FIRST HEAVY ION PHYSICS RESULTS FROM THE LHC Arturo Fernández Téllez Universidad Autónoma de Puebla
Plan Detectors Bulk Proper>es Flow correla>ons Quarkonia R AA and jets.
ALICE ACORDE V0 T0 ZDC FMD PMD Technologies:18 Detector: Size: 16 x 26 meters XQCD11, San Carlos Arturo Fernández Tellez Weight: 10,000 tons Tracking: PID: 3 Calo.: 7 6 5
ATLAS Detector
CMS Detector
Pb- Pb Data Taking 2010 Pb- Pb collisions took place at the LHC for the first >me in November and December 2010. Three of the LHC experiments took part: ALICE ATLAS CMS The collision energy was 2.76 TeV, i.e. the magnet currents for the LHC machine magnets were kept at the same values as for 7 TeV pp collisions.
QUARK MATTER 2011 23-28, ANNECY, FRANCE
BULK PROPERTIES
Charged Par>cle Mul>plicity The mid- rapidity pseudorapidity density at a collision energy of 2.76 TeV per nucleon was found to be dn 2 dn = 1584 ± 4 ± 76; = 8.3± 0.4 dη N dη part This corresponds to an increase over the corresponding RHIC pseudorapidity density for 200 GeV Au- Au collisions by a factor 2.1. de T /dη ~ 2.7 (de T /dη ) RHIC Toia ALICE
Number of par>cles produced per par>cipant Steinberg ATLAS ATLAS showed that the number of par>cles produced per par>cipant pair shows the same behaviour at RHIC and at the LHC. This indicates that what changes is the shape of the mul>plicity distribu>on itself.
HBT and system size REMINDER: HBT measurements look at the correla>on between the momenta of iden>cal bosons The correla>on func>on uses the momentum difference between the two iden>cal par>cles q = p 2 - p 1 The Bowler- Sinyukov correla>on func>on is given by {( λ) λ inv [ ]} Cq ( ) = N 1 + Kq ( ) 1 + Gq (, ( 2 2 2 2 2 2 ) out out side side long long Gq ( ) = exp R q + R q + R q
Increase in system size R out = 6.92 fm R side = 6.36 fm R long = 8.03 fm V ~ 4900 fm 3 Kisiel ALICE HBT studies show that the system size increases linearly with the mean mul>plicity of the system.
FLOW CORRELATIONS
Expansion of the system - Flow For these studies, it is more useful to study non- central collisions, where the impact parameter of the collision centres defines a reac>on plane. Reac>on (differences are smaller than shown) Plane Geometric asymmetry Arturo Fernández Tellez Momentum asymmetry
V n coefficients The asymmetry in dn/dφ can be described in terms of a Fourier expansion E 3 2 d N 1 d N = = 1+ 2vncos( ϕ- ΨR) p p p y 3 d 2π Td Td n= 1 v 2 [ ϕ R ] = cos 2( Ψ V 2 describes the deforma>on from an isotropic (circularly symmetric) azimuthal distribu>on to an ellip>c one. Hence it is said to describe ellip1c flow. Mathema>cal methods exist (cumulants, Lee- Yang zeros) that allow v 2 to be calculated without the need to have determined the reac>on plane.
Integrated Flow The mean value of v 2 increases by ~30% with respect to the mean value obtained at top RHIC energies. K. Aamodt et al. PRL 105(2010)252302
Varia>on of v 2 with p T Here the new LHC values are shown as a func>on of p T compared to the corresponding RHIC measurements. We see that the p T dependence is the same, indica>ng that the difference comes in the shape of the p T spectrum.
