Heavy Ion Physics at ATLAS, CMS and LHCb

Transcription

1 Heavy Ion Physics at ALAS, CMS and Michael Schmelling - MPI for Nuclear Physics on behalf of the collaborations Outline Introduction Quarkonia production Correlation studies Ultra-peripheral collisions Fixed target physics Summary XXXII Les Recontres de Physique de la Vallée d Aoste Heavy Ion Physics M. Schmelling, La huile, February 5 March 3, 8

2 Introduction theoretical understanding of strong interactions: the QCD Lagrangian is well known and tested I good agreement between data and theory where perturbative QCD is applicable many open questions in the non-perturbative regime, such as : : : I properties of hadronic matter at high densities and temperatures (QGP) I bound states, e.g. nucleon structure (vital for BSM searches) I nuclear effects in multiparticle production (nuclear PDFs, energy loss) I dynamics of soft processes, e.g. diffractive scattering and hadronisation I also interesting: QED at extreme field strengths Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8

3 Experimental approach different nucleon-nucleon centre-of-mass energies different beam-target combinations comparison of different systems always look at the complete picture Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8 3

4 Angular coverage of the LHC experiments ALICE I central detector I forward muon coverage ALAS & CMS I central tracking detectors I forward calorimeter I forward detector I tracking, PID and calorimetry in the full acceptance Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8

5 rich harvest of papers and conference notes generic topics addressed in papers: ALAS CMS Flow- and correlation measurements 7 Jets and QCD 9 Quarkonia 3 Particle production 6 5 Electroweak gauge bosons 3 5 QED total 7 7 plus > papers by the ALICE collaboration ( next talk) many papers touch on more than a single topic textbook results from the LHC Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8 5

6 Melting of bound states in QGP v check the Matsui-Satz-idea regarding b b and c c systems heavy-quark bound states melt in the hot medium of the deconfined colour charges of a QGP PLB77(7)357 Ü experiment: production in pp and PbPb collisions negligible recombination less tightly bound states are strongly suppressed Ü intriguing QGP signature Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8 6

7 Jet quenching dn dx J N < p < 6 GeV - % ALAS 3.5 anti-k t R =. jets 3 Pb+Pb pp % energy loss of hard partons in QGP look at the p -ratio for jet pairs x J = p p with p > p dn dx J N dn dx J N % 3 - % - 6 % s NN =.76 ev 6-8 % - Pb+Pb data,. nb 3 pp - data,. pb preference for balanced jets comparison of pp and PbPb I fewer high-energy jets in central PbPb collisions I same behaviour for pp and peripheral PbPb collisions signature of a dense deconfined QCD medium PLB 77 (7) 379 x J x J Heavy Ion Physics - Introduction M. Schmelling, La huile, February 5 March 3, 8 7

8 Quarkonia production study p-pb collisions to probe cold nuclear matter effects effects of energy loss in nuclear matter modification of parton densities of bound nucleons study by inclusive particle production of heavy resonances probe two x -values for given rapidity y and mass M : x ; e y M ps Pb p bwd fwd Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8 8

9 parametrisation of nuclear PDFs by ratios of nucleon PDFs: F N (Pb)=F N (free) valence quarks gluons arxiv:7.36 still large uncertainties - EPPS6 error band for gluons larger than EPS9 suppression at small x shadowing enhancement at medium x anti-shadowing enhancement at large x EMC effect Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8 9

10 v experimental observable sensitive to nuclear effects: ( ) = A nuclear modification factor: RpA y d pa =dy d pp =dy central detectors: simultaneous measurement of forward and backward production forward detectors: flip beam directions to measure both hemispheres p Pb FORWARD (p hemisphere) Heavy Ion Physics - Quarkonia production BACKWARD (Pb hemisphere) M. Schmelling, La huile, February 5 March 3, 8

