Jet measurements in heavy-ion collisions with the ATLAS detector

Transcription

1 Jet measurements in heavy-ion collisions with the detector Laura Havener, Columbia University on behalf of the Collaboration ISMD 07 laxcala City, Mexico hursday, Setember th, 07

2 Jets in HI collisions? q q Jets in + collisions

3 Jets in HI collisions? q q q q Jets in + collisions Jets in Pb+Pb A+A collisions Jet quenching: henomena where artons are exected to lose energy in interactions with the hot dense medium roduced in HI collisions. s are thus sensitive to the microscoic structure of the medium. 3

4 ) dn/da (/N J evt Many measurements of quenching done in HI collisions at the LHC and RHIC. 3 Jets in HI collisions Jet measurements with in run ( snn =.76 ev): Di asymmetry: dis are more asymmetric in Pb+Pb comared to MC 0-0% J J ) dn/da dn/da evt evt (/N (/N % 0-00% ) dn/da (/N J evt 3 PRL 05 (00) 5303 =.76 ev 0-0% Pb+Pb L int =.7 µb A J AA J J A J

5 Jets in HI collisions Many measurements of quenching done in HI collisions at the LHC and RHIC. Jet measurements with in run ( snn =.76 ev): Di asymmetry Jet suression: yields are R AA R AA suressed in Pb+Pb comared to R AA 0 0 anti-k t R = 0. s =.76 ev PRL (05) Pb+Pb data, 0. nb 03 data,.0 b 0-0 % 30-0 % % y 0.3 < y <. < - - raidity deendence 0. < y < [GeV] 5

6 Jets in HI collisions.6 Many measurements of quenching done in. HI collisions at the LHC and RHIC. Jet measurements with in run ( snn =.76 ev): Di asymmetry Jet suression Jet fragmentation: the internal structure.8 of s is modified. in Pb+Pb Pb+Pb 0-0% > 00 GeV Pb+Pb 0-30% > 00 GeV Pb+Pb data, 0. nb.6-03 data,.0 b. Pb+Pb 0-0% < < 6 GeV.6.. Pb+Pb 60-80% Pb+Pb 60-80%.8.8 > 00 GeV 00 < < 6 GeV Pb+Pb 0-30% 0 Pb+Pb Pb+Pb data, % nb - s Pb+Pb NN = % ev. 03 data,.0 b anti-k R = 0. s. Pb+Pb 0-0% t 00 < < 6 GeV < < 58 GeV Pb+Pb 0-0%.8.8 > 58 GeV Pb+Pb 0-0%.8 > 00 GeV < < 6 GeV < < 58 GeV D() Pb+Pb 0-0% Pb+Pb 0-30% Pb+Pb 30-0% > 00 GeV > 00 GeV > 00 GeV =.76 ev.6 anti-k R = 0. s t. Pb+Pb 0-0%.8. 6 < < 58 GeV Pb+Pb data, 0. nb - 03 data,.0 b Pb+Pb 0-0%.8 00 < 00 < 00 < Pb+Pb 0-30% Pb+Pb 30-0% EPJC (07) 77: < 6 GeV.6 < 6 GeV.8 < 6 GeV.8 Pb+Pb 0-0%.6 > 58 GeV

7 J ) dn/da dn/da J evt evt (/N (/N Jets in HI collisions Jet measurements with in run ( snn =.76 ev): PRL 05 (00) Many measurements of quenching done in HI collisions at the LHC and RHIC. Di asymmetry Jet suression Jet fragmentation etc. 0-0% 0-00% A J A J J ) dn/da ) dn/da R AA R AA R AA 0 0 anti-k t R = 0. s =.76 ev Pb+Pb 60-80% [GeV] s 0-0% PRL 0-0% (05) 0730 =.76 ev 0-0% NN =.76 ev 0-0%.8 > 00 GeV Pb+Pb 0-30% 3 Pb+Pb 0 Pb+Pb data, 0. nb Pb+Pb 0-30% Pb+Pb Pb+Pb 0-30% - here is something data,.0 b.8 > 00 GeV.8 Pb+Pb < 6 0-0% GeV.8 00 < - L L.8 6 < < 58 GeV int =.7 µb int =.7 µb.8.8. Pb+Pb 0-0%.8.6 > 00 GeV < < 6 GeV.6.6 here but we need to dig deeer J evt evt (/N (/N A J A J ) dn/da (/N J evt ) D() R Pb+Pb 0-0% > 00 GeV ) R D() 0 Pb+Pb data, 0. nb 03 data,.0 b 0-0 % 30-0 % % A J ) dn/da (/N y <. 0.3 < y < 0 Pb+Pb data, 0. nb.6-03 data,.0 b. Pb+Pb 0-0% < < 6 GeV.6.. < y <.. J evt R ) D() EPJC (07) 77: 379 A J Pb+Pb 0-0% Pb+Pb 0-30% Pb+Pb 30-0% > 00 GeV > 00 GeV > 00 GeV =.76 ev.6 anti-k R = 0. s t. Pb+Pb 0-0%.8. 6 < < 58 GeV.6.. ) D() 7

