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Inclusion, Diversity, Equity, and Accountability Moments

Native American Heritage and Land Acknowledgements/

As a part of recognizing Native American Heritage Month in November, we discussed the use of land acknowledgments as a way to honor Native American cultures.  A land acknowledgment is a way of understanding and honoring the long-standing history that came before and has led us to reside or work on the land, and is a way to seek to understand our place in that history.  In many Native American cultures, when an introduction is made this includes the lineage of an individual, which is strongly connected to the land on which their ancestors lived.  As such, land is a central part of culture, and though we often may not recognize it, is key to who we are and how we live.  

Internationally, land acknowledgments are becoming increasingly common.  For those of us at Berkeley Lab, if we want to include a land acknowledgment at the beginning of an event, for example, to recognize and honor the local Indigenous communities, the following is one way to phrase such a message:

The land we work on is in Huichin (Xučyun), the ancestral and unceded territory of the Ohlone People.  

We acknowledge the Chochenyo Ohlone people of the Bay Area and California and recognize their continuing connection to land, waters, and culture.  We pay our respects to their Elders, past, present, and emerging.

Recent IDEA topics and NSD Staff Meetings

Luminary Cards 

We’d like to remind everyone, as we continue to largely work remotely, that the Luminary Card program is virtual!  You have the opportunity to recognize your co-workers with a virtual Luminary Card for any action fostering inclusion, diversity, and equity within our LBNL community.  Recipients who register their cards may choose to be named in this space in a future NSD newsletter.

LHC and LHC experiments recommissioning – First collisions since 2018

The Large Hadron Collider is emerging from Long Shutdown #2. This three-year break in the operations schedule was spent on intensive work to improve the accelerator performance (e.g. new and more powerful intensity setup, in particular) and upgrades to the detectors. LBNL scientists from the Nuclear Science and Physics divisions worked on two of these detectors – ALICE and ATLAS. The last weekend of October (2021) provided an excellent opportunity to verify the readiness of the instrumentation.  Low intensity probe-beams of protons (about 3.5 x 1011 particles per beam) were injected into the LHC from the Super Proton Synchrotron and accelerated to a kinetic energy of 450 GeV. The circulating beams in the LHC were brought to collisions at the main interaction points for a total of about 40 hours over 5 days. During this time all four major experiments ALICE, ATLAS, CMS, and LHCb recorded millions of collisions; testing the old and new detector elements as well as the computer systems and new software.  

ALICE during install
Fig. 1 ALICE ITS during installation. The orange-colored inner-surface of the LBNL-built middle ITS layers are shown in the upper right corner of the figure. The lower half-barrel of the inner ITS is shown close to the beam pipe while the green back plate of the Muon Forward Tracker is shown at the back.
Fig. 2: Vertex reconstruction in the ITS using pp collisions from the October 2021 LHC pilot beam studies.
Fig. 2 Vertex reconstruction in the ITS using pp collisions from the October 2021 LHC pilot beam studies.

During the long shutdown, the ALICE detector underwent a major facelift – to the point that improvements were made in all subsystems. In particular, the heart of the particle tracking system was redesigned and rebuilt. The new Inner Tracking System (ITS) was installed in May 2021 and was, in part, built at LBNL by Nuclear Science Division scientists and supported by funding from the DOE Office of Nuclear Physics. The ITS is an ultralight detector using Monolithic Active Pixel Sensor (MAPS) technology and is currently the largest device of its type. [MAPS were also used to upgrade the forward tracking – MFT detector in ALICE.] Figure 1 shows the ALICE ITS during installation – with the staves of the LBNL-built middle layers of the detector already installed. Figure 2 shows the reconstruction of p-p collision vertices as seen by the ITS . The detector technologies developed and employed for the ITS are also being considered for several applications in other experiments at accelerator facilities, including the vertex detector of the sPHENIX experiment at RHIC where NSD scientists are also involved.

Other major ALICE improvements include the redesign of the Time Projection Chamber readout planes (also supported, in part, by the DOE), the trigger detectors, and a complete revamping of the computing infrastructure with a 2000-GPU farm for online calibration and data processing.

These upgrades will allow ALICE to improve the precision of the measurements characterizing the quark-gluon plasma created in heavy-ion collisions. For many critical physics studies, the statistics collected over the next decade will be enhanced by 100-fold.

The beam tests in October show that the new ALICE systems will be ready for data taking  of proton-proton and heavy-ion collisions in Spring 2022. After an extended period of recommissioning of the LHC itself, the first collisions for physics are expected in the second half of the year.

[1] CERN Courier –
https://cerncourier.com/a/alice-tracks-new-territory/

Mirror Nuclei Reflect the Quark Structure of Protons and Neutrons

A great deal is known about the quark structure of nucleons (protons and neutrons), yet key questions remain. Of particular importance is understanding the difference between the up- and down-quark contribution. The difference between up and down quarks manifests itself in the difference between the proton (u-u-d) and neutron (u-d-d) structure. However, measurements of neutrons are challenging as free neutrons are not stable. Much of our information on the neutron comes from scattering measurements on the deuteron – a nucleus composed of one proton and one neutron. This requires subtracting the dominant proton contribution, correcting for the motion of nucleons in the nucleus, and accounting for the possibility that the nucleon structure changes inside of the nucleus, making such extractions less reliable than a direct measurement would be.