11 Results from prompt J= and J= from b-decays dσ dy [mb] dσ dy [mb] ppb, Pbp pp rescaled prompt J/ψ snn = 8.6eV < p < GeV/c. 5 5 y ppb, Pbp pp rescaled J/ψ -from-b-hadrons snn = 8.6eV < p < GeV/c. 5 PLB 77 (7) 59 5 y dσ [nb/(gev/c)] dp dσ [nb/(gev/c)] dp backward Pbp pp rescaled prompt J/ψ, Pbp 5. < y <.5 snn = 8.6eV 5 p [GeV/c] J/ψ -from-b-hadrons, Pbp backward Pbp pp rescaled 5. < y <.5 snn = 8.6eV 5 p [GeV/c] dσ [nb/(gev/c)] dp dσ [nb/(gev/c)] dp ppb pp rescaled prompt J/ψ, ppb.5 < y <. snn = 8.6eV 5 p [GeV/c] ppb pp rescaled forward J/ψ -from-b-hadrons, ppb forward.5 < y <. snn = 8.6eV 5 p [GeV/c] prompt J= compared to 8 pp (red) delayed J= compared to 8 pp (red) Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8

12 nuclear modification factors in the forward/backward region RpPb..5. HELAC Onia with EPS9LO HELAC Onia with nceq5 HELAC Onia with EPS9NLO Energy Loss CGC (5eV) (8.6eV).5 prompt J/ψ < p < GeV/c y consistent results for data with p s NN =5 and 8.6 ev nuclear effects clearly visible in the forward region RpPb..5. FONLL with EPS9NLO (5eV) (8.6eV).5 J/ψ -from-b-hadrons < p < GeV/c y stronger effects for prompt J= production than for J= from b-meson decays J= from b-meson decays described by effects of NLO npdfs prompt J= described by NLO npdfs plus energy loss effects Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8 PLB 77 (7) 59

13 nuclear modification factors in the central region R ppb < p Data - - ppb 3.6 nb, pp 8. pb < GeV/c EPS9 NLO (Vogt) EPS9 NLO (Lansberg-Shao) nceq5 NLO (Lansberg-Shao) (5. ev) CMS Prompt J/ψ y CM - - ppb 3.6 nb, pp 8. pb (5. ev) CMS Nonprompt J/ψ R ppb < p Data - - ppb 3.6 nb, pp 8. pb < 3 GeV/c EPS9 NLO (Vogt) EPS9 NLO (Lansberg-Shao) nceq5 NLO (Lansberg-Shao) (5. ev) CMS Prompt J/ψ y CM - - ppb 3.6 nb, pp 8. pb (5. ev) CMS Nonprompt J/ψ EPJC77(7)69 nuclear modification factors close to unity theory lower, though consistent, with the data similar behaviour for prompt and non-prompt J= mesons indication for a slight enhancement for lower p R ppb.8 R ppb < p < GeV/c.. < p < 3 GeV/c y CM y CM Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8 3

14 closer look at p dependence R ppb.8 ALAS.6 Prompt J/ψ -. < y* < p+pb, pp, s - s NN = 5. ev, L = 8 nb - = 5. ev, L = 5 pb R ppb.8 ALAS.6 Non-Prompt J/ψ -. < y* < p+pb, pp, s - s NN = 5. ev, L = 8 nb - = 5. ev, L = 5 pb R ppb ALAS ϒ(S).5 -. < y* <.5.5 p+pb, pp, s - s NN = 5. ev, L = 8 nb - = 5. ev, L = 5 pb arxiv: p [GeV] p [GeV] p [GeV] small nuclear effects for centrally produced J= mesons indication for slight enhancement of prompt production no significant p dependence for prompt and non-prompt J= production indication of p dependence for production I open and hidden heavy flavour seem to be affected differently I maybe related to breakup of bound states in nuclear matter, which for J= from b is compensated by recombination and/or anti-shadowing? Heavy Ion Physics - Quarkonia production M. Schmelling, La huile, February 5 March 3, 8

15 3 Correlation studies distribution of phase space distance between particle pairs probing the underlying dynamics, e.g. I dimensions of the particle emitting regions Bose-Einstein correlations, HB I particle production in jets fragmentation dynamics I flow effects due to properties of QCD medium example: per trigger-particle associated yield vs angular distances and d N pair N trig d d S ( ; ) = B(; ) B( ; ) I -dim correlation functions of prompt particles in ( ; ) I select particles in fixed p -range as trigger and study all pairs with the trigger I compare associated yields per trigger, within an event (S ( ; )) and with random combinations (B( ; )) from mixed events Heavy Ion Physics - Correlations studies M. Schmelling, La huile, February 5 March 3, 8 5