8 Jets in HI collisions New results dig deeer to better understand quenching: More recise measurements with better control over the background subtraction and systematics and unfolded so they can be directly comared to theory. Better statistics allows for measurements at high and differentially in and raidity that address secific questions such as what is the flavor deendence of quenching and what haens to suression at high. Measurements at different center-of-mass energies. What haens in boson+ systems, etc. 8

9 Jet reconstruction: rocedure Jets are reconstructed using the anti-k t algorithm for R=0. in, +Pb, and Pb+Pb collisions. Uncorrelated underlying event (UE) contributes background energy inside that cone that varies with η and Φ and hugely event-by-event. Background is subtracted using an iterative rocedure that is modulated by harmonic flow. de dηdφ de dη ( + n Measured quantities are influenced by both the effect of the UE and the detector. v n cos (n(φ ψ n ))) Removed through an unfolding rocedure that is under better control if UE is subtracted -by-. 9

10 Jet reconstruction: erformance Measure of how well you can do any measurement. MC s (with a simulated detector resonse) are embedded into real Pb+Pb data and reconstructed in the same way as data. Jet energy scale (JES) and energy resolution (JER) are the mean and the width of the reco / true distribution. 0

11 Jet reconstruction: erformance..08 Simulation Preliminary Powheg + Pythia 8 Pb+Pb data overlay Measure of how well you can do any measurement. MC s (with a simulated detector resonse) are embedded into real Pb+Pb data and reconstructed in the same way as data. Jet energy scale (JES) and energy resolution (JER) are the mean and the width of the reco / true distribution. JES is ~% above 00 GeV for 0-0% meaning the additive UE background was removed to within % of the energy. truth / reco anti-k t 0-0 % 0-0 % 0-30 % 30-0 % 0-50 % % % % = 5.0 ev R = 0. HI s, η < truth [GeV]

12 Jet reconstruction: erformance..08 Simulation Preliminary Powheg + Pythia 8 Pb+Pb data overlay Measure of how well you can do any measurement. MC s (with a simulated detector resonse) are embedded into real Pb+Pb data and reconstructed in the same way as data. Jet energy scale (JES) and energy resolution (JER) are the mean and the width of the reco / true distribution. JES is ~% above 00 GeV for 0-0% meaning the additive UE background was removed to within % of the energy. truth / reco ] truth / reco σ[ anti-k t 0-0 % 0-0 % 0-30 % 30-0 % 0-50 % % % % = 5.0 ev R = 0. HI s, η < Powheg + Pythia 8 Pb+Pb data overlay anti-k t Fits: σ = = 5.0 ev R = 0. HI s, η <.8 a b truth truth truth [GeV] 0-0 % 0-0 % 0-30 % 30-0 % 0-50 % % % % 0.05 Simulation Preliminary truth [GeV] JER in 0-0% is ~6% at 00 GeV and decreases to a constant value at ~6%. c

13 arxiv: Di asymmetry A traditional method of studying quenching is through the di asymmetry. q q he s lose different amounts of energy because they travel different aths in the lasma. A+A 3

14 arxiv: Di asymmetry A traditional method of studying quenching is through the di asymmetry. q q he s lose different amounts of energy because they travel different aths in the lasma. x J = A+A Use ratio of sub-leading to the leading.

