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MVD Reaction Plane analysis. Ben Norman & G.J Kunde, H. van Hecke, J. Sullivan. Definitions. p y. p x. z. y. y. x. x. Reaction plane defined by (1) beam direction and (2) impact parameter. anisotropy in momentum space. initial spatial anisotropy. 3  /4.  /4. “In-plane” region.

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Mvd reaction plane analysis

MVD Reaction Plane analysis

Ben Norman &

G.J Kunde, H. van Hecke, J. Sullivan

Muon and Forward Upgrades Workshop Santa Fe, NM


Definitions
Definitions

py

px

z

y

y

x

x

Reaction plane defined by (1) beam direction and (2) impact parameter

anisotropy in momentum space

initial spatial anisotropy

3/4

/4

“In-plane” region

“Out-of-plane” region

-/4

-3/4

Muon and Forward Upgrades Workshop Santa Fe, NM


Physics motivation
Physics Motivation

y

x

  • At DNP (10/03) and QM04, STAR demonstrated the suppression of hadrons as a function of orientation wrt/ the reaction plane.

  • Reaction plane measurement allows studying path-length dependence (medium modification) of charmonium and open charm.

Muon and Forward Upgrades Workshop Santa Fe, NM


High p t pairs wrt reaction plane
High pT pairs wrt reaction plane

y

x

  • Trigger on one high pT particle, plot azimuthal distribution of the rest.

  • 2 Effects seen:

    • v2 (elliptic flow)

    • forward/back jet correlations

  • Away-side suppression enhanced for out-of-plane sample

Muon and Forward Upgrades Workshop Santa Fe, NM


How much asymmetry
How much asymmetry?

200 GeV v2 3-50%

200 GeV v1 6-55%

  • v1, v2 measure asymmetry of system

  • Forget flow for now

  • effects are at the few % level

    • nontrivial measurement

    • must understand asymmetric efficiency/ acceptance/ background

PHOBOS Preliminary

Muon and Forward Upgrades Workshop Santa Fe, NM


How much asymmetry ctd
How much asymmetry? ctd

b

y

STAR TPC: 4.5% v2

PHENIX MVD: 3.3% v2

PHENIX BBC: 2.8% v2

200 GeV v2 3-50%

PHOBOS Preliminary

v2 decreases with h

v1 increases with h

MVD sees somewhat stronger v2 signal than BBC

200 GeV v1 6-55%

Muon and Forward Upgrades Workshop Santa Fe, NM


Where does the mvd sit
Where does the MVD sit?

Beam-beam counter

(BBC) |h|=3~4

64pmts in each BBC

charged particles

MVD: |h|=1.8-2.6

3k channels per side!

collision point

beam line

two central arms

(CNT) |h|<0.35

Dch,PCs,TOF,EMCAL

tracking, momentum, PID

Muon and Forward Upgrades Workshop Santa Fe, NM


Intro to the mvd pad planes
Intro to the MVD pad planes

  • z = ±35 cm

  • 1.8 < h < 2.6

  • 6048 channels

  • f resolution of 2.4°

  • r resolution of 2-4.5 mm

Muon and Forward Upgrades Workshop Santa Fe, NM


How to calculate reaction plane
How to calculate reaction plane (Ψ)?

Σ wi*sin(2i) - <wi*sin(2i)>

tan(2Y2) =

Σ wi*sin(2i)

Σ wi*cos(2i) - <wi*cos(2i)>

tan(2Y2) =

Σ wi*cos(2i)

  • In general,

  • In practice, the procedure is involved:

    • Determine efficiency/acceptance/background correction for each channel (wi)

    • Subtract <wi*sin>, <wi*cos> to better isolate azimuthal anisotropy.

    • Flatten Ψ distribution by shifting to remove remaining asymmetries

Muon and Forward Upgrades Workshop Santa Fe, NM


Acc eff bck correction
Acc/Eff/Bck correction

  • Integrate hits for entire data set

  • Find most probable population(≡ #hits/#events) over all channels

  • Select only channels within 50% of the population MPV. This removes hot/dead channels from consideration. Large corrections are useless: If a channel is on 50% of the time, it will bias the f distribution in all events (weighted either too much or too little)

Muon and Forward Upgrades Workshop Santa Fe, NM


Poisson fill
Poisson Fill

  • In excluded (dead/hot) channels near healthy channels, we can do a Poisson fill on an event by event basis

Muon and Forward Upgrades Workshop Santa Fe, NM


Event plane distribution
Event plane distribution

  • After subtracting <w*sin> and <w*cos> and poisson-filling excluded channels, the distribution of Y should be flat (assuming isotropic acceptance).

