# Presentation: 682265

## J/ suppression in p-A and In-In collisions at 158 GeV/nucleon 

- R. Arnaldi – INFN Torino (Italy)
- for the NA60 Collaboration

-  Introduction
-  J/ suppression in In-In collisions
-  New results from p-A collisions
-    at 158 GeV
-     study of the pT distributions and
-         comparison with In-In
-  v2 of the J/ in In-In
-  Conclusions

## J/ suppression at SPS energy

**J/******** ****suppression at SPS energy**

-  Nuclear collisions results: Pb-Pb (NA50) and In-In (NA60)
-  p-A reference results: from p-A collisions at 400/450 GeV (NA50)

- R. Arnaldi et al. (NA60), PRL99, 132302 (2007)

-  Observed suppression exceeds nuclear absorption
-  Onset of the suppression at Npart  80
-  Comparison between different systems  Npart scaling
-  At RHIC (s  10 sSPS) a very similar suppression pattern is observed

## Nuclear absorption reference

-   (Glauber analysis) absJ/ = 4.2±0.5 mb, and (J//DY)pp =57.5±0.8

-  The expected J/ yield for In-In and Pb-Pb collisions is calculated
-  assuming absJ/ (158 GeV) = absJ/ (400/450 GeV)
-  rescaling (J//DY)pp to 158 GeV with a semi-theoretical procedure

- Preliminary!

**Nuclear absorption reference**

-  Preliminary pA results from NA60 at 158GeV
-   (averaged over nuclear targets) seem to
-   validate the nuclear absorption normalization
-   extracted from 400/450 GeV data

-  Results on absJ/ will appear soon (HP08)
-    crucial to confirm (or modify) the         anomalous suppression pattern

## J/ transverse momentum

-  Main features:

-  pT2 (and T) linearly increase with L   (mean thickness of nuclear matter)

-  Phenomenological description  with
-    the expression

- with an energy dependent pT2pp and
- a common slope:
- gN= 0.081±0.002 (GeV/c)2/fm

- pT distributions for pA and AA never studied in the same energy/kinematical range

**J/******** ****transverse momentum**

## p-A collisions at 158 GeV

-  A target system including 7 different nuclei (Be, Al, Cu, In, W, Pb, U) has been used
-  Accurate target ID thanks to the NA60 vertex spectrometer (pixel)

- pCu

-  Mass resolution: 100 MeV at the J/, 40 MeV at the 
-  Under the J/
-  Combinatorial background is zero
-  Drell-Yan contribution is small (<2%)

-  A simple event counting technique can be used to extract NJ/

**p-A collisions at 158 GeV**

## Study of pT distributions in pA at 158 GeV

-    correction method
-  The input distributions for the other kinematical variables (y, cosCS) have been    obtained starting from a 3D correction algorithm and then adjusted iteratively on the    data

-  Rapidity coverage 0<yCM <1
-  Same as in NA50(Pb)/NA60(In)
-    extrapolation needed for
-       upstream targets

- Study of pT distributions in pA at 158 GeV

-  y distribution  gaussian with y=0.52
-  cosCS distribution  flat
-   (no J/ polarization)

## pT distributions for 158 GeV pA

- Teff values slightly increase with A

- 0<ycm<1

- |cos|<0.5

**p****T ****distributions for 158 GeV pA**

- in order to obtain the inverse slope
- Teff values

## mT distributions for 158 GeV pA

- In the explored mT-M range,
- no deviations from the
- exponential behaviour can
- be appreciated

**m****T ****distributions for 158 GeV pA**

## Dependence of pT2 on L 

-   due to the choice of the
-   generated y and cos
-   distributions in the
-   acceptance calculations

-  Applying more severe event
-   selection cuts there is no
-   effect on the results

- We observe a linear increase of <pT2> with L,
-  consistent with gluon scattering in the initial state

**Dependence of ********p****T****2******** on L**

- smaller than statistical errors

## Comparison p-A vs In-In (Pb-Pb) 

- in p-A and A-A, in the same energy/kinematical range

- <pT2>pp=1.13 ± 0.04 (GeV/c)2
- gN=0.029 ± 0.011 (GeV/c)2 / fm

- <pT2>pp=1.27 ± 0.09 (GeV/c)2
- gN=0.058 ± 0.014 (GeV/c)2 / fm

- <pT2>pp=1.19 ± 0.04 (GeV/c)2
- gN=0.072 ± 0.005(GeV/c)2 / fm

**Comparison p-A vs In-In (Pb-Pb) **

- Pb-Pb

- In-In

- p-A

-  pT2 increases linearly with L in both p-A, In-In and Pb-Pb
-  However, the scaling of pT2  with L is broken moving from p-A to A-A
-  On one hand comparing p-A and peripheral In-In the suppression scales with L
-  On the other hand  the J/ pT distributions do not scale with L !
-  gNAA ~ 2 gNpA  does one simply add up projectile and target broadening ?