16 example: two-particle correlations in p-pb collisions forward (p-pb, p direction) backward (Pb-p, Pb direction) p+pb s NN = 5 ev Pb+p s NN = 5 ev. < p <. GeV/c Event class 5 %. < p <. GeV/c Event class 5 % d N d η d trig N p+pb s NN = 5 ev. < p <. GeV/c Event class 3% η d N d η d trig N Pb+p s NN = 5 ev. < p <. GeV/c Event class 3% η PLB76(6)73 low activity d N d η d trig N η d N d η d trig N η high activity Heavy Ion Physics - Correlations studies M. Schmelling, La huile, February 5 March 3, 8 6

17 -integrated yields in p-pb/pb-p outside of the jet peak vs Y()-CZYAM Y()-CZYAM Y()-CZYAM Y()-CZYAM Y()-CZYAM < p <. GeV/c. < p <. GeV/c. < p < 3. GeV/c C ZYAM=.6 (p+pb) C ZYAM=.6 (Pb+p) C ZYAM=.83 (p+pb) C ZYAM=. (Pb+p) C ZYAM=3.7 (p+pb) C ZYAM=5.78 (Pb+p) C ZYAM=5.3 (p+pb) C ZYAM=7.8 (Pb+p) C ZYAM=5.67 (p+pb) C ZYAM=8.63 (Pb+p) C ZYAM=.3 (p+pb) C ZYAM=.37 (Pb+p) C ZYAM=.56 (p+pb) C ZYAM=.7 (Pb+p) C ZYAM=.8 (p+pb) C ZYAM=. (Pb+p) C ZYAM=.9 (p+pb) C ZYAM=.78 (Pb+p) C ZYAM=.39 (p+pb) C ZYAM=.7 (Pb+p) s NN = 5 ev p+pb data Pb+p data C ZYAM=.8 (p+pb) C ZYAM=. (Pb+p) C ZYAM=.3 (p+pb) C ZYAM=.6 (Pb+p) C ZYAM=.9 (p+pb) C ZYAM=.36 (Pb+p) C ZYAM=.3 (p+pb) C ZYAM=. (Pb+p) 5-% 3-5% -3% -% -3% Y() CZYAM after offset subtraction (Zero-Yield-At-Minimum): I near-side ridge largest at <p < GeV/c I fixed relative activity (left): ridge of the 3% most active Pb-p events stronger than the ridge of the 3% most active p-pb events I fixed absolute activity in the acceptance: similar ridges in p-pb and Pb-p events s NN = 5 ev Activity bin I C ZYAM=. (p+pb) C ZYAM=. (Pb+p) < p <. GeV/c Activity bin II C ZYAM=.3 (p+pb) C ZYAM=.6 (Pb+p) Activity bin III C ZYAM=. (p+pb) C ZYAM=.7 (Pb+p) Activity bin IV C ZYAM=.5 (p+pb).5 C ZYAM=.38 (Pb+p)..5. Activity bin V C ZYAM=.6 (p+pb) C ZYAM=.5 (Pb+p) PLB76(6)73 Heavy Ion Physics - Correlations studies M. Schmelling, La huile, February 5 March 3, 8 7

18 v results from central measurements Pb-side trigger -.< η < (radians).8 < η < 3. (radians) - 3. < η < I pair.5 dn [per unit of η] Ntrig d φ pair dn [per unit of η] Ntrig d φ PRC96 (7) 98.5 I < 6 Ntrk < pair.5 offline Ntrk PRC96 (7) 95 < η <. dn [per unit of η] Ntrig d.3 < p <3 GeV/c pair dn [per unit of η] Ntrig d p-side trigger CMS ppb snn=5. ev φ (radians) φ (radians) outside the jet peak (bottom) the ridge appears in high-multiplicity events (red) similar strengths for p-side and Pb-side Heavy Ion Physics - Correlations studies I I ridge also in high multiplicity pp events universal feature when many QCD degrees of freedom are present? M. Schmelling, La huile, February 5 March 3, 8 8