15 arxiv: Di asymmetry A traditional method of studying quenching is through the di asymmetry. q q he s lose different amounts of energy because they travel different aths in the lasma. x J = A+A Use ratio of sub-leading to the leading. Measure xj as a function of leading and centrality. Comare to dis. Kinematic selections: two highest s in each event with > 00 GeV and > 5 GeV and Δϕ > 7π/8. 5

16 arxiv: Di asymmetry A traditional method of studying quenching is through the di asymmetry. q q he s lose different amounts of energy because they travel different aths in the lasma. x J = A+A Use ratio of sub-leading to the leading. Measure xj as a function of leading and centrality. Comare to dis. Kinematic selections: two highest s in each event with > 00 GeV and > 5 GeV and Δϕ > 7π/8. Unfolded using D Bayesian unfolding in and. 6

17 xj distribution dn dx J N < < 6 GeV 0-0 % Pb+Pb anti-k t R = 0. s 0-0 % centrality deendence.5 00 < < 6 GeV 0-0% 0-0% dn dx J N % 30-0 % % 30-0% dn dx J N % =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b % % 60-80% arxiv: x J x J 7

18 xj distribution dn dx J N < < 6 GeV 0-0 % Pb+Pb anti-k t R = 0. s 0-0 % centrality deendence.5 00 < < 6 GeV 0-0% 0-0% xj in Pb+Pb is more asymmetric in more central collisions. dn dx J N % 30-0 % % 30-0% dn dx J N % =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b % % 60-80% arxiv: x J x J 8

19 xj distribution dn dx J N < < 6 GeV 0-0 % Pb+Pb anti-k t R = 0. s 0-0 % centrality deendence.5 00 < < 6 GeV 0-0% 0-0% xj in Pb+Pb is more asymmetric in more central collisions. he most robable configuration for collisions is xj ~. For central Pb+Pb collisions it is xj ~. dn dx J N dn dx J N % 30-0 % 0-30% 30-0% 0-60 % =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b % % 60-80% arxiv: x J x J 9

20 xj distribution dn dx J N < < 6 GeV 0-0 % Pb+Pb anti-k t R = 0. s 0-0 % centrality deendence.5 00 < < 6 GeV 0-0% 0-0% xj in Pb+Pb is more asymmetric in more dn dx J N % 30-0 % central collisions. he most robable configuration for collisions is xj ~. For central Pb+Pb collisions it is xj ~. dn dx J N % 30-0% 0-60 % =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b % As Pb+Pb becomes more eriheral the xj is like in. arxiv: % x J 60-80% x J 0

21 deendence xj distribution 0-0% dn dx J N arxiv: % Pb+Pb 00 < < 6 GeV 6 < anti-k t R = 0. s < 58 GeV.5 00 < < 6 GeV 6 < < 58 GeV dn dx J N < < 00 GeV =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b > 00 GeV.5 58 < < 00 GeV > 00 GeV x J x J

22 deendence xj distribution 0-0% dn dx J N arxiv: % Pb+Pb 00 < < 6 GeV 6 < anti-k t R = 0. s < 58 GeV Significant deendence on < < 6 GeV 6 < < 58 GeV dn dx J N < < 00 GeV =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b > 00 GeV.5 58 < < 00 GeV > 00 GeV x J x J

23 deendence xj distribution 0-0% dn dx J N arxiv: % Pb+Pb 00 < < 6 GeV 6 < anti-k t R = 0. s < 58 GeV 00 < < 6 GeV 6 < < 58 GeV Significant deendence on. Pb+Pb becomes like at high. dn dx J N < < 00 GeV =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b > 00 GeV.5 58 < < 00 GeV > 00 GeV x J x J 3

24 deendence xj distribution 0-0% dn dx J N dn dx J N arxiv: % Pb+Pb 00 < 58 < < 6 GeV < 00 GeV x J 6 < anti-k t R = 0. s =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b < 58 GeV 00 < < 6 GeV 6 < < 58 GeV > 00 GeV 58 < < 00 GeV > 00 GeV x J Significant deendence on. Pb+Pb becomes like at high. Probe of the flavor deendence because quark/gluon fractions change with!

