For FY 2001 running
BRAHMS
Collaboration
Brookhaven National Laboratory - Jagellonian University, Kracow, Poland - John Hopkins University - Niels Bohr Institute, Denmark - New York University - Texas A&M University -University of Bergen, Norway -University of Oslo, Norway - University of Bucharest, Romania - University of Kansas
Abstract
The
2000 running RHIC period at RHIC with
Au- Au
collisions at ÖsqrtsNN=130 GeV and an integrated
luminosity of an a few mb-1 albeit with a very large diamond size,
enabled BRAHMS to record a significant dataset.
For
the FY2001 run the primary BRAHMS physics goal is to study Au+Au collisions at ÖsNN =200 GeV. Emphasis will be
placed on studying
the process of stopping of the incoming baryons by measuring proton
rapidity and pt distributions. The basic properties mechanisms of
particle production will also be investigated by measuring rapidity and
transverse momentum distributions of produced pions and kaons as a function of reaction centrality.
The rapidity region will be 0<y<4.0 [SJS1]4,and the
coverage in transverse momenta will be from .2 to about 1.5 GeV/c for the full
rapidity range and to 4 GeV/c for selected rapidities. An integrated
luminosity of about 20 mb-1 at about 10%, and about 150 mb-1 at 50% of full luminosity is
requested for these measurements. As a second priority Additionally we
request a run period (~4
weeks) at the previous energy of ÖsNN =130 GeV to complete
measurements at a the lower energy. As the its third
priority BRAHMS requests a significant running period with a lighter
system (S+S or Si+Si) at the same ÖsNN of 200 GeV as measured with the
Au-Au system.
The
BRAHMS experiment took its first Au-Au data during the summer 2000 run at RHIC.
Data was
obtained using the The mid-rapidity
and front forward spectrometers took data,
and the initial commissioning of the back forward spectrometer was initiatedaccomplished.
The experiment is now ready to explore further heavy
ion collisions at the RHIC top RHIC energy
with symmetric Au beams. These
conditions should lead to where the
highest energy densities are expectedthat can be
achieved at RHIC.
With
the ongoing upgrade of the 2 O’clock power substations, all of the BRAHMS magnets
can be powered to full field and particle production can be explored at the
most forward and highest momentum
reachable by BRAHMSmomenta of the design acceptance.
The
ongoing
uncertainty uncertainty in funding for this years runthe coming
year has made this this planning
very difficult. The present plan assumes a run period of about 22 weeks of
beam, with 4 weeks of cool-down. This may or may not be the actual
conditions for this yearwhat actually happens.
Adjustments will then have to be made in discussion with RHIC management. The
collaboration prefers an earlyto start the next run (on March 1) for next
years run in order not to delay further the measurements and the
analysis of the Au-Au system at the highest available energy. Brahms is not requesting dedicated pp
running as explained later.
Most
data were recorded in the last month of the running period. Spectrometer data
were recorded at angle settings of 90, 45 and 40 degrees of using the Mid-Rapidity
spectrometer with two
field settings at both polarities., and at 4 and 8 degrees for
Tthe
forward spectrometer was
run at 4 and 8 degrees with one
magnetic field [SJS2]setting (both polarities).
The data,
which iare s currently being analyzed, will give the first indication allow us to
characterize of particle production and spectra at
y~0 and y~3 in the low pt region. The dataset is presently
being analysed.
Despite
the impressive gains made in luminosity during the run, reaching about 10% of design value, the integrated number of
useful events was not high. This was due toa consequence
of two effects: a) the
interaction vertex had a sigma of about 65 cm, extending
outside of our spectrometer acceptance, and b) the experiment was plagued
by a high background stemming from the ~45 m accelerator warm section upstream
of D0. This These problems should
be remedied for the next yearsupcoming
run by the introduction of the storage RF, and by a
necessary bake-out of the warn warm sections.
The
BRAHMS detector situated in the 2 O'clock IR consists of 3 major spectrometer
components. The forward spectrometer will be fully instrumented
with its detectors, and the magnets will be able to operate at full field. To
optimize the running run
plan, the forward spectrometer will be commissioned during the initial part of
the run period so that it is ready for full operation this will
first be utilized when the RHIC luminosity reached s itsthe highest
value later in the year. The Mid-Rapidity Spectrometer should have additional
TOFW panels installed, but not commissioned[SJS3], thus
enabling simultaneous measurements of hadrons of both charge during this year.
The spectrometers will be able to cover their full design angular range.
The
BRAHMS also detector
has a set of global detectors that are used for event characterization,
triggering and timing measurements, all of which were successfully commissioned this
year.:.
