1. NA61 and NA49 Collaboration Meeting May 14-19, 2012, Budapest
Event-by-event
azimuthal angle fluctuations in NA49
(status report)
Katarzyna Grebieszkow
NA61 and NA49 Collaboration Meeting May 14-19, 2012, Budapest

2. Energy dependence (7.2% most central Pb+Pb) of azimuthal fluctuations
Motivation: search for plasma instabilities (PL B314, 118 (1993)), critical point and onset of deconfinement, flow fluctuations (APP B34, 4241 (2003); arXiv:nucl-ex/ )
Background effects: resonance decays, momentum conservation, flow, (di-)jets, quantum statistics (APP B31, 2065 (2000), PR C83, (2011))
SQM 2011
slide
NA49 preliminary
NA49 preliminary
Ff (negative) > 0; different than in UrQMD (1.3) (f in UrQMD rotated by FR)
Ff (positive) consistent with zero
forward-rapidity region; limited azimuthal acceptance (see PR C70, (2004) and PR C79, (2009))

3. System size dependence (at 158A GeV) of azimuthal fluctuations
NA49 preliminary
SQM 2011
slide
Ff > 0, maximum for peripheral Pb+Pb
UrQMD (3.3) does not reproduce data (f in UrQMD rotated by FR)
The magnitude of Ff reproduced by the effect of v1 and v2; the difference between positively and negatively charged particles also reproduced
In MC v1 and v2 (for pions and protons at forward-rapidity) taken from PR C68, (2003); <N-> and <N+> from this analysis; effect of limited NA49 acceptance taken into account; percentage of protons in the studied kinematic rage estimated from UrQMD

4. Huge systematic errors
The problem:
Huge systematic errors
How are they calculated?
Stability of Ff versus several event and track selection criteria (the largest contribution comes from bx, by, and np/nmp cuts – see backup slides and slides from Wrocław)
Cut on |by| was always ½ of cut on |bx|
Thick dashed line – range used to calculate systematic error
Thin dotted line – cut used in the analysis

5. VENUS, central Pb+Pb at 158A GeV
Wrocław
VENUS, central Pb+Pb at 158A GeV
Ff values in miliradians
1. Primary particles (for |bx|<2cm and |by|<1cm)
Ff (neg.) = ± <N>=97.4
Ff (pos.) = ± <N>=113.2
2. Matched particles (for |bx|<2cm and |by|<1cm)
Ff (neg.) = ± <N>=84.5
Ff (pos.) = ± <N>=99.3
3. Simulated tracks (y, curve, pt cuts included)
Ff (neg.) = ± <N>=100.6
Ff (pos.) = ± <N>=118.5
Simulated tracks
(y, pT vs. azimuthal angle, pT cuts included)
Ff (neg.) = ± mradians <N>=100.6
Ff (pos.) = ± mradians <N>=118.5
The same effect can be observed for primary and for matched particles!!
The whole effect may be generated by our detector!!!

6. What kind of particles we reject by our bx and by cuts?
accepted
rejected
1. (upper) no bx, by cuts
2. (middle) |bx|<2 cm |by|< 1 cm (typical cuts used in analysis)
→ accepted particles (94.2% in this kinematic region)
3. (middle) |bx|>2 cm and |by|>1 cm
→ (0.1% in this kinematic region)
4. (lower) |bx|>2 cm or |by|>1 cm
→ rejected particles (5.8% in this kinematic region)
azimuthal angle of neg. charged – always reflected to be the same as for pos. charged

7. Observation:
Azimuthal angle distribution changes with changing bx and by cut (and we are studying azimuthal angle fluctuations...). FpT was much more stable with bx and by cuts (but pT distribution was not so much sensitive to bx and by cuts).
But:
Similar changes of azimuthal angle distribution are observed in NA61 p+p data (see Bartosz's presentation in Wrocław) and Ff is stable there...
New idea:
The changes of azimuthal angle distribution may be connected with changing fraction of wrong side and right side tracks. Repeat the analysis for these different group of particles.

8. Right side accepted tracks: charge*px > 0
rejected

9. Wrong side accepted tracks: charge*px < 0
rejected

10. Some summary numbers:
a) Within accepted particles |bx|<2 cm |by|< 1 cm
we have:
58.9% of right side tracks and
41.1% of wrong side tracks
b) Within rejected particles |bx|>2 cm or |by|>1 cm
46.45% of right side tracks and
53.55% of wrong side tracks
c) Within particles with |bx|>2 cm and |by|>1 cm (a part of rejected)
31.3% of right side tracks and
68.7% of wrong side tracks
Wrong side tracks have higher contribution to high bx and by values

11. Qualitatively the same behavior for right side tracks, wrong side tracks and their sum
The magnitudes different due to different multiplicities (see next slide)
The reason of unstable Ff dependence still not found. Any ideas??
Reminder: Ff is also not stable with n_point/n_max_point ratio

13. Back-up

14. Components of systematic errors
Values of several cuts were varied in reasonable ranges. The “partial” systematic errors was taken as a half of difference between the lowest and the highest value. Final error is a maximum from partial error (measurements are correlated)
negatively charged
positively charged
all values in miliradians
ntf – number of tracks used to fit main vertex
nto – number of tracks registered in TPCs
np – number of measured points for a track
nmp – maximal number of points (from geometry of the track)

15. negatively charged
positively charged
all values in miliradians
for centrality bins 5, 4, and 2 – linear fit taken from bins 6, 3, and 1
ntf – number of tracks used to fit main vertex
nto – number of tracks registered in TPCs
np – number of measured points for a track
nmp – maximal number of points (from geometry of the track)