25 x J γ γ- asymmetry -CONF-06-0 =,, γ he hoton does not interact with the lasma so the energy loss of the recoiling can be robed. Measured xjγ for γ > 60 GeV,, > 30 GeV, Δϕ > 7π/8 5

26 x J γ γ- asymmetry -CONF-06-0 =, 0-0%, γ he hoton does not interact with the lasma so the energy loss of the recoiling can be robed. Measured xjγ for γ > 60 GeV,, > 30 GeV, Δϕ > 7π/8 Pb+Pb has more asymmetric airs than and MC. increasing γ (/N γ )(dn/dx Jγ ) < γ < 80 GeV 0-0% Pb+Pb, 0.9 nb -, 6 b PYHIA Data Overlay γ 80 < < 00 GeV Preliminary 5.0 ev 00 < γ < 50 GeV x Jγ Corrected for background and JES but not unfolded. x Jγ x Jγ 6

27 γ- asymmetry -CONF-06-0 (/N γ )(dn/dx Jγ ).6. - Pb+Pb, 0.9 nb -, 6 b PYHIA 8 + Data Overlay Preliminary γ 60 < < 80 GeV 5.0 ev centrality deendence 60 < γ < 80 GeV % 0-0% 0 (/N γ )(dn/dx Jγ ) % 30-50% he distributions become less asymmetric with increasing centrality. 0 0 x Jγ 0 Jγ Jγ x Jγ 7

28 γ- asymmetry -CONF-06-0 (/N γ )(dn/dx Jγ ) (/N γ )(dn/dx Jγ ) Pb+Pb, 0.9 nb -, 6 b PYHIA 8 + Data Overlay 0-0% 0-30% 0 Preliminary γ 00 < < 50 GeV 5.0 ev 0-0% 30-50% x Jγ 0 Jγ Jγ x Jγ centrality deendence 00 < γ < 50 GeV he distribution becomes like simulation for 30-50% suggesting that the fraction of energy loss decreases with arton. 8

29 γ- angular correlations No evidence for large modifications of angular distributions in Pb+Pb comared to collisions for hoton+. -CONF-06-0 Normalised entries < γ < 00 GeV 0-0% Pb+Pb, 0.9 nb -, 6 b PYHIA 8 + Data Overlay - 00 < γ < 50 GeV Preliminary > 50 GeV 5.0 ev 0.0 π / 3π/ π π / 3π/ π φ φ 9

30 Jet suression -CONF Jet quenching imlies yields in Pb+Pb are exected to be suressed at a fixed comared to collisions. Comare the number of s in to Pb+Pb vs.. Jet yield measured in heavy ion collisions Nuclear thickness function Jet crosssection measured in collisions he nuclear thickness function (< AA>) contains the effects of nuclear geometry and accounts for the fact that er Pb+Pb collision there are multile chances for hard scatterings. 30

31 Jet sectra -CONF Jets are measured in six bins of raidity (out to.8) [nb/gev] σ dy d d and u to a ~ ev in anti-k t 0 y < 0.3 ( 0 ) 0.3 < y < ( 0 8 ) 6 < y <. ( 0 ). < y <.6 ( 0 ).6 < y <. ( 0 ). < y <.8 R=0. s, 05 Preliminary s=5.0 ev - data, 5 b [GeV] N d [nb/gev] dy d evt N AA y <.8 anti-k t 0-0% 0-30% ( 0 ) 30-0% ( % ( 0 data ) 6 ) R=0. s, Preliminary =5.0 ev - 05 Pb+Pb data, 0.9 nb 05 - data, 5 b [GeV] Sectra is unfolded using D Bayesian unfolding. 3

32 RAA vs. -CONF R AA.5 RAA is < for all centralities. Preliminary anti-k t R = 0. s, = 5.0 ev y < % - 05 Pb+Pb data, 0.9 nb 30-0 % - 05 data, 5 b % [GeV] 3

33 RAA vs. -CONF R AA.5 RAA is < for all centralities. RAA is lower in central (~) than eriheral (~0.9) Preliminary anti-k t R = 0. s, = 5.0 ev y < % - 05 Pb+Pb data, 0.9 nb 30-0 % - 05 data, 5 b % [GeV] 33

34 RAA vs. -CONF R AA.5 RAA is < for all centralities. RAA is lower in central (~) than eriheral (~0.9). RAA rises with until ~300 GeV where it begins to flatten. Preliminary anti-k t R = 0. s, = 5.0 ev y < % - 05 Pb+Pb data, 0.9 nb 30-0 % - 05 data, 5 b % [GeV] 3