The forward spectrometer is fully instrumented with its
detectors, and the magnets will be able to operate at full field. To optimize
the run plan, the back
forward
spectrometer will be fully commissioned during the initial part of the run
period so that it is ready for full operation when the RHIC luminosity reaches
its highest value later in the year. The Mid-Rapidity Spectrometer should have
additional TOFW panels installed thus
enabling simultaneous measurements of hadrons of both charge during this year.
The spectrometers will be able to cover their full design angular range.
Physics
Program
The
first task at RHIC is to establish an energy budget for Au+Au collisions and to
determine how that energy is partitioned between particle production and
transverse and longitudinal momenta.
Secondly the ``chemistry” of the system can be tied down by measuring
the fraction of strange to non-strange particles and the yield of baryons.
The
amount of nuclear stopping of the incoming baryons determines the energy
deposition in the reaction volume. An estimate of the energy density in the
initial stage of the collision is of prime importance for the understanding of
reaction dynamics. The rapidity shift and the energy loss can be determined by
the measurements of the proton rapidity distributions over a wide range in y.
Pion and kaon spectra measure the basic
properties of particle production. An enhancement of strangeness production has
long been predicted to be an important signature of the color de-confined phase
of nuclear matter. The integrated kaon yield, measured over a wide range in y
and pt , can be regarded as a measure of the total strangeness
production, and a change in K/pp ratio vs. centrality is an important measure for understanding the strangeness chemical potentialobserved
behavior.
The freeze-out properties, e.g., collective
transverse and longitudinal expansion, of the hot nuclear system formed in the
reactions will be established by measuring the transverse momentum spectra of
pions, kaons, and protons. The yields will be measured at several rapidities
and at several transverse momenta so that the expected average momentum of each
species will be covered. Comparisons will be made with thermal models, and
cascade models to shed light on collective effects. The size of the system at
freeze out can be investigated from HBT measurements and studies of small
baryonic clusters (e.g. deuterons, tritons and their anti-clusters).
The centrality dependence of these data, as
measured by the multiplicity array, may or may not show discontinuities, but in
either case this information will be vital to understanding what is going on in
this new regime.
The initial parton scattering plays an
increasing important role
with energy
in the heavy ion collision as the beam energy increases. The study of particle spectra in intermediate
pt range of 1-4 GeV/c will help in the understanding of media modification of pt
spectra and yield through initial scattering (Cronin effect), shadowing and jet quenching.
The importance of these processes depends on energy, rapidity and collision
system.
When
the beam turns one some time will be spent on tuning of
detectors already in place, on checkout of the trigger system and on
commissioning of detectors then ready for beam for the first time ( Drift
Chambers T4, T5, the calibration wire chambers and the additional tow time-of-flight panels).
.
Our estimate is that about 2 weeks will be required to make the detector fully
operational. Some of this, but not all can take place during the initial
commissioning and tuning of the ÖsNN =200 GeV 100+100 Au
beam.
The first segment of physics measurements
will be
·
Global
multiplicity distributions. Measurements of the shape and magnitude of the
charged particle distributions will help pin down the relation between energy
flow and particle production as a function of beam energy. Comparing mutual
colomb dissociation of nuclei at ÖsNN =130 and 200 GeV should clarify the electromagnetic and
nuclear components of the total cross section. Finally Van Der Meer scans of
the two beams across each other will allow us
to measure total cross section.
·
A
systematic survey of charged hadron rapidity distributions from Au on Au
collisions at transverse momenta between pt= .2 and ~1.3 GeV/c (i.e. the soft physics) at
rapidities between 0 and 4. This requires a fairly large number of angle settings, each
with 4 field values and 2 polarities (4 setting per angle). A minimum bias
trigger will be employed to cover all centralities, but goals will be set to
achieve satisfactory statistics for central collisions (5-15% software
cut). An example of expected distributions obtained within the Brahms coverage
is shown in figure 2a and 2b. { An open
period of about 1 week some time in the later half of the running period will
be required to move the spectrometer to the most forward angle (2.3 degrees)
for which a special adjustment of the beam pipe is necessary. The stands and
beam-pipe is constructed with this in mind (movement of 1 cm), but manual
intervention and coordination with the RHIC operation group is required.
Following this change the forward angle measurements (at 2.3-3.5 degrees) can
be made. This period will also be used to install additional shielding of the
detectors necessary at the most forward angles } It is my understanding for now
that it might be possible to get to 2.3
The second segment will be devoted to a lower
energy measurement. The preferred energy will be ÖsNN =130 GeV for which a data set has already
been collected that can be used in such a survey. This will entail a fairly complete survey of the soft physics.
The third segment will be devoted to high
luminosity running at selected rapidities to study
high pt (i.e 1-4 GeV/c) devoted to a study of
spectral shapes, and aiming to understand mini-jet production and its characteristics. This segment requires a
large integrated luminosity, as well as implementation of a forward
spectrometer setting. A forward
spectrometer trigger will enable us to utilize the luminosity available later
in the running period. At
the same time we will collect a large statistics data sample near mid-rapidity
for HBT studies.
