS), y=0 s NN S η < NLO (npdf=eps09, FF=fDSS), y=0 ALICE η <0.3 S η < ALICE η <0.3 [GeV/c] - < Pb > = mb Fully correlated < syst. uncert. Pb > = mb otal syst. uncert. Fully < correlated Pb > uncertainty syst. uncert. otal syst. uncert. Low (< GeV/c) article roduction dominated by softer scattering Mid (-5 GeV/c) range RPb is = 5.0 ev, L = 35 nb < Pb > uncertainty [GeV/c] High rise beyond theoretical exlanation M. B. onjes (UMD) Nuclear modification of jet and hadron sectra with S, HP IS I? S EPJC 7 (0) 945 Paukkunen arxiv.org: ALICE EurPhysJ C74 (04) 3054 ALICE-S differences rimarily from reference

31 what is going on? [vox ouli]

32 what is going on? [vox ouli] [some] data [or scaled reference] is wrong

33 what is going on? [vox ouli] [some] data [or scaled reference] is wrong ersonally cannot do anything about it

34 what is going on? [vox ouli] [some] data [or scaled reference] is wrong ersonally cannot do anything about it [exotic] mechanism in A roduces high- t ions [not from a jet]

35 what is going on? [vox ouli] [some] data [or scaled reference] is wrong ersonally cannot do anything about it [exotic] mechanism in A roduces high- t ions [not from a jet] such ions would be reconstructed as jets and show u also in jet sectrum [standard] hysics is being overlooked

36 at a risk Milhano, Wiedemann, Za

37 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage

38 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators

39 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators colour reconnections are an essential rescrition for descrition of average t / low t sectrum

40 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators colour reconnections are an essential rescrition for descrition of average t / low t sectrum colour reconnections :: ossibility of colour neutralization involving artons with different colour histories that haen to be close in (η,φ) lane

41 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators colour reconnections are an essential rescrition for descrition of average t / low t sectrum colour reconnections :: ossibility of colour neutralization involving artons with different colour histories that haen to be close in (η,φ) lane no available [validated] A event generator

42 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators colour reconnections are an essential rescrition for descrition of average t / low t sectrum colour reconnections :: ossibility of colour neutralization involving artons with different colour histories that haen to be close in (η,φ) lane no available [validated] A event generator At hadronization stage A and differ in magnitude of UE and colour correlations of artons

43 at a risk Milhano, Wiedemann, Za modification of hadron sectrum without modification of jet sectra can only originate at the hadronization stage hadronization not under theoretical control but successfully modelled in event generators colour reconnections are an essential rescrition for descrition of average t / low t sectrum colour reconnections :: ossibility of colour neutralization involving artons with different colour histories that haen to be close in (η,φ) lane no available [validated] A event generator use generator with augmented UE [ 3 times MB ] and scrambled initial colour correlations At hadronization stage A and differ in magnitude of UE and colour correlations of artons

44 colour reconnections and high-t

45 colour reconnections and high- t what do colour reconnections have to do with high- t?

46 colour reconnections and high- t what do colour reconnections have to do with high- t? hadronic multilicity from colour neutral object dictated by its invariant mass M inv = k [cosh ( k ) cos ( k )] k R

47 colour reconnections and high- t what do colour reconnections have to do with high- t? hadronic multilicity from colour neutral object dictated by its invariant mass high- t hadrons originate from low invariant mass clusters/strings where high- t arton retains most [or all] of its momentum M inv = k [cosh ( k ) cos ( k )] k R

48 colour reconnections and high- t what do colour reconnections have to do with high- t? hadronic multilicity from colour neutral object dictated by its invariant mass high- t hadrons originate from low invariant mass clusters/strings where high- t arton retains most [or all] of its momentum colour neutralization of high- t arton with low- t arton from UE favours roduction of hard hadrons low UE high UE higher invariant mass :: higher multilicity :: softer lower invariant mass :: lower multilicity :: harder M inv = k [cosh ( k ) cos ( k )] k R

49 non-decaying clusters [high- t hadrons]

50 non-decaying clusters [high- t hadrons] M cut >M inv k R maximum invariant mass for non-decaying cluster

51 non-decaying clusters [high- t hadrons] M cut >M inv k R maximum invariant mass for non-decaying cluster robability of soft arton from UE within R roortional to UE multilicity R / t

52 non-decaying clusters [high- t hadrons] M cut >M inv k R maximum invariant mass for non-decaying cluster robability of soft arton from UE within R roortional to UE multilicity R / t for fixed UE multilicity P CR t

53 non-decaying clusters [high- t hadrons] M cut >M inv k R maximum invariant mass for non-decaying cluster robability of soft arton from UE within R roortional to UE multilicity R / t for fixed UE multilicity P CR t effect dies out much slower than other ower corrections

54 generic effect [very difficult to argue away]

55 generic effect [very difficult to argue away] does it work?