35 RAA vs. -CONF R AA R AA.5 RAA is < for all centralities. RAA is lower in central (~) than eriheral (~0.9). RAA rises with until ~300 GeV where it begins to Preliminary anti-k t R = 0. s, = 5.0 ev y < % - 05 Pb+Pb data, 0.9 nb 30-0 % - 05 data, 5 b % [GeV] Preliminary 0-0 %, = 5.0 ev, this analysis anti-k t R = 0. s y <., =.76 ev, arxiv: Pb+Pb data, 0.9 nb - 05 data, 5 b [GeV] flatten. RAA is indeendent of snn (over a narrow range) when comaring run and run results. 35

36 RAA vs. raidity Sectra is steeer with increasing raidity at fixed for the same amount of energy loss and since RAA ~ red/blue. lower RAA mid-raidity foward-raidity Guark and gluon fraction changes with raidity and with more quarks at forward raidity which should be quenched less. higher RAA Cometing effects: which one wins or do they cancel? 36

37 RAA vs. raidity Ratio of the RAA vs. y to the RAA for y < 0.3 in R AA ( y )/R AA ( y <0.3) % Preliminary anti-k t R = 0. s, = 5.0 ev 58 < 00 < < 00 GeV < 5 GeV y different ranges. Large cancelation of systematics in ratio < 36 < < 36 GeV y < 56 GeV y 05 Pb+Pb data, 0.9 nb data, 5 b CONF y 37

38 RAA vs. raidity Ratio of the RAA vs. y to the RAA for y < 0.3 in R AA ( y )/R AA ( y <0.3) % Preliminary anti-k t R = 0. s, = 5.0 ev 58 < 00 < < 00 GeV < 5 GeV y different ranges. Large cancelation of systematics in ratio. RAA is flat with < 36 < < 36 GeV y < 56 GeV y raidity at low. 05 Pb+Pb data, 0.9 nb data, 5 b CONF y 38

39 RAA vs. raidity Ratio of the RAA vs. y to the RAA for y < 0.3 in R AA ( y )/R AA ( y <0.3) % Preliminary anti-k t R = 0. s, = 5.0 ev 58 < 00 < < 00 GeV < 5 GeV y different ranges. Large cancelation of systematics in ratio. RAA is flat with < 36 < < 36 GeV y < 56 GeV y raidity at low Pb+Pb data, 0.9 nb - 05 data, 5 b R AA decreases with raidity at higher. -CONF y 39

40 Jet fragmentation functions (FF) Measures how the articles within the are distributed. Nch is the number of charged articles D() = dn ch N d = cos ΔR D( )= N dn ch d Jet axis associated with the. R=0. s with charged tracks starting at GeV for R=0. Pb+Pb and GeV +Pb. FF are background subtracted, corrected for Jet ΔR tracking efficiency, and fully D unfolded in and. 0

41 Jet fragmentation: and +Pb D() 8, 0 - s = 5.0 ev, 6 b +Pb, - = 5.0 ev, 8 nb 0-90% y* <.6 arxiv: Ratio needed to see modification. 0 0 = D() Pb D() y* <.6 0 < 60 < 0 < 80 < 60 < 5 < 5 < 60 GeV (x 0 ) < 0 GeV (x 0 ) 3 < 60 GeV (x 0 ) < 0 GeV (x 0 < 80 GeV (x 0 ) 0 < 60 GeV (x 0 ) ) 0 D() = dn ch N d

42 +Pb RD() in bins = D() Pb D().. 5 < < 60 GeV y * <.6 60 < < 80 GeV 80 < < 0 GeV 0.6 +Pb,, - = 5.0 ev, 8 nb, 0-90% - s = 5.0 ev, 5 b < y < 60 GeV * <.6 60 < < 0 GeV 0 < < 60 GeV 0.6 arxiv: Pb,, - = 5.0 ev, 8 nb, 0-90% - s = 5.0 ev, 5 b No modification of structure in +Pb.

43 Jet fragmentation: Pb+Pb D() Preliminary, s = 5.0 ev - 5 b 6 < 58 < 00 < 5 < 36 < 398 < < 58 GeV x 0 < 00 GeV x 0 < 5 GeV x 0 < 36 GeV x 0 < 398 GeV x 0 < 50 GeV x 0 ) - D( Pb+Pb, 0.9 nb - Preliminary = 5.0 ev, 0-0% 0 0 y <. y < CONF Need ratio to see modification. 0 = D() PbPb D() 0 D() = dn ch N d 3

44 -CONF Pb+Pb RD() = D() PbPb D().. Preliminary 6 < 6 < < 58 GeV, < 58 GeV y <. =.76 ev 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb, 0-0% - s = 5.0 ev, 5 b 0 No snn deendence.