19 Ultra-peripheral collisions exploit the high-intensity photon flux from relativistic Pb nuclei v ~ c Pb em fields em fields Pb v c ~ = Z Pb 8+ γ γ Pb 8+ Z X.. field strength amplified by em-coupling amplified by Z strong coupling regime of QED distinguish two photon-processes (depicted above) and photoproduction (not shown) common characteristic: low transverse momentum of the final state system existing/upcoming results also from Heavy Ion Physics - Ultra-peripheral collisions M. Schmelling, La huile, February 5 March 3, 8 9

20 Coherent production of J= mesons in PbPb collisions Events / (.5 GeV) - Pb+Pb Pb+Pb+J/ψ (X ) 59 µb n 8 n CMS p (µ + µ ) <. GeV -.8 < y(µ + µ ) <.3 (.76 ev) CMS data γγ otal - µ + µ Events / (.5 GeV) Pb+Pb Pb+Pb+J/ψ (X 6 CMS 8 6 n n - ) 59 µb CMS data Coherent J/ψ Incoherent J/ψ γγ -.8 < y(µ + µ ) <.3 otal -.6 < m(µ + µ ) < 3.5 GeV + - µ µ (.76 ev) / dy [mb] dσ coh - Pb+Pb Pb+Pb+J/ψ 59 µb (.76 ev) 9 CMS data CMS 8 ALICE data Impulse approximation 7 Leading twist approximation PLB77(7) m(µ + µ ) [GeV] p (µ + µ ) [GeV] y experimental selections with a breakup neutron accepts coherent (on the entire nucleus) and incoherent (on a single nucleon) production clean signal on top of a small and well understood background measurement of the photoproduction cross-section probes the gluon density cross-section consistent with nuclear effects as expected from gluon shadowing Heavy Ion Physics - Ultra-peripheral collisions M. Schmelling, La huile, February 5 March 3, 8

21 Evidence for light-by-light scattering X X Data, 8 µ b- γ γ γ γ MC γ γ e+e- MC CEP γ γ MC ALAS Pb+Pb snn = 5. ev Signal selection no Aco requirement Nature Physics 3 (7) 379 Events /.5 X back-to-back photons transverse to the beam 3 candidates in 8 b expected background.6.7 events cross-section consistent with SM..5.6 γ γ acoplanarity Heavy Ion Physics - Ultra-peripheral collisions M. Schmelling, La huile, February 5 March 3, 8

22 5 Fixed target physics v exploit the SMOG System for Measuring Overlap with Gas inject noble gases ( 7 mbar) into the interaction region: He, Ne, Ar motivation: beam-profile measurements with beam-gas interactions plus: full charm and (soft) QCD fixed-target physics program with p and Pb beams Heavy Ion Physics - Fixed target physics M. Schmelling, La huile, February 5 March 3, 8

23 links to cosmic ray and astroparticle physics: antiproton/proton ratio JCAP 9 (5) 3 I indication of antiproton excess I dark-matter annihilation? I large cross-section uncertainties for ph! px I predictions vary within a factor : measure phe! px at p s NN = GeV -CONF-7-7% uncertainty data compared to EPOS-LHC Heavy Ion Physics - Fixed target physics M. Schmelling, La huile, February 5 March 3, 8 3

24 6 Summary extremely rich (heavy) ions physics portfolio and results at the LHC simultaneous views are the key to the understanding of non-perturbative QCD I study of the same observables in pp, p-pb and Pb-Pb collisions I central and forward measurements understanding QGP signatures requires understanding of nuclear effects heavy flavour measurements probe nuclear PDFs and properties of the medium correlation measurements probe collective effects in the final state I hints of universality when sufficiently many degrees of freedom are excited fixed target physics radiates also into neighbouring fields ultra-peripheral collisions test soft QCD and QED under extreme conditions Stay tuned for more from the and collaborations! Heavy Ion Physics - Summary M. Schmelling, La huile, February 5 March 3, 8