56 event generator evidence [SHERPA] dσ ch /d [b/gev] charged articles SHERPA normal underlying event SHERPA enhanced underlying event reliminary dσ jet /d [b/gev] 5 jets 4 3 SHERPA normal underlying event SHERPA enhanced underlying event reliminary R MC 0.8 R MC [GeV] [GeV] smaller than in data but clear effect :: much more statistics needed [only very conservative CR considered]

57 outlook origin of centrality binning roblems inned down to hard+ue strong correlation strong constraint for hard+ue A MC :: seems worth the trouble as essential to access imact arameter deendence a laboratory for roton-size studies :: no clear ath ut forward R A meets R A conundrum may have natural exlanation very difficult to argue away violation of universality of FFs :: fundamental hysics oortunity can be checked in high multilicity need validated A MC

58 backus

59 correlations detailed 3 >0 GeV/c, >30 GeV/c, φ < π/3, η <3 PYHIA ruth η dijet x -

60 correlation detailed :: different estimators 0.6 PYHIA + HIJING Matched x > 80 GeV/c Fractions defined by: Pb E +E Pb E E at 4< η <5 > <η dijet forward E

61 N coll centrality deendence >0 GeV/c, η <3, jet Centrality definition: Pb Σ [3.<η<4.9] E Minimum bias HIJING x matched PYHIA+HIJING Event fraction Event fraction % % N coll % N coll Event fraction Event fraction Event fraction Event fraction % % -5-0 % % N coll N coll N coll N coll bin migration but overall distribution unchanged

62 N coll definitions :: 0-% R Pb.5.<η-η <.8 ALAS 0-% PYHIA+HIJING 0-% x matched.<η-η <. 0.8<η-η <. 0.3<η-η <0.8 HIJING.5-0.3<η-η < <η-η < <η-η < <η-η <-. R Pb R Pb (GeV/c) (GeV/c) (GeV/c) (GeV/c) same event ALAS R Pb.5.<η-η <.8 ALAS 0-%.5 PYHIA+HIJING 0-% x matched R Pb.<η-η <. R Pb.5 0.8<η-η <. R Pb.5 0.3<η-η <0.8 R Pb.5.<η-η <.8 ALAS 0-%.5 PYHIA+HIJING 0-% x matched R Pb.<η-η <. R Pb.5 0.8<η-η <. R Pb.5 0.3<η-η < < η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) < η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) R Pb R Pb R Pb R Pb R Pb R Pb R Pb R Pb (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c)

63 N coll definitions :: 0-30%.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η < R Pb R Pb R Pb R Pb HIJING.5-0.3< η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) R Pb R Pb R Pb R Pb ALAS 0-30% PYHIA+HIJING 0-30% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) same event ALAS.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η <0.8.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η < R Pb R Pb R Pb R Pb R Pb.5-0.3<η-η < <η-η < <η-η < <η-η < < η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) R Pb R Pb R Pb R Pb R Pb R Pb ALAS 0-30% PYHIA+HIJING 0-30% matched x ALAS 0-30% PYHIA+HIJING 0-30% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c)

64 N coll definitions :: 60-90%.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η <0.8 R Pb.5 R Pb.5 R Pb.5 R Pb.5 HIJING.5-0.3< η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) R Pb R Pb R Pb R Pb ALAS 60-90% PYHIA+HIJING 60-90% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) same event ALAS.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η <0.8.<η-η <.8.<η-η <. 0.8<η-η <. 0.3<η-η < R Pb R Pb R Pb R Pb R Pb.5-0.3< η-η (GeV/c) < < η-η<-0.3 (GeV/c) -.< η-η<-0.8 (GeV/c) -.<η-η<-. (GeV/c) <η-η < <η-η < <η-η < <η-η <-. R Pb R Pb R Pb R Pb R Pb R Pb ALAS 60-90% PYHIA+HIJING 60-90% matched x ALAS 60-90% PYHIA+HIJING 60-90% matched x (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c) (GeV/c)

65 hard rocess / UE [ centrality ] correlation Event fraction 0.5 η <3, φ >π/3 Minimum bias 0. PYHIA and HIJING matched according to x, jet >0,,, >30 GeV/c E dijet E dijet < 350 GeV > 00 GeV Event fraction 0.5 η <3, φ >π/3 Minimum bias 0. PYHIA and HIJING matched according to x, jet >0,,, >30 GeV/c η η dijet dijet - η - η < > E [4< η <5.] E [4< η <5.]

66 with fixed roton side E > <η dijet S Pb 35 nb = 5.0 ev s NN E (GeV): All < φ > π/3, 9 - > > 0, > 30 GeV/c,, Pb E (GeV) LAB > dijet <η E LAB (GeV) PYHIA+HIJING ruth Matched x > 80 GeV/c Pb E LAB (GeV) same trend and magnitudes in data and MC lowest activity [lowest N coll ] not described :: over simlistic treatment of Pb see recoil of UE [different sloe for each E class]

67 no CR vs CR [not colour scrambled] charged articles (background subtracted) jets R MC SHERPA w/o CR SHERPA w/ CR R MC SHERPA w/o CR SHERPA w/ CR Ratio 0.8 Ratio [GeV] [GeV]