45 -CONF Pb+Pb RD() = D() PbPb D().. Preliminary 6 < 6 < < 58 GeV, < 58 GeV y <. =.76 ev 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb, 0-0% - s = 5.0 ev, 5 b 0 No snn deendence. Enhancement at low, suression at intermediate, enhancement at high : low missing from 5.0 ev because trk cut at GeV. 5

46 -CONF Pb+Pb RD() = D() PbPb D().. Preliminary 6 < 6 < < 58 GeV, < 58 GeV y <. =.76 ev.. Preliminary 6 < 00 < 36 < < 58 GeV < 5 GeV < 398 GeV y <. 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb, 0-0% - s = 5.0 ev, 5 b 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb, 0-0% - s = 5.0 ev, 5 b 0 0 No snn deendence No deendence. Enhancement at low, suression at intermediate, enhancement at high : low missing from 5.0 ev because trk cut at GeV. 6

47 Summary Wide variety of measurements from : di and γ+ balance, inclusive suression, and substructure in Pb+Pb and +Pb Era of recision measurements with careful underlying event subtraction, reduced systematic uncertainties, and unfolding for detector effects. Increased statistics in run allowed for differential and high studies: Single s are suressed u to high (ev scale). No deendence in internal structure modification. Jets are more balanced at higher values of. 7

48 Backu 8

49 Centrality most central: 0-0% most eriheral: 70-80% y b = imact arameter Flux of nucleons increases with collision centrality. Define centrality classes : Events with similar degree of overla. In exeriment the total article roduction is used as a roxy for b. 9

50 Jet reconstruction: rocedure Anti-kt Algorithm + Calorimeter towers Jets Average transverse energy + Flow modulation (ν, ν3, ν) Reconstructed HI Jets Iterative de dηdφ de dη ( + n v n cos (n(φ ψ n ))) 50

51 Jet erformance: JES >.5 truth / reco < % no flow correction 0-0% 0-30% 0-50% 60-70% Simulation Preliminary Powheg + Pythia 8 inclusive s Pb+Pb data overlay anti-k t R = 0. s, = 5.0 ev Ψ - φ truth truth 00 < η <.0 < 00 GeV Ψ 3 - φ truth 5

52 Effect of unfolding on xj dn dx J N Pb+Pb data, 0. nb anti-k t R = 0. s =.76 ev s NN 0-0 % Measured Unfolded % - 03 data,.0 b < < 6 GeV x J x J x J Moves s in and eriheral to more balanced configurations and s in central to both more balanced and asymmetric configurations at xj ~ 5

53 JES/JER systematics JES: rigorous uncertainty broken down by source that is, η, and centrality deendent JER: dominant contribution comes from the UE which is described well in the MC samle (data overlay) xj systematics Fractional JES uncertainty Preliminary anti-k t R = 0. HI s =.76 ev 0 < η < CONF Uncertainty comonents Baseline in situ JES Flavor : inclusive s Cross calibration Data eriod Quenching otal uncertainty 0 Pb+Pb : 0-0 % 0 Pb+Pb : % 03 0 Evaluated by rebuilding the resonse matrix with a systematically varied relationshi between the true and reconstructed kinematics 3 0 [GeV] JES is the largest uncertainty in this measurement: 0% at x J ~ and 5% at xj ~ in central collisions Analysis secific systematics for the combinatoric background and unfolding Unfolding systematic can be as large as JES in central at lower xj 53

54 xj systematics summary dn dx J N Relative error in < < 6 GeV 0-0 % 0 Pb+Pb data, 0. nb otal JES JER Unfolding data,.0 b anti-k t R = 0. s =.76 ev 0. Combinatoric x J x J 5

55 R=0.3 xj dn dx J N < < 00 GeV 0-0 % Pb+Pb anti-k t R = 0.3 s 0-0 % Centrality deendence of Pb+Pb comared to dis for 79<<00 GeV. Same analysis for R=0.3 s since effects of the JER and the background are much less R=0.3 s corresond to R=0. s at a larger energy due to the smaller cone so the R=0.3 are shifted to one bin lower in leading. dn dx J N dn dx J N % 30-0 % 0-60 % =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b % x J x J 55