## Comparison p-A In-In vs. Npart

- We find an approximate
- scaling of pT2 with the logarithm of the number of participant nucleons

## Comparison pA 158 GeV vs pA 400 GeV

-   domain covered by p-A data previously collected by NA50
-  Compare (as a check) the results of the two experiments

-  The slope of the p-A points at 400 GeV
-   is compatible between NA50 and NA60
-   (1.2 )

- NA60 p-A 400 GeV
- gN=0.104 ± 0.013

- NA50 p-A 400 GeV
- gN=0.087 ± 0.004

-   New 158 GeV data show that  at SPS gN depends on the energy of the collision

**Comparison pA 158 GeV vs pA 400 GeV**

## RAA for In-In at 158 AGeV

-  Build a J/ pT distribution using the functional form

**R****AA**** for In-In at 158 AGeV**

- with T obtained from the value of pT2 pp
- coming from the fit of the p-A data

## RAA for In-In at 158 AGeV (2)

-  Clear rise at high pT consistent
-   with the Cronin effect

-  RAA much lower than 1 at low pT
-  Effect seen dominated by   nuclear absorption

-  A systematic error (11%) due to
-   the data normalization is common
-   to all points

## RCP for In-In at 158 A GeV

- Normalize pT distributions to the most peripheral In-In bin,
- corresponding to Npart50

- We see that moving towards central collisions there is an increasingly
-  large suppression at low pT (already seen in Pb-Pb)

**R****CP**** **for In-In at 158 A GeV

## Comparison with PHENIX

- RAA similar at SPS and RHIC at low transverse momentum (pT < 1.5 GeV/c)

## v2 measurements at NA60

-  Use elliptic flow v2 to estimate the reaction plane (v1 = 0 at midrapidity)‏
-  Determination from charged particle tracks as measured in the vertex tracker

**v****2**** measurements at NA60**

- v2 for charged particles

## J/ azimuthal anisotropy (1)

**J/******** azimuthal anisotropy (1)**

-  Limited statistics (<30000 J/ events) prevents a fine binning in centrality/pT
-  Define 2 broad centrality classes

- v2 consistent with zero for central events, v2 > 0  (2.3) for peripheral

## J/ azimuthal anisotropy (2)

| Centrality | pt<1GeV/c | pt>1GeV/c |
| --- | --- | --- |
| 0.5% < σ/σgeo < 28% | 0.00±0.03 | -0.01±0.03 |
| 28% < σ/σgeo < 83% | 0.03±0.05 | 0.11±0.05 |

**J/******** azimuthal anisotropy (2)**

-  In spite of the relatively low statistics, we    see an anisotropy for peripheral events,
-    concentrated at high pT
-  Hardly a signal of elliptic flow (charm    collective motion), since at SPS
-  Ncc is low (no recombination)
-  Difficult to have charm thermalisation
-  Effect likely to be connected with   anisotropic absorption in QGP/nuclear   matter

-  Introduce a rough pT binning

## Conclusions

-  We observe a linear increase of <pT2> with L, consistent with gluon scattering
-    in the initial state
-  However
-  The slope is smaller than in In-In and Pb-Pb at the same energy
-  Peripheral In-In and p-A collisions with approximately the same L
-   have <pT2> different by ~ 200 MeV

-  First results on the v2 of the J/ at SPS energy
-  v2 significantly larger than zero for non central events at pT >1 GeV/c
-  Effect likely to be connected with anisotropic absorption
-   in QGP/nuclear matter

**Conclusions**

-  The J/ suppression scales with L in p-A and peripheral In-In and Pb-Pb
-  The L scaling is broken when looking at the pT distributions

-  One key ingredient in the overall J/ suppression picture still missing
-    absJ/ (158 GeV)
-  Results are coming.... stay tuned!