Increase in the range of v 2 measurements. New ATLAS values greatly extend the range of v 2 measurements in p T. We see that for p T > 8 GeV/c the value becomes stable. Jiangyong Jia ATLAS
Iden>fied par>cle v 2 I
Iden>fied Par>cle v 2 II There are significant differences in the behaviour of π, K, p with v 2. Unlike RHIC, v 2 scaling with n q ( cons>tuent scaling ), does not work at all p T values. Not too bad at high p T. K and π >e up reasonably well; the major difference is in the behaviour of p (p).
v 3 Snellings ALICE We see that v 3 has non- zero values. It is necessary to take this contribu>on into account in describing the momentum anisotropy.
What about other v n? At QM11 several studies have analysed the behaviour of the azimuthal discribu>on in terms of a Fourier series with several terms v n. As expected, this allows us to describe a number of other structures seen in the azimuthal distribu>ons. This new use of the Fourier formalism does not mean that all these structures have been explained, but gives us a new way to describe them. Adare ALICE
Applica>on of similar technique in ATLAS ATLAS has also used a more complete expansion in Fourier coefficients v n, in this case to analyse the ridge structure. Complementary approach to event plane. Steinberg ATLAS
Centrality dependence of the ridge ATLAS has studied the centrality dependence of the ridge structure. We see that for very central events there is only one (near side) structure, Then we see the ridge emerge, and then it becomes less dis>nct. Jiangyong Jia ATLAS 1.02 1.01 1 0.99 1.1 1 1.1 1 0.9-1 0 1 2 3 4-1 0 1 2 3 4-1 0 1 2 3 4-5 -4-3-2-1 -5-4-3-2-1-5 -4-3-2-1 0-1% 0 1 2 3 4 20-30% 0 1 2 3 4 60-70% 0 1 2 3 4 1.02 1 1.2 1.1 1-1 0 1 2 3 4 0.9-1 0 1 2 3 4 1.2 1.1 1 0.9-1 0 1 2 3 4-5 -4-3-2-1 -5-4-3-2-1-5 -4-3-2-1 0-5% 0 1 2 3 4 30-40% 0 1 2 3 4 70-80% 0 1 2 3 4 1.04 1.02 1 0.98-1 0 1 2 3 4 1.2 1.1 1 0.9-1 0 1 2 3 4 1.4 1.2 1 0.8-1 0 1 2 3 4-5 -4-3-2-1 -5-4-3-2-1-5 -4-3-2-1 0-10% 0 1 2 3 4 40-50% 0 1 2 3 4 80-90% 0 1 2 3 4 1.1 1.05 1 0.95-1 0 1 2 3 4 1.1 1 0.9-1 0 1 2 3 4-5 -4-3-2-1 -5-4-3-2-1 10-20% 0 1 2 3 4 50-60% 0 1 2 3 4 ATLAS Preliminary -1 Ldt = 8 µb a T b T 2 < p, p < 3 GeV
Flow & 2 Par>cle Correla>ons 2 Particle correlation C ( ) v 'Near Side 1 +v 2+ v Ridge' 3+ v 4+ v 5 broad away side structure v 3 v 2 Giubellino Erice (2011) Projec>on on for > 0.8 Clean double Hump (aka 'Mach Cone') appears for ultra-central (without any flow subtraction!) Full correlation structure described by Fourier Coefficients v 1,v 2, v 3, v 4,v 5 (for h >0.8) v3 very visible, indeed, v3 v2 for very central 'Mach Cone' & 'Near Side Ridge' shapes evolve smooth with magnitude of v 2 and v 3
QUARKONIA Arturo Fernández Tellez
J/ψ en PHENIX REMINDER Earlier this year the PHENIX collabora>on presented an unexpected dependence of the J/ψ R AA on rapidity. PHENIX
R AA is defined as R AA d N /d Npart AA = < N > d N /d N coll part R AA for the J/ψ has been measured at the LHC for the first >me. The values found are larger (less suppression) than in the PHENIX case. pp J/ψ R AA ALICE (Pb-Pb >0 (preliminary) 1.4 s = 2.76 TeV), 2.5<y<4, p NN T PHENIX (Au-Au s NN = 0.2 TeV), 1.2< y <2.2, p >0 (arxiv:1103.6269) T 1.2 1 0.8 0.6 0.4 0.2 (*) ALICE <N > is weighted by N part coll 0 0 50 100 150 200 250 300 350 400 <N part *> Note that the rapidity ranges are different. MarUnez ALICE
Direct J/ψ CMS has also measured R AA for J/ψs. They have also studied the contribu>on from secondary J/ψs from B decays. The remaining J/ψs are direct, i.e. coming directly from the primary vertex. Silvestre CMS
ϒ(1S),ϒ(2S), and ϒ(3S) states Silvestre CMS The ϒ states have been measured by CMS. The produc>on of ϒ(2S) and ϒ(3S) is suppressed rela>ve to pp collisions.