56 R=0.3 xj deendence Pb+Pb 0-0% centrality comared to dis. dn dx J N % Pb+Pb 79 < < 00 GeV 00 < anti-k t R = 0.3 s < 6 GeV.5 dn dx J N < < 58 GeV =.76 ev - 0 Pb+Pb data, 0. nb - 03 data,.0 b > 58 GeV x J x J 56

57 xj data to MC comarison dn dx J N 3 03 PYHIA 6 Pythia 8 Herwig++ - data,.0 b Powheg+Pythia 8 MC/Data 0 00 < < 6 GeV anti-k t R = 0. s =.76 ev x 57 J 57

58 xj 3rd See less nearby s in more central collisions. PLB 75 (05) 376 R R ρ.5 Pb+Pb 0 =.76 ev - L int =0. nb 0-0% 0-0% 0-0% 0 nbr E > 30 GeV anti-k t d=0. < R< E test [GeV] nbr E > 5 GeV anti-k t d=0. < R< [GeV] ested this by unfolding with a new resonse that takes into account the contribution to the 3rd with a weighting alied to match the 3rd distribution in data Deviations from the result was well within the systematics of the measurement E test nbr E > 60 GeV anti-k t d=0. < R< E test [GeV] 58

59 γ- JER Jet energy resolution ev, γ+ γ > 60 GeV, Simulation Preliminary η <. 0-0% Pb+Pb 30-50% Pb+Pb Efficiency [GeV] 59

60 γ- systematic uncertainties Jets: JES is 5% at low and decreases with Cross calibration: % addition JES uncertainty JER is evaluated by increasing the resolutions measured in by a few ercent Uncertainty on flavor comosition and different in flavor resonse is % at low and decreases with Addition JES uncertainty in Pb+Pb that is % for > 50 GeV and u to 5-0% above 50 GeV from comaring charged-article s to calorimeter s, studying the resonse of simulated quenched s, and residual non-closure of simulated s at low Photons: Photon urities adjusted by their statistical uncertainties Photon isolation cut increased by GeV in both and Pb+Pb, which increases efficiency and lowers urity Non-tight selection varied Photon energy uncertainties evaluated in which are less than % Assumtion that the distribution of background hotons factories 60

61 γ- background subtraction wo contributions to the background: Combinatoric: estimated by embedding PYHIA8 hoto+ events into real Pb+Pb data Di: er-hoton distributions subtracted using nontight hotons, after scaling by the hoton urity Normalised entries < γ < 80 GeV Preliminary γ [GeV] 80 < γ < 00 GeV Pb+Pb 5.0 ev nb 0-0% [GeV] 00 < < 50 GeV Raw data Background Corrected data Combinatoric imortant at low, di at high γ [GeV] 6

62 x J γ =,, γ γ- asymmetry s comared to MC generator increasing γ (/N γ )(dn/dx Jγ ) < γ < 80 GeV -, 6 b PYHIA 8 γ 80 < < 00 GeV Preliminary 5.0 ev 00 < γ < 50 GeV x Jγ x Jγ x Jγ 6

63 RAA systematic uncertainties Jet energy scale Standard JES comonents + 5 ev flavor and HI crosscalibration (following AL-CONF-05-06) HI secific uncertainty due to quenching (estimated using studies of the ratio of calo- to track- ) Jet energy resolution Standard comonent Established HI comonent Luminosity Nuclear thickness function Unfolding By comaring to results unfolded using the resonse matrix without the reweighting 63

64 RAA systematics summary uncertainties on the cross section uncertainties on Pb+Pb yields uncertainties on RAA cross-section uncertainty [%] Simulation Preliminary y <.8 JER JES Unfolding [GeV] Pb+Pb yields uncertainty [%] Simulation Preliminary y <.8,0-0% JER JES HI JES Unfolding [GeV] uncertainty [%] R AA Simulation Preliminary y <.8,0-0% JER JES HI JES Unfolding [GeV] 6

65 RAA vs. Nart R AA. = 00-5 GeV Internal y <. anti-k t R=0., =5.0 ev - 05 data,.7 b Pb+Pb data, 0.9 nb N art RAA decreases with Nart 65

66 Energy loss: flavor deendence How does energy loss deend on the details of the arton show? Vary the quark and gluon contribution of the s since gluons are quenched more than quarks. Naively: ~ 9/ x Measure suression as a function of raidity or since gluon fraction decreases with raidity and. Higher RAA at forward raidity and high. 66