## The NA60 Collaboration

- ~ 60 people
- 13 institutes8 countries

- R. Arnaldi, R. Averbeck, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis, C. Cicalò, A. Colla, P. Cortese, S. Damjanović, A. David, A. de Falco, N. de Marco, A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A.A. Grigoryan, J.Y. Grossiord, N. Guettet, A. Guichard, H. Gulkanyan, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço, J. Lozano, F. Manso, P. Martins, A. Masoni,
- A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher,
- P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht,
- R. Tieulent, E. Tveiten, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri

**The NA60 Collaboration**

- _http://cern.ch/na60_

## Backup

## The experimental apparatus

- Muon trigger and tracking
- (NA10/NA38/NA50 spectrometer)

**The experimental apparatus**

## Influence of Drell-Yan contamination

-    and its pT distribution is not known

-  Describe the Drell-Yan  pT shape with the
-   same function used to fit the J/ distributions

-  Assume the usual  dependence of pT2 on L,
-   <pT2> = <pT2>pp + qN * L,   with qN = 4/9 gN

-  Use pT2pp = 1.25 (GeV/c)2, as given by PYTHIA
-  2 assumptions for qN:
- a) qN = 0 (no dependence on L)
- b) qN = 4/9  0.081 (GeV/c)2/fm (dependence      on L as measured by NA50 in PbPb)

- Teff changes by less than 0.4 MeV
- pT2 changes by less than 0.01 (GeV/c)2

**p-Pb**

**Influence of Drell-Yan contamination**

## <pT2> vs NPart

**<p****T****2****> vs N****Part**

## Comparison p-A and In-In

- Comparison peripheral In-In vs p-Pb

**Comparison p-A and In-In**

## <pT2> vs L – different y ranges

**<p****T****2****> vs L – different y ranges**

- <pT2>pp=1.13 ± 0.04 (GeV/c)2
- gN=0.029 ± 0.011 (GeV/c)2 / fm

- p-A

- <pT2>pp=1.14 ± 0.04 (GeV/c)2
- gN=0.015 ± 0.012 (GeV/c)2 / fm

- p-A

## RAA*(pT) for In-In at 158 AGeV

-  Effects connected with Cronin and nuclear absorption should scale with L
-  Extrapolate T to the L values reached in In-In and build the corresponding pT
-   distribution, which is then used to normalize the measured In-In distributions

- The suppression effect is
- mainly present at low pT

- But we still observe an
- enhancement at high pT
- (is the L extrapolation from p-A to A-A a good one?)

**R****AA*********(p****T****) for In-In at 158 AGeV**

## RAA

**R****AA**

## Systematic errors

**Systematic errors**

## Comparison with theoretical predictions

- Suppression by hadronic
- comovers (co = 0.65 mb,
- tuned for Pb-Pb collisions)

- Dissociation and
- regeneration in QGP
- and hadron gas

- Percolation, with
- onset of suppression
- at Npart~140

-  Size of the anomalous suppression reasonably reproduced
-  Quantitative description not satisfactory

- centrality dependent 0

- fixed termalization time 0

- A. Capella, E. Ferreiro
- EPJ C42(2005) 419

- R.Rapp,
- EPJ C43(2005) 91

- S. Digal, S. Fortunato, H. Satz,
- EPJ C32(2004) 547

**Comparison with theoretical predictions**

## Maximum hadronic absorption

-    calculations assuming
-  Nuclear absorption
-  Maximum possible
-    absorption in a
-    hadron gas
-         (T = 180 MeV)

-  Both Pb-Pb and (to a lesser extent) In-In show extra-suppression

- L. Maiani et al.,
- Nucl.Phys. A748(2005) 209
- F. Becattini et al.,Phys. Lett. B632(2006) 233

**Maximum hadronic absorption**

**Notes:**
this is a note

## J/ suppression in In-In collisions

**J/******** suppression in In-In collisions**

## Smooth effect or sharp drop?

- Step position: Npart = 86 ± 8
- ( Bj ~  1.6 GeV/fm3 )
- A1= 0.98 ± 0.02
- A2= 0.84 ± 0.01
- 2/dof = 0.7

-  Taking into account the EZDC resolution
-    data are compatible with a sharp drop
-  An onset smoother than our resolution on Npart (~20) is disfavored

**Smooth effect or sharp drop?**

## ’ in In-In collisions

-  Study limited by statistics (N’ ~ 300)
-  Normalized to Drell-Yan yields

-  Most peripheral point
-   (Npart ~ 60) does not show
-   an anomalous suppression

-  Good agreement with
-    Pb-Pb results

- Preliminary

- 450, 400 and 200 GeV points
- rescaled to 158 GeV

******’ ****in In-In collisions**

## ’ in p-A collisions

- L = 3.4 fm

- Also the ’ value measured
- by NA60 at 158 GeV is in
- good agreement with
- the normal absorption
- pattern, calculated from
- 450 (400) GeV data

- 450, 400 and 200 GeV points
- rescaled to 158 GeV

******’ ****in p-A collisions**