The fourth segment will be devotedis for to measurements
with a lighter projectile. Our choiceOur choice from a
physics point of view is Si (S) . Much lower energy data exists
at AGS and CERN for thissuch
collision system (S at
SPS). In addition when considering the number of #participants in the reaction such a
light system gets access to a region that cannot really be measured by
peripheral Au-Au collisions. These measurements should be done at the same
energy as Au-Au i.e. ÖsNNsqrt(s)=200 GeV. For this system
the focus will be on central collisions where trigger and global detectors will
be fully efficient..
Shorter access periods, on the order of hours will (based on experience) also be required on a weekly basis to fix minor problems and/or make small adjustments to electronics in the IR.
No
request is made for pp running this year. Comparison to pp will be important
both for the soft physics as well as for the understanding of the development
of mini-jets with pt. BRAHMS is though, is not yet in a position to utilize pp experimentally.
The trigger efficiency is estimated to less than 40% with the present beam-beam counter setup;
in addition start-time is not well determined. Capital request have been made
for detectors additions that will remedy this. It is toughtthought unlikely this
will be ready for this years run.
Summary
of Run Plan8 wks of Au-Au at sqrt(snn) = 200 with about 10%
luminosity.
1.
4 wks of Au-Au qt sqrt(snn) = 130 at similar
luminosity
1.
8 wks of Au-Au at sqrt(snn) =200 at 50% luminosity
1.
4 wks of
Si-Si at sqrt(snn) = 200.
Should the
amount of available time for Au Au+Au running not allow this program our
highest priority is to complete the program with Au-Au at the highest energy i.eenergy i.e. point 1. and 3.
|
System |
Weeks |
Luminosity |
Physics |
Note |
|
Au-Au at 200 |
6+2 startup |
~20 mb-1 ~10% |
Survey of soft physics |
Rate limited by DAQ |
|
Au-AU at 130 |
4 |
~15 mb-1 ~10% |
Survey of soft physics |
Rate limited By DAQ |
|
Au-Au at 200 |
8 |
~150 mb-1 ~50% |
High pt, heavy clusters HBT at y~0 |
Spectrometer
t |
|
Si-Si at 200 |
4 |
|
Survey of soft physics |
Central collisions only. |
During most of the second year of running the
data taking is limited by the DAQ, and we will record a mix of central and
minimum bias data with a simple trigger defined by the beam-beam counters. At full (half)
nominal luminosity, additional multiplicity and spectrometer triggers and (forward
spectrometer triggers)
will be ecome
essential for event selection and recording of interesting events.
The
very long anticipated running periods will put a severe strain on the
collaboration, a strain that is not helped by the inadequate funding for
several of the Brahms collaborating groups. To maximize the resources it is the
intention to man the data taking shifts in the following way.
-
During
beam conditions when physics data can be taken, the experiment will man 3 shift
per day with 2-2-1 persons (i.e. 5 per day).
-
During
machine studies (50% at year start, 20% at year end) a single shift-supervisor
will perform shift checks, but will otherwise be on call.
-
For
almost all of the FY2000 running allthe shifts were
manned with 2 people. With the moreexpected more routine data taking the 5 person5-person scheme should
work well.
The
collaboration has provided input to evaluate the available manpower for running
and analyzing data from the experiment. The resources are summarized in the
table below indicating the number of people assigned to BRAHMS from each
institution, the number of planned shifts manned (measured in months) ,), and man months for
data analysis. Both for manning the shifts and for the data analysis sufficient
manpower is available (30 shift months are needed for 6 months of running)
under the assumption that funding from DOE and foreign funding agencies
continues at the present level.
|
Institution |
Data taking Shift months |
Data Analysis |
|
BNL |
10 |
18 |
|
Bergen/Oslo |
5.6 |
22 |
|
NBI |
8 |
28 |
|
TAMU |
4.2 |
17 |
|
U.Kansas |
3.5 |
8 |
|
J.Hopkins |
1.8 |
2 |
|
NUY |
1 |
2 |
|
U.Krakow |
3.5 |
12 |
|
U.Bucharest |
3.5 |
12 |
|
Total |
41 |
95 |
Summary
BRAHMS
wants
would like to run Au+Au collisions at full energy for a total of 16
weeks,
including 2 weeks startup and with a
minimum of 150 mb-1 integrated luminosity in two
periods to make a complete survey of particle spectra over a wide range of
rapidity, and to high pt for a small set of rapidities. Additional time is
requested for Au+Au collisions a lower energy, 130 being
the preferred energy, since data from 00 can supplement thesethis data set.
As the last priority, time is requested to perform a first survey
of a lighter system (Si+Si) at the same energy as measured with Au+Au.