67 D() MC to data Simulation / data.5 5 < < 60 GeV PYHIA6 AUEB CEQ6L 60 < < 80 GeV PYHIA8 A NNPDF3LO 80 < < 0 GeV HERWIG++ UEEE5 CEQ6L s - = 5.0 ev, 5 b y * < Simulation / data.5 0 < < 60 GeV PYHIA6 AUEB CEQ6L 60 < < 0 GeV Simulation / data PYHIA8 A NNPDF3LO 0 < < 60 GeV HERWIG++ UEEE5 CEQ6L s - = 5.0 ev, 5 b y * <

68 Systematic uncertainties on +Pb RD() Jet energy scale Jet energy resolution Unfolding [%] δ Pb, = 5.0 ev, 8 nb -, s= 5.0 ev, 5 b JES JER Unfolding MC non-closure racking otal rack reconstruction MC non-closure y * <.6 5 < < 60 GeV

69 +Pb RD() in bins New reference at same center of mass energy ) R D(.. 5 < < 60 GeV y * <.6 60 < < 80 GeV 80 < < 0 GeV 0.6 +Pb,, - = 5.0 ev, 8 nb, 0-90% - s = 5.0 ev, 5 b ) R D( < y < 60 GeV * <.6 [GeV] 0 60 < < 0 GeV [GeV] ) R D( 0 0 < < 60 GeV [GeV] 0.6 +Pb,, - = 5.0 ev, 8 nb, 0-90% - s = 5.0 ev, 5 b 0 [GeV] 0 0 No modification of structure in +Pb [GeV] 0 0 [GeV]

70 racking efficiencies racking Efficiency Simulation Preliminary Pb+Pb = 5.0 ev truth -.0 < η <.0 racking efficiency. Simulation +Pb = 5.0 ev % 60-80% 0 truth [GeV] < η truth < < η truth < < η truth <.0.0 < η truth <.0 0 truth [GeV] 70

71 Systematic uncertainties on Pb+Pb RD() Jet energy scale Jet energy resolution Unfolding rack reconstruction MC non-closure [%] δ Preliminary Pb+Pb, = 5.0 ev, 0.9 nb -, s= 5.0 ev, 5 b JES JER Unfolding MC non-closure racking otal 0-0% y <. 6 < < 58 GeV - 0-7

72 Systematic uncertainties on Pb+Pb RD() 7

73 Pb+Pb RD() in bins.. Preliminary y 6 < <. < 58 GeV, 0-0% Preliminary y 6 < <. < 58 GeV, 0-0% Preliminary y 6 < <. < 58 GeV, 0-30% 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b Preliminary y 6 < <. < 58 GeV, 30-0% Preliminary 6 < y <. < 58 GeV, 0-60% Preliminary 6 < y <. < 58 GeV, 60-80% 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b 0 0 Jets are more modified in central collisions 73 0

74 Pb+Pb RD() in centrality bins ) R D(.. Preliminary y 6 < <. < 58 GeV, 0-0% Preliminary y 6 < <. < 58 GeV, 0-0% Preliminary y 6 < <. < 58 GeV, 0-30% 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b ) R D(.. 0 Preliminary y 6 < <. 0 [GeV] < 58 GeV, 30-0% 0 Preliminary 6 < y 0 [GeV] <. ) < 58 GeV, 0-60% R D( 0 Preliminary 6 < y 0 [GeV] <. < 58 GeV, 60-80% 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b 0 0 [GeV] 0 0 [GeV] 0 0 [GeV] Jets are more modified in more central collisions 7

75 Pb+Pb RD() in bins ) R D(.. Preliminary y 6 < <. < 58 GeV, 0-0% Preliminary y 58 < < 00 GeV, 0-0% <. Preliminary y 00 < < 5 GeV, 0-0% <. 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b ) R D(.. 0 Preliminary y 5 < <. < 36 GeV, 0-0% 0 [GeV] ) R D( 0 Preliminary 36 < y < 398 GeV, 0-0% 0 [GeV] <. ) R D( 0 Preliminary 398 < y < 50 GeV, 0-0% 0 [GeV] <. 0.6 Pb+Pb,, - = 5.0 ev, 0.9 nb - s = 5.0 ev, 5 b 0 0 [GeV] 0 0 [GeV] 0 0 [GeV] 75