  • Any remaining structure is due to asymmetric acceptance.

  • This remaining structure can be corrected by the “shifting method”: Fourier decomposition of distribution

Muon and Forward Upgrades Workshop Santa Fe, NM


Shifting method
“Shifting Method”

Usually 1 <= n <= 32

Muon and Forward Upgrades Workshop Santa Fe, NM


Does shifting work
Does shifting work?

  • One measure of effectiveness is correlation between YNorth and YSouth.

  • See results for toy MC of MVD:

  • Throw Y flat

  • Smear YN & YS with gaussian

  • Throw hits in N & S according to YN, YS

  • Remove hits in dead sectors

  • Recalculate YN, YS

Muon and Forward Upgrades Workshop Santa Fe, NM


Correlation correct y
Correlation => correct Y?

  • Does correlating the north & south imply correct determination of plane?

  • Try more toy MC and compare BBC, MVD, and STAR TPC. (PHOBOS data => different v2 => different sensitivity to Y. Also different rapidity ranges and number of particles measured.)

Muon and Forward Upgrades Workshop Santa Fe, NM


Correct y ctd
Correct Y? ctd

  • Q: Grossest binning in Y is ±p/4 (in-plane vs. out-of-plane). If we require |YN - YS|< p/4, how often to we guess the true reaction plane within ±p/4?

  • A: 70-75% in all cases (50% means no resolving power)

Y Resolution vs N/S average Y

BBC

~125 hits/side

V2 ~ 4.5%

MVD (raw)

~75 hits/side

V2 ~ 3.3%

STAR TPC

~50 hits/side

V2 ~ 2.8%

MVD (shifted)

~75 hits/side

V2 ~ 3.3%

Muon and Forward Upgrades Workshop Santa Fe, NM


Current status of mvd analysis
Current status of MVD Analysis

  • As soon as expected N/S correlation is observed, single muon and J/Y vs reaction plane analysis can begin.

  • Only limitation right now is statistics. We expect a ~15% peak->peak correlation between N & S, statistical errors are higher than that for the current sample. A larger sample is being processed as we speak.

~15% peak-to-peak

Muon and Forward Upgrades Workshop Santa Fe, NM


Summary
Summary

  • MVD analysis is more complicated than BBC due to large acceptance gaps.

  • MVD reaction plane is progressing, so far results are promising.

  • Capability to extract MVD reaction plane will be in CVS by the time run 4 AuAu analysis code is run.

  • The MVD (hits) will live in EVE_DST and be available on disk.

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Extras
Extras

Muon and Forward Upgrades Workshop Santa Fe, NM


Reaction plane defined
Reaction plane defined

ShinIchi Esumi

y

y

Reaction plane

Reaction plane

i

1

2

x

x

i

plane with

the directed moment

plane with

the elliptic moment

Σ wi*sin(i)

Σ wi*sin(2i)

tan(1) =

tan(22) =

Σ wi*cos(i)

Σ wi*cos(2i)

(wi: 1 or pT)

Muon and Forward Upgrades Workshop Santa Fe, NM


Mass dependence of m t slope radial flow
Mass dependence of mT slope - Radial Flow

STAR 130 GeV Au-Au

  • The different mT slopes indicate that the slope should not be interpreted as a simple thermal temperature.

  • It also has a component from collective radial velocity.

L

T = TTh + mb2


Why is elliptic flow interesting
Why is elliptic flow interesting?

y

x

py

px

  • Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric)

  • Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp) It’s strictly a medium effect.

  • Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow

coordinate space

Momentum space

Muon and Forward Upgrades Workshop Santa Fe, NM


Time evolution in a ideal hydrodynamic model calculation
Time evolution in a ideal hydrodynamic model calculation

dn/dr (dP/dr) higher

dn/dr (dP/dr) lower

  • Elliptic Flow reduces spatial anisotropy -> shuts itself off

Muon and Forward Upgrades Workshop Santa Fe, NM

“PV = nRT”  dP ~ dn


V 2 versus centrality
v2 versus centrality

STAR PRL 86, (2001) 402

PHOBOS

|| < 1.3

0.1 < pt < 2.0

PHENIX

First time in Heavy-Ion Collisions a system created which at low pt is in quantitative agreement with hydrodynamic model predictions for v2 up to mid-central collisions

Muon and Forward Upgrades Workshop Santa Fe, NM


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