However, just as the u-d difference can be measured through p-n comparisons, the p-n difference can be studied by comparing the mirror nuclei 3H (p-n-n) and 3He (p-p-n). In this case, the nucleon motion and nucleon modification should be larger than in the deuteron but nearly identical in both nuclei. An experimental comparison is thus a significantly more reliable indicator of the basic difference between up and down quark contributions to the structure and dynamics of nucleons.

The MARATHON experiment at the Thomas Jefferson National Accelerator Facility (JLAB) measured deep inelastic scattering from 3H and 3He to extract the ratio of the neutron-to-proton quark distributions.

Figure 1: The neutron-to-proton structure function ratio from the MARATHON data [1] (red points) versus x, the fraction of the nucleon’s momentum carried by the struck quark, along with bands indicating the range of results from all deuteron/proton extractions (cyan band), and only those extractions that assume no modification of the proton structure in deuterium (shaded region) [2].

Figure 1 shows the neutron/proton ratio as a function of the nucleon momentum carried by the struck quark (x). The uncertainties are significantly smaller than the previous work, such as the cyan band which shows the range of results from extractions based on the deuteron data (using different models for the momentum distribution and nucleon modification). The dark shaded band shows the deuteron results excluding models that allow for nucleon modification. The MARATHON data which are shown in Figure 1 require nucleon modification to explain the data at large x; a first ever confirmation that the proton and neutron in deuterium are modified from their free state. And, the MARATHON data delivers a significantly more precise extraction of the true n/p ratio. Immediately after the release of the MARATHON data, two preprints using these data to test proton modification were posted to the arXiv.

Shujie Li and John Arrington led the commissioning effort for the set of four experiments that which will use the new tritium target at Jefferson Lab.  John is the Co-Spokesperson for MARATHON.

[1] D. Abrams, et al., arXiv:2104.05850 (submitted to PRL).

[2] J. Arrington, J. G. Rubin, and W. Melnitchouk, Phys. Rev. Lett. 108 (2012) 252001

Figure 2: One of the three 25 cm gas cells, machined from a single block of aluminum, is visible at the top, with optics and solid foil targets mounted below

CUPID Proceeds Towards Critical Decision One (CD-1)

CUPID is an experiment to search for neutrinoless double beta decay (NLDBD).  The DOE Nuclear Physics program granted Critical Decision Zero (CD-0, “mission need”) to the experiment in 2018. CUPID, and two other US efforts to search for NLDBD (nEXO & LEGEND), recently participated in a DOE Portfolio Review and an interagency North American and European NLDBD Summit. The respective review panels noted the strengths of all three experiments. The DOE has given subsequently an unofficial endorsement for CUPID to proceed to the next level of review – Critical Decision One (CD-1: “approve alternative selection and cost range”).  

NLDBD is a hypothetical nuclear decay where two electrons are emitted without any anti-neutrinos. Since the decay creates particles (the electrons) without any corresponding antiparticles, the observation of NLDBD would establish that the neutrino is a Majorana fermion (whereby the neutrino and antineutrino are identical particles).  The new physics mechanism behind NLDBD violates the conservation of lepton number and so could also explain the matter-antimatter asymmetry we observe in the universe. The Nuclear Science Advisory Committee placed a ton-scale experiment to search for NLDBD as the second recommendation in the 2015 Long Range Plan and set a goal of reaching the so-called Inverted Mass Hierarchy (IMH) regime.  We expect NLDBD to be an extraordinarily rare process with a half-life of 1027 years or longer in the IMH regime. This long half-life requires that NLDBD searches employ massive low background detectors with roughly a ton of double beta decay isotopes and have excellent energy resolution. CUPID (Cuore Upgrade with Particle IDentification) will be a nearly ton-scale cryogenic detector consisting of 1600 Li2100MoO4 crystal calorimeters that will search for 100Mo NLDBD. The calorimeters will measure the energy of decays inside the crystals by employing a sensitive thermometer that records the slight temperature rise with excellent resolution.  In addition to recording a heat signal (like CUORE), CUPID will register light with light-sensing calorimeters above and below each Li2100MoO4 crystal. This light signal gives CUPID particle identification capabilities, demonstrated by the prototype experiment CUPID-Mo [3].  CUPID is an upgrade of the successful CUORE (Cryogenic Underground Observatory for Rare Events) [1,2] currently operating at the Gran Sasso Laboratory in Italy.  The cryostat and refrigerator will be taken from CUORE and will be reused for CUPID which helps to make it a cost-effective experiment.

CUPID is a collaboration between institutions in the US, Italy, France, Ukraine, Russia, Spain, and China. Berkeley Lab is the lead DOE laboratory on CUPID. NSD senior faculty scientist Yury Kolomensky is the US Project Director and Chief Scientist. NSD staff Brian Fujikawa is the US Project Manager, and NSD postdoc Chiara Capelli is the Level 3 Manager for computing.

[1] arXiv:2104.06906 (replace with a Nature article and press release if it gets published in time).

[2] D. Q. Adams et al., Prog. Part. Nucl. Phys. 122, 103902 (2021).

[3] E. Armengaud et al., Phys. Rev. Lett. 126, 181802 (2021).

Figure 1:  Artist conception of CUPID. The tower-like structure in the middle contains the Li2100MoO4 crystal calorimeters. The surrounding structure is the shielding and vacuum vessels for the cryostat. The cryostat contains a 3He dilution refrigerator (not shown) that will cool the calorimeter to a temperature of about ten millikelvin.