Comment The principal interest in the behaviour of the ϒ states is that, assuming QCD- Debye screening, the screening factor is given by the quark- an>quark separa>on, i.e the radius of the par>cle. The ϒ allow us to study a range of different radii The ϒ(1S) is smaller than the J/ψ so is the least likely to be affected by colour screening The ϒ(2S) has a similar radius to the J/ψ. However, because of the larger mass of its cons>tuent quarks, it can only be formed through the ini>al collisions, i.e. with no regenera>on component.
R AA AND JETS Arturo Fernández Tellez
R AA We need a quan>ta>ve measure of the effect of the QGP medium on jet produc>on. R AA is the scaled ra>o between the produc>on spectrum for a given par>cle (or jet) in AA and the corresponding produc>on in pp. the scaling factor is given by The number of par1cipants N part in the case of global phenomena or those involving soy hadron produc>on, since here every par>cipant gives a certain overall yield of par>cles; The number of collisions N coll in the case of hard processes, since in this case the produc>on depends on the number of pp collisions, which can be more than the number of par>cipant pairs. production enhanced in AA R AA d N /d pt AA = < N > d N /d p coll T pp 1 production suppressed in AA p T (GeV)
R AA At the LHC the R AA factor is measured over a much greater momentum range than was previously possible. We see that, ayer a minimum at around 8 GeV/c, R AA starts to rise again, reaching a value of almost 1 at the highest measured transverse momenta. Appelhauser ALICE
ALICE- CMS Comparison ALICE and CMS have both measured R AA in a similar kinema>c range. There is excellent agreement in the measured values of R AA. Appelhauser ALICE
Azimuthal Dependence A more detailed study shows that R AA depends on the direc>on of the emized par>cle. A larger effect is seen out of the reac>on plane than in the reac>on plane. Dobrin ALICE
R AA measurement for D 0, D + Measurement of R AA for charmed mesons (D 0 andd + ). Both show a similar strong suppression, similar to that for other hadrons, such as π + and π -. D 0,+ π ± Dainese ALICE
Arturo Fernández Tellez
Arturo Fernández Tellez
Arturo Fernández Tellez
Arturo Fernández Tellez
Z 0 Centrality Dependence Z 0 produc>on per collision is a constant. Z 0 does not interact via the strong interac>on (as in the case of the photon). Wysluch CMS
Summary The mean pseudorapidity density <dn/dη> has been measured and is at the lower end of the available es>mates. HBT studies show the volume of the QGP to be propor>onal to the mul>plicity, Flow effects are even stronger than at RHIC The behaviour of other coefficients in the Fourier expansion of the azimuthal distribu>on are now also being studied. Strong ac>vity is seen in R AA. R AA values for widely differing hadron species (e.g. D 0 and π ± ) is similar. However, at the LHC, unlike RHIC, cons>tuent scaling v 2 /n q does not lead to a universal curve. Z 0 produc>on per collision seems to be constant. Jet produc>on at the LHC shows several previously unexpected features, but is being unravelled. Very rapid progress has been made since the data were taken in November and December of last year, but many new results will be available soon.
SPECIAL THANKS TO: Orlando Villalobos (Birmingham) & Daniel Tapia (Orsay) For their help and frui ul discussions on the